Bass Trapping Ideas for Non-Ideal Spaces

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admin

Audioholics Robot
Staff member
Bass traps control low frequency issues in rooms. Simply, they are the single most effective investment toward a quality audio experience that is rarely made by the home theater enthusiast. The information contained within this article may not allow you to unleash your own plan for optimal bass trapping, but it may point you towards that result. Proper bass trapping is a 100% guaranteed investment and is worth a close look for those serious about achieving the best bass response their home theater systems have to offer.


Discuss "Bass Trapping Ideas for Non-Ideal Spaces" here. Read the article.
 
Glenn Kuras

Glenn Kuras

Full Audioholic
WOW What a awesome article.:D:D:D Very well written and easy to read.

3 cheers for Jeff Headback. He has to be one of the smartest and nicest guys around!:):)

Glenn Kuras
 
N

ned

Full Audioholic
Bag End E-Trap System

Anyone has experience with this?
 
Davemcc

Davemcc

Audioholic Spartan
Good article. I've been considering trying out a Helmhotz resonator tuned for 40hz but I can't really find any info on how to design, build or buy one. Any help would be...well...helpful.
 
J

Jeff Hedback

Audiophyte
Thanks Glenn (Nedd and DaveMCC as well)...glad you enjoyed the article

Ned, I have not used the Bag End piece yet...hope to soon in couple studios. There is a wonderful application review by Bob Hodas at Mix Magazine you may find helpful. Think of this piece as two highly specialized Helmholtz traps...that's what you're getting for $$$'s.

Dave, there are calculators around. Once you have an accurate calc or formula the math isn't that hard. It's more about placing right unit in right location and execution. Feel free to contact me directly as I'd be glad to assist.

Again, thanks

Jeff H
 
Davemcc

Davemcc

Audioholic Spartan
Thanks. This is the closest to what I'm thinking of. I don't have a riser in my room.

Straight up, I got 4% in my final year of HS math before I dropped the course. The equations may seem simple enough for those that know what they're dealing with, it still seems quite challenging to me. I'll be honest, I was hoping that somebody could just say something like "get a 3' piece of 4" tube, seal it and put a 1" diameter port on it that's 2" long" or something to that effect. I imagine that targetting 40Hz is going to take a good size resonator.

Building something is easy. It's knowing what to build that's hard.
 
J

Jeff Hedback

Audiophyte
DaveMCC,

That formula offered by Jeff Szymanski (and BTW- it was blessed to work with Jeff for 6+ years, I knicknamed him "Acoustic Savant" which duly stuck)...is not the right application for your possible solution. Too tough to get needed absorption.

Ironicaly, I just built a Helmholtz Resonator for a different application entirely at that same freq range (actually is 42 Hz right now and it will actually create resonance in a space rather than trap when all's done). It's cool. When talking about a riser or something in that volume, applying this application could up the science effectively.

Back to the point: a perforated panel Helmholtz trap is going to be the best bet in that freq range.

Again, though...passive traps take that mystery out of the effort.

Hope this helps a bit.

Regards,

Jeff H
 
Davemcc

Davemcc

Audioholic Spartan
Back to the point: a perforated panel Helmholtz trap is going to be the best bet in that freq range.

Again, though...passive traps take that mystery out of the effort.
I already have two corner traps, 7' tall, triangular base 17" x 17" x 24", mineral wool triangles stacked to fill the full height of the traps. These max out the available space I have for passive treatment but they don't do a complete job. It's a pretty small room with a ~30dB spike at 40Hz.
 
J

Jeff Hedback

Audiophyte
Well to offer a more proper "diagnosis": room dimensions, sub/speaker locations & listening position(s).

It could be that your speaker/listener locations are exciting a 1st order mode to the point that your very nicely executed existing trapping can't touch the 40Hz problem.

As you likely know already, a high quality digital parametric might be able to slice that specific issue down...maybe better than trapping.

I'd be glad to offer a more qualified review if I got the above data...we'll see. Shouldn't be tough to identify real issue. Have to then see how to attack.
 
Davemcc

Davemcc

Audioholic Spartan
As you likely know already, a high quality digital parametric might be able to slice that specific issue down...maybe better than trapping.
I also have an SMS-1. I don't think it's working properly and I've taken in out of the system. I had some very good initial results with the SMS-1 but it took some very significant eq cuts along with the passive traps to achieve nice flat bass response. But that's a whole other time consuming process to diagnose what the SMS-1 is or isn't doing and I really haven't had the time. I've been thinking lately that it may be easier just to fix the room.:confused:

The room is 11' W x 14' 8" L x 7' 11-1/2" H. The system arranged along one of the 11' walls. The two traps are at the front corners of the 11' wall. The sub is corner loaded at the front left because there is simply nowhere else to put it in this small room that is also our main living room. Some pics here.
http://forums.audioholics.com/forums/showthread.php?t=49281

Many more pics here. It shows the system in a different configuration, but the also shows the room better, doorways, closet, windows, etc.

http://forums.audioholics.com/forums/showthread.php?t=33902

Graphs of the room showing it's native response.

http://forums.audioholics.com/forums/showpost.php?p=467167&postcount=54
 
Last edited:

captiankirk28

Full Audioholic
Great read, i have to get some of those bass traps but the wife is the problem as they dont look good enough.

Would it help to have a corner type in the same corner as my sub? I could put one back their and never see it.
 
J

Jeff Hedback

Audiophyte
There is a similar answer to both Davemcc and captiankirk28: symmetry.

captainkirk28: yes a single bass trap will help, but if at all possible try to implement bass traps symmmetrically.

Dave...I've reviewed the links and I can identify the nearly unbudgeable 40Hz (actually 38 Hz) issue. Now, in reality your open spaces on the right side of the room could be helpful. If at all possible can you (or have you) located sub in front right corner? Your current location of front left sub is making the worst of the given situation.

As far as trapping, the rear left corner should have as aggressive as posisble trapping across that corner (like the mineral fiber traps you previously described).

The main pressure points of your 38Hz issue are the halfway points of the sidewalls and as one is glass you're not going to be too successful trapping there (actually some of that 38Hz energy is going through the glass thus weakening the mode).

Options: I've been able to identify that the only seating location that improves your concern substantially is the halfway point front to back..this does worsen the 75-80 Hz zone (but your trapping is more effective in that region)...OK, nice analysis but not reasonable.

Options to consider:
- rear wall/ceiling soffit trap...would have to be 3-4' but could certainly be designed/built to be acoustically effective and architecturally interesting (aesthetically as well).
- commercial traps: the RPG Modex Plate does work. The 35 Hz version exists...pricey though, likely $2K-ish retail/ea.
- the Bag End E trap is a very good option...again, has a cost/benefit equation involved.

My guess is that your room correction had to be so aggressive to address this peak that you lost headroom and overall dynamics of system. If you can manually go in a reduce peak but not allow typical auto-resolve process which raised dips...you might get a more natural response.

In summary...most curious if moving sub to front right corner helps.
 
Davemcc

Davemcc

Audioholic Spartan
Thanks Jeff. The front right location actually measured worse than the front left corner. The peak was several dB higher. You can see in one pic that I tried to run two subs, a Hsu STF-3 with my PB12-Plus. Even this did little to tame that peak.

I wish I could put some traps in the back left corner but that is the front door of the house. When the front door opens, there is literally only the width of the door frame between the front door and the side wall. That doesn't leave any room for the thickness of traps required to tame the frequencies involved. I have been considering opening up the bottom of my sofa and stuffing 6" of mineral wool into the sofa frame, essentially giving me a horizontal trap about 6' x 2' x 6" thick.

Virtually all of my active eq attempts so far have been focussed on creating the maximim cut at 40Hz and leaving the rest pretty much alone, with minimal or no boost. It looks like my best bet is to spend the time and figure out why my SMS-1 isn't giving me the results I've come to expect. Tuning bass is time consuming and expensive when you start with a room that sucks this bad.:D
 
J

Jeff Hedback

Audiophyte
That's adventurous (placing mineral fiber under sofa).

interesting sub placement research by Floyd Toole confirms that a single corner loaded sub verses two front corner subs results in variances + 35 dB, like you're experiencing.

The best 2-sub location is 50% back both sidewalls (180 degrees out of phase). This would, in theory minimize your primary axial mode issue the best.
Doubt that's even possible with sofa, etc...

You do have a tough situation Dave. Sorry no easy answers.

Hopefully the SMS-1 can come back into the equation successfully.
 
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