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PostPosted: Thu Feb 08, 2007 1:19 pm 
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Aloha,
Thanks, however I'm having a hard time visualizing it. The 2 dimensional pictures don't always work for me. I quickly just threw together this representation of what I think you were trying to show, is this what you were trying to pictate?

Also, it doesn't matter how high they walls are, correct? or should you cap the top at a certain height? as in picture "topcap".


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PostPosted: Thu Feb 08, 2007 3:18 pm 
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I've been searching meticulously for a decent example in the Completed/under construction pages off of johns site. The best example i found seems to be here. http://johnlsayers.com/Studio/Mainpage/MP-SProductions.htm

Still can't quite get the best look inside, but it seems to me like i was right about the slot above the speaker (see front.jpg above)

However, it seems that the slot doesn't go through the speaker box, but around it on the left. Does only one side of the plywood base touch the actual wall, (see base.jpg)?

thank you


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PostPosted: Fri Feb 09, 2007 11:36 am 
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when you think about what is happening in this construct - you don't have a perfect seal betweem the upper and lower space because you have the vent port but you do want to put the dividing plate almost out to the walls to force any air movement through the insulation and yet construct the box to avoid flanking-vibration transfer.

overall, you want to cause the sound pressure to have an easy time to get in, and work hard to get out of the box in order for it to effectively absorb bass.

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PostPosted: Fri Feb 09, 2007 3:05 pm 
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Thanks for the reply, but perhaps you missed the question. The question was where do you put the vent port. through the box? or through the dividing plate as you called it.


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PostPosted: Fri Feb 09, 2007 3:11 pm 
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Vent convection flow goes like this

near floor under bottom of soffit (as per drawings)
through hole in bottom plate
through bottom rear hole in your external speaker housing
through top rear hole in your external speaker housing
(If you have a REALLY tall ceiling I would use a top plate but again have holes in it above rear of speaker housing)
through vent at top of soffit - between ceiling and top /front ply.

One would think that holes not directly above each other will stop or slow hot air convection - so maybe this drawing has a mistake?

Hope this helps. 8)

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Last edited by Sideshow on Fri Feb 09, 2007 3:16 pm, edited 1 time in total.

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PostPosted: Fri Feb 09, 2007 3:16 pm 
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Yes thank you, that clears it up completelly


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PostPosted: Fri Feb 09, 2007 10:38 pm 
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oops. sorry, I though you were asking about the gap in the separation plate. sideshow has it correct.

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PostPosted: Sun Jul 29, 2007 9:29 pm 
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Hi! This is my first time posting, although I've been lurkyng the forum for quite some time now!

Anyway, to the point.

I realised that problems can arise when soffiting ported speaker designs wich have the bass reflex port on the back of the speaker (suck as the new Genelecs). Any thoughts on this?

Cheers!


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PostPosted: Wed Aug 08, 2007 5:40 am 
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since you're going to get a bass boost due to the soffit mounting, the bass port in the back might not matter. unfortunately unless someone has done it or the manufacturer has details, its a matter of trial and error...

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PostPosted: Sun Aug 12, 2007 9:31 am 
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Can you cover the ports with a light fabric such as Muslin?

Or should they be left completely open?

I alomost wonder if small quiet computer fans could be installed in the bottom ports to pull the hot air out? Or maybe in the top port to draw cool air in?


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PostPosted: Sun Aug 12, 2007 11:01 am 
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if you check on the SAE site, you'll find a drawing for the soffit mounting which incudes an air port to allow air flow to move heat and let the port function.

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PostPosted: Sun Aug 12, 2007 9:40 pm 
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gullfo wrote:
if you check on the SAE site, you'll find a drawing for the soffit mounting which incudes an air port to allow air flow to move heat and let the port function.


this looks like the top is open and the bottom vent is covered in fabric:

Image


looks like the bottom is open but no vent at the top:


Image

My design has an open back for the speaker. Meaning the box has a bottom, top and two sides only. The back of the box is open. I have a port cut above the speaker, in the wall, to allow heat to escape and a small port at the bottom of the wall and just to the left of the speaker.

The speakers are sitting on top of concrete blocks cemented in place, completely detached from the wall.


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PostPosted: Sun Aug 12, 2007 10:46 pm 
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check on the construction forum - there's a number of folks who have built soffits which are open enough for rear ported speakers - Kendale, Djo, Giles, etc...

on the top soffit drawing though, the cloth is acoustically transparent to allow sound in - and air. so this design should work. you could modify to make the entire open back to get more flow.

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PostPosted: Sun Sep 30, 2007 3:34 am 
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[size=12]Hi .
Sound good, around here.

Ok, now I know a little more and I'm ready to deal with "soffit" !
Almost ready to start designing it, but still have questions:

1- I hesitate between the 60° or 90°, as I wonder if the 60° is not a little better for a person sitting behind point 0.
.......
2- the second question is:
In witch angle would you place the hangers in the bass traps bellow the speaker corner ?
(See joined image for details.)
And also, how many and how close should they be to be effective enough
in the space i can give them.
If the box becomes too deep, my seat
moves further back in the room, and it's getting close to "forbiden zone" (?!?!)

John, we can only trust your stoffit drawing, but it would be so great to have a top view of it !



Please help !

I live in France, good for wine,
but for sound .... help !!


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PostPosted: Sun Sep 30, 2007 1:25 pm 
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option 1 or 3 for the traps.

for the monitor angles, even though the general rule is 30 degrees, if the speakers need to be 45, or 38, or 26, or 22.5, then thats what they need to be... a long control room tends to benefit from the speakers having less of an angle, and actually, in general, positioning the speakers so that you get a proper image (whether stereo, 5.1 etc) is important, and having the speakers "flatter" may be the answer regardless of room length.

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