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How to measure Magneplanars

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Posted on March 24, 2021 at 03:20:05
SteveJewels
Audiophile

Posts: 196
Location: OH
Joined: August 11, 2018
Contributor
  Since:
September 22, 2019
Perhaps you have seen the thread regarding the train wreck of a 'review' of LRS's including a disastrous attempt at measuring them.

There are a number of people on this forum who, it would seem, have successfully measured Maggies as part of characterizing and modifying them, I would like to hear from them how it was done.

I am about to embark on such and effort myself and would appreciate the insight.

References to REW and microphones used and their placement would be especially helpful.

Thanks!

 

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RE: How to measure Magneplanars, posted on March 24, 2021 at 03:53:18
andyr
Manufacturer

Posts: 12206
Location: Melbourne
Joined: September 2, 2000
Mmmm, interesting.

Yes, I have used REW to measure the output of my 3-way active Maggies (+ subs) ... but I measured them after I had implemented my miniDSP XOs.

That just measures the FR at the listening position (ie. the mic position) - so I have no idea how that compares to the ASR measurements.

I simply place the mic at my listening position - and then measure each channel independently, in case the R PEQ needs to be different to the L PEQ.

Andy

 

RE: How to measure Magneplaners, posted on March 24, 2021 at 07:11:51
dumpingground
Audiophile

Posts: 240
Joined: February 23, 2011
I also have used REW to measure my maggies during various crossover upgrade experiments. My typical scenario is to measure the standard OEM crossover and then from the same measurement position and settings in REW I repeat the measurements to validate/calibrate my crossover mods. I typically will measure 1 meter from the speaker and at the main listening position. For me the most important conclusion is the relative comparison of the before and after.

Where the speakers sit in the room, and where the microphone sits for measuring does make significant differences in the resulting measurement. However, in my case I am most interested in the relative before and after MOD measurement.

 

RE: How to measure Magneplanars, posted on March 24, 2021 at 11:56:25
emailtim
Audiophile

Posts: 2308
Joined: July 2, 2017
A quick, cheap and easier way to get started with REW is to use a USB mic (like the miniDSP UMIK-1 (limited to 48kHz) or the new UMIK-2 (44.1 to 192kHz and lower noise floor) that come with a factory calibration file (not necessarily the most accurate calibration).

Be advised that using a USB mic and USB DAC has the downside of having 2 different clocks which are not in sync. The next best thing is to use a single soundcard for both the mic and the DAC so the clocks are in sync. The downside is it costs more is more complex. You can also Master/slave clock both devices if they provide such features, but again, it adds more complexity and expense.

Since you said you do NOT have a PC source in your signal chain, you will have to follow a different procedure than many here. You will have to use REW to create some sweep wav files with timing chirps and then burn the REW generated wav files to a CD so you can play them on your [CD|multi-disk] player. The sweeps need to be of the same sample rate as your intended measurement sample rates (e.g. limited to 48kHz for the UMIK-1 so you would need a DVD player). It also requires the reference timing channel to be able to play high frequencies so if you are going to measure a sub by itself on the left channel, the timing chip should be on the right channel that is capable of a HF output.

This allows you to measure a playback system without physically being attached to it.

If you intend to measure each driver independently, you will have to protect each driver and only send it a signal within its usable range. This can be done in a variety of ways depending on how you are measuring.

If you measure with a higher sample rate, you will get a better HF measurement if your mic and playback chain is capable of handing the higher sample rates.

You can get a calibrated mic from Cross-Spectrum Labs or they will calibrate your mic if you already have one. They will generate files readable by REW. Note, they are slow. My experience has been that mics are off the most at low and high frequencies.

As for XO's. That is another issue. You need to level set your drivers first because the XO point changes as the magnitude of the individual drivers change.

 

RE: How to measure Magneplanars, posted on March 24, 2021 at 16:13:02
triamp
Audiophile

Posts: 664
Location: USA
Joined: August 6, 2008
I've been using a DEQX with my MG 3.6 for years. Measuring it was pretty much like any other speaker, though I did try to put the mic farther away than I would for a monkey coffin. The hard part always is avoiding reflections.
As the window you need to use is going to be too short to accurately measure bass, measuring the low end is always tricky and when you go to EQ things down below about 150 Hz there's something of an art to it. When I work to set up the low end, I look at graphs I make and I also use warble tones and an SPL meter. Iterate enough over a few weeks and you can get good sound.

I would caution folks against spending too much time fiddling with EQ in a single session, some kind of aural confusion or fatigue sets in and your ability to critically judge the sound of the frequency range you are working to balance can elude you. Better to come at it another day with "fresh ears."

I've gotten what I think are very good results with the DEQX, to which I add some manually set parametric EQ points which I **think** help compensate for room modes, but which may actually be just personal preference.

Here is a plot of the correction filters my DEQX designed, please note that this is also compensating for differing gain levels in the amplifiers that drive the low, mid and tweeter drivers of my MG 3.6

Results for both MG 3.6 speakers were close to each other as you can see from the different colors in the plot.

Very likely that some room correction got "built in" to the woofer filter. I know I have a strong room mode at 50 Hz and you can see a dip in filter response at 50 Hz.

Note that these are NOT frequency response graphs- they are the "correction filters" my MG 3.6's need to bring them close to + / - 1 dB from ~100 Hz to 20,000

Note the increasing level of boost above about 15 kHz. I can't hear much above 12 kHz so I don't care about that, really. Maybe the tweeters do, but so far they have not burned our nor have fuses opened, so I am OK with that boost.




Science doesn't care what you believe.

 

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