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Speaker impedance patterns - how to read them?

I know this has probably been discussed ad nauseam, but here's my question. I'm grateful for any sensible opinion.

Premise.
A speaker system may have a complex impedance pattern that can vary from 3-ohms to 30-ohms depending on frequency. Some speaker systems with similar impedance patterns may be stated as being 8-ohm loads because the speaker is 8 ohm in an important part of its frequency response, but only there.
A tube amp, as a voltage amplifier, likes a regular impedance pattern. Almost no speaker system has a constant, regular impedance pattern. I am aware that solid state, powerful amps are built to compensate for modern speakers' complex impedance patterns, but there are tube amps around and people who love them. It's difficult to understand what average load a given speaker system will present to the amp.

Question.
When looking for suitable speakers for a tube amp - mine is a PrimaLuna EVO 100, 40w x 2 from EL34s - what must be looked at? How to best interpret the impedance pattern, whenever available? Assuming that one listens at normal levels in a medium-sized room, what are the criteria for matching speaker and amp?

Thanks for your views. M.
martinguitars
clearthinker's avatar
clearthinker
1,582 posts
 
@martinguitars              Hope you're back on thread.  Don't feel picked on by miller, he can't help it, he does it to everyone.  He will never reform, he thinks too much of himself.   Best to just ignore him like the rest of us do.


In almost all affected speakers, low impedances occur only across short frequency ranges.
Low impedance points  at bass frequencies causes amplifiers the most problems.

The phase angle at low impedance points should also be examined.  Where this is low, it should not cause the amp too much difficulty.  But a combination of low impedance and high phase angle at any point will mandate a more muscled amp.

Some of us remember the Apogee Scintilla that had an average impedance of pretty well 1 ohm.  In those times only big Krells could drive them.  Things are better now.
rudyb
141 posts
 
Although all the technicalities and electronic measurements can be interesting, with an amp + speakers combination there's only one determining factor ... your ears. No matter what weird variations in impedance they may have, in the end it's how they sound that matters. By the way, room acoustics will probably contribute a great deal to the overall sound.
martinguitars OP
23 posts
 
clearthinker,

thanks, those are the criteria I am currently considering of importance; as for the Asperger affair, I am always amazed at how people feel entitled to throw judgments and epithets into the discussion because they are safe this side of the Internet... But I am no newbie to forums.

rudyb,

if the only determining factor were one's ears, audiophiles wouldn't spend a lot of time, money and mental energy changing and listening.. I find it funny that most of them buy a car, a fridge, a pair of shoes with the outmost care then rely on absolute lack of science and on hearsay to assemble a music system that is supposed to rely on science to do its job properly. Nothing wrong with some objectivity I think. Thanks for your opinion.

Max 
rudyb
141 posts
 
@Max Yes, doing our research, our reading, and maybe even some measurements, is big part of the fun of the hobby, as is exchanging knowledge, ideas and opinions on a forum like this. But while I might buy a new photo camera solely based on reviews ... amps, speakers and headphones are the kind of products I would never buy without having heard them myself first, no matter what raving professional- or user reviews or semi-scientific analysis may say.
erik_squires
16,042 posts
 
@timlub You are mixing up the impedance of a driver for the impedance of a completed speaker, meaning 1 driver on your desktop vs. multiple drivers attached to a crossover.

Of course anything with a coil will eventually behave like an inductor, and woofer’s are the easiest of these to use to make an example. However to tell an end-user that has much to do with the end result is really not a good characterization.

Here’s a typical impedance curve for a simple 2 way:

https://speakermakersjourney.blogspot.com/2016/12/crossover-basics-impedance.html

It’s very very different than the impedance curve for the woofer it used, which can be seen in this impedance chart:

https://www.blogger.com/blog/post/edit/8271724650517523711/3931230143413830127

To say all speakers rise with frequency ignores everything that happens in between, and ignores both frequency and impedance equalization, not to mention the basic high and low pass filters as well.

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