Which SW type for our HT? - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

Old 03-23-10, 07:36 PM Thread Starter
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Erwin

Join Date: Mar 2010
Location: Belgium
Posts: 326
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Re: Which SW type for our HT?

Yes, 61,4 cm
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Old 03-24-10, 01:26 AM
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Mike

Join Date: Apr 2007
Posts: 19,397
Re: Which SW type for our HT?

61.4 cm = 24". The port should be 3" high x 24" wide x 42" long. You should consider the port exit being at the bottom of the cabinet, running across the floor and up the back wall. Also round over the edges of the intake and exit. The port will take up 61 liters of space.
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Old 03-24-10, 04:28 AM Thread Starter
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Erwin

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Location: Belgium
Posts: 326
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Re: Which SW type for our HT?

Quote:
Mike P. wrote: View Post
61.4 cm = 24". The port should be 3" high x 24" wide x 42" long. You should consider the port exit being at the bottom of the cabinet, running across the floor and up the back wall. Also round over the edges of the intake and exit. The port will take up 61 liters of space.
Mike,

Thx for that! Port H 3" = 7,5 cm so I estimated correct. L 42" = 105 cm which is a lot shorter than I designed. If the port is angled, where do you measure, in the axis? There would be no point in making the port higher and keep the length more like my design? Is the ratio between section and length of the port fixed or variabel? (ie fixed ratio: H=3">L=42", so if H=4">L=42"*4/3=56" while keeping the W=24")
EDIT: I understand a longer port decreases the resonant frequency, so I will stay at H=3" * W=24" * L=42"

If the port exits at the bottom (enter somewhere halfway up the back), this would mean that the LR speaker space will be positioned higher and the part behind the LR speaker space would be about 4" narrower. This is OK? Why would the port be better at the bottom?

Ofcourse the edges will be round, but can you advise me on the bracing? Should all 3 planes be inforced (horizontal/vertical/frontal)

Also, really no problem if the LR speakers are seated in the SW? I mean, they will not fall out because of vibrations? I would use absorbing foam sheets surrounding them, but I am not sure how effective these are. And the whole SW box would again be surrounded with the foam sheets.

Last edited by erwinbel; 03-24-10 at 06:21 AM. Reason: Port length vs resonance
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Old 03-24-10, 08:27 AM
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Mike

Join Date: Apr 2007
Posts: 19,397
Re: Which SW type for our HT?

Quote:
If the port is angled, where do you measure,
Through the center of the port.
Quote:
Is the ratio between section and length of the port fixed or variabel?
The cross section determines the length for a specific tuning frequency. If the cross section increases, the length of the port increases.

Quote:
If the port exits at the bottom (enter somewhere halfway up the back), this would mean that the LR speaker space will be positioned higher and the part behind the LR speaker space would be about 4" narrower.
I'm not good with metric, how much space would there be between the LR speaker space and the port if you did run the port up the back?
Quote:
Why would the port be better at the bottom?
The intake and exit would have less turns in it compared to your drawing. Less turns means less turbulence.

Quote:
can you advise me on the bracing?
I suggest side to side and front to back with a window pane style of bracing.

Quote:
Also, really no problem if the LR speakers are seated in the SW?
As long as the sub cabinet is properly braced vibration won't be an issue for the LR speakers.
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Old 03-24-10, 08:41 AM Thread Starter
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Erwin

Join Date: Mar 2010
Location: Belgium
Posts: 326
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Re: Which SW type for our HT?

Mike,

The remaining space between the LR speaker and the port would be 5 1/2" (13,6 cm)

Would it be OK to switch the port exit position and the SW? The port would be at the bottom, the LR would be at about the same height as the center speaker and the Maelstrom would be on top of this. I know a SW is supposed to be put on the floor for the highest output, but this way the SW is also put into the largest section of the cabinet.
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Old 03-24-10, 08:48 AM
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Mike

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Re: Which SW type for our HT?

That would work.
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Old 03-24-10, 10:29 AM Thread Starter
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Erwin

Join Date: Mar 2010
Location: Belgium
Posts: 326
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Re: Which SW type for our HT?

Ronse2010B_MaelstromSW2.pdf

Here is version 2. I have to make sure that the 500 liters net is as correct as possible or can it be more? I am at 546 liter without the port. I might position the LR a few inches higher though.

Also is it OK if the port W / H ratio is 8 / 1 (24" / 3") because I read some are against that and suggest 5 / 1 or even 3 / 1?

You see I really rounded up the exit and entrance. I took the port lenght without the flared parts (where the axis is on the design)

Still confused about the bracing, Mike. Do you mean a vertical brace from front to back and a vertical brace from side to side? So no horizontal braces?
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Old 03-24-10, 01:25 PM
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Mike

Join Date: Apr 2007
Posts: 19,397
Re: Which SW type for our HT?

Quote:
I am at 546 liter without the port.
Make the port 43.5" long and you'll be tuned to 15 hz.

The port air speed is very low for that size of port, 24" / 3" will be fine. You should angle the port at 45 degrees around the cabinet corner.

Due to the cabinet height there will be a resonance issue, you will have to pack in 8" of fiberglass insualtion at the top of the cabinet to eliminate it.

I'll find a pic of some bracing to show you what I mean.
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Old 03-25-10, 02:08 AM
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Mike

Join Date: Apr 2007
Posts: 19,397
Re: Which SW type for our HT?

This is what I was referring to, it's a pic from another build. The vertical one would go side to side, parallel with the port on the back wall. The horizontal ones would go front to back.

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Old 03-25-10, 03:29 AM Thread Starter
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Erwin

Join Date: Mar 2010
Location: Belgium
Posts: 326
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Re: Which SW type for our HT?

Mike,
You are the best!
I will add the braces to my design. I shall have one @ 8" from the top to hold up the fiberglass.

We have been working around the 500 liter mark, but would bigger be even better and what exactly would be the benefit? I mean, it would be possible to add an extra 2" of dept, even 3" or 4". Each inch would add about 5% to the volume. The port would be higher/longer also, no?

Quoting Steve Callas:
"The size of the LLT has to be large, sometimes very large. ~300 effective liters for most 15" drivers is common, and ~650 effective liters for 18" drivers."

If I add 4" to the dept (would be convenient for the AV-rack anyway) and max the height, I am at 722 liters gross without the port. If I distract extensive bracing (B&W style, 2 vertical braces and 6 horizontal comes to 48 liter) and the driver (no more than 4 liter behind the baffle) it would be 670 liter air volume. Good idea? How does this affect the size of the port?

Am I correct in asuming that a SW does not need as much bracing compared to a normal speaker? Because a normal speaker is working with higher frequency (+ 80 Hz) which in turn needs smaller bracing distances? I was looking at the B&W Custom Theatre brochure which has a rendering of the interior of the flagship CT8 LR (costs 15K euro, each!, can handle 1000 watts). For a size of 110x32,5x55 cm (HWD 44x13x22 inch), it uses 2 side-to-side braces and 9 horizontal braces, for the bass compartiment only!

Slowly building a 9.2.6 HT with 24" SEOS LCR, LLT subs (done) and much, much more...
LLT design: http://www.hometheatershack.com/foru...pe-our-ht.html

LLT Build: http://www.hometheatershack.com/foru...roem-18-a.html

Last edited by erwinbel; 03-25-10 at 12:09 PM.
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