Magneplanar Tympani 1C crossover

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GregDunn

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Magneplanar Tympani 1C crossover
« on: 7 Jan 2018, 09:06 pm »
Hi, first time poster here.  I've owned my Tympani 1C speakers for 42 years and up until now haven't been too adventurous with them.  I have taken the time to work with speaker placement and they are bi-amplified.  But it's very hard to find information about active crossovers for these speakers; I've scoured the net for data, and of course had conversations with factory personnel but there doesn't seem to be a large database of people who have done this.

Of course there are people who have worked with the Tympani 1D and IV, as well as many who use the newer MG series speakers - but they all behave a little differently and of course all have different default crossover frequencies.  What I have done so far, based on limited anecdotal data and of course the original Audio Research recommendations, is to set them up with a crossover frequency of 1 KHz and the default 6 dB/octave Butterworth slopes (incidentally, the passive crossover is set to 1325 Hz, but active crossovers seem to typically be set lower with the Tympanis).  My crossover was based on the original ARC designs, and they're pretty simple.  If this is optimum for the speakers, so be it, and I'll leave it alone; they do sound great as they are.  But I'm curious whether anyone else has these speakers and has played with the crossover frequency or slope and learned anything helpful in the process.

I know if I change the slope, I'm going to have to reconsider the tweeter phase as well, based on whether it's an even- or odd-order system.  That's so much easier to do today than when I originally built my crossover, so it's already been factored in.

So, anyone with info to share?  I'm willing to play around with it myself of course, but I figure I might as well see what everyone else has done before I get involved in a lengthy listen/adjust/correct/listen cycle that will take a while.

Roger Gustavsson

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Re: Magneplanar Tympani 1C crossover
« Reply #1 on: 8 Jan 2018, 02:51 pm »
There is not much to gain by biamping with such a high crossover frequency. The coil and cap needed for the passive high level crossover are really a very short signal path. It is a totally different thing to do it below 300 Hz or so and with higher order crossovers. Then you distribute the power more even. A first order line level crossover calls for double the power amps.

GregDunn

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Re: Magneplanar Tympani 1C crossover
« Reply #2 on: 8 Jan 2018, 06:31 pm »
I am in the process of merging a subwoofer into the system as well; right now, it's crossing over at 60 Hz and I think I'm using 12 dB/octave cutoff on both the mid and sub amps.  The sub has a 1200W amp to itself, and the mid-high portions of the system each have their own 200 w/channel amp.

As for the mid crossover frequency, I think it's about as low as I can safely go; I doubt the tweeter panels have much response below 1K and they're already taking about as much power as the LF panels on most program material (I have LED power meters hooked up separately to the mid and high amps).  One of the thoughts I had was that increasing the crossover slope could possibly reduce the power demands to both panels by minimizing the overlap - but if it causes problems with the crossover region and frequency response then of course it would be a poor compromise.  That's why I was curious about what others are doing with active crossovers. 

The factory recommendations are very vague: "through the use of ideal crossover points and slopes, most systems will provide higher musical definition through bi-amplification." and the specs say "1325 Hz - 6 db / octave; may be bi-amplified with 1000 Hz external crossover."  So the implication is that 1 KHz is a better choice, though they don't suggest a slope; the ARC active crossovers of the era were all 6 dB though.

GregDunn

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Re: Magneplanar Tympani 1C crossover
« Reply #3 on: 17 Jan 2018, 08:57 pm »
I decided to go ahead and experiment with the crossover, since there doesn't seem to be much data available.

I'm using a miniDSP 2x4HD for the mid-high crossover, and it has a variety of options available for the filtering.  I originally set it up so that I have a 1 KHz crossover, both filters 6 dB/octave Butterworth and listened to it for an extended period of time to be sure I had everything else right.  The miniDSP has a nice feature where you can set up multiple configurations and switch between them, which was very helpful in that I can make two configs with only one parameter changed between them, and switch quickly while playing music.

I set up a second config with a 12 dB/octave Linkwitz-Riley (which looked like the best option among the higher-order crossovers) and fiddled with it for a while.  I did have to adjust the mid/high relative levels (and of course the tweeter phase, it being a property of the 12 dB L-R that it's reversed) because there was less driver overlap and it affected the mids a bit (this was evident by listening alone, and confirmed with sweep measurements).  Once I had this config set up to my liking, I did an extended session where I switched between them and tried to hear differences.

The result?  For all practical purposes, I can't hear a difference that I can put into words.  I think maybe the 12 dB crossover might be a little better through the midrange, though it's anything but dramatic and it might be a result of the level adjustment as much as reducing the driver overlap.  I spent a lot of time listening to selections which demanded good transient response because that is supposed to be a potential weakness of the higher-order crossovers.  Again, nothing substantive to report.

The main difference, which is not imaginary, is that my tweeter amp is not being asked to deliver as much power now; the power meter indicators are clearly not registering the same values as before.  This is not a surprise, as it's one of the benefits I hoped to accomplish by switching crossover types - the amp is being asked to put out much less power below 1 KHz.  I don't see an obvious difference on the mid amp, though surely it's not being pushed as hard above 1 KHz now either.  These are good things.

So, preliminary results seem to be positive.  The system still sounds great and possibly has improved a minuscule amount.  I've learned more about integrating crossovers and though the information is mostly anecdotal, I wanted to share it anyway.