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Old 12th December 2011, 06:45 PM   #1
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Default 3 bass towers of 4 15" woofers

Hi all,

I'm finalizing my HT this winter and I will be building my speakers soon and I need a bass/subwoofer solution. I started another thread regarding my main speakers which will all be line arrays (cheap ones with old 4" NSB drivers and Apex JR tweeters). I will build most of them as 2 ways and while this might be okay for the surround channels playing down to 80 or 100HZ, the main front channels probably need to be three way. I was thinking on making bass towers to handle all the low end for the front.

I was thinking of doing 3 towers of 4 15" woofers. I found the following 15" woofer for only around 20$. MCM Audio Select 15" Woofer with Poly Cone and Rubber Surround 200W RMS at 8ohm | 55-2974 (552974) | MCM Audio Select

I was hoping it could fulfill two needs.

1. Handle the frequency range below 80 HZ for the front 3 channels.
2. Handle the subwoofer duties in the same time.

All my speakers will be active using the miniDSP platform so I will have an capable way of doing crossover and eq.

Yes, that woofer might not be the best but shouldn't it be capable enough if its 12 of them?

Is this feasible? Can the towers do both duties and if so how low could I expect them to play?

Thanks.
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Old 12th December 2011, 07:06 PM   #2
sreten is offline sreten  United Kingdom
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Hi.

Its a cheap driver and needs about 10 cu ft per driver
sealed, and that gives you a f-6dB of around 38Hz.
(Though I'd say around 5 cuft is the best choice.)

Each tower would need to about 40 cu ft which is massive.

Around 2.5 cuft per driver and and a Linkwitz Transform
with very big amplifiers will work better at some extra cost.

12 15"ers with 6mm Xmax should be enough for most people.

rgds, sreten.
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Last edited by sreten; 12th December 2011 at 07:17 PM.
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Old 12th December 2011, 08:00 PM   #3
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Are you planning to have them shipped from US to France? Have you thought that through? The shipping costs will far outweight any savings on the drivers. I don't order from MCM because even shipping to Canada is so expensive!
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Old 12th December 2011, 09:34 PM   #4
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Quote:
Originally Posted by sreten View Post
Hi.

Its a cheap driver and needs about 10 cu ft per driver
sealed, and that gives you a f-6dB of around 38Hz.
(Though I'd say around 5 cuft is the best choice.)

Each tower would need to about 40 cu ft which is massive.

Around 2.5 cuft per driver and and a Linkwitz Transform
with very big amplifiers will work better at some extra cost.

12 15"ers with 6mm Xmax should be enough for most people.

rgds, sreten.
yea 10 cuft per driver will be a massive tower! Anything between 2.5-4 cuft per driver might be feasible though since I will have these behind a transparent movie screen and won't be seen. Linkwitz transform can be done with the miniDSP. When you say very big amplifiers how big are you referring to? Will 300w per tower be enough?

Quote:
Originally Posted by leadbelly View Post
Are you planning to have them shipped from US to France? Have you thought that through? The shipping costs will far outweight any savings on the drivers. I don't order from MCM because even shipping to Canada is so expensive!
International shipping might indeed be to expensive but I have not yet investigated it. I arranged for LCL shipping of all my NSB drivers from PartsExpress many years ago so its not a dead end problem for me. But if I can find an equivalent type of driver here for similar funds it will indeed simplify things.
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Old 12th December 2011, 09:50 PM   #5
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Quote:
Originally Posted by exipnos View Post
When you say very big amplifiers how big are you referring to? Will 300w per tower be enough?
That's 75w per driver. Make it more like 200w per driver and I reckon you're on to something.

When it comes to bass, its all about headroom.

Chris
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Old 12th December 2011, 10:00 PM   #6
mdocod is offline mdocod  United States
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With 12 of these and 800W and 200ft^3 worth of vented boxes, you are talking about reproducing pretty much the entire 20-100hz range at around 125db.

This is a HT build? You sure this isn't a sound reinforcement system for a club?
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Old 12th December 2011, 10:10 PM   #7
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Originally Posted by mdocod View Post
With 12 of these and 800W and 200ft^3 worth of vented boxes, you are talking about reproducing pretty much the entire 20-100hz range at around 125db.

This is a HT build? You sure this isn't a sound reinforcement system for a club?
125dB peaks at 20Hz? You might even hear it.

Note it was 800w per tower, so 2400w total. If you want to get loud and low in a small box, you gotta throw power at it.

And with 12 of 15" drivers each doing 6mm of one-way travel, you get 115dB @1m @20Hz, assuming a sealed box.

Chris
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Old 12th December 2011, 10:17 PM   #8
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Originally Posted by mdocod View Post
With 12 of these and 800W and 200ft^3 worth of vented boxes, you are talking about reproducing pretty much the entire 20-100hz range at around 125db.

This is a HT build? You sure this isn't a sound reinforcement system for a club?
Yes HT build that also will include 7 line arrays. Its in a purpose built room (two de-cupeled walls, well insulated) and it will contain a lot of bass treatments as well.

Yikes. 800w per tower sure does add up. I keep it in mind though. If I can cover that full range at 125db I'll be very happy. Probably won't ever use it but who knows.......
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Old 12th December 2011, 10:25 PM   #9
mdocod is offline mdocod  United States
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No, 800W TOTAL. In fact, in that box size vented, you will run out of Xmax at around 800W divided amongst all the drivers.

I just tried modeling a sealed box alternative, I'm still running out of Xmax ~900W divided amongst all these drivers in sealed boxes 5^3 per driver worth of sealed. So.. hmmm...

How much box space can you afford?

Last edited by mdocod; 12th December 2011 at 10:30 PM.
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Old 13th December 2011, 04:45 AM   #10
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Originally Posted by mdocod View Post
No, 800W TOTAL. In fact, in that box size vented, you will run out of Xmax at around 800W divided amongst all the drivers.

I just tried modeling a sealed box alternative, I'm still running out of Xmax ~900W divided amongst all these drivers in sealed boxes 5^3 per driver worth of sealed. So.. hmmm...

How much box space can you afford?
Actually I can probably afford around 3.7 ft3 per driver. I was thinking towers of 1ft deep 2 feet wide and 6.5 ft high. This way they will match my line array dimensions.

Thanks for modeling them for me. I have not actually learned how to do that!

But if that volume will play the low range at 125db why would I need bigger boxes? Quality of sound?
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