Apologies here is the correct link to Jeff’s review:
https://techtalk.parts-express.com/...-full-review-of-atc-sm75-150s-midrange-driver
https://techtalk.parts-express.com/...-full-review-of-atc-sm75-150s-midrange-driver
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Joined 2003
General rule is dont measure anything with equipment that you wouldn't listen to it on. If you want to reduce sources of error to a minimum, use the best equipment you have.
For most of what I do, I have a LM3886 (Mauro Penasa's My_Ref) that does well enough, and nCore is used for the high end stuff.
For most of what I do, I have a LM3886 (Mauro Penasa's My_Ref) that does well enough, and nCore is used for the high end stuff.
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Seems like it. I'm ordered a cheap class AB and will be performing a test on a full range driver with the 3 amplifiers mentioned in the original post. We shall see if there is a difference.
For the smoke test I use a cheap 50W amp from PE. I don't care if it burns up. Then I go to my Beringer A300 which seems to be able to power anything. It's not the best but it's pretty darn good for $99 used. Then after everything measures OK I might start switching out amps of different kinds. I haven't made my Le Monstre yet. 🙁
For me, yes. This is mostly out of convenience on a few fronts:
1) Test amps are smaller and lighter than my main system amp, so more convenient on a roll-around cart.
2) Similar to Arthur Jackson's point, my test amps are cheaper so not as much of a concern if something goes wrong.
3) As I hinted at earlier, on multiway speakers I typically start with an amp channel for each driver. That's not the way I intend most projects to end, it's just convenient because I can use an active crossover and control gain for each driver independently. It lets me get a feel for basic performance of the driver combination more quickly.
4) I tend to have some speaker project going all the time. It's more convenient to leave that hooked to an extra system. I also periodically compare new speakers directly to my main system, so having an extra source and amplifier lets that happen almost instantly during listening tests. If you have to rewire things it takes too long, so minor differences in balance or detail would be much harder (or impossible) to accurately discern. There are switch boxes to handle some of this, but you also have to match gains between the two systems, and for me it just makes more sense to have the extra equipment for testing.
I would imagine that the soundcard/audio interface used for the measurements has a greater impact than the amplifier used.
My test amplifier is based on the old National Semiconductor LM12CLK power op amp, now obsolete. Main attraction was simplicity and small footprint, as I was able to squeeze everything into a salvaged aluminium extruded case. It's simply a non-inverting op amp using two resistors and the LM12, plus two diodes spanning the power rails and the output. Nagging concern has been minor dc offset at output and the knowledge that the circuit may not be as good as might be had these days. However, I have on occasion used a Rotel RB-976 instead, with no noticeable difference. Nevertheless, I would like to ultimately get something the likes of a composite LM3886 to put my mind at ease.
I've used a few different amp setups over the years, each with their own pros and cons. I pretty much only do active/DSP builds these days so for me I need to have some kind of DSP in my measurement chain.
Started out with a miniDSP 2x4 + Crown Xli2500. The software interface for that DSP is still probably the best I have used. The software is reasonably fast, has an easy to understand UI, and takes biquad files straight from REW.
Moved up to a miniDSP 4x10HD for the extra channel count. Still had the crown XLi, but had to add a second & third one for testing multi-way systems, which got pretty annoying to lug outside and set up every time I wanted to take measurements. The XLis are nice because of the power they have on tap and they're happy to drive high sensitivity tweeters/compression drivers with a relatively low noise floor otherwise.
I now use a Linea 88C10 and am probably the most happy with it overall. The GUI and preset management is slick and it has tons of useful features including FIR.
Honorable mention is the Hypex amps, although my gripe with them is the filter designer software has a bit of a learning curve to get used to, and presets don't really translate over very well from other DSPs. In terms of perceived (my own flawed perception that is) sound quality, I really think they've got some good stuff. Incredibly low noise floor even when driving a 109dB sensitivity compression driver with no padding.
Started out with a miniDSP 2x4 + Crown Xli2500. The software interface for that DSP is still probably the best I have used. The software is reasonably fast, has an easy to understand UI, and takes biquad files straight from REW.
Moved up to a miniDSP 4x10HD for the extra channel count. Still had the crown XLi, but had to add a second & third one for testing multi-way systems, which got pretty annoying to lug outside and set up every time I wanted to take measurements. The XLis are nice because of the power they have on tap and they're happy to drive high sensitivity tweeters/compression drivers with a relatively low noise floor otherwise.
I now use a Linea 88C10 and am probably the most happy with it overall. The GUI and preset management is slick and it has tons of useful features including FIR.
Honorable mention is the Hypex amps, although my gripe with them is the filter designer software has a bit of a learning curve to get used to, and presets don't really translate over very well from other DSPs. In terms of perceived (my own flawed perception that is) sound quality, I really think they've got some good stuff. Incredibly low noise floor even when driving a 109dB sensitivity compression driver with no padding.
No, not for me at least. I use AVRs for everything, except on occasion, I use a slightly better pre-amp, and amp when I feel like being an audiophile. I don't see any reason to use anything better than an AVR for measuring. After all, I'm designing a x-over. I think any AVR is basically flat in the range I'm looking at. For a 2-way, basically that's 300hz to 10k.
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Joined 2003
Let's be clear, nothing happens automatically, and the only compensation available is linear magnitude response.
For impedance measurement, the calibration process compensates for non-linear response of the interface used and test leads.
For frequency response, either a soundcard calibration is required (simple loopback measurement) or full dual channel measurement used (measure with "use ref as timing and cal").
Poor performance in distortion, crosstalk, channel mismatch, noise floor is not easily compensated for. Friends don't let friends use Behringer UCA202 😉.
I took some measurements with a class D and an AB amp. There was a slight difference. The class D shows much higher peaks. The AB seems to be more linear. Outside of that they are within 1 DB of one another.
I measuremed all the drivers of my current project last night. I used the class D amp. Interestingly, I forgot to put a cap inline with the ribbon tweeter. It did not blow up the amplifier as I was told it would. It warmed up for sure, but it was fine. This is good because now I know my tweeter is totally in the right phase for making the filter. I forgot to take ascreenshot of the comparison.
I think everyone is good using whatever amp they want for measurements. Any peakiness would be smoothed out when you export the frd with the standard 1/24 smoothing.
I measuremed all the drivers of my current project last night. I used the class D amp. Interestingly, I forgot to put a cap inline with the ribbon tweeter. It did not blow up the amplifier as I was told it would. It warmed up for sure, but it was fine. This is good because now I know my tweeter is totally in the right phase for making the filter. I forgot to take ascreenshot of the comparison.
I think everyone is good using whatever amp they want for measurements. Any peakiness would be smoothed out when you export the frd with the standard 1/24 smoothing.
Be aware of possible DC between power amp output, which is important if you connect it to your interface input! I bet nobody wants to fry their sound interface. So the advice should be rewritten to something like this:
I think everyone is good using whatever amp they want for measurements using a microphone. If you are probing power amp output with second channel, use amplifier that has no DC on the outputs!
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Yes, a real risk. Last year I fried a laptop for this very reason... Some mistakes are painful enough to make a memorable impression.
While I won’t play DC risks down, lots if not most audio interfaces have coupling caps on the input. Mine do. It’s sound practice in PA and recording to block DC wherever possible.
Furthermore: use pads and protecting zeners. Serious AC signals ruin inputs too.
Furthermore: use pads and protecting zeners. Serious AC signals ruin inputs too.
I honestly forgot to check the distortion and the waterfall measurements. I was mostly concerned with frequency response accuracy where the difference was negligible.
I use whatever amp with no regard other than convenience. I guess cause I measure/tune so many different 4-5 ways and other speakers in different locations, indoors and out, that logistics matter more than anything.
Plus, in complete frankness, I don't think it makes a bit of difference unless you're into chasing how low you can get distortion measurements (which I also don't think make much of a difference beyond about 60 dB down).
Needless to say that's for small signal, or close to it, measurements. Large signal is with whatever amp will be doing the driving.
Plus, in complete frankness, I don't think it makes a bit of difference unless you're into chasing how low you can get distortion measurements (which I also don't think make much of a difference beyond about 60 dB down).
Needless to say that's for small signal, or close to it, measurements. Large signal is with whatever amp will be doing the driving.