This driver is not bad. I measured it as a nude midrange a couple of years back. The FR is usable, but it definitely has higher distortion than the SB17MFC. See attached measurements of front on and off axis, harmonic distortion, and front vs rear (0 vs 180deg) frequency response.
For comparison I am also posting my measurements under similar test conditions of a nude SB17MFC. IMHO the FR is smoother and stays together from 1k to 4k compared to the Audax.
I also measured this driver and used it in a system once, but I cannot find the measurements data now. IIRC distortion was relatively low but FR not as smooth as either the Audax HM170 or the SB17MFC. I am glad that Peerless is resuming production of this driver and it will or should again be available for DIY purchases.
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While we are talking drivers and nude midranges in particular, another good one is the little Audax HM130C0. FR is great in that application (beautifully controlled cone breakup!), and only the distortion performance is a little worse than other drivers (it has the same motor design as the HM170). It is a 5.25" class driver, so it can work a bit higher in frequency when used nude, but on the low side should probably be crossed over around 700Hz. So the next driver down in frequency must be able to crosso over that high. For comparison, I use a 6.5" class driver down to 350Hz and this makes is possible to build a 3-way dipole speaker, whereas the 5.25" drivers probably must be used in a 4-way system.
See attached plots. For the front vs rear plot, I forgot to match the levels but you get the idea. The driver is built like a tank and is not all that expensive. Looks cool, too.
See attached plots. For the front vs rear plot, I forgot to match the levels but you get the idea. The driver is built like a tank and is not all that expensive. Looks cool, too.
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@CharlieLaub Those are interesting measurements. The last time I measured the HM170CO, it was lower in HD than your data. That was likely due to the baffle size (or lack of it in your case). Its also possibly due to more of the driver being exposed, with the entire chassis contributing to the measured response, "warts and all".
Many drivers emit all sorts of weirdness when the entire chassis backside is exposed. Because these aren't necessarily the conditions a manufacturer intends for their driver to operate under, its going to show some increase in HD compared to a driver measured in an infinite baffle with the microphone placed and listening only at the front (cone axis) of the driver.
Many drivers sound quite bad when being listened to from the front with the entire chassis being exposed ie. smaller open baffle arrangement. This is specifically the case at lower frequencies, where much of the fundamental LF range of the driver is being canceled out from the lack of an enclosure or large enough baffle. This ends up with a higher percentage of "junk" being left over, mainly distortion laden harmonics.
Drivers like the majority of the Peerless NE series are unicorns. They have exceptionally low levels of HD, often less than far more expensive drivers that are equipped with far less fancy motors. The Audax CO drivers sound very natural and effortless in standard box style speaker or even a large open baffle design. They do lack some distortion lowering features but sound natural and "correct" to my ears at the circumstances I've used them under. This is why I always say HD measurements on their own aren't showing the entire picture of a driver's capability to deliver very good overall fidelity or tasteful presentation of music.
Many drivers emit all sorts of weirdness when the entire chassis backside is exposed. Because these aren't necessarily the conditions a manufacturer intends for their driver to operate under, its going to show some increase in HD compared to a driver measured in an infinite baffle with the microphone placed and listening only at the front (cone axis) of the driver.
Many drivers sound quite bad when being listened to from the front with the entire chassis being exposed ie. smaller open baffle arrangement. This is specifically the case at lower frequencies, where much of the fundamental LF range of the driver is being canceled out from the lack of an enclosure or large enough baffle. This ends up with a higher percentage of "junk" being left over, mainly distortion laden harmonics.
Drivers like the majority of the Peerless NE series are unicorns. They have exceptionally low levels of HD, often less than far more expensive drivers that are equipped with far less fancy motors. The Audax CO drivers sound very natural and effortless in standard box style speaker or even a large open baffle design. They do lack some distortion lowering features but sound natural and "correct" to my ears at the circumstances I've used them under. This is why I always say HD measurements on their own aren't showing the entire picture of a driver's capability to deliver very good overall fidelity or tasteful presentation of music.
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On a roll now... another GREAT driver for a nude midrange despite it being a bit larger is the SB Acoustic MW19TX. It offers low distortion, decent FR extension up top as high as 4kHz where it is in a well controlled cone breakup, and the front and rear responses are nearly identical to almost 2.5kHz except for a small blip in the rear response around 1.2kHz. Because of its greater Sd and Xmax being 6.5mm you can use it even lower when nude and or get higher playback SPL before the driver sounds stressed. IIRC distortion starts to climb only once you get below 250Hz or so. See attached measurements.
I will be using this driver again, when ever I finally get back into speaker building here.
I will be using this driver again, when ever I finally get back into speaker building here.
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@CharlieLaub I totally agree with you about the HM130CO. It makes a fantastic cone mid with decent sensitivity and low level detail retrieval. I spoke with a rep from Audax back in the 80s and asked them about the design strategies they set for the carbon fiber woven cone HMxxxCO series. They commented that not having to rely on induction control measures on these drivers helped retain more base sensitivity. Most people don't understand that using shorting rings in the motor actually reduces sensitivity. This is due to the dampening losses shorting rings create along with the increased VC gap width needed to fit them, reducing gap flux density). So, together with the careful motor design, using flat profile VC wire and not relying on shorting rings, they retained a higher BL factor. This gives you a stronger, lower loss motor without most of the bad side effects from oversizing it.
Thanks for providing the measurements!!
Nice driver, as you wrote, but 700Hz xo won't work with my midbass section.
BTW, I'm doing 4 ways:
4 sealed subs (12" Rythmiks in DIY boxes) up to 60Hz
SLOB with 8x 6.5" up to 470Hz
B&C 8PE21 on a 12" open baffle up to 1.1kHz
Beyma TPL-150H open back
In an active setup using Acourate for xo and filters, so linearphase steep xo are easy to do.
For now I'm considering the subs and midbass "done". Looking to improve midrange and tweeter. So the midrange needs to xo at 470Hz max.