Bass Traps (1 Viewer)

[Sonnie Parker]

That company link that I mentioned having those absorbtion panels at a reasonable price is: Acoustics First


Rutgar... check out filter 5L in the chart above. It shows I boosted 40hz by 12db with a bandwidth of 8/60.

Typically the general rule is to not boost low frequencies and had this been a dip that drastic at 20-30hz I might not have boosted it. It also depends on what it sounds like after I boost it. In my previous setup I tried boosting a 50hz area and it sounded terrible and didn't get rid of the dip. I could tell that 50hz boost was putting a strain on the sub amp. In my current set up the boost at 40hz doesn't sound bad at all and it actually did get rid if the dip with no evidence of strain on the sub amp.

I would probably never say don't boost at all but rather try it and see how it sounds and see if the boost creates any strain on the sub amp or any other weird noises. I would also want to see what effect it has on other frequencies as well.

 

[Paul Spencer]

Sonnie,

I had a look at your HT setup, nice work!

A couple of comments regarding using eq with subwoofers:

1. Using eq should not be a problem for the amplifier provided that it is not underpowered for the driver in question and the eq isn't excessive. By "weird sounds" I assume you mean clipping? Ideally, the subwoofer driver should reach xmax before the amplifier is clipping. If this is not the case you don't get to achieve that extra level of dynamic range and impact that bass can impart.

2. Eq below 40 Hz of 10db is possible without increasing the amplifier power above that which is required above 40 Hz.

This is discussed briefly in this article:

ESP article

This is true for music, I'm not so sure about HT, but in most cases it is likely to be true.

 

[Sonnie Parker]

Thanks Paul...


and thanks for that link. This might be something worth studying a little more for myself.

This quote got my attention:


Not being too knowledgeable about physics and his formulas, I'm not sure I understand how he came up with the results.

Of course Wayne has a good explaination in his link about boosting frequencies as well.


When I mentioned wierd sounds I guess clipping could be one of those although I was referring more particularly to what I heard when I tried to boost my previous null at 50hz with our old setup in our great room. In that set up I had a 18db null at around 50hz. I tried boosting it by 18db and it made a terrible wierd sound around that frequency when testing and measuring with sinewaves. It wasn't actually clipping the amp but it didn't sound like it was supposed to either. The new boosted measurement was only up 8db or so although I had boosted it 18db. I tried several different gains and settled on a 10db boost which didn't make the sub sound wierd and still kept my measurement up by 8db (I could never get a gain of more than 8db regardless of how much I boosted that frequency.) I could only contribute the wierd sound to that 18db boost (or a boost of more than 10db) and the fact that this is a room null. Our great room has 3 large openings into other rooms and that null was always going to be impossible to tame.

Quite the contrary with our new setup and the boost at 40hz of 12db. It just leveled it out to where I wanted it and the 12db boost actually gave me a 12db boost. I contribute these differences to the two completely different rooms... one being small and totally enclosed and the other being very large and open.

All in all I agree that's it's okay to boost frequencies when needed but I would just never suggest boosting all your dips instead of cutting all your peaks.


It would be good for me to learn more about this though.

 

[Rutgar]

Sonnie, If I understand your post, you actually had better luck in balancing your bass in a smaller room? If so what are the demensions? The reason I'm asking is because right now, my kitchen and living area are one big room divided only by three feet of wall sticking out on one side. I'm planning on building a wall to fully divide the two rooms with a pair of double french doors for continual access. The entire reason I'm planning on doing this, is gain more control over the room acoustics. So, I'm trying find out as much as possible before I actually build the wall. After the wall is built, the room will be 17.5'W x 19'L x 8'H.

- Rutgar

 

[Wayne A. Pflughaupt]

Actually Rutgar, I think it’s easier to get smooth bass response and better acoustics in a larger, open room like you have now. I have one like that myself, with the kitchen and dining room are behind the HT area.

The open area decreases the effect of reflections. Between the physical distance and dispersion qualities provided by the furnishings and fixtures, unwanted reflections from the rear are pretty much moot. A small, enclosed room would require significant acoustical treatments to accomplish the same thing you’re getting now for free.

Larger rooms have less of a problem with standing waves than smaller rooms.

Small, enclosed rooms have weird bass characteristics, in my experience. The bass is strong along the boundaries and gets progressively weaker the further you move away from the boundaries. The center is the deadest place in the room, from a perspective of perceived bass output. This situation makes it very difficult to equalize bass for anything but a single seat. With a larger, more open room bass (once equalized) will sound better over a much broader area.

The only downside to the large open area is that it requires larger and/or more power subwoofers to get the output and extension we need for home theater.

Regards,
Wayne A. Pflughaupt

 

[Rutgar]

Hi Wayne, Yes, most people agree that a larger room is better. But, all of the problems you just associated with a small room are exactly the problems that I'm having now. I've spent thousands of dollars on room treatment (absorption, diffussors, and bass traps) which all helped in the quality of the high end, but did absolutely nothing for the bass. This room, as it is, is the worst sounding room I've ever had. The bass doesn't sound "warm", and has major, noticeable "dropouts" when listening to music. To experiment, I made sort of a "faux" wall, which is 5 feet high, and covers most of the open area between the two rooms, and seems to have improved the bass. Which is why I had the Wall idea. But, I also realize that a real wall, sealing off the kitchen is an entirely differnet matter.

- Rutgar

 

[Sonnie Parker]

Rutgar... indeed I've had better success with the sound in all regards in the small room.

Of course I contribute this success to not just the size but the design and construction as well.

My room is 11.5'W X 19.5'L X 8'H.

 

[Sonnie Parker]

I think what might make my small room better than some other small rooms is the width is so narrow which supposedly helps to eliminate standing waves.

There are a couple of room dimension calculators that might be worth checking into including some good info on room dimensions. It seems like for room with an 8' ceiling the narrower the room (as in 10' wide or so) the better chance of not having standing wave problems. I couldn't accept 9-10' as my width as that was just too narrow for seating but settled on the 11.5' and it's worked fairly well except for the low frequency boost I get off the rear wall.

http://www.loudspeakers101.com/RoomDim.htm

http://www.cinemasource.com/articles...des/modes.html

I think what Wayne says is true though. For the most part the edge of the room will have a low boost while the center will have more nulls or standing waves. I believe room dimensions can play an important role in helping to eliminate some of these problems. Of course I was able to get a good results with my front 3 listening positions using the BFD but it didn't help for the rear seating.

 

[Rutgar]

Sonnie, I agree that the seats next to the rear wall are going to be a problem. That area is a problem now, even without the wall. I too have a double-car garage. But it's a little smaller than yours, and would be impossible to turn half of it into a theater. I could use the whole thing, but then I'd have to build another garage. Although that's doable, it would be awfully expensive. As far as the room calcs go, my room demensions wouldn't come close to any of those.

- Rutgar

 

[Sonnie Parker]

I was reading somewhere that a fellow solved his problem of the bass heaviness on the rear wall by placing his sub near the rear wall. He overcame his phase problem 180 degrees.

I have given some thought to this idea although I don't have the cables long enough to try it right now and not even sure if I'd have the room but it's a thought none the less.

I didn't have this problem in our great room because the main listening position is about 4 feet out from the rear wall and there is an opening right behind it. While I could get an acceptable response curve at the main listening position (not perfect but acceptable), the other seating positions stunk pretty bad as best I can remember.

 

[Paul Spencer]

If your room is big enough, you don't have any room modes at all!!! This is usually the case with comercial theatres.
I have found small rooms harder to deal with in terms of bass. In my bedroom sitting against the back wall my TLs sounded like subwoofers. But when I actually put subwoofers in the room it was almost impossible to get good bass with placement. A bigger room is usually more flexible to allow you to place speakers where they sound best, and your seating position as well.

Rutgar:

perhaps you haven't really been able to absorb any of the bass and therefore smooth its response. You need at least 4 big bass traps to achieve anything, but I think a better way is to actually build the walls to act as bass absorbers. This can be achieved by flexible mounting of dual plasterboard layers with a flexible layer inbetween - constrained layer damping. This is described in the book I mentioned earlier and shown to be effective at taming room modes and smoothing them out. Another advantage is that this will not affect the mids and up, which you sound as if you are happy with.

 

[Rutgar]

Paul, Actually I purchased the book you recommended, and I'm waiting for it now.

- Rutgar

 

[Andrew Steel]

Hi All,
Just a few comments on this long thread.

Optimised room ratios dont eliminate room modes, they make the distribution of modes i.e. how they are spread or bunched, better. Different room ratios will just have different modes.

If we assume a reasonably 'flat' speaker response but a non flat response in the listening area, then obviously the room is having an effect. Even listening in the open air, the floor will have an effect. EQ may be able to correct some of the room effect for a single position. To acheive a good response for an area bigger than one person, like a couch or 2 rows of seats, the room must be treated to eliminate the effects causing the uneven frequency response. Try using EQ to get the same response anywhere in the room, or even in a reasonable area say 2 metres square. You can do it with acoustic treatment (albeit a lot of work)

The comments are right that you can get away with different things in a studio as the attitude, budget and often size is different. This doesn't mean that the principles don't still apply. The main difference is between small rooms and large ones. Broadband absorption and tuned absorbers still work the same. Diffusion does not scale down so well.

Get the acoustics of the room right first and then as a last resort use EQ. Unless you are setting up a sweet spot, not a sweet area.

Andrew

 

[darron Z]

my room is 19.5 long ,13 wide (only half the length of the room),10ft high, but i have a 1ft soffit running around the perimeter of the room about 1 ft from the cieling, AND toward the screeen area where the main speakers are, to the right is a consession bar, that opens the room up to 19ft wide . i have no idea where to start on sound management. any basic "must do"? i was thinking of making panels out of high density insulation covered in accoustic material ,and space them out along all of the walls , is that wrong?

 

[Paul Spencer]

One of the best ways to deal with room acoustics is with the speakers, which might sound contradictory and counter-intuitive. The speakers and the room together should be considered a system, and if you want the best system, then aim for a synergy between the two.

There are two approaches:

1. use conventional speakers and try to tame the ill effects of their interaction with the room with room treatment and eq

2. select speakers that have a more desirable interaction with room acoustics and use minimal room treatment - the room can then be more live and it will give a greater sense of spaciousness without causing problems

The latter approach includes waveguides (horns designed for constant directivity over efficiency), open baffle dipoles and line arrays. These speakers are more directional and by their design limit room reflections, and those that do exist, arrays excluded, the off axis response is flatter and thus the reverberant field is less coloured. Room treatment can smooth the bass, but in the mid to upper range it tends to be more useful for dealing with reflections. These types of speakers become more attractive when you consider the room and the speakers as a system, although they are difficult to design, large and costly. However, perhaps they are not so costly if the alternative is spending thousands on room treatment and not getting a satisfactory result. If this kind of approach appeals, perhaps another avenue to consider is the Linkwitz approach.

Linkwitz Lab

I'm no expert and I'm fairly new to all this, but I'm putting this out there for you to consider

 

[Andrew Steel]

Darron,
Sounds reasonable. Remember to put them where the early reflections would occur. Consider some across the room corners too.

Paul,
I agree with you completely. That is one of my favourite sites. Most people though have standard speakers etc and will have room problems. The basic treatment is very easy and should be cheap. It will yield good results. If you want perfection the last few percent can cost a lot which I dont think is necessary in most home theatres.

Andrew

 

[Sonnie Parker]

Very interesting Paul. I'll have to study on that more so I can learn. Of course I don't know that I might be a little late to start. But then again I only have a small problem with my bass heaviness in the rear. Everything else is jam up and jelly tight. The bass is not like a extremely serious problem... several people have voiced that they like sitting back there... it's just that I know it's not what is intended to be heard.

Darron, I know of several people in these forums that have used John Mansville Acoustic Permacoat ductliner insulation which comes in 4' X 100' rolls at 1" and 2" thick. A fairly local plant to us sells this same stuff made by Owens Corning as well as they sell the 4' X 8' sheets too. It's not very expensive either. Several people have used this material covered with fabric on the bottom 4' of their entire room with very good success.

 

[darron Z]

guys- i actually have an account (im in boat supply sales)who buys resin from me , and uses it to make acoustic panels for offices and auditoriums .. they take the rigid fiberglass panels(comes in 4x8 ft sheets i think), and coat the edges with polyester resin, which makes a nice hard sharp edge when cured, then they stretch various open weave fabrics over it . simple, and they sell them for alot $$$ of course theres more to it than that , like whow they fasten the fabric ,and special hang clips etc. but i got the general idea how to do it. thnkas for the tips . keep em coming !

 

[Paul Spencer]

Sonnie,
learning can be a bit of a double edged sword! On the one hand, it can be very enjoyable and stimulating, but on the other it can make you wish you had done things different, and breed some discontent, and make you want to start again!!!

Still Linkwitz Lab is a good site to keep referring to. Dr Earl's site which I referenced in my first post about his book has some interesting info and his two books. I have concluded that from an audio theory point of view, there still is no substitute for reading books. There are some books on amazon.com where disapointed readers commented that the book provided nothing that couldn't have been obtained online for free. However, with the better audio books, online reading/forums can go together with good books and IMO not in place of. A good book puts you on a steeper learning curve, and usually has more detailed and better quality information. One of the most informative websites I have seen is ESP Very well written articles on a range of topics.

 

[Rutgar]

One book that I have, that I think is worth mentioning here, is "Master Handbook of Acoustics" by F. Alton Everest. I have the forth edition, and it is a great reference book. Over 600 pages, and runs about $35.00 list.

- Rutgar