SOLID STATE AMP IMPEDANCE QUESTION

[Nigel Goodwin]

I think it might also depend on how they are acoustically coupled. If they are in the same box, they may act more like a single speaker than if they are in separate boxes.

Makes no difference, both are commonplace in the professional audio business.

 

[crutschow]

Speakers in series sound boomy because they do not have the extremely low output impedance of a solid state amplifier damping the resonance.

It would seem that two speakers in series act more or less like one speaker that has twice the speaker impedance, so would still be significantly damped by the low output impedance connected to them.

 

[audioguru]

I have been reading too many lies from high-end amplifier manufacturers like Crown.

 

[unclejed613]

I think it might also depend on how they are acoustically coupled. If they are in the same box, they may act more like a single speaker than if they are in separate boxes.

there are effects acoustically coupled from other cabinets, maybe not the same magnitude, but they are there, and they do cause a certain amount of back emf.

 

[unclejed613]

I have been reading too many lies from high-end amplifier manufacturers like Crown.

depends on where the measurement is done..... if it's done at the output connection on the amp board, i can see it being that small, but then you have to add in the wiring, speaker relays, and speaker terminals, and is it still that small at the speaker terminals? i've measured many amplifiers at the speaker terminals, and they average anywhere from 0.0500-0.1000 ohm (and that's at 100hz, where most amps still have their full gain margin available.... measure it at 1khz or higher, and the damping factor will change). add speaker wire to the mix, and the actual damping factor will fall further. the amplifier still exerts control over voice coil movement, but not as much as if the speaker were connected directly to the amp board. you could take the hot end of the feedback network and connect it to the speaker itself, but strange things happen in the amp if you have 20 feet of wire in the feedback loop.

 

[audioguru]

An 8 ohm woofer usually has a resonant impedance of 40 ohms or more at a low frequency.
Then I think the damping from an amplifier is even more than simply with its 7 ohms resistance in series with it.

 

[unclejed613]

with a test generator directly connected to the speaker (usually 50 or 600 ohms) you will definitely see and hear that resonant peak.... but try it with a good amp (like a Crown) and compare the results once the voice coil's back-emf is under effective control. even when there's no audio and the amp is on, the speaker behaves differently... tapping on a woofer gives "thump-thump" with the amp off, and "tap-tap" with the amp on.

 

[rjenkinsgb]

An 8 ohm woofer usually has a resonant impedance of 40 ohms or more at a low frequency.
Then I think the damping from an amplifier is even more than simply with its 7 ohms resistance in series with it.

Looking at low frequency response, don't forget that a lot of better subwoofers use motion feedback of some sort to get around problems with resonance and nonlinear response that happen with open-loop amp-speaker setups at low frequencies.

The speaker cone is under direct servo control so moves as commanded.

Even my old sub-£100 Yamaha sub has motion feedback..

 

[unclejed613]

An 8 ohm woofer usually has a resonant impedance of 40 ohms or more at a low frequency.
Then I think the damping from an amplifier is even more than simply with its 7 ohms resistance in series with it.

somehow the second time i read this i realized i must have missed something the first time... yeah, the amplifier damping is much more effective damping the resonant peak because the peak is 40 ohms damped by the <0.1 ohm output impedance of the amp (which would make the Crown damping factor effectively 7500 at that particular portion of the speaker's impedance curve , but only there). i know musicians that don't like solid state amps because they "don't have a sound of their own" like tube amps do... well... that's the point... the goal of a good solid state amp is wrapped up in David Hafler's "piece of wire with gain" analogy. for a musician, the amp is part of the instrument, the amp SHOULD have a "sound of it's own" but you don't want to filter recorded music through that...

 

[audioguru]

I think that "fuzz" and "overdrive" is produced by musicians how are deaf to the millions of awful-sounding harmonics of the distortion they produce.

 

[Nigel Goodwin]

I think that "fuzz" and "overdrive" is produced by musicians how are deaf to the millions of awful-sounding harmonics of the distortion they produce.

You're rather missing the point, which is they WANT the distortion and harmonics. Perhaps you just like mellow cello music, but the rest of the world has more varied tastes

 

[Mickster]

You're rather missing the point, which is they WANT the distortion and harmonics. Perhaps you just like mellow cello music, but the rest of the world has more varied tastes

Like this?

A Queen Mystery: The Legend Of The Deacy Amp

It sounds like a scene from a movie. A dark night in London, 1972. A young man walks alone, heading home after a long night of practicing with his band. His heavy Fender bass slung over his back, h…

hackaday.com

 

[audioguru]

The "clipping light" on an amplifier is red as a warning. It is not green to light whenever there is audio.
In the article about Queen, it says that guitarist Brian May used a treble booster (to makeup for his deafness?).
In the early '60ies I played with AC128 transistors and I laughed at the distortion produced by amplifiers that used AC128 transistors and transformers like in the Deacy amp.

 

[Mickster]

I laughed at the distortion produced by amplifiers that used AC128 transistors and transformers like in the Deacy amp.

And queen laughed all the way to the bank.

 

[audioguru]

And queen laughed all the way to the bank.

Are you hinting that I should sell my stash of germanium transistors?

 

[Nigel Goodwin]

Are you hinting that I should sell my stash of germanium transistors?

They can be quite valuable these days.

 

[audioguru]

They can be quite valuable these days.

For old electric geetar players.

 

[KeepItSimpleStupid]

I got a macintosh tube amp to repair. The guy wanted it louder, so he connected the output of one amp to the input of the other. I got it after that boo boo.

 

[gophert]

I got a macintosh tube amp to repair. The guy wanted it louder, so he connected the output of one amp to the input of the other. I got it after that boo boo.

Add some protection diodes on the input in case he does it again.

 

[KeepItSimpleStupid]

I had this other amp, 250 W/ch, to repair that was borrowed from a relative of the disco owner. 5 shops refused to do the repair. Metal film resistors 'puddled' on the board.

Basically thespeaker terminals were shorted at the binding posts: excess speaker wire stranding. He wanted it repaired at any cost to avoid friction with the relative.. It looked worse than the repair actually was. I added simple thump supression, speaker disconnect relays.