Bass traps benefits or drawbacks

[Peter C]

My listening room is a challenge for bass, even with my 5AC's bass adjustments, in my experience. The addition of three  GIK Acoustic corner bass traps with built in range limiters, which absorb only below 400hz, has made the bass cleaner and provided more slam.  I have heard that these traps may have deleterious effects on the midrange, and I'm wondering if anyone can explain why this would be so. I would think with the range limiters, which are basically panels on two sides of the rectangular trap that you aim into the room to prevent absorption of the mids, would mitigate any such problems, although I don't understand the potential problem in the first place.

Edited October 18, 2022 by Peter C

[Richard Vandersteen]

Bass traps and other room treatments for practical reasons are made of relatively thin panels which resonate at higher frequencies.  These higher frequencies can inject noise into the room causing imaging problems.  If they are needed it could be the best of two evils.  Alway use them sparingly.  RV

[Ipspam]

First, it's a velocity absorber(?) That means it only works on the velocity portion of the wavelength. It also means it can absorb higher frequencies BETTER, but "Non-linearILY".  This is where the potential issue you reference comes from.

In order to negate this,  you may choose to use reflection or diffusion for higher frequencies.

The question becomes what frequency is the "crossover"? And how effective is the crossover?

I prefer pressure based absorbers because I believe them to be MORE linear. I can't present to you the science of this,  it's not yet mine to behold. I have no idea how linear or Non-linear it is, though I believe it to be more linear.

Having perused the GIK website, I don't actually see any products that purport to do as you say.

I will give credit where credit is due and acknowledge that they provide charts for all their products, which can and will be used against them in a court of law.... Err.. I mean on web forums.

It is my educated guess that your expectations and the hard data charts are at odds.

Please provide model information, and we can look at the hard data.

 

 

[Peter C]

Here’s the comparison data for their Soffit bass trap with and without range limiters: 

https://www.gikacoustics.com/product/gik-acoustics-soffit-bass-trap/

if that link doesn’t take you directly to the graphs, look for the Features tab and look for “Technical Specs”

Edited October 19, 2022 by Peter C

[Ipspam]

That's pretty nice. I missed that product 🙂 

400hz seems to be a nice crossover point. Others use that frequency as well. I have a small room, my corners are only slightly offset with speaker drivers as seen from listening position to corner of room. So I don't want that treble reflection in time that is 6ms VS about 20ms. 14ms difference. I don't like it, that back corner bounce. Not yet anyway. Sounds nice for a while, but tiring and degrading to iinteligibility due to timing.

So I think you are on the right track if your room isnt huge. Taking those corners out, as heard by the ear, really allows me to hear the speaker better, and these seem to be very similar traps in terms of performance.

But back to your question, It's the mids that are easiest to suck up, and to fuck up,  as heard by the human ear at the listening position.

Good luck with the bass. There are only 20-80 cycles in the bottom two octaves,  and the traps can only work once per cycle.  It's a chore to pull too much energy out on the low end.

The highs are highly directional, and the tweets are pointed at your ears. Some  paths of treble you are going to want to block due to bad timing bounces causing intelligibility issues. Then you have to make up for that by preserving treble energy in other places in other ways to keep everything in the right proportion in the room! So you can screw up the treble, but the direct tweet to ear path being directional renders these mistakes less relevant proportionately.

That leaves the mids. Let's say 2000hz down to 500hz. I've used down in frequency directionaly because it's harder to take out as you move to the bass.

The corresponding quarter wavelength is from roughly 0.6" to 6.78", which is what's required to suck those ffrequencies.

That means anyone blanketing their room with 1.5", or 2", or 3", or 4" or even 5" of fiberglass wall treatments is destroying the linearly. They are only treating partially into the sensitive midrange. Highly destructive and audible.

I think that's where that idea comes from.

 

[Ipspam]

Peter C, One more attempt at answering your question. I have been thinking about it for many days. Succinctly, it is an issue of velocity VS pressure portions of the audio wave. Secondarily,  linear VS Non-linear absorption.

On second attempt,  framed differently,  and contradicting my "acceptance" of the stats provided, it is the attempt to operate on the velocity portion of the sound wave rather than the pressure portion of the wave that leads to the issue you are concerned about. I have struggled hard for many years in this area, all the while with time and phase coherent vandersteens.

I accept and wear on my sleeve that I am an Art Noxon \ ASC fanboy. No one else comes close. I do love Ethan for making basic concepts available to the everyday user,  and I own several gik panels (no longer in use) so Take it for what it's worth. (ASC is the behemoth you have never heard of. A "secret" organization that has 120+ patents and produces products for many many companies that rebrand it as theirs) I believe this issue to be one that most audiophiles don't even attempt to start because its so complicated, and even with the appropriate knowledge, geometry is still king. Perfect geometry is near unattainable. So why bother? Because once you start hitting new highs, there is great joy. And the new highs are available every month with careful study and experimentation.

Quote from: https://www.acousticsciences.com/reviews/your-room-the-final-link/

Note the source, Peter Moncrieffs IAR, which claims to be totally independent because they take no money from anyone except for their magazines. I only came to believe this man credible when what he presented helped me immensely with what I had, tube traps.

 

"Note, incidentally, that conventional acoustic absorbent materials, such as panels and foam, are acoustic velocity absorbers rather than acoustic pressure absorbers. Therefore the common practice of placing them flush against room surfaces such as walls (or in corners) is incorrect. So doing limits their effectiveness to merely the treble frequencies, because at most frequencies there is minimum acoustic velocity (and maximum pressure peaks) within a couple of inches from every surface and corner. And, with their effectiveness thus limited by flush wall placement, one tends to use more and more of these absorbent panels in a vain attempt to solve the room’s problems, until one suddenly finds that the room has become too dead (especially at upper frequencies) with all these absorbent panels, while the room’s resonant mode and mud factor problems have still not been solved. So the room winds up sounding tonally dull and reverberantly dead, while still sounding muddy. The correct way to use absorbent panels and foam would be to suspend them in the middle of the room, away from surfaces (or perpendicular to them). Such placement intrudes into the middle of your room’s space, and might not sit well with those of you who value your room’s space and decor.

In contrast, since the ASC TubeTraps are designed to be primarily pressure rather than velocity absorbers, they perform at their best when placed unobtrusively flush against the walls and in the corners. And because they are performing at their best in such locations, fewer are needed and the wall surfaces do not need to be blanketed with absorbent treatment. Therefore one can conquer the room’s resonant mode and mud factor problems, while still having neutral (not dull) tonal balance and a richly reverberant (not dead) room that does not require much amplifier power."

I have perused the description of the soffits you have purchased,  and they make no claims re pressure, and use language adjacent to products that use the velocity portion of the wave. I am still unsure, but I believe the answer to your concern of "deleterious effects on the midrange" of  lies somewhere in and around the areas I have touched upon.

Again, this is so complicated most audiophiles don't even attempt to touch it. Kudos to you for starting your journey. I hope I have provided something to think about.

 

[Holmz]

50 minutes ago, Ipspam said:

... The correct way to use absorbent panels and foam would be to suspend them in the middle of the room, away from surfaces (or perpendicular to them). Such placement intrudes into the middle of your room’s space, and might not sit well with those of you who value your room’s space and decor..

…

^That^ is almost understated. Especially the second sentence with the WAF.

[Peter C]

@lpspam you have given me much to ponder. Thanks very much. I’ll reply again once I think I have something significant to contribute.

[Oregon]

Base traps being misunderstood over here, I have aped the appearance of "things to fill the room corners" via the use of an old pair of AR-11 loudspeakers, foam shapes and k'nick k'nacks to occupy space in the room corners. It seems to have helped. Also, subwoofers helped with standing waves considerably!

[Holmz]

Cool…
What resistor value are you using across the AR-15 terminals?

[Oregon]

3 hours ago, Holmz said:

Cool…
What resistor value are you using across the AR-15 terminals?

Huh? You're question suggests I know what I'm doing. I do not.

[Holmz]

29 minutes ago, Oregon said:

Huh? You're question suggests I know what I'm doing. I do not.

This is new to me as well.
But maybe Jim, or RV himself, mentioned shorting unused speakers to prevent the cones from moving and sucking the bass out of the room.

I always seem to get confused on how a cartridge and a speaker work, and I want to believe that shorting them allows the current to flow easier.
But I think it is the other way around, where a short is a huge load that the diaphragm is trying to push against, and shorting them makes them stiffer, and nothing on the terminals makes the cone limber.

it is possible that resistance or maybe an inductor across the terminals would tune the unused speakers to target a more narrow band of the bass, and it could be a selective bass trap.
Hang on… Maybe it is a capacitor… as that would look like a short for high freqs, and an open circuit for low freqs.

 

Where in Oregon are you?
My old buddy moved to Bend a year ago.

[Oregon]

OK. Connecting a line from positive to minus across the speaker terminals? Will that work?

 

I am in Medford, well south of Bend.

[Stringreen]

On 10/18/2022 at 7:22 AM, Richard Vandersteen said:

Bass traps and other room treatments for practical reasons are made of relatively thin panels which resonate at higher frequencies.  These higher frequencies can inject noise into the room causing imaging problems.  If they are needed it could be the best of two evils.  Alway use them sparingly.  RV

...now I see this post.....    I moved in this house about 12 years ago or so.   In the search for perfection as always, I found Roomtunes, and bought triangle soft pillow-like gizmos for the corners of my listening room.   I applied them to every corner including the adjacent hallway.   I guess my chore is to eliminate some and listen for changes. Perfection is oh so elusive.

[Holmz]

15 hours ago, Oregon said:

OK. Connecting a line from positive to minus across the speaker terminals? Will that work?

As I recall… I think maybe you want no connection, as it keeps the cone limber, and then it sucks out bass.
And you want it shorted to not suck out sounds.

if it sounds good now, then just mark it as a win.

If I have it right:

• Inductor = high pass suck-out/trap.
• Capacitor = Low pass suck-out/trap

@TomicTime or @Richard Vandersteen likely know it… or a few others.

 

15 hours ago, Oregon said:

I am in Medford, well south of Bend.

I know it.
did a ski clinic up at Mt. Ashland for a week many years ago.

[GdnrBob]

@Holmz,

Do you do overnight trips to Ayres Rock? 😘

B

[Holmz]

9 minutes ago, GdnrBob said:

@Holmz,

Do you do overnight trips to Ayres Rock? 😘

B

Bob,

If you, RV or others show up, I will personally bring you there.

The last time I went was for a astronomy conference. Cleo Loi’s advisor was there.

The last time I talked to her prof, she was in Cambridge or Oxford and in addition to the doctorate was also playing concert violin.

Your summer is the idea time, as it is Class-D weather at the moment… feels like 100F.

 

[GdnrBob]

@Holmz, If I can survive the flight, I'll take you up on your offer. Hopefully, the dingos won't be around.

B

[Peter C]

I recently got a pair of Model 7 Mk 2s, which replaced my 5ACs. I went back and forth a couple of times with listening with and without the bass traps. I found that without the bass traps, some overhang remained on certain notes. With the bass traps, I was able to achieve smoother measured response, and to my ears, quicker, punchier and more tuneful and articulate bass. The bass quality is substantially improved over what I was able to achieve with the 5ACs, but it took some work to tune them to my room. I think it was more challenging with 7s because they seem  to be more powerful in the bass. I think they can easily overpower my room if I turned up the volume. My room is L shaped, 22 * 11, with a 16 foot wide section on the speaker side. It is only seven feet tall - it's in my basement.

With the traps, I still remain a bit concerned about possible excessive absorption in the critical low loudness region from 120 to 400hz, but I'm not yet hearing a problem there with the traps vs without. I may take some measurements with REW to check that out. The midrange sounds very natural. As an aside, I did remove most of my absorption panels and now I mainly rely on diffusion and scattering from diffuser panels, room objects, and ceiling absorption.

But overall, I think I'm getting phenomenal bass quality with the combination of the 7Mk2s and bass traps.  As you can see in my conclusions below, it definitely was easier to set the EQ with the traps in place. I followed the directions provided and I only came up or down by 1/3 where I could.

The attached spreadsheet has tables that are based on the available setup worksheet.

I welcome any feedback.

 

Bass EQ Analysis.xlsx

[Richard Vandersteen]

2 hours ago, Peter C said:

I recently got a pair of Model 7 Mk 2s, which replaced my 5ACs. I went back and forth a couple of times with listening with and without the bass traps. I found that without the bass traps, some overhang remained on certain notes. With the bass traps, I was able to achieve smoother measured response, and to my ears, quicker, punchier and more tuneful and articulate bass. The bass quality is substantially improved over what I was able to achieve with the 5ACs, but it took some work to tune them to my room. I think it was more challenging with 7s because they seem  to be more powerful in the bass. I think they can easily overpower my room if I turned up the volume. My room is L shaped, 22 * 11, with a 16 foot wide section on the speaker side. It is only seven feet tall - it's in my basement.

With the traps, I still remain a bit concerned about possible excessive absorption in the critical low loudness region from 120 to 400hz, but I'm not yet hearing a problem there with the traps vs without. I may take some measurements with REW to check that out. The midrange sounds very natural. As an aside, I did remove most of my absorption panels and now I mainly rely on diffusion and scattering from diffuser panels, room objects, and ceiling absorption.

But overall, I think I'm getting phenomenal bass quality with the combination of the 7Mk2s and bass traps.  As you can see in my conclusions below, it definitely was easier to set the EQ with the traps in place. I followed the directions provided and I only came up or down by 1/3 where I could.

The attached spreadsheet has tables that are based on the available setup worksheet.

I welcome any feedback.

 

Bass EQ Analysis.xlsx 54.63 kB · 2 downloads

Not easy to provide feedback as it sounds like you are happy.  Your corrected room response is flatter than most speakers in an anechoic chamber so what's not to like.  As a side note most bass is mono so the composite of left and right would average very well.  It's always an advantage to have different "EQ" solutions for the left and right because the brain perceives less correction.  Base traps have always caused midrange problems for me because of their structure which is the reason after all these years all of our speakers have "Room EQ" if I have the margin to do it.  RV

[Delkat]

How’s your decay time?  I can get my frequency response pretty good with the pots on the Kentos but my decay time is over 2 seconds in the bass frequencies. Not sure what to do about it given I’m using our family room so I can’t add a bunch of bass traps. 

[Holmz]

On 12/6/2022 at 7:40 AM, GdnrBob said:

@Holmz, If I can survive the flight, I'll take you up on your offer. Hopefully, the dingos won't be around.

B

“A dingo ate my bobby.”

[ctsooner]

I had A dealer friend who sold the traps come over and try them. 2 at first and then added from there. He left without a sale.  I’m careful with room tuning per se.  a little here and there goes a long way. Drapes, carpet, wall hung quilts and book cases have helped me greatly. 

[Peter C]

Here's the before, without traps, and after, with traps, shown with the left and right channels averaged together. You can see mild trending towards flatter response from pot 5, 42 hz  and on up.

Edited April 1, 2023 by Peter C
typo

[Peter C]

On 3/23/2023 at 10:17 PM, Delkat said:

How’s your decay time?  I can get my frequency response pretty good with the pots on the Kentos but my decay time is over 2 seconds in the bass frequencies. Not sure what to do about it given I’m using our family room so I can’t add a bunch of bass traps. 

I don't know how to measure that. I have REW, so let me try to figure it out. Any quick pointers would be appreciated.