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Andy,Many AC voltmeters don't have flat response to 20khz. Many don't have response above approximately 400Hz.You can check yours as Speedskater suggested by attaching directly to your signal source to verify it.Dave.
Yes, your scope should work okay.BUT, be VERY careful with grounding since your scope is AC powered and probably not floating like your voltmeter.I would recommend using your voltmeter to be on the safe side......but (obviously) only if it has response to 20khz. (You need to characterize it for future usage anyway.)Dave.
Yes, your scope should work okay.BUT, be VERY careful with grounding since your scope is AC powered and probably not floating like your voltmeter.Dave.
* the mic is a calibrated mic (so has a calibration file which is fed into REW)
Thank you Dave for your suggestion that the multimeter was not reading true. Did the same measurements with the CRO this evening - and got an identical voltage reading from 6khz to 30khz. So that is a relief - it would seem my amp does not 'have a problem' with 2 ohms ... it can pump out the same signal voltage from 6Khz to 30Khz.So this leads on to ... if the amp is not at fault ... why does REW show a steep drop-off at 16Khz when:* the mic is a calibrated mic (so has a calibration file which is fed into REW)* the amp is delivering flat to 30Khz?Andy
A microphone measuring system is a poor choice for testing amplifiers.
andyr, where is your mic located when the measurement is taken? It is common to see a roll off in high frequencies at the listening position due to the rooms absorption characteristics. If the mic is maybe 3 inches away from the tweeter on axis and time gated eliminate the sound from the other drivers then you have a problem. You haven't quantified the magnitude of the HF roll off. How many dB down is it at 20kHz.?Scotty
Dunno. Either your speakers are indeed rolling off above 16khz and/or it's something in your measuring setup/scheme.Dave.
I believe that you can't use REW without using a mic?....................................... ........Regards,Andy
Then it's the wrong tool for measuring an amplifier.Only use microphones for measuring rooms and loudspeakers.
Perhaps you should read my thread, Kevin - so as to get the full story?I'll summarise for you, if you don't 'get it'.Andy
A different thread than this one?In this thread, post #1 you are measuring an amplifier.
Now that we know you own Maggies, have you looked at Stereophile's measurements of the MG 3.6R? Might be useful:http://www.stereophile.com/content/magnepan-magneplanar-mg36r-loudspeaker-measurements#E5xw1jfjkmOsWYVL.97Best,Anand.
Another thing. If you were measuring at the listening position, and making measurements greater than 300Hz, you will have some erroneous data if measuring both speakers at the same time due to comb filtering. Best to do either measurements outside (groundplane would be best) or have the mic within a few inches of the ribbon (as Scotty suggested) in order to minimize room effects. And measure one speaker at a time.
Andy,At this point I'm not sure what your objective is.You've pretty much confirmed your amplifier is not rolling off drive at high frequencies. Unless you have some other mystery device between the tweeter and your amplifier, there's nothing left to test.If both left and right tweeters are measuring the same, then you must assume they're working correctly. Any measurement anomaly from the expected flat response to 40khz MUST be the result of your measuring scheme and not a problem with the tweeters themselves.I hope you're not going to apply equalization to the tweeters to boost their outputs. My recommendation would be to declare victory on this and move on to the next issue.Dave.
He's either not telling the truth or doesn't have a clue what he's doing. (I'd bank on the latter.)Dave.
If you really want to know what's going on, just post a query to the other forum. That "other guy" Satie will reply and set you straight. He's got an answer for everything. Dave.
