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
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
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.
http://www.diyaudio.com/forums/multi-way/285030-bookshelf-multi-way-point-source-horn.html
http://www.diyaudio.com/forums/multi-way/285030-bookshelf-multi-way-point-source-horn.html
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.
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.
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.
Attachments
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
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
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.
You keep making the statement that a low-Qts driver is better suited for a TL than a higher-Qts driver, although you're not specific regarding what you consider low or high. My experience in designing and building TLs for personal use and designing many, many TLs for others has shown low-Qts drivers to be far more difficult to achieve good TL performance with than higher-Qts drivers. I shy away from drivers with Qts below 0.3, prefer drivers with Qts in the 0.35 to 0.45 range, but have been pretty successful with Qts values in the 0.45 to 0.55 range. I suspect we have far different opinions of what constitutes a good performance, however.
Paul
Edit: Also, if a driver works well in a tapered TL, it will also work just as well in an ML-TL almost all the time.
Paul
Edit: Also, if a driver works well in a tapered TL, it will also work just as well in an ML-TL almost all the time.
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I was specifically talking about Qts of the SB23 which is 0.38 and perfect for TL, and MLTL as Scottmoose has shown. I also stay awat from anything sub 0.3 Qts for a TL - just difficult to get it to work right.
I agree that if the Qts is 0.38, that would likely allow it to work well. The actual Qts of the SB23, as measured by Meniscus Audio and Zaph Audio (John Krutke) is higher, around 0.5, which obviously increases with added series resistance like from a crossover inductor. I do remember other posts from you on presumably other drivers where you've made the low-Qts statement, without being specific on the Qts values, and I assumed you literally meant low Qts, like 0.3 and lower.
Paul
Paul
Just curious. Which design of mine that used the SB23 in an ML-TL did you come across? My personal build for this driver, the Sonatello, used it in a tapered TL. I did do an ML-TL design for Dennis Murphy's Model 1 (Philharmonic Audio) that used this woofer in an ML-TL. I just sent Beau my write-up for the Sonatello, BTW.
Paul
Paul
ML-TL for the SB23
Real quickly I modeled an ML-TL for the SB23 using the same T/S measurements I used for the Sonatello design (that I sent to Beau). The line is 60" long with a constant cross-section that's 10"W x 7"D. The woofer's center is located 12" from the beginning of the line and the mass-loading port's center is located 3.5" from the end of the line. I modeled with port dimensions of 2.5"D x 4"L. The first half of the line's length is stuffed with polyester fiber at a density of 0.75 lb/ft3 (about 14 ounces total of poly fiber). The system tuning frequency is 28 Hz and I modeled with 0.25 ohms added in series with the woofer as occurred via the crossover in my Sonatello build. I've attached the modeled anechoic system bass response (red line) for an input of 2.83v/1m (baffle step losses and room effects not taken into account, obviously). For an input of 28 watts into this actual impedance of 6 ohms, the woofer's excursion will reach Xmax+15% (my design default) at a frequency of 40 Hz, and the port's air velocity will peak at just above 17 m/s at a frequency of ~23 Hz, with the system output being ~103 dB SPL above the knee in the response curve. If you make the port's diameter 3", it needs to be 5.5" long, which will lower the port's air velocity to 12 m/s for a 28-watt input and a driver excursion of Xmax+15%. The clearance between the internal entrance of the port will only be 2.25" instead of "1 pipe diameter" that's often recommended, however.
Paul
Real quickly I modeled an ML-TL for the SB23 using the same T/S measurements I used for the Sonatello design (that I sent to Beau). The line is 60" long with a constant cross-section that's 10"W x 7"D. The woofer's center is located 12" from the beginning of the line and the mass-loading port's center is located 3.5" from the end of the line. I modeled with port dimensions of 2.5"D x 4"L. The first half of the line's length is stuffed with polyester fiber at a density of 0.75 lb/ft3 (about 14 ounces total of poly fiber). The system tuning frequency is 28 Hz and I modeled with 0.25 ohms added in series with the woofer as occurred via the crossover in my Sonatello build. I've attached the modeled anechoic system bass response (red line) for an input of 2.83v/1m (baffle step losses and room effects not taken into account, obviously). For an input of 28 watts into this actual impedance of 6 ohms, the woofer's excursion will reach Xmax+15% (my design default) at a frequency of 40 Hz, and the port's air velocity will peak at just above 17 m/s at a frequency of ~23 Hz, with the system output being ~103 dB SPL above the knee in the response curve. If you make the port's diameter 3", it needs to be 5.5" long, which will lower the port's air velocity to 12 m/s for a 28-watt input and a driver excursion of Xmax+15%. The clearance between the internal entrance of the port will only be 2.25" instead of "1 pipe diameter" that's often recommended, however.
Paul
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Not really. As noted above, if a driver is suited to a bass reflex, then it is automatically suited to any other type of vented enclosure, be it a back-horn, mass-loaded horn, tapered (as in narrowing toward the terminus) quarter-wave, or a straight mass-loaded quarter-wave (a tapered quarter-wave is inherently mass-loaded). It's simply a matter of degree / tailoring as appropriate to the design goals & the specific characteristics of each enclosure subset.
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