Does the first reflection point actually matter??

I am suspecting the common issue between these two ideas is the speaker dispersion: the wide dispersion having a stronger effect on first reflections, the narrower having less impact on reflection points. It is quite possible we do not know what the mid and/or tweeter dispersion of our speakers really is. If we don't know, we could attribute a lot of audible results to things that may be unrelated. The specs we are given don't come close to revealing this super important info.

Yes I think that to.
One concrete example that come to mind is the Klipsh RP600m (and for that matter any horn speaker.
The tweeter is reassess into a horn and some reviewers says that it is not a horn but instes a wave guide.. (Poteto potato)
Most reviewers has as the most no/little treatment in their listening space. And it gets product of the year reward and so on..
And I have thought of why it could be that higly prized by them.
And here is two reasons why among others. Is that the tweeter is so far in that if you look from the reflection points on the sidewall for example. Then you can't see the tweeter at all..
In comparison to a soft dome tweeter that is on the front baffle. The dome shape is there for making a wider dispersion pattern. 
So in other word the RP600m reduce sidewalls reflections and ceiling/floor depending how far our distances are. With the horn directivity.
The other party trick is that the tweeter plays down to 1500 Hz were the x-over point is before the woofer takes over. And the woofer has of course a wider dispersion.

Those two party tricks is a welcomed addition to its presentation. And something that may help it to win get some love from the reviewers in their space.

Acoustic treatment and acoustical control may and must cost peanuts if you listen to your ears and to nobody else....Make any change you are moved to do and listen....

Discount experts that sells something, the other experts argue against one another anyway ....Then your ears are master of your audio future, listen to them with trust....

I did it.... :)

I succeed....

Any upgrade seems ridiculous and worthless when you succeed....

Piano and symphonic masses dont forgive any room....

In a vast room , hall concert for example, equations do well.... Vast room are created for hundred of ears.....In a small room with diverse complex acoustical content and a peculiar geometry and topology, inhabit only by your 2 ears, you cannot replace the ears with simplistic rules and  general equations....

Listenings experiments are the golden rule here...

My listening  room is 12 x 12 with closet like alcoves on each corner.

I had bare walls and corners for a couple years.

I recently completely peppered the back wall near my listening position with small picture frames and was stunned by the improvement!

The best part: no cost. :-)

Erik talks about how he doesn't hear much difference with absorption at first reflection zones.

I have not actually said this.  I've taken like 2 dozen posts to explain this.

I think many of the mysteries discussed in this thread make it difficult to grasp the unifying issue.  Different rooms and different speakers, its extremely complex behavior.  ( I swear acoustics is a black art) Is it the speaker or the room?  Erik talks about how he doesn't hear much difference with absorption at first reflection zones.  Another poster says absorption at first reflection zones is HUGE, big difference.  How could they both be true?    

I am suspecting the common issue between these two ideas is the speaker dispersion: the wide dispersion having a stronger effect on first reflections, the narrower having less impact on reflection points.  It is quite possible we do not know what the mid and/or tweeter dispersion of our speakers really is.  If we don't know, we could attribute a lot of audible results to things that may be unrelated.  The specs we are given don't come close to revealing this super important info. 

Brad  

If I ask someone with Floyd Toole level knowledge of loudspeaker-in-room acoustics (which I can with Billy Woodman at ATC), he would tell me that consistent spectral content of direct vs reflections is the key to imaging. If the reflections look very similar in spectral content to the direct sound it will image well. That’s why he builds wide dispersion loudspeakers. Narrow dispersion loudspeakers, having different spectral content off axis than on axis, sends spectral energy that does NOT sound like the direct sound on reflection "zones" (love this word Duke, well done). Its all about the sum of these two complex sources of (direct vs reflected) energy at your ears, because when they combine with each other they partially cancel or completely cancel each other. Longer path = longer time= phase shift. This is the idea of nearfeild monitoring in studios, reduce the amount of reflected energy by sitting closer and moving the speakers further from the walls (smaller triangle). Now you can hear more of your monitor and less of the room. Engineers use this idea to help them get a more consistent sound in the different rooms they work in without changing speakers, using EQ or DSP (all of which adds another "veil" to the direct sound). I remember seeing Kevin Shirley mixing about 2 feet from his speakers which were about 2 feet apart. Not so much "room sound" in such a set up.

Thanks very much for this informative very important post for me....

That help me to understand the way my controls devices work....And damn ! they work amazingly but i was not being able to understand why.... Your post is the first step for me to understand....The concept of the "spectral content" was lacking in my ignorant and rudimentary acoustical knowledge.... I created my acoustic controls by listenings experiments and intuition without being able to understand why my results at the end were so totally transformative, even if they are unorthodox to say the least....I will not go further here about that tough....

My best to you....

Hi Brad,
Yep, that's one reason I often recommend audiophiles listen to their speakers from 2' away.  The difference in clarity and resolution and tonal balance between that and the normal listening position is mostly the room.  Once they understand that, they can better decide if treating the room would be wroth it.

Best,
Erik

If I ask someone with Floyd Toole level knowledge of loudspeaker-in-room acoustics (which I can with Billy Woodman at ATC),  he would tell me that consistent spectral content of direct vs reflections is the key to imaging.  If the reflections look very similar in spectral content to the direct sound it will image well.  That's why he builds wide dispersion loudspeakers. Narrow dispersion loudspeakers, having different spectral content off axis than on axis, sends spectral energy that does NOT sound like the direct sound on reflection "zones" (love this word Duke, well done).  Its all about the sum of these two complex sources of (direct vs reflected) energy at your ears, because when they combine with each other they partially cancel or completely cancel each other.   Longer path = longer time= phase shift.   This is the idea of nearfeild monitoring in studios, reduce the amount of reflected energy by sitting closer and moving the speakers further from the walls (smaller triangle).   Now you can hear more of your monitor and less of the room.  Engineers use this idea to help them get a more consistent sound in the different rooms they work in without changing speakers, using EQ or DSP (all of which adds another "veil" to the direct sound).  I remember seeing Kevin Shirley mixing about 2 feet from his speakers which were about 2 feet apart.   Not so much "room sound" in such a set up.

Brad    

There is so many variables. 
We have all different speakers with more or less amount of high frequency output.
Some sit with a "full range" tang band 8" and others has more/higher frequencies + added super tweeters. 
I guess the last example will probably more likely need more absorption coverage area of the walls.
(Then it is a good idea to take in and out the carpet if switching between those two different speakers in the room. A way of "Tuning" the room depending on what gear is used.)

OK, we can see it as the acoustics in the listening ROOM and the acoustics in the recording ROOM. 
The record "CHASING THE DRAGON - AUDIOPHILE RECORDINGS VOL 1" from Mike Valentine. Has two tracks:

2. Cello Interior: Bach's Cello Suite No. 1
Interior: In an English church, 3 M50's were set up to record cellist Justin Pearson performing Bach's Prelude. Between the mic, a Jecklin Disc was placed. This increased the separation of the spaced pair. The acoustics of the church are wonderful!
3. Cello Exterior: Bach's Cello Suite No. 1
The same microphones, performer, cello and the same piece of music... but this time recorded outside in the graveyard! How important are acoustics? What would it sound like to be able to remove the church from the last recording? Compare the tracks to hear for yourself the results of this interesting experiment! Which do you prefer?

It is very benefiting that our room do not has its own colorfull acoustics then you are not hearing what Mike Valentine intended us to hear in his recordings.
If we exaggerate and take and rig our stereo in the "big English church" as our listening room and listen to track "3. Cello Exterior".

Then we will hear almost the same as if we used well treated room/earphones and listening to track "2. Cello Interior"!

So if we are listening in a reverberant, colorful room. We will get used to that and at the end it will be our preferences. But everything we play will get that reverb and color. That were not intended to be there by the technician/artist. But you now prefer it but we can if we want always adjust our preferences. (See below) :)

As in those two tracks, examples above I actually in the beginning preferred track "2. Cello Interior" over the "3. Cello Exterior". 
Because that is the normal sound that we are USED to hear it in a reverberant space as a room is.

But after a while I noticed that I changed opinion and started to like "3. Cello Exterior" more and more. When I discovered that when the room were removed and all of its reverberation and color THEN I easily could hear how the cello itself sounded and how the whole resonant cello body sounded without any room smearing all over it. That were a great educational experience for me (not every day you hear a cello playing in free air outside (closest we get to a anacoic chamber))

Yes, reflections can 'enhance' the sound - though unchecked they will play havoc with precise imaging/scaling and the individuality of recordings.
Some can't get enough of reflections - Amar Bose built a company on speakers leveraging enveloping reflected sound. Not for everyone though. 

I've certainly enjoyed previous systems in rooms without any acoustic treatment, though wouldn't go back to that now.

This has been an interesting thread. I’ve got a buddy who has gone completely opposite.

14x15’ room with 10’ ceilings, hardwood on concrete, drywall... listening sofa backed up to the rear wall... subs in both front corners... speakers pulled out 6’ from the front wall and positions to take advantage of reflections to create a sound presentation that can best be described as total immersion.

Ok, maybe imaging is not the best and some songs can be a little bright but overall the sound is very lifelike and enjoyable.

Another observation is that low bass is radiating omnidirectional so those low frequencies are radiated behind the speakers. I see great corner bass absorbers. But there is also thin foam that will not help against that the bass is reflecting from those surfaces. Instead those foam will only take hi frequency reflections and also contribute towards "over-damped" feeling. Maybe remove or replace with thicker absorbers. 

I found some mid/high absorption behind the speakers to be beneficial, the corrugated foam is there for that. As you say, it won't provide any absorption at low frequencies. It's a balancing act though, too much absorption definitely kills the sound. I've tried diffusers in place of the absorbers in that position, but I prefer the mix of both.

When my house was built I had some input into the room dimensions, which follow one of Sepmeyers ratios to avoid stacking of bass modes. This seems to have alleviated the need for heavy bass trapping, I certainly don't have any obvious bass drone or boom.
It probably also helps that my ATC speakers are blessedly free of bass bloat. Though quite extended, the active SCM100 maintains iron fist control of the bass for a taut linear sound. 

Is those cool white 3d diffusers the "styrofoam" or other material? 

They are Vicoustic DC2 styrofoam diffusers. Lightweight and easy to hang with removable 3M velcro tabs.  
The diffusers can be applied more liberally than absorbers before detrimental effects on balance - but everything has its limit, so best to add any treatment in steps rather than slathering it everywhere.

Success on Audiogon means one thing:

When people follow you from thread to thread and post the first knee-jerk reaction they can think of.

Worship me, A’goners, for I have achieved the highest level of satus among Audiophiles, and my evolution among many many lifetimes can stop. I have become perfect among the dissatisfied ne’er do wells who frequent these halls and where I shine my light they must attend.

Dance upon my threads of enlightenment, sing for my enjoyment, and never cease looking to me for approval, you jerkers of the knee,  you mighty mighty spleen venters and I will acknowledge you in time.

What a bunch of baloney.

Wait a minute. Wait just a doggone minute. The man clearly said:
"it is my experience that even then we hear not photonically but statistically." You call that baloney? Word salad, I say!

"In a modest, average home listening environment, you can’t do much for the acoustics with just 4 panels, no matter how ideally placed they are."

why 4 panels? 2 for each side walls, one for behind the listening position, 1 for ceiling (but really a cloud needs to be at least 2-3 panel wide) and 1 for the floor= minimum of 5.
not sure who told you 4 (I guess some dont treat the floor)

the definition of FRZ is at least covering the 5 early reflection points. so only 4 panel is not reallya chieving a free-reflective zone (FRZ)

" Part II:
The overall decay rate of the energy in the room will probably so obscure the original and early reflected signals requiring a minimum critical mass of room treatment, or minimum sound field quality that must be achieved before those original 4 panels mean anything. Control the reverberation time first, and with 4 panels you are barely getting started."

this is quite confusing. early reflections are well established to be detrimental to SQ. secondary reflections (which you refer here as "sound field") have been well established to actually be desired for good sound. hence some studio room desing with trying to actually reflect the secondary reflections to the listening position.

" Part III:

"Once the overall sound field is treated, the _exact_ placement of the original 4 panels. becomes moot. You can move around the room and everything sounds good, no matter where you are, and no matter if the current reflection points (which change based on your position) are covered or not."

the definition of a early reflection must be located at one spot. its that one spot that determine the early reflection points. if you want to cover early reflections with multiple listening position that are far apart from each other, this is a almost impossible (unless you have every listening position on the same couch for example, there youd just have to have wider panels to englobe every different listening position) task as each different listening position will have its own different early reflection.

" Part IV:

"While the overall idea of our ears seeing / hearing mid-treble frequencies as light beams is attractive, it is my experience that even then we hear not photonically but statistically. Covering up that magic reflection point to 1 ideal seated location is a trivial if not imperceptible change. Treat early reflections statistically, not precisely. "

what a bunch of baloney. early reflection points are physics. its not magic, they are a fixed point related to the listening position.

about the behind the speakers panels. by definition, there’s no early reflections coming off behind the speakers (unless your speakers are toed in 45 degree). those "behind the speaker reflections" are called SBIR and its a entire different discussion.

just to add a bit, early reflections are those over the 300hz barrier. bass frequencies being omnidirectional are not related to early reflections. for bass, you need deep bass traps, as deep as possible.

sorry if yesterday ive acted a bit rude, in retrospect it was. sorry

Let me alter my thesis, because the original was so hard to transmit, even by those who really know their stuff. In fact let me reword it ENTIRELY.


"In a modest, average home listening environment, you can’t do much for the acoustics with just 4 panels, no matter how ideally placed they are."
There.

And that is what I was sold, long ago, as something useful. Get 4 panels, put them on the reflection points and imaging and detail will get better. I’ve done this. It does not. You can’t do anything with these 4 by themselves.

Part II:

" The overall decay rate of the energy in the room will probably so obscure the original and early reflected signals requiring a minimum critical mass of room treatment, or minimum sound field quality that must be achieved before those original 4 panels mean anything. Control the reverberation time first, and with 4 panels you are barely getting started."


Part III:

"Once the overall sound field is treated, the _exact_ placement of the original 4 panels. becomes moot. You can move around the room and everything sounds good, no matter where you are, and no matter if the current reflection points (which change based on your position) are covered or not.

Part IV:

"While the overall idea of our ears seeing / hearing mid-treble frequencies as light beams is attractive, it is my experience that even then we hear not photonically but statistically. Covering up that magic reflection point to 1 ideal seated location is a trivial if not imperceptible change. Treat early reflections statistically, not precisely. "
Of course, much here in part IV can probably be informed by Head Related Transfer Function research, which I have not looked into.

I'm clearly not saying not to treat the wall behind the speakers or to the sides, or the floor or ceiling.  I'm saying that the original messaging, that there are 4 magical places you must put panels on and that alone will provide noticeable improvement oversells the benefits.


Best,
E

Keep in mind that bass traps can go in more places than behind the speakers. Every corner, including wall to ceiling, and wall to floor can be a good place for them. The GIK soffit traps for instance are meant to be mounted along the soffits, or the line where the wall and ceiling meet.

Yes, overdamping is always possible, which you can prevent by carefully picking the products used as well as making sure to include diffusion.

One trick I often suggest listeners missing bass is to add mid-to-high frequency absorbing panels. They will act like an equalizer, and lower the overall mid-treble energy, and boom, like a ship emerging from the water at low tide, here is the basss!! It’s amazing how you can do this with small speakers.


Best,

Erik

I found too much absorption on the side reflection points over-damped the sound. I opted for Vicoustic Wavewood diffuser/absorbers in that area, which sounded much more balanced than my thick DIY absorber panels.

That is good to hear! I love your room!
As you say the "Vicoustic Wavewood" is not the same as absorbing panels when they reflect more of the higher freqencies sound on most of the area.

I look at your pictures. And that mat is great for just that. To tweek how much "over-damped" sound we like to have or not.

As we know the floor mat does nothing for the first reflection point on the floor but it acts as a thin absorber that it what it exactly is.. So it absorb only the high frequencies (she the link on the subject that I posted earlier)

So if you experience "over-damped" then out with the mat. If it is to lively in with the mat. :)

Another observation is that low bass is radiating omnidirectional so those low frequencies are radiated behind the speakers. I see great corner bass absorbers. But there is also thin foam that will not help against that the bass is reflecting from those surfaces. Instead those foam will only take hi frequency reflections and also contribute towards "over-damped" feeling. Maybe remove or replace with thicker absorbers.

Is those cool white 3d diffusers the "styrofoam" or other material?
(I never had any experience of them and it is great to hear that they work in that material in that case)

I've found treating first reflection 'zones' to be very beneficial in my 6 x 4.3 x 2.7m (L/W/H) room.

Many other things come into play of course. Optimum speaker positioning for best sound balance is fundamental and should be determined before adding treatment IMO - the latter should not be used as a bandaid for lazy positioning/toe-in etc. 

I used experimentation to determine what sounded best to my ears, propping up panels with stacks of books or whatever else I had handy so I could move/orientate panels and then listen.
I found too much absorption on the side reflection points over-damped the sound. I opted for Vicoustic Wavewood diffuser/absorbers in that area, which sounded much more balanced than my thick DIY absorber panels.
Treating the ceiling reflection 'zone' between the speakers and listening position with eight 600x600mm diffuser panels provided one of the most profound improvements in clarity and image focus/stability.
https://systems.audiogon.com/systems/2229#&gid=1&pid=1

ADMINISTRATIVE ALERTS

murphythecat has been ignored due to the use of word salads to belittle others. 

Please ignore it without fear of being impolite.

This concludes this alert of common sense and good manners.

ok, after reading the OP’s. he’s full of cough cough
clueless dude when it comes to acoustic. hahaha.
I suspect he read Toole "studies" then drink the cool aid. worst, you think you understand room acoustic now.
Eric, yes first reflection points are a "myth" like you say. you can sleep soundly now.

EDIT:
" Wow, @lemonhaze you misread my original post and misread my "preaching to the choir" post and now are all mad about both.

Let’s just agree to disagree and move on."

I guess I did too eric misunderstand your OP. you begin the thread with "1st reflection is a myth", then finally go on to admit you know close to nothing to "should noobs buy a mic or ask experts at GIK".

Understanding the basic of room acoustic honestly took me a good week of reading, asking experts at gearslutz, GIK, in order to simply understand the basics of it. I wasnt sure if I should trust GIK alone, so went my own way and must have read at least 100 hours on room acoustic subject. Gik are mostly right btw. I personally think they sell too thin panels however, DIY is much much much better value for money if you want to create a FRZ (free reflective zone). 

for the OP

Are you sure you have well determined the 1st reflection points? have you treated all 1st reflection points? meaning the 1st reflection at the ceiling, at both side walls, behind your listening position and off the floor?

ime, even just treating the side walls, then removing the side-panels, makes a tremendous difference. but the magic happens when all 5 first reflections points have been dealt with.

as the post prior to mine mention, make sure your panels are thick enough with good fiberglass or real material used from the likes of GIK. carpets actually make thingrs worst cause they absorb upper mids and treble, but do nothing in the bass and mids. ideally, you want your 1st reflection panels as thick as possible (mine are 8 inch thick). the goal of room treatment is to acheive even decay (ETC) at all frequencies, but carpets will make just the opposite (will absorb the highs, but do nothing in the bass therefore it really doesnt acheive the goal of even decay at all FR)

may I suggest that moving speakers into a near-field listening position,

To no avail.... People dont realize that nearfield listening cannot canceal the room acoustic at all... I know that firsthand, i listen to the 2 positions and i had implemented not only passive but also active room controls...

The impression that listening nearfield gives you some freedom from the room acoustic is only an illusion born with a comparison between the 2 positions before any working methods of controls were incrementally put in place....Without any changes in acoustic of the room, nearfield ans regular position of listening for sure are different but they are greatly affected by the presence or absence of room controls and treatment anyway....

You can’t do much with room acoustics until you reach a critical mass.

My experience concur with that... Optimal results cannot be gained without this critical mass of active controls and passive treatment...An equilibrium between absorbing, reflecting and diffusing for me....And more than that also the use of active devices....


In acoustic of "small room" only your EARS can do the job, because of the geometry and topology of the room and because last and not least of the acoustical variable content of the room furnitures and objects.......

Timbre instrument perception and imaging perception are phenomenon for living ears only.....They dont comes at their OPTIMAL actualization only by virtue of a correcting apparatus of any kind....

Ears are king in the kingdom of sound.... Especially " biased" one because it is these biased ears of yours that will listen your music in this room of yours....There is no 2 identical pair of ears by the way....And the complex structure and dynamical properties of your ears and of the room are ONE indissocciable phenomenon in the music experience....

:)

I saw a interesting video about carpet and first reflection floor points.

Here is a myth to bust!

The carpet that we can see as a thin sound absorber do NOTHING to the first reflection point on the floor.

Instead what the carpet do is that it absorb only/mostly the high frequencies instead from 2nd and higher order of reflection.

Something to keep in mind. Look at the graph in the video:
https://youtu.be/GpDHo1jNhss

This example with thin carpet shows that we should always go for the thickest absorbers that we can get.

There really is no issue in my mind to be fixed. 

It's more of a theoretical discussion. 

Maybe another way to word it is this:

You can't do much with room acoustics until you reach a critical mass. 4 2' x 4' panels in a modest living room are probably not going to do anything by themselves no matter how well placed.

This is a great thread,

may I suggest that moving speakers into a near-field listening position, i.e. far away from the walls or using omnidirectional speakers is a better way to address the issue than selectively cutting out some reflections and parts of the frequency spectrum. If needed, bass traps in the corners of the room are obviously useful.

It is easy to absorb frequencies down to about 250 Hz. If one does not get overly aggressive with the treatment the spectral balance of the sound will not shift much. For those of us with full spectrum room control it does not matter as any shift can be easily corrected. 

20% is a huge amount of wall area. First of all, the area you treat is going to depend on a number of variables like how big the room is, were your listening position is relative to the speakers, the type of speakers used, etc. Only 4% of my front wall is treated. 

Brownsfan, I mention this above. Speakers with limited or controlled dispersion patterns will require less treatment than speakers that are omnidirectional. They will have fewer early reflection points/zones.
Examples are horn speakers, dipoles and line sources. 

Imo there is an alternative approach which starts out with the design of the loudspeakers themselves, and which does not call for anything remotely approaching treatment of entire room surfaces in order to get good results. Briefly, the loudspeaker sends spectrally-correct energy in directions which minimize early sidewall reflections, and the reverberant energy is allowed to decay more or less naturally, perhaps using diffusion, as opposed to being rapidly absorbed. If anyone is interested I’ll go into detail.

@audiokinesis , I’m very interested in what you have to say on this, so if you are so inclined, please elaborate. Not that I want to distract you from completing my Swarm! ;>)

"You could easily circumnavigate the laser point and it would be much much better than merely putting panels on that point."

I don’t think I’ve ever advocated a "reflection POINT" paradigm; I think I’ve been talking about a reflection ZONE.

"And that unless you are in a small home recording studio, where you can touch the left and right walls at the same time, the correct placement being off 6" here won’t matter."  

Are we actually within six inches of agreement?

Duke

Imo "best acoustic principles" in a small room includes correct PLACEMENT of acoustic treatments.

And that unless you are in a small home recording studio, where you can touch the left and right walls at the same time, the correct placement being off 6" here won’t matter.

You could easily circumnavigate the laser point and it would be much much better than merely putting panels on that point.

" My gods we are being so literal."

Let’s not descend into arguing about arguing.

" I’m saying that if best acoustic principles call for 20% absorption on a wall surface near the speakers, whether those panels EXACTLY cover a reflection point which works for exactly one seated position is irrelevant. "

I understand what you are saying.

And I disagree.

Imo "best acoustic principles" in a small room includes correct PLACEMENT of acoustic treatments. 

Duke

If I understand correctly, you are still looking at small rooms as if they were large ones, where 20% wall coverage has the same effect no matter where that 20% is located.

My gods we are being so literal.  I'm saying that if best acoustic principles call for 20% absorption on a wall surface near the speakers, whether those panels EXACTLY cover a reflection point which works for exactly one seated position is irrelevant.

You can be off that singular, zero size point by a couple of feet and it will still sound good.

Conversly, ONLY covering that zero area point with a 1'x1' panel will be negligible.

@erik_squires wrote:

" What matters is that portion of the wall, and the overall, average results. For instance, covering 20% of the wall with absorption and 5% of it with diffusion, as needed. "

It sounds like you are still looking at small rooms as if they were large ones, where 20% wall coverage has the same effect no matter where that 20% is located. And I disagree, because in a small room the earliest reflections will not only be the loudest but also the most likely to be detrimental, therefore THOSE are the ones we should pay the most attention to.

And I think that in general you lean more towards absorption, whereas in general I lean more towards diffusion, because I want to preserve the spectral balance of those reflections. If their spectral balance is inherently bad (because of poor radiation pattern control), that’s a different situation - then we would be using room treatment in an attempt to FIX a problem which ORIGINATES with the loudspeakers. And that is not easy to do well because room treatments are generally not frequency-region-specific enough in the RIGHT regions; room treatments generally paint with broad brushes, so to speak.

I’ll go along with the "AS NEEDED" part, with each of us obviously having a different idea of what that means.

Duke

First, to the extent that absorption is more effective at short wavelengths than at long ones, it will change (darken) the spectral balance of those first reflections. That may still be a worthwhile net improvement if the room is overly reflective, but in general it is desirable for the reflections to have approximately the same spectral balance as the direct sound.

Yes, that is a problem higher frequencies is easier to absorb than lower ones. And will result in darken and we loose the "spectral balance".

It is good to always keep that in mind when we choose asorbent treatment. When we known that the lower frequency gets and the wave lengths get longer the thicker the panels need to be. For them to to have a high absorption coficient lower down in frequency.

Yes in practice the depth will be unreasonably thick.. So you can never have to thick panels so no worry there.

But if we always go as tick that we can or care for is desirable. 

To lessen the risk to end up with a dark/lifeless acoustic sounding room. 

We see that it is not only coverage area that matters. It is the thickness also. 

I would chose fewer and thicker absorbers than many more of them and thinner ones. To not get the issue that is in citation above.

Remember it is in bass their is the most energy and the most difficult frequency range to treat and therefore the most problematic. And will not get solved easily.

I have big few panels that are 19 cm thick (I wish they were thicker) on first reflection points (and two in the corners their bass builds up) I always think "bass first". When we put up absorbers we get a reduction of high frequencies "automatically". 

Another "trick" to get the absorbers you have to get better asorbtion coefficient at lower frequencies is to distance your panels from the wall. They will act as they are thicker than they are. All to just try to optimize bass absorption that we are in disadvantage at the get go.

I hope this helped someone. :)

My reservations about using absorption on the entire surface,

Also not what I meant, sorry.  I meant treating the surface appropriately.  That rarely means covering the entire surface but considering the entire surface.

You have this 1" by 1" reflection point.  That is irrelevant. What matters is that portion of the wall, and the overall, average results.  For instance, covering 20% of the wall with absorption and 5% of it with diffusion, as needed. 

 Great dissertation Duke.

 The rooms most of us listen in usually do not reverberate, they are to small. A 10,000 seat indoor venue reverberates.

The reflections in our rooms occur relatively early and die off quickly. The early ones that reach your ears are interpreted as part of the music the effect being that of a blurred picture which in audiophile terms is a lack of detail and a blurred image. Preventing the earliest reflections from getting to your ears is always worth while including those of us with full spectrum room control. Zones, points or whatever the goal is to block reflection by absorption. We have discussed how to locate these areas. Absorbing sound below 200 Hz is difficult. The lower you go the more difficult it becomes.

Over doing it is just as bad as not doing it at all. It is just a waste of money and cosmetically unacceptable not to mention that it sounds as if your head is stuffed full of cotton.

Duke alludes to a very important point. Certain speaker designs by virtue of the way they radiate sound create fewer and/or less powerful  reflections. Horns, dipoles and line sources are examples. You don't have to worry about absorption below 200 Hz if there is no reflection.

@erik_squires wrote:

"I believe most audiophiles would be unable to tell if those treatments were at the reflection points or not, and that in many cases 4 panels of 2’x2’, no matter how well placed, would be unable to effect an audible improvement."

and

"By ["treat"] I mean to alter the [room] surfaces by increasing the absorption and decreasing the ability of those surfaces to throw a coherent reflection by both absorption and diffusion."

Thank you Erik.

My reservations about using absorption on the entire surface, rather than just on the places where it has the most beneficial effect, are twofold.

First, to the extent that absorption is more effective at short wavelengths than at long ones, it will change (darken) the spectral balance of those first reflections. That may still be a worthwhile net improvement if the room is overly reflective, but in general it is desirable for the reflections to have approximately the same spectral balance as the direct sound.

Second, absorption continues to be effective long after the first reflections... ALL subsequent reflections which strike the absorptive material have their spectrum and overall loudness altered accordingly. So treating entire room surfaces can result in an overly dead room.

Reverberation time is seldom an issue in small rooms unless they have a slap-echo issue, and even then treating the entire wall with absorption is probably unnecessary. (Some argue that the term “reverberation” is actually inappropriate for small rooms because discrete reflections dominate, but I think it conveys a useful concept.)

As has been mentioned, loudspeakers are not true point sources, nor do we normally sit with our heads sufficiently in a vice that a 1 foot square treatment panel is what anybody is advocating. So I think "first reflection zones" is a more useful concept than "first reflection points."

I think you and I disagree on whether the timing and magnitude of reflections matters. If not, then neither does it matter where your absorptive panels go. If it does, then where they go also matters.

As I stated before, imo your assumptions are valid for large rooms (wherein the reverberant field is uniform enough that the reflections average identically at any given location) but not for small ones (wherein we have discrete reflections at any given location).

It sounds to me like you want to use enough absorptive acoustic treatment panels to make a significant difference throughout the room. Imo that would make sense ONLY if the speaker’s off-axis response is so bad that the reflections are generally detrimental. If the reflections are beneficial, weakening all of them and degrading their tonal balance with absorption would be detrimental. I’m not saying absorption has no place in home audio, but I am saying that the less of it we "need", the better.

Imo there is an alternative approach which starts out with the design of the loudspeakers themselves, and which does not call for anything remotely approaching treatment of entire room surfaces in order to get good results. Briefly, the loudspeaker sends spectrally-correct energy in directions which minimize early sidewall reflections, and the reverberant energy is allowed to decay more or less naturally, perhaps using diffusion, as opposed to being rapidly absorbed. If anyone is interested I’ll go into detail.

Duke

Erik, first reflection "point" is probably an unfortunate term, which probably derives from conventional techniques used to determine the area in question.   First reflection zone would probably be much more accurate. Look at your REW impulse graphs.  You don't see a single intense reflection at, as example, 9.6 ms.  That is what you would see if the side wall early reflection came from a single point.  Instead, you see a cluster of reflections in a band that may be 3 ms wide or more.   All of those early reflections, or at least the higher frequency component of those reflections, are going to compromise image. 

An interesting experiment is to look at REW impulse graphs before and after adding conventional absorbing panels to those first reflection zones.  Even a GIK 6" full range Monster trap won't attenuate side wall first reflections anywhere close to the -20dB (compared to impulse) level necessary to mitigate 1st reflection erosion of spacial clues in most rooms.   An angled barrier that reflects sound back to the front of the room is a much better approach.  Depending upon the size of the barrier, some of the sound (low frequencies) will just wrap around the barrier as if it weren't there.  But the shorter wavelength (higher frequency) sound that is responsible for localization, won't wrap around the barrier but instead is reflected back towards the source.  The sound isn't turned into heat by absorption, it is just turned from an early reflection into a later reflection that adds to the perception of spaciousness. 

Maybe the only real problem is how I interpreted this information early on.  Maybe it was never meant to be a point thing but a starting place?

Of course quantity trumps.

If you have 6 or 40 panels. 40 is 6.66 times more area than only 6 panels.
And when a reflection is more than reflecting one time. Let say it bounces 3 times before it is so week that it is -60 dB.

Then we have 6.66 times x 3 bounces gives us 20 time more treatment... 

So that is why we do not react or find any big difference on if you treated the first reflection points or not when I'm comparison to a room that have 20 times more treatment than the other!

I still say not all have of different reasons (time, founds or ascetics) not willing to get 40 pieces of treatment all over the room.

In most cases maybe you only buy 2/4/6 panels maybe bigger and thicker 1m x 0.5m each.

And we known for each reflection sound does it get weaker and weaker. So if/when you only got a few panels (less of a coverage area) then we start to treat the strongest reflection that is the first one. Of course absorbers will not take all reflection away. And of course the few panels will not contribute as much as if you had 6.66 times more panels and coverage area.

But it is for most of us a starting point and we can always add more panels along the way.

@erik_squires , 

Floors are a different thing, but we don't spot treat floors. We treat the entire area in front of a speaker. I've never seen anyone put down a 2'x2' carpet exactly in the first reflection point, and this is kind of what i mean. 

Eric, I have a dedicated room.  I made 2'x4'x4" OC 703 panels that cover first reflection points on both the floor and ceiling.  The rest of my floor is untreated.  I realize this is not common, but I have a dedicated room and I am the only listener, so I can do what I want.   Both ceiling and floor "treatments" have very little influence on imaging in comparison to my side wall "treatment."    They certainly offer other benefits. which more than justify their use.  I have considered modifying my ceiling panels in order to add forward facing reflection to the existing absorption, but have not done so yet. 

As I recall, my measurements show that the floor and ceiling reflections are delayed about 4-8 ms, whereas the side wall reflections are more in the 6-12 ms range.   Without treatment, the ceiling and floor reflections are louder than those from the side walls.   With treatment, the side wall reflections are substantially reduced, whereas the ceiling and floor reflections remain relatively high.  To a certain extent, I think this is indicative of how much more effective reflection is compared to absorption.  

From my perspective, sidewall 1st reflection point treatment is conceptually sound, and in my room, theory has been supported empirically.  Imaging and localization in my room is superb.  It is the best by far that I have ever heard in a narrow room.  If you have experienced something different, perhaps that is because you are attempting to "treat" your sidewalls using panels that are not up to the task.  Again, I'm going to suggest that before you discount the concept, you evaluate the approach articulated at least twice by Duke and several times by me.   Rip a 4x8 sheet of half inch plywood into 2 x 8 sheets and place them along the side wall behind the first reflection points angled so as to reflect sound back to the front of the room and away from the MLP.  This is enough to reflect the wavelengths that are important to localization clues, and it turns early reflections into late ones.  It is a cheap and easy experiment.  Keep in mind that the first reflection "point" is far from a point, because the sound coming from your tweeter and midrange will spread out as it travels rather than proceed as a laser like ray.  So you will need to experiment with placement and angle.

Let me try this another way. Imagine a highly reflective room with a pair of traditional 2 way speakers and 1 listening chair in a fixed location. The room is 20’x20’x15’ tall.

There are at least six (eight if we include the ceiling) first reflection points. Being points, they are infinitely small. The audio legend is that these specific points are more important, by far, than any other place in the room. In this room we may place 1’x1’ absorptive panels.

My argument is that the legend/myth is wrong. The first six reflection points are not going to be noticeably better than any other place to put an absorber or diffusor.

Lets go through a bit of a mental exercise. We’ll consider two sides to this.

First, the very sparse case in which we treat six points and only those. At six absorbers the room remains too lively to make much of a difference.

Let’s consider the opposite situation. We have 40 panels of the same 1’x1’ dimension. Now we can make enough of a difference in the reverberant field to affect the sound quality. We put 20 or uniformly spread across the wall behind the speaker, and 10 on each side on the speaker end.

Let’s say by chance, four of these panels (2 on the rear, and 1 on each side) are exactly on the first reflection points in terms of the listening chair. In this case, removing those four panels and randomly relocating them will make a very small, if any, noticeable difference.

And this illustrates my point. Treating the initial reflection points is actually not as important as treating the room. The audiophile using a mirror to place a panel exactly on that spot is wasting his/her time.  What is more important, by far, is getting a critical mass of room treatment so that the reverberant field becomes well controlled.

So if I understand correctly, you are saying that treating the relatively small area where a reflection occurs is "practically useless"

Yes, in that I believe most audiophiles would be unable to tell if those treatments were at the reflection points or not, and that in many cases 4 panels of 2'x2', no matter how well placed, would be unable to effect an audible improvement.

And, just so we’re on the same page as much as possible, can you describe what you mean by "treat"?

By this I mean to alter the surfaces by increasing the absorption and decreasing the ability of those surfaces to throw a coherent reflection by both absorption and diffusion.



Best,

Erik

Erik wrote: " We shouldn’t spot treat surfaces. We should treat the surface. That is, putting 2’x2’ panels in exactly the side, rear and even floor reflection points is practically useless. What does work is to treat the floor, side and rear. "

So if I understand correctly, you are saying that treating the relatively small area where a reflection occurs is "practically useless" - instead, we should treat the ENTIRE room surface - the entire wall, or the entire floor, and/or the entire ceiling.

Am I understanding you correctly?

And, just so we’re on the same page as much as possible, can you describe what you mean by "treat"?

Thanks!

Duke

Floors are a different thing, but we don't spot treat floors.  We treat the entire area in front of a speaker. I've never seen anyone put down a 2'x2' carpet exactly in the first reflection point, and this is kind of what i mean.

Audiophiles at some point were encouraged to use a flashlight and mirror to find first reflection points and center acoustic panels there. I call that particular practice bunk. 

We shouldn't spot treat surfaces.  We should treat the surface.  That is, putting 2'x2' panels in exactly the side, rear and even floor reflection points is practically useless. What does work is to treat the floor, side and rear.

Get a carpet to put in front of the speaker, treat the side walls and rear wall and wall behind the listener. Where the mirror points are won't matter.

Best,

E

hsw, I'm only going to answer for myself here.  My understanding is that humans are naturally more adept at localizing sources in the horizontal plane.  Our outer ears are mounted on the sides of our heads and aren't especially well designed to pick up vertical clues.  Presumably, our brains are similarly well suited for localization of sources in the horizontal plane.   What I can tell you is that in my room, which is 14 ft wide with 8 ft ceilings, effective "treatment" of the side wall 1st reflection point is orders of magnitude more important than "treating" the ceiling and floor 1st reflection points in providing a deep and wide image with good localization of instruments and voices.  My floor is not carpeted, and my ceiling is typical texture over drywall.   I'm not going to say that rugs and room furniture don't matter, just that in most rooms, treating the floor and ceiling don't matter nearly as much as treating the side walls with respect to imaging.  If you have a room that is atypically wide, or speakers that don't have wide dispersion, you may see something different.  Also, what you do with the floor and ceiling can certainly impact other aspects of room performance.  Floor to ceiling bounce can be a big contributor to slap echo, as example. 

@erik_squires, have you tried what Duke is suggesting on the sidewalls?  I stumbled onto this idea of redirecting the sidewall 1st reflections to the front of the room several years ago quite by accident.  Every attempt on my part to reproduce the benefit of redirecting by using absorbance has failed.  The image just collapses.  Had I not experienced just what this technique can do myself, I might be arguing as you are.  

Hsw wrote:  " Is this discussion only limited to lateral reflections? It seems to me the floor is the largest first reflection. "

The floor bounce usually is the strongest early reflection, but perceptually is is not as detrimental as its magnitude seems to imply.

The floor bounce doesn't have a strong spatial effect, as it occurs in-line with the direct sound from each speaker.   

The floor bounce does result in a cancellation (comb filter) notch in the  frequency response at the listening position at the frequency were the reflection arrives 1/2 wavelength behind the direct sound.   

From a perceptual standpoint, the floor-bounce notch can be filled in by energy which arrives within a few milliseconds, such as by the ceiling bounce.  The ceiling bounce and the floor bounce will have different notch frequencies and will tend to perceptually fill in one another's bounces.   

The floor bounce notch is most audible when there are no soon-arriving reflections to fill it in. An example of this situation would be when talking with someone outdoors.  There will be a lower midrange frequency response notch from the bounce off the ground or pavement, with no other reflections arriving to fill it in.  Walk indoors to continue the conversation and the timbre of the person's voice noticeably warms up, and I think this is at least in part due to the floor bounce notch being filled in, perhaps largely by the ceiling bounce.   

The argument has also been made that our ears are so accustomed to the floor bounce notch and other naturally-occurring comb filter effects that we largely tend to ignore them.  That's NOT to say that there is no benefit from minimizing or removing them - only that they do not tend to cause colorations which draw attention to themselves.   

Imo there IS benefit from reducing the magnitude of the floor and ceiling bounce notches, or otherwise breaking them up.  But it is also my understanding is that they tend to be perceptually relatively benign in a home audio setting.   

Duke

Is this discussion only limited to lateral reflections? It seems to me the floor is the largest first reflection. Is there a contention that rugs or room furniture don’t matter?

We think we know acoustic.... But acoustic is like other science full with unresolved mysteries....

I just read an article, an interesting one, where 3 specialists discuss without being able to be in total accordance about the basic acoustical treatment....And they are specialists....

https://www.acousticsciences.com/media/articles/room-acoustics-audios-final-frontier

Myself how can i change my room acoustic with cheap metal buckets glued together with an array of different stones on them ? The stones making a difference in the reverberation time control....

Is there a set of linear differential equation to explain that?


:)

For reflections we can use them or neutralize them..... In a small listening room it is better to use them......In a control room it is better to neutralize them.....

Myself i use them .... With success.....



« Complex waves of sound are akin to some cellular animals, they live a long life themselves but that look like milliseconds for us» -Groucho Marx