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Multi-Way Conventional loudspeakers with crossovers

Has anyone tried these MMTMM configurations?
Has anyone tried these MMTMM configurations?
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Old 8th April 2018, 02:13 AM   #11
ewollowe is offline ewollowe  Australia
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Quote:
Originally Posted by zmyrna View Post
yes; similar idea

by inverting the drivers and using concave placement, they are trying to avoid beaming. Q is how effective is this?

if it helps beaming, what about lobing? (C to C distance vs. CO frequency)

my idea is similar; keep the MTM front firing and add two more inverted Ms.
I do recall some people commenting on mid/woofer arrays in this ilk and their opinion was that it would have a very small sweet spot. How low will you run the tweeter? That might help avoid a lot of issues?
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Old 8th April 2018, 08:56 AM   #12
zmyrna is offline zmyrna  United Kingdom
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Originally Posted by chris661 View Post
I'd seriously consider one of the 18Sound 6.5" midbass units. I'm using the 6ND430 for my home HiFi. They also see use for acoustic gigs, without LF support.

IMO, better to have one or two good drivers instead of a bunch of not-as-good ones.

Chris
I think this driver would be better for my application; 102 a piece, same as 4x Faital
6NMB420
Neodymium magnet, solid frame and demodulation ring
However I am not sure whether I can run the 2x per side 6NMB420 down to 200hz
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Old 8th April 2018, 08:57 AM   #13
zmyrna is offline zmyrna  United Kingdom
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Originally Posted by ewollowe View Post
I do recall some people commenting on mid/woofer arrays in this ilk and their opinion was that it would have a very small sweet spot. How low will you run the tweeter? That might help avoid a lot of issues?
MT crossover point will be 2000hz
I plan a small waveguide for TPL
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Old 8th April 2018, 09:24 AM   #14
chris661 is offline chris661  United Kingdom
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Quote:
Originally Posted by zmyrna View Post
I think this driver would be better for my application; 102 a piece, same as 4x Faital
6NMB420
Neodymium magnet, solid frame and demodulation ring
However I am not sure whether I can run the 2x per side 6NMB420 down to 200hz
They appear to have a sliding scale, with the 6ND430 being optimised more for bass reproduction, and the 410 being a dedicated midrange, with the 420 being somewhere between the two.

I expect they'll get down to 200Hz just fine, but haven't worked with that particular unit. Some EQ (or series resistance) will probably be required to get the lower end up - they're low-Q drivers.

Chris
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Old 8th April 2018, 11:48 AM   #15
LewinskiH01 is offline LewinskiH01  Argentina
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Quote:
Originally Posted by chris661 View Post
I'd seriously consider one of the 18Sound 6.5" midbass units. I'm using the 6ND430 for my home HiFi. They also see use for acoustic gigs, without LF support.

IMO, better to have one or two good drivers instead of a bunch of not-as-good ones.

Chris
Hey Chris.

Interested in your comment about this 18Sound 6.5". Could you please put it into context: you really like it compared to what other drivers?

I'm also considering several midranges to pair with a TPL-150H from 350 to 2000Hz, and I'm considering the 6ND410. Looks good on paper. The 10NDA610 actually looks better with that very low Le, but at 10" it's probably beaming by 2kHz. But all this is on paper and I haven't heard them or got first hand opinions from users that have also tried Faitals (considering 8PR155) or B&C 8PE21 - of course both are 8".

Thank you!
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Old 8th April 2018, 04:58 PM   #16
chris661 is offline chris661  United Kingdom
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Hi,

I'm not keen on using HiFi-speak to describe speakers. What's "detailed" to you might be "bright" to me.

Before these cabinets, I had a pair of Behringer B3030A monitors, which I never quite got on with. Despite some modifications (a little cabinet bracing, chamfering the baffle around the midbass unit), there was still some lack of resolution in the midrange - they didn't allow you to hear into a recording that well.
The speakers I have now (18Sound 6ND430 + Das M3) are much better in that regard, but do lose out on a little bass extension. A larger cabinet might fix that, but I like the cabinets they're in - nice and small, and pack a surprising punch.

Bear in mind that the sound of an overall speaker is also about the crossover design, internal acoustics, baffle diffraction, etc etc.

I can say these little cabinets do get rather loud - I recently used them for stage monitoring at a theatre where the cast (around 14 of them, all singing) needed to hear the live band more clearly on-stage. They sound just as good even if you're hitting them with a few hundred watts.

Once you've got the cabinet, crossover etc sorted, these drivers let the music through - there's no obvious signature of their own.

Chris
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Old 10th April 2018, 02:59 PM   #17
zmyrna is offline zmyrna  United Kingdom
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Originally Posted by Gnobuddy View Post
The audio would come from a source that is maybe fifteen inches wide (four 6" drivers spaced several inches apart) below the crossover frequency, and only about an inch wide above it.

This means you have an enormous jump in sound dispersion pattern as you transition through the crossover frequency. The sound is tightly beamed below the crossover, and widely dispersed above it.

This is the sort of thing that ruins stereo image and the size of the "sweet spot" for listening. IMO it would be a real shame to pay a lot of money for a good tweeter, and then ruin its good sound dispersion properties by engineering a speaker design like this.

Though Beyma suggests a crossover frequency of "1 kHz or higher" ( Beyma TPL-150 pleated diaphragm tweeter - Beyma TPL-150 - Beyma TPL-150 high frequency tweeter. Beyma TPL-150 high frequency tweeter is available here at US Speaker. Beyma TPL-150 speaker components. ), the published frequency response suggests a crossover above 2 kHz would be better.

Severe beaming occurs if the driver diameter is much larger than a half-wavelength of the highest frequency being emitted.

By 2 kHz, a 15" wide woofer (or cluster of four woofers) will suffer from a lot of treble beaming, because the half-wavelength of a 2 kHz tone is only about 3.5 inches, which is much smaller than 15 inches.

This is the reason why 3-way speakers were invented, with a midrange driver that is much smaller than the woofer, and therefore able to provide good treble dispersion all the way up to its tweeter crossover frequency. Meantime, the woofer-midrange crossover frequency is much lower, so that the big woofer still provides good dispersion all the way up to the frequency when it hands over to the midrange driver.

Back to your idea, if you must use multiple drivers driven from the same signal (i.e. operating over the same range of frequencies), stringing them all in one vertical line is "less-bad" than an arrangement that spreads them out horizontally.

This vertical-in-line driver arrangement causes less-bad beaming in the horizontal direction (than the vertical). Less-bad dispersion in the horizontal direction is at least a tiny step in the right direction, because our ears are spaced apart horizontally, not vertically, our stereo speakers are spaced apart horizontally, not vertically, and because we ourselves are more likely to move about horizontally than vertically.

-Gnobuddy
yes, a larger driver starts beaming at a lower freq
however, diameter is not the only determinant; concave shape of the diaphragm also contributes, ie shallower cones beam less
in that sense the dispersion of 2x adjacent 6" drivers is probably not the same as a single 12"
furthermore, inverted cone drivers are omnipolar between certain freqs

thus my original question:
can we arrange 4 cone midrange drivers (2 inverted) in such a way that the dispersion is much better than a single 12-15" (and not worse than 6" MTM)
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Old 10th April 2018, 07:45 PM   #18
adason is offline adason  United States
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6fe200 may be cheap, but its a great mid...
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Old 11th April 2018, 04:59 PM   #19
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by zmyrna View Post
however, diameter is not the only determinant; concave shape of the diaphragm also contributes, ie shallower cones beam less
True. There is a specific amount of beaming determined by the physics of a flat diaphragm, and the frequency of the sound.

You can make a speaker beam worse than a flat disc by using a cone instead of a flat disc. But, very importantly you cannot make it beam less.

In real life, woofer cone shape is to provide mechanical strength to the cone, not really to control dispersion.

We can get a rough idea how important the cone shape is by comparing the depth of the cone to the wavelength of the reproduced sound. If the woofer were to cross over to the tweeter at, say, 2 kHz, the wavelength is about 17.15 centimetres, or 6.75 inches.

The depth of the cone is probably less than an inch - a lot less than the wavelength of the highest frequency the woofer will be asked to reproduce.

Things that are much smaller than the acoustic wavelength have little effect on the dispersion. The depth of the cone will not have much effect on the sound dispersion pattern within the frequency range of the woofer.

The diameter of the woofer cone (probably about 5"), on the other hand, is nearly equal to the wavelength (6.75"), so we can expect considerable treble beaming due to the size of the woofer cones.

Quote:
Originally Posted by zmyrna View Post
in that sense the dispersion of 2x adjacent 6" drivers is probably not the same as a single 12"
If four adjacent 6" drivers are mounted with edges touching, and axes all pointed in the same direction, they behave very similarly to a single circle with a 12" diameter. (Not exactly the same, because four 6" circles in a four-leaved-clover shape is not exactly the same shape as a circle.) That's what the physics says.

The claim that the dispersion of four 6" closely spaced drivers is better than a single roughly 15" one would be easy to prove - we can believe it when someone shows us trustworthy (i.e. not faked) polar frequency response plots of both setups made under the same conditions, showing the improved performance. Until then, be extremely suspicious of the claim.

Quote:
Originally Posted by zmyrna View Post
furthermore, inverted cone drivers are omnipolar between certain freqs
This doesn't compute - the front and back of a speaker behave pretty much identically, except for the magnet and basket blocking some of the treble radiation from the rear.

Therefore radiation from the back of a speaker at bass frequencies is very similar to radiation from the front. There is no radiation directly to the sides, so no omni-polar radiation. What you get is the well-known dipole radiation pattern - sound to front and rear, nothing directly to the sides.

The whole idea of inverting two woofers doesn't make a lot of sense to me. They have to be wired electrically out of phase, otherwise the bass would cancel out. Once they're wired out of phase, and pointed in opposite directions, they behave pretty much identically at low frequencies - all four cones move in the same direction at the same instant - so there is no benefit (at low frequencies) to pointing two of them backwards.

But at higher frequencies, where the speaker magnet and basket assembly block some of the treble coming off the back of the speaker cone, there will be a difference. The two inverted speakers will individually do a better job of radiating treble (not bass) to the rear. Collectively - both together - they will suffer from the same problem as before, of behaving roughly like one 15" x 6" elliptical-shaped driver, i.e., dispersion will be worse in one plane than the other.

In short, pointing two woofers backwards is presumably to provide more treble to the rear of the speaker, and has nothing to do with improved bass in any direction.

Quote:
Originally Posted by zmyrna View Post
thus my original question:
can we arrange 4 cone midrange drivers (2 inverted) in such a way that the dispersion is much better than a single 12-15" (and not worse than 6" MTM)
Arranged in a single straight line, they are no worse than one single driver in one axis (but much worse in the other axis). Any other pattern almost certainly makes things worse than a single 6" driver.

If you must use multiple drivers all covering the same frequency range, and of a size comparable to a half-wavelength of the highest frequency they produce, then putting them all in one straight vertical line is less-bad than any other shape.

This is only because we humans tend to remain upright (and so have our two ears spaced apart horizontally), move mostly in the horizontal direction (we don't climb walls well), and so, are likely to be more tolerant of poor vertical dispersion than poor horizontal dispersion.

Again, polar frequency plots will tell the truth, one way or the other. Without proof in the form of those plots, be skeptical.

-Gnobuddy
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Old 11th April 2018, 07:26 PM   #20
adason is offline adason  United States
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"If you must use multiple drivers all covering the same frequency range, and of a size comparable to a half-wavelength of the highest frequency they produce, then putting them all in one straight vertical line is less-bad than any other shape."

What's wrong with this arrangement?
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