Regarding speaker impedance, I was not making this out to be a big issue, just something to be aware of.

We have done extensive testing of a range of speaker sytems for a client including the EV TS940D cinema system. In that particular case we found that the impedance (nominal 8 ohm) varied from a minimum of 3 ohms at 160Hz to a maximum of 24 ohms at 3.15kHz The impedance was less than 4 ohms between 100Hz and 300Hz. Their surround speakers showed a simlar trend, so the impedance dips are not necesarily at quite as low a frequency as you may surmise Steve.

But as you say, with well designed amps this is not a problem.

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Ray Derrick
President
Panalogic Corporation Pty Limited
44 Carrington Road
Castle Hill NSW 2154
Australia
Phone: 61 (0)2 9894 6655
Fax: 61 (0)2 9894 6935

When you did your tests on the EV...did you use their crossover or in bi-amped fashion. The bass section of the TS940D is a 4-Ohm cabinet (dual 8-Ohm drivers). I am a bit surprised by the low impedance in the 160Hz region. The driver used in the TS940D is the DL-15W...I shall pull EV's specs on it. Thanks for the enlightenment.

Steve

I've done a bit of downloading from the EV web site...

The impedance curves on the DL18W and the TL606 (the dual 15" bass section of the TS940D) concure with your findings on the low point of the impedance curve within the pass band (above 40Hz) but, according to EV the MINIMUM box impedance of the TL606 is 4.0-Ohms...and one would find that in the range from 100-200Hz. Now the fact you find it to be an Ohm less isn't surprising to me...driver construction is a bit wild and from unit to unit people would be surprised at how differently they respond. Professional drivers are quite a bit hand made and not as exacting as one would hope in this day and age....but I digress

One thing I did note about EV's impedance ratings...they tend to make their "nominal" their minimum. Their current surround speaker the SL12-2V follows this trend but seems to err on the side of higher impedance. The Older TS8-2 does have a low minium impedance of 7.2 with a nominal 8-Ohms.

I have generally found that EV publishes accurate spec sheets. In fact they tend to tell it like it is more than other manufacturers. I'll stand by my statement earlier...I wouldn't be too worried about the minimum impedance being significantly below the nominal impedance in Cinema applications. I have even run into applications where the impedance was significantly higher. So much so, I have had 6 "8-Ohm" speakers all paralleled and still didn't drop below 2-Ohms in the pass band.

I do appreciate your point though and agree one should check their speakers with an impedance bridge if they haven't worked with that type before.

Steve

However the overall system is rated by the manufacturer at 8 ohms.

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Ray Derrick
President
Panalogic Corporation Pty Limited
44 Carrington Road
Castle Hill NSW 2154
Australia
Phone: 61 (0)2 9894 6655
Fax: 61 (0)2 9894 6935

What's an impedance bridge and how's it done?
By the way after reading your post, Steve, I got out my QSC manual and checked the specks on the DCA 1222 and I think I'll be mustering out the good old SAE and replacing it with the QSC. Thanks for the tips

Some links:
http://www.mitedu.freeserve.co.uk/Theory/inzoz.htm
http://www.purebits.com/appnote16.html
http://www.purebits.com/scplugins.html#anc#6

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Greg an impedance brigde is kinda like an Ohm meter but measures the impedance at various frequencies. (an Ohm meter only measure the DC component and will often be lower than the impedance but not always).

Steve

You are obviously very experienced and skilled in your craft and would avoid using such amplifiers under low impedance conditions but many techs don't have that experience. So in my opinion unless you really know the gear, it is much safer to stick with series parallel than work a system at 2 ohms.

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