Help with bass trapping

[weemies]

That's right, yet another bass trapping thread. If you're sick of them, my apologies.

I recently DIY'd nine 6" bass traps, and while they helped flatten the bass response tremendously, I'm still far from satisfied.

Here's a pic of my room layout:



I already sent this pic to Ethan Winer a while ago via email (hi, Ethan ), when I was planning a RealTraps purchase. I got some good pointers from Ethan. I however decided that RealTraps were too much for my wallet, especially because of overseas shipping, so I went the DIY way.

Anyway, the pic is totally accurate, except it doesn't show the traps. I have two traps on top of each other in every corner of the room (at the back they are in the alcove back corners), covering the corners from floor to the ceiling. That's eight traps right there. The one spare trap I have is currently lying at the right wall-floor corner, as I can't very easily hang the traps at wall-ceiling corners, because my traps haven't got any frames - just fabric wrapped around them.

My problem is with the lower bass range. I used the RealTraps sonar project of 1 second sine waves from 40 to 300 Hz to measure the bass response. At ~60 Hz there's almost a total cancellation, and below ~130 Hz the overall volume level is probably like 10 dB lower than from ~130 Hz upwards. My ears can easily tell that there simply isn't enough bass at the listening position.

I'm considering making even more traps at some point and placing them to wall-ceiling corners, but I'm hoping to get other ideas here. Another listening position perhaps? I've experimented a little already (a a foot towards the front, towards the back, towards the right), but it isn't really helping. The overall flattest response has been at the position shown in the picture.

I'd appreciate any ideas you might have. Great forum, btw, but not good for the wallet.

[tINY]

You are probably fighting room modes.

Notice that your head is almost exactly in the middle of the room? You shouldn't have it there in a small room like this.

I calculate the side-to-side first mode at about 50Hz. Setting your speakers wider _may_ help this some. Front to back, you should have pretty good nulls at about 30 and 90 Hz. Moving closer to the window will help this.

Bottom line: move things around until its a bit better, naybe you can find an arangement you can live with. The bass traps will help, but in a small room, the center is a bad place for your head.




-tINY

[gurubuzz]

I would build two Helmholtz resonators in the corners each side of the window.


An air tight box from floor to ceiling, triangular to fit on the corner

6mm MDF slats ranging from 1mm to 6mm gaps between the slats...

of course I believe a ceiling trap that sits on 4 legs would work better as you can have more air inside the trap thus effecting lower frequencies.

have you tried having the doors of your cupboard slightly open like 10mm???

It may act as a bass trap on its own.......

you could have airtight seals on your cupboard doors and drill the right amount and size holes in one side...this will make an excellent trap as your clothes inside would act as the "suspension"...

[gurubuzz]

How about your bed???

is it a box style base...

if so the correct vents placed in it could also make an excellent trap...

[gurubuzz]

looking at your diagram again I don't like that the whole left side of the room has two massive openings do they have doors on them???


I would try to have your back facing the kitchen....

It's worth trying every position before you spend the time/money to treat it..

[soupking]

The best absorver in the world is an open window.

That's brilliant. Of course, I'm in a closed room.

[Glenn Kuras]

[QUOTE=weemies;1390889]

"I already sent this pic to Ethan Winer a while ago via email (hi, Ethan ), when I was planning a RealTraps purchase. I got some good pointers from Ethan. I however decided that RealTraps were too much for my wallet, especially because of overseas shipping, so I went the DIY way."

Well if nothing else I hope you offered him some kind of payment for his personal time he spent helping you.



"I'm considering making even more traps at some point and placing them to wall-ceiling corners, but I'm hoping to get other ideas here. Another listening position perhaps? I've experimented a little already (a a foot towards the front, towards the back, towards the right), but it isn't really helping. The overall flattest response has been at the position shown in the picture."

Sounds like to me you just need to keep adding more bass traps in the room. Not sure where you have all the traps now, but cover floor to ceiling in all wall to wall corners and at that point start to cover ceiling to wall corners. Also you may want to place a couple traps on the back wall. How did you make the traps?
BTW your room set up looks fine also.

Glenn

[weemies]

Originally Posted by tINY

You are probably fighting room modes.

Notice that your head is almost exactly in the middle of the room? You shouldn't have it there in a small room like this.

Actually, as you can see in the pic, my ears are exactly 38% from the front wall (if we consider the back of the alcove the back of the entire room), which is the optimal position according to Ethan.

I calculate the side-to-side first mode at about 50Hz. Setting your speakers wider _may_ help this some. Front to back, you should have pretty good nulls at about 30 and 90 Hz. Moving closer to the window will help this.

Bottom line: move things around until its a bit better, naybe you can find an arangement you can live with. The bass traps will help, but in a small room, the center is a bad place for your head.




-tINY

Thanks for the tips, I'll try setting the speakers wider.

Originally Posted by myfipie

Sounds like to me you just need to keep adding more bass traps in the room. Not sure where you have all the traps now, but cover floor to ceiling in all wall to wall corners and at that point start to cover ceiling to wall corners. Also you may want to place a couple traps on the back wall. How did you make the traps?
BTW your room set up looks fine also.

Glenn

Thanks Glenn. Currently I have all wall to wall corners covered from floor to ceiling. The way I made the traps was I bought some rock wool that was dense enough (about 70 kg / m3, I believe). Then I just stuck three 2" slabs together, wrapped them with some fabric and stapled the fabric in place nice and tight, using a single board of wood at the back. Maybe I'll go into more detail and post some pics once I make more of them.

[gurubuzz]

The rock wool is very hit and miss.

How are you working out which frequencies the rock wool is acting on.

If you build a helmholtz resonator you can tune the specific frequency and broaden or tighten the "Q"....

Building a helmholz trap is like EQing the room...

putting up piles of rock wool is like using a tape machine to tame the dynamics of a bass guitar...

You could end up with a room full of rockwool .. and a really dead sound ad the rock wool will definitely diffuse mid and hi frequencies...


the rock wool idea sounds like a good Idea but in practice its like a fire blanket....

A helmholtz resonator is relatively cheap to construct....

I can design one for you if you like???

The formulas are good for working out the problem frequencies but a frequency response test of the room from your listening position is the best way to find the troubling frequencies...

[Glenn Kuras]

Originally Posted by weemies

Thanks Glenn. Currently I have all wall to wall corners covered from floor to ceiling. The way I made the traps was I bought some rock wool that was dense enough (about 70 kg / m3, I believe). Then I just stuck three 2" slabs together, wrapped them with some fabric and stapled the fabric in place nice and tight, using a single board of wood at the back. Maybe I'll go into more detail and post some pics once I make more of them.

I got some really bad news for you but you built them wrong. Having the wood on the back is taking away all the effect of straddling corners. The best you can do with what you built is to flat mount them on walls for reflections.
I am sorry to tell you that as I am sure you spent a great deal of time and money on them.

Glenn

[Glenn Kuras]

"Building a helmholz trap is like EQing the room... "

Your RIGHT! But the problem with most small rooms is there are problems throughout the spectrum and building helmholtz resonators for all problem areas would be pretty darn hard (plus there would not be to much room for you equipment left ). The best thing to do is use rigid fiberglass or mineral wool in as many corners as possible and at that point you could follow up with a tuned trap as to put "icing on the cake" of tuning the room.

Glenn

[chris carter]

Originally Posted by weemies

Then I just stuck three 2" slabs together, wrapped them with some fabric and stapled the fabric in place nice and tight, using a single board of wood at the back.

The board at the back may very well be sabotaging your traps. It's better to make a frame of wood at the back out of 1"x2" or something. That way the back is entirely exposed. The theory being that the sound that goes through hits the airspace behind, bounces off the corner wall and then has to re-enter the trap. But putting a full board behind, it's kind of like just taking your 6 inch trap and hanging it flush on a wall.

So first thing I'd do is disasemble your traps and take the board out and replace it with a frame. Then set them up and listen again. That's the cheapest, fastest, and easiest solution and although I can't promise it will completely work, I know it will DEFINITELY improve the sound. You'll need to buy some wood and probably a little more fabric as you've got a little more surface area to wrap... but we're about the same money as you'd spend on a nice lunch so not too bad :)

[gurubuzz]

Yes it is easier to do it with rock wool etc..

Here is a bass trap that I designed and it works from about 60hz to 280hz..

nearing the finishing stages..

It was constructed on the floor and gently jacked up to touch the ceiling (airtight) and 4 legs bolted to the sides..the legs U see are temporary stands...

IT worked out better than I expected as the room had a double standing wave at 132 hz as the length and width had coinciding frequencies..no the room was not square.


The slats were 90x45 pine and the gaps were 6 mm and 4 mm...

the deep end was about 90cm and the shallow end about 30cm..

These type of traps do take a bit of brain work and forethought this one was in a rented property so there is nothing attached to any walls or ceiling....very heavy.... but very happy...

[weemies]

Originally Posted by myfipie

I got some really bad news for you but you built them wrong. Having the wood on the back is taking away all the effect of straddling corners. The best you can do with what you built is to flat mount them on walls for reflections.
I am sorry to tell you that as I am sure you spent a great deal of time and money on them.

Glenn

Originally Posted by chris carter

The board at the back may very well be sabotaging your traps. It's better to make a frame of wood at the back out of 1"x2" or something. That way the back is entirely exposed. The theory being that the sound that goes through hits the airspace behind, bounces off the corner wall and then has to re-enter the trap. But putting a full board behind, it's kind of like just taking your 6 inch trap and hanging it flush on a wall.

So first thing I'd do is disasemble your traps and take the board out and replace it with a frame. Then set them up and listen again. That's the cheapest, fastest, and easiest solution and although I can't promise it will completely work, I know it will DEFINITELY improve the sound. You'll need to buy some wood and probably a little more fabric as you've got a little more surface area to wrap... but we're about the same money as you'd spend on a nice lunch so not too bad :)

We're talking about a very small and thin piece of wood, something like a long single piece of venetian blinds, which is there simply to keep the fabric in place tightly. It's not a board covering the entire back.

[bpape]

If the back isn't covered much with the wood, you'll likely be OK. But if it covers the whole thing, really doesn't matter much the thickness for the most part it will hurt things.

IMO there are 2 other issues besides doing the wall/ceiling corners (which you should consider).

- The null off the back wall should be addressed with some thick absorbtion behind the mix position back by the bed.

- In a room that long with the mix position at 38%, it's very likely that the monitors you have just don't have enough on their own at the bottom end without being closer to a boundary for some added room gain. Have you tried moving the speakers more toward the front wall and a bit farther apart?

Bryan

[megl]

Originally Posted by myfipie

I got some really bad news for you but you built them wrong. Having the wood on the back is taking away all the effect of straddling corners. The best you can do with what you built is to flat mount them on walls for reflections.

In Ethans BT's:

http://www.ethanwiner.com/BTPlans.gif

there's thin plywood in the front ... I guess it's to make sure higher frequencies doesn't travel through, so the trap only takes care of the deeper frequencies? So couldn't weemies just flip his around for bass trapping ... or am I confusing things?

/megl

[Ethan Winer]

Originally Posted by megl

there's thin plywood in the front ... I guess it's to make sure higher frequencies doesn't travel through

The main purpose of the front panel is to act as a resonator at the desired center frequency you want absorbed. So it's not just to block mids and highs.

--Ethan

[megl]

Originally Posted by Ethan Winer

The main purpose of the front panel is to act as a resonator at the desired center frequency you want absorbed. So it's not just to block mids and highs.

And can it only work as a resonator if the chamber is closed?

/megl

[Glenn Kuras]

Originally Posted by megl

And can it only work as a resonator if the chamber is closed?

/megl

Yes panel traps have to be sealed.

Glenn

[megl]

Originally Posted by myfipie

Yes panel traps have to be sealed.

Ok!

Glenn and Ethan thanks for clearing this up - and thanks for all the great information you both are sharing in here!!!

/megl