I read this and listened to this on my ipad. Not interested in responses related to the ipad. I heard a difference. I thought recording two was, a little crisper, analytical, forward, livelier, compared to the first. I thought it fun and i did it without foreknowledge of amps (not that it would have mattered for i have never listened to either but knowing the brands could have made a guess according to my readings not listening, which would have confirmed what i heard). Very imteresting and a fun experiment. Thank you.
A listening test of two power amps
Hello,
It's my first post here. I've been using two power amp setups for my main stereo and I've been curious to see if I can really discern any acoustic difference between the two. One setup involves a bi-wired high-powered stereo power amp and the other uses a pair of identical lower-powered amps with which the speakers, a pair of Tannoy System 12 DMT II monitors, are vertically bi-amped.
I decided to devise a listening test involving a mono acoustic recording made with a valve-condenser mic positioned at my usual listening position. I've used a relatively simple method to ensure that the recordings are level-matched. I've chosen a mono recording method since my goal is, principally, to evaluate the "tone" of the two recordings. I've been inspired to do this test after reading W. A. James' eBook "High end audio on a budget". The aim of the listening test is to try and discern which power amp setup provides the most realistic rendering of acoustic instruments. I thought that a mono recording might help the listener concentrate on the tone. After listening, I think it does. It's less distracting, especially on piano, where stereo or other multi-mic recording setups tend to splay out the notes across the stereo field.
I made two recordings for the test and will place links below so that the audio can be downloaded. I won't at this point give the make and model of the power amps involved, but this is the method used:
Method
1. I created an audio file with white noise at -10dB RMS and put the file on a Logitech Media Server so that I could play it on my stereo using a Raspberry Pi 3 with Audio Injector Pro card and RCA interface (192kHz 24bit DAC).
2. I then put on an LP on a Pro-ject 1.2 and set the volume to my usual listening level on a Quad 34 preamp. Following this, I then played the white noise and used a decibel meter, positioned next to the mic, to measure the level. It measured 67.3 dB.
3. Still playing the noise, I set the record level on a portable Tascam digital recorder arbitrarily to somewhere above -15dB. The microphone used was a large diaphragm valve condenser mic. The Tascam was set to record at 192kHz 24bit.
4. I then recorded the first track of the LP on the Tascam.
5. After that, I wired up the other amp configuration. I played the white noise and adjusted the volume of the preamp such that the decibel meter again measured 67.3dB at the position of the mic. The volume control on the Quad 34 is stepped, so I was lucky it matched!
6. I then recorded the same track on the LP as before, leaving the Tascam record levels unchanged.
7. I tidied the two recordings in Ardour (trimming start and finish only) and exported each as a 192kHz 24bit Flac file. I did not adjust the gain on either recording.
8. I listened to the recordings on the computer with a pair of AKG K501 headphones and Focusrite Scarlett interface.
Results
At first, I could distinguish a marked difference between the two. But now, I'm uncertain of the first qualitative difference that I'd noticed but I have noticed other more subtle differences (for the moment anyway). And that's why I'm here!
It would be wonderful if some people here could listen to the recordings and say which recording produces the most realistic rendering of the three instruments therein, and why. The instruments being piano, drums and string bass.
I've given the two files nondescript names: e.flac and t.flac. If anyone needs a different format or for me to down-sample, please let me know.
Finally, here are the files:
https://escuta.org/webtmp/e.flac
https://escuta.org/webtmp/t.flac
Cheers,
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- 65 posts total
BTW, I don't believe in static tests very much. That is, as a builder I use static tests such as frequency sweeps, voltage, etc. to guide my work, but I also know that these types of static tests may not cover all possible dynamic situations. By this I mean frequency response, output, distortion. We use these static tests and basic models because they are damn convenient and accurate for what they are, but the testing I'd want to see done, which I never see done, is to compare the output at the speaker or across the speaker cable with actual music. With demanding speakers or loads we may very well see and measure dynamic behavior which is more complicated and unexpected based on the traditional static measurements say taken by Stereophile. |
@erik_squires "1. Match level by multimeter instead of SPL. Get a 60 Hz signal and check the output on either speaker. You can get really accurate this way." I am a little ambivalent about using 60Hz sine and voltage to verify output level balance. It can tell you something about what an amplifier is doing, and something about speaker efficiency, but I am not sure it can translate into anything about sound quality. There is also the problem of ensuring the meter you are using is measuring true RMS versus average AC voltage. If you are trying to use that method to balance output level, I think you would be better to use pink noise which has a full frequency range. Measurement becomes more of a problem, but it more closely resembles what you may hear when converted to sound using real music. In other words, since speakers are a reactive load, frequency and duration affect response and the amplifier’s drive of voltage across a frequency and time response will vary and may affect actual perceived sound volume. I don’t really understand why SPL would be frowned upon. It is specifically an agreed measurement of perceptual sound volume reference. It is tailored for a specific frequency range and can be A or C balanced for perceptual preference favoring broad frequency response (A) or lower frequency weighted (C). The only caution for use in this testing is that the ambient noise level is maintained the same, and the SPL is taken from the same location in the same environment. If you are within 0.1 or 0.2 db that is considered well matched. |
The anti-testing and anti-measurement crowd certainly makes an impression. It's a good thing those folks aren't doctors or pharmacologists, or we wouldn't have gotten any further than "which medicine do I think makes me feel better..." [which, back in the day, is how people chose which, literally, snake oil product they'd consume] I think it's a great post and even if not scientifically perfect, this is the type of thing that can actually validate all these claims of magnificent differences in amps, cables, whatever. So I have to assume they don't want to know what the emperor is wearing, or not. |
- 65 posts total