Imagine you have a 3 way speaker and you want to Tri-amp it using an analogue active crossover. The amps are not all the same and let’s say that 2 of them have 20dB gain but the 3rd one has 26dB gain. What I am trying to get my head around is this; if I use a dedicated volume control to effectively reduce the gain of just that amp from 26dB amp to 20dB and permanently leave the volume control at that level of attenuation, have I effectively reduced the gain to 20dB for all input levels, or will the attenuation in dB be different as I vary the input level ie turn the volume of the source up or down ?
Not easy to describe, hopefully you will get my drift . . .
Not easy to describe, hopefully you will get my drift . . .
I would use a fixed 6dB pad in front of the amp, assuming you need the same gain on all channels. All channels will now have the same gain at all playback levels.
The pot could introduce level and noise problems.
The pot could introduce level and noise problems.
Don't forget the drivers may have different efficiency. You have to compensate for that as well. So it becomes AmpGain + SPL@1W must be constant for each channel. But to answer your question, yes, if you adjust the gains at a specific volume level, they will be correct at all levels.
If there are only small differences in efficiency between the drivers I would adjust for them in DSP.
If all gains are otherwise correct, yes. You could install an L pad (two resistor attenuator) in the crossover
circuit for the higher gain amp. The L pad attenuation is not a function of the input level.
circuit for the higher gain amp. The L pad attenuation is not a function of the input level.
Won't that analogue XO have it's own adjustments for levels built in?
Certainly I used the CX3400 that way
Certainly I used the CX3400 that way
Yes I’ve been thinking about equalising sensitivities as well! Ideally I suppose your amp gain adjustments would perfectly compensate for the sensitivity differences between the drivers, but that is never going to happen in practice. Some people seem to prefer autoformers to resistors for making adjustments - is their a consensus view that they are more transparent ? (I’m certainly a fan of TVCs / AVCs).
My understanding is that you want a woofer that is less sensitive than the tweeter because you don’t want to be padding down a woofer as it would require huge values.
That is typical. And you cannot use a pad between the amplifier and woofer regardless.
Can't is a strong word. However it shouldn't be necessary in any case when you are using a gain control for the purpose.
Why do you say it will not?
I have indeed seen some use a significant value of power resistor in series with the woofer.
It is obviously physically possible to do so. However, this did not work out well.
And of course there is a large amount of wasted power.
It is obviously physically possible to do so. However, this did not work out well.
And of course there is a large amount of wasted power.
As you say, generally you do not want a resistor (or L-pad) in series with a woofer as it degrades damping factor.
Why degrades, why not say changes? Of course the change may not be wanted if you haven't anticipated it.. but for this discussion if you do it right then there shouldn't be a problem.
I was referring to the chances of the gain factors of your chosen / available amplifiers exactly compensating for the sensitivity variances between your chosen drivers.
Where a gain (volume) control is available, I'm thinking you wouldn't say the same thing?
It's not. It was being discussed over whether it's possible at all. (It's not exactly on topic.)
if the amps had volume controls (as referred to in my opening post) then of course you could pretty much level things up, but I wasn’t referring to that type of situation.
A simple method is get a commercial analog active XO unit and use it to find out where the levels and XO frequencies sound best with your drivers and amps. I'm using the ART CX310 and CX311 which have 40dB of level control on all outputs. They are not expensive and actually work very well. The flexiblity certainly made the switch to active very easy. Later if you wish to replace it with something of your own design, at least you will have some target values.