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Old 16th April 2007, 03:38 AM   #281
agent.5 is offline agent.5  United States
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Quote:
OTOH, Eminence DOES have a hemp cone guitar driver...Imagine that cone paired with a cast frame and a neodymium magnet.
It could be had with the built in horn for a coax or with a 4" voice coil and no dust cap so our ribbon driver could be attached...
The hemp cone Eminence speakers are called cannibas rex

http://www.eminence.com/pdf/cannabisrex.pdf

http://www.eminence.com/pdf/cannabisrex-16.pdf

On the other hand, we can probably get the HempAcoustics 12" coaxial for a pretty good price if we order 100. I am thinking around $300 each.
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Old 16th April 2007, 04:42 AM   #282
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Although Romy the Cat's posts are a bit on the "poetic" side, he's got a good point about crossing ribbons too low. Ribbons have essentially zero linear travel, unlike most conventional VC+magnet assemblies. This means getting greedy and crossing them too low is asking for a massive jump in coloration and an even bigger drop in resolution - the whole point of using a ribbon. Remember, the analog is a ribbon mike - and ribbon mikes are easily overloaded by modest wind currents.

But using ribbons to complement a compression driver makes sense - they're usually starting to fade at 15 to 18 kHz, and notching out the typical aluminum or titanium peak is a good idea, even if the peak is at 22 kHz (it is STILL audible in terms of increased IM distortion).

It always makes sense to use drivers well within their useful bandwidth - horns are not happy handling energy close to the edge of the bandpass (the region of greatest HOMs and greatest impedance variation), and running drivers where they exhibit HF peaks isn't such a great idea either. I'm one of those guys that prefers to select cone drivers with very smooth rolloff characteristics, cross them an octave higher than most folks, and use the tweeter very conservatively. That results in low tweeter IM distortion and much more relaxed and natural sound.

Accordingly, I'm looking at a coax with the best-looking rolloff regions from the bass cone, and plan to cross somewhere between 1.8 and 3.2 kHz, depending on what I can get away with. Yes, I plan to rely on the proposed cone treatments to optimize the cone performance - at least I'm not trying to get the bandwidth the Walsh folks are aiming for over in their thread.

With a ribbon taking over at the highest frequencies, the performance of the compression driver above 12 kHz is less critical. Squeezing extra bandwidth out of a horn is always difficult - they are not intrinsically wideband radiators, so attempts to extend the HF exacts a cost at the other end.
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Old 16th April 2007, 04:50 AM   #283
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Quote:
Originally posted by DougL

I have an OB test baffle / test System I can try things on.

Does anyone have a recommendation on a hole pattern to implement this? I was thinking of treating the outer inch with 4 rows of holes with the outer row having holes on 1/2" centers.

Rather than a round-over, would some felt (or other material) Half-round be more appropriate as edge treatment?

Also, how should I treat the Floor transition? Holes, felt or some combination?

Doug
My thoughts: the floor transition should be left alone, no treatment whatever. The floor reflection is there no matter what you do.

However, the sides and top edges do need treatment. I'd space the holes closest to the edge most closely together, and open up the spacing for the rows further away. Maybe you could follow a golden-section ratio (0.618:1.0:1.618:2.618) for the spacing of the rows as they get further away from the edge of baffle. Again, make the holes small, no more than 1/4" across, and maybe smaller, like an 1/8" or less.

You don't need to go crazy drilling holes over the entire edge of the baffle - the regions closest to the driver are most important, while the regions 2 or 3 feet away are less important, since local surface pressures drop off rapidly with distance.

I'd simply round-over the edge of the baffle, so a 3/4" baffle has a round-over with a 3/4" diameter.

Don't forget to use golden-section ratios for the L/R distances. For example: for a 15" driver, imagine the distance between the Left edge and the driver centerline is 10". If you choose 10", then the distance between the driver centerline and the Right edge should be 16.18". I'd split the difference going to the top, so the distance between the driver centerline and the top would be about 12.5" or so.

(The baffles should be mirror-imaged, of course. This example only applies to the Right speaker. The Left speaker should be the mirror image of the Right.)
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Old 16th April 2007, 05:09 AM   #284
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For a coax, is a compression tweeter mandatory but still not end up with something like a car audio driver? eg Using one of the Eminence coax woofers there is plenty of room in that CD horn to mount a small tweeter. For pro applications or if you're shooting for close to 100db/w/m, I understand the need for the high efficiency, but in the 93-95 sensitivity range doesn't a non-compression tweet make sense? I understand some kind of waveguide may be necessary, but otherwise is there anything inherently wrong in that approach, especially since it offers the opportunity for more ideal physical alignment?
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Old 16th April 2007, 05:19 AM   #285
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Default Big Driver, Big Sound

People ask why I'm interested in such a big midrange driver, when the most straightforward way to get flat response and an easy join to the HF driver is an 8-incher - which goes out to 5, 8, or even 10 kHz without breaking a sweat.

Well, it was listening to the 12-inch wideband driver in the Bastanis Apollo that left such a strong impression. Yes, there were issues (but then every speaker has "issues") but the commanding in-the-room presence and the impression of weight and size from pianos and drums was unmatched by any speaker with smaller drivers - including small-driver arrays and planars. At the same time, vocals were realistically sized, and most important of all, unstressed, with almost no "loudspeaker" coming-out-of-a-box impression. That, of course, is the sound of a big pro-quality driver, in an open baffle.

That's what big drivers do - and without that "projected", in-your-lap quality of horns. Getting big drivers to behave well above 1.5 kHz is difficult, challenging maybe, but not impossible. Robert Bastani succeeded with his very exotic cone treatment - which led to thinking about other ways to get good performance in the 1.5 kHz to 5 kHz region - and then on to this thread here in diyAudio.

It was that experience that made me realize the way forward wasn't to wait patiently from the Loudspeaker Gods for new wonder drivers, but take things into your own hands and make the drivers that needed to be created. I'd been waiting 15 years for Scan-Speak, Vifa, Seas, and Dynaudio to come through with high-performance high-efficiency drivers, and you know what, 15 years is too long to wait!
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Old 16th April 2007, 05:35 AM   #286
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I agree that big drivers sound different, and those speaker gods just don't want to come around, though I haven't been waiting as long. My wait has been for an OB driver, which are slim to none if you want to cross low.
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Old 16th April 2007, 06:04 AM   #287
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Quote:
Originally posted by Lynn Olson

Accordingly, I'm looking at a coax with the best-looking rolloff regions from the bass cone, and plan to cross somewhere between 1.8 and 3.2 kHz, depending on what I can get away with. Yes, I plan to rely on the proposed cone treatments to optimize the cone performance - at least I'm not trying to get the bandwidth the Walsh folks are aiming for over in their thread.

With a ribbon taking over at the highest frequencies, the performance of the compression driver above 12 kHz is less critical. Squeezing extra bandwidth out of a horn is always difficult - they are not intrinsically wideband radiators, so attempts to extend the HF exacts a cost at the other end.
Hi Lynn, have a look at the P.Audio SN15B which seems to have a smooth rolloff at about 3kHz. This is, of course, if you believe the P.Audio graphs are accurate - and in some cases they're definitely not. However, I have a custom pair of coaxes made by P.Audio from SN15B chassis/cones with SD750N compression drivers. OB mounted of course. I'm running the woofers virtually full-range, compression driver kicks in at about 3K 1st order with a Fostex Ft17 helping out at the top and they sound pretty good to me!

Cheers,
Mike Spence
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Old 16th April 2007, 06:21 AM   #288
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Quote:
Originally posted by johninCR
I agree that big drivers sound different, and those speaker gods just don't want to come around, though I haven't been waiting as long. My wait has been for an OB driver, which are slim to none if you want to cross low.
This problem partitions quite easily - the Qts of the wideband driver doesn't matter if another driver is helping out at lower frequencies - and the LF driver does have an appropriate Qts between 0.65 and 1.1. The LF can have a complementary "flavor" since it shares the 80 to 300 Hz region with the wibeband driver. For example, a pair of 12" Alnico Tone Tubby's (mounted right at floor level) might be just the perfect complement for the P.Audio SN15B mentioned below.

Too efficient to match the wideband driver? Excess efficiency, along with huge cone area, is exactly what we want in the 1/f rolloff region. Instead of a lot of equalization, we bring in extra drivers, and help them out by placing them next to the floor (which creates an image, thus doubling the effective radiating area).

The overlap in the crossover - by using tapped inductors or bi-amping with parametric EQ - is how the response in the midbass is shaped. Since listening rooms need to be individually compensated from 300 Hz and below, this adjustability is a good thing to have. In fact, in most listening rooms, you'll need different equalization for the L and R channels in the 100 to 300 Hz region.

Quote:
Originally posted by mikey_audiogeek

Hi Lynn, have a look at the P.Audio SN15B which seems to have a smooth rolloff at about 3kHz. This is, of course, if you believe the P.Audio graphs are accurate - and in some cases they're definitely not. However, I have a custom pair of coaxes made by P.Audio from SN15B chassis/cones with SD750N compression drivers. OB mounted of course. I'm running the woofers virtually full-range, compression driver kicks in at about 3K 1st order with a Fostex Ft17 helping out at the top and they sound pretty good to me!

Cheers,
Mike Spence
Thanks for the tip, very much appreciated, especially the info about the custom SN15B + SD750N compression drivers. Sayonara, low-efficiency audiophile drivers!
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Old 16th April 2007, 06:22 AM   #289
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Linkwitz's recent Epiphany is that the best dipole speakers maintain the dipole radiation pattern over the full frequency range. For the Orion+ he added an identical monopole rear tweeter back-to-back with the front tweeter, and is very positive about the audible improvement.

I live with full range dipole Apogees and also found that full range dipole radiation is best, and ended up with just a rear wall diffuser.

A coaxial speaker would add complications to maintaining dipole radiation over the full frequency range. A simple DIY dipole ribbon tweeter, large enough to be crossed at 1-1.5Khz to a standard mid-woofer, might be worth discussion if all-dipole becomes a lock-out spec as Linkwitz would recommend.
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Old 16th April 2007, 07:39 AM   #290
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Quote:
Originally posted by Lynn Olson


This problem partitions quite easily - the Qts of the wideband driver doesn't matter if another driver is helping out at lower frequencies - and the LF driver does have an appropriate Qts between 0.65 and 1.1. The LF can have a complementary "flavor" since it shares the 80 to 300 Hz region with the wibeband driver. For example, a pair of 12" Alnico Tone Tubby's (mounted right at floor level) might be just the perfect complement for the P.Audio SN15B mentioned below.



Thanks for the tip, very much appreciated, especially the info about the custom SN15B + SD750N compression drivers. Sayonara, low-efficiency audiophile drivers!
Hi Lynn, a bit more info: I'm powering the whole caboodle with a John Swenson transconductance amp, lightly modified to give an output impedance of about 20R. This "modifies" the Qts sufficiently such that the SN15B is flat to 40Hz (resonant freq) on an OB that measures 1200mm x 750mm. No sub!

Quote:
Originally posted by LineSource
Linkwitz's recent Epiphany is that the best dipole speakers maintain the dipole radiation pattern over the full frequency range. For the Orion+ he added an identical monopole rear tweeter back-to-back with the front tweeter, and is very positive about the audible improvement.

I live with full range dipole Apogees and also found that full range dipole radiation is best, and ended up with just a rear wall diffuser.

A coaxial speaker would add complications to maintaining dipole radiation over the full frequency range.
Not if you take the back off the compression drivers to expose the diaphragm for dipole operation, like I (and others) have...
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