-it's the opposite of that.
(..low Qms is believed to reduce low-level detail. Low Qms generally means a stiffer spider, and perhaps a stiffer surround as well. Really, Klippel's Kms(X) is the best graphical display I've seen that shows the amount of resistance relative to excursion - with a low "0" resting Kms being preferred. The Peerless driver I mentioned has a very low Kms at rest.)
Great suggestion Wolf.
I looked at that one and it's enticing indeed. I've used PRV drivers before and had a few inconsistencies with published specs. The 6MR500 does add up to it's specs when looking at the performance potential. The ugly dust cap logo can be hidden easily so that's no big deal and the frame will need a router template to countersink.
I agree the 6ND430 is a fantastic driver. My concern is they supposedly changed it (according to another guy who uses these in his designs).
If anyone has recently purchased this driver I'd like to know for sure if specs changed.
You have a good point. I have a few of these drivers stashed away when I heard they were being dropped due to the new high purchase quantities stipulated by Tymphany. I made some measurements a while back and they're being held hostage by my old PC's crashed HD. I do recall mid band efficiency to be slightly higher than spec, but the NE180 suffers from some production inconsistencies if I remember correctly. I have enougb drivers to make a close matching pair.
The NE180W-08 efficiency being borderline may still work out in the design when factoring the potential bandpass gain that results from driver response overlap in such a narrow pass band of 300 to 1000 Hz. I may be looking at a gain of about 1 dB if this is the case and as long as i don't need any BSC, I might be ok.
I'm going with the SB34NRXL75-8 LF driver in a 90L ported cab for my design. This is a very accurate woofer that can cross higher than most other 12 inch drivers. Distortion is very low across the board and it doesn't suffer from much power compression. The measured base efficiency is 0.8% (works out to about 91dB/2.83V) and with a low series R of the LP inductor combined with BSC, it should be possible to use the NE180W-08 with it. I love the overall sound of this driver. It has a revealing open sound that make it a nice midrange and possibly a good match for the other drivers. I've been patiently waiting for the weather down here to cool off for some outdoor measurements. So far we've been having 100+ degree temps here in AZ and that does mess up the measurements a bit.
I use them and like them a lot. I didn't measure the specs and simply plopped them in a box and measured for frequency response which looks just like the plot on their web site. I used REW to cook up a crossover. High Q second order high pass at 400hz. Low Q second order low pass at 2Khz.
Waste of money imho. The Purifi only makes sense when used at lower frequencies than 200Hz.
Qms is on the low side despite the low distortion figuresOtherwise it looks like a nice driver overall. That surround sure looks ugly.
-it's the opposite of that.
(..low Qms is believed to reduce low-level detail. Low Qms generally means a stiffer spider, and perhaps a stiffer surround as well. Really, Klippel's Kms(X) is the best graphical display I've seen that shows the amount of resistance relative to excursion - with a low "0" resting Kms being preferred. The Peerless driver I mentioned has a very low Kms at rest.)
Yes, a neutral zero preload condition at rest is ideal. Thats hard to achieve assembling a driver in mass quantities and demands precision engineering to avoid any tolerances causing a preload situation at rest. Thats why higher compliance acoustic suspension optimized drivers are more linear, mainly relying on the more linear air volume to provide the actual returning force.
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As soon as a drivers suspension has both the spider and surround assembled with one preloading the other, it creates a non-linear condition and responds with different compliance in one direction to another (even more so the greater the preloading force).That increases non-linear distortion that carries into low level distortion performance and raises overall THD.
The Kms curve of a given driver shows compliance non-linearities of both surround and spider being the dominant mechanical causes for driver odd order THD. An antagonistic pre-tentioning of both spider and surround will always increase Kms non-linearities. Of course varying Le and BL also creates (electrical) non-linearity, adding to the issue.
High compliance drivers rely on the air in a sealed cabinet to provide most of the cone's restoring forces and control. Air is more linear than any spider or surround combo ever will be. I've done my own research on this and have verified it through measurements. This type of driver's own mechanical compliance Kms is less of an influence on the total compliance compared to the enclosure air volume Vb, unless the volume becomes too large and mechanical compliance Kms progressively takes over. Playing the driver louder will make Kms take over and cause high level THD to creep in. This becomes less the case when the air volume is smaller, because the Vb compliance becomes the dominant restoring force of the driver suspension. Discounting the cabinet losses caused by air leaks, dampening material and cabinet wall compliance/resonances, the Vb will always be more linear.
http://www.klippel.de/fileadmin/_migrated/content_uploads/Loudspeaker_Nonlinearities%25E2%2580%2593Causes_Parameters_Symptoms_01.pdf
The Kms curve of a given driver shows compliance non-linearities of both surround and spider being the dominant mechanical causes for driver odd order THD. An antagonistic pre-tentioning of both spider and surround will always increase Kms non-linearities. Of course varying Le and BL also creates (electrical) non-linearity, adding to the issue.
High compliance drivers rely on the air in a sealed cabinet to provide most of the cone's restoring forces and control. Air is more linear than any spider or surround combo ever will be. I've done my own research on this and have verified it through measurements. This type of driver's own mechanical compliance Kms is less of an influence on the total compliance compared to the enclosure air volume Vb, unless the volume becomes too large and mechanical compliance Kms progressively takes over. Playing the driver louder will make Kms take over and cause high level THD to creep in. This becomes less the case when the air volume is smaller, because the Vb compliance becomes the dominant restoring force of the driver suspension. Discounting the cabinet losses caused by air leaks, dampening material and cabinet wall compliance/resonances, the Vb will always be more linear.
http://www.klippel.de/fileadmin/_migrated/content_uploads/Loudspeaker_Nonlinearities%25E2%2580%2593Causes_Parameters_Symptoms_01.pdf
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It's all relative or a tradeoff. If you use a cone that benefits from some preloading in the way that breakup behavior gets less bad, it might be perfectly valid. As the extreme excursions appear in non-breakup frequency domains and in that case the rigidity of the cone is big enough, the resulting force/excursion function still can be pretty linear.
I can see some preload benefiting a less than optimal cone design for given bandwidth of operation. This would likely more pertain to drivers with very light weight cones that have a wider band of breakup mode or a harder cone with a severe edge resonance. In the situation of low compliance drivers, they usually exhibit better in box linearity and low frequency distortion characteristics than stiff suspended drivers in a larger box. The table can turn when the driver operates at higher excursion levels and that would be where a higher Kms would be beneficial, plus also provide better protection against VC damage from over excursion.
If you look at their documentation, they state how their testing procedures are different:
"For a typical mid-woofer, the voltage should be about 1 V (rms)
at the resonance frequency."
https://sbacoustics.com/wp-content/uploads/2021/01/Measuring-Thiele-Small-parameters.pdf
Most other companies do tests at small signal levels.
You convinced me. This is the mid for the job, and best thing is I already have these. I didn't recall these being so efficient, although it still needs verification on my behalf. It does look promising though. I built some 2 ways with CAT378s using these and have no complaints. Too bad they aren't so easy to get anymore thanks to Tymphany's idiotic minimum quantity policy.
The response is really linear on this driver. The 4.6-4.8 k peak is easily dealt with and lands evenly off axis too, although I'm crossing at around 900-1000 hz, so it should be 40 dB down and not need attention. The peak does vary from unit to unit so matching them will be necessary if I can detect the peak with the LP. The motor does get warm on these and I may employ some extra heatsinking to it so power handling and compression are decent in a small sealed chamber.