Low-mid driver question

[Luke]

Hello

I'm actually planning a 4 way system.
So one of my concern right now is to choose the best Low-midrange 8 inches driver.
And it's for covering the band 90 to 550Hz, very possibly with LR4 crossover.
My choices would be Peerless HDS nomex 830869 or HDS aluminum 835026 drivers.

The HDS aluminum cone is 2 dB less efficient but this does not cause me problem.
And its HF ringing happens a full decade away so I don't feel bad about this.
Frankly? I'M looking for low midbass distortion.
I remember having heard few times magnesium or aluminum drivers excelling in this particular band but I could be wrong.
Despite this the HDS Nomex could be better for some reasons.
What would you suggest and why?

Luke

[JonMarsh]

What is your budget and sensitivity goals? "Best" based on what criteria? Nonlinear distortion? Linear distortion? I suspect there are better drivers available with regards to those criteria, but without a budget limit, hard to recommend. Do you have review data form somewhere that inclines you towards these, as opposed to say, a Dayton RS225? The RS225 is well documented in the past for it's relatively low distortion, and it's priced quite competitively. Since you've linked to Parts Express for the Peerless woofers, I'm guessing/assuming that PE is ok with you as a vendor. It's an aluminum cone driver.

BTW, the biggest thing affecting distortion in the band you're interested in is not the cone material, but the motor design, and to the degree that it uses copper in the VC gap to reduce inductance and inductance modulation. This is why the RS225 works very nicely at it's price point.

[TMM]

Between the two Peerless drivers, assuming they are exactly the same except for the cone material the aluminium one is better. This is because if you inspect the frequency response curves the aluminium cone does not begin to breakup until 3kHz. The roll off beginning about 1kHz and continuing to 3kHz is caused by the voice coil, you can work this out by calculating the L-R lowpass frequency from the voice coil resistance and inductance in the datasheet - 5.5ohm and 0.57mH. 5.5/(2*pi*0.00057) = 1536Hz. Because the response starts picking up again after 3kHz instead of continuing to roll off, the cone must be significantly breaking up at this point. This means that 3rd order harmonic distortion will start to rise about 3kHz/3 = 1kHz, 5th order distortion will rise above 3kHz/5 = 600Hz and so on. Typically distortion above 5th order is already at a low level in a decent speaker so we assume this woofer will be exceptionally clean up to 600Hz.

Now look at the datasheet for the Nomex woofer - the voicecoil resistance and inductance are similar but the frequency response is totally different. Instead of beginning to roll off after 1kHz it actually starts to rise! This means that significant cone breakup is already occuring from 1kHz. Thus the 3rd order distortion will being to rise at 1kHz/3 = 333Hz and 5th order at 1kHz/5 = 200Hz.

Of course, using this method tells you nothing about how low the base level of distortion is but it is still useful to weed out drivers which have a distortion profile that can only be made worse by a less than well behaved cone.

IMD from voicecoil inductance modulation isn't going to be a big factor in overall distortion when crossing at 550Hz because you are sufficiently below the point where the voicecoil inductance has a big effect on the frequency response (1kHz+). Just avoid drivers with excessive inductance (1mH+) and you should be ok in that area.

[Ray_D]

+1 for the RS225. You said that sensitivity did not matter; but, this is the exactly frequency range where speakers transition to full space and you will lose 6 dB if you do full BSC. Two drivers are frequently used in parallel to recover that sensitivity as well as get more swept volume.

[JonMarsh]

+1 for the RS225. You said that sensitivity did not matter; but, this is the exactly frequency range where speakers transition to full space and you will lose 6 dB if you do full BSC. Two drivers are frequently used in parallel to recover that sensitivity as well as get more swept volume.

+1 on this comment- in fact, that's why for a planned system upgrade from 3 way to 4 way, I'm going with two 9 ohm drivers in parallel in the mid bass, (75Hz to 400Hz) some 7.5" Accuton's. Especially at the price of the RS225-8, doubling down wouldn't be a bad idea at all- it would be a very good one, of course, depending on your planned woofer sensitivity. One way to work around that would be to floor load the woofer so that it's working into a half space setup- that would be highly recommend to do a Roy Allison style boundary load for the driver. Then you would get the full half space/IB sensitivity of the woofer system.

[Face]

For a little more efficiency, there's the paper version: http://www.parts-express.com/dayton-...8-ohm--295-367

[augerpro]

In the same vein as the above drivers, consider the Aurum Cantus AC200-50C2C. Lower distortion in that range than anything mentioned so far, higher sensitivity, and the breakup isn't so bad.

EDIT: looks like this is NLA, damn that's too bad

[5th element]

Another vote for the RS 225. These are very hard to beat in that frequency range.

[TMM]

For a little more efficiency, there's the paper version: http://www.parts-express.com/dayton-...8-ohm--295-367

It's only a theoretical efficiency from the T/S parameters though. If the frequency response plots in the datasheet is to be trusted then the aluminium cone is more efficient through the midrange. The aluminium version will be cleaner through the midrange than the paper for the same reasons I detailed above for the Peerless woofers.

[Luke]

Hello

Thanks guys...that was really amazing and helpful replies!

Jon Marsch
I knew that the coppered gap technique was a great way to control Inductance and by consequence some distortion mechanisms.
Like previous SS SD-1 , Aura woofers and few others.
So by the way, thanks for showing me that there was such a feature for the Dayton RS225.
It's something they don't mention in their spec sheets.
This driver is a really great candidate for me and above this it has good price.

TMM
Amazing and of course, thanks!
You just showed me very interesting mathematical considerations about Le.
And also you suggest the Peerless Aluminum version over the Nomex one.
So you're just confirming I was right to have positive doubts about the Al cone over Nomex.
Another driver to consider.

Augerpro

Thanks for pointing me Aurum-Cantus even if your suggestion is discontinued.
I didn't know them. Good discovery.
Amazing products by themselves.
it should be considered in future designs.