Bass Traps - Difference in Thickness, Floor to Ceiling?

[Umlaaat]

Hey y'all..

I did a search for bass traps and can't seem to find what freq differences there are to thickness in traps..

I did the diy thing a while ago and built (stupidly, now that i see what i should've done) some monstrosities that have 5/8" plywood backing and built it from floor to ceiling, about 6'.. they also only have one layer of 703... and although they look nice, i have a MAJOR bump around 250-300hz..

So i'm using my existing materials and rebuilding them, but want to know how thick they should be and why not build them floor to ceiling...?

[Glenn Kuras]

Originally Posted by Umlaaat

Hey y'all..

I did a search for bass traps and can't seem to find what freq differences there are to thickness in traps..

I did the diy thing a while ago and built (stupidly, now that i see what i should've done) some monstrosities that have 5/8" plywood backing and built it from floor to ceiling, about 6'.. they also only have one layer of 703... and although they look nice, i have a MAJOR bump around 250-300hz..

So i'm using my existing materials and rebuilding them, but want to know how thick they should be and why not build them floor to ceiling...?

You want them to be no less then 4" thick. I like 6" myself, but if money is tight, 4" will work. Make sure they do not have a solid back to them.

Glenn

[danbronson]

The frequencies a panel will absorb don't depend just on thickness. Gas flow resistivity and the air space behind the panel to the wall will also affect this. Gas flow resistivity is related to the density of the panel among other things.

Unfortunately information like that is hard to find and varies when you do find it. So just know that 703 is good and should get the job done at 6" thick, with an airgap.

[Ethan Winer]

Originally Posted by Umlaaat

can't seem to find what freq differences there are to thickness in traps.

The relation is simply that thicker traps absorb well to lower frequencies. That, and an air gap can also extend the frequency lower as Dan explained. There are trap designs that target specific frequencies, but that type is not recommended for smaller rooms.

i have a MAJOR bump around 250-300hz.

250-300 Hz is easy to achieve, so that tells me the main problem is you just don't have enough traps. As Glenn said, four inches thick is a good minimum.

--Ethan

[jwl]

The bumps you are experiencing could also be a result of the room. We don't know much about it though. How big is the room? How far from the rear wall are you? Bumps like this are often helped with bass traps on the rear wall (additional ones, not moving existing ones from the corners).

[Umlaaat]

Originally Posted by Glenn Kuras

You want them to be no less then 4" thick. I like 6" myself, but if money is tight, 4" will work. Make sure they do not have a solid back to them.

Glenn

what freq range does the 6" do that the 4" won't?

[Umlaaat]

also - why dont people make traps to go from floor to ceiling?

[Glenn Kuras]

Originally Posted by Umlaaat

what freq range does the 6" do that the 4" won't?

There is no way to tell when you DYI, but you can see the numbers between our 244 and Monster to give you some idea on how much better it is.

Glenn

[dredbird]

Originally Posted by Umlaaat

also - why dont people make traps to go from floor to ceiling?

I did. I have 12 floor to ceiling traps in a 15 X 11 room.

[jwl]

2x4 is a common size for acoustic panels and bass traps for many reasons, not the least of which is shipping cost. If they were taller shipping would get much more expensive. So many people make or buy 2x4 panels and install them in the corners. If you have 8' ceilings, then 2 of them stacked floor to ceiling is better. DOn't forget the room has 12 corners (or more).

[mattianlaseppia]

ok 6" but how much for density?

and how much the air gap?

[Glenn Kuras]

Originally Posted by mattianlaseppia

ok 6" but how much for density?

and how much the air gap?

The higher density rigid fiberglass or mineral wool will work a bit better, but you can use OC 703 also (3 pound). As far as air gap, if flat mounted on the wall you want 4" to 6", if straddling the corner, have the sides of the panel touch the walls.

Glenn

[mattianlaseppia]

but isn't too much 6" for bass trap? i mean is too hard, is like another wall.. is too reflective, don't you think?

bass trap have to absorb the lows not to reflect them inside the room

i thought that 2" of 50 kilograms x square meter of density (i don't know what unit do you use to calculate density) was a good size for bass trapping

to improve the room acoustic in the lows

[Glenn Kuras]

but isn't too much 6" for bass trap? i mean is too hard, is like another wall.. is too reflective, don't you think?

Not even close. 6" will work just fine, in fact will work pretty darn well. What reflects (for the most part) on the high end is the first little bit of the face. So 1" 703 with frk will reflect hights the same (well almost the same) as a 6" with frk.

Glenn

[St. Kelly]

I will be doing my bass traps with Roxul... and there's a fair number of options for density.

To create 6" thickness I will use two 3" pieces together.

What density is OPTIMAL? Since I have the choice of 3pcf -> 8pcf, I might as well go with what one of our wizards on the subject feel is the best choice...

This is for the "bass" absorption. I will be adding broadband panels in the room as well.

Is 6pcf the standard "best"?

Sorry, I know that words like "best" and "optimal" are annoying as each situation is different.

My room is 17x14, ceilings about 7.5'

I will be adding a SUB at some point... oi vey

[St. Kelly]

Originally Posted by St. Kelly

I will be adding a SUB at some point... oi vey

I thought the "air space" behind bass traps was important (like it is for the broadband absorption panels)

But with some more reading on this forum tonight, perhaps what I'll really want to do is the "Chunk" traps?

Cutting the panels into many triangles, and stacking them up.. all the way from floor to ceiling is best, i assume.

Then there would be not space between the wall and the rockwool. But this is superior is it?

I need to catch that LOW bass.. what do I want to do to absorb the most, and lowest.

I will be mixing in this room (also some tracking, as well, actually).
Some of the urban music got that "big" bass.. low subs at high volumes, etc.

What to do to get the most out of my room?

[avare]

For 6" thick traps, 3 lb/ft^3 is the best from the range you listed.

Yes, I am writing the lightest of the density range you listed. The effectiveness of the absorber is a function of the gas flow resistance at the the surface of the absorber. The thicker the material the lower the resistivity per inch thickness is better. That is within the range of densities of materials we normally use and thicknesses.

Absorbent, and light,
Andre

[St. Kelly]

Thanks for the info, avare..

Care to comment on the different between straddling the corner with a 6" thick board, verses "filling" the corner with a triangle shaped "super chunk" trap?

[avare]

Originally Posted by St. Kelly

Care to comment on the different between straddling the corner with a 6" thick board, verses "filling" the corner with a triangle shaped "super chunk" trap?

Leaving a gap, which is what the triangular space, is done in home studio building in order to save money on material. Sound is reflected to a certain degree whenever the sound goes through a change in the medium it is in. Air, dense insulation, thin insulation, are all different mediums to sound. Denser insulation has greater acoustic resistance per inch of thickness than lighter insulation. To absorb effectively at low frequencies, the absorbent material has to be where the sound wave velocity is high. All sound waves have zero velocity at hard surfaces, like a corner.

Putting the two together a denser absorber will be thinner while having some refections from the inside surface of the absorber, and be more reflected by the material. Filling the space with a lighter material will have no reflections inside and less will be initially reflected by the absorber.

Note that the internal reflection is quite minor.

The big factor that is so often overlooked, even by acoustics experts is cost. 70x is the great informal material used for most absorbers. By the point where material is 4" thick, 701 (1.0 lbft^3) is more effective than 705 (5.0 or 6.0lb/ft^3 depending on which data sheet you use) at 125 Hz. All other things being equal, which they are not, 701 is one fifth the price of 705, material being the major cost. So at that point in absorber design, the more expensive material is less efficient!

A big factor also is the suitability of home construction insulation for filled bass traps. The cost savings here are due the different marketing channels. Home insulation is almost sold on a cash (or credit) and carry basis. 70x and similar products are through industrial suppliers where price includes service etc. The cost difference is amazing. In my part of the world about 12 to 1. 703 is around $4.00/ft^2 in 4" thickness and Roxul Safe n Sound (3.5" thick) is 27 cents per square foot.

Straight substitution is a cost savings of a factor of 12. A filled corner with Safe n Sound as opposed to 703 straddling the corner would cost one quarter in insulation costs and give better performance.

I used density in the writing above. The actual physical property that is important is gas flow resistance. For (a rather long winded) discussion on this topic this thread will help.

I am trying keep this relatively simple, but few things in acoustics are simple and intuitive. I hope this helps.

Andre

[mattianlaseppia]

so here Could someone help out interpreting material's gas flow properties is written that is better using low density glass wool but very tight?

i've understood right?

[avare]

Originally Posted by mattianlaseppia

so here Could someone help out interpreting material's gas flow properties is written that is better using low density glass wool but very tight?

For deep traps, low density is better. I don't understand what you mean by "very tight."

Andre

[mattianlaseppia]

sorry i mean very thick.. my english is bad ;) and sometimes i'm confused with similar words..

and how to build deep traps? could you make me some examples? and also some examples of low density expressed in kg/m3? because i don't understand well with your units.. (if you can)

thanks

(i have to make some trap for my new room.. tomorrow i will do some measurement with mic and i will post some pics and all the rest)

[avare]

There are many threads here showing how they built their bass traps. Basically for what we are writing about here it is frame to hold insulation in the corner, with the frame covered with some fabric to look good.


By light I mean less than 48 kg/m^3. Even 16 kg/m^3 is good.

Good luck!
Andre

[mattianlaseppia]

in this link http://www.gearslutz.com/board/bass-...-new-post.html

i've seen that the best is 10cm of 24 kg/m3 because is at 0.84 (at 125) and is also much more inexpensive

so i'm trying to think how to put them to fill the corners.. and hold the dust of glass wool.. to have clean air..

do you have some link to pm me?

thanks

(do you think that in that link the best way is 24kg and 10cm or other?)

no sorry i've seen now.. is not directly on wall.. is at 16 inch.. so something like 40 centimeters

very distant..i think.. but is referred at corner or side wall front/rear wall..

ok, probably i haven't understood correctly

[avare]

i've seen that the best is 10cm of 24 kg/m3 because is at 0.84 (at 125) and is also much more inexpensive

You read the thread about air flow resistance. What is good depends also on the thickness and where it is located, in terms of sound velocity. 0.84 and density is meaningless. Even the density spec by itself is meaningless. 703 @125 Hz is much worse than Safe n Sound (3.5") than can be due the thickness difference. Yet the two are almost identical in density.

"Inexpensive" is also meaningless. In parts of the world one type insulation is much cheaper than another. In other parts of the world the cheaper one is more expensive. This can even change within a country form region to region.

Andre