Flush Mount/Soffit Mount Build - Questions

#1

Hi y'all, my name's Tim, i'm from germany and i'm currently building my new Studio. For a long time i wanted to try Flush Mounting/Soffit Mounting because i have read a lot about the benefits and how it should work. Now i think i have understand it in concept and i am already building a type of Wall in my studio but have some questions in my current build where i can't really get my head around.

Let me first explain my thoughts on my build (will post some pictures after that).

First i measured my Room empty and located the best listening spot/best balanced low frequency spot. I then started to build a wood framework which has an airgap of 30cm left, right and behind against the back wall. I am now encasing the whole framework with sheetrock which i wanted to paint. Everything is sealed except the upper part because i can't reach the ceiling. The speakers will be placed on home made speaker stands filled with sand to make them really heavy. Front holes for the speakers will be cut through the sheet rock and the whole cavity will be filled with mineral wool with a low density.

Hope this gives a quick overview where i am at right now.

Speakers for flush mounting will be HEDD Type 30's by the way.

After reading many posts (i just discovered this forum) i have some questions left:

1. I am not quite sure about the air cooling for my speakers and if they need to be in a box or could be just lying on the speaker stands. I potentially could disconnect the amps from the speakers but then i need to solder all cables and i just read that i need to close the back of the speakers again with something like aluminium/or heavier material cut to the same thickness like the backplate. All in all i would opt for a solution where i could just leave an air gap where the air from behind the speaker could leave the cavity (like i said the whole upper part is open). Also i'm not really sure about buying some MDF and building a Box for my speakers. Maybe i can just made a wooden frame on top of the speakers stands, so that now fiberglass will fall on the speakers when i am inserting them onto the speaker stands?

2. Next question has to with the density of absorbing material. In many pro studios (northward acoustics studios) i have seen that there different layers of density absortion material used. I understand that for a small absorber which is not really thick its best to use a high density material and for more mass/more thickness like in my build (60-100cm) you need low density material so that there will be no reflection backwards. But i can't get my head around why to use different layers. Maybe for breaking the soundwaves making them absorb some specific frequencies in these different layers? Maybe someone can elaborate on that.

3. Will the front wall with only one sheetrock be heavy and ok enough or should i make the speaker bezels with some mdf frame? Recommandations welcome.

That god i found this forum, i am feeling like there is so much great information here. Will dig through the posts in the following days.

Greetings from germany,

Tim

PS: You can find some photos from the current build below. (Don't know why they show up sideways..)

#2

1. you need to vent the speakers or move the electronics away from the speaker (heat rises) and seal the opening back up and do the wiring as you described. you might also lose any warranty on your new expensive speakers as well as not getting the specs desired since now the new wiring can impact the response. so i'd build the speaker box in the soffit with the isolating materials (sorbathane for example) to decouple, and a duct board venting duct across the back of the box from the floor to the top to get the best passive flow.

1a. before covering the frame, consider if moving the amps, put them in the middle with other electronics like x-over units etc into a rack mount w/ covers, so you minimize heat rising in front of the speakers thus interfering with HF response.

2. the different densities cause impedance shifts (as does layering in MLV and other membranes etc) and of course also target different frequency ranges. to get this right requires some engineering work. if you want it done right, you spend a lot of time to learn it by calculating then doing empirical testing, repeat until you find the answer.

#3

Hi Glenn, thank you for the quick answers!

1. & 1a. I will then go with the speaker box in the soffit and the speakers decoupled with sorbathane/regufoam or sylomer into them. The other method will probably lead to more complex problems like you said.

Q: The box should be heavy, right? Like out of mdf or maybe three panels of sheetrock on each side? I have also read that stuart recommended to drill some holes in the side and that you can have the back of the box open. Would you recommend that too? I have never before calculated the math for decoupling speakers with x weight on sorbathane/regufoam or sylomer to get the resonant frequency down below 20hz but i think i will find out how to do it. Can't be that complicated. Will search in this forum.

Also the idea with the duct board venting duct sounds good!

Q: Won`t the venting duct be a pathway for high frequency's? Like a tunnel system?

2. Sounds like you need some time and focus to get your head around that. I will keep that in mind to get into that topic before building the next studio. Or better hire an professional to get this right. For now i will stick with the low density absorbtion material.

3. I have thought about the frontwall and will now start with only one layer of sheetrock and the measure the results. If the wall starts resonating or i am getting sbir i will then put to more layers of sheetrock onto it. That's what i have seen in other big studios. Does the rule apply the heavier the better for the front wall?

I will post some more photos of the build and then measurements later on. Maybe this also helps somebody else.

Thanks again and greetings,

Tim

#4

the box should be heavy to ensure it's not resonating - and since the soffit will be filled with insulation of reasonable mass, this shouldn't be an issue.

having the back of the back open to interface with the duct board will give you the best circulation. since the interior of duct board is insulation designed to damp sound, it's not an issue.

my recommendation is minimum equiv of 2" of MDF. the problem is drywall is it's not really good for precision cuts and not flaking as well. also, consider how you will maintain the speakers. access is needed. a good way to handle it is to use a bezel to marry the speaker to the baffle plate (leave small gap to avoid coupling, then seal it).

#5

Thanks again Glenn! I will incorporate your ideas when moving forward. And will post along with the project evolving. Will get back with new infos about the build in about a week!

Greetings,

Tim

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