View Single Post
Old 07-12-2019, 08:59 AM   #23
Peterk312
Human being with feelings
 
Peterk312's Avatar
 
Join Date: Feb 2012
Posts: 118
Default

Quote:
Originally Posted by serr View Post
Looks pretty conclusive all right!
Yes. And I can't thank you enough for suggesting this kind of test.

Quote:
Originally Posted by serr View Post
If you were to render those test samples first, you'd be able to see the waveform and then tell conclusively WHICH speaker is reverse polarity.
I think I can still add that to the test project, right? Just add a track above each pair of test tones with the JS plugin and I can record the output of the plugin without a mic? Or do I need to do the test over again?

Quote:
Originally Posted by serr View Post
If I were betting on a race, I'd speculate that the one not labeled "positive phase" is reverse.
That's the speaker that also has the later firmware version. One of the only things I've been able to get out of a tech support rep from Alesis is that the firmware revision may have been because of a change to "internal parts." On that sticker that says "Positive Phase" it says the words "MICRO EEPROM," and that's some kind of memory chip controller. I don't know if that's what was changed between the two monitors, but it would be a plausible reason for firmware revision. Just wish Alesis would give me a definite reason. You'd think they still have archives on this, but the rep seems too disinterested.

Quote:
Originally Posted by serr View Post
You mentioned a digital connection on these speakers? Purely academic but it might be interesting to see if they're still reverse with a digital input. I'm not familiar with a digital audio connection over a serial com port. You mean that old 9 pin serial port from late 20th century?
The serial port is not for audio signal. It's only for communicating with the PC through a Windows application (XP believe it or not) by connecting from the PC to one monitor and then that monitor to the other. The Windows application allows you to assign the monitors to a Channel, and then from the PC you can change trim, EQ, mute, and presets to both monitors at the same time. This works perfectly with both monitors, as I can tell from the LCD screen in the front. The out of phase relationship appears to be due to something else.

Quote:
Originally Posted by serr View Post
I'd rewire the input jack on the reversed one. (You may be able to correct for the digital input if you find the analog signal coming out of the built-in DA converter. Should be feeding the same input to the built-in crossover.) Then I'd scribble on the front with a sharpie "positive phase". That way people will ask you what that's about and you can tell them about Alesis screwing up.
I still have one issue though that makes me lack confidence in using these as reference monitors. These monitors have a spec that says the frequency response is 50Hz - 20kHz +/- 1.5 dB. I don't know if reversing polarity on one monitor is going to alter this. That's one reason I was going to record a sweep and look for obvious irregularities in output. You'd think though it's the out of phase relationship that causes irregularities, but you'd have to record both speakers at the same time to detect that. I think I need to do this:

1. Sweep with each speaker individually (as per above procedure), both in phase and out of phase. If the out of phase condition shows irregularities in response then the quoted spec should be okay if I go ahead and use these by swapping polarity on one monitor.

2. Sweep with both speakers both in phase and out of phase, again to detect if there are odd irregularities. I think here I have to put the monitors close to each other and the mic fairly close (maybe a foot away) so that the room acoustics don't get picked up.

Last edited by Peterk312; 07-12-2019 at 09:08 AM.
Peterk312 is offline   Reply With Quote