[Ethan Winer]

> There's just no room to get the speakers away from the front wall to avoid bass boom <

That's an interesting point. Though with enough bass trapping you can reduce the effects of speakers being near to a boundary. My partner Doug has a home recording studio and his control room is 16 by 10 feet, with the speakers firing the longer way down the room. Because the room is on the small side his speakers are only a foot or so in front of the wall. These speakers (Mackie HR824) have serious low end. But Doug has a lot of bass trapping - though not as much as I do! - and he has no problems with proximity-related bass buildup.

There are two different "classes" of bass issues in small rooms. One is bass buildup near a boundary, which is what you described. This has a simple rising shelf curve that is easy to counter electronically. In fact, many professional powered monitors include switches to compensate for this.

The other type of problem is comb filtering. This is also due to proximity, but it manifests as a series of peaks and deep nulls. These are impossible to get rid of electronically because 1) the frequencies change with distance, and 2) there are nulls as well as peaks and you can't raise nulls with EQ.

--Ethan

[cminer]

I truly appreciate all your good advice and I'm going to try out most of it.

I've been reading up on acoustic treatments, and have decided to try a few DIY projects.  Jon Risch's tube bass traps seem worth trying.

I also think the eighth nerve concepts are worth a shot.  The front is reflective, the back absorptive.  I got to thinking; cut a piece of 2 inch thick Owens Corning 703 into the right shape and size, bevel the back, slap some wallpaper on the front and mount like it shows on the website.  Quick and easy with a reflective front and an absorptive back.  Plus, the wallpaper will tend to camouflage it.

Do you see any pitfalls here?

Thanks again,

Curt

[8thnerve]

I truly appreciate all your good advice and I'm going to try out most of it.

I've been reading up on acoustic treatments, and have decided to try a few DIY projects.  Jon Risch's tube bass traps seem worth trying.

I also think the eighth nerve concepts are worth a shot.  The front is reflective, the back absorptive.  I got to thinking; cut a piece of 2 inch thick Owens Corning 703 into the right shape and size, bevel the back, slap some wallpaper on the front and mount like it shows on the website.  Quick and easy with a reflective front and an absorptive back.  Plus, the wallpaper will tend to camouflage it.

Do you see any pitfalls here?

Thanks again,

Curt

Wallpaper would be better than nothing, but isn't a great reflector at all frequencies.  I would use a thin wooden membrane about 1/16th to 1/8th of an inch instead, and then you can put the wallpaper on the front of it for aesthetic concerns.

Best Regards,

Nathan Loyer
Eighth Nerve

[cminer]

Thanks, Nathan. 

During a recent trip to a certain home improvement warehouse I saw some ceiling tiles that look to be made out of pretty much the same material as the OC rigid fiberglass, and were faced with textured vinyl.

How would it work if I bonded this to the OC 703?  It would add about 1/2 inch to the thickness, but would the reflectivity be any better or worse than the wood?

Oh yeah, any suggestions for a bonding agent between the wood and fiberglass?  Liquid nails?

Curt

[bgewaudio]

Cminer, we stock these ceiling tiles at our store, and I don't think the density is quite as thick as 703.  It's probably only like 2 lbs/inch at most.  I think It would be more effective to construct a wood panel and put the 703 on the outside, this way, the higher freq would be absorbed, but then reflected and brought back into the fibreglass to be absorbed again, then you would get more subtle diffusion in the midrange.

I would say the best bonding agent would probably be some sort of contact cement, that you could apply and would dry quick to save time.  However, being in the building material business, they is nothing I have here that recommends good bonding to fibreglass, but I think contact cement would work.

[cminer]

When you say put the 703 on the outside, it sounds like you're saying to sandwich the wood between two layers of 703.  Is that right?  Or are you saying put wood on the wall side with the 703 facing into the room?

[bgewaudio]

Yes, I would say have the 703 mounted on the wood backing (with fibre facing out), you could even staggar them in and out to make an abfusor, this way mids and highs will enter the material, hit the wood and exit back out through the fibre, then anything left over will be diffused.

[8thnerve]

Thanks, Nathan. 

During a recent trip to a certain home improvement warehouse I saw some ceiling tiles that look to be made out of pretty much the same material as the OC rigid fiberglass, and were faced with textured vinyl.

How would it work if I bonded this to the OC 703?  It would add about 1/2 inch to the thickness, but would the reflectivity be any better or worse than the wood?

Oh yeah, any suggestions for a bonding agent between the wood and fiberglass?  Liquid nails?

Curt

That surface isn't very reflective, and the density is much lower than 703.  I would go with a thin wood, you can affix it with 3M's Super 77 spray glue.

And to reiterate, I would NOT recommend facing the absorptive side out into the room.  All you'll do is roll off your high frequency response.  If you want to place it against a wall, an inch of space behind it will help as well.  You'll get best results though if you position it diagonally in the corner with about a half inch gap between the wall and the edges of the panel.

Best Regards,

Nathan Loyer
Eighth Nerve

[ctviggen]

Do you have the book Master Handbook of Acoustics by F. Alton Everest?  If so, he details on page 210 how to create a typical resonant panel absorber for corner (or horizontal) mounting.  It's very easy to make (well, saying that having never built one, which invariably means I'm wrong), and has a fairly absorption profile (see the next page). 

[cminer]

How about facing the fiberglass with drywall instead of wood (paneling) since I'm going to be wallpapering it anyway?  Bad idea?

I'm definitely going to be making triangles for the top corners, and rectangles bo bridge the ceiling/wall joint.  What about the four corners of the room - bass tubes or more rectangles?

[JLM]

Using drywall just makes it gypsum board construction (the fiberglass behind could only serve to help provide sound insulation).

The vinyl faced fiberglass ceiling pads are the cheapest possible drop ceiling panels.  The fiberglass density is way less than 703.  Over time those pads sag under their own weight (and they're very light weight).

[srlaudio]

I have been championing some new design concepts.....here is a quote from an interview with David Moulton (Berklee School of Music) a consultant in acoustics and speaker design.

"NB: The conventional wisdom is that you want to absorb sounds coming from the sides of the mix position because they arrive at the same time as the direct sounds, which muddles things up.

You say Balderdash and Hodgepuckey to that.

DRM: I'd like to redefine what we mean by a sound. The conventional definition is that sound is something that emits from a musical instrument. Psychologically speaking, that's not quite true. It's the energy emitting from a musical instrument plus its volley of early reflections that actually goes into our perception of what a sound really is.

So I don't see any difference between a loudspeaker and any other musical instrument, except for one specific and important quirk. We have a long history of knowing that we prefer to hear musical instruments in reverberant spaces with reflections; there's no reason we shouldn't hear loudspeakers the same way.

NB: But with the loudspeaker you're trying to evaluate sounds that have their early reflections recorded.

DRM: That's right, and that's the reason you have to question what I just said!

But if you take a look at what's really going on in recordings, playback rooms are generally small and the early reflections happen very quickly-whereas in a recording space (or simulation of a recording space that we do with artificial reverb), those reflections are much, much later in time.

What happens is that the early reflections of the playback room carry information about the recording room quite well. At this point, I'm satisfied from my own research that this is true.

NB: How did you come to that conclusion?

DRM: At one point I began working with some omnidirectional loudspeakers.

NB: Your own.

DRM: Yup. We invented some prototypes, and I sat down to listen to them. What I heard was phantom images that came from places in the room that were incompatible with what I thought I knew about how phantom images behaved.

It turns out that happens because of the way we gather early reflections from walls in a room. In actual fact, loudspeakers themselves are perceived in stereo as early reflections of a sound whose direct version we missed. So we're listening to the first of a set of early reflections that includes all of the walls and so on.

What we've found in our ongoing research-and there's a substantial body of agreement among other loudspeaker designers-is that imaging and timbre sounds improve when we have good wide dispersion of high frequencies.

For instance, I was one of a group of speakers at the American Loudspeaker Manufacturers Association symposium in January. Both Floyd Toole of Harman International and Joe D'Appolito, who's a fairly well known speaker and systems designer, made the case: we now know that wide dispersion of high frequencies, resulting in a reasonably flat power response laterally, is ideal behavior.

NB: Why laterally and not vertically?

DRM: Right now there seems to be a fairly clear sense that vertical reflections (from the floor to the ceiling) tend to upset our perception. I'm not sure if that's true, but there is some evidence based on the Archimedes Project that was done in the early '90s in Denmark.

NB: Psychoacoustics?

DRM: Yup. And for me the final proof is in the pudding. I have very wide dispersion speakers in a very wet, large room. Intuitively, you'd say that has to be the worst possible setup.

Yet a mastering engineer, Bob Ludwig, said it was fabulous when he came to listen. I've had similar experiences as well. One major loudspeaker designer had to check that the center speaker was off, because in 2-channel stereo the imaging was so good that he couldn't believe he was hearing a phantom.

NB: Is there any reason that wouldn't hold as true in smaller rooms?

DRM: No, it should get better in small rooms."

   Sou you see, nothing is cast in stone......We have been designing and equiping recording studios for 30 years......It was a revelation to us when we actually pointed a speaker at a large diffusor (prototype pictured in avatar) and panned the speaker across the wall.  No amount of words and theories can describe what we heard, suffice it to say it was desireable.  So recent control rooms we have treated have uses diffusion at the first reflection points.  The comments from engineers and musicians have been nothing but postitive.......

[cminer]

Two more for Nathan -

In another topic you recommended making the panels 4 or even 6 inches thick.  I was planning on making corners (triangles) out of 2 inch OC 703 faced with a thin piece of wood.  Do you recommend 4 or 6 inches for that?

And, you said I should use a 1/16 or 1/8 wood membrane.  How would 1/4 inch oak plywood do?  Too thick?

Thanks again

Curt

[8thnerve]

Two more for Nathan -

In another topic you recommended making the panels 4 or even 6 inches thick.  I was planning on making corners (triangles) out of 2 inch OC 703 faced with a thin piece of wood.  Do you recommend 4 or 6 inches for that?

And, you said I should use a 1/16 or 1/8 wood membrane.  How would 1/4 inch oak plywood do?  Too thick?

Thanks again

Curt

1/4 will work fine.  It will be heavier though so consider that when determining how to place it.

-Nathan