Anyone used the sb20pfc 8" woofer?

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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).
 
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.
 
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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.
 
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.
 
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.
 
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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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).
 
Hi folks; I have bassbox pro and DATS, and do know how to calculate various alignments from measured parameters. I do appreciate people taking the time to sim them though :) In this case I would probably use an EBS or similar alignment, though I will be using a hypex fa123 plate amp with DSP for amp/crossover duties, so will also have the option of 6th order vented or other EQed alignments. By all means feel free to continue your discussion of theoretical vs non-standard alignments; but what I was looking for were first hand experiences with these drivers and perhaps even some comparisons to other more well known woofers.
 
I am currently using these as mids in a 3-way OB design. I cannot attest to their bass prowess but they are outstanding from 200-5k. IMHO they are a hidden gem in sound quality performance vs. price. The frame shape is unfortunate but I cannot find another driver that does what these do in this price range. I am definitely a fan.
 
I am currently using these as mids in a 3-way OB design. I cannot attest to their bass prowess but they are outstanding from 200-5k. IMHO they are a hidden gem in sound quality performance vs. price. The frame shape is unfortunate but I cannot find another driver that does what these do in this price range. I am definitely a fan.

Thank you for this! Great to hear your experience, I think you are the first person I've read of who has actually used this particular driver. My own plan is to use 2 or 3 of them as woofers in a largish vented box, but I've a few other options (2x Peerless SLS or HDS) that are appealing as well. The efficiency and suitability for a ported box attract me towards the SB, whereas the distortion and more advanced motors of the peerless drivers pull me the other way.

I'm happily surprised to hear you're happy with their midrange performance, the distortion results from hificompass (SB Acoustics SB20PFC30-4 | HiFiCompass) made me a bit hesitant to run them above 300hz or so. Of course distortion plots are not everything, but when they are all one has to go by, they can make one think twice!
 
I've tried the 6.5" version as a subwoofer by tuning the box really low (circa 30 or 35Hz) I think. This is much lower than the standard alignment. Then use DSP to boost the bass at the port frequency to level up the bass response. The sound is quite good.

Oon
 
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I am currently using these as mids in a 3-way OB design. I cannot attest to their bass prowess but they are outstanding from 200-5k. IMHO they are a hidden gem in sound quality performance vs. price. The frame shape is unfortunate but I cannot find another driver that does what these do in this price range. I am definitely a fan.

Agreed. I used them as a 2-way crossed over to SB tweeters at ~1.4k. I really enjoyed them. Distortion was good, not great, as one would expect. 2nd Harmonic about -45, 3rd a little lower than that. Smooth, no aberrations. I had them in about 1ft3 box, so not bass monsters but good enough for my needs. Mids were excellent. Should be way more popular than they are. I think the square frame makes them look 'cheap', but the SB quality is there...
 
Thank you for this! Great to hear your experience, I think you are the first person I've read of who has actually used this particular driver. My own plan is to use 2 or 3 of them as woofers in a largish vented box, but I've a few other options (2x Peerless SLS or HDS) that are appealing as well. The efficiency and suitability for a ported box attract me towards the SB, whereas the distortion and more advanced motors of the peerless drivers pull me the other way.

I'm happily surprised to hear you're happy with their midrange performance, the distortion results from hificompass (SB Acoustics SB20PFC30-4 | HiFiCompass) made me a bit hesitant to run them above 300hz or so. Of course distortion plots are not everything, but when they are all one has to go by, they can make one think twice!

I can whole heartedly agree with the Peerless SLS line for woofer duties as well. I'm running SLS 12's and have run SLS 10's also. They just do what they are supposed to.

As far as distortion in the SB20's is concerned, I will politely dissuade you from that concern. I am continuously amazed and gratified by what I hear. For the money they are a steal. I've tried smaller full range drivers during the development of what I have now but I always circled back around to the SB20's. They keep up with the dual 12's and sound amazing; detailed, clean and will play loud with authority.
 

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excellent feedback, thank you everyone!

Leaning towards the SLS as I'm only needing them to cover the <300hz range, and because 3 of the SB drivers a side would dip too low in impedance for my amps. But, I plan to build the boxes with a removable face, so if the fancy strikes, will be able to test all 3 options (SLS/HDS/SB) if I'm not happy with the result.
 
Z 1 kHz 6Ohm / 8,3
Z 10 kHz 20,2 Ohm / 27,2
Fs 32 hz / 34,1hz
Re 3,64Ohm
Rms 1,74 / 1,94
Qms 2,67 / 2,71

Qes 0,39 / 0,49

Qts 0,34 / 0,42

Cms 1,1 / 0,88
Mms 23,1 g / 24,5g
BL 6,62 / 7,77
VAS 77 L / 63,5 L
Le 0,4 / 0,53
SD 227 qcm
Xmax 5,6 mm


But i would highly suggest to use this driver only as a sub, due its resonating nature in the mids.
A quick simulation at 40; 50 and 60 liters with an vent of 70 mm at a length of 30 cm.


Swann
 

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