AVS Forum banner

Status
Not open for further replies.
1 - 13 of 13 Posts

·
Registered
Joined
·
67 Posts
Discussion Starter · #1 ·
I don't understand the purpose or how bass traps work.


Can someone point me to some information on the purpose of bass traps and how they work? Or if someone can share what they know about them, that would be great too?


Thanks in advance.
 

·
Registered
Joined
·
283 Posts
A bass trap is used to help control bass response in a room. It absorbs lower frequencies to help prevent standing waves which can develop in smaller rooms. Typically they're placed in corners or trihedral areas because it will have it's strongest effect on the standing waves in those positions. When used properly they are one part of what you would use to keep the decay times relatively even across a broad frequency spectrum. The result (when used properly) is a better sounding room, more natural sounding room, and a closer re-creation of what the audio engineers intended when they mixed the movie you're watching (or the music you're playing).
 

·
Registered
Joined
·
236 Posts
When I did a freq response test form my new IB sub I found that i have a large null at 50 Hz..will a bass trap help rmove that?
 

·
Registered
Joined
·
3,301 Posts
Quote:
Originally posted by Andrew Pratt
When I did a freq response test form my new IB sub I found that i have a large null at 50 Hz..will a bass trap help rmove that?
I'll take a stab at this, but hopefully others will come to the rescue, since I'm no expert here.



The short answer I believe is (a qualified) yes. Standing waves bouncing between walls for example (23.5 feet in your room) will reverse the phase upon every relection of a boundary. So therefore it is quite possible to have a cancellation effect due to 180 degrees out of phase at the measuring point. If the base trap (or other acoustic treatment) absorbs the standing waves, then there is less chance for cancelation.


Regards, Bruce
 

·
Registered
Joined
·
647 Posts
You can also try moving the sub around the room. Another way is to walk around the room with a sound meter and experiment with placing the sub at your strongest and weakest areas.


Also when designing a room it is best to not have any dimensions the same. There are actually forumlas (sorry don't remember them) that you can use to determine the "best" sounding room. For instance a room 8x8x8 would be the worst for resonating standing waves.


If you have a polarity switch on your powered sub try changing the phase and see if that makes a difference.


You can also try this link http://www.diysubwoofers.org/
 

·
Registered
Joined
·
7,655 Posts
I definitely vote for the moving the sub option. Actually, the easiest way is to put the sub where your seat(s) will be and then measure from various sub locations to see where the best overall response for the most seats is. (Unless you just want to be selfish and get great bass in your chair!)


While this may not yield the total solution, it will get you 90% of the way there and you may find you need to move your chair a little and or a small amount of either bass trapping or diffusion.


Good luck
 

·
Registered
Joined
·
575 Posts
I have made bass traps based on High Fidelity Engineering’s design-- www.decware.com . They do wonderful things for the bass in the room. I never was able to get a real flat response curve but, the results were dramatic. The bass traps seemed to double the amount of bass in the room.


Does the bass sound smooth? Do you feel engulfed by it? Do you have any graphical readouts that you can post?
 

·
Registered
Joined
·
67 Posts
Discussion Starter · #8 ·
JamesE, how easy were the High Fidelity Engineering’s traps to make?


I was thinking of pursuing them. However I was also concerned about the weight of them being 120 lbs. Wow. Pretty heavy.
 

·
Registered
Joined
·
718 Posts

·
Registered
Joined
·
541 Posts
B/c of very limited ceiling height, I will not have soffits along my side and back walls. The stage will have a soffit (rounded to match the stage) above it treated with TS. Also, I will have side walls to the stage treated with TS.


I'm doing the typical ts lower wall, poly on the upper. But in the back corners, I thought I'd do 18"x18" pieces of TS on the back and side walls instead poly. I thought this would be an effective enough bass trap. Anyone try this or have any thoughts? Do I risk making the room to flat?
 

·
Registered
Joined
·
718 Posts
By no means am I an expert on this, but from what I have read this is ok if you are using the room as a dedicated HT. If you are using it for music also you might reconsider. I wouldn't mind hearing the opinions of those more knowledgable as I was considering something similar.
 

·
Registered
Joined
·
67 Posts
Discussion Starter · #12 ·
Patrick C,


I've done considerable reading on bass traps since I originially started this thread. And from what I've learned, bass traps need to be positioned in the corners of the room, where you are more likely to get standing pressure waves.


You'll definitely have standing waves along the sides of the walls, but I believe that the corners are more prenounced when it comes to LF waves.


I've also had an opportunity to hear a bass trap in action. And I can tell you first hand that they "can" make a difference if positioned correctly (in the corners).


You may want to consider putting diffusers along your back wall.
 

·
Registered
Joined
·
541 Posts
Funboy,


Thanks for the reply. Actually, I'm talking about the rear corners. I want to minimize the tri-corner effect, by placing TS under the fabric in the upper rear corners of the rear and side walls. Basically, I was going to cut 4 pieces of 18" square TS and staple them up on the top-back of the right and left walls, and the upper right and left corners of the back wall. frequncies would not bounce around in the corner. I'm also placing TS all the way up the wall at the point of first reflection (probably a 12" strip all the way to the ceiling). When I get my drywall up, I'll experiment and take some measurements to let you guys know how it goes.


Thanks,


pc.
 
1 - 13 of 13 Posts
Status
Not open for further replies.
Top