John Sayers' Recording Studio Design Forum Archive

it's all about trade offs - the reason for the flat face instead of angles is simply the S3 is going to be hot so a few inches above "perfect" is going to be OK on your ears, as is the A7 slightly below, you're likely to find that the acoustic centers are what, 6" apart? but again, if you want to angle them do so...

on the soffit faces, the soft face is only say 25mm-50mm deep and backed by hard surfaces so the diffraction on the mid-high is attenuated and the low mid and LF is not significantly affected. on the RS/LS, perhaps if you cannot soffit mount you'll want to make sure your baffle compensation can be set to match the front (one of the reasons to just freestand the 5.1 units) and if the speakers don't have sufficient granularity in this regard, get a crossover unit which can.

Thank you, Glenn.

Regarding the tilt or not tilt thingy: I do not plan on buying Adam S3a (or similar) for the upper stereo pair. If anything, I would use them as a replacement for the 5.1 speakers (at least the LCR). But that is just speculation for the future and not the important thing here. I am thinking about getting Klein und Hummel o300s for the upper stereo pair. Fortunately, those have a very low acoustic axis, about 145mm from the bottom. With the acousic axis of the Adam p22as (it's not a7s, but close enough, I guess) being very high, I indeed thought about putting them on top of each other.
However, somebody adviced me, it is crucial to be EXACTLY ON the axis, with your avarage ear height (or rather slightly below.
What do you think? Would the o300s change you position on that matter? And what about the exact height of both monitors (apart from things standing in the way of the source, like PC-monitors and the working desk in general- I'll figure that out): Would you choose the average ear height in between both acoustical axis?
(what is the plural of axis, by the way? )

Regarding the dampened soffit face:
Ok, so I plan to meet the monitor front with the clothing, right?
What material would you choose as insulation under the clothing? Dense mineral wool? Is there something like a kg per cubic meter that would be advisable? For 25mm I guess it will not be loose mineral wool, will it? Maybe dense foam?

on the RS/LS, perhaps if you cannot soffit mount you'll want to make sure your baffle compensation can be set to match the front (one of the reasons to just freestand the 5.1 units) and if the speakers don't have sufficient granularity in this regard, get a crossover unit which can.

Sorry, but I don't quite get, what you mean by that: By baffle compensation you refer to the -6dB EQ to compensate for the increased low end? The Adam P22s do have a +/-6bB at < 150Hz. I hope, that is the right frequnecy, otherwise I will buy a Hardware EQ or use the DSP-EQ of my RME soundcard.
But what has to be compensated for the free standing LS or RS apart from a general adjustment to the room after treatment? Sorry, I don't understand what you mean by that ...

In the lowest part of the soffit mount I plan to put my PCs and some 19" units in. I forgot to mention that before. The PCs need to be silenced, so there need to be 2 doors in the soffit front (on the bottom, of course). This is the main reason, why I don't want to go with free standing speakers, as I want to keep the space behind the desk accessible.

the O300 would be less hot on the HF so i'd suggest going more on-axis there. (plural would be "axisesses" )

the soffit face would be something like 25mm 96kg/m3 semi-rigid insulation covered with cloth.

yes, the baffle step for the soffit mount would get the normal -6db treatment but because your other units are not soffit mount and depending on their final position relative to the boundaries, you might not find a simple switch setting that sufficiently matches so you're probably going to rely on your eq/daw settings to zero in on.

if you mount your pc into the front center, you're likely to find you need that depth to then be 20" (500mm) which might not be desirable (too deep?). do you have an option for a machine closet outside the room or perhaps an iso cabinet under the desk?

Thanks again, Glenn. What you said about the o300 being less hot on high frequencies, I can confirm! So I decided to go the extra way and tilt it by 7°. Plans will follow here, as soon as I had the time ...

Regarding the Rack-Space under the speakers ... yes, I loose a bit more space that way. But I absolutely want the PCs to be silent and not to be exposed directly to them. Before, I had them in the second room, which is going to become the recording room now. I always had problems with e.g. USB cable extensions not connecting to the Virus synth, etc. So I decided it would be the best choice to have them under the soffit mount, as this is close to my working space (max. cable length 3m, which is good and makes everything easier), but isolated sound wise.
I will try to integrate that plan into the illustration to follow soon. Let's see, maybe I didn't plan this to bad ...

Iso-cabinet under the desk was an idea, I also considered. I always have 2 - 4 PCs though, as I compose film music and need PC slaves for orchestral samples. It is just to much for one desk to hold comfortably. I have enough complications to get that built to be optimized for working ... getting 3 PCs, isolate them well enough and keep them accessible at the same time would complicate that even more. The space under the speakers would be wasted otherwise, anyway ...

One other thing you might want to consider with the position of the PC's, is the effect of a lot of hot air rising past your speakers by convection. The effect is small, but if you are a perfectionist, it might be of concern. Sound travels at different speeds through air at different temperatures and pressures...

Probably not a biggie, but you should be aware of that.

The space under the speakers would be wasted otherwise, anyway ...

Actually, it would not be wasted! It should be used for acoustic treatment, such as hangers. There's a nice large unused volume under the speaker shelf, ideal for a good size bass trap with a few hangers, and a nice large port at the bottom, against the floor, where it is the most effective.... Without that, you'll be short on bass trapping at the front of the room. Take a look at John's soffit design, the get the idea.


- Stuart -

Thanks Stuart for chiming in!

Quote:
The space under the speakers would be wasted otherwise, anyway ...
Actually, it would not be wasted! It should be used for acoustic treatment, such as hangers. There's a nice large unused volume under the speaker shelf, ideal for a good size bass trap with a few hangers, and a nice large port at the bottom, against the floor, where it is the most effective.... Without that, you'll be short on bass trapping at the front of the room. Take a look at John's soffit design, the get the idea.

You are right. It wouldn't be wasted that way. However, the way I planned doing it it would be, because I went with an easier system, where the space for the speaker just goes from the floor to the ceiling, sealed by the soffit front. Then I saw, there wouldn't be a better space for my PCs ...

Regarding heat flow: I build a sealed iso box in the bottom (MDF) with ventilation pipes going up, exiting above the speakers. I have yet to speak about the details with a knowledgable friend, as I am no expert in air flow and ventilation. He is, though. At this point I just told him about it and he said, it was possible.

I think I didn't explain the point very well: If you use the space under your speaker soffits as isolation cabinets for your computers, then you will not be able to use that same space for what it is REALLY needed for: bass trapping. So you will not have enough bass trapping in the front end of your room. Since the soffits take up the entire front wall, there just isn't any other place to put the bass trapping that you need. You'll end up with a sort of combination RFZ and LEDE design, with all the drawbacks of pure LEDE. That is valuable acoustic treatment space under the soffits.

I'm not saying you should not do it that way: I'm just pointing out that you'll be missing low-frequency absorption in the front of the room, so you'll need to take that into account in your acoustic design, and compensate for the lack of absorption in some other way.


- Stuart -

Ok. Would bass trapping in the back of the room compensate for that?
I guess, by LEDE you refer to the fact, that having bass trapping only in the back would be less preferable than having it both in the front and the end of the room. Right?
What I meant is, I didn't really include hangars in my plan from the beginning. There is however much unused space behind the soffit mount, that will be filled with loose mineral wool. I understand, this is not the same as a bass trap, but it should also work on low frequencies, I suppose, as really low frequencies will not be stopped by gypsum boards or MDF pannels with 3 - 4cm thickness and therefore bass would be dampened by huge amounts of mineral wool.
If I am wrong about that, what would your advice be? Where could the bass trapping be placed, if not under the speakers?

Ok. Would bass trapping in the back of the room compensate for that?

Well, you'll need bass trapping at the back in any case, but you'll also need it at the front. That's a small room, so it will need lots of bass trapping, and there simply isn't enough space at the back alone. Besides, you need bass trapping in the places where it can be effective at damping all of the modes. Bass trapping on the rear wall alone cannot deal with modes that do not interact with the rear wall!

It looks to me like you are trying to follow the RFZ design concept for your room, which is a very good and quiet common way of doing it. RFZ implies a more live front end that directs all first-order reflections to the rear of the room, where they are either heavily absorbed (in small rooms) or diffused (in rooms that are large enough for diffusers). So the entire rear will have to be highly absorbent in your case, due to the design concept. But if the front end is totally hard and reflective, with no absorption at all, then the room is too much like the old LEDE concept, which RFZ replaced. LEDE was abandoned precisely because it just doesn't "sound" right, and isn't comfortable to work in (it is rumored to be rather fatiguing on the ears after many hours of critical lsitening).

RFZ takes the basic concept of LEDE (which is a good concept), but improves on it by dealing with the problems in LEDE. Part of that problem was the imbalance in absorption between front and back. If you look at John's soffit design, he has some pretty major absorption at the front of the room, even though it is mostly reflective: the entire bottom section of the soffits is filled with hangers, plus he also puts deep absorption on the lower half of the soffit front panels. That helps very much with reflections off the back of the console and desk, but also "softens" the front end of the room in general. In some of his designs, John also adds more absorption up front, for the same reason: so that the room is better "balanced", front to back, in terms of "live" and "dead". Yes, the front is still much more live than the back, but it is nowhere near as live as a true LEDE design (which was the other way around, in any case). John also uses some reflection on the sides and even the rear, as needed, to keep them room from being too dead, and once again to balance toe overall effect.

At least, that's my take on what John does, from trying to analyze the way his rooms work! I may be wrong on some of the details, but take a close at his designs and you'll get the general concept: balance and neutrality, with a generally more reflective front end and a generally more absorptive rear, and combined absorptive/reflective/diffusive sides.

There is however much unused space behind the soffit mount, that will be filled with loose mineral wool.

Yes, but that is inside the soffit cavity, and its purpose is to damp the multiple resonances going in in there. It won't have much effect on bass in the room, since technically the speaker cavity is not really part of the room, but rather is part of the speaker.

I understand, this is not the same as a bass trap, but it should also work on low frequencies, I suppose, as really low frequencies will not be stopped by gypsum boards or MDF pannels with 3 - 4cm thickness.

You'd be surprised! The surface density of a 4 cm panel of MDF is about 34 kg/m3. That gives you roughly 32 dB of transmission loss over the range 100 Hz to 3200 Hz. According to mass law, you are still getting 21 dB of TL at 80 Hz. (kick drum fundamental, aprox.) and even way down at 35 Hz (low bass guitar) there's still 15 dB of isolation. So no, not much bass energy will be getting through to that insulation inside the cavity.

what would your advice be? Where could the bass trapping be placed, if not under the speakers?

I really don't know, to be honest! Perhaps at the top, in the wall/ceiling corner, if you have enough space up there? Or maybe Glenn has a better take on how to deal with that? My concern with leaving a gap above the top of the soffit would be that you'd still get edge diffraction going on up there at the top edge of the soffit, since your top speakers would be so close to the ceiling anyway. Another option might be in the top half of the front center soffit?

It's a tough situation...

- Stuart -

generally speaking, the front soffit wall can provide a significant amount of absorption and since you're also shaping the room, mode shifting. if the speaker boxes are sealed (because you don't need the venting for example a front ported speaker) or the venting of the speaker boxes is via some ducting, then you can leverage the entire soffit space for absorption. having a similar sized set of absorption on the back wall and ceiling then work to create the desired balanced response most folks are looking for. side walls can be fully absorptive + slats + etc or spot treated depending on the room, options for placement, and overall response you're looking for.

on the PC (as well as power amps, x-overs, power supplies, etc) heat rising in front of the speakers - not so good. if you can put them into a vented cabinet it helps - reduce or eliminate any fan noise, directs the heat via venting/duct to be above the speakers (and into the room air supply or return) etc. if you don't need frequent access to the device, the cabinet can simply be a screwed on panel in lieu of a hinged door.

Glenn, thank you for your answer! This is exactly what I hoped for. Just a few things, that I get this right:

1) When I build an iso box with ventilation like in your picture (which is what I planned), do I need additional ducting for the speakers above or will this alone be sufficient to cool down the speakers (given, the back of the speaker is not closed - like this design: http://www.johnlsayers.com/phpBB2/viewt ... f=12&t=718). I believe P22a is a front ported speaker, while o300s by K+H are closed design. I am not sure, what consequence that will have for the construction.

2) If I understood you correctly, I can leverage all the remaining space behind the soffit for absorbing. How is that going to happen? When I completely seal the soffit mount (triple layer of gypsum boards and acoustic caulk), so that no air can pass inside the wall except for venting inlets of the iso boxes and outlets above the speakers, I wouldn't have much absorption, right?
So, I would have to make at least parts of the soffit mount permeable for air. Would that force me to build separate ducting for each speaker? What would the replacement for the gypsum boards be? And the absorbing material: Just plenty of loose mineral wool, keeping the spaces where airflow is necessary free, or does it have to be those hangars? There is not much space left for hangars, lots of space for simple mineral wool though.

http://recording.de/uploads/newbb/7cc6f ... 79db7d.jpg

In John's design, only the bottom part of the soffit, where there is only the cloth front, seems to be permeable to me. So, could I just build an air grit on the bottom on all soffit walls and build gypsum above that?
The other choice seems to be, forgetting about gypsum boards for the hole wall and use MDF, kind of like in John's design. I hope I am close to getting it!

One by one ...

I started designing the Iso-box. The height can coexist peacefully with the Adams above!
Wether the ventilation on top is attached to some ducting or just goes in to the soffit is optional at this point of time ...
I had to lift the whole thing up by 8cm, as I need a cable bay in front of the soffit at ground level, as this should stay accessible, but it would prevent the air from going in. The cables for the PCs can also go through the air port on the front.

yes, John's design is the right one to follow. creating a single solid face for your soffits would not be useful.

on the venting - taking the warm air and mixing into the room space is good or if you directly vent it into return that is also nice. i would not vent into the soffit space itself.

So, you would suggest to lead the warm air from the ventilation via ducting to ceiling level? That would mean, I cannot use the same air inlet for the fresh air for the speakers, which is fine, as I suppose the air from the side panels would be ok for the speakers, right? However, this air would not come from directly beneath the speakers ... not sure, if that is ok.

I am kind of in the middle of doing the final design for the soffit mount. Due to the changes suggested by Glenn, I am missing some information to complete it:

1) To absorb some of the energy of the surround monitors you suggested to use plywood or MDF with insulation and clothing finish. I thought of high density mineral wool for the absorbing part first, but recently I found this: It is a lightly compressed fiber-plate 12mm thick and weighs 2.76 kg m2. It is kind of the same material used for bulletin boards. Would that be suitable? I could easily attach (glue or screw) one or two layers of this to the plywood front. I guess, with this material a cloth finish would only be an optical matter ...

2) Where should I get the cooling air for the speakers? I am not sure, if it has to originate from directly under the speakers or if it may also come from the side panels of the construction?

3) Here I did a rough sketch for the stereo panels of the soffit mount. I think about fitting the speakers between two MDF boards attached to the wooden frame construction, decoupled by sylomer. Not sure, if this will work? At first I just wanted to go with a system like this, which seems to be not decoupled:
http://www.johnlsayers.com/phpBB2/viewt ... f=12&t=718
With sylomer holding the speakers from two sides I guess they would be save from moving against the bezel and would be decoupled. What about John's design? There it is always a second frame, holding the speaker. Where ist that decoupled, or is it?
4) This is a top view of my construction, as planned. Aside from the iso boxes and the speakers above, I have plenty of unused space for absorbing material (blue, green and orange). Should I just put some mineral wool in there or would those hangars be preferred? I just don't get, what the advantage of those is over just mineral wool alone. And not awfully many hangars would fit in there. But lots of wool, if I separate it with a net from the areas, where free flowing air is necessary ...
5) Regarding bass trapping, you told me to stick with John's design. However, due to the iso boxes I cannot make these parts of the wall permeable for air (the pink ones in the last picture). So, I guess I should do that with the "green" parts of the wall. As I understand it, it is a mix of areas to let air through (only clothing, to let air to the hangars), partly absorbing areas (insulation on top of ply wood, finished with cloth) and reflective areas (timber finish). Is that right? And if so: how much of which is giving me a good balance?

6) Where should I place the subwoofer? I always read, the subwoofer should roughly come from the same direction, as the stereo sources and have the same distance as they do. But how can that be achieved with a soffit mount? There simply is no space in front of the mount, where my Adam sub12 would have the same distance as the speakers ...???

7) The tilt is 10° now. I am afraid, 7° didn't give me the necessary room to keep the speakers on axis to my ears. Is 10° still ok? Stuart said, 7° would be better, but 10° would be the maximum some would allow ... not sure ...