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Woofer/Amplifier questions [message #39269] Fri, 29 November 2002 00:12 Go to next message
Anonymous
Take two different amplifiers;

Amplifier #1

100w into 8 ohms
200w into 4 ohms
400w into 2 ohms

Amplfiier #2
100w into 8 ohms
100w into 4 ohms
100w into 2 ohms


Amplifier #1 is a conventional design where power doubles
as impedance halves.

Amplifier #2 is a breed that monitors load and lowers the rail
voltages to maintain the same power regardless of load.


Two questions.

1. If amplifier #2 has variable rail voltages, would clipping
occur sooner at 2 ohms vs. 8 ohms load? Suppose rails are +40v/-40V
at 8 ohms, and +20v/-20v at 2 ohms. I argue that you would
clip easier on transients at 2 ohms vs. 8 ohm, others say
100w = 100w, makes no difference.

2. Woofers have an impedance curve that varies with frequency.
Hypothetical -> if an 8 ohm woofer's impedance is 2 ohms
at 60hz, does amplifier #1 output 400w @60hz whereas amplifier #2
only outputs 100w across all frequencies, in which case, people
may interpret amplifier #1 as driving woofers better due to
more power ?



Woofer/Amplifier answers [message #39270 is a reply to message #39269] Fri, 29 November 2002 00:56 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18726
Registered: January 2001
Illuminati (33rd Degree)
Since power is proportional to the square of current, changes in current effect power even more than changes in voltage. So a feedback mechanism should sense not only voltage but current also.
Re: Woofer/Amplifier answers [message #39284 is a reply to message #39270] Fri, 29 November 2002 22:56 Go to previous messageGo to next message
Anonymous
This whole thing started on the car sound forum where
someone posted a message saying that the Brax X2000 car amplifier
sounded ballsy as compared the JL audio 300/2 amplifier,
both rated similar in power, 190w/ch into 4 ohms (Brax),
150w/ch into 4 ohms (JL). The author of the message
wanted an explaination why Brax sounded like it was
driving the dynaudio drivers better.

Since nobody offered a reason why Brax was sonically better,
I offered a possible reason. In a nutshell, I said it
was power that was the determining factor. The Brax is a dual mono
bridged design, it almost doubles power as impedance halves,
1100 watts total @ 1 ohm.

The JL is the amplifier that lower rail voltages to maintain
a constant 300 watt in the 1.5 ohm - 4 ohm range.
I was being nice and said you are comparing a 1100 watt amplifier
to a 300 watt amplifier, this is technically an unfair comparison - hehe.. I also offered an esoteric thought --> Dual mono bridged brax,
the speaker sees 2x rail voltage since it's bridged, clipping occurs
probably at a higher voltage whereas the JL amp will lower the voltage
rails if impedance dropped, hence I'm thinking it may clip sooner.

The JL audio guy comes on the forum to defend his amplifier technology stating that the ideal amplifier doesn't double power as impedance is
halved, instead, the ideal amplifier supplies constant power
regardless of load. This is fine theoretically, but you
can't defy the laws of physics - hehe To maintain constant power
at varying loads, there is a hidden penalty, the penalty is that
the rails voltage drop. The drop in rail voltage would seem
to cause a loss of dynamic headroom as the audio signal may
reach clipping much sooner.

I posted a message on another forum and Nelson Pass
said JL audio is more concerned with marketing than amplifier
design - lol You know who Nelson Pass is? Famous amplifier
designer, founder of Threshold and now Passlabs.com

Another esoteric thought --> if someone made a 1/4 ohm
woofer and a matching amplifier that is 1/4 ohm stable,
suppose the rail voltages are +10/-10v to produce 400w peak.
The output signal swings from zero to 10 volts, anything
higher is clipping correct?

Take the amplifier of today, +55/-55v rails, driving
a 8 ohm woofer, that is about 400w peak. The output
signal swings from zero to 55v, anything higher is
clipping correct?

What I'm wondering is --> can you distinguish between
these two hypothetical amplifiers, both the same power rating,
or will the low voltage amplifier be more likely to clip
on transients and would it be more audible ?

So far, nobody has not offered an explaination on
various forums, even the technical ones. The solid
state forum, people are scratching their heads.

Perhaps I think too much ?


Re: Woofer/Amplifier answers [message #39286 is a reply to message #39284] Sat, 30 November 2002 00:15 Go to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 18726
Registered: January 2001
Illuminati (33rd Degree)

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