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PostPosted: Mon Aug 18, 2003 8:45 pm 
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Hi!

I was hoping for some assistance in finding out whats wrong with my soffit construction. :shock: I am using Adam S2.a speakers that sound great freestanding but when soffited they loose definition and detail to my ears, the bass frequencies sound fine it is more in the midrange and top end i hear this. So im suspecting it could have something to do with the soffit construction.

Here is how i did it: I've used Johns Soffit plan with a few tweaks. Whats different is that i did a box within a box construction for the reason that if would want to to change speakers i wouldnt have to rebuild the framing. Another thing i did different is how the speaker box and the front baffle joins, in johns drawing the front baffle overlaps the speaker box edges, in my construction i mounted the front baffle before the box with a hole cut out of the size of the speaker box. The box was then pushed through the hole in the baffle. I used a trim on the baffle around the speaker box to cover any air gaps between the box and the baffle and the speaker and the box.

So the question is, what did i do wrong?

Also i missed the plywood plate infront of the hanger section below the soffit box. Would this affect the performance of the hangers?

Thanks
Glenn


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PostPosted: Mon Aug 18, 2003 10:38 pm 
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And the soffits are at a 60 degree angle, for mix position?

Are the baffles angled down as we see in the diagram? if so, what is the construction of the rest of your studio? That may be affecting the imaging as well.

Do you have a pics of what you did and what your room looks like?

Bryan Giles


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PostPosted: Tue Aug 19, 2003 12:12 am 
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Bryan..
Yes...60degrees at mix position, angled 10degrees down, 135cm (53.1") from the floor to the bottom of the speaker . I dont think imaging is the problem here...cause you can hear the defects when listening to one speaker only. It is hard to describe with words what im hearing, the sound is not muffled, more like small and one-dimensional.
something happens in the upper midrange.

Here's my studioplan..
And whats been done acoustically:
The backwall is fibreglass lifted of the wall, hangers behind it in the upper left corner,
Side walls are slot resonators
Frontwall is fibreglass lifted of the wall.
Hangers under the soffits
No ceiling treatment yet,,concrete


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PostPosted: Tue Aug 19, 2003 3:09 am 
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Hmm, Interesting. The only weakness I can see is that rear plywoon panel board. It closes the area underneath so it acts as a bass trap, and with the insul on the front of that section it abosrbs mids and higs to elimiate thenm reflecting back and smearing the image.

I had to use my room as I was bulding it and noticde the changes as I added each piece to the construction. Especially in the mids, it was noticable when I added the plywood (for me particleboard) section that goes underneath the speakers.

Also, what have you done to your ceiling?

Also, what kind of fiberglass?

Bryan Giles

Sorry for my limited help. I mountes my units at ear level. Without an angle baffle.


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PostPosted: Tue Aug 19, 2003 4:31 am 
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Glenn,

I see a few problems:

1. As far as I can tell the S2A doesn't make specific provisions for soffit mounting. As I've discussed in several threads, free standing speakers require a 6dB shelf filter (low boost or high cut) to compensate for the fact that the low frequencies radiate omni directionally while the high frequencies are forced by the front speaker baffle to radiate only in the forward hemisphere. The S2A has a 22cm wide front baffle so the 3dB inflection point of the shelf filter is centered at about 525 Hz. In order to correctly soffit mount this speaker you would need to insert the reverse shelf filter (low cut or high boost).

2. The Adams have those angles on the front baffle. Is your soffit opening shaped such that it smoothly merges with the trapezoid created by those angles - like I've illustrated below?

3. The purpose of soffit mounting is to correct for the hi/low radiation mismatch (hemispheric/omni) associated with freestanding speakers. To this end the front wall should simply act as a large extension of the speaker baffle. The absorption system below the monitors in your drawing is contradictory to this aim. The entire front wall should be solid and reflective (illustrated below). If you want to use the volume behind the soffits as bass traps then put the wall openings near the floor and ceiling intersections, as far from the monitors as possible (green areas illustrated below). Putting the openings in these areas will also make the traps more effective.

Thomas


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PostPosted: Tue Aug 19, 2003 5:18 am 
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Thanks for clearing that up Barefoot.

That explains why, before I put the particle board lower section in on mine that 100Hz and 80 Hz were so finicky, but as soon as I inserted that part of the soffit, it cleaned it right out up.

However I did build mine like John suggested. I have installed Rockwool in that front section for absporption from the mix desk.

Bryan Giles


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PostPosted: Tue Aug 19, 2003 6:09 am 
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Thanks a lot for your replies Thomas and Bryan.

Thomas.. So with the Adam S-2s limited shelf filter 3db +- at 150hz could it still work satisfactory soffit mounted?

I did not take the front trapezoid shape into account when cutting the baffle opening...i used trims on the surface on the baffle and shifted the speaker a couple of centimeters forward in the box so the trims aligns exactly where the speaker is fully square behind the trapezoid angle(hope this makes sense, english is not my main language). So basically the speaker is slightly forward in the design, not perfectly flat with the baffle.
Is it critical that the baffle is perfectly in level with the speaker baffle at all angles?
Bryan,, no celing treatment yet. pure concrete.

Thanks
Glenn


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PostPosted: Wed Aug 20, 2003 6:50 am 
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asdf
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PostPosted: Wed Aug 20, 2003 7:20 am 
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Glenn,

I think your speaker mounting should be ok. The design you attached is also fine - as long as you keep the framing and plywood below the speakers. That lower "plate" properly extends the speaker baffle like I discussed before. The relatively thin insulation in front of it will not have much absorption below about 1kHz, so it won't really affect the baffle performance. Plus it provides a bottom opening to the bass traps like I suggested.

Give the shelf filter a try. See if the -3dB position helps. If it does, then we can design you a simple passive circuit to experiment with even further - assuming you or a friend can do some very basic soldering.

Thomas

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PostPosted: Wed Aug 20, 2003 5:40 pm 
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Thanks alot Thomas...Ill give it a try.
So what im hearing in the midrange is caused by the bassboost?
MDF or plywood for the baffle? does it matter?

Glenn?


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PostPosted: Thu Aug 21, 2003 5:30 am 
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Remember that everything is relative. A low boost is no different than a high cut, if the levels are adjusted properly. You had also removed the bottom plate in your design, so that may have created some odd effects.


So, first modify the soffit such that it conforms to the design you attached. Then set the bass EQ to -3dB and see how it sounds. If this doesn't show much improvement, then there may be other things going on. But let's just move in the right direction and solve the issues one by one.:)

I don't think it matters much as far as MDF or plywood.

Thomas

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PostPosted: Wed Oct 22, 2003 6:28 am 
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Mike,

That email from ADAM got me thinking about your soffit mounting method

I don't know how far you are with your framing, but I have an alternative method of mounting your S2As. Instead just moving the speaker out from the soffit such that only the top corner is flush, I suggest tilting the speaker such that both the top and bottom corners are flush (as illustrated). This brings the entire speaker in closer to the wall and further reduces diffraction. It also gives a natural downward tilt to the speaker so you don't necessarily have to tilt the soffit face. The fact that the speaker baffle and soffit face are no longer parallel is not a problem.

Thomas


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PostPosted: Mon Oct 27, 2003 11:56 pm 
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Thomas,

Thanks!! that seems like a great idea, (the framing was already done when i asked my initial question). But i was thinkin as im gonna redo the bafflefront anyway i could move the speakerbox higher within the soffit so if angle the speaker like you desribe maybe the listening axis will be the same or close in the end. In your drawing did you happen to measure the degree of tilt required?



cheers
/mike


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PostPosted: Tue Oct 28, 2003 3:07 am 
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I don't know the details of the angles and dimensions of the S2A baffle, so I cant give a precise angle.

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PostPosted: Wed Feb 04, 2004 8:57 am 
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-=glEnn=- wrote:
Thomas,

Thanks!! that seems like a great idea, (the framing was already done when i asked my initial question). But i was thinkin as im gonna redo the bafflefront anyway i could move the speakerbox higher within the soffit so if angle the speaker like you desribe maybe the listening axis will be the same or close in the end. In your drawing did you happen to measure the degree of tilt required?



cheers
/mike


Glenn, I'll be using ADAM s2.5a monitors for my studio as well, and I'm about curious how this solution worked out?


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