Compact sub for low efficiency 3" FR drivers

[sreten]

Hi,

Just done some quick Win ISD modelling of this 8" subwoofer:
Aurasound NS8-385-4A 8" Woofer: Madisound Speaker Store

It appears to be ideally suited to compact low efficiency
4th or 6th order bandpasses. (For compact subwoofers
low efficiency is required for decent bass extension.)

4th order : 3L front tuned to 90Hz. 8L rear sealed.
This has a flat section rising 2dB from 60Hz to 115Hz.
High pass roll-off : -3db : 150Hz, -6dB : 170Hz, -12dB : 215Hz.
Low pass roll-off : -3db : 47Hz, -6dB : 41Hz, -12dB : 31Hz.
(note actual levels for the LP are 2dB lower due to flat section
rise, i.e. the low pass roll-off is referenced to -2dB@63Hz.)


6th order : 3L front tuned to 90Hz. 12L rear tuned to 27Hz.
This has a flat section rising 3dB from 44Hz to 115Hz.
High pass roll-off : -3db : 150Hz, -6dB : 170Hz, -12dB : 215Hz.
Low pass roll-off : -3db : 33Hz, -6dB : 28Hz, -12dB : 21Hz.
(note actual levels for the LP are 3dB lower due to flat section
rise, i.e. the low pass roll-off is referenced to -3dB@44Hz)

The 6th order puts out substantially more output than the 4th
in the 20Hz to 50Hz region, 6th is a very impressive curve.

However I must stress for bandpasses acuracy is everything,
I cannot guarantee the driver specs or WinISD's modelling
accuracy. The results should be checked in other programs.

Parameters used are : Fs - 40Hz, Vas - 17L, Qts - 0.34.

rgds, sreten.

[mondogenerator]

nice sim, i wonder how the group delay would compare? Id guess the 6th is well over 30ms, in fact id be shocked if the 4th was under 20ms. Would be interesting to compare the 6th with max flat vented. Ive never found much advantage to 6th order bp using winisd compared to regular vented. But then i only have the beta version. The 4th bp is, however, more interesting, at least to my eyes, and truly compact. Venting 12L at 27Hz would give me nightmares! Nifty though

[sreten]

Originally Posted by mondogenerator

nice sim, i wonder how the group delay would compare? Id guess the 6th is well over 30ms, in fact id be shocked if the 4th was under 20ms. Would be interesting to compare the 6th with max flat vented. Ive never found much advantage to 6th order bp using winisd compared to regular vented. But then i only have the beta version. The 4th bp is, however, more interesting, at least to my eyes, and truly compact. Venting 12L at 27Hz would give me nightmares! Nifty though

Hi,

Some good points, most of which are inevitable. Your right 12L @ 27Hz
is a nightmare, PRs/ABRs are probably the only sensible practical solution.

The driver itself in a sealed say 6L box would be great for max output,
but it must be used as a bass only unit in a 3way, or with a FR unit.

TBH for $20 the latter could be compeletely its forte.

rgds, sretyenm/.

[MisterTwister]

Originally Posted by sreten

However I must stress for bandpasses acuracy is everything,
I cannot guarantee the driver specs or WinISD's modelling
accuracy. The results should be checked in other programs.

I don't trust WinISD's bandpass and PR modeling too. Sometimes its results are totally weird.
Like this woofers specs by the way, looks like a real bargain.

[mondogenerator]

agreed paired with a suitably cheap fr it would make a good sub, either sbb4, bp4 or bp6. I just have an perhaps illogical hatred toward the bp6s ive heard, the bass thud always seems like an echo of the actual transient. Ive got a pair of poly 2inchers from some aldi pc speakers that could work though.

[mondogenerator]

with those woofers going so cheap i wonder what a 2 or 4 driver isobaric bp sub would be worth trying.

[sreten]

Originally Posted by mondogenerator

with those woofers going so cheap i wonder what a 2 or 4 driver isobaric bp sub would be worth trying.

Hi,

Due to the high driver mass, 54g, stiff suspension, hence high
Fs, and consequently very low Vas, isobaric is utterly pointless.

A 2 or 4 driver normal box is sensible, and would ease the venting,
it would also be possible to build in force cancelling mode easily.

rgds, sreten.

[sreten]

Hi,

Some info on normal box loading, its very compact. Nevertheless this
driver is ideal for a first order series c/o at the baffle step frequency
to a typical 3" good FR like the B3S or NS3. Not bad for $20.
Throw in a FR notch filter and you get a killer small budget speaker.

rgds, sreten.

I like the one with the best -6dB (and -10dB) point.

[sreten]

Hi,

And for those that are into group delay here are the plots,
not surprisingly the red curve is the best of the vented,
as it has the most smoothly bending bass roll off, and
hence the best transient response.

rgds, sreten.

[mondogenerator]

ah yes.... Vas is a bit low for it to be practical. teach me for thinking aloud....or not thinking aloud lol

group delay isnt too bad either so bandpass would be reasonable, compared to other drivers of similar size.

hmmmm the pink response DOES look interesting