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Old 16th November 2004, 08:22 AM   #1
Prune is offline Prune  Canada
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Default Crossover points and music power distribution

I'm working on plasma tweeters, and, assuming it all pans out, I'll need to find a proper crossover point. Of course, I'm limited by the hardware, but I also want to take into consideration what the best crossover point from the point of view of sonics is. The engineering limits of where I can crossover is perhaps even below 500 Hz, certainly no higher thank 1 kHz. With this in mind, what is recommended?

Additionally, so that I can calculate how much power the low-end frequencies amplifier (driving dynamic speaker) will need to get a matched setup, does anyone have any information on the approximate distribution of power vs frequency of various music types?
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Old 16th November 2004, 03:28 PM   #2
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Well, the ear is most sensitive in the 1kHz to 4kHz range, so it would be desirable to cross over before that, with 500Hz being a very good choice. Crossing over even lower, say 300 Hz, has its attractive aspects as well, however, power handling requirements go up dramatically. The information I have shows that for typical orchestral music, the 250-500hz octave contains the most energy, on average, reaching 10 acoustic watts, peak. (vs. 4 peak watts in the next lower octave of 125-250, and 2 peak watts in the next higher octave, 500-1k). The classic crossover point of 500Hz seems to be the best balance, as well, since it equally shares the audio spectrum. 5 octaves to the bass transducer, and 5 octaves to the treble transducer.
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Old 16th November 2004, 04:05 PM   #3
Ron E is offline Ron E  United States
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FYI, Relentless heavy metal music approximates pink noise in spectral content, this means equal power per octave..

Some studies have shown RMS power is less for most music in the treble, but peak power is the same as in the bass octaves...
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Old 16th November 2004, 04:37 PM   #4
Pan is offline Pan  Sweden
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The amplitude sensitivity is highest at 1-4k but I have not seen any studies showing that this goes for phase distoriton. Some authors have claimed high sensitivity below 1.5-2k, so crossing above that would be recommended according to that. I like to think that with the fundamental as a basis and starting point, the higher up the crossing the better. The first harmonics are much higher in amplitude normally and it seems they should be most important to be in correct phase relationship with the fundamental.

Power/peak power requirements,

think that 400Hz is the point for most music in general where the power is equal above and below. The amplitude demand is highest in the mids, almost as high in the tweeter range and the lowest in the bass.

Some modern synth/electric music may alter this thumb of rules though. So, a 200W amp to the mid, 100W amp to the tweeter and 50W amp to the (sub)woofer may not be as crazy as it sounds.

As always, it depends..

/Peter
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Old 17th November 2004, 12:06 PM   #5
Andy G is offline Andy G  Australia
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Default A simple little Excel app...

.. based on a breakdown of power levels in a PA book I have ,
I designed this little application.

http://users.tpg.com.au/users/gradds/power.xls

naturally its only very rough...

for a 2-way just enter the same no in each cell.
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Old 17th November 2004, 02:59 PM   #6
markp is offline markp  United States
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Quote:
Originally posted by Hornlover
Well, the ear is most sensitive in the 1kHz to 4kHz range, so it would be desirable to cross over before that, with 500Hz being a very good choice. Crossing over even lower, say 300 Hz, has its attractive aspects as well, however, power handling requirements go up dramatically. The information I have shows that for typical orchestral music, the 250-500hz octave contains the most energy, on average, reaching 10 acoustic watts, peak. (vs. 4 peak watts in the next lower octave of 125-250, and 2 peak watts in the next higher octave, 500-1k). The classic crossover point of 500Hz seems to be the best balance, as well, since it equally shares the audio spectrum. 5 octaves to the bass transducer, and 5 octaves to the treble transducer.
500hz is right in the middle of the male voice and is not ideal for a crossover freq as such, lower than 300hz is much better to avoid the problem. It is much easier to create 10 acoustic watts at mid freqs than it is to make 4 watts at lower freqs, it takes many more electrical watts for the movement of enough air to get the same spl at 200hz as 1khz. I have read that it is actually 200hz for the 50/50 point in electrical power over the audio spectrum.
Plasma drivers have only been used for the very to end of the audio spectrum, how low do you think your going to get? Below 5khz is not going to happen! The amount of power(and voltage) needed to get below that in a plasma will be aproaching the limits of relativity and also make one helluva lot of ozone!
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Old 17th November 2004, 03:36 PM   #7
Prune is offline Prune  Canada
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Regarding phase, what about his crossover design that passively equalizes the phase:
http://www.geocities.com/kreskovs/Crossoverdoc.html

In a 2-way system crossed over at 500 Hz, using a passive line level crossover, about equal power for each amplifier would be a good assumption then?
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Old 17th November 2004, 03:36 PM   #8
Prune is offline Prune  Canada
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I'm not talking about corona discharge tweeters, but Hill Plasmatronics-style DC glow discharge tweeters. Originally crossed over at 1 kHz, I've been in correspondence with owner Jay Philippbar and he says crossing over at 500 Hz looses only a couple of dB. My design is derived from these and I'm expecting similar results.

Anyway, this has been discussed in a couple other threads.
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Old 17th November 2004, 03:37 PM   #9
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Markp, you are corrent in that 500Hz is in the voice range, however, in many tests we have run, it has been found that the ear is very tolerant to a crossover point of 500Hz. It would be nice to have the luxury of a lower crossover point. We typically use 500 because we are using compression drivers for midrange use, and have limited availability of drivers or horns to cross over lower than 500 (there are always compromises, huh). I got my figure of the most energy in the 250-500Hz octave from information gathered by Altec-Lansing, showing power distribution of a typical symphony orchestra. Undoubtedly, various other music sources will have various other energy distribution spectrums. For rap, by what I hear in teenagers cars, it seems to be centered at about 70Hz. By using 500Hz as a good dividing point, 5 octaves for each, it was based more on distortion reasons, not energy distribution.
Obviously, choosing an optimum point is based on many factors, which is typical for real world problems, and solving them usually means a compormise somewhere. Good engineering tries to make the compromises livable.
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Old 17th November 2004, 04:29 PM   #10
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Quote:
In a 2-way system crossed over at 500 Hz, using a passive line level crossover, about equal power for each amplifier would be a good assumption then?
For a 500Hz crossover point, assuming both sides were equal in sensitivity, you could probably get by with 3db less power on the high end.
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