Posted by halojoy [ 213.100.118.115 ] on October 31, 2004 at 12:17:46:

In Reply to: Re: active speakers posted by Wayne Parham on October 03, 2004 at 03:48:51:

I agree with Wayne, about drawbacks for lsp-cables vs. signal-cables.
Also true that problems very small when we talk about only 2-3 meters of lenght.
Most active speakers amplifiers are put close to or within lspeakers.
Like in subwoofers.

I am thinking of building an active sytem now.
With three-way speakers. And 3+3 chip-amplifiers.
Right now my idea is to fit all active filters and those six amplifier-ICs onto heatsinks IN ONE COMMON ALUMINIUM BOX.
And to have loudspeaker cables for those 2-3 meters going to lspeakers.
Cables will be standard low price LSP-cables at least 2x6 mm2 area.

The benefit from this will be I can have six volume-potentiometers.
One for each amplifier - lsp-driver (element).
(I will also have one master dual volume knob).
And I have all controls in same box, at my listening position.

When you put all controls in same box as active filter
and use six longer signal cables to amps near to LSP,
you will need VERY good sheilding!
This is because when you turn down volume, a very weak signal will be passed through the signal cables, those 2-3 meters.
And the smaller (maybe below 0.1 Volt RMS) the signal, the less distance to the NOISE-floor will be.
How strong the signal is compared to noise
is expressed as SIGNAL to NOISE ratio, counted in decibel.
for example: S/N 60 dB
The signal is 60 dB stronger than noise.
Turning down signal will give less S/N.

So if we have a long signal cable, we would want the signal to be strong for the lenght of the signal cable.
Preferable 1-2 volt RMS = the full output of a CD-player.

The volume control should then be put very close to power-amps input pins.
As I said, my choice was having all volume controls + Amp-chips in same box
and to have long lsp-cables instead.
Only in the low-impedance thick lsp-cables will the signal be very weak.

/halojoy

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