Attic Shaped Studio

[endorka]

Cutting holes in the baffles to match the speaker is tricky. Here's how I did it.

Screw the router router template to the speaker box, then shim it out a bit to allow for the gap between speaker box and baffle.

Remove the speaker - easily done by lifting it out through the removed top of the box - and put it exactly where it's going to be on the shelf.

Attach the baffle face to the soffit structure, clamber inside the soffit and draw around the outside of the template.

Remove the baffle from the soffit structure. The pencilled rectangle shows where the router template was. The black squares in each corner are pads of 4mm thick MLV, because that's what's going to be added under the whole baffle face.

Align the router template to the transcribed rectangle on the back of the baffle face then screw it in place.

Route out the speaker hole using the template bit.

Well, now it's done, and we take it upstairs praying it will fit...

And it does

Then repeat all that for the other speaker

Cheers,
Jennifer

[endorka]

After I cut the speaker holes in both baffles I cut the inside edge of both to match the drop from the sloped ceiling. It has a bevel of 26 degrees, and so will the baffle on the side, allowing for a "hidden" join. Talk about a pressure cut, if I messed these up all the good work done previously would have to be done again.

Two layers of 2mm MLV added to the back of each baffle. That's 18mm of MDF, and two layers of 5kg/m2 MLV, giving a total of 21 kg/m2. I had to use MLV instead of another layer of MDF because the latter would have made the baffle face too thick, and the speaker would be recessed. I used offcuts left over from the door project. Nice! I smoothed off the edges of the MLV around the speaker hole with putty from the electrical outlet putty pads.

[gullfo]

nicely done! now hurry because we want to know how it all sounds

[endorka]

Getting the speaker boxes together. As Stuart suggested, I have some cooker hood insulation to line the inside of those to reduce resonances within the box. Fitting that will be fore another day though.

The test fit showed the shelf was at a slight angle, tilting the speaker box forward. A 2mm shim of MLV brought it back into trim.

Test fit of the baffle face once the speaker box was trimmed. You can see the intentional gap between the baffle face and speaker box so they are decoupled.

Transcribed a circle through the duct hole in the bottom of the speaker box onto the shelf. This is drilled out with the same holesaw to give perfect alignment.

80mm diameter duct flange attached.

I covered the speaker box in 4mm of MLV, so surface density is now about 20 kg/m2, equivalent to the 30mm of MDF recommened in the Genelec flush mount instructions.

Ventilation and cable / DIP switch access holes.

As there is now a small gap between the speaker box and shelf due to the shim, I surrounded the duct hole with putty from the putty pads to form a gasket when compressed.

Speaker box in place.

Checking the gap before attaching baffle.

Well there it is. There's a clean gap of about 2mm around the speaker so it's functioning well. It could do with a little bit of refinement around a few parts of the edge for visual perfection but that can wait for another day.

[endorka]

Source of the post nicely done! now hurry because we want to know how it all sounds

LOL! I'm on full speed ahead at the moment trying to get as much as possible done before a busy week of sessions starting on Tuesday. Hopefully I'll get this done on the other speaker tomorrow. Alas, "soft" stuff like insulation and ducting will have to wait until after that

Cheers!
Jennifer

[gullfo]

one thing to consider before painting - if the edge towards the windows will poke out like that, i'd give the edge a slight rounding - say 5mm radius - not that there should be any refraction which matters but the LF waves across the surface will enjoy a smoother interface transition off the plate (same reason the speaker edges are smoothed). the back won't matter for this purpose.

[endorka]

Thanks Glenn, that makes sense, I'll try to make that happen once the side baffles are in place.

In terms of sound, aside from the obvious bass boost due to the speaker being in a wall, it might be my imagination but I'd swear I can hear the room sound and other ambience in recordings more clearly, particularly on drums.

Cheers,
Jennifer

[gullfo]

yes because you have better transitions to the walls on LF and LMF which frees up a portion of the speaker response as those LF / LMF comb filtering + harmonics, which are generally low-level enough to not be considered an issue, until you no longer hear them and thus no longer minutely masking things in the higher ranges. transients will benefit from the soffit mounts for sure. the directivity also improves as the scattering effects are reduced at MF and partial LHF ranges (again small levels which are the result of wide dispersion from the speakers).

"infinite baffles" are going to give the best truest response from a speaker you can get unless it was designed specifically to use open space - Bose 901, Barefoot, many other audiophile systems, etc, all benefit from open space as part of their operation. rear-port speakers are 50-50 imho. sealed and front-ported are best for the baffle treatments.

[endorka]

That makes sense Glenn thank you. Today I got the other baffle and speaker box fully MLV'd and installed. It's much easier and faster once you know how! This time no shims were required for millimetre perfect alignment.

I even became more proficient at cutting the MLV out around the speaker hole in the baffle. As per your advice, no putty applied this time The little rectangular cutouts in the top layer are for the iso feet which protude slightly in front of the speaker box.

And then there were two. They sound subjectively very good indeed, the improved revealing of ambience even more so in
stereo. The clarity of electric guitars has also vastly improved, and I noticed some distortion of the unwanted kind I hadn't previously noticed on a song. It's good but a bit disconcerting hearing things on familiar recordings I've never noticed before.

[gullfo]

Source of the postIt's good but a bit disconcerting hearing things on familiar recordings I've never noticed before.

welcome! it's the beginning of the journey to proper acoustics for critical listening many other people have often been surprised by listening to their older recordings in a new environment.

[eightamrock]

I have been going back and forth on soffit mounting my speakers in my own build, I think you are really making me realize its a must. Well done, this looks fantastic.

[endorka]

Thank you! Even in this unfinished state they've added another dimension of enjoyment to recording, listening to and mixing music. That big far clear sound is righteously joyous to behold. And I was reading Bruce Swedien's book recently where he discussed the importance of the accurate reproduction of early reflections in recorded music. Having these reveal more of this is just great.

Cheers,
Jennifer

[RJHollins]

Just following your Build thread.

Very nice work ... with attention to details.

[endorka]

Thank you!

Stuart mentioned this with regard to dealing with unwanted audio resonances within the speaker box:

...for resonance. There will "stuff" going on in there, between the speaker and the box. Cutting large holes and using abundant insulation around the speaker can help deal with that. I suggest very low density insulation partly filling the gap between speaker and box, such as the type of filter material used in kitchen hoods...

That's a great idea, and the official Genelec flush mount boxes have a similar thing with some sort of foam:

I bought some of the kitchen hood material as suggested, and it will be a good fit without touching the speaker. Unless anyone has any better suggestions I'm planning on gluing this to the speaker box with the spray on contact glue, like I did with the duct lining in the plenum.

Speaking of duct lining, the larger gap between the speaker and top of the box might allow the thicker duct lining to be used there instead of the cooker hood filter material. The official Genelec box has thicker foam at the top too. Do you think this would offer and benefit or detriment?

Cheers!
Jennifer

[endorka]

On to connecting up the ventilation for the speaker boxes with 80mm diameter acoustic flex flex duct. One end will be attached to the smaller flange on the top of the plenum. The room ventilation will be attached to the larger 200mm diameter flange.

Here's the inner hose of the flex duct attached to the plenum and bottom of the speaker box. Running a frequency sweep through the exposed a problem though - the hose buzzes like a jar of angry wasps at certain frequencies e.g. 120Hz!

Here's the description of the flex duct:

The Sonodec 25 consists of a perforated aluminum/polyester laminate inner duct thermally and acoustically insulated with glass wool and is provided with an aluminium laminated outer jacket. A plastic barrier between the duct and the glass wool prevents the diffusion of glass wool particles.

Well, it's the "plastic barrier between the duct and the glass wool" that's buzzing. Stretching the hose tighter reduces but does not eliminate the buzz. Putting the insulated outer jacket on reduces but does not eliminate the buzz. The only solution I can think of is to remove the plastic barrier (easily done). This means that "glass wool particles" could enter the air in the room though. Perhaps covering it with the fabric I use to cover panel absorbers would deal with this, and not buzz...?

Cheers!
Jennifer