Addicted to Fun and Learning
- Oct 10, 2020
Indeed - but we should qualify the extent of these differences - even pretty 'bad' amplifiers in this sense (high output impedance) typically result in around ~1dB variation in FR across the audible spectrum, one 'bad' example here:I agree but surely if EQ frequency correction is assumed it should be stated. Differences in FR are clearly fairly important differences.
Amplifier output impedance:
Resulting amplifier FR deviations:
You see that the FR deviation across the whole spectrum is ~1dB maximum even in this severe case. Audible for sure, but subtle and definitely not terribly offending.
In practice IMHO it makes no sense to correct even for this, as most of the variation is in the low frequency region where one will typically anyway apply EQ based on in-room-measured loudspeaker response (to fix room resonances). ~1dB differences in amp response then become completely insignificant.
With amplifiers that have much lower output impedance (e.g. Hypex, Purify, Benchmark, new Topping amps etc...) the FR deviations will become much smaller (here's a nice article and spreadsheet from Benchmark that shows how this can be calculated) - so it is realistic to expect around 0,2-0,3dB variations with well performing amps. Probably no need to EQ the amplifier response anymore with such low variations
This is why I said:Thing is the amps did sound distinctively different and if they all sound the same that shouldn't be true.
often misquoted "all amplifiers sound the same" argument
To my understanding the "all amplifiers sound the same" argument is often linked to the famous Richard Clark $10,000 Amplifier Challenge - you will see the challenge conditions also specify the use of EQ to remove FR deviations between amps (such that may also come from differing load dependence between amps). This is of course completely reasonable - the challenge was in my view well thought-out.
Maybe we should instead be saying "all non-broken amplifiers sound the same with a little EQ, assuming no-clipping condition and identical levels". A mouthful - no wonder people shortened it
The FR deviations will be fully determined by the amp-loudspeaker combination and therefore are static as long as you use the same combination. I.e. the theoretical amp corrective EQ does not need to change for as long as you use the same amp-loudspeaker combination.Am I right in thinking that some amplifiers will have varying FR depending on the load? If so, does this not mean that it cannot be simply sorted out via EQ? ie if you have a changing FR, you need a corresponding changing EQ correction?