Size of Midrange Drivers

08-25-14: Psag
TAD concentrics use a 6.5" midrange.

Point?
_

08-21-14: Dweller
Ptss: So you're saying that most of everything emanating from a symphony orchestra can be reproduced by a five inch driver?
I think we're just brain-locked into the current paradigm and are waiting for our "Einstein" to show us the way to the next level.

We've been shown various paradigms concurrent with the development of the loudspeaker. Klipsch horn loaded everything starting in 1949. The electrostatic has been around since 1919 and has had a presence in high fidelity since the mid-'50s. The Magnepan has been around for 45 years, and the Heil air motion transformer has been in production for 44 years. Even within pistonic loudspeakers, there are variations such as high excursion drivers, line arrays and other arrays of multiple drivers, downfiring woofers to couple with the floor, transmission lines, etc.

Personally, I choose the planar magnetic. My humble Magneplanar 1.7s have 509 sq. in. of diaphragm area per speaker, and in my experience provides a decided advantage in preserving clarity and voice placement in larger works, such as full scale orchestra plus 100+ voice chorus.

Each of these driver designs presents strengths and weaknesses unique to each design. We're left to pick our poison.

If you consult the wavelength calculator, you'll find that a 6.5" driver starts beaming at 2086 Hz, whose wavelength is 6.5". By the time you get to 3Khz the wavelength is 4.5", which would be a total beam from a 6.5" driver.

This beaming isn't noticeable on-axis, especially if you're listening nearfield, but it disrupts the in-room power response and you'll get cupped-hands sounding suckouts right in the midrange where it counts when you have too large a midrange crossed over too high to the tweeter. A 6.5" mid crossed over at 3Khz will beam from 2K to 3K Hz--1/2 an octave in the midrange.

08-22-14: Timlub
Johnnyb53, are you saying that all 6.5 inch drivers start beaming at 2086hz....???

Actually no; it's not that simple. The significant measurement is the actual moving cone's diameter. A 6.5" driver with a large surround might have a 5" cone, but that would still beam at about 2700 Hz, somewhat shy of 3K. However, this can be offset by a 1st order slope for the tweeter crossover. If a tweeter crosses over at 3K at a 6dB/octave slope, then it's still putting out significant output at 1.5K, and would be down only 3dB at 2250Hz, which would be enough for good dispersion at the crossover point.

There are other ways to cheat the dispersion formula somewhat with phase plugs, waveguides, and whizzer cones. Still, I mentioned the formula with a link to the wavelength calculator to answer the OP's question--why have a small diameter midrange when a larger one would provide larger radiating surface? One answer is that the larger driver has the potential to create an in-room 1/2-octave wide suckout around the crossover point.

A better solution might be dual mids or dual or triple tweeters. Dual small mids would provide more radiating surface while maintaining small diameter diaphrams for better dispersion. Multiple tweeters would allow using a lower crossover point without overdriving the tweeter. This is what Tekton does in mating a 10" woofer with a 1.5" ring radiator. Some of the 10" woofers have whizzer cones with 3 tweeters instead of one on his top line models. This enables lowering the crossover point to let the tweeters cover for the woofer's beaming.

The worst case is a 2-way with a large woofer, small tweeter, and 4th order (24 dB/octave) crossover to increase power handling. It means the tweeter wouldn't be able to improve dispersion just below the crossover point because output would be too far down to help out.

Why do you think there are so many speaker manufacturers and DIYers? Dynamic speakers in boxes present balancing acts with an infinite number of possibilities in driver sizes, driver numbers, crossover points, crossover slopes, as well as cabinet size and bass alignment. Not to mention the actual individual driver characteristics.

Kijanki: I just checked out the 6Moons in-depth review (from 10 yrs ago) of the Hyperion hps-938. The midrange unit addresses this dispersion challenge in its design. Notice that the Hyperion midrange has a large, flat dustcap. It's not a typical dustcap, however. Hyperion called this the SVF--Synchro Vibrate Flattop. This dustcap floats independent of the main diaphragm and is connected directly to the voice coil. What this does is provide a midrange-within-a-midrange of smaller diameter to ensure wider dispersion of high frequencies that would beam at 6-1/2" but not at 3" (or whatever diameter this floating dustcap is). That's a pretty ingenious solution to have it both ways--larger diameter for more radiating surface and deeper reach while keeping dispersion consistent as frequencies rise toward that rather high 3K crossover point.

That's what whizzer cones and phase plugs are used for in many fullrange drivers (e.g. Fostex and Audio Nirvana). But Hyperion's flattop dust cap strikes me as a more ingenious and precise way to achieve that.

And Magneplanar X.7 series--1,7, 3.7(i), and 20.7--have sort of blown past the stereotypycal limitations of Maggie speakers. My 1.7s are dynamic, coherent, and can play loud and clean on 100 wpc (200 into thei 4 ohms) in a vaulted ceiling open architecture living room. The X.7 series are the first Maggies not to have been designed by founder Jim WIney. They were designed by his son, who apparently successfully addressed the chronic complaints about the previous iterations.

The Tannoy Kingdom Royal has NO MIDRANGE driver contrary to what you seemed to allude to.

Their new HF compression driver tweeter is doing all the midrange.
Like you seemed to indicate - Tannoy is not foolish & they wouldn't put a 12" midrange! The 12" unit does upper bass to 700Hz & the lower bass unit does the bottom-most octave.

700 Hz wavelength is over 19" long, so a 12" driver wouldn't even be close to beaming. Tannoy knows what they're doing, but apparently you refuse to catch on, even with multiple corroborating explanations.

Fool that I am, I'll give it one more go:

In the '70s I owned a pair of Altec-Lansing 9845a professional studio monitors. They had the typical Voice of the Theater (VOTT) components--15" woofer and compression-driven aluminum horn. Around that same time I worked at a stereo store where we carried Altec, including some home versions of the VOTT.

But they sounded significantly different. My pro audio VOTT crossed over at 500 Hz, which is a 27" wavelength and well outside the beaming frequency (900 Hz) of a 15" wavelength. The home version, however, crossed over at 1200 Hz, which is an 11" wavelength. That means that *that* 15" woofer was beaming from 900 Hz on up past the 1200 Hz crossover frequency. And you could hear the difference--a kind of "cupped hands" coloration in the crossover frequency area.

I think the difference in crossover frequency was due to the pro version having a better, more expensive and rugged compression driver that could play lower. The cheaper home version crossed over at 1200 Hz for power handling. These days, no one in their right mind would cross over a 15" woofer that high without a wave guide, whizzer cone, or at least a phase plug.

Unaware at the time about beaming, dispersion, and in-room power response, we typically figured that the horn was making the music sound horn-like. Yet my pro monitors had no such coloration (in fact, they kicked ass!). I also found that this suckout wasn't very noticeable when playing jazz combos and larger scale instrumental music, but was immediately noticeable on solo voice. From that point on--as much as I like instrumental music--I can't consider a speaker without hearing what it does with vocals.

So there's a little more anecdotal evidence for the impact of beaming on an inappropriate crossover point.

johnnyb53, I get it. the point is do the likes of you & Dweller get it?
Once again: Tannoy smart as they are did not try to do any more midrange with the 12" driver - that was my point. Hopefully you got that?
thanks.

That was sloppy editing on my part. I was totally agreeing with you. Where I said "apparently you refuse to catch on..." I was addressing Dweller, not you.

I was trying to corroborate your assertion about the 700 Hz crossover, that it's well below the frequency where a 12" driver would start beaming, and that the Tannoy 12" driver functions more as a woofer than as a midrange. I don't usually get that jumbled up in pronouns and their antecedants.

08-25-14: Dweller
Thanks guys for trying to teach an old dog new tricks.
I'm looking for a way to get a more life-like listening experience.
You're trying to tell me why I can't have it.

Nobody said you can't have midrange coming from a large radiating surface. Some of us were pointing out that as the wavelength approaches and exceeds the diameter of the driver, the driver starts beaming and continues from there on up. When you have a range of beaming frequencies, it may sound OK on-axis, but those beaming frequencies go missing in the overall in-room balance. This is expressed as in-room power response.

A couple of the exceptions cited in this thread have reasons to work. We established that the 6.5" midrange of the Hyperion hps-938 has an active dustcap that funcions as a small-diameter midrange to offset the beaming of the 6.5" section between 2K and the crossover at 3K.

Furthermore, I read up on your Dvoraks with their MTM arrangement with 8" midranges, and it turns out that this is a dipole design. That makes a world of difference, because even though the 8" midranges would be beaming at 1700 Hz, since they're also firing backward and hitting the wall behind, this compensates for the beaming by adding to the power balance in that frequency range. It's also how panel speakers, which tend to have narrow dispersion, have good overall in-room power response, because the backwave hitting the back wall compensates for the narrow dispersion to the front.

As for getting a large radiating surface for the midrange, there are several approaches. First is panel speakers. I have Magneplanar 1.7s. They have approx. 456 sq. in. of bass/midrange radiating surface--radiating both front and back. They are transparent and (with good setup), well-focused. Second, you can get a speaker with dual or multiple midranges such as your Dvoraks had. If you have 8" midranges it helps if they're mounted in an open baffle as your Dvoraks were.

Third, you can get a large diameter full range driver which has compensations for the beaming aspect. I recently visited an audio buddy whose main speakers are Audio Nirvana 15" full-range drivers. These raw drivers are $500-$1000/pair depending on magnet type. His are mounted in large ported enclosures--2'x2'x4'tall, with three big ports to the front. Despite the large diameter, these speakers had excellent power response. I detected no beaming when listening off-axis, and walking around the room the overall tonal balance was excellent with no noticeable suckout.

How'd they do this? The speaker has both a whizzer cone and a copper phase plug. This is exactly what whizzer cones are for--they provide a small diameter cone to keep higher frequencies from beaming. The phase plug also gives a focused surface for these frequencies to bounce off of, futher improving dispersion of the highest frequencies.

He is considering remounting the speakers in an open baffle (like your Dvoraks), however, to open up the sound a bit and eliminate cabinet resonances.

Yet another way to increase radiating surface is with multiple dynamic drivers, with two or more 4-5" midranges. Axiom makes some examples of this including their M100, which has three 6.5" woofers, dual 5.25" midranges plus dual 1" tweeters. They also make an omnidirectional speaker with the same front array plus two more 1" tweeters and two 5.25" midranges firing to the rear. These speakers are engineered by Andrew Welker, who designed those great omnidirectional speakers for Mirage before Klipsch shut them down. Bryston's new line of speakers show a decided dependence on Axiom for their design philosophy, including dual mids and tweeters for lower distortion and greater dynamic range.

Yet another alternative is a tall column speaker with a dozen or so midranges and even more tweeters in a line array.

Finally, the name of the game isn't just radiating area; it's air displacement. A 4.5" driver has a radiating surface of 15 sq. inches. My Mag 1.7s have a radiating surface of 456 sq. inches. Yet, a premium 4.5" midrange might have a maximum excursion of .2", which amounts to around 3 cu. in. of displacement. My big panel, if its excursion is .01" (I'm guessing here, but it's probably in the ballpark), displaces about 5 cu. in. of air even though it's spread over a wider area. So two of those 4.5" midranges would displace about the same amount of air at full excursion.

Phusis
My impressions is that it's not without audible importance how a given amount of air is moved; either "gently" via a larger area, or "forcibly" through a smaller ditto. My preference - if it is indeed explained fundamentally through this aspect - is for the former, and this goes for the whole frequency spectrum.

And I agree with you. The larger the radiating surface, the smaller the excursion required to achieve the same SPL. A 5" midrange has about 19.5 sq. in. of radiating surface; The Magnepan 1.7 has 456, or 23 times as much. The Magnepan's microscopic excursion has a profound effect on inertial artifacts--the mechanics of acceleration, stopping, ringing, and reversing. It results in a relaxed, natural presentation.

Note the expensive and herculean efforts to reduce this in a pistonic driver: the TAD coincident drivers are made of vapor deposited beryllium--brittle, fragile, but incredibly light to minimize inertial effects.

Moreover, the number of point sources (convering the same frequency span) is also a factor. With regards to bass (and the rest of the sprectrum), generally, I'd rather have one unit covering what two or more units equaling the same radiation are can muster.

I agree here, too The miraculous thing about the Maggie 1.7 is that it speaks in such a single, coherent voice for just $2K/pair. The TADs also do it with a 6.5" coincident driver that covers 8 octaves. Its point source would have an imaging advantage over the Maggies' line source, and the upper models have more bass reach, but at a significant price difference.