Hi everyone, interesting discussion, if I may add a couple of thoughts.
First of all XRK971 is correct, the AC130F-1's T/S parameters don't measure well to published specifications. However, the actual measured parameters were even better for the Continuum's design. My early samples measured very consistently, and essentially identical to Zaph's measurements. So, the driver was consistent, the published data just wasn't accurate. The higher Qts made for a better small sealed speaker though.
Because of the higher Qts value, it is really not a very good choice for a vented box, which would require a larger vented box to flatten the response, and this would in-turn increase distortion and lower power handling. Although there are a couple floor standing transmission line Continuums out there, I think the driver is best suited for a small sealed enclosure and I would not normally recommend its use in a vented box.
The quote above where I talked about the Continuum's distortion is still correct. When I said it that above 100 Hz it has the lowest nonlinear distortion of any speaker I have measured, I didn't mean to imply that it went whacky below 100 Hz. It is significantly better than the SB15NRX in the Piccolo, and even better than the Satori MW16 in a vented box like my Kairos. The Continuum has lower distortion than those speakers below 100 Hz too.
The comment about 6% distortion above is without reference - at what frequency? I don't see anything this high. However, if in a larger vented box, then I might. The AC130F-1 benefits a great deal from the stiff compliance of the small sealed box. This is an important part of what keeps the distortion low. This compliance controls the cone excursion and keeps the motor more linear. It is only a 5" driver, we really can not expect high SPL's or deep bass response, but it delivers a midrange that is truly wonderful.
I should note, that I have recently built a newer Continuum kit in order to compare the response with my 2006 original. The AC130F-1 now measures a bit lower on the Fs and the Qts, and as a result the newer kits extend a bit lower in the bass, to about 60 Hz. Otherwise, the response if the same.
Also, XRK, the little two-way with the Fountek driver is a nice little speaker, and that Step Response is excellent. Very cool.
Jeff B.
First of all XRK971 is correct, the AC130F-1's T/S parameters don't measure well to published specifications. However, the actual measured parameters were even better for the Continuum's design. My early samples measured very consistently, and essentially identical to Zaph's measurements. So, the driver was consistent, the published data just wasn't accurate. The higher Qts made for a better small sealed speaker though.
Because of the higher Qts value, it is really not a very good choice for a vented box, which would require a larger vented box to flatten the response, and this would in-turn increase distortion and lower power handling. Although there are a couple floor standing transmission line Continuums out there, I think the driver is best suited for a small sealed enclosure and I would not normally recommend its use in a vented box.
The quote above where I talked about the Continuum's distortion is still correct. When I said it that above 100 Hz it has the lowest nonlinear distortion of any speaker I have measured, I didn't mean to imply that it went whacky below 100 Hz. It is significantly better than the SB15NRX in the Piccolo, and even better than the Satori MW16 in a vented box like my Kairos. The Continuum has lower distortion than those speakers below 100 Hz too.
The comment about 6% distortion above is without reference - at what frequency? I don't see anything this high. However, if in a larger vented box, then I might. The AC130F-1 benefits a great deal from the stiff compliance of the small sealed box. This is an important part of what keeps the distortion low. This compliance controls the cone excursion and keeps the motor more linear. It is only a 5" driver, we really can not expect high SPL's or deep bass response, but it delivers a midrange that is truly wonderful.
I should note, that I have recently built a newer Continuum kit in order to compare the response with my 2006 original. The AC130F-1 now measures a bit lower on the Fs and the Qts, and as a result the newer kits extend a bit lower in the bass, to about 60 Hz. Otherwise, the response if the same.
Also, XRK, the little two-way with the Fountek driver is a nice little speaker, and that Step Response is excellent. Very cool.
Jeff B.
Jeff B.:
Thanks for replying to my question - and thanks for kind words on the Fountek 2in and AC130F1 speaker. Here is the measurement I made with the AC130F1 in circa 5.7liter boxes.
Here is a comparison of a good and bad driver in frequency response. I think these were made at 0.5m and 1.4v:
Here is the measured HD of the "good" driver - this is running full range (cursor was at 80Hz so about 3% distortion):
Here is the measured HD of the "bad" driver - cursor was at 80Hz and about 6% harmonic distortion. I was sent two additional units and they both measured like the "bad" one so it would appear the "good" one is an anomaly. Both have distortion starting to rise below 200Hz:
And when I measured in an open baffle, with no pressurization, the difference in the HD went away. Although the difference in H3 between the two below 200Hz is significant.
"Good" unit in an OB:
"Bad" unit in an OB:
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I have the Bagby continuum for a couple of years now. Lovely speakers, very smooth, good controlled bass. The only culprit for me is imaging is only average. I also find some low level details missing.
I have had sooo many speakers, but the Continuum are still here in my secondary system.
I have had sooo many speakers, but the Continuum are still here in my secondary system.
XRK971 - I really don't have any problem with what you are posting. The AC130f-1 is not a high end driver, it's more of a middle range midwoofer with a fairly conventional motor design.
I've got speakers that use Scanspeak Revelator, Illuminator, Satori, Audio Technology, and the Morel Supreme, which use multiple shorting rings or even full copper sleeves to reduce distortion. The AC130 doesn't employ anything like this, but it is only a $60 woofer too.
It's not perfect, but it came down to what my goals were for the Continuum - a smaller speaker capable of excellent midrange reproduction, that would normally work with a subwoofer. I felt the AC130 did a remarkable job at hitting this mark. I really didn't expect this speaker to deliver too much below 100 Hz, just enough to handle lower SPL's and be able to cross to the subwoofer.
However, it did surprise me when I started taking nonlinear distortion measurements and saw that it was significantly lower than the SB15NRX in the similar sized Piccolo. I didn't expect this since the SB15 used shorting rings. But, like with the ATC SM75, the AC130 uses Ferrous mass to help lower distortion. I did make a comment to SB Acoustics about this disparity though.
Another thing, small sealed enclosures with reach the point where the compliance begins to increase the distortion. I even created a program to calculate this, so there is a balance between enclosure and distortion. It's a tight rope walk sometimes.
I found some graphs of the Continuum at 2.83V at 1 Meter, but this only shows distortion at 84 dB reference level. This graph shows about 3% at 50 Hz. I may have some at a higher test level, but I will have to look.
I don't believe it will compete with a Revelator in the bass distortion though when pushed, but like I said, for its price it performs very nicely.
Jeff
I've got speakers that use Scanspeak Revelator, Illuminator, Satori, Audio Technology, and the Morel Supreme, which use multiple shorting rings or even full copper sleeves to reduce distortion. The AC130 doesn't employ anything like this, but it is only a $60 woofer too.
It's not perfect, but it came down to what my goals were for the Continuum - a smaller speaker capable of excellent midrange reproduction, that would normally work with a subwoofer. I felt the AC130 did a remarkable job at hitting this mark. I really didn't expect this speaker to deliver too much below 100 Hz, just enough to handle lower SPL's and be able to cross to the subwoofer.
However, it did surprise me when I started taking nonlinear distortion measurements and saw that it was significantly lower than the SB15NRX in the similar sized Piccolo. I didn't expect this since the SB15 used shorting rings. But, like with the ATC SM75, the AC130 uses Ferrous mass to help lower distortion. I did make a comment to SB Acoustics about this disparity though.
Another thing, small sealed enclosures with reach the point where the compliance begins to increase the distortion. I even created a program to calculate this, so there is a balance between enclosure and distortion. It's a tight rope walk sometimes.
I found some graphs of the Continuum at 2.83V at 1 Meter, but this only shows distortion at 84 dB reference level. This graph shows about 3% at 50 Hz. I may have some at a higher test level, but I will have to look.
I don't believe it will compete with a Revelator in the bass distortion though when pushed, but like I said, for its price it performs very nicely.
Jeff
Jeff B,
Good to hear that you think this is normal. Probably lack of shorting rings and small enclosure combine to make it so. So ideally more of a mid bass than a woofer. It has a remarkably smooth mid range though so great performance there. I am not criticizing the Continuum design at all - great speaker and might build one some day given that I have the AC130 and the RS28F (not A). Maybe there is a simple XO tweak for the F silk dome tweeter?
Good to hear that you think this is normal. Probably lack of shorting rings and small enclosure combine to make it so. So ideally more of a mid bass than a woofer. It has a remarkably smooth mid range though so great performance there. I am not criticizing the Continuum design at all - great speaker and might build one some day given that I have the AC130 and the RS28F (not A). Maybe there is a simple XO tweak for the F silk dome tweeter?
Yes, there is a crossover tweak for the RS28F, but I never consider that one a Continuum, because I don't really care for the RS28F, it just simply doesn't sound as good to me as the RS28A does. I'm not the only person who feels this way, either.
FWIW, there's an obvious problem with overly tight closed box.
It's called "Rocking Mode".
See the woofer is severely constrained by air-pressure from behaving like a piston. So it starts to rock sideways to preserve pressure overall. Increasing distortion. Down to the spider to restrain this unfortunate tendency. 🙂
It's called "Rocking Mode".
See the woofer is severely constrained by air-pressure from behaving like a piston. So it starts to rock sideways to preserve pressure overall. Increasing distortion. Down to the spider to restrain this unfortunate tendency. 🙂
and here i thought i was being cheap by not adding a lot of gasketting. turns out i was avoiding rock mode. makes sense since i only play western and country....lol
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