Bass Traps: Front corners or back wall?

[Glenn Kuras]

Would I get an improvement putting the two traps that are currently in the front corners on the the back wall instead?

All rooms are different but generally speaking you would start with the front corners. If you want to make sure you can test the room with them in the back vs the front with the following program
REW Room EQ Wizard Room Measurement Tutorial video

I also have two traps either side of the listening position for first reflections.

Don't forget about the ceiling.
GIK Acoustics: Early / First Reflection Points

[Ethan Winer]

Originally Posted by schismatic

Would I get an improvement putting the two traps that are currently in the front corners on the the back wall instead?

Probably not, but you would get an improvement by adding additional traps in the rear.

--Ethan

The Acoustic Treatment Experts

[kasmira]

Originally Posted by schismatic

Would I get an improvement putting the two traps that are currently in the front corners on the the back wall instead?

Its possible. Why don't you just move them and try it?

4 panels total in a room is not going to do much acoustically though. First reflections will definitely be noticeable but only 2 traps in corners for bass trapping wouldn't make a very obvious difference (at least, not that I've found)

[schismatic]

Thanks for the replies all. It's only a temporary issue as I am intend to build a further 4 panels for the room anyway.

Given the shape of the room, I will be able to place 2 directly flat on the back wall which will cover roughly 50% of the area of the back wall. I am unable to place traps across the back corners unfortunately because they are blocked by necessary furniture and the door to the room.

I will also be building a further two smaller traps to place on top of my current floorstanding traps in the front corners (those in question in the original post). These straddle the front corners, and with the two smaller additions, will give coverage from the floor up to roughyl 75-80% of the total height of the room.

Another question I have:

Is there a general rule or figure for total area coverage of wall surfaces (say a particular percentage) at which trapping and treatment really start to come into their own? Perhaps a minimum %?

I ask as one of the replies mentioned that 4 traps wasn't going to do a lot, and there must therefore be a certain point where there is sufficient trapping? Can it also be over-done? Can you trap too much?

[akebrake]

schismatic,

Can you give us a little more information about your room. Concrete walls, sheet rock, wood? Ceiling height? A photo?

Originally Posted by schismatic

Another question I have:
Is there a general rule or figure for total area coverage of wall surfaces (say a particular percentage) at which trapping and treatment really start to come into their own? Perhaps a minimum %?

This is a good question and I'm curious if Rod or Jeff can chime in on this one.

Philip Newell (author of the book: Recording Studio Design) suggests that 20% of the total area of a room will make a significant change. So in your room this means roughly 100 sqft of effecient trapping.
4 panels means 32 sqft.

But we do'nt know how effeciant your traps are (in the low end.)

Can it also be over-done? Can you trap too much?

Probably not in the low end. With only soft traps the danger is to much absorption in the high end.

Cheers

[schismatic]

These are the dimensions of my room:

Width: 274cm (8' 11.75")

Length: 385cm (12' 7")

Height: 242cm (7' 11.25")

The mixing desk and computer are setup just in front of a window which is on the front wall (short wall). The door is at the back right corner of the room.

Walls are generally plasterboard I believe (it's a rented house). Apart from music stuff, there is a wooden wardrobe in the room on the right-hand wall about 75% of the distance back from the front wall with the window.

My traps are DIY built using Rockwool RW3 slabs which have a density of 60kg/m3. They are 1.2m x 0.6m in terms of front area, and are 10cm deep. I built a small frame out of pinewood for them, so they have an additional inch of wood between the Rockwool and the walls. They are covered with cotton.

See photo and Google Sketchup render:

[schismatic]

I have just added two additional 4 ft x 2ft traps to the back wall (wall with the door), and I now intend to take some measurements using REW.

I'll post results here once finished.

[akebrake]

schismatic,

Can you give us a little more information about your room. Concrete walls, sheet rock, wood? Ceiling height? A photo?

Thanks for your effort!
It's much easier to avoid misunderstanding with this information.

Originally Posted by schismatic

I have just added two additional 4 ft x 2ft traps to the back wall (wall with the door), and I now intend to take some measurements using REW.

I'll post results here once finished.

That's great!

Good luck with the measurements.

Best

[kasmira]

Unfortunate I didn't reply soon enough, but I would recommend moving that shelf/wardrobe/whatever to the back wall..you may very easily skew your stereo image with that placed as is...

However...bass traps are more important for positioning than a wardrobe IMO so if they are now in the way and working very well, I wouldn't worry about it!

[schismatic]

Originally Posted by kasmira

Unfortunate I didn't reply soon enough, but I would recommend moving that shelf/wardrobe/whatever to the back wall..you may very easily skew your stereo image with that placed as is...

However...bass traps are more important for positioning than a wardrobe IMO so if they are now in the way and working very well, I wouldn't worry about it!

I'd love to move this beast but unfortunately it has to stay there. Out of interest, would an absorber simply placed on top of the wardrobe do anything for me? Although I can't move it anywhere else, I'm still concious of my stereo image.

After all of my traps are installed, I intend to run my mixes through IK ARC (let's not go there - I'm well aware it's not a room fixer, but it should help to polish things off a tiny bit for me in an already treated room). Based on my past experience with it, I would expect it to help towards correcting the slight variance in stereo imaging that I am likely to encounter.

[boggy]

Originally Posted by akebrake

..........
Philip Newell (author of the book: Recording Studio Design) suggests that 20% of the total area of a room will make a significant change.

"Significant change" may not mean good treatment.

Direct way to calculate how large area need to be covered, is to use RT60 formula from, e.g. AESTD1001 document, and insert it in to Sabine formula... if floor is fully reflective, of course... and result is room dependent at the end. Also, we don't have often luxury of alpha=1 at low frequencies, so we must increase surface if we need efficiency...

it is not that simple, at least.

Originally Posted by akebrake

..........
Probably not in the low end. With only soft traps the danger is to much absorption in the high end.

Not much danger if we make traps covered with air transparent diffusers (MyRoom Acoustic Design)

LF problem in small rooms is a way too difficult, so we don't have too much reasons to make compromises from the beginning, because room (possibly) may become "too dead"... at end we usually left with not enough bass treatment... especially with only porous absorbers. Bringing back liveliness is a way easier than good bass treatment in the small rooms.

[akebrake]

Originally Posted by boggy

"Significant change" may not mean good treatment.
....

Hi Boggy,
you are correct. He (Newell) doesn't promise anything. I just wanted to give an example from one designer that just a few sqft of trapping is not enough.

Direct way to calculate how large area need to be covered, is to use RT60 formula from, e.g. AESTD1001 document, and insert it in to Sabine formula... if floor is fully reflective, of course... and result is room dependent at the end.

Interesting reading, especially together with your white paper where we can see the practical results. Impressive.

0.2 s and below is quite short reverb time. I noticed that the AES people avoided the RT60 term in the paper.
Did you calculate with Fitzroy? Absorption is fairly well distributed anyway.

Also, we don't have often luxury of alpha=1 at low frequencies, so we must increase surface if we need efficiency...

We are back to the old problem finding efficient absorbers (optimum GFR)

Is there a practical and fairly cheap way to measure the gas flow resistivity on a sample in stead of just take a chance with an unknown brand?

Especially if we need to fill half of the room volume with soft traps...

Think we need a larger room than the average spare bedroom
to start with

Best

Ake

[boggy]

Originally Posted by akebrake

Hi Boggy,
you are correct. He (Newell) doesn't promise anything. I just wanted to give an example from one designer that just a few sqft of trapping is not enough.

I know. I only want to comment your example...

Originally Posted by akebrake

......
Did you calculate with Fitzroy? Absorption is fairly well distributed anyway.

You can use whatever you think that will fit...

Originally Posted by akebrake

We are back to the old problem finding efficient absorbers (optimum GFR)

Is there a practical and fairly cheap way to measure the gas flow resistivity on a sample in stead of just take a chance with an unknown brand?

AFAIK, no.

Originally Posted by akebrake

Especially if we need to fill half of the room volume with soft traps...

Think we need a larger room than the average spare bedroom
to start with

You're right.

Originally Posted by akebrake

Best

Best

Boggy

EDIT:

Originally Posted by akebrake

..... I noticed that the AES people avoided the RT60 term in the paper.
......

Ok, please, call it reverberation time, if you like.

[akebrake]

Thanks for the detailed response !

I really appreciate

Cheers

[chinni123]

Originally Posted by Ethan Winer

Probably not, but you would get an improvement by adding additional traps in the rear.

--Ethan

The Acoustic Treatment Experts

Ethan,

I read that size of each super chunk bass trap need to be same of size on either left or right side of corner in the rear wall I am limited by door on one side. Trying to understand what would happen if they are different size.

Thanks

[kasmira]

Originally Posted by chinni123

Ethan,

I read that size of each super chunk bass trap need to be same of size on either left or right side of corner in the rear wall I am limited by door on one side. Trying to understand what would happen if they are different size.

Thanks

I am not Ethan, but: They do not need to be the same size. They only need to be the largest you can use in that space. However, if you can only make a small trap in that corner, I don't see a point to use one at all, just use a larger one elsewhere.

Sent from my Nexus S 4G using Gearslutz App

[Ethan Winer]

^^^ Exactly. And don't forget that rectangle rooms have 12 corners, not just four where two walls meet. Further, traps can be placed flat against a door and the adjacent wall, with or with a small air gap.

--Ethan

[chinni123]

Originally Posted by Ethan Winer

^^^ Exactly. And don't forget that rectangle rooms have 12 corners, not just four where two walls meet. Further, traps can be placed flat against a door and the adjacent wall, with or with a small air gap.

--Ethan

Thanks Ethan. I am doing first on corners from floor to ceiling. Then on front and back walls from left side to right side on the floor (17x17x24). It is difficult to do super chunks at the ceiling. I may add few 4 inch 2x4 p panels (hopefully these are broadband) on ceiling corners.

[JLiRD808]

Hopefully Im adding to this discussion and not taking away....are corner traps better with the air gap behind them? What about "pillar style" traps...just a big chunk of 703/705 (12" x 24" thick...ceiling to floor) nestled in the corner?

[jimmyboy7]

Listen to Glenn from GIK, helped me a lot

[Glenn Kuras]

Originally Posted by jimmyboy7

Listen to Glenn from GIK, helped me a lot

Thanks!
Here is a neat way to test the corners to find the best one for trapping first.
Video: Testing Bass Trap Placement

[JLiRD808]

Originally Posted by Glenn Kuras

Thanks!
Here is a neat we to test the corners to find the best one for trapping first.
Video: Testing Bass Trap Placement

^^ Ha yeah I was playing with that again last nite. Bust out an SPL meter and pretend ur Egon from Ghostbusters.



I also found out that my floor-wall corners and the area behind my desk were my biggest issues

[Glenn Kuras]

Bust out an SPL meter

The other day I found a SPL meter app on my android phone. I don't think I would totally trust it but it could show where things build up. I will let you know if I get a chance to test it.

[Syncamorea]

Originally Posted by akebrake

Is there a practical and fairly cheap way to measure the gas flow resistivity on a sample in stead of just take a chance with an unknown brand?

I don't know about practicality or cost ($41 just for the .pdf!) but look at this:

ASTM C522 - 03(2009)e1 Standard Test Method for Airflow Resistance of Acoustical Materials

Originally Posted by Glenn Kuras

The other day I found a SPL meter app on my android phone. I don't think I would totally trust it but it could show where things build up. I will let you know if I get a chance to test it.

Will it work while you are talking on the phone? I could find out how loud my friends yell at me on a call? Or how loud my Monster Beats buds are hipping and hopping?

[akebrake]

Originally Posted by Syncamorea

I don't know about practicality or cost ($41 just for the .pdf!) but look at this:

ASTM C522 - 03(2009)e1 Standard Test Method for Airflow Resistance of Acoustical Materials
....

Thanks, that's great!

The right kind of GFR will certainly not hurt if you are building a studio with rock wool or whatever velocity absorbers

Cheers

[jimmyboy7]

Originally Posted by Glenn Kuras

Thanks!
Here is a neat way to test the corners to find the best one for trapping first.
Video: Testing Bass Trap Placement

No problem