SB Acoustics SB23NRXS45-8 MLTL? - diyAudio
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Old 15th January 2016, 03:05 PM   #1
cbarth is offline cbarth  Norway
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Default SB Acoustics SB23NRXS45-8 MLTL?

Hi guys,

I just saw Troels Gravesen new speaker the www.troelsgravesen.dk/SBAcoustics-3WC, and his measurement and review of the SB acoustics woofer. For me that looks like a very good 8 inch woofer with those TS specs, and as I always look for: high QMS.

I have built several of Troels's speakers (cno 25, DTQWT, CA-RNX 2,5).
I kept the CA-RNX in my secondary system. But then I came over Paul K. MLTL design of the same woofer, so I built new MLTL cabs and retro-fitted the drivers/crossovers in the new cab.

Holy cow, what a difference in bass! Now this speaker is fairly large, but it will challenge speakers many times the cost, that is for sure.

I modelled the SB woofer in WINISD, and it models very good in BR enclosure, it goes deep and with good sensetivity for a 8 inch down to 30hz.

I really wonder how this would do in a MLTL cab...
Have any of you guys any experience with this woofer?

Cbarth
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Old 15th January 2016, 03:24 PM   #2
xrk971 is online now xrk971  United States
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What a coincidence - Bushmeister picked this woofer for the bookshelf point source horn as band pass injection. It has nice TS parameters and would probably make a better TL than a MLTL as the Qts is lower. You want mid 0.5 for a MLTL I think.

A Bookshelf Multi-Way Point-Source Horn
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Old 15th January 2016, 04:33 PM   #3
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If a driver is suitable for any other type of vented enclosure, it's suitable for an MLTL. A higher Q can be advantageous if you want to force a very small driver, such as a 3in wideband unit or similar, to produce low frequencies a la the TABAQ or similar (at the price of extremely limited dynamic range / output level & usually high HD). Otherwise, not necessary.
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Old 15th January 2016, 04:54 PM   #4
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I've taken a quick look; something along these lines should do nicely enough:

Internal dimensions (HxWxD) 48in x 9.5in x 13.5in
Zd (driver centre from internal top of cabinet) = 9.625in
Zv (vent centre from internal top of cabinet) = 45in
Vent = 3in diameter x 7.5in long. May be positioned on front, rear or side of enclosure
All internal faces lagged 1in acoustic fibreglass, F-10 felt, Ultratouch recycled denim or similar.

The alignment is lightly damped; Fb = 22Hz. 4.5in vent length gives a maximally flat Fb = F0 alignment.

CSA is fixed, as is height & location of the driver centre & vent relative to the internal top. The WxD ratio can be adjusted as desired providing CSA is maintained. Attached are 1/2 space plots of the enclosure, not including diffraction effects & step loss, so those will have to be factored into the crossover design, as usual.
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Old 15th January 2016, 05:06 PM   #5
cbarth is offline cbarth  Norway
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Thanks a lot Scottmoose!
That looks rather impressive. But I didn't understand the part with the 4,5 inch port. Another higher tuning with the same cabinet dimensions?
Cbarth
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Old 15th January 2016, 05:14 PM   #6
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Right. That will raise effective tuning to Fb = F0 (as in box tuning = the driver's free-air resonant frequency).

Note that you can adjust tuning (and I suggest you do) via lengthening or shortening the vent of each cabinet as appropriate to achieve the smoothest response in-room.
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Old 15th January 2016, 05:22 PM   #7
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Quote:
Originally Posted by cbarth View Post
But then I came over Paul K. MLTL design of the same woofer, so I built new MLTL cabs and retro-fitted the drivers/crossovers in the new cab.
Can anyone please provide a link to the Paul K design?
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Old 15th January 2016, 05:32 PM   #8
cbarth is offline cbarth  Norway
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Thanks Scottmoose.
I'm seriously thinking of trying out this woofer.
But I have another question.
When I model this woofer in Winisd with a 3 inch port I get quite high air vent speed. Normally I try to model for maximum 20 m/s at maximum linear excursion above tuning frequency. Would it be possible to use a 4 inch port installert? (And of course compensate for length to keep the same tuning )
Thanks
Cbarth
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Old 15th January 2016, 05:45 PM   #9
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You can, the trade-off being that vent harmonics (since a duct is a 1/2 wave resonator) may become an issue. So it's a case of balancing one off against the other. This is about the limit that I'd personally go to in terms of duct length, at least as far as standard types are concerned. Flared vents can help, as can positioning them on the rear of the cabinet if that is a concern. Likewise, you can add a small amount of damping to the vent (i.e. line it with some thin damping material), which will take things down.
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Old 15th January 2016, 05:52 PM   #10
xrk971 is online now xrk971  United States
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Nice design Scottmoose. I think in practice the circa -5dB baffle step loss will make this an 85dB sensitive system? I agree with 3in dia vent and not making it more than 7 or 8in long. I made a vent 14in long once to discover first hand what vent harmonics can do.
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