Determining a nominal impedance of a finished speaker

[rabbitz]

I've been trying to find if there is any set guidelines to determining the nominal impedance of a finished loudspeaker. You get your peaks and dips in the impedance plot and wonder if it's a percentage added to the lowest impedance, or average over a certain portion.

I'm looking how it applies for amplifiers that specify say 4 ohm min impedance and am wondering how low the dips can go and for how much of the plot.

 

[speakerdoctor]

The best way I know is to run a test with a Woofer Tester. It will show you the complete imp. plot for the entire freq. spectrum. Then you can find the lowest impedance point along the curve and decide if it's a real problem for your amp.

 

[BobEllis]

How low an impedance dip an amp can handle depends on many factors - the magnitude and phase of the load, the signal level at the dip, the heat sinking, number of output devices, how aggressive the protection circuit is, etc.

For a bit of a rule of thumb, if your worst dip is to 3 ohms or greater with less than 45 degrees phase, you're probably safe with any 4 ohm rated amp. Worse than that (greater phase angle, lower impedance) then look for an amp with lots of output devices and massive heat sinks.

 

[rabbitz]

Thanx for the replies.

I've got a dip down to 3R6 and 22° phase. My AKSA 55 has no problems with it but I tried a new Yamaha A-S1000 last week.

The day after running the speakers the Yamaha went belly up stuck in protection mode when running other speakers that have a minimum impedance of 6R9 and 4° phase. I'd say the amp has an internal problem not related to the speaker as it's stuck on protection mode with nothing attached.

 

[HK26147]

I use WTII and also recommend it.
I think you are right about the defective amp.
I have used the same amp for over 25 years and put a wide variety of cabs ( mostly DIY ) on it. I have observed the effect of EPDR but have not had it cause a problem.