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Discussion Starter #1 (Edited)
Hello,

I am new here and I am looking for an alternative to the rather expensive B&W CT SW15 pair from their CT700-series. We will be building a new house with a HT / Family room in it. I Have B&W CM7 speakers in our current house now (which we will keep) and I really like them, especially the FST (fixed) midrange is very accurate. The CT7.3 in cabinet speaker has these too and they sound very impressive for LCR. Surrounds will be the (new) matching in ceiling CCM7.3. We are looking for a 7.2 Height system (with DPLIIz). The Heights will be the smaller in ceiling CCM7.5. The matching in cabinet SW are passive designs and need the the SA 1000 amp (with crossover settings). More info on the site from B&W

We would have picked 2 of the CT SW15, with 2 amps. This would cost 5500€ in total. Since cabinet making is my profession and since there seem to be so many people building SW themselves, I thought it would be worth at least investigating the possibilities for making a pair of subs myself. And if I read the specs, even go lower than B&W... even lower than their CT 800 SW!

Use will be music, both audio and music video (Funk, Jazz, Rock) + PS3 (son) + movies ofcourse.

Please check the PDF floorplan from the room:

View attachment Ronse2010B_HTplan.pdf

The room:
W850 x D673 x H240 cm (W28'4"" x D22'5" x H8'), but the open plan HT zone (grey area) has a higher ceiling H255 cm (8'5") with acoustic material (black coloured).
This is 5000 ft^3 in total.
Rear and 2/3 of left wall and the window to the left of the screen are triple glass from floor to ceiling with heavy black curtains before them. Right wall is a kitchen.
Front wall are made to size cabinets of which 470 cm (15'8") is for the screen, the LCR and the SW. Dept is 2 feet, but can be a bit deeper if needed.
Screen width is 300 cm (10')

Subs: 2 please
Really like what I read about the LLT, though any suggestion is welcome.
I could make 2 horizontal boxes flanking the C speaker, this could be each about 450 liter (incl port etc).
Tall units (H8'5") could even be 650-700 liter but these would have to be U-shape to make room foor the LR speaker CT7.3 cabinets (W24" x H14,5" x D10,5")

Driver 15" or 18"? Brand? How low Hz should I aim for?
Amp: being placed against the back wall, a plate amp woul be less convenient, but I suppose I could build them into the inside flanks, below the C speaker. Rack mount would be my first choice though? Beringer?

Any input will be highly welcome. Tight and distortion-free bass is what I like: I have a pair of Jamo R909 open baffle giants, if you know what I mean.
 

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Welcome Erwin! Box size is definitely not an issue for you, a pair of 18's would work well in your room size. A LLT design with a 15 hz tuning frequency would allow you to use a Behringer amp with no hi-pass filter. The question will be what drivers are available to you, what country are you in?
 

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Discussion Starter #3
Welcome Erwin! Box size is definitely not an issue for you, a pair of 18's would work well in your room size. A LLT design with a 15 hz tuning frequency would allow you to use a Behringer amp with no hi-pass filter. The question will be what drivers are available to you, what country are you in?
Thanks for the warm welcome and the info, Mike. I am in Belgium and actually found this "Shack" from the CSS website with their SDX15. I know they have a reseller in Holland. If you say two 18" SW would be better, I would have to find a brand first. I can always have them shipped from the USA, no? Can you name some good 18" woofers, then I can try to find them in the EU first?

If I read the other threads correct, a 18" LLT for 15 hz would need round 700 liters + the volume for the port, bracing, woofer? Depending on the exact type of woofer?

Behringer is easy enough to get, they are German. Which type please, because they have some choice.
 

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Each sub has it's own volume requirement, some need more then others. A pair of SDX15's can be run off one EP4000 amp. A pair of 18" Exodus Audio Maelstrom-X subs can handle 2 EP4000 amps. It will depend on how much money you are willing to spend. Shown is a SDX15 with 1000 watts and a Maelstrom-X 18 with 1800 watts. Depending on how much output you are looking for a pair of SDX15's may be all you need. If you ran a pair of Maelstrom-X's off one EP4000 they would have about the same output as the SDX15's.

sdxmael.JPG
 

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Discussion Starter #5 (Edited)
Mike,

The Behringer EP 4000 sells for 350 € / each. The B&W SA 1000 on the other hand, costs 1500 € / each!
The Maelstrom will probably cost me more than 500 € / each, but compared to the 1500 € that each B&W LCRS will cost me, still no big deal. And MDF I got heaps of in the workshop I share with my father.

Which would you reccomend? I am all for saving money when I can, but I often found that paying for a more powerfull solution saves money in the long run because you never get that feeling "what if..." That's why I drive a 3.0 BMW Z4 while 90% in Belgium bought a 2.5. After almost 7 years, I am still happy and I am keeping it for another 4 -5 years for sure. Others have long since traded in for a new toy.

Is that 120dB you are showing me in the graph?

How many liters would the Maelstrom need? Which port size and lenght?
Choosing the Maelstrom 18" (If I can get them, I mailed to Kevin Haskins) would mean tall units to be positioned in cabinet style where the LR are in my floorplan. This would mean a cut-out in the box to make room for the LR from B&W. If I stick to the standard 24" deep cabinets, this would come to 660 "gros" intern liters. If I would make the cabinets 28" this would be 807 liters. I think the port would start somewhere round the back-high corner, come forward, go down and exit just above the LR speakers. The port would be 60 cm wide (24"). How high and how long would the port need to be?
 

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Discussion Starter #7
500 liters is the netto volume, yes? Without bracing, port, woofer?

Kevin pointed me towards the dealer in Holland. Price is 485 € each, even lower than I aspected.
Link to shop:
http://www.speakerworld.nl/
 

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Discussion Starter #9
View attachment Ronse2010B_MaelstromSW.pdf

Here's my first design attempt. Ok if the B&W CT in cabinets are there?
I included a port because without it, it would not be clear what I meant, but ofcourse it has to be adjusted according your calculation.
The SW will be put between other tall units, again with 1" foam sheet to the side and back. Bottom can be 2" raised, with foam sheet.

Sizes are cm (10 x 10 x 10 cm = 1 liter), I am now at 612 liter gros, so plenty to waist.

I checked our workplace: There are still some left-over panels in 18 mm (3/4") birch plywood from a large project a decade ago, they have the wrong wood fibre direction, otherwise they would long have been used. These should be better than MDF?
 

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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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Discussion Starter #13 (Edited)
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.
 

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If the port is angled, where do you measure,
Through the center of the port.
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.

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?
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.

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

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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Discussion Starter #15
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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Discussion Starter #17
View attachment 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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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.

port.JPG

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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Discussion Starter #20 (Edited)
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!
 
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