Ngjockey,
Thanks for the reference information. I was actually hoping the nonparallel walls would be helpful, not detrimental. Such is life!
I have some work to do. I now have an idea what to look for. I will do more detailed measuring with the easy modifications and see if I can't find a pattern as you and others have suggested.
I can eliminate the furniture 1 piece at a time and make sure it is not a suckout issue. There is an open stairwell right around the corner from the listening position that may be providing a broad suckout. Not as easy to deal with, but I can work a temporary solution for testing.
Anyway, thanks for your time and advice!
Jim S. |
Thank you all for your responses. I was hoping to see 7 or 8 posts saying that's easy, diffusion. But I posted to leverage your experience before purchasing and it has already paid off.
Did a little more testing and review of the data. Found some hope in speaker placement and an interesting (and depressing) overall trend.
The room is a 60' long X 30' wide irregularly (almost a backward L) shaped finished basement. There is a "stadium" wall 9' wide at a 45 degree angle in one corner. That is where the system is set up, shooting out into the long part of the room. The only wall parallel or perpendicular to the speakers is the angled "stadium" wall. I think this contributes to the lack of boomy nodes.
The really serious nulls (-20 db.) are very location dependant. Move your head (or the meter) a foot or two and they change. Common sense seems to say that you would never be able to eliminate all the 2, 3, 4 hz. wide strong cancellations at a single position.
I moved the 1.6's straight back 5 inches and most of the nulls improved 4 or 5 db. I don't know if I like how it sounds as much (soundstage), but I may have to move my listening position to correspond to speaker movements. Classic chasing your tail.
The disturbing overall trend is.... the 1.6's probably average -7 or -8 db. from 80 hz. to 290 hz. (the range of this test CD is 10 hz. to 300 hz. in 1 hz. increments). That seems like a lot. A quick review of old Stereophile freq. response graphs shows the speakers fairly flat from 50 hz. to the crossover @ 600 hz.
Care to venture an opinion of the trend?
FYI- The 1.6's are -15db. @ 35hz., -7db. @ 40hz. -3db. @ 47 .hz or so. Didn't change a lick with speaker movement or starting SPL.
Jim S. |
Again, THANK YOU ALL for taking the time to post your thoughts, even as I was typing the extra information above. I would have posted more at first but didn't want to complicate what may have been a simple situation.
You have provided a multitude of great places to start.
And the measuring will not be... the be all, end all. I was just very impressed with the clarity in our friends heavily treated, dedicated room and was hoping to add a little bit of that to my system. It may be that I can't get there with the components I have, but, any room improvements will be in place as I move on.
Will update as I try your suggestions.
Jim S. |
Plato,
Thanks for the encouragement. I will work at it and see what I can learn.
Soundgravy,
No, I did not know the Rat Shack SPL meter was seriously inacurate. I will reread the thread (probably many times) and try to understand. Thanks for posting.
BTW- Do you guys miss Sean? (From the RS meter thread, and many others, that Soundgravy cited.) He really relished the technical and did a lot of work to solve problems. I notice he doesn't post as much as when I started following Agon threads.
Jim S. |
Onhwy61,
Understand your first point. I am trying to look at trends over 20 to 30 hz. ranges. Started with the LF as it seems from previous threads that is where the largest gains for the effort come from.
I was thinking about your second point last night and wondering the same thing. Am I misusing or misunderstanding the info? The CD I am using for LF is from Real Traps. The CD has a white noise track to set a start level. I have assumed that start level would correspond to an SPL baseline and db. readings above that baseline level were bumps and below were nulls. That may be correct, but not necessarily so. If not correct, the data is valid (the amplitude swings are still there), but the description and amplitude I had assigned to null and bump are invalid.
Anyway, I should have done a little more prep work and broader data gathering before posting. I may have jumped the gun. Back to work on it.
Audiotomb,
Yeh, I wish I had 1800sq.ft. to play with. It is an odd shaped room that follows the contours of an irregular foundation. Because of the backwards L shape with a few extra zig-zags thrown in, the usable space is much smaller There are framed in steel support columns and beams. Also seperate rooms for laundry/storage, furnace/water heater and a bathroom with a Jacuzzi. Why the previous owners put the Jacuzzi in the basement is anybody's guess? Sounds a lot bigger than it is.
Thanks for your observations.
Jim S. |
Ok, I got it. To do a really serious analysis and correction, I am in way over my head and resources.
But, believe it or not, what everyone has generously posted makes sense and has helped my understanding. I just don't know enough to know how to make a direct quantum leap in results (it ain't gonna happen overnight). I do know that a little knowledge is dangerous, so I will go slow, keep studying, keep measuring, and keep experimenting. I will post the setbacks and breakthroughs.
Thanks and Best Regards to All,
Jim Still |
Per Shadornes' reco I purchased Rebecca Pidgeon, The Raven. Shadorne is absolutely correct. On "Spanish Harlem", the bass sequence cleary shows intensely audible bumps. Dumm, BOOM, BOOM, - BOOM, BOOM, Dumm, - BOOM, Dumm, Dumm. It is not subtle, nor musically pleasant.
I have heard the BOOM and new it existed in the setup. I use the bass boost from the room nodes to alter (amplify) the lower-mid bass for some of the music I like. But taken as a single note, it really sounds horrible, bloated, and out of place.
Very enlightening. The Raven is pretty good music too.
Best Regards,
Jim Still |
I have discovered a new way for the CIA/FBI/DOD to coerce information from suspects. Make tham listen to test tones all day! Doing room measurements manually with a CD and RS SPL meter is agonizing and time consuming.
Jim S. |
I said I would try follow-up with the setbacks and breakthroughs. I do not know how to post the graphs in this format so I will just try to accurately describe the highlights and observations.
I spent 2 days measuring under the most controlled circumstances I could manage. Focusing on speaker position, this is what I found.
Started at my established listening position. Speaker centerlines - 50" from back wall, 83.5" apart, 36.5 from angled (45deg) sidewalls, and 115" from listening postion. Speakers were tilted back 4 degrees (guess, one washer in the bottom of the stand mount, will measure exactly later).
I will descibe the sequential set up for 7 different test runs with the Real Traps Test CD, because the measured results changed very little.
#0.. Baseline
#1.. Changed tilt to upright.
#2.. moved speakers straight back 6".
#3.. moved speakers forward 12".
#4.. moved speakers toward each other 6" each.
#5.. moved speakers back 6".
When I sat down and graphed the numbers...
Steady rise from 53db @ 32hz. to 63bd @ 38hz
6db drop @ 42hz. rising steadily to 76db @ 55hz.
9db dip @64hz rising to 77db @ 70hz.
Drops to 67db @ 86hz.
Rises to a steady 69bd @ 90hz. to 118hz.
Starts to dip steadily @ 118hz. to 53db @ 138hz.
Broad null for 10hz.
Rises steadily to 67db @ 172hz.
Things get real eratic at this point with wide 2,3,4hz wide swings down to < 50db and back up. Does seem to be another deep (<50db) broad null at 230hz. to 270hz.
In general terms, and to my untrained eyes, I have a big boost from 45hz to 82hz with a little dip thrown in the middle of that, another small dip @ 85hz, and 2 serious nulls @ 135hz to 175hz and 230hz. to 300hz.
Experimenting a little more
#6.. Opened laundry room door, checking for suckout.
Virtually no change. (big surprise).
#7.. Pulled single speaker out into middle of room (13' from back wall, facing into open area) and measured @ 2' with mono source. (closed LR door)
Same pattern of boosts and nulls, just a little less dynamic. Who would have thought? The tones really started to audibly oscillate @ 105hz through 135hz. Reinforcement/filtering, who knows?
Really surprised me how little the pattern changed through all 8 tests. I took the time to listen to familiar music in-between each test run and the position changes were easily perceptable.
At this point, I have some acoustic reference material coming for study so, although I can recognize the pattern, I don't know what it really means.
Other interesting (to me) observations. Putting the 1.6's closer together than I remember trying before starts to push the sound stage to the front of the speakers instead of behind and starting to produce the clarity in the vocal registers that I was seeking at the start of this. Despite the nice clarity, it is too bright to listen to anything but female vocals and acoustic instruments in that position and the soundstage is too narrow.
Next step... read a little theory and build some really big DIY bass traps to test.
Please forgive the typos, mispellings, and my grammar.
Regards,
Jim S. |
Ngjockey,
Thanks for the advice and sources. I found a couple of DIY bass traps recipes on AA posted by Jon Risch. I can afford to put together a couple of 18-20" tube replicas to test. They seem to be rather narrow range in absorption and if big enough can work down into the double digit frequencies.
I also have my eye on a corner, angled just off (4-5') the left speaker, that houses a fireplace. Not sure that is the problem, but I never did like that fireplace anyway.
I can't knowledgably comment on the meter accuracy or my testing accuracy. One thing that gives me some confidence in the measurements, are the repeatability I am observing. And the fact that the 70-80hz boost correlates to Shadornes recording reference. If the bass note progression is described correctly (and I believe it is), the third note in the beginning progression is consistantly much louder.
Do I just not understand all that is involved? Certainly possible/probable!
Regards,
Jim S. |
Acoustat6,
I have read through the Real Traps site and a lot of Ethan Winer's posts on AA. Learning a lot.
Thanks,
Jim S. |
Shadorne,
Thanks for your input again. I have read your suggested links and am trying to assimilate the info. I would like to make a couple of smart changes and not a couple of hundred dumb ones. But, to be honest, I am something of a slow study.
As I see it, I have a room mode boost peaking at around 75hz., and a set of cancelation nulls peaking at 127hz and 250hz., with a few anomalies thrown in to confuse the uninitiated (me). Makes me wish I hadn't cut most of Senior year in High school.
It fits what you have described. I keep trying to figure out how the angled walls off to the sides of the speakers fit in. Maybe they really don't change the equations!
If the analysis is that straight forward, surely there is some corollary that dictates the solution is going to be complex!!!!!
I have unknowingly played with positioning that would significantly change quarter wave cancelation when I first got the 1.6's, 6 yrs. ago, and was trying to optimize bass output. At the time I didn't like it, but now I am wondering if it wasn't reinforcing the bass (or more accurately covering up for lack of bass) of the Maggies with a room mode and cancelations.
Anyway, more food for thought. THANKS for the info and analysis. I will try to post meaningful information and conclusions as things go forward.
P.S. I can mount the 1.6's into the wall behind them (soffet mounting taken to the extreme). It opens into a laundry room. Might try that someday.
Best Regards,
Jim S. |
OK, this is not supposed to work with Magnepans but you have to follow the trail and see where it leads, if that makes sense.
I try what is written in the Genelec sites, that Shadorne has lead me to, about positioning to avoid 1/4 wave cancelations. According to everything written (their manual and everywhere else I have read) about positioning Maggies, they should be as far out from the back wall as possible.
Well shoot.... I do the calculations on the site, follow their recommendation to keep back wall distance 1 meter or less, and figure I am trading one set of cancelations for another. Low and behold, I move the speakers back from 50 some odd inches to about 30" from the back wall and play Patti Smith's Gung Ho, (not exactly an Audiophile recording but what the hey). OMG, the bass is up a notch and very clear! I mean, it is not subtle.
Ok, so I measure with my limited means and where I thought I would have traded an 60 or 90hz. null for a 110hz. null. the 60 was still there, the 90 wasn't as deep and the broad 100hz. to 160 hz. deep null was just gone. Replaced by a slight bump.
Ok, what is going on? I do the calculations for a 1/2 wave and it should be close to the 1/4 wave but instead there is a null at 230-240hz. Back to reading!
Anyway, what shouldn't work with Maggies does. At least in my room.
In all fairness it does generate some other issues. The tweeters are now close enough to the back wall and directionally pointed at the listening position to beam. Also brings into play reflections from a patio door behind and to the left of the LP that wasn't a concern before. Lessened those effects by tilting the speakers back a little.
FWIW,
Jim S. |
Shadorne, you're a good man. You have helped through the foolishness and learning.
I think it goes something like this.... Place the 1.6's for the best soundstage coherence? Trap for standing waves and trap for quarter wave cancelations? Readjust, remeasure, readjust?
Absorb and diffuse for the rest? I still don't understand the rest, but I have some reading material coming that I hope will help.
Everyone that shared their advice was correct in their way. Measurement, placement, appropriate treatments are part of the equation. You can quit anywhere along the process you are happy with the results.
And....... yes, I am headed for a little bit of "Flash Gordon", but what the heck, life is getting really short!
And, yes, 8' out into the room puts the quarter wave cancelation at 35hz. Yes, it does sound really, really good, if not practical.
Cheers, and Good Evening,
Jim S. |
