Mercenary Audio - How to Soffit Mount Speakers

Why are monitors placed in walls (“soffit mounted”) in the first place?

Bass energy likes to couple to hard surfaces; ever notice that as you walk around a room there is always more bass by the walls than in the middle of the room? That's because the bass energy is coupling to the walls.

When you have a speaker cabinet hanging out in space, the bass energy rolls around the side of the cabinet and dissipates. By mounting the speakers in the wall we can harness that bass energy and send it back out into the room, increasing the speakers’ efficiency in the bottom… meaning, you can get more bass from less speaker/amplifier.

While this can be of great assistance with increasing the low end efficiency (which gives you greater headroom through out the entire monitoring system), if the speaker cabinet isn’t properly coupled to the front wall you can seriously screw up the low end response of the system.

Move the cabinet forward, different response… back a smidge, different response… to the left, well it’s either closer or farther from the corner where the front wall meets the side wall… different response… Higher? Lower? Different coupling to the ceiling, which leads directly to, you, guessed it… a different response.

I get a real laugh out of these chuckleheaded morons who build speaker soffits that are basically the same size as the monitor; like they have some kind of divine guidance telling them exactly where the monitor will couple best to the front wall. The fact of the matter is that you need to build a soffit that has a whole bunch of extra space around it so you can move the monitors around until you find the right spot where you are able to get the most even/efficient bass response from the monitor possible.

Now with all that space around the monitor won’t you get “resonances”?

Damn good question. The answer, like most answers in audio, is “yes, no, maybe”. If the soffit is designed properly it will be decoupled from the front wall and from the subfloor. The inside of the soffit needs to be addressed so any resonances that do exist will cancel each other or at very least won't be allowed to resonate in a sympathetic manner .

This “decoupling” means the monitor thinks it’s floating in space.As you go to install the monitors you will need to build a wall around the monitor every time you try a new position for the monitor [take some measurements andkeep notes because this shit is all trial and lots and lots of errors at this point].

Any ideas about where I could get info on how to do this without screwing up the sound of my monitors?

There are other factors that determine the bass response of the monitors as they couple to the front wall. One is how you build the soffit; it should be floating in space on a pillar of concrete. Some guys actually float the top part off the bottom part of the stand with springs!!! It’s a great technique but will add a few thousand dollars to the process. It should be heavy and rigid while having a good ½ inch air gap between the soffit and any part of the front wall. Another factor is the construction of the front wall, which should have an incredible amount of mass and be more rigid than a nun at a Catholic prep school.

The angles of the front wall (where the wall bends) the width of the glass, the angles of it’s relation to the side walls, to the ceiling, whether the ceiling is a compression ceiling or expansion ceiling [or combination of both!!] all play a TREMENDOUS role in the process. The school of front wall design to which I subscribe kinda has the wall almost working like a horn [not really a ‘folded horn’, but kinda] in an attempt to focus the bass energy to the engineer position, the net result being the greatest bass efficiency which will net you greater efficiency throughout the entire monitor system.

Every time you try a new position, you need to build a new section of wall around the monitors [usually eats up several sheets of dry wall as you invariably end up cutting a ton of pieces of it for the ‘test sections’]. You move the monitor, build a wall [that is anchored to the soffit, not the room!!] around the speaker, take some measurements, lather, rinse, repeat until you have found the spot where the monitor seems to have the most even bass response and greatest efficiency. [It’s way easier to turn down the bass in relation to the mids and highs than the other way around].

In other words, soffit mounting not something you really want to play with in your spare time unless you have some kind of background in theory, a whole lot of time, and a nearly endless supply of building materials along with some carpentry skills.

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