Why Does my room need to be one big bass trap???

[The Studio RI]

Ok, I've been sketching some designes to acoustically redesign my control room and I just had a few questions about how sound travels in a room.

My room is small, 13x9x7 and is rectangular. I have severe bass problems! I know how various sorts of filtering can cancel frequencies in the room and such, but my question would be... what does bass trapping really do to the bass waves? does it just try to suck up bass like a black hole? is that the desired result, to suck up as much bass as possible? If I make my room one big bass trap, with 6" traps over all the walls and clouded ceiling, would that give me the best results?

[TheArchitect]

Originally Posted by The Studio RI

Ok, I've been sketching some designes to acoustically redesign my control room and I just had a few questions about how sound travels in a room.

My room is small, 13x9x7 and is rectangular. I have severe bass problems! I know how various sorts of filtering can cancel frequencies in the room and such, but my question would be... what does bass trapping really do to the bass waves? does it just try to suck up bass like a black hole? is that the desired result, to suck up as much bass as possible? If I make my room one big bass trap, with 6" traps over all the walls and clouded ceiling, would that give me the best results?

In terms of an even response perhaps, but it would be awfully dead. Generally a compromise between all of the factors involved results in the better option

[jayfrigo]

Several things - first, don't try to filter frequencies to fix room problems. Fixing a time domain problem in the frequency domain is not helpful; and even in the frequency domain, filters may improve the frequency response in one specific location while actually increasing problematic ringing, and making the frequency response for the rest of the room worse. Unless you put your head in a vise, the filtered response is far less helpful than one might think.

On to why bass frequencies are trouble... When sound energy with a wavelength that corresponds mathematically to a room dimension reflects and bounces between two surfaces, a standing wave is created. This causes areas of constructive and destructive interference, which in practical terms means there will be areas with deep nodes, or nulls, where certain frequencies disappear, and other areas of antinodes, or peaks, where the bass at some frequencies will be far greater than what's recorded and intended to be reproduced.

As you add bass trapping, you stop these reflections from happening, which in turn prevents the resonance from building as they repeat between the surfaces, evening out the room response. Since the standing wave is diminished or eliminated, the nodes and antinodes are also diminished or eliminated, and ringing at modal frequencies is similarly improved.

The most common modes to treat are axial, where two opposite surfaces are involved. However, more complex paths including 4 and 6 surface interactions are also possible, causing oblique and tangential modes.

The other item to be concerned about is modal density. For high frequencies, there are plenty of reflections, spaced densely enough in time and frequency that they constitute ambience, and don't create such significant static peaks and nulls. At low frequencies in small rooms, the modes bunch up in some places, and leave others sparse, and end up causing the obtrusive nodes and antinodes.

As a room gets larger, the cutoff frequency gets lower. The is the frequency below which the modal density is not sufficient to be perceived as ambience rather than causing the detrimental interference. Small rooms have a high cutoff frequency, meaning there will be problems well up into the hundreds of Hertz. Large rooms, like concert halls, have a cutoff frequency so low that the modal behavior below it is no longer of concern. There are many other factors concerning large room acoustics that are not relevant here, so I'll leave it at that.

In practical response to your question, trapping the living daylights out of the room is fine as long as you include reflective and diffuse elements on top of enough of the trapping to create a well-balanced room.

Originally Posted by The Studio RI

Ok, I've been sketching some designes to acoustically redesign my control room and I just had a few questions about how sound travels in a room.

My room is small, 13x9x7 and is rectangular. I have severe bass problems! I know how various sorts of filtering can cancel frequencies in the room and such, but my question would be... what does bass trapping really do to the bass waves? does it just try to suck up bass like a black hole? is that the desired result, to suck up as much bass as possible? If I make my room one big bass trap, with 6" traps over all the walls and clouded ceiling, would that give me the best results?

[Weasel9992]

That's as well framed an explanation as any I've ever seen. Sticky, Jay?

Frank

[avare]

Excellent description Jay.

Impressed,
Andre

[jayfrigo]

Thanks guys. Sure, we might as well stick it for a while.

[The Studio RI]

very nice description! Before I start building, I'll post the designs here and get some feedback. BTW, would it be expensive to have someone design the treatment for my room just given the dimentions and some pics? I just want to do this once and do it right, rather than trial and error.

[Weasel9992]

Originally Posted by The Studio RI

very nice description! Before I start building, I'll post the designs here and get some feedback. BTW, would it be expensive to have someone design the treatment for my room just given the dimentions and some pics? I just want to do this once and do it right, rather than trial and error.

I know that we don't charge for it.

Frank

[The Studio RI]

Hey Frank,

the only problem is that I'm working on a very tight budget, and would not be able to actually purchase products from your company. If I could pay someone, say $100-200 to come up with a sketch of what treatement to put where, I could swing that, but the money I would have left would have to go to materials.

Right now, i'm considering covering the front half of the room with 6" of 703 from top to about 3 feet from the bottom, and then a couple of 2x4 panels in the back room, with some kind of cloud on the ceiling above the mix position. Instead of panels, I was considering just custom making frames and covering everything. I've attached a quick sketch for a visual.

Having someone design something for me would just save me a lot of aggrivation and probably turn out much better. No matter what I do, I just can't tame the bass!

[dft3670]

"trapping the living daylights out of the room is fine as long as you include reflective and diffuse elements on top of enough of the trapping to create a well-balanced room"



I have a room just about this size as this one with 19 bass traps in all the normal locations. (corners, back and side walls, first reflections, cloud, etc.) At the moment they are covered with fabric.

What are the best elements to use on the front of these traps, which ones are the best to treat and which are the best to leave with just fabric on them?

Thanks

[DanDan]

Hi Ben,
Jay has done a wonderful job of the why. I will try to show you how to minimise the problems for little cost.

Such a small room will have very strong bass variations with location. The materials of your room surfaces might have some influence on recommending treatment. If they are mostly sheetrock you are very lucky. I have concrete and brick.
Put the speakers close to, or even mounted on, a narrow end wall. Speakers with rolled off bottom, wall mounted are a good shot (Mackie/Genelec). Some will disagree with this. If in doubt put your speakers on stands and try them in various positions for best bass. Suffice it to say I have settled on this 'wall or very close to' by measurement and listening in the majority of small rooms I have treated recently. Try to make an equilateral triangle to your listening position. Ideally this position would be 38% of the room length. No matter what, stay away from the room centre, there will be no bass there.
Construct Superchunks (www.studitips.com) in ALL corners, floor to ceiling. If you can't afford that, use two rolls of attic insulation, in their wrapping, stacked in each corner. Cover with cheap fabric. If you have a concrete floor and or ceiling there is more....
Create an RFZ around your listening position. 2 inch 703 is thick enough. If your floor is not carpeted, put more 703 on the ceiling at other reflection points. Use a mirror to find them.
Cover the door with a wall hanging rug or other fabric. Put light paper roll blinds or such in any windows. You might put a rug on the floor under yourself. Consider frequenting a second 'sweet spot', 38% from the back wall. Put a couch at the back. Put in as many racks, flightcases, drum cases, etc. as possible. Pop some fabric in the cases which could double as tables or seats perhaps. Put stuff everywhere, pictures without glass, hanging tapestries, whatever. This 'stuff' causes some diffusion with little cost.

All of the above will result in a horrible dead room. :-)

However a little creative lighting can achieve a Zen like peace in there.
( I am no longer joking, almost everyone coming into my lair says this. SoundSound - Gear)
From here on my opinion may differ from most. I am very happy working in such a dead space. I got used to it very quickly. The the clarity, imaging etc. is stunning, so you might have to turn down your tweeters a little. I now look forward to going to work and am finding that mixes translate very well to outside. Mix reviews are quick and subtle now.
So, don't be afraid of the dead. For rooms of this size there is simply no option and they can work surprisingly well. Your sketch above has large amounts of treatment in places where they have little to do. The plan above is essentially the same advice that you will find at RealTraps, GIK, Studiotips, John Sayers, etc. Corners first, RFZ etc..... Consider the room, speaker, yourself, positions, as a whole. Speaker height, Tweeter tweaks and so on. When all these factors are in tune I believe you will be surprised at how good it can get.
Best Regards, Dan FitzGerald
SoundSound - Homepage

[The Studio RI]

Hey guys, thanks for all the help. I feel like such a newbie! I guess when it comes to real acoustics and treatment, I still am. I'm learing a lot, though! Anyway, I re-read many posts, and took all of your advice and I think I have a plan that may work for me. Granted, it is pretty labor intensive, but if it works really well, I'm more than willing to do it. I've attached some pics for reference.

My plan is essentially several fabric covered 1'x1'x6" squares of 703, "floating" 4" off of the wall, taking up as much usable space as possible around the mix position. Not pictured is the ceiling, which would be a 4'x6'x"8" box of 703 on an angle above the mix position, covered in fabric, with 4 recessed lighting fixtures inside. Each corner would have a wedge of 703 (12 sheets put together and cut diagonally) from top, to about 1' from the floor.

The floor is wood on top of plywood, 2" off a concrete floor (sadly, no filler between the joists). The front and left wall are sheetrock over soundboard, about 6" from concrete (some insulation between the studs), and the right wall is sheetrock over soundboard with insulation leading into the next room. The back wall is sheetrock leading into the other rooms. The ceiling is a drop ceiling with acoustical tile and some insulation above that.

If there is a better way to do this, of course, I'm all ears! Speaking of ears, I do like the "dead" sound of a room since I have a slight case of tinnitus, and it tends to lessen the effect for me. I also like to hear some "air" moving which I believe the gaps in the squares off the wall would provide.

[The Studio RI]

more pics

[The Studio RI]

And lastly...

[jwl]

Those squares aren't a bad idea, but you want to make sure you have a Reflection-Free Zone at your mix position. See this article for more detail on this idea. If I'm reading your diagrams correctly, you might get some reflections that you don't want. The first-reflection points should be all absorptive.

[Glenn Kuras]

Originally Posted by jwl

Those squares aren't a bad idea, but you want to make sure you have a Reflection-Free Zone at your mix position. See this article for more detail on this idea. If I'm reading your diagrams correctly, you might get some reflections that you don't want. The first-reflection points should be all absorptive.

I believe he has absorption in the early reflections but Studio RI see the following diagram on this page and make sure you are set up something like it. Any diffusion should be in the back of the room.GIK Acoustics: Room Setup

[The Studio RI]

Thanks guys. The design looks cool, but I was concerned about the functionality.

I placed and order with GIK last week to try to fix the room problems. Yesterday I did a frequency sweep test of the room at the mix position and client position, using two different sets of monitors, and the results were horrific! I'm missing CHUNKS of low end, and comb filtering out the wazoo on the high end.


I'm going to start a new thread soon in the contruction forum as soon as I get the materials in. I'll post all the data as well.

[steveschizoid]

Don'r worry, GIK will help! Bryan has been consulting with me, and he's just gone on vacation unfortunately, but things are definitely changing for the better! I have 2 244's vertical in the side corners, one horizontal at the wall/ceiling corner, and 2 on the wall below that. The "before" measurement is based upon a prior arrangement of 244's. I also moved my speakers back a few inches. I am sure we are not done, but it seems to be going in the right direction.

I found that if i moved my desk back a bit (a few inches) much of the comb filtering went away. I just have to have my computer keyboard and mouse at the very edge of the desk.

[The Studio RI]

wow, what a difference! I think I ordered about 13 panels in all. Two 244's on either side of the mix position, two 244's on the front wall, Several 244's for the corners, and a monster trap on the back wall. There will be a custom made box frame filled with 703 and some light fixtures for the ceiling. I'm hoping this will do the trick.

what else are you going to do with your room?

[steveschizoid]

I forgot to mention the 2 244's over my head.

I will probably continue to add traps. Bryan called my room "unpredictable," so there will no doubt be considerable trial and error. I don't know what will happen if I put some to the sides of the monitors or even in the wall to ceiling corner to my right. You may have noticed that the wall to my left is diagonal. Perhaps some on the rear wall as well. Bryan had me try moving just one trap to several different points and measure the result, and they all seem to have an impact on the null in the bass, so I guess the next step will be to cover multiples of those spots while keeping everything else as it is. It's kind of fun really.

I really like the guys at GIK because they really seem committed to figuring out solutions. I've spent around $900 since november '07 at GIK, but, as you know, that's chump change in this game. I get the feeling Bryan is the sort of guy who churches and concert halls consult with, so the fact that he is spending the time whipping my bizzare acoustical issues into shape - at no extra charge - speaks pretty well for them as a company.

Also, I just agreed to purchase some Adam S3a's, so I'll need to revamp again once they arrive. I'd like to figure out a way to keep the Hs80m's; they are truly great speakers for the price. But I may need to sell them to finance more treatment. Wanna trade 3 boxes of 244's for 'em Glenn?

[Glenn Kuras]

I really like the guys at GIK because they really seem committed to figuring out solutions. I've spent around $900 since november '07 at GIK, but, as you know, that's chump change in this game. I get the feeling Bryan is the sort of guy who churches and concert halls consult with, so the fact that he is spending the time whipping my bizzare acoustical issues into shape - at no extra charge - speaks pretty well for them as a company.

Yea I guess we will keep him around for a while!!! But can you believe he has the nerve to take a few days off for a little R and R?? The gull of some people!!


Glenn

[steveschizoid]

A bit of a prima donna I guess, how long is his usual workday - 12, 14 hours?

[Glenn Kuras]

Originally Posted by steveschizoid

A bit of a prima donna I guess, how long is his usual workday - 12, 14 hours?

More like working half days, 12 hours.

Glenn