Measurements - Clearly Explained

Hi Everyone,

I found a page which explain amplifier measurements which I think many would find useful on the SoundStage web site:

They seem to be suffering from bad links. If you get directed to "" just remove the "Magazine" part.

One thing a lot of people have questions about are the impedance of "real-world" loudspeakers. This I found at the Stereophile site, here:

Of course, this is 1 specific speaker load, but it does represent the challenges posed by many 2-way, dynamic loudspeakers.


Hi Everyone,

I put together simulation files. If you have a PC or at least a Windows VM you should be able to grab the XSim crossover software (free!) and these files and play around yourself.

The simulation file I put together uses the Steroephile simulated 2-way load, and it is especially useful in examining how an amplifier’s output impedance affects the speaker frequency response.

Of course, buy what you like to listen to! The docs I present here are merely to enhance our technical understanding and to accelerate the sharing of knowledge.

If you want to play around with simulations, please join me over at the DIY site where we can attach images and files.


I would like to add that measurements and amplifier measurement tools are needed to design amplifiers. They are not needed for buying amplifiers, since they tell you nothing how an amp will sound. Remember, most amplifier designers do the final voicing of there amps by ear, not measurements
Hi Ahendler,

I'm not sure how much voicing you think happens without tools, but yes, the point to the links and simulations is to help the layperson see exactly what the amplifier/speaker interaction is like in terms of impedance and output.


The Dennis Had "Inspire Fire Bottle" amp I bought recently has NO specs anywhere I can find, except descriptions in his Ebay comments regarding things like output from various tubes and power supply design…I bought it because it’s cute (the first consideration by any true audiophile), and after reading 10,000 pages of comments here and there. Had says things like "You’ll be listening to your record/music collection as if you were hearing the performers for the first time. This jewell delivers the emotion of the music ... big time. The amp plays like a 50 watter with amazing control and slam." As far as my experience with it goes, he’s utterly correct. It works well with what I already have (preamp, DAC, cables, efficient speakers, etc.) so maybe I’m just lucky.
Hi Wolf!

Those are always great finds.

But as an engineer, anything that sounds good, I'd like to know why so I could replicate it, whether or not it goes with established dogma.

Like, maybe it adds plenty of 2nd order distortion, or has noise in the treble which enhances digital recordings.


Had does go on about the 2nd order harmonics inherent in this amp, and regarding "dogma," the entire SET (or SEP in this case) world has its own dogma it seems, and I'm all for it as it's a thing that has transformed my thinking about such things (although I've used relatively low wattage guitar amps for many years…including a hand made single ended amp with a tube rectifier). Regardless of all that, this amp "seems" to have less distortion of ANY kind at even louder levels, and the openness and apparent clarity may be the amp simply fooling me, which as long as I like the results is just fine.  As Fremer said in a recent article, "my hearing gets worse, but my listening gets better," which certainly applies to my old person self as I continue to produce and mix concerts and play music. Had's new stuff since retiring from Cary seems like an assault on convention (and pricing), and if he makes a remote preamp I'm in with one of those too! Note no measurements are around for the Fire Bottle amp unless somebody else has tested one, but Had certainly measures things and his idea of what sounds good might just be the same as mine.

Nothing wrong with that at all in my mind. :)

I just don't like influence/idea peddlers promoting ideas about power and impedance not supported by facts.

Buy and listen to what you like!! :)


Erik, Agon has always been big on "alternate" facts, long before the term came about.  Where else can you find clever lil clocks and pebbles?
Here is a paper I just discovered an excellent paper on Damping Factor from Wikipedia:

which also references a paper from Nelson Pass discussing how matching the amplifiers to specific speakers (lots of full-range and high efficiency drivers could be useful):

While the paper focuses on HE speakers and using current source amplifiers (i.e. very high impedance output)  I think it's a great way to dive in deep into speaker / amplifier interrelationships.

I'm not sure if I can create a current source amp in Xsim, but it is a fun challenge. :)


@erik_squires you may also find this article interesting (written by the chief engineer of ElectroVoice):