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Multi-Way Conventional loudspeakers with crossovers

Anyone used the sb20pfc 8" woofer?
Anyone used the sb20pfc 8" woofer?
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Old 11th July 2019, 02:21 AM   #1
morbo is offline morbo  Canada
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Default Anyone used the sb20pfc 8" woofer?

This one:

SB Acoustics, SB20PFC30-4 - Meniscus Audio

I'm contemplating 2 a side for the woofer section of a 3 way floorstander... wondering if anyone has played with them yet? The pricing at solen is too good to pass up, so now I have 4 of them sitting here... along with other options, but those are better known. These I'm finding next to nothing for. Anyone?
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Old 11th July 2019, 08:43 AM   #2
Ugg10 is offline Ugg10  United Kingdom
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Quick check on the MH-Audio Bass Reflex calculator give these as having a 42l box with 3"diam x 6" long port and an F3 of 42hz (QTC = 0.53)- you will obviously need 84l if you need two and either two ports or a single port of the same combined area. That's quite a big box when you add a volume for the mid (3-15l depending on which mid you use).
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Old 11th July 2019, 09:26 AM   #3
denibeni is offline denibeni
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Quote:
Originally Posted by Ugg10 View Post
Quick check on the MH-Audio Bass Reflex calculator give these as having a 42l box with 3"diam x 6" long port and an F3 of 42hz (QTC = 0.53)- you will obviously need 84l if you need two and either two ports or a single port of the same combined area. That's quite a big box when you add a volume for the mid (3-15l depending on which mid you use).
Ahh, the so called optimal box design.
You can put any speaker driver to any enclosure, smaller or larger box than optimal are all viable options, if you know what are you doing, but fortunately we have now computer modelling help.

Of course I am not against the optimal box size, but the optimum can be different, depending on the tuning (power handling, bass extension etc..) or other things (design, looks..) we are trying to achieve.

Last edited by denibeni; 11th July 2019 at 09:31 AM.
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Old 11th July 2019, 11:37 AM   #4
Mario Pankov is offline Mario Pankov  Europe
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Anyone used the sb20pfc 8" woofer?
Quote:
Originally Posted by denibeni View Post
You can put any speaker driver to any enclosure...if you know what are you doing
If you do that than you obviously don`t know what you`re doing
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Old 11th July 2019, 11:58 AM   #5
denibeni is offline denibeni
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Quote:
Originally Posted by Mario Pankov View Post
If you do that than you obviously don`t know what you`re doing
Of course i don't put a an EBP 40 value woofer to a sub-horn enclosure, because i don't want that response which can be achieved with that combination.
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Old 11th July 2019, 12:15 PM   #6
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by Mario Pankov View Post
If you do that than you obviously don`t know what you`re doing
I would not be so dismissive about denibeni's comment. There is much more than just a grain of truth to what he wrote!

There is ASOLUTELY no reason to use a "textbook" alignment, like some simple box calculators will advise. In fact there are some very good and smart reasons to use something that might be considered "non optimal" if you consider how the prediction by the the Thiele-Small parameter values will change with increased displacement, higher V.C. temperature, etc.

This is certainly the case for closed box speakers, but even in vented enclosures there are concepts like compliance scaling that can allow the designer to use some different tunings and box volumes. These of course will produce somewhat different responses, but they will not necessarily be any worse performing (e.g. in the time domain) than the standard alignments. Also, it has long been known that an "extended bass shelf" type vented alignment, which looks a bit "saggy" based on the T/S parameters alone, sound very good in actual use. This is because the designer understands how the TS parameters will change as the V.C. heats up, how that will change the overall response, etc.

Using modern modeling software one can drift away from standard alignments to fit a driver to a particular application or target. This is true because the textbook alignments are really just points on a curve that satisfy some particular criteria, and there are many "nearby" alignments that can work in a similar fashion.
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Old 11th July 2019, 12:39 PM   #7
denibeni is offline denibeni
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Thanks Charlie, I thought of that.
I commented at the beginning because it bothers me when someone speak of a loudspeaker that this should be in X box with Y tuning and nothing else.
Then we don't even know if the published T/S values reflect the reality.
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Old 11th July 2019, 01:05 PM   #8
Ugg10 is offline Ugg10  United Kingdom
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Sorry for steering this thread in a particular direction, my aim by quoting the "quick and dirty" figures was to try and elicit from the OP what his aims for the project were other than using this available and cost effective driver e.g. size, volume, xover points, other drivers, room size, listening preference, passive or active etc.


Also agree that speakers can be used outside of the "optimum design" but without knowledge of other requirements it is difficult to advise.


Hopefully with the info above then we can get a bit more of a steer to advise more effectively.
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Old 11th July 2019, 01:05 PM   #9
Mario Pankov is offline Mario Pankov  Europe
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Anyone used the sb20pfc 8&quot; woofer?
My comment was not regarding flexibility in terms of design goals, I agree with some of the points. But a generalisation as the above also includes putting a large woofer in a very undersized sealed box or using drivers with inappropriate T/S parameters for the allignment decided, and can create confusion among readers and misleading interpretations.
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Old 11th July 2019, 01:36 PM   #10
sangram is offline sangram  India
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Quote:
Originally Posted by Mario Pankov View Post
My comment was not regarding flexibility in terms of design goals, I agree with some of the points. But a generalisation as the above also includes putting a large woofer in a very undersized sealed box ...(snip)
Even that specific condition has interesting use cases. I've done this with a woofer demanding a 60L closed box, we put it in a 15L box and used the series cap trick to sort out the low end. Placed at about a foot from the wall - you won't notice any problems at the low end.

I gave up trying to use the default alignments from WinISD (though I do use them as a starting point). I look for a little smoother rolloff than the 24dB/oct, but less gentle than the sealed alignment. Obviously have to look at the crossover as well - a bit of peaking from the woofer cap allows a very neutral bass response. Of course you have to watch impedance when using larger shunt caps.

There are many ways to skin the cat - even if it intuitively seems wrong. The driver, box, crossover can be manipulated to best suit the specific application and room. What matters is not what any software tells you, but what you know as a designer (usually from bitter experience).
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