Attenuators and "Speaker Interaction"

tekbow

I've been looking at buying a more modern attenuator than the basically a big resistor network thing I have now.

One of the units I've been looking at was the rockcrusher recording, and I thought I'd ruled out the likes of the 2 notes torpedo reload, until I started finding threads on issues with squealing from some rockcrusher units that Rivera don't seem to be able to explain.

So I looked a little deeper.

Both units are reactive loads, but the the 2 notes Reload reactive load feeds a built in power amp whereas the rockcrusher does not.

So it's said that the reload isolates the speakers from the amp and that there is no longer any amp/speaker interaction, whereas the Rockcrusher does not isolate.

Can anyone quantify speaker interaction for me?

Does this even make a difference if the 2 notes power amp is a wideband hi-fi power amp? Should it not faithfully reproduce and amplify the amps signal which is then filtered by the response curve of a given speaker?

If the point of a reactive load is that the amp sees a "speaker like" impedance in the attenuator, is the rockcrusher not isolating the amp from the speakers to an extent also?

ICBM

All attenuators isolate the amp from the speaker and prevent interaction. Those which are dummy load/re-amp systems do it completely - there is no way anything happening at the speaker can influence the amp at all - and those which are resistive/inductive conventional attenuators almost completely once the setting is below about -3dB. Whether it matters is debatable.

A bigger problem with most conventional attenuators as that as the level goes down, the damping on the speaker increases - this is what's mostly responsible for the 'strangled' sound that attenuators often cause, and probably why some people think the load/re-amp systems sound better. In fact, it would be possible to design this problem out of a conventional attenuator, but as far as I know it hasn't been done.

tekbow

Thanks @ICBM, so in summary, no reason to fear the load re-amp solution because the non re-amp solutions are in fact isolating the amp from the speakers reasonably quickly in any case.

ICBM

tekbow said:

Thanks @ICBM, so in summary, no reason to fear the load re-amp solution because the non re-amp solutions are in fact isolating the amp from the speakers reasonably quickly in any case.

Yes.

tekbow

ICBM said:

tekbow said:

Thanks @ICBM, so in summary, no reason to fear the load re-amp solution because the non re-amp solutions are in fact isolating the amp from the speakers reasonably quickly in any case.

Yes.

Thanks @ICBM. Think it'll be the 2 notes for the added functionality then.

TimmyO

I had a Reload when I have a JCM800 - it was awesome. Feel was great and the tone control was great for a little tweak to the sound to match the unattenuated 

tekbow

@TimmyO, thanks mate, good to know that contour knob does actually compensate

ecc83

The speaker is pretty well "decoupled" from most valve amps! Those amps without feeback have virtually no "damping factor" and even the bigger, 50W + jobs with some NFB probably only manage a DF of 1 or 2! There are amps with feedback "resonance" controls but I always found this pretty subtle (but then I AM rather mutton)

It is in fact this high output impedance that makes valve amps so loud compared to a watt for watt transistor. The "current drive" tends to beat thermal compression in speakers.  Put another way, valves ain't TOO fussy about loads.

ICBM has a point about the "clamping" of an attenuator. Do simple sums and  the bottom R comes out at only an Ohm or two, far lower than most valve amps manage.

Then, any speakers put in series means even an INFINITE damping factor does sqaut.

Dave.