How To Measure "Current" In An Amplifier?

@unsound

Thanks so much for using a very specific example, it makes discussion a lot easier. The example you’ve shown for a Thiel is quite benign and an example of thoughtful design.

Please note the minimum impedance is around 4.5 ohms (by eyeball). The Thiel CS3.5 isn’t lowering the impedance to 3ish ohms, but rather it’s lowering what would otherwise be pronounced impedance peaks around 12 Ohms or much higher to be more "normal." This type of network, while drawing a little more power, makes the speaker very tube friendly, while maintaining good performance with solid state amps. The frequency response of tube amps often track the speaker impedance so by flattening the impedance above the woofer's resonance Thiel was making sure the speakers would behave similarly regardless of amplifier used. Good for Thiel for thinking of this in advance.

That’s not the kind of charlatanism I’m talking about though. In fact what I'm describing is the opposite, where impedance is brought to 3ish ohms or less, and reviewers, like buyers, are amazed that the speakers can sense such a difference in amplifiers. The Thiel CS3.5 on the other hand would play very nicely with a variety of amplifiers.

Best,

Erik

@gdhal

So low impedance = low ohms.

8 is really high impedance, 4 starts getting lower. What you want to look at is how well it drives 4 ohms. It should be close to double the 8 ohm spec. So, 220 x 2 = 440 Watts at 4 ohms.

But more importantly, what is your amp and what are your speakers? :)

Best,

Erik

Erik, can you give examples?:-)
It's hard for me to understand why a speaker designer would want to discourage potential sales just to make a point. 

Sadly, these impedance issues don't often discouarage sales.  Instead they are sold at a premium for being more "discriminating."  with the idea that somehow they will reveal more in the music.

I did a thorough electro-acoustical analysis of a Focal Profile 918. And by this I mean I measured each driver electrically and acoustically as well as reverse engineered and simulated the crossover.

To simplify it, perhaps too much, the bass section had an array of 8 power resistors (8 x 10 = 80 watts) to deliberately leave the midbass with a very low impedance (3 Ohms).

Replacing these resistors and associated parts with a coil left the complex frequency response identical but raised the impedance to similar amounts as the Thiel you mentioned, around 4.5 ohms.

Since then I've noticed a wide variety of Focal speakers, regardless of woofer or woofer count seem to share the same impedance profile, though not as blatant an approach.

Best,

Erik

@unsound

Take a look at my blog post about it, and scroll down to the "Bogus Woofer Cap" section. The original minimum impedance for this speaker was 2.6 Ohms.

http://pqltd.blogspot.com/2016/01/focal-profile-918-ultimate-upgrade-guide.html

There is 1 cap and 4 resistors that are simply completely unnecessary. They are the same type of conjugate network Thiel used, but instead of being for the buyer, are for the seller.  It's designed to waste up to 40 watts of power in an area where it's easy to hear.



Best,

Erik