Priniciples in building the ultimate electrodynamic speaker system - diyAudio
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Old 13th March 2005, 03:18 PM   #1
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Default Priniciples in building the ultimate electrodynamic speaker system

So I'm dreaming of building the ultimate speakers and I want to see if I've got some of the right priniciples, so far.

1. Active crossovers - the benefits of active vs. passive is a given, so no explanation needed, right?

2. Use large drivers for the bass because of doppler distortion or whatever you want to call it. Try to have these drivers operate cleanly to about 300Hz because of midrange drivers (see 3). Given this, you'll probably want a 4 way system if you're going to use it for home theater, because finding drivers that play cleanly and loudly from 20 Hz to 300Hz is very unlikely or very very expensive.

3. Use approximately 5" metal drivers. OK, here's where I get a little contronversial. The more I read about the mid/woofers, the more I see the value in smaller drivers. Those 7 and 8" drivers are great for getting down to close to 40Hz in a 2 way but they are often difficult to crossover at 2-3kHz because of the the resonance peaks they have near 4-6khz. The smaller 5" drivers seem to give you a much smoother transition to the tweeter, as long as your bass drivers can help it out on the other end.
The other thing that I've been looking at is the use of metal cone drivers. If you check out the harmonic distortion figures for the metal Seas L12 http://home.new.rr.com/zaph/audio/4.5test/ compared to the damped paper Vifa TC14 http://home.new.rr.com/zaph/audio/surface5test/ you'll notice that the metal less distorted - I think I'm reading that right? With the right active crossover (metals all have such high resonances that I wouldn't want to use all the passive components necessary because of the phase shifts, etc) they might sound pretty good. Linkwitz chose the metal Seas W18 for his midrange (with an active crossover) so maybe there is something there.

The other benefit of using a smaller midrange driver and crossing it over around 200 hz is that you wouldn't have the floor cancellation that you see by mounting a midwoofer close to ear level, right? Maybe use a MTM arrangement to give greater sensitivity, power handling and even less vertical dispersion acoustic issues.

4. Buy a really great tweeter - but since you've used a smaller midrange you don't have to worry about one that crosses low (like 1.5kHz) and get's close to it's Fs.

Am I on the right track, or have I missed something?
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Old 13th March 2005, 04:42 PM   #2
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Pretty much similar to my implementation of a front running speaker. One high quality treble, a good strong true midrange and finally 8" drivers from 380hz and down. Only 3 way but it has a trick up its sleeve:

'Perceive' Contruction Diary

Only thing I've deviated on is the large bass driver and instead chose 2 or 3 x 8" drivers along with a LT circuit to boost low end. Response should be in the order of 15hz-40Khz in room.

This is only one way and there are others, though this is definitely the easiest way for me to get top performance from good drivers.
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Old 13th March 2005, 05:37 PM   #3
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First thing - you shouldn't be concerned about budget.

Seems to me that the best way method of picking drivers is to pick the largest ones that won't beam at the frequency you want to cross at.
Larger drivers tend to have lower distortion at the same given frequency and output level, because they have to move less.

Note that the crossover frequencies aren't static - you can change them to suit, not the other way around. Linkwitz uses a 1.4kHz crossover between tweeter and midrange - you can use one that's lower or higher depending on what drivers you use.

Now, the driver(s) covering the modal region (generally starting around 200Hz and going down to the frequency whose wavelength is 1/2 the length of the room), should be operated as a dipole, not monopole. This is because dipole bass is almost always less peaky/nully (not a word, I know) than monopole bass in this region. With dipole bass, you'll need either EQ or lots of space in order to achieve a flat response, and I'd prefer the latter, as you need extra power (i.e. more distortion) to get the same output level below the point where dipole cancellation (6dB/octave rollof) occurs.

Since this has all been covered in numerous threads in this forum, just do a search.
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Old 13th March 2005, 10:49 PM   #4
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Anyway, my pick for a system with minimal need for EQ and no separate subwoofer, listening distance around 4m or less:

Bass: Precision Devices 24" PD2450 - dipole operated on a flat baffle up to 200Hz-250Hz, 4th-order linear phase crossover or steeper. Although all the drivers are vertically aligned, the drivers aren't placed symmetrically on the baffle for smoother response.

Midrange: JBL 12" 2206, probably cardiod operation (theoretically, more seamless merging between dipole and monopole), crossed to tweeter at about 1kHz-1.2kHz.

Treble: Probably a 1"-throat beryllium-diaphragm compression driver + plug-filled OS waveguide designed by Dr. Geddes (phase plug and waveguide matched). The treble response will have to be EQed as the on-axis response drops as frequency increases.

Quick and easy, although that can be improved upon tremendously. A good start for a highly dynamic, relatively flat (in any room) system.
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Old 14th March 2005, 12:14 AM   #5
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Quote:
Originally posted by 454Casull
Midrange: JBL 12" 2206, probably cardiod operation (theoretically, more seamless merging between dipole and monopole), crossed to tweeter at about 1kHz-1.2kHz.


12" for the midrange
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Old 14th March 2005, 01:55 AM   #6
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Is there a problem? If you take a look at the response chart, at 1kHz the off-axis response (the line indicated is 45 degrees off-axis, I believe) is down only about 2.5dB. Going up to 1.2kHz, it's down 4dB. It's fine.


EDIT: I would like to change "listening distance 4m or less" to "about 4m", as you can definitely choose drivers that are smaller in size for closer distances like 2m. That's Post #4.

EDIT2: Also in Post #4 is a typo. "cardiod" should be "cardioid".

EDIT3: Another reason why I chose that woofer is because the response is very very flat. Other high-sensitivity woofers with the required power handling (over 100W or so, for a headroom of over 20dB) either have unlisted distortion - which tends to mean relatively high distortion - or have a crappy response.

EDIT4: Forgot the requisite link:

http://www.jblpro.com/pub/components/2206.pdf
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Old 14th March 2005, 02:57 AM   #7
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David,

Where in the great "Republic of Vancouver Island" are you

You'll probably find as many different opinions as there are people... as much to taste as to differing needs.

Metal drivers -- IMHO these that are worth using are few & far between. 1st most of them ring like crazy... any ringing needs to be down at least 40 dB, 50 in a world class loudspeaker. I don't like to see any XOs in the critical part of the midrange, so XO points outside of 250Hz to 5 kHz, a little more would be better. My favorites are the Joran JX92 and the Fostex FE108E Sigma -- my 1st choice would probably be the latter. Crossing these over this high, open baffle is doable & good... otherwise some sort of aperiodic TL

Your woofers should reach up quite high... 1 kHz isn't unreasonable... you won't find many better than the Llambda 15" Apollos (you'll also have trouble finding them )... they are probably usable up to 2.5-3k. Since these are pretty much unobtainum one has to start looking at what is available, but it sets a goal to strive for.

Tweeters... i'm not a big dome tweeter fan. Ribbons are probably your best bet of what is available... the smaller the better. A dipole would be best, but you'd have to make them yourself (not all that hard actually if you are mechanically adept -- or know someone who is). And if you are going to make your own an ESL tweeter also becomes a consideration,

dave
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Old 14th March 2005, 03:11 AM   #8
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True. There are many ways to achieve low distortion, low power compression, uniform power response, minimal lobing, minimal beaming, etc.

However, many of the drivers you listed have a relatively low maximum SPL. Ideally, one should be able to re-create the levels of live listening.

EDIT: A 15" will beam like crazy at 2.5kHz. At that frequency, most 15" drivers with a flat on-axis response tend to be more than 10dB down at 45 degrees off axis. How do you suggest using it up that high?
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Old 14th March 2005, 03:33 AM   #9
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One thing I dont understand is how everyone talks about driver size and beaming so generically. Just because two drivers are the same size does not mean they will have the same dispersion characteristics. Does cone shape not mean anything?
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Old 14th March 2005, 03:42 AM   #10
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Quote:
Originally posted by BassAwdyO
One thing I dont understand is how everyone talks about driver size and beaming so generically. Just because two drivers are the same size does not mean they will have the same dispersion characteristics. Does cone shape not mean anything?
Not so much as the size. You can engineer the diaphragm so that while breakup the radiating area decreases and effectively radiates like a smaller diaphragm, but not much else.

A rule of thumb is that a rigid piston starts beaming when the frequency being reproduced is shorter than the circumference of the piston.
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