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Help defeat my REL subwoofer resonance

post #1 of 13
Thread Starter 
Hi everyone,

I have finally pinpointed the source of my itching dissatisfaction with my stereo performance, and it results from my sub placement. What I'd like help with is figuring out the best way to defeat the resonant sound that occurs as a result of my somewhat mandatory sub placement.

In the two pictures, you see one of my pride and joys - my home theater bookshelf. In the other picture, you see my REL meekly confined to its cabinet space. After having listened to my theater for two years, I was trying to optimize what felt like inaccurate bass. I moved the REL out of the cabinet and suddenly everything fell into place, there was a smooth bass response that I hadn't yet found. I usually have to 1) chase after bass lines while the vocals and other instruments present themselves fully, or have to deal with whomp and a certain flubb. I'm exaggerating, but seriously, things were off.

So I can't very well stick my REL in 3 feet in front of my front door; it has to remain confined in its cabinet. My conclusion is that, currently, the enclosure is breeding resonance of bass below 100 HZ (the crossover frequency). I suspect the enclosure boosts some frequencies and dampens others, all the while delaying the release of some sound waves that have been bounced around the cabinet a couple times, creating a "smeared" or "echo" response to the otherwise incredible REL tightness.

What I'm looking for are recommendations on how to enclose it so that it sounds like it's not confined. My first though is to simply add some kind of sound proofing. Would this make a difference, and if so, what density and thinckness of material is optimal for this enclosure and the REL's frequencies?

For those interested:
Emotiva UMC-1
Carver Sunfire Cinema Grand 200w x5
REL T2
2x Def Tech Mythos 8
Mythos 7 center channel
2x Mythos gem XL
Panasonic VT-garble 50" plasma
PS3




Looking forward to hearing from you all..

-Adam
Edited by silver_sailor - 10/8/12 at 8:50pm
post #2 of 13
Quote:
So I can't very well stick my REL in 3 feet in front of my front door; it has to remain confined in its cabinet. My conclusion is that, currently, the enclosure is breeding resonance of bass below 100 HZ (the crossover frequency).
What a stupid idea to put a sub in a resonating enclosure, but at least you identified the problem yourself.
Two solutions: get rid of the sub
mount the sub so the driver fires from the front of the cabinet without the bloody door, suspend the sub inside the cabinet or set it on top of a styrofoam pad.
post #3 of 13
Thread Starter 
It's really not as bad as you think - those doors are just speaker grille and fabric, totally transparent to sound waves. In effect, I've already removed the "bloody door" because there's nothing solid in the way. tongue.gif

There is no problem with the sub living there but for a small yet noticeable floppiness, described earlier.

The REL is engineered to have the floor-directed reflex woofer fire at the floor from a specific distance - the distance provided by it's own feet. As far as suspending it goes... sounds like a bad idea. Not sure raising it on some blocks would improve things, it's designed to fire directly at the floorboards, which it currently does without issue.

Anyone have thoughts on sound dampening to help isolate the sub's sound from it's enclosure?
post #4 of 13
Quote:
It's really not as bad as you think
The REL you show here fires to the front but is designed as a downfiring?
That room acts like an echo-chamber, doing all kinds of nasty things to the sound waves.
You could line the cabinet walls, I would not recommend fibreglass insulationl in this situation, with glassfibers all over the room, try styrofoam.
This on the other hand will likely absorb most of the sound.
It is a bad situation.

The problem with the door is the frame and the hinges, all nicely resonating.
I have a freestanding subs and when I crank up everything that can resonate will.
Edited by kraut - 10/9/12 at 11:23am
post #5 of 13
Thread Starter 
Yep, that REL, the T2, is designed with a downwards firing main driver (8") in conjunction with a forward facing passive unit (10"). The recessed lighting clatters and shimmies, for sure, but the cabinet door frames haven't really been an issue. It's a rather solidly built wall unit, not prone to shuddering from the music or theater. I'm really looking for a variety of dampening materials for the enclosure, as they tend to come in a variety of thicknesses and densities. Also, I'd like to keep my eye on aesthetics, since I've already made a number of concessions on performance to maintain a certain visual appeal.
post #6 of 13
Quote:
Originally Posted by silver_sailor View Post

those doors are just speaker grille and fabric, totally transparent to sound waves.

Yes, but the sub is still bounded on five sides, and that cavity definitely adds resonance. As an experiment, try moving the sub to somewhere else and see what happens.

--Ethan
post #7 of 13
Good call Ethan, he said he moved it out and everything fell into place.

Is that sub vented (ported)? That will make things harder...

The usual advice is to cram dampening material all around (bottom, sides, top, back) of the sub to fill all available space and hope it's enough. You'll still have the coupling effect of the sub driver to door opening, and acoustic impedance of the door itself which may be significant (I don't know but have seen similar setups sound better with the door removed or even just wide open).
post #8 of 13
Thread Starter 
It's not a ported sub, but it is driven downward, to help sub-sonic waves reach out into the listening area through the floorboards - it works well, I kid you not! There are just some notes that are best experienced as vibration in one's bones. The sub is designed this way, and I don't want to compromise that design by decoupling it from the floor. Also, the door issue isn't as much an issue as it seems, it's speaker grille and speaker cloth, no problems there (you can see this in the photo)

I've found Blackhole 5 and NoRez products for the dampening material. Any other suggestions? I think my plan at this point is to create removable panels of the baffling material. Why do it on removable panels? Because life is always a compromise and I don't want to permanently deface the appearance of the cabinet interior with foam that won't come off. Ultimately, the space may need to revert back to a usable set of shelves. I figure if I am diligent in the design, I can create baffling panels that cover the top, rear, and both sides with both increased mass (hardwood panels) and baffling materials for secure resonance defeat. I don't always need to optimize for critical listening but I've learned I need to heft the sub out of the cabinet for when that''s the need. It will be great to stuff it back in its enclosure and not have to remove it for the sake of critical listening, as I prefer the clean lines of the cabinet and also have a 3yr old daughter who would probably climb on the sub eek.gif

Thanks for the thoughts!
post #9 of 13
Just buy some mineral wool at a local building supply center, or even the pink attic insulation, and stuff the area all around the sub (don't forget behind it). Get the sub as far forward as possible. You might find it sounds better with the cone facing directly out instead of down.
post #10 of 13
silver_sailor:

Did you ever implement a fix, such as stuffing the cabinet with sound deadening material? If so, how did it work out?

I have basically the same situation, only I am about to build mine. I am going to have cabinets built into the wall, and I need a place for my subwoofer. (My wife has no interest in the sub being in front of the cabinets -- oh well.) My plan is to include a space in the cabinet for the subwoofer, about 14"W x 24"D x 24"H, but obviously I am concerned about resonances also.

In addition to sound deadening, I am considering a trapezoidal cabinet to reduce standing waves, with the top slanting downward towards the back, so the front opening would be 24"H, but the back would be significantly lower. However, with only about 14" of width available I can’t make the sides a trapezoid.


Thanks,
parkerea
post #11 of 13
Quote:
Originally Posted by parkerea View Post

In addition to sound deadening, I am considering a trapezoidal cabinet to reduce standing waves...

After a bit more reading, and considering subwoofer wavelengths, I suspect standing waves are not an issue for these dimensions, so my trapezoid idea is probably misplaced. Of course, I would appreciate any input.


Thanks again,
parkerea
post #12 of 13
I have always used acoustic cotton with good results while avoiding mineral fibers in the air. Also could try using Auralex Subdude or similar product. I also agree with Kraut and would try putting it on its side to fire forward.
post #13 of 13
Thread Starter 
Hey parkerea,

Never did get past the design phase of the enclosure, so I have no results for you to consider. Ethan Winer is currently in the running for most astute diagnosis. When I haul the sub out of the enclosure, things sound much better.

PS: I'm not sure why these folks think putting an REL on its side would be a good idea, a good review of my comments and a quick google reveals it has an active down-firing woofer AND a passive front firing woofer. There are other reasons as well, but I'll let them look into those.
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