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Multi-Way Conventional loudspeakers with crossovers

Mini towers for home theater & crossover phasing
Mini towers for home theater & crossover phasing
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Old 16th August 2019, 01:20 AM   #11
GM is offline GM  United States
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Understood and counter intuitively, larger drivers work better in smaller environments due to having increasing directivity to reduce/eliminate early reflections among other things. As for power handling, the 8"ers would barely move in your app Vs the little drivers pumping at much higher distortion.

Regardless, not trying to convert you per se, mainly just using you to further DIYer's education.

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Old 16th August 2019, 07:54 AM   #12
system7 is offline system7  United Kingdom
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Quote:
Originally Posted by BIGlep View Post
System7, my main worry right now is how low I need to cross the drivers. I read that it is optimal to have a crossover with a wavelength of about the center to center distance between the two midranges. In my case that is 16cm or 2140 hz.

I'm having a hard time finding tweeters suitable for this low of a crossover. The XT25SC90 looks amazing but I have read that distortion increases below 2500 hz. The Dayton ND25FA doesn't look too bad either but I've read it also likes 2500+ hz. The OC25SC65 also looks good, but I don't know how to go about mounting a faceplate-less tweeter.

Although in the design you linked, the center to center distance is quite a bite larger and they are using a 3200 hz crossover.

Would 2500hz be okay with a LR2 crossover in this type of design with any of these tweeters? Particulatily the XT25 or ND25? They both have very smooth response out to 20 khz.

Any given tweeter will have an Lpad applied to bring the 2.83V sensitivity down to 88 Db, which should tame the resonance peak in impedance, though it needs to keep up to 102 dB 1m of max output.
Sounds like you have a very good technical level. Let's talk mini towers since that is the topic.

Here's one by one of this forum's brighter lights, Mr. Joachim Gerhard:

Click the image to open in full size.

Sonics by Joachim Gerhard cabinets and kits.

I would imagine that is a TMM rather than a 2.5 way.

My own view is an MTM is really not far different except on lobing. MTM has symetrical lobing, but really I don't think it matters much.

Crossover point is often a matter of taste. Cross low, and the tweeter struggles, cross high and you hear midbass breakup. All made worse by shallow filters. I happen to be in the high order (LR4) crossover and highish 3kHz XO camp, because I like complex and spectrally dense classical music alongside almost any other music you might mention.

Another fine MTM design is by our own learned member, Mr. Lynn Olson:
The Ariel, Part I

There's bags of interesting articles at Lynn's site. An experienced builder. The miracle of MTM or TMM is that it produces the same sound levels at the listening spot, with half the power to the room, which keeps the neighbours happier.

For your small room, this Peerless 830860 looks like the modern equivalent of Lynn's Vifa unit:
Peerless HDS PPB 830860

It's almost trivial on the crossover to convert an MT to a series MTM. Double the coil and resistor values along with the box and vents, and halve the capacitor values in the bass section. The tweeter section is unaffected. It all works out and gives you an amp friendly higher impedance. I call that WIN-WIN!

I am quite interested in this dome mid design by Mr. Troels Gravesen:

SP38/13

I can think of cheaper alternatives to those Scan drivers. It's the idea that counts. You are giving the midbass and tweeter an easier life by letting the dome mid deal with the area where they struggle.

Choice of drivers is all about finding good and flat ones in the first place, since every crossover adjustment tends to worsen impedance, which matters with feedback amps. TBH, I don't like LR2. It's OK for jazz and acoustic music, but plain distorts my favourite Mozart and Debussy and Chopin. There's a reason the low order crossover people always play the lovely jazzy Miss Diana Krall at HiFi demos!
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Last edited by system7; 16th August 2019 at 08:18 AM.
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Old 16th August 2019, 08:14 AM   #13
Zuhl is offline Zuhl  England
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I've never like MTM designs. The only way to listen to them is directly on tweeter axis. If you listen above or below then the mid driver offset is going to be different for each mid driver, which is likely to 'muddy' the sound.
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Old 16th August 2019, 09:00 AM   #14
system7 is offline system7  United Kingdom
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I have always had misgivings about MTM myself, so you could say I agree with you.

It's actually a Mr. Joe D'Appolito BW3 solution in reality. But we tend to implement it as LR4.

The real LR4 mathematical solution is MTTM. It looks like this, if you accept that a long ribbon has much the same dispersion as two dome tweeters:

Click the image to open in full size.

I have to be careful what I say here, but I have heard this sort of cost-no-object system, but I honestly think that given enough money and some serious subwoofering in an acoustically treated room, this is about as good as it gets.

Not many people know this, but with every symmetry comes a conservation law. Emmy Noether (the best female Mathematician, ever, respected by no less than David Hilbert and inevitably hated by the Oafs of the Third Reich...) proved that principle. Mostly applied to Quantum Mechanics these days, but works for speakers too. FWIW, we still use the Hilbert Transform to relate frequency response to Phase and Time Delay in speakers. It's how Simulators work.

Myself, I'm a real Socialist. I want good speakers for everyone. Preferably under 200 for the whole lot. I can dream.
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Last edited by system7; 16th August 2019 at 09:27 AM.
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