shallow enclosures (on-wall)

[tom31415926]

I have tried to search for this topic, and found only some scattered information.

Does anyone know of design considerations and techniques for shallow enclosures (about 6 inches deep) intended for "on-wall" installation?

In rooms with limited space, placing the speakers a few feet out from the wall is difficult. For HT, the on-wall placement may be desirable. check out the Morel Vario for a commercial product.

I know that baffle step correction (BSC) often integrated into the crossover would be different.

Another issue is the resonance between the cone and the back wall of the enclosure. The enclosure back would be a node, the cone itself would be an antinode. I suppose some sort of absorption of diffusion directly behind the speaker would help, but what form might this take?

Another issue is the front panel diffraction. The front panel dimensions may be quite a bit bigger than those that would be used with a deeper enclosure, in order to achieve the desired enclosure volume. I suppose that beveled or rounded edges would be helpful. I also see absorptive material on the front panel sometimes, especially around tweeters. What considerations might there be for this issue?

Finally, looking at overall sound quality, does an on-wall system have any inherent disadvantages compared to boxes placed at some distance from the room walls?

Thanks

Tom

[Svante]

Here is a simulation showing what happens for different positioning of the loudspeakers. On-wall speakers typically have a dip in the response (in this case at 300 Hz). The dip is very hard to compensate for. One common way to reduce the problem is to make the baffle non-parallel to the wall.

[holdent]

Zaph developed a wall mounted speaker and documented the process. It might help. Go to http://www.zaphaudio.com/ and look at "Slimline Wall-Mounted Speaker" Parts 1 & 2. Part 2 explains the design.

[David Gatti]

I've been thinking about the same issue Tom.
My current thought is to have wide tapered edges (maybe 6 inches) from the front baffle to the wall, making a smooth transition and thus hopefully reducing the diffraction. In a wide enlosure you could have an internal V section of wood behind the midrange to deflect the rear wave sideways. Another option could be to have a large opening behind the midrange and the entire enclosure resting on a 1" layer of felt.

[tom31415926]

Thanks David, Holdent, and Svante.

Zaph has a great example. I suppose that the angle of his boxes helps to make the frequency response dip inaudible. In my case, I'm wondering if I can surround the speaker with damping using a specially-constructed channel around the edge (as deep and as wide as the box thickness?) filled with absorbing material, that is open to the front.

If anyone has any more links to relevant information, please post.

Tom

[Svante]

Originally posted by tom31415926
Thanks David, Holdent, and Svante.

Zaph has a great example. I suppose that the angle of his boxes helps to make the frequency response dip inaudible. In my case, I'm wondering if I can surround the speaker with damping using a specially-constructed channel around the edge (as deep and as wide as the box thickness?) filled with absorbing material, that is open to the front.

If anyone has any more links to relevant information, please post.

Tom

Hmm, I am not perfectly sure about this, but a knowledgeble person I know told me a while ago about a similar experiment. It did not involve a back wall, but it was about diffraction. If the sides of a box is covered with absorbing material, it actually makes the baffle step stronger. Not much, but a little.

It makes sense actually, once you think of it, the diffraction comes from the baffle support disappearing at the baffle edge. Absorbing the sound that goes around the corner also removes the support of the side wall.

On the other hand, when there is a back wall involved... I don't know.

From experimenting in Basta! i have found that if the distance from the driver to the baffle edges varies considerably more than the box depth, the dip can be reduced a lot. Unfortunately, this leads to a box that is some 80 cm wide if it is 10 cm deep. This is not very beautiful...

I think the way to go is to put the baffle at an angle.

[David Gatti]

Surround speakers may give you some ideas, for example this Focal:

[richie00boy]

Keeping an eye on this thread as I'd like to make some wall mounted speakers.

[soongsc]

I've spent some time on shallow designs, and still trying to figure things out. But it seems that absorbing material on the wall between the speakers help create better focus. Idealy it's better to start with the absorbing material from the edge of the driver inward. The wall itself needs to be a solid wall that does not have a hollow sound when you knock on it.

[FastEddy]

Of interest on this wall mount subject: http://www.magnepan.com/model_MMGW . I just obtained a pair and the mounting instructions suggest mounting on the wall about head high. The mount kit includes a set of hinges to accomplish this. When not listening, the planar speakers mount flat (about 2" thick). For the best listening the speakers should be angled out from the wall about 30 degrees. They don't have nearly the full range response when flat against the wall (probably having a similar curve to the above as per Svante), but they do sound very nice indeed when angled out. The Magnepan factory does have a tech support line and they apparently can supply pictures, diagrams, response curves, etc. if needed.

I also have a set of the Magnepan MMGs (maggies), and will shortly mount these on the wall in a similar fashion, aiming for some improvements as otherwise, these have to be placed far from any wall or corner. (When the MMGs are angled close to a wall, they do sound a whole lot better, but the solid wall mounts are supposed to contribute to another level of improvement.) I like both sets and recommend them and they sure could be a space saver when wall mounted. (Both types do need a sub woofer to bring out the whole full sound. MMG-W roll off ~ 155 Htz, MMG roll off ~ 110 Htz)