[SteveRB]

Hello,

This is my first post in this thread. Please take it easy on me...

My open baffle speakers are pretty much set in place for best sound plots with the help of Danny Ritchie and locked in place to keep domestic bliss. They are GR Research V1's: all open baffle with four 12" servo subs. Needless to say they can get really low and loud in the right room. Problem is I have the wrong room...

I have recently moved and now have a smaller and more central room for my hifi. I would like to start treating this room to get the most out of the hifi. I hope the experience in this forum can put me on the right track.

Here is a basic layout of my hifi room and the adjoining spaces:




Here is the last plot from my in room response, LEFT:


and, RIGHT:


I will be adding some curtains to the window opening directly behind the speakers and hifi shelf. As well, a small upholstered chair will be added to the right wall. I am less concerned about the plot above 500Hz.

However, I am very worried about: the dip between 100Hz-300Hz, the peak at 107Hz, the peak at 90Hz, and the peak at 50Hz. I have the PEQ on my Servo amps doing their best to deal with the two lower peaks.

I am certainly open to some DIY traps and treatment options. But, as always, they have to be approved by all members of the household.

Please help.

[Ethan Winer]

The main problems I see are a lack of symmetry, and that you're sitting directly in front of a reflecting wall. At the minimum you should have thick absorbers on the entire area behind your head. Then treat as usual with bass traps and an absorber on the left side to match the opening on the right.

Is there any chance you could move to the other rectangular room on the left?

--Ethan

[SteveRB]

Thanks Ethan,

The room to the left is a possibility. But it is pretty small and would not work with my current speakers and hifi. the speakers require at least 3' from back and side walls. I thought long and hard about that before moving into this apartment.




Regarding the difference between absorbers and bass traps. It is my (limited) understanding that absorbers are full frequency absorbers (should be roughly 4" thick) or even furniture of some type. Where as bass traps are similar but with a thin membrane to reflect sound above 300Hz or so...?

Absorbers on the rear and side walls should be no problem. I will need to get a little more creative with bass traps in the two rear corners.

[SteveRB]

First pass on treatment plan.

[bpape]

Try a couple of diffusers on the front wall to address the rear wave of the speakers.

If you can do larger corner traps, they'll go deeper in frequency.

Bryan

[SteveRB]

If you can do larger corner traps, they'll go deeper in frequency.

Thanks Bryan,

I see most panel traps are 24x48x4. I am a little more interested in a freestanding solution that can 'double' as furniture. Is there a relationship between surface area and or volume of a trap as to it's low frequency effectiveness?

24x48x4 and 12x12x32 both have a volume around 4600...

the flat panel does have a bit more surface area though.

[SteveRB]

Also,

I see many traps have a certain level of hf reflection designed into them. Could a large bass trap be wrapped in a paintable material (canvas, wallpaper)? It could help the trap be more 'invisible' in the space...

Thanks for the replies. I have just begun down this road of acoustics. Very interesting but I feel a bit lost right now.

[Ethan Winer]

Regarding the difference between absorbers and bass traps. It is my (limited) understanding that absorbers are full frequency absorbers (should be roughly 4" thick) or even furniture of some type. Where as bass traps are similar but with a thin membrane to reflect sound above 300Hz or so...?

A thick absorber works over the entire frequency range, down to some low frequency (gradual) cut-off based on thickness. Yes, some bass traps (such as RealTraps) add a semi-reflecting front membrane. This limits absorption at mid and high frequencies to keep the room from becoming too dead sounding. And when the membrane is bonded properly to the absorbing material it also increases absorption at bass frequencies quite a lot.

I am a little more interested in a freestanding solution that can 'double' as furniture. Is there a relationship between surface area and or volume of a trap as to it's low frequency effectiveness?

Surface area and depth both directly affect how low a bass trap will absorb to. I think GIK has a "table" shaped trap, and RealTraps MegaTraps are pretty innocuous when stacked in a corner even given their large size:



If the trap color is neutral and matches the walls,  you hardly even notice them in the corner.

--Ethan

[Alex Reynolds]

Thanks Bryan,

I see most panel traps are 24x48x4. I am a little more interested in a freestanding solution that can 'double' as furniture. Is there a relationship between surface area and or volume of a trap as to it's low frequency effectiveness?

24x48x4 and 12x12x32 both have a volume around 4600...

the flat panel does have a bit more surface area though.

The extra surface area would likely result in a bit more absorption. I usually suggest making square corner traps at least 16-17" thick.

I see many traps have a certain level of hf reflection designed into them. Could a large bass trap be wrapped in a paintable material (canvas, wallpaper)? It could help the trap be more 'invisible' in the space...

As long as the absorber isn't in a direct reflection point this should be fine.

[SteveRB]

Thanks for the help guys.

I am looking around for OC703 supply. I have found a couple suggested alternates but the stock all has FRK or ASJ jackets. Should these be avoided or are they fine for bass traps?

I ask because the GIK site has them as DIY supplies...

Thanks again.

[Alex Reynolds]

The facing is okay so long as you aren't putting multiple sheets in one panel. But if you want to treat bass frequencies, you'll need thicker than 2" traps, so multiple 2" thick panels with facing in one trap wouldn't be best. Also, the facing is somewhat reflective of high frequencies, so you won't want to use any facing sticking out into the room at reflection points or any areas that would otherwise direct sound at the listening position.

[SteveRB]

Thanks Alex,

I have recently tracked down a local supplier for OC 703 -- it is working out to be just over a dollar per square foot for the 2" thick version. This adds a bit of flexibility: 2" absorbers for reflection points and 4" for bass trapping...

I think I will go with this option which allows me to make all custom sized panels to integrate them onto the asymmetrical walls.

Current plan is 2'x3'x4" panels in corners behind the walls; 2'x2'x2" at reflection points; 1.5'x7'x4" behind the listening area...

[SteveRB]

OK, CRAZY IDEA:

what are the pros and cons of treating the entire front wall (behind the speakers)...?

I would use 2" and 4" thick panels and tile the wall behind the speakers... I could certainly get the wife behind that idea as opposed to 'bumps' and corner traps. It would only total about 150 sqft given the size of the window in the centre.

I could even build a couple QRD diffusors into a matching panel that would help scatter rather than absorb...

[Ethan Winer]

OK, CRAZY IDEA: what are the pros and cons of treating the entire front wall (behind the speakers)...?

Yes, it's a crazy idea because your speakers face the other way.

This explains in much more detail:

Front Wall Absorption

--Ethan

[SteveRB]

Yes, it's a crazy idea because your speakers face the other way.

This explains in much more detail:

Front Wall Absorption

--Ethan

my speakers are dipole, 20Hz-20,000Hz in both directions...

The thought being that I could use 4" thick OC703 floor to ceiling in the corners 24" wide as bass traps. the rest of the wall would have the same fabric covering with limited absorption be hind it.

My main goal in this process is to smooth out the 50-300Hz response. (...While keeping everyone else in the house happy)

[Alex Reynolds]

Of course, you have speakers that are one of the only exceptions to Ethan's article on front wall absorption. Typically, if you've got dipoles, you will want to do quite a bit of absorption on the front wall around the speakers. Since the wall is so close, you will likely get a comb-filtered like response at the listening position with dipoles. To be honest, I'm not quite sure why people sell dipoles when they know they'll be going into an untreated room...

Bryan suggests diffusion on the front wall often with dipoles, so that you retain the energy from the soundscape that is radiating behind the speaker onto the front wall, instead of completely killing it. Personally I think either method is fine, obviously personal taste will weigh in here.

[Ethan Winer]

my speakers are dipole, 20Hz-20,000Hz in both directions.

I missed that. I even Googled your speaker models and thought the photo showed a normal "box" speaker! Yes, in that case absorption or diffusion on the wall behind each speaker will help. But if your in concern is 300 Hz and below, you need bass traps rather than thin absorbers or diffusers.

--Ethan

[SteveRB]

Thanks for keeping up with me, and now that we are all on the same page. Here is a mock up of potential treatment.

I can build a 1x4 frame with 4" OC703 at the wall/wall and wall/ceiling boundaries. Inside the framing can be a symmetrical amount of diffusion towards the centre. (Remembering that there is a large window in the middle of the wall). The entire wall would then be panelled with a fabric grid that is both acoustically transparent and beautiful...!

I would hope that this does not kill the room but still tames my 50-300Hz issues.

[PDR]

Seems to me I've read that if you pull your panels away from the wall
an additional 4"....leaving an air space....it improves their effectiveness
in absorbing low freq......in other words 4" can be as effective as 8"
I'm sure the experts will straighten me out if I'm incorrect....I often am...

Steve are you planning on covering the QRD with fabric as well?
I've read this isnt a good idea...but again, lets see what the doctors say.

I use the diffusion directly behind mine, but absorption above....see avatar.
This works very well for me, its close to what your planning, and of
course we have the same speakers.

Nice thread, be interesting to see how it ends up!......good luck.

P.S. Dont know where your getting your insulation
       from but you should try STEELS building supply, in Surrey and Burnaby.
       You may get a better price from them.

[SteveRB]

Seems to me I've read that if you pull your panels away from the wall
an additional 4"....leaving an air space....it improves their effectiveness
in absorbing low freq......in other words 4" can be as effective as 8"
I'm sure the experts will straighten me out if I'm incorrect....I often am...

Steve are you planning on covering the QRD with fabric as well?
I've read this isnt a good idea...but again, lets see what the doctors say.

Thanks for chiming in -- you certainly know how to treat a room for the V-Series. Danny has been a big help too. I can pull them out to allow for an inch or two, but don't have the space for a full 4" in this room. I was hoping to cover the QRD -- domestic bliss will be achieved if the wall has a nice consistent look. If covering the diffuser in cloth will kill it's effectiveness, I can just put in a few blank panels. My hope was to add a layer of diffusion or reflection to balance the amount of absorption. ...also the QDR can only then be as deep as the frame (4-5"), not sure how effective that will be either.

Honestly, this is a rental suite and the hifi is set up in the main room (tv and kids in the smaller den). i'm not going for perfect acoustics; just better than what I currently have. I'm pretty handy with a chop saw. This project seems like I could knock off in a weekend and add a level of refinement to the hifi as well as give the room some added ambiance/modern feel. Off the shelf bass traps are a "no-go".