Acoustic treatment

Anything the right size with any damping material can be a bass trap. A walk-in closet is a bass trap. Robert Harley's The Complete Guide to High End Audio has a whole section on the design of bass traps, a lot of which is probably also available on-line for free. Just as available on-line for free you can read about distributed bass arrays and why they work so much better and make bass traps so much less important.

I’m a big fan of tiny little bowl acoustic resonators as opposed to big ugly Tube Traps or mattress size panels. They’re much easier to set up, too. As it turns out corners aren’t even the right place for Tube Traps half the time.

+1 millercarbon

     Bass tube traps, imho, are big, expensive, ugly as sin and are completely unnecessary if you invest in this instead:

https://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/

     This distributed bass array system will provide sota bass response in any room and seamlessly integrate with any pair of main speakers.  It'll also look a helluva better in your room than bass traps.
     I've been using this with large Magnepan panels for the last 4 yrs and can verify the review is very accurate.

Tim

Helmholtz resonators’ effective frequency is a function of volume of the bottle, the diameter of the nozzle and the length of the nozzle so even a Coke bottle can be converted into a tube trap. It’s not rocket science! 🚀 The problem arises at shows where many Coke bottles and beer bottles litter the room randomly, creating acoustic chaos. 

It is easy to Dampen frequencies 250 Hz and up. Doing so creatively can make a big improvement in imaging. Unfortunately as you go further down especially as the wavelengths get longer than 100 Hz it becomes progressively harder. I have played with tube traps in two installations with severe comb filtering and irregardless of anything I did with the traps could not get the variation below 10 db. This is walking around using a volume meter and tone generator. In both instances I told the customer that he needed a new room. Back then we did not have room control. Using a good room followed by careful positioning of the speakers and the listening position and damping primary reflections with the goal of improving imaging is the best way to deal with the problem of bass in an enclosed room. Some speakers and sub woofers are significantly easier in this regard. I have never seen tube traps work and my own opinion from my admittedly limited experience is that they are a waste of money. 

Oh and Mr Rocket science. How big would a helmholtz resonator have to be to resonate at 20 Hz? Anyone care to guess?

Size isn’t everything. I just got through explaining it. Hel-loo!

zardozmike,

     Simple, just buy and install the AK Swarm and forget about bass traps, room correction software/hardware, Helmholtz resonators, mijostyn and Mr. Rocket Science forever.

Tim

Or just buy more subs. I don’t see anything magical about the AK Swarm. What I gathered is that 4 subs, semi-carefully placed will essentially do a better job of EQ-ing itself than room correction software.

dtximages:
"Or just buy more subs. I don’t see anything magical about the AK Swarm. What I gathered is that 4 subs, semi-carefully placed will essentially do a better job of EQ-ing itself than room correction software"

Hello dxtimages,

     You're correct, the key to the distributed bass array (DBA) concept's effectiveness is having 4 subs distributed throughout the room and anyone can create their own custom DBA system using any subs they prefer.  Four small DIY subs or four huge and expensive JL Audio subs, or any subs in between, will work.  The DBA concept is scalable and flexible and provides accurate, detailed, smooth and natural bass response in virtually any room and seamlessly integrates this bass with any pair of speakers, even fast planar-magnetic and electrostatic speakers.
     You're also correct that you don't see anything magical about the AK Swarm or a custom DBA system, all the magic is heard and felt but not seen.

Tim

In the case of the much maligned CD not very much of the bass frequencies are coming through anyway so what’s the difference?

Has anyone ever tried having a single big sub and a few more smaller ones?  I'd think a single sub that goes to 20hz would be enough and then 3 smaller ones that only maybe go down to 30hz could be used to even out the response.  Locate the big one in the best spot for very deep bass and the other three can even out the response from 30-80hz.  There tends to be a huge price difference between subs that will go to 20hz vs 30.  

geoffkait:
"In the case of the much maligned CD not very much of the bass frequencies are coming through anyway so what’s the difference?"

Hello Mr. Rocket Science,

      True RS, most cds and vinyl recordings only contain summed mono bass from 20 to about 100 Hz but reproducing whatever bass there is on the source material with high fidelity is still important for an optimum listening experience.


Tim

jon_5912:
"Has anyone ever tried having a single big sub and a few more smaller ones? I'd think a single sub that goes to 20hz would be enough and then 3 smaller ones that only maybe go down to 30hz could be used to even out the response. Locate the big one in the best spot for very deep bass and the other three can even out the response from 30-80hz. There tends to be a huge price difference between subs that will go to 20hz vs 30."


Hello jon,
     Very good question.  I've never tried this myself but I don't believe there's any reason this wouldn't provide accurate, detailed, smooth and natural bass with deep bass extension down to 20 Hz.  I suspect, however, having only one sub extending down to 20 Hz might limit the power and impact heard and felt at that deep bass frequency.  But It may be possible to compensate by having the volume set higher on the sub that goes to 20 Hz or you could always use two and still be saving money, just a bit less.  
     You should also probably go look and hear some subs, 30 Hz sounds and feels quite deep and may be sufficient for some.


Tim       

noble100
geoffkait:
"In the case of the much maligned CD not very much of the bass frequencies are coming through anyway so what’s the difference?"

Hello Mr. Rocket Science,

True RS, most cds and vinyl recordings only contain summed mono bass from 20 to about 100 Hz but reproducing whatever bass there is on the source material with high fidelity is still important for an optimum listening experience.

>>>I’m afraid you missed my point. The bass information’s there on the disc, and tons of it, it just isn’t being retrieved properly or completely - not by a long shot! Even when bass is mono it should have slam, go low in frequency and be articulate. It shouldn’t be wimpy, thin, rolled off or bland. As fate would have it the CD playback systems are plagued by a number of technical problems - even after all these years that prevent a lot of information from getting to the speakers. Primarily, scattered light and vibration of the CD itself, but also some other problems.

I'm not going to address the reasons why you might, or might not want bass traps.  I'll just answer your question.  I've used Cotton Batting panels, Rockwool and Pressed fiberglass panels to make acoustic panels and bass traps.

I prefer making panels out of Owens Corning 703 & 705 fiberglass.  It cut's more easily and straighter than the other two options.  Additionally, when covering it with cloth, I find it comes out smoother than with the other two options if the cloth has contact with the insulating material. 

If you wear long sleeves, disposable respirator and safety glasses you will not be bothered by the fiberglass. 

Here is a link to a project that I did with fiberglass panels;
https://photos.app.goo.gl/1oKg2mjmU1tcBe4V9

geoffkait:
">>>I’m afraid you missed my point. The bass information’s there on the disc, and tons of it, it just isn’t being retrieved properly or completely - not by a long shot! - As fate would have it the CD playback systems are plagued by a number of technical problems even after all these years that prevent a lot of information from getting to the speakers. Primarily, scattered light and vibration of the CD itself, but also some other problems."

Hello geoffkait,

Yes, I did miss your point. Maybe if you didn’t wear that huge hat, your point would be more easily seen. Oh, Wow! Wowie Wow Wow! Now that you’re hat’s off and I’m closer, I can see you obviously have a very significant point there. Oh my god! No way! What the....Wow, maybe you should put your huge cowboy hat back on now, that point you have there on your head is really freaking me out!
Anyway, I completely agree with you that CD recording and playback does have its problems and has the capacity and potential to be of much higher quality. Those issues you mentioned and the serious issue of compressed dynamics (Loudness wars) caused me to now use less CD content and more 24bit/96KHz FLAC downloads, especially those recorded direct to digital.
However, this thread was started inquiring about bass room treatments and my suggestion was to invest in a better bass system like a DBA instead. While I believe the subjects of the quality of CD recordings and playback are very valid and important ones, I think it may be better suited for its own thread or threads.

Tim

Tim, I think you should find a job as a used car salesman, excuse me salesperson.
Actually summed bass below 100 Hz is an advantage in most acoustic situations you would have in the typical home.
Jon, It would be easier with identical subs. But if you have to use the large sub midway between your speakers and the small ones flanking. I would mono the lot. 
Geoffkait  you did not answer the question, how big? Wikipedia has the equation. I'll give you a hint. It is highly unlikely that anyone here has a room large enough to fit a Tube Trap that large.
Back to Tim, The term "room control" is a misnomer. You are not controlling the room. You are controlling the speaker to correct response abnormalities of the speaker/room system, to make both sides have exactly the same response and correct timing so that the sound from each driver hits the listening position at exactly the same time. With a good unit the listening position can be any where in the room! Where ever you plant the microphone. You still have to minimize acoustic aberrations in the room or you will waste a lot of power and even bottom out a sub driver. Any sub woofer system is going to sound better because you can correct and improve the sub inherent frequency response which is hardly ever flat. Every uncorrected smaller (12" and less) sub that I have ever measured has a response curve that falls off as you go down. 
This can be correct and I even give them a response that rises to +3 db at 20 Hz then at 28 Hz falls off like a rock 10th order! Tim, if you want your bass to really perk up you want to make sure each one is exactly the same distance from your listening position. You can put them anywhere in the room as long as the distance is the same. They should preferably all be up against a wall. It also helps if your speakers are also that same distance assuming everything is phase correct. 
                                         
                            

Huh? OK, I’ll repeat it. Maybe it will sink in this time. The frequency of operation for a Helmholtz resonator is a function of 3 variables - volume, nozzle diameter and nozzle length. Therefore, you would be able, well, maybe not you personally, but someone who knew what he was doing, to construct a Helmholtz resonator for 20 Hz that did not (rpt not) have a very large volume. You can also affect bass performance with tiny little bowl resonators. There’s lots of ways to skin a cat.

Sorry folks. It falls off like a rock at 18 Hz. My typing is worse than awful.
They did not teach boys how to type because we did not become secretaries. 

Geoffkait. Still not a direct answer. I probably knew what a Helmholtz resonator was before you were born. In 1978 I had two RH Labs (Randy Hooker) sub woofers. They were essentially enclosed Helmholtz resonators adjusted to 30 Hz if I remember correctly. They were by today's standards huge. I do not have a scientific calculator but to make something the shape of a tube trap a 20 hz Helmholtz resonator it would have to be huge. Think of a 20 Hz organ pipe. 32 feet long. Yes I know it is a different principle. Oh, and the equation is

                          F = v/2 pi times the square root of A/V L

F is the frequency, v is the speed of sound, I hope you know what pi is,
A is the cross sectional area of the stem, V is the volume of the chamber and L is the length of the stem.

I must have gone farther in math than you did. No offense,

The reason I ask about adding smaller subs to a big one is that I, like a lot of people I'm sure, already have one big expensive sub.  I would never buy three more like it.  I measured the response with the Behringer ultracurve and measurement mic, and equalized out the worst of the problems.  I'm not unhappy with it how it is but if I could add a few smaller, cheaper subs and get a dramatic improvement I might consider it.  

Deeply discounted subs are common.  For example, I could get three KEF Q400s for about a grand.  It's a sealed box like my current sub so I'd expect them to blend fairly easily.  Adding three more drivers would allow me to let the big sub take it easier.  The question is whether adding fairly cheap subs would solve more problems than it causes.  Would they start audibly distorting if I turn the volume up a bit or would the fact that there are three of them plus the big one allow for more clean dynamic range than I have now?  Maybe I'd leave them off if I want to listen loud and only use them to create really high quality bass when I'm listening at moderate volumes.  

Here is a good site with various materials and their effectiveness
https://www.bobgolds.com/AbsorptionCoefficients.htm

I have had good results with some bass absorbing materials, multiple subwoofers and using the free software REW and MSO (Multi-sub Optimiser). 

Most anything big and absorbing can work. I have a wall to wall closet stuffed with pillows, sleeping bags, boxes of clothes etc.

Working with fiberglass is not bad unless you cut it. You can wrap 703 in muslin (cheap cotton fabric) before working with it or just leave in the box and throw the whole sealed box in the corner. Wrap it if you like. Aesthetics is another issue. Thinner panels only do so much   

mijostyn:
" Tim, I think you should find a job as a used car salesman, excuse me salesperson.
Actually summed bass below 100 Hz is an advantage in most acoustic situations you would have in the typical home."

Hello mijostyn,

     No thanks, I enjoy being semi-retired and performing only the occasional brain surgery.
     All 4 of the subs in my system are run as mono and I have no current issues with summed bass below 100 Hz, although those wanting or expecting stereo deep bass from their systems will likely be disappointed.

  mijostyn:
" Back to Tim, The term "room control" is a misnomer. You are not controlling the room. You are controlling the speaker to correct response abnormalities of the speaker/room system, to make both sides have exactly the same response and correct timing so that the sound from each driver hits the listening position at exactly the same time."

     I don't recall ever using the term "room control".  However, I do understand the 4-sub DBA concept works so well due to creating numerous well dispersed additional bass room modes (bass peaks and dips) at various frequencies in the room.  And I understand the psycho acoustics identified principle of our brains processing these numerous varied bass room modes by averaging them out which results in the perception of the bass as accurate, detailed, fast, smooth and natural. But I agree with you that this is properly described as controlling the speakers to correct abnormalities of the speaker/room system, not as "room control".
     The time domain aspect, or the timing of bass sound waves reaching the listening position, is of much less importance for deep bass frequencies than it is for mid-range and treble frequencies.   We're actually not very sensitive to arrival time in the bass region.  It's been proven that we don't even hear a deep bass frequency until the full duty cycle of the frequency sound wave has been released into the room.  In other words, we cannot detect the presence of bass from less than one full wavelength.  We also need to hear multiple full wavelengths before we can detect pitch.   A 56 foot 20 Hz sound wave released into a normal sized room means it is going to bounce or reflect at least once before the entire duty cycle is detected and be able to be heard at the listening position.  We also need to detect multiple cycles at the listening position to determine pitch. 
      This implies that relatively small timing differences - 'small' relative to the wavelengths in the bass region - are not going to make an audible difference in and of themselves.
     I think you're stating there's a requirement for the "correct timing so that the sound from each driver hits the listening position at exactly the same time"  seems unreasonable and unlikely given the reality of our bass sound wave perception capabilities.  

Tim

I'm using Owen corning 703 rigid 48"x24"x2".

Thanks 

jon_5912:
"The reason I ask about adding smaller subs to a big one is that I, like a lot of people I'm sure, already have one big expensive sub. I would never buy three more like it. I measured the response with the Behringer ultracurve and measurement mic, and equalized out the worst of the problems. I'm not unhappy with it how it is but if I could add a few smaller, cheaper subs and get a dramatic improvement I might consider it."  

Hello jon_5912,
     I think you may have missed my response to your question earlier in this thread. Here it is again:

Hello jon,
    Very good question. I've never tried this myself but I don't believe there's any reason this wouldn't provide accurate, detailed, smooth and natural bass with deep bass extension down to 20 Hz. I suspect, however, having only one sub extending down to 20 Hz might limit the power and impact heard and felt at that deep bass frequency. But It may be possible to compensate by having the volume set higher on the sub that goes to 20 Hz or you could always use two and still be saving money, just a bit less.  
    You should also probably go look and hear some subs, 30 Hz sounds and feels quite deep and may be sufficient for some.

Tim

Geoffkait I would like to understand the bowl resonator you mentioned. I don’t mean to derail this discussion but if you could post a link to what you refer to I would investigate further. Are they examples I can research? Thanks-
mike. 

You can research the original Franck Tchang Acoustic Resonators. Here is one of the excellent reviews in 6 Moons,

https://6moons.com/audioreviews/francktchang/resonators_2.html

Not mentioned in the review or in the patent disclosure is how shear energy and material velocity only in solids is what  reforms compressive waves and actually makes for the differences we hear when various materials and shapes are introduced into an acoustic space. Tom

Or it could be just the pressure equalization and electromagnetic wave absorption the review discusses. Hel-loo!

But its not that..It is the same way shear waves in the earth travel at different velocities and with different polaraties thru different types of rock ..more solid vs dispersed and porous determines the distance from the epi center the waves can be felt. Tom

Who cares? I know you keep saying that. It simply doesn’t apply here. You can’t use it to explain everything. Anymore than repeating over and over, the sky is blue. Even if you say it a hundred times, which you actually have. Remember, one of us has a theoretical fluid dynamics and physics background. The other doesn’t? Go peddle your theory someplace else. How about visiting the library and come up with some new material?

Particle motion in various shapes, mass, density and material is what makes for the change in the solids that causes the air molecules to move and collide. That collision is what we hear..shear wave and particle wave motion in rubber or steel is the precurrsor to the audible. Their different particle motion and velocity potential stimulates the air and makes their resulting sound output indiviual and distinct. When you have different materials like the Resonators touching a different surface shape like drywall..then you will have shear waves traveling traveling in different direction and speeds changing the air motion and vibrational speed which again makes for a different sound result..Look some more Geoff.
Tom

You’re stuck in a rut. You need professional help. Deprogrammers are standing by 😳 😳 😳 😳

Sounds as if you don't understand nor care to learn about the origins of sounds in materials and the resulting sound in air. Tom

Deprogrammers are standing by. You can’t use that shear velocity baloney for everything. You can’t use it for isolation, much less tiny little bowls. It’s a nice day. Go out and get drunk.

“If I could explain it the average person they wouldn’t have given me the Nobel prize.”

The tiny bowls shape and material determines the shear wave pattern and velocity that makes the sound changes in the air. Copper, Silver, Gold and Platinum all have a diferent shear speeds and they all result in a different acoustic out come.
Put a stone or diamond if front of all that hang it on a wall and you have an acoustic resonator. All starts with material or materials and shape..keep looking. Tom

Enough jibber jabber. The reason tiny little bowls work is that the diameter of the bowls and corresponds to an acoustic wavelength AND an electromagnetic wavelength. That’s why Franck Tchang was able to *measure* effects up into the GHz range. In the acoustic domain the tiny bowls “equalize sound pressures” in the room by reducing (absorbing) unwanted high sound pressures like standing waves. We know that’s how they work because the high pressure zones in the room is where the tiny bowls are located ideally. Hel-loo! In the electromagnetic domain the tiny bowls absorb rf. It’s an acoustic resonator. And an electromagnetic resonator. It’s nothing so mysterious and goofy as shear wave velocity.

So you don't know the origins of sound. Tom

Earth to Tom - I know in space no one can hear you scream.

Add your can of hot air to outer space with the shear thats already there then you will have the potential of sound..just like you do here on Earth..Tom

Boy are you out to lunch on this one Tim. It is not what you hear. It is about what you feel. I would bet that you have never played with a system in which you can control phase and arrival times which is why you have this rather flaky opinion. This makes a major difference in the realism of the system. Just wire one sub out of phase and see what you get. I've got news for you. You have to be in phase the entire cross over region. If you are 1/2 wavelength out of time you have one sub wired backwards. This would be the kind of biased unacceptable opinion you swarm guys would come up with. If you think the bass you have now is good, you have a long way to go. 

Oh and geoffkait, I am a physician and we are notoriously bad at math but you keep avoiding the question which means to the rest of us that you have no idea what you are talking about.
My experience with tube traps under the most scientific conditions I could create is not good  and I do not intend on going down that road again. I see it as a waste of money. There are better ways to deal with room acoustics

I’m filing your post under Whatever, Doc. And I have no idea what question it is I didn’t answered but I actually don’t care as the subject for today’s class is tiny little bowl resonators, not Tube Traps. Are physicians notoriously bad at staying on the subject? The last thing I mentioned on the subject of Tube Traps was most likely how difficult they are to set up, anyway. I have no idea what problems you had with Tube Traps. Most people don’t.

Try Acoustic Feilds dot com

With regard to the OP's question, I understand that Rockboard 60 is highly regarded. I didn't try it because the minimum order in my neck of the woods was a pallet.

I have some extra beer bottles.....

On the off chance nobody mentioned it already one key element of Tube Traps, the real ones, is that there is a reflective side that should face the room. This is also true for Michael Green’s corner tunes. Coincidence? In the immortal words of Acoustic Revive regarding the dodgy subject of damping, “One should be careful or else over-dumping can occur.” The other trick is to determine the actual standing wave location in room corners which may or may not be in the actual corner per se.