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Old 21st August 2003, 09:59 PM   #1
Bricolo is offline Bricolo  France
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Default What is a difficult load?

I always wonder what this does mean, when someone talks about "a speaker being difficult load for an amp"

Is it a low impedance loudspeaker?
Very inductive or capacitive?
Low efficiency?

Or something else?
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Old 21st August 2003, 10:14 PM   #2
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Default Re: What is a difficult load?

Quote:
Is it a low impedance loudspeaker?
Very inductive or capacitive?
Low efficiency?

Or something else? [/B]

A combination of those three makes a very difficult load
I think you understood perfectly what makes a load difficult.

A lowering impedance with rising frequency as with electrostatic loudspeakers could be on the list too. Few amps like that.
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Old 21st August 2003, 10:32 PM   #3
Bricolo is offline Bricolo  France
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Default Re: Re: What is a difficult load?

Quote:
Originally posted by jean-paul



A combination of those three makes a very difficult load
I think you understood perfectly what makes a load difficult.

A lowering impedance with rising frequency as with electrostatic loudspeakers could be on the list too. Few amps like that.

OK,


I'm still not decided to build Bob's Peerless Pipes
http://geocities.com/rbrines1/Pages/Peerless_Pipe.html

because of theyr low efficiency (84dB/w/m)
I'm not sure my gainclone would work good with those speakers.


Btw, is a low efficiency speaker, at low volume, a more difficult load that a normal efficency at normal volume? (so, both recieving the same poser)


Jean-Paul: I've read your topic about your hard disk problem. That's a bad news (don't tell me you had the marantz CD62 service manual on it!)
I have some basic skills on computers, and already used data recovery softwares.
Mail me if you want, I'll be glad to help you if I can
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Old 21st August 2003, 10:33 PM   #4
PMA is offline PMA  Europe
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A speaker with impedance highly dependent on frequency. Like Wilson Audio Maxx, declared as 8 Ohm its impedance falls to 2.2 Ohms near 250 Hz.
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Old 21st August 2003, 10:49 PM   #5
Bricolo is offline Bricolo  France
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ok, so:

-low impedance (or low impedance at some frequencies)
-capacitive or inductive
-low efficiency


another thing to consider?
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Old 21st August 2003, 11:00 PM   #6
sam9 is offline sam9  United States
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D. Self has a section in his amplifier book about reactive loads. It is rather involved and the conclusions are not what one might think in all cases.

"...a truly 'difficult' load impedance is one with lots of humps and dips giving significant phase shifts and increased peak dissapation qacross most of the audio band. Impedance dips cause more stress than peaks, as might be expected. Low impedance at the high-frequency end (above 5kHz) are particularly undesirable as they will increase amplifier crossover distortion."

He goes only to deliberatly model some artifially difficult impedance patterns that cause a speaker to draw more current than appears possible but conclused the chances of finding such a bizare curve in real life is very small.

Anyway, it's not a causual bead-time read, but if you are really interested you should read him, if only to disagree.
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Old 22nd August 2003, 12:09 AM   #7
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This is an ugly load:

http://www.quadesl.com/madisound/con..._impedance.gif

Sheldon
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Old 22nd August 2003, 09:55 PM   #8
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Quote:
Originally posted by stokessd
This is an ugly load:

http://www.quadesl.com/madisound/con..._impedance.gif

Sheldon
After 10khz


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Old 23rd August 2003, 01:50 AM   #9
sam9 is offline sam9  United States
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Per the Self article, speaker makers who add Zobels to reduce rising impedance as frequency goes up actually make life more difficult for amps. Ironic, if true.
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Old 23rd August 2003, 03:37 AM   #10
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Default Flat Impedence Sounds Better...

A non zobelled speaker exhibits a rising impedence characteristic, which implies less current at high frequencies but says nothing about the load phase angle.
IME a flat impedence characteristic which implies a load zero phase angle pays much bigger sonic dividends with a typical feedback amplifier than the additional distortion caused by additional load current.
A flat impedence load implies no reflected energy, and it is this reflected energy that causses sonic problems with typical loop feedback amplifiers.

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