Is there any merit in designing a high resonant frequency sub (maybe several large drivers in a small sealed box) and using it entirely below it's resonant freq? I've heard that the freq response of such a design would likely be very smooth - although I appreciate I'd probably need to provide considerable bass EQ (lift) to compensate for early roll-off.
Are there any commercial designs based on this principle?
Are there any commercial designs based on this principle?
Hi,
The short answer is yes, and its very common commercially.
Linkwitz Lab - Loudspeaker Design covers the basics but doesn't
go into the the variable compression commercially exploited.
You need lots of power, comparatively speaking, and in
fact the arrangement is the the only way the drivers
can handle such high powers, do the maths / physics.
rgds, sreten.
The short answer is yes, and its very common commercially.
Linkwitz Lab - Loudspeaker Design covers the basics but doesn't
go into the the variable compression commercially exploited.
You need lots of power, comparatively speaking, and in
fact the arrangement is the the only way the drivers
can handle such high powers, do the maths / physics.
rgds, sreten.
I think there is merit in using a 'too small' sealed enclosure for a subwoofer for the reason of small footprint. As said above it requires more amplifier power and a suitable EQ/filter. From an efficiency standpoint it may be a good idea to try to keep the resonance still in the pass band. At and around the resonant frequency the power efficiency is the best. You can see it in the impedance graph where the peak is many times higher than the nominal impedance. The drive current at and around that frequency will be much smaller.
Also, watch out for harmonic distortion at f/2 or f/3 (f = resonance) if your pass band is below f. Any non-linearity in the voltage-current transform in the loudspeaker coil can generate harmonic distortion in the current waveform which will quite efficiently drive the loudspeaker at resonance. Add in the fact that below resonance the loudspeaker is inefficient you may run in to high distortion levels.
You could get around this and linearize the operation by using current-drive. With current-drive the current will be linear and you bypass the poor voltage-current transform of the loudspeaker. You lose all electrical damping of the resonant system (gives you a very high Q of 2 to even 20+!). But given that the resonance is suitably far above your pass band you need not care if you can filter your input signal well enough.
You could get around this and linearize the operation by using current-drive. With current-drive the current will be linear and you bypass the poor voltage-current transform of the loudspeaker. You lose all electrical damping of the resonant system (gives you a very high Q of 2 to even 20+!). But given that the resonance is suitably far above your pass band you need not care if you can filter your input signal well enough.
As far as I know they are pretty output limited, for obvious reasons. IMHO, if you can spare the space, you are better off with a large ported sub with low tuning and Q. The slow roll off will blend well with room gain, and the low tuning will push the group delay low enough to make it unnoticable.
Thanks for your interesting replies. Had a look at the Linkwitz Lab closed-box spreadsheet and will try out a few design possibilities when I've got time.
The reason I'm looking into this type of sub is due to space constraints. I'd really like two subs, each acting as a stand for small active studio monitors. Each sub will need to have the same footprint as the small monitors and needs to be 600mm tall. This gives an internal volume of each sub = 20 ltrs approx. Due to dimensions, largest driver I could accomodate would be 200mm or thereabouts. I had thought about using 3 x 200mm bass drivers in each side panel of each sub (12 drivers in all).
The reason I'm looking into this type of sub is due to space constraints. I'd really like two subs, each acting as a stand for small active studio monitors. Each sub will need to have the same footprint as the small monitors and needs to be 600mm tall. This gives an internal volume of each sub = 20 ltrs approx. Due to dimensions, largest driver I could accomodate would be 200mm or thereabouts. I had thought about using 3 x 200mm bass drivers in each side panel of each sub (12 drivers in all).
Sounds like a semi-viable option, but you will need to build them extremely heavy to function as a good stand, like 100+ lbs.
I would consider using relatively cheap bass drivers because with a fair amount of cone area (12 x 8" units), massive excursions shouldn't be necessary and it seems that big excursions = big money, understandable really. Cheaper, lighter, lower powered drivers would likely be more sensitive too, so as long as they can handle enough power...
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.
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.
This velodyne is a small one, and there are definitely others across a range of sizes.
MiniVee 8 Inch Subwoofer
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?
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?
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 .
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 .
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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.
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.
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.
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.
http://www.studiospares.com/studio-monitors/studiospares-seiwin-powered-monitors-pair/invt/248030/#ReviewHeader
I suppose so, I guess every litre helps. Percentage wise, I could probably gain an extra 20-25% volume.
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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