Large midrange for OB??? Scott G ?

[Paul W]

Hi Lynn,
Since you are looking hard at the 12NDA520, I was going to take some FR and CSD shots of the smaller 10NDA520 for you this past weekend.

Unfortunately, the spring yard workers were out in force both days so you'd have seen the response of various leaf blowers, lawnmowers, etc Hopefully I can do it next weekend.
Paul

[MBK]

Hi Lynn,

I think the final word(s) are still out... it all may depend on application and on which priorities one sets. For instance I haven't tried the 15" crossed high in a proper design yet, in practice I still use it up to 300 Hz only, with a midrange, because I have no tweeter capable of going down to 1-1.2k. Such a higher X-O has only been a preliminary investigation. And PaulW seems to still have a soft spot for his ribbons even though the 1" compression driver likely would win on dynamics.

So why are these large drivers so good? I suppose it's a combination of factors. The specific high end pro drivers we discussed here in fact incorporate all the technology of the better audiophile drivers, yet at high efficiency and high power handling. To some extent I also believe it's a matter of "no replacement for displacement" , similar to what the line array people already know... Then, I strongly suspect experienced pro audio designers design with experience from musical intrument application in mind. In other words they might have a good handle on what types of trade offs are more musically acceptable. Although, the distortion measurements of these drivers are also objectively very good.

I'm curious as to Paul's CSD results for the 10" (somehow I haven't succeeded in convincing my software yet do produce a CSD, something is wrong with the gating. or maybe it's me). Maybe here one will see a weak point of the larger drivers.

[Lynn Olson]

Well, ScottG, you were right all along. The Azurahorn AH-550 looks like an obvious match for the BMS 4540 and 4552 - assuming there aren't weird conflicts in the throat area of the AH-550.

The 300mm mouth diameter even matches the 18Sound 12NDA520 in size, although in practice I suspect it will actually overhang the front baffle in order to have good time alignment. With a cutoff of 550 Hz, it looks any crossover between 1.4 kHz and 2 kHz would work fine, since both drivers have extensive flat-response regions above and below the crossover point. As mentioned earlier, this "cross well above horn cutoff" is sanctioned by Le Cleac'h himself, who ought to know.

Has anyone tried the BMS 1" compression drivers with the small Azurahorn? Results? Comments?

P.S. If anyone has any comments, feel free to answer here or in that "other" thread.

[ScottG]

Originally posted by Lynn Olson
Well, ScottG, you were right all along. The Azurahorn AH-550 looks like an obvious match for the BMS 4540 and 4552 - assuming there aren't weird conflicts in the throat area of the AH-550.

The 300mm mouth diameter even matches the 18Sound 12NDA520 in size, although in practice I suspect it will actually overhang the front baffle in order to have good time alignment. With a cutoff of 550 Hz, it looks any crossover between 1.4 kHz and 2 kHz would work fine, since both drivers have extensive flat-response regions above and below the crossover point. As mentioned earlier, this "cross well above horn cutoff" is sanctioned by Le Cleac'h himself, who ought to know.

Has anyone tried the BMS 1" compression drivers with the small Azurahorn? Results? Comments?

P.S. If anyone has any comments, feel free to answer here or in that "other" thread.

Its an infrequent thing.

I'd also bet that you could do the B&O filter design without serious combing problems.. consider using a 12 or 15 inch co-axial model without the compression tweeter and instead replacing with a more standard tweeter "flush" mount, (with baffle), centered in the larger coax driver. Move the mid driver just below 1 kHz for its midpoint (based on its operating passband). That should work. But again, it IS a different design.

Also, I think that the open baffle bipole hypercardoid would work rather well to - Unlike most fullrange drivers, a 12 inch driver typically has a large center motor assembly and does not radiate enough high freq. "penetrating" sound to the rear of the driver that could pass through a typical 12 inch driver's diaphragm (..an obvious exception might be the 12" PHY driver - but that isn't a driver thats really been considered). (..and this is even more different design-wise.)

I honestly think that it all depends on the implementation and what you really want out of the design. Get those goals down (ALL the goals), and I can prob. recommend just about any driver known to man that would have the best chance of accomplishing that.

As to the BMS compression driver:

Generally: These "ring" drivers (once "broken in") are extremely detailed in sound but can be rather "hifi" in sound - i.e. "pin point" imaging but not as 3D'ish. (..and I suspect you want something more 3D, but I could be wrong.) Anyway.. At the bottom of its passband (resonance area), all the drivers will exhibit time domain problems, but in reality (at lest compared to most commercial designs), the BMS drivers decay rather well - and to an extent it is dependent on the horn's design.

From what I've gathered information on - the 4540ND is the best sounding driver of the group (as mentioned by an other that has had access to all but the most recent drivers under production), despite its lower price and its supposedly lesser low-freq. passband.

Now as for the Horns..

The first thing that concerns me is horizontal polar deviation. What *I* really want to see is a polar plot that has no more than 1-2 db of deviation from its on axis response over its intended passband and uniform directive limit (typically expressed as -3db point over a coverage angle.. i.e. 90 degrees). This is something I'd first discuss with the Azurahorn people before purchasing. Of course at its freq. extremes this constant coverage won't hold true, BUT the low freq. portion should have an appropriate filter for that and it isn't as important for the highest freq.s as long as the constant coverage extends for most fundamentals (i.e. you can always add a super tweeter).

Then next thing I want to see is a W I D E dispersion horizontally. At least to me - EVERY moderate to low coverage angle horn I've heard sounds completely artificial (i.e. exceedingly poinpoint, bright, poor soundstage, poor depth, 2D in the worst sense). On the other hand though, I've personally never heard a design that has a uniform coverage angle down through the midrange that was low in coverage (i.e. highly directive) - so who knows, a hypercardoid midrange might well work with such a directive horn?

Also, (at least with most horns) - with fairly steep high pass filters you should have your crosspoint at least half an octave above the horn's cuttoff freq.. Example - The DDS 90 degree waveguide that Paul has specs 900 Hz, so with a LR 4th order I'd want a highpass crosspoint of at LEAST 1350 Hz. Of course lower order filters need to have considerably more bandwidth between its crosspoint and the horns cutoff freq.. Also, there is a lot more to this - looking at the horn and driver freq. response typically shows where the crosspoint is maximally lowest. Additionally, roundover's like the Le Cleac'h based Azurahorn can often extend this freq. a bit lower than the general rules (as above) would imply.

Finally, I want a lower freq. driver that has as close as possible a radiation pattern for at least most of its upper passband that will sum "correctly" to the coverage angle of the horn (+/- a few db) for at LEAST a half octave below the crosspoint, and hopefully that much above the crosspoint as well.

IF you fairly well follow those 4 basic rules - you'll almost certainly get good sound (with other proper design), if perhaps not exactly the sound you are looking for.

In the case of the 18Sound 12NDA520, (and assuming I had a horn coverage angle that was appropriate with a cutoff of around 500 Hz), Looking at its freq. response I'd probably choose about 900 Hz for the crosspoint with a LR 4th order. An LR 2nd order? - about 1200 Hz. Here the LR version allows a bit more "give" to the lower freq. response because its a -6db design, if instead it was a -3db then I'd worry some because the crosspoint would need to be a bit higher in freq., (and particularly with a lower order crossover), would likely cause problems with the 12" driver becoming too directive above 1.4 kHz.

If your contemplating the BMS 4540ND, then you would need to factor in its freq. response. - and THAT would suggest a LR 4th order of about 1.4 kHz with the 18Sound 12NDA520.

IMO though, I would NOT use any of the BMS models. I'd want a lower freq. response that the 450ND and 4552ND just can't provide. Additionally, I'd want something that was a bit more "3D" in sound. Instead I would choose any of the 2 inch exit compression drivers from Radian. With the most expensive 950 probably providing the best sound and allowing for something like a JohnK transient perfect 2nd order around 1.2 kHz.

But again though, thats just another idea!

Oh, BTW - IF you want a "2.5" helper design for the open baffle loss I have several ideas. If you want to keep with the 12" 18Sound drivers AND are willing to use a parallel crossover then look at the costly (but worth it) Zero Ohm inductors by Mundorf. (I have an alternate suggestion for the Tone Tubby.)

[MBK]

It seems we're all on a very similar page here, both in design goals and in ideas to achieve them. Ironically I have friends here who have Azurahorns with Lowthers, and just a few weeks ago I drew a LeCleac'h contour for a 500Hz horn to be produced in small series by a friend here. The main horn will be for 2" drivers, and in fiberglass (see my post #131 for pic for pic). I also drew attachments for 1.4" and 1" drivers one can later have made on a lathe or a CNC, in wood, to extend the horn for the smaller drivers.

My own goals are very similar to ScottG's comments above, I posted this here some time ago as well - ideally let the 15ND930 go up close to 1k +-200 Hz, with a compression driver on top (the 1.4" 18Sound NSD1480 looks very good on paper) and a wide 120 degree coverage to match the 15" in dipole or cardioid mode (see my post#130 for pic). The question is whether the 15" satisfies this high up in the long run, or whether a midrange is necessary. Right now I still have a 6.5" midrange between the 15" and the tweeter because no way I can use the dome down to the 1.2k range in normal listening. I only could do some preliminary testing at low listening levels, which indicated promise.

In any case the 12" would be an easier choice on the upper side of the passband, question is how much added IMD you'll get from added bass stress in dipole operation, compared to the 15". Maybe not much, especially with the AIC model.

[Lynn Olson]

ScottG, your info is much appreciated, especially your experience with drivers I know little about, such as prosound anything.

I have to "read between the lines" because my design priorities are somewhat different than yours. My preferences have been formed by speakers I've liked from other designers (that I've heard for myself) and the sonic qualities I've liked and disliked in my own designs.

Constant directivity vs frequency is fairly low on my priority list. I'm the guy that usually crosses over an octave higher than anyone else - the Ariel, for example, with its Scan-Speak tweeter with 1mm excursion, has a measured 4th-order acoustic crossover at 3.8 kHz.

Since driver excursion increases at a rate of 12 dB/oct in direct radiators, even fairly small increases in crossover frequency decreases the "area under the curve" for excusion quite substantially - and this is audible as IM distortion, grain, congestion, and an overall stressed sound. With horns, it seems they fall off the cliff even more severely, with gross horn coloration when pushed too close to the edge.

I guess this is partly because I'm an old-school BBC-style designer, and never believed the data coming out of Canada from the NRC and the popularized data from the HT crowd. Probably more significantly, I've never heard a constant-directivity speaker that I liked, so this design parameter doesn't carry much weight with me.

It sounds like your design experiences are different than mine, and you like different things, which is good! I surmise we hear stereo in somewhat different ways, and have different sets of expectations of what a "good stereo image" sounds like. As an old quadraphonic guy, my expectations are quite different than the direction that the mainstream has taken over the last 20 years.

I'm curious about this 1" versus 2" business. I've heard that small-format CD's are more "strained" and "hifi" sounding, vs the more relaxed sound of the large-format CD's. But I've also heard that 2" CD's get into trouble at high frequencies, and need a supertweeter to make it past that last 15 kHz or so. What's the deal here?

Are small HF horns even available for 2" throat size? I really don't want a 3-foot horn crossed at 500 ~ 800 Hz: that pretty much defeats the whole idea of the widerange dipole in the first place. If I can't find a good-sounding horn/driver that isn't insanely huge, I'll get a high-efficiency ribbon (or maybe the Mundorf AMT) and be done with it.

Since directivity isn't that important to me, my upper limit on the 12" driver is set by the onset of breakup - which for the Tone Tubby and 12NDA520 appears to be around 5 kHz. Depending on sonics, I might not use a lowpass filter at all - but then again, with the Ariel, I ended up tracking the natural rolloff of the Vifa drivers, and giving them a speedup around 4 ~ 5 kHz.

I definitely want to avoid notch filters. I've always had reservations about my speakers that used them - there's a fairly considerable loss of transparency, dynamics, and most serious of all, a flattening of tone color.

Going through your criteria, we're in agreement about having an adequately high crossover for the horn. No argument there; I'm probably further out on that limb than you are. As for frequency vs directivity, well, we can agree to disagree, since I think we're aiming for different goals, especially regardling perception of stereo. I'm pretty far from the mainstream when it comes to stereo, surround sound, and spatial impression.

If the best 1" BMS 1" is more "mechanical" and "hifi" sounding than the best 2" Radian, that makes a difference to me, a big difference. Also very curious about your thoughts on 2.5 designs that overcome the baffle loss - for the 18Sound and Tone Tubby drivers, since I'm still undecided on these things. Something tells me I'll be buying several sets of drivers. Oh well.

[mige0]

hi Scott,

how would you rate the BMS coaxial driver H4590 on 2230 horn?

http://www.lautsprechershop.de/pdf/bms/bms-4590.pdf
"http://www.lautsprechershop.de/pdf/bms/bms-4590.pdf"

It seems to have excellent FR, fairly low distortion up from around 1 kHz and FR at 30 degree goes down only around 10 dB from 1 kHz to 20 kHz in a flat and uniform manner.

Greetings
Michael

[mige0]

Hi MBK,

what kind of software do you use?

If you can not fix it you might try ARTA which is a no brainer for CSD and all the other loudspeaker measurements.

http://www.fesb.hr/~mateljan/arta/
"http://www.fesb.hr/~mateljan/arta/"

greeings
Michael

[jamikl]

Are guitar speakers, eg Celestion or Selenium or Fane, too coloured to use in this application and also in the other somewhat similar thread.
jamikl

[Paul W]

Lynn,
You might find pattern control more important in systems with significant directionality. For example, I found the 10NDA520 crossed to the DDS WG sounded "forward" crossed at 1.1k. A check of off-axis response showed the WG losing pattern control just above XO so there was a sharp off-axis response flare in that range. Moving the XO up to 1.5k put the WG in a range where the radiation pattern more closely matched the 520. So, even with the same on-axis response, a significantly different system sound. While "constant" directivity may not be on your list, smooth directivity vs frequency may yield more predictable results.

Agree the small BMS drivers are not an optimal solution below about 1.1k. The 1.4" 18 Sound MBK suggests looks very good if one wanted to go lower...maybe we can motivate MBK to move forward with his WG

Since there seems to be a general shortage of measurements, I volunteer to measure promising horn/WG candidates, on and off-axis, and post results in your thread...I'm curious too .
Paul