Sonic ' problem ' with in walls?

mayhem13

Member
2008-09-22 4:37 am
I'm about to embark on an upgrade to my current PC 2.1 system which. The new workstation ( at home of course) is a build in 26" deep and 9ft wide with the Monitor centrally mounted. In other words, not the deepest desktop so an In-Wall speaker makes a lot of sense for space saving and to avoid the midbass ' bump and run' of bookshelf speakers mounted almost on the wall.

I've been trying to find a reason 'NOT' to do an In-Wall yet all i can find are positives. For starters, i'll be building MDF enclosures to go in the wall and a 1/2" baffle overlapping the enclosure. They'll be relatively narrow and only 3.5" deep so just as rigid as a stand alone box. There won't be any need for BSC so increased efficiency and a lower XO parts count. There should be little to no diffraction issues either.

So what gives? There's the obvious issue of cutting into your walls and the permanence of the installation, but in my case they're both non issues. Anyone see anything wrong with my reasoning here before i start cutting into the wall?

Oh...final opponent would be limited enclosure volume but i'm 2.1 with a sub below the desk to plenty of sub 100hz reproduction capabilities.
 

CLS

Member
2005-06-17 6:58 am
Taiwan
Or, maybe not necessary to be totally flush with the wall surface. The speaker baffles can be popped up a little, to gain some more internal volume, or with the toe-in angle built-in (talk about built-in :D ).

Or, push the speakers into the corners, with 2 incline planes facing inward, even more internal volume is obtained, and much more room gain for the LF (and of course the strongest room modes).

Wow! that seems a pair of big guys like those in the recording studios :D
 

mayhem13

Member
2008-09-22 4:37 am
I'm thinking a slightly angled baffle if needed as well but if i go with a 3/4" dome, i won't have to worry about off axis behavior too much as these generally have excellent response at 30 degrees out to 20khz. A 1" dome....not so much. That's where the possibility of a ribbon might come into play as well
 

CLS

Member
2005-06-17 6:58 am
Taiwan
The considerations of toe-in are not entirely covered by the off-axis response of the tweeter at 20kHz. More important is the overall directivity, and the target coverage.

For ordianry cone/dome mono pole speakers and stereo configuration, I usually prefer large toe-in angle which provides better imaging stability across various positions. Of course YMMV.
 
I've designed a lot of in-wall speakers for PSB and Snell. They have some real advantages if you fix the problems.

Building your own enclosure helps, since drywall caveties aren't great cabinets. Keep the front surface as smooth as possible, the freedom from diffraction and back wall reflections is your main benefit. Don't bother trying to angle woofers. When mounted in the wall they have virtually no directivity so toeing them in doesn't do anything. You can angle your tweeter inwards and if you give it some directivity with a waveguide this can work very well.

Here is a unit that had a rotatable waveguide on the tweet. It gave the ability to steer response and also reduced bounce back off the woofer cone behind.

PSB Speakers - CW180R In-Wall Speaker

David S.
 

MCPete

Member
2005-11-01 1:00 am
Is there any difference between in-wall and free standing away from the rear wall in terms of stereo imaging? I don't recall where I read it, but I'm fairly certain that I did find the opinion that in-wall speakers are lacking in terms of generating a convincing stereo image. It would be great if there is a scientific explanation for the difference (if there is this difference), but I wonder if at least there is a consensus that this is subjectively true.

-Pete
 
In 2-way, the 'woofer' plays quite high as to show its directivity above several-hundred Hz.

You really need to measure the polar pattern of a few woofers when mounted in infinite baffle. It is totally different than the polar response in a cabinet.

The unit in a wall will have no directivity at all up to a fairly high frequency. In a cabinet it will have some directivity from even fairly low frequencies.

David S.
 
Is there any difference between in-wall and free standing away from the rear wall in terms of stereo imaging? I don't recall where I read it, but I'm fairly certain that I did find the opinion that in-wall speakers are lacking in terms of generating a convincing stereo image. It would be great if there is a scientific explanation for the difference (if there is this difference), but I wonder if at least there is a consensus that this is subjectively true.

-Pete

You know, I hear that from time to time, but the only possible difference is that conventional speakers will have an added, delayed, rear wall bounce (wall behind the speakers). I'm not sure how that would improve imaging but it would have to be considered as giving a less accurate response than the reflection-free case of in-wall mounting.

Still, it wouldn't be too surprising that extra reflections would give more sense of space.

David
 

MCPete

Member
2005-11-01 1:00 am
Colloms in his book High Performance Loudspeakers says that "the room acoustic is more strongly excited" with in-wall speakers compared to free-standing, and this interferes with perceiving stereo depth and alters the tonal balance. In his opinion, later the listener can become acclimated to the different acoustics and once again perceive depth.

Best Regards,
Pete