Does impedance matter?

Magfan, impedance actually is pretty important. I've read the whole thread here and not seen any of the important issues addressed- here they are.

1) The lower the impedance, the more power you will get from a transistor amp, within the limits of that amp's individual abilities. This is not to say that it will sound better- low impedance is only an advantage if you want sound pressure. The effects that low impedance loads have on any transistor amp are otherwise bad for sound **quality**.

2) Tubes prefer higher impedances as well but for different reasons. Reducing the impedance of the load will cause a tube amp to loose bandwidth, power and increase distortion, even if there are taps on the output transformer for the load. Many tube amplifiers will actually run cooler on higher impedances- the output transformer or output section if there is no transformer will be more efficient.

3) Higher impedances thus sound better on both transistors and tubes, all other things being equal, a 16 ohm speaker will thus sound better than a 4 ohm speaker. 'All other things' seem like they are never equal, but going to 16 ohms is an easy way to make a speaker seem more transparent and relaxed, regardless of the amplifier.

4) Lower impedances demand far more out of the speaker cable, for best results it has to be kept short and with larger conductors. Higher impedances are far more forgiving of speaker cables- you can use longer lengths and lesser materials and not loose resolution.

In general, higher impedances are preferred if sound **quality** is your goal, low impedances are preferred if sound **pressure** is your goal, but only with transistor amps. Tube amps will not loose power with higher impedances but transistors usually will.

BTW, the difference between sensitivity and efficiency is worth discussion here. Sensitivity is 2.83 Volts at 1 meter, Efficiency is 1 watt at 1 meter. Let's say you have a system that uses 2 8-ohm drivers in it. Furthermore, the drivers are 90 db 1 watt/1 meter. If the 2 drivers are in parallel (4 ohms), the sensitivity will be 93 db, but the efficiency will still be 90 db. If the speakers are wired in series (16 ohms), the sensitivity will fall to 87 db, but the efficiency will again be 90. IOW, the sensitivity of the speaker can be affected by the impedance, but does not affect the actual efficiency.

Depending on the amp, this can have a big effect on how it will behave on that speaker! Going from 4 ohms to 16 ohms will cut the power of most transistor amps by 75% (although it will sound better). Let it not be said that impedance is unimportant :)

A speaker with a higher impedance might theoreticaly sound better, and even then within some limits, but in practice that isn't always the case. I have yet to hear speakers with a "high" impedance load that I would care to own.

Has anyone looked at the link to the Smith Chart....
It is a VERY interesting way to view the impedance curve of a speaker VS phase angles, which is really a much better way to evaluate 'is it a good or bad load?'

I read the article, and it is indeed somewhat interesting, and I don't see anything wrong in it technically. The article does a good job of emphasizing that the magnitude and the phase angle of the speaker impedance, as functions of frequency, must both be taken into account in assessing how difficult a load it represents.

I see two basic problems, though. First, it is difficult to interpret due to the lack of frequency information on the plot. The author himself acknowledges this:

The main drawback compared to the normal, two-plot method is that we lose the frequency dependence of the impedance.

The second problem is general lack of availability of this kind of plot across a wide range of speakers. I think that being able to meaningfully utilize this kind of plot for a specific speaker would require prior familiarity with what the plots look like for a large number of other speakers, of various types.

Thanks for the interesting read!

Regards,
-- Al

Agreed on both points....But, nobody ever said it was supposed to be easy. Also, once you are accostumed to this presentation of phase/impedance it is fairly easily seen.
Frequency data would be Very helpful.

Hi Ralph,
all your points on impedance are well taken.

IMHO Magfan's original post did not imply that impedance was not a useful number; in reality it is! I quote from Magfan's thread-starting post:

When looking at a speaker then, it is important in evaluating the load it represents by not only the impedance, but the inductance and capacitance as well. As voltage leads or lags current, the strain goes back to the amp.

I believe that point that he wanted to highlight was that we need to look @ impedance using BOTH the impedance & phase plots as a duo. All what you wrote in your post applies.
Most people just blow off the phase plot because they do not understand how to use it & they think that the impedance plot is it. Wrong!
I think that you understand this (& I'm sure, besides Magfan, Almarg & a few others out there do as well).