Finding (calculating?) speaker and amp impedance

I don't know how to do those calculations but I can say I have never been unable to find that information by just using Google or an email to the manufacturer.  Not the answer you were looking got but maybe helpful?

If not published by the vendor/manufacturer, is there a way to determine the impedance curve from the specs that are provided?

Sadly unless some one like Stereophile or Soundstage reviews and measures them there is not. At best many of these measurements are "aspirational."  There's no math, it's all eyeball and feelings between the complex curve and published nominal value, so vendors have a lot of leeway and there's no way to reverse engineer from the rated impedance alone.

A vendor appealing to tube amp lovers may specify both a "nominal" (i.e. in name only) measurement as well as a minimum impedance which is really useful. A typical minimum for 2 way speakers for instance is around 3.8 Ohms.

Recently in another thread we discussed a Kef monitor which is nominally 4 Ohms. In reality is is a 2 Ohm speaker, so this is how far the gap can be.

One thing you may do is seek out speakers with series crossovers like Fritz which have very flat impedance curves compared to other speakers. That tends to make them easier to drive and provide more consistent performance across different amps.

I mean if you look at a lot of Stereophile measurements you kind of get a sense for how a typical 2 or 3 way speaker will behave, but then there’s no guarantee at all that say a monitor like the Kef is going to be at all typical. In addition to driver impedance a lot of equalization and level adjustments happen in the crossover. That can make some impedance curves look very different from another.

Forgot to mention, you CAN measure this yourself using Dayton Audio DATS or a rig built for Room EQ Wizard.

Wow! Lots to consider.

I guess my real concern is knowing if my amps have "high enough" current for speakers that present a challenging load.

Surprisingly (to me) was finding out that my old 80 db sensitive little monitors are known to be great with tube amps. These are Rogers LS3/5a from the early 70s.

@erik_squires is there anything you know of that will measure speaker impedance across the frequency range?

Forgot to mention, you CAN measure this yourself using Dayton Audio DATS or a rig built for Room EQ Wizard.

It is a measured parameter. The speaker designer needs to have this as a priority in their design. One speaker designer who does a great job with flat impedance/response and phase angle is Eric Alexander.

I was just thinking about this issue this morning. Those who design speakers that present very difficult loads to amplifiers must believe that there is no other way to get as good a sound, otherwise why do that? 

@asctim  Outside of exotic manufactured speakers like full-range ribbons or ESLs, I think there are a couple of reasons.

One is lack of decent tools and practice.  Old Genesis speakers sometimes showcase this.  The crossovers were "tuned" by ear and impedance be damned.  Given that a software spreadsheet had just been invented, there was not a lot of handy tools like we have now to tune a speaker's crossover for impedance, frequency response simultaneously. 

Another, and I've seen Focal do this, is that a difficult to drive speaker is seen as "discerning."  No, I'm not going over this detail, either you believe me or you do not, but reviewers give far too much positive press to a speaker that shows you the difference between an integrated and million dollar monoblock. 

Lastly, and I think the Kef is an example, is that they have a big problem with power efficiency and need a lot more current to make the design work.

@asctim Don’t assume everyone that puts their name on a product is above average intelligence.

reviewers give far too much positive press to a speaker that shows you the difference between an integrated and million dollar monoblock

+1

Every budding audiophile should endeavor to hear a time aligned [studio monitor] system with electronic XO and beaucoup watts per driver. They'd then know they were being had.

Regarding reviewers:  "and the triangle in 3rd chorus is delineated like never before" is laughable.

How to stop worrying about speaker impedance The Audiophiliac and ELAC’s speaker designer Andrew Jones set out to demystify speaker impedance.

Thank God for John Atkinson.  From my long experience in reading Stereophile technical reports it's very rare that some part of a speaker's impedance curve isn't below 4 ohms.  And vanishingly rare at 6 ohms.  Accordingly most valve amps should almost always be set to their 4 ohm tap.  If they have one.  Atkinson nearly always recommends this.  Flea power examples should really only be run into 'full' range horns with sensitivity in the high 90s and above.

@hleeid 

Surprisingly (to me) was finding out that my old 80 db sensitive little monitors are known to be great with tube amps. These are Rogers LS3/5a from the early 70s

This represents the significance of the speaker impedance load and curve characteristics. Yes, these were very low sensitivity speakers, however they were 15 ohm impedance, so very easy to drive.

The sensitivity measurement of a speaker has more to do with limits of volume/SPL for a given amount of amplifier power. How easy a speaker is to drive has more relationship and effect due to the impedance load/characteristics.People could drive the Rogers monitor speakers (82 db sensitivity) easily with low power tube amplifiers due to the very friendly 15 ohm impedance it has.

Charles

Good timing for this topic. Using a pair of Focal Aria 936’s with a PL HP Integrated and all is good. But…I just had my 45 year old Sansui AU-717 fully restored and it’s in transit as I type this. Per Stereophile’s review, these speakers drop to about 2.7 ohms in the mid/bass region, yet publish as 8 ohms nominal. The PL tube amp handles it just fine in either mode (70 wpc in ultralinear, about 40 wpc in triode).

Im eager to try the vintage Sansui in this system upon its arrival. Bad idea?

@chocaholic 

I have a Sansui AU-20000 that will not come out of protection mode.  I've been told it is essentially a boat anchor.  Used it for many years and really liked it, put it in a closet when the ARC amps appeared out of nowhere (wink).

Would you please share the repair shop who did your 717.  Thanks.

Regards,

barts

@barts I was referred to a gentleman on AudioKarma that specializes in vintage Sansui. He stripped boards, removed all old corrosive glue, completely recapped in addition to countless other parts, extensively tested, adjusted bias, burn-in, more measurements, etc…and kept me updated with details and photo’s throughout the process. He’s in a small town in Mississippi and prefers not to ship equipment. So, a 10 hour round trip for drop off and retrieval from here. 
 

Bottom line, it’s more of a hobby for him than a business. I’d want to check with him before passing his name along. 
 

@chocaholic 

Thanks...Mississippi is quite a drive for me, so that is out, but I am slightly confused due to you saying the 717 "it's in transit as I type this".  Does this gentleman sometimes ship and sometimes not?

Regards,

barts 

@barts Sorry…I should have been more clear. My wife went to visit her mom this weekend…about 2 hours from his location. She picked up my amp on her way. I married a good woman!

@chocaholic 

Thanks.  I married a good one also.  Music lover and doesn't give a hoot about $$ spent on audio.  In fact, she hears things and complains to me "that is not right!".

Regards,

barts

Someday, equipment makers will do what Technics does and employ something like their LAPC function which "looks" as the speaker impedances with a series of test tones and adjusts the amps output to match it as closely as possible.

Other makes must have done something like this as well (I can't recall any at the moment) but it can be done, simplifying the matter, somewhat.

All the best,
Nonoise

Technics does and employ something like their LAPC function which "looks" as the speaker impedances with a series of test tones and adjusts the amps output to match it as closely as possible.

@nonoise

I must admit that this is a pretty cool application, but kind of limited in benefit. Perhaps the biggest benefit is to switching amps which tend to suffer (relatively) high output impedances at high frequencies.

@erik_squires 

Every little bit helps. And, if done enough times by manufacturers, someone else will eventually come up with a better mousetrap.

All the best,
Nonoise

@nonoise True, but you also have to then accept the ADC / DAC of the amp. If you want to keep an analog chain after that DAC you spent 2 years pickinmg out this tech is wrong for you. :)

@erik_squires , I have zero issues with the sound of the amp and it's internal ADC/DAC. To my way of thinking, that's way overthinking the problems one might encounter 2 years down the line. I've never been into the DAC flavor of the month club. 

All the best,
Nonoise

@erik_squires 

Another, and I've seen Focal do this, is that a difficult to drive speaker is seen as "discerning."  No, I'm not going over this detail, either you believe me or you do not, but reviewers give far too much positive press to a speaker that shows you the difference between an integrated and million dollar monoblock. 

I was afraid to but almost said something along these lines in my earlier post. A hard to drive speaker can give a very expensive amp a reason to exist, and the amp can then complement the speaker's "revealing" capabilities. So both sort of act together in a mutual appreciation club. But I recall some speaker manufacturer's mantra that "watts are cheap!" to explain why he designed inefficient speakers. Apparently he thought inefficient designs sounded better overall if you just gave them enough cheap watts. 

@asctim 

A hard to drive speaker can give a very expensive amp a reason to exist, and the amp can then complement the speaker’s "revealing" capabilities. So both sort of act together

I believe that there is solid reasoning to support this suspicion. One would indeed necessitate the other.

Charles