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.

 

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.

 

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?

 

That's one sub at 120 db (ballpark figure) without room gain added. You won't be wondering "what if" with a pair of them. :hsd: :hsd: The Maelstrom is shown in 500 liters. Figure out your box size for that and I'll do the math on the port.

 

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/

 

500 liters is net volume, give me the width and depth and I'll figure out the height and the port.

 

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?

 

The internal width of the port is 61.4 cm, correct?

 

Yes, 61,4 cm

 

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.

 

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.

 

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.

 

That would work.

 

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?

 

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.

 

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.

 

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!

 

On the amp. Found no reviews on the Behringer EP4000. The user comments I found on the EP2500 (year 2005-2006) were almost all negative: "sounds bad, no good for bass, gets very warm..."

Better reviews on the Palladium P-2000! And it's even a few euro cheaper. Will I need 2 (bridged) for the 5000 qft room or just one for the 2 SW?
Watt RMS:
2 x 1025 / 4 ohm
1 x 2050 / 8 ohm bridged (is that OK because the Maelstrom is 4 ohm?)

 

1 x 2050 / 8 ohm bridged (is that OK because the Maelstrom is 4 ohm?)

No, the amp needs to deliver the power into 4 ohms. The Palladium P-2000 can't be bridged into 4 ohms. The EP4000 is just a rebadged EP2500. Lots of people use then for subwoofers in Home Theater will good results. The fan is noisy though and can be changed to a quieter one.

 

Understood, the bad press were indeed from people (DJ's) who did parties etc.

Can you comment on the LLT with 650 to 680 liters?

 

Yellow is your design compared to 680 liters. They both have the same output at 14 hz, your design has more output above that point where most of the low frequencies are in DVD's.

 

Then I shall keep it to around the 550 liter point. We are talking NET airvolume, yes?

 

550 liters is the gross volume before any subtractions as in post #18 and is what your current port length is designed for.

Am I correct in asuming that a SW does not need as much bracing compared to a normal speaker?

Your horizontal braces should be spaced every 30 cm to ensure a vibration free cabinet.

 

550 liters is the gross volume before any subtractions as in post #18 and is what your current port length is designed for.



Your horizontal braces should be spaced every 30 cm to ensure a vibration free cabinet.

Mike,

The other Mike (ie, "IB" Mike) said that the Maelstrom beasts need strong bracing and thick panels to encounter vibrations. I have the horizontal braces at 10" max now. The panels are plywood birch 18 mm (0.75"). Are you sure this is enough?

 

View attachment Ronse2010B_MaelstromSW3.pdf

The final design... Feel free to comment.
Want to start building soon.:sn:

 

Looks good. Start building!

 

I am going ahaed with the order of the Maelstrom 18".
Instead of the plate amp, I will be screwing a terminal plate on for the wires. These shall be behind the LR speakers, thats why I added an extra inch.

Now, you swear that I will never regret not picking the 21"?
You know I can stretch to a few more liters. The guy from the Dutch store told me that the 21" and the 18" share the same motor, so I suppose the power handling is the same. What would the 21" do more? Lower Hz? More output SPL? If I do the math, the 21" has 35% more surface area.

Price for the Maelstrom 18" is 485€ + shipping (comes to 1062€ total)
The 21" is 600€ + shipping
Can do that, IF it performs better in a box no more then 720 liter gross...

 

720 liters gross would be about 650 liters net. The 21" would have 2-3 db more output in the 20 - 80 hz range, below 20 hz they would pretty well be the same.

For the size and shape of your cabinet, braces at 10" will be good.

 

When I put the 2-3 dB more above 20 Hz on your graph in #24, I think it is not worth the extra expense since I am not looking for extremely loud, but extremely flat and extremely complete from 15 Hz. So you were right not mentioning the M-21 in the first place. Afterall, we have 2 of the M-18, and we are not in the open air:devil:

OK, we're done. I will wire the payment for the 2 M-18's today, so we have them next week. My kids have free from school for 2 weeks then and since my son Robbe (°1995) will be occupying the HT for many hours (PS3 junkie), he can help me! He already agreed...

I would consider it an honour to start a building thread here.:nerd: