MAJOR bass cancellation probs.(bass traps?) HELP PLEASE (1 Viewer)

[chris_everett]

How can EQ fix a cancellation problem? It can't! If you cut the offending frequency, you have less cancellation, but the same result, areas of lots of bass, and areas of none. Same with an EQ boost. Does this mean that EQ is useless? No, by no means. EQ can fix all sorts of problems, and most systems will benefit from an EQ on the subwoofer channel. Bass frequency response can be smoothed out by EQ, but it can't create something out of nothing.

I don't know why you can't stand bass traps so much Rutgar, but I can assure you that nearly every pro recording studio out there uses them, lots of them, and that they are most certainly not bi-wiring the speakers or buying $1000 power cords, or other such nonsense.

Perhaps you have "active" bass traps, that are designed to absorb only a specific frequency, if so, I can understand your frustration, as these will be very difficult to implement correctly without lots of tools that a typical HT builder does not have.

This is from a FAQ on the Auralex website (a competitor of Ethan's)




Also, I have been involved in pro audio for a number of years before I was interested in HT, and I can assure you that Ethan is a well respected member of the pro-audio community, and has a wealth of knowledge that we can all benefit from. As I recall, he operated his website simply to educate people on building their own bass traps for years before starting his company.

 

[Mike<>P]

Uh oh, CAN'T WE JUST ALL GET ALONG!

Look, all I know is that an EQ isn't the answer in this situation. I figured that out before Ethan and Chris even posted, but it was nice to get a few more opinions. To me anyway, it seems like common sense. If there is nothing there to begin with, due to CANCELLATION, then EQ'ing the offending frequencies down or out will do nothing. The cause (room dimensions, etc...,I assume) of the cancellation will still be there. It's probably as useless as EQ'ing my Klipsh Heresys to reproduce as low as my Cornwalls. I know it's a poor, dissimilar analogy but.......

Hank, my response sucks whether I run either sub or both together. I wish it didn't but it does. Maybe if I put some cushions and armrests on top of the sub.........nah!

Believe me, I really don't want to invest another 1-2 thousand dollars, many hours playing with fiberglass and inevitably filling my room with monolith looking bass traps. It's a H/T, not Stonehenge, but I am sure as hell not going to leave it as is.

I respect and appreciate EVERYBODY'S opinion here, but after reading the responses so far(+ info I've found on the web), I am going to try DIY bass traps. It seems like the logical and most cost effective solution.

If anyone has additional input, please start typing.
Thanks, people!

 

[Rutgar]

Mike, all I'm saying is D'L the Excell spreadsheet, and test tones (free). Buy the Radio Shack Sound Level meter (under $50.00, and you need one anyway). And plot out your room responses. When you can "see" what's going on with your sound, then it really helps in deciding what to do about it. It's very possible that all you need is to do some creative positioning. Especially if you're running multiple subs (as I do). Also, the spreadsheet will show you what adding the fiberglass to you room does, and doesn't do.

Keep us posted

- Rutgar

 

[Kevin Patterson]

Hey have you ever tried turning off just one sub? You should double check all your wiring to make shure it is all in phase and the dual woofers in you diy sub may be out of fase. these are just some things i would check over.

 

[Mike<>P]

Kevin, If I had a nickel for everytime I checked the connections and phase.....bla bla. That would be so sweet to find a mistake in the wiring, though. The only thing wrong was the bass driver I discussed earlier.
Yes, I did try running a single sub.

Rutgar, I have the RS test meter, but I only have a spreadsheet viewer. Do you know about how much the program is?
If by creative positioning you mean subs and mains then I've already tried that too. I even flipped that giant thing so it was firing down. The mains cannot be moved, at least permanently, as they are built into a wall. That wall is 3' in front of the actual rear wall. There are openings(60"H x 32"w)on each side for the mains. In the middle there is a 69"H x 62"w opening for a TV. and a 22"H x 46"opening for the sub. My rack is also built into this.
Behind the wall is exposed insulation(no drywall). I would think that area would act as a bass trap. There isn't a TV in place yet either so I assume sound waves have no problem getting back there.

 

[Rutgar]

The spreadsheet requires Microsoft Excel. I'm not sure how much it costs. My copy came with Microsoft Office (which isn't exactly cheap). I don't know if there is a way to use the spreadsheet without Excel. Maybe someone else here can help.

By posistioning, I meant trying your set-up on different walls in the room, and moving your listening position. But, since you already have built-in's, that's going to be a major problem. Like you, my room is a very difficult room to get the sound right. It opens up to a kitchen on one side, has a hallway that opens in the middle (between the kitchen and theater room), has a fireplace across one corner, which leaves only one "real corner" in the listening room. Unlike you, I waited to build anything in, until I solved my bass problem. I tried setting up across all three walls (only three because the forth opens to the kitchen), and across the corner without the fireplace. The bass sounded like crap in all of these positions. About six months ago, I decided to try something I hadn't thought of. I set everything across the corner with the fireplace. Placing the mains about mid-way down adjacent walls from each other. This put the right sub in the one true corner, and the left sub along the wall that extends into the kitchen. The left sub itself isn't in a corner, it stops at the kitchen boundary. This configuration put my listening area in the corner where the french doors go into the hallway. There is also about 8 feet of wall by the french doors, between the listening area and the kitchen. With this setup, I lose the fireplace. But, the sound is so incredible that I don't really care (as you might have guessed, I'm not married).

Like I said earlier, this configuration worked so well, that I'm only using 5 absorption panels, no bass traps, no BFD.

- Rutgar

 

[Mike<>P]

Rutgar, unfortunately I don't have any options as far as placement goes (with the exception of the sub).

Also, your room has something extremely significant that mine does not.......openings. I believe if I had designed mine that way, which wasn't possible anyway, I wouldn't have these problems. Like I said in earlier posts, the 2 previous rooms were open to other spaces, especially the log cabin, and I did not have this issue.

I really feel the room configuration is the issue here. To make things worse, I put 2 layers of 1/2" sheetrock on the wall opposite my speakers to cut down on noise going into the house(duplex). I understand while sheetrock is a mid/upper freq nightmare it can be very effective, if applied properly( small gap between layers) at taming bass frequencies. Oh well....next time.

I went to Comp USA with a friend a while ago so he could pick up MS Office for school. I believe it was $100, and that was the cheap version. I'm sure purchasing just Excel won't be as pricey.

 

[Rutgar]

Mike, did you use resiliant channel in-between the 2 layers of sheetrock? Resiliant channel turns your entire wall into a bass trap. What's more you only need resiliant channel on one of two parallel walls for it to work. In other words, the back wall, a side wall, and the ceiling. There is book available called "Premium Home Theater" Design and Construction by Earl Geddes. I think it can be bought from Amazon.com. If not, a Google search will find it for you. A "must have" book, for anyone building a Home Theater, in my opinion. It explains a lot about resiliant channel, and bass frequency problems.

You said your room is enclosed. I'm curious what the dimensions of your room are.

- Rutgar

 

[Mike<>P]

Rutgar, I just put 2 layers of drywall on the studs. I really REALLY wish I had just done a little research on resilient channels. I knew they were available but just never thought I would need them. Its just another thing I've learned for "next time". There is no way I would strip off 1 layer of drywall to install anything now. Besides, it would be nearly impossible to do without spending BIG bucks and trashing the room.

The room itself is 21x31 (21x34 if you measure to the actual front wall). It has a cathedral/tray ceiling with a height of 12'6". I have a slider, 4 large windows and 4 large skylights. I would love to post some pictures (I have a ton) here but I guess I have to post them to a website first. I tried making a page at yahoo/geocities but I can't figure it out, but thats a different post in a different forum. The only pics I have on my webpage are the 3 posted earlier. It wont let me upload from my computer

I have NEVER heard a room with a bass response like this. It really is the weirdest thing. Big mains, multiple large subs and lots-o-power = .......NO BASS! I am not talking about just the couch/listening position area having no bass. Like I said it's a pretty large room so there is plenty of open space in the middle to walk around and listen. The mains crank but to see the drivers in my DIY box totally pounding away and barely hearing them is bizarre. It's like watching them on TV with the volume muted!

 

[Sankar]

This is the first time I've read (though that probably just means that I have not read enough) that resilient channels can double as a bass trap! I am in the process of building a h/t and chose to go with the "room within a room" design (+ acoustiblok) rather than resilient channels. However, while the framing is complete, the sheetrock etc have not gone up yet ...
Has anyone else had experience with resilient channels acting as bass traps?

 

[Rutgar]

Sanker, it's my understanding, that building a "room within a room", and using "acoustiblok" will help in sound proofing, but won't do a thing to help with room acoustics. Using Resiliant channel is for bass management, not sound proofing. In other words, you still need the resiliant channel, even with the acoustiblok, and double studs. Like I suggested earlier, buy the book, "Premium Home Theater" Design and Construction by Earl Geddes. It tells how to properly install the channel without "shorting" it out. Plus, it explains the physics involved with rooms, and low frequencies as well.

- Rutgar

 

[Sankar]

Thanks Rutgar.
I had read a fair bit about resilient channels on the internet (e.g NAIMA,SoundProofing,Acoustics101,ACS ISO-Wall, etc) and my understanding was that it too was designed for sound proofing by providing a flexible separation between the drywall and frame (assuming that we avoid the infamous "shorting" problem!). However, I must confess that I did not read the book by Earl Geddes ... is it there that he makes explicit mention that resilient channels also assist in bass management?

Its probably too late for me to go for resilient channels now and I may be forced to go with conventional approaches to bass management such as my trusty BFD and bass traps. I wish I had read Earl Geddes' book :frowning: --- my primary sources were Alton Everest's "Master Handbook of Acoustics" and "Sound Studio construction on a Budget" where he makes no mention of resilient channels (not even for sound proofing). He does discuss the physics of porous and resonant absorbers though.

 

[Rutgar]

Again, according to Geddes's book, the main idea behind resiliant channel is low frequency absorption, without killing high frquencies (high frequencies are what give the room "perceived spaciousness", which is why you don't want to "kill" them). The moving wall dissapates energy through friction (All absorption is friction of some sort). With resiliant channel, absorption decreases with frequency. In other words, the higher the frequency, the less absorption, the lower the frequency, the more the absorption. Large sound absorption at low frequencies help to smooth out low frequency response irregularities. Which, in turn, gives a small room smooth clean bass.

I think you really should go ahead and add the resiliant channel, and another layer of sheetrock. I know it might mean that you have to back track a little, but it would be well worth the effort. Like I said before, according to Geddes, you only have to have it on one opposing wall for each of the three pairs, for it to work.

- Rutgar

 

[Sankar]

Thanks again Rutgar!

I'll try and see if I can get the contractor to install RCs. So Geddes' point is that only 1 wall need be set up with RC? i.e. of the 5 available walls (sides, front6, rear and ceiling)?

 

[Rutgar]

It must be one of each parallel opposing wall. In other words, when finished, you will have RC on three walls. for example: the ceiling, the front wall, and the left wall.

And one other thing, you must be careful to not "short out" the sheetrock mounted on the RC. Do a search on RC on the web. There are several sites that talk about how to properly install RC.

- Rutgar

 

[Sankar]

Thanks again. That would be consistent.
I have read about RC quite a bit ... the "shorting" issue relates to sound isolation right? At least that's what all the web sites I listed earlier indicate. If my understanding of how this is supposed to work is correct, it would appear that the bass trapping ability is unaffected *even* if there were some shorting involved (since its the flexible vibration of the sheetrock that reduces its reflectivity of bass frequencies). Admittedly one should avoid the shorting problem, but since I already have a room within a room + acoustibloc, I would guess that I am less concerned with the sound blocking ability of the RC (which would be nice of course).

Has anyone else had experience with the bass trapping ability of resilient channels? A second opinion would be nice before I go to war with my contractor at this late stage of construction

I did not have any luck in finding the book at Amazon or Barnes and Noble :frowning:. I did find Geddes' website and the book can be purchased there (unfortunately I do not have the luxury of stopping construction for a week to have it shipped etc ...). For those that do have time on their side, the website is http://www.gedlee.com .

 

[Sankar]

Rutgar ... I think that I will try and see if I can convince my contractor to hold off a couple of days and install resilient channels on the walls + ceiling. You have indeed gotten me thinking now

In the absence of Geddes' book (it is only available through the web site and that will take a few days to reach me), could you advise me if the RC MUST be only put on one of the parallel walls or whether I can put in on all of them? If I am going to put RCs then I may as well go all the way since the extra cost is not that high. In other words is it better (purely from the bass absorption perspective) if I were to put it on the 2 side walls, front wall, rear wall and ceiling (not on the floor!)?

Are resilient channels available through Lowes, Home Depot etc or are internet suppliers the only reliable source?

Thanks

 

[Ethan Winer]

Sankar,

> Has anyone else had experience with resilient channels acting as bass traps? <

A sheetrock wall with resilient channel will give more bass trapping than a rigid sheetrock wall. However - and this is a big one - the trapping will be effective over only a fairly narrow range of low frequencies. All rooms need substantial absorption at all low frequencies, so in the larger picture an RC wall is not an effective bass trap.

--Ethan

 

[Sankar]

Thanks Ethan,

Actually, I was not planning on relying on the RC completely. I'm sure that I'll have to add acoustic treatment once the room is built. However, the option of including resilient channels will not be available at that juncture. Hence my thinking is that if the inclusion of RCs now makes bass management somewhat easier later, then it may be worth giving it a shot.

Question is whether I should put it on all 4 walls and ceiling or should I just put it on 2 adjacent walls + ceiling ...

 

[Steve::Weaver]

Okay, I'm a relative newbie, not audio engineers like you guys but couldn't there be additional cancellation problems caused by both the mains and the subs puting out bass?

Mike, have you tried crossing over your mains higher to see if that helps?