Hi guys. I was able to mount and measure these new SB15CAC30-8 woofers on my 48" x 48" infinite baffle today. Far field is 25" mic distance. Near field is ~1/4" from dust cap. 1/48th octave, 5 ms gate.
The 25" distortion test isn't at a level high enough to really discern the driver distortion from the noise floor. You'll want to test at a high level to get a meaningful result, like 90+dB. FWIW Zaph tested 5.5" drivers at 96dB@0.5m.
What I am reading into it is they suffer the same drawback as a lot of other very stiff coned drivers - the nearfield reveals the breakup does not really go down in magnitude in the off-axis so will probably require an aggressive notch. These days, though, it is pretty easy to pinpoint these filters.
Nice that there doesn't appear to be a lot of distortion by-product from the cone break-up. You can see a slight rise at 5K in 3rd order but it's not that bad compared to other stiff cone drivers.
I don't know what SB does with their woofers to achieve this but I saw the same thing on the little 4" aluminum cone.
My guess is that it has to do with the "geometric reinforcing". I believe this is radial ribs they have on the back of the cone. Perhaps they function similar to the slits on the Revelators?
Looks like an excellent mid to me. Am I interpreting the distortion correctly that it's greater than 50 dB down from around 300 Hz through 4k?
It's hard to see in the pictures but there are 5 radial creases that start a little outside the dust cap and extend all the way to the surround. From my hot rod days I know that a little crease, bend, bead, etc. can really help stiffen a sheet metal panel. I would surmise that these creases help move breakup modes even higher. I seem to remember that the aluminum cone SB driver that Ani used had those same 5 creases.
EDIT: I just looked at SD DIY event page and see that it was Jason P's project that used the SB aluminum cone with creases, not Ani's. Here is a pic:
Some same-old/same-olds that I already have on hand, like the RS28A or RS28F, or the Peerless XT25TG30-04. Maybe my pair of Dynaudio D28/2. Also considering the Seas 22TAF/G but I would have to purchase those. The TL's ceramics look awesome but they would push this project way beyond budget.
Hi Paul, looks like we were posting at the same time this morning.
My box modeling of this driver indicates it will also make a great mid bass driver with an F3 in the mid 30's in about 12 L ported.
The distortion measurement I did was really loud and the driver had zero reinforcing help from an enclosure! I could see and hear the driver in distress under 50 or so Hz. It was hitting its mechanical excursion limits for sure.
Change of plans... I don't need yet another 12ish Liter 2 way bookshelf. What I really need is a largish 3 way LOL! Think 2 piece enclosure like my "Trials" project or Paul C's Tarkus.
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Comments
Far field frequency response:
Far field distortion:
Near field frequency response:
Near field distortion:
The 25" distortion test isn't at a level high enough to really discern the driver distortion from the noise floor. You'll want to test at a high level to get a meaningful result, like 90+dB. FWIW Zaph tested 5.5" drivers at 96dB@0.5m.
Jim
I don't know what SB does with their woofers to achieve this but I saw the same thing on the little 4" aluminum cone.
Looks like an excellent mid to me. Am I interpreting the distortion correctly that it's greater than 50 dB down from around 300 Hz through 4k?
I wonder if the 8" is as good.
It's hard to see in the pictures but there are 5 radial creases that start a little outside the dust cap and extend all the way to the surround. From my hot rod days I know that a little crease, bend, bead, etc. can really help stiffen a sheet metal panel. I would surmise that these creases help move breakup modes even higher. I seem to remember that the aluminum cone SB driver that Ani used had those same 5 creases.
EDIT: I just looked at SD DIY event page and see that it was Jason P's project that used the SB aluminum cone with creases, not Ani's. Here is a pic:
Looks like Jason used the XT25!
Some same-old/same-olds that I already have on hand, like the RS28A or RS28F, or the Peerless XT25TG30-04. Maybe my pair of Dynaudio D28/2. Also considering the Seas 22TAF/G but I would have to purchase those. The TL's ceramics look awesome but they would push this project way beyond budget.
My box modeling of this driver indicates it will also make a great mid bass driver with an F3 in the mid 30's in about 12 L ported.
The distortion measurement I did was really loud and the driver had zero reinforcing help from an enclosure! I could see and hear the driver in distress under 50 or so Hz. It was hitting its mechanical excursion limits for sure.
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