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Old 21st August 2012, 02:42 AM   #11
sreten is online now sreten  United Kingdom
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Location: Brighton UK
Hi,

6 x 8" drivers in each 20L box will need shedloads of power to drive
them to there excursion limits in the bass*, and at 3.33L per driver
your living in cuckooland regarding any suitable drivers for the job.

You need to do some proper modelling.

rgds, sreten.

* Well beyond their thermal limits I suspect, but
I'm too lazy to do the actual modeling for you.
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Old 21st August 2012, 01:41 PM   #12
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Quote:
Originally Posted by AJ34 View Post
Are there any commercial designs based on this principle?
This velodyne is a small one, and there are definitely others across a range of sizes.

MiniVee 8 Inch Subwoofer
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Old 21st August 2012, 01:54 PM   #13
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I picked out some cheap woofers for you:

Aura NS6-255-8A 6" Paper Cone Neodymium Magnet Woofer 299-030

Here's a sim of one woofer in 15L....

Another Jambox on the Horizon?

So I think you're asking alot, but feel free to model it yourself and see if it will work or not. Maybe 4 woofers in 30L per side?
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Old 21st August 2012, 05:11 PM   #14
sreten is online now sreten  United Kingdom
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Hi, attached is 1, 2, 4, 6 and 8 NS6's into 20L sealed, rgds, sreten.
Attached Images
File Type: gif guff.gif (21.5 KB, 74 views)
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Old 21st August 2012, 10:41 PM   #15
sreten is online now sreten  United Kingdom
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Hi, same thing with 30L instead of 20L, rgds, sreten.

The above also shows 40L by transposing, blue = 2 drivers.

FWIW searching indicates a better choice than the NS6 is
a shedload more expensive. The nature of the NS6 motor
indicates progressive lower harmonic distortion as levels
increase but no real critical excursion point where higher
harmonics suddenly appear, see Home .
Attached Images
File Type: gif guff.gif (21.4 KB, 64 views)
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When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 21st August 2012 at 10:48 PM.
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Old 21st August 2012, 11:34 PM   #16
AJ34 is offline AJ34  United Kingdom
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Thanks again for your input folks - your assistance is very much appreciated.

As regards subwoofer design, I feel I'm currently at the "brainstorming" stage. All possibilities are still under consideration although I am driven by domestic compromises rather than potential sound quality - shame but I guess that's life! This means that my design options appear very limited.

Two, small (approx. 20ltr) subs that double as stands for my active monitor speakers would be the domestic ideal but it seems unrealistic to load each sub box with six, cheap 6" drivers, let alone 8" ones! - thanks for the plots, sreten. As mention before, the sub's size is determined by them needing to double as stands therefore I have little flexibility regarding size. For me, it looks like two, 20ltr box subs are the way to go so I'll look into more suitable driver line-ups. One final thought...

What about this unusual (to me, anyway) Celestion open baffle, series dipole(?) design from the 1980's - pictured near the end of the article...

Designing Loudspeakers - Part 15 Open Baffles and Bass

Two, 12" units are used in open baffle but with one driver positioned behind the other and both cones move in the same absolute direction. I guess adding the back driver has the same acoustic effect on the front driver as curving the front baffle around the sides but without reflection problems? Maybe I could use two banks of three, 8" drivers (probably not cheepies - possibly PA types) instead of the two 12" drivers Celestion use? Also, the drive units will need to face the listening position, more or less, so I can't position them at the sides.
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Old 22nd August 2012, 12:02 AM   #17
sreten is online now sreten  United Kingdom
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Hi,

In the UK your driver choices are limited. What are the speakers you
want to add a sub/stands to ? You can angle the back backwards
to give you more box volume to work with if its needed.

The SL600 open baffle sub is a strange beast for a box speaker,
good information is hard to find and your completely on your
own with a triple arrangement, not something I'd recommend.

KISS should be your principle, related to your main speakers.

rgds, sreten.
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Old 22nd August 2012, 11:15 PM   #18
AJ34 is offline AJ34  United Kingdom
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Quote:
What are the speakers you
want to add a sub/stands to ?
http://www.studiospares.com/studio-monitors/studiospares-seiwin-powered-monitors-pair/invt/248030/#ReviewHeader

Quote:
You can angle the back backwards
to give you more box volume to work with if its needed.
I suppose so, I guess every litre helps. Percentage wise, I could probably gain an extra 20-25% volume.

Quote:
The SL600 open baffle sub is a strange beast for a box speaker,
good information is hard to find
Indeed it is. Each Celestion sub occupies a really small space considering that two 12” drivers are used – that’s what attracted my attention. Having trawled the internet looking for info, a few points come to light: they seem to be heavily EQ’d (as one might expect), they are prone to bottom out at the very low end, they don’t manage high SPL’s due to the design, they need to face forward and their sound quality is fantastic, evidently.

Found some QTX drivers. The 902.208 in particular seems good value. TS parameters are given.

http://avslgroup.com/en/product/902.208UK

Its been discontinued but some outlets are still advertising them for between £10 and £15 each – hopefully, they still have stock. I’ll have a play with the Linkwitz Lab closed-box spreadsheet and try out some possibilities.
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