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In the Forum: Audio Discussions
In the Thread: Exceptional loudspeakers drivers
Post Subject: Corrections & thoughts on drivers perceptionPosted by jessie.dazzle on: 4/7/2007
I was thinking about what I previously wrote while driving today... thinking about the way people "see" the function of a driver... and about resonant properties of various materials used for speaker cones... I think it is more interesting than comparing notes about the Aura and McCauley drivers.
Never the less, I will first respond to the subject at hand, putting these potentially more interesting thoughts at the end...
Regarding Xmax :
Oops, yes you are correct... double the Xmax figure for both drivers... The relative difference between the two remains the same (1.42" vs 1.2").
And a couple more corrections/explanations :
Sensitivity :
The difference in sensitivity (if we can believe the spec sheets in both cases) between the McCauley and Aurasound driver is not 5dB, but 2dB.
The McCauley 6174 is quoted at 94dB/watt @ 1m
The Aura NRT18-8 is quoted at 96dB/watt @ 1m
Aurasound is presumably getting an additional 2dB sensitivity via their super-magnet (?).
Cone material :
The new version of the Aura driver (see material link below) uses fiberglass, where the version you are referring to may not. The older version may be closer to what you originally identified as an exceptional 18" driver. I was replying in the context of NBC's questions, who, if he wants an Aurasound driver, is presumably going to have to buy the evolved version (as first and second generations of this driver are impossible to find on the used market). The details of the currently available version, the NRT18-8, state that the cone material includes fiberglass, most likely on the back side of the cone. Fiberglass must be laminated with some sort of resin, presumably epoxy or polyester.
See the evolved version and some details of the materials here :
http://www.madisound.com/cgi-bin/index.cgi?cart_id=3766372.28865&pid=2076
The McCauley driver is not better in this regard; they start off with a nice pressed paper cone, and then unfortunately dope one side.
Suspension :
The Aura NRT18-8 uses a polyester suspension (polyester fabric) which is also likely impregnated with resin (probably epoxy) so that it will hold its form.
Though epoxy damps resonance somewhat, it is not as bad as rubber. This is one area where the Aura driver is more to my liking, as McCauley use resonance-killing rubber, but then they do have lower Fs, and this is probably why.
In the end, I would agree that either of these drivers would be a good choice... As far as I know, they are alone in their class. The Aura driver seems to take a more high-tech approach, and in some cases has more impressive numbers (BL factor for example), while McCauley tends to be more "old-school". As mentioned, my choice was based as much on availability as projected preference.
On a more interesting note...
I was thinking about it while stuck in traffic getting supplies for the horns... I am convinced that the key to tone lies in the resonant properties of the material(s) from which it is made, and of course its architecture... Ok, what I just wrote might seem obvious, but people tend to see the cone as piston in an air pump. I feel strongly that this is incorrect. Just as when you strike a tuning fork to set up a secondary resonance, I don't believe the sound of a driver is a direct result of the first action; i.e. the cone being projected outward or sucked back... Instead, I think the sound is gnerated by the resonance this action initiates. Different materials will sustain the resonance differently, or absorb it... The magnetic force of the motor can initiate resonance, or cancel a sustained resonance. Again, maybe it is obvious, but I feel this is a more correct vision of what is really going on, and goes a long way to explaining the tone of a driver.
Getting back to the above discussion; rubber suspension, speaker dope, and epoxy/polyester resin, go against tone, as they all kill resonance to varying degrees.
But it is not so simple... Obviously a metal diaphragm will resonate nicely, but in a way that is probably not good for bass... The character of the resonance should match the application... Metal has a more MId-Range resonance.
I have to think more about this, but not in this thread.
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