Large midrange for OB??? Scott G ?

[Paul W]

The 10NDA520 is around 200 Euro, 10NDA610 around 220 Euro. The 12NDA520 is about 130 Euro.

[MBK]

Thanks Paul. Odd indeed. BTW none of the three AIC drivers mention shorting rings, that wouldn't make much sense anyway. The 520 models, 10 and 12", are similar in voice coil size and lower BL, probably same motor. The 10NDA610 is different in its larger voice coil and much higher BL (20ish vs. 14ish for the 520 models), and half the xmax.

[ScottG]

I not only know drivers.. I also know distributors/resellers (well.. some US anyway).

Your best bet in the US:

http://www.loudspeakersplus.com/html/18sound.html

Another place that is usually overpriced:

http://www.usspeaker.com/homepage.htm

Some of the prices seem toooo high though (considering dollar vs. euro), on the other hand I wouldn't expect shipping to be cheap from somwhere in Europe. I'd still check to see what they would charge though from these two resellers before purchasing abroad.

BTW, that 12NDA520 price (130 euro) seems VERY attractive!

Why the 12" vs the 10" of the AI 18 sound drivers.. The 12 inch has greater surface area = greater spl's.. and its a good bit more eff. at lower freq.s. It also means that it has more dispersion lower in freq.s. - in fact it appears to have a more constant -3db from 600 Hz to 1.4 kHz (-45 degrees). I wouldn't recomend a lowpass any higher than 1.4 kHz with a LR 4th order.

Absolutely GORGEOUS ribbon! At some point I may take you up on the offer. At this time though, I have non-diy projects taking up my time (..and I'm still thinking about a lower midrange radial project I've got "going".. don't know if anything will come of it though, and likely not anytime soon.)

Note that for your waveguide driver selection.. I think I remember the woodhorn reseller mention that his favorite of all the BMSpro compression drivers was the 4540ND.. (..and strangely the lower freq. bandwidth of the driver isn't much different than the 4552ND.) Again, about 1.3-1.4 seems about right. There are of course good drivers from radian and B&C to consider as well.

[Paul W]

Those were two of my US sources for the 10M600. Unfortunately, neither lists the 10NDA or 12NDA. I saw the ~130 price on two different sites in Europe so the price is real, just need to find out what is going on with the Le spec for the 12.

Loudspeakersplus does list the 10NDA610...and that is actually the one I was asking you about (not the 12"). It's a little feeble on the bottom end, but...

For compression drivers, I'm thinking 4552ND...though both the 4550 and 4540ND come highly recommended.

Don't faint, but I have a question in to DSS to see if waveguide is available in 1.5" for the 4555. I like the idea of a lower compression ratio down low and can't hear much above 14k anyhow. Do you have a view of whether the 1.5" exit would dominate top-octave polars or would the waveguide dominate?

[ScottG]

Originally posted by Paul W
Those were two of my US sources for the 10M600. Unfortunately, neither lists the 10NDA or 12NDA. I saw the ~130 price on two different sites in Europe so the price is real, just need to find out what is going on with the Le spec for the 12.

Loudspeakersplus does list the 10NDA610...and that is actually the one I was asking you about (not the 12"). It's a little feeble on the bottom end, but...

For compression drivers, I'm thinking 4552ND...though both the 4550 and 4540ND come highly recommended.

Don't faint, but I have a question in to DSS to see if waveguide is available in 1.5" for the 4555. I like the idea of a lower compression ratio down low and can't hear much above 14k anyhow. Do you have a view of whether the 1.5" exit would dominate top-octave polars or would the waveguide dominate?

The driver itself will be the determining factor.

The problem I have with the larger drivers and waveguides generally - is actually the dispersion pattern. Specifically it isn't constant and particularly between 3-11 kHz. What happens here is typical beaming and image shift. Also the soundstage is pushed forward and effectivly compressed in depth. At its worst you'll move a little off-axis and everything seems to be comming from the loudspeaker you are closest to. As you might imagin - it isn't to great for tonal balance either. The "cure" then is a wide dispersion super tweeter like the Beyma CP25 (..even it isn't rated from more than about 18 kHz, and even thats optimistic) - and here you can see that it isn't a matter of freq. extension per-se, but rather dispersion vs. freq. extension.

the 610 10" just doesn't have the dispersion pattern for anything but a fronthorn/waveguide and despite it being a purist midrange you'll still need to cross it over low (or with a shallow filter) to blend the dispersion patteren of the compression driver/waveguide to its upper freq. response. In otherwords its a LOT more work to get it right, but its likely that IF thats acomplished - that the driver will be even better (..particularly that the driver will almost certainly have a cleaner linear decay between 1-2.5 kHz).

[MBK]

Just browsing the 18Sound catalogue, the 12NMB420 looks almost more attractive than the AIC drivers: more extended constant off axis directivity, later breakup, and similarly low Le (0.2 mH). It has Faraday rings instead of AIC, and the same low mass, high eff., etc etc. Seems like a case of, you can design a good driver with a whole set of different technologies.

18Sound 12NMB420 data sheet

[Paul W]

Scott,
An Acapella is the only horn I've ever liked, so it might seem strange that I'm trying one. This is just a pleasant journey, so it isn't the end of the world if the result is NG.

To your point, in looking at the different flares in Hornresp, it does seem nearly all of them are beamy on the top end, except the Obulate Spheroid. The OS isn't perfect and DSS doesn't specify the flare, but the photo looks very close. At any rate, it has a good reputation and should make a good baseline for comparison.

Agree on the 610...just wanted to hear your thoughts.


MBK,
Good catch! The 12NMB looks like another viable candidate.


What does everyone think of the JBL 2012H?

[ScottG]

The 12NMB does look very nice..(good catch MBK.) Note - looking at this vs. the AI version, you would have to conclude that the AI version has a misprint on Le and that its .09 not .9. I do like the slightly extended dispersion of the AI version better and I'm not sure how the lack of spl off axis will play-in with a steep filter between 1-1.5 kHz and the compression driver w/waveguide.

The JBL - overpriced (based on the original retail) but with overall superb engineering, it doesn't have the dispersion pattern you want, it isn't as eff., and the frame isn't exactly unobtrusive (considering a dipole). I had looked at this one before - but getting it in the US (new) can be difficult.

[MBK]

BTW Paul what are your reasons for wanting a large diameter driver - in open baffle the dispersion is quite predictable anyway, to match with a compression driver... and a 10" or 12" might have a much less favorable linear distortion / decay behavior, especially considering you've had ribbons and line sources (didn't you have this gorgeous B&G line with Seas Excel at some point? I thought I saw this on this site somewhere).

I say all this tongue in cheek because I have also been toying with options in this direction for my open baffles. Vested interests in this thread...

I now have double 10"'s crossed in the 100-200 range (depends on the mood of the week, with active x-o settings can be changes easily), 6.5" up til 1700 Hz and then a dome tweeter. The baffle is a 7.5" deep U-frame, 24" wide, total 48" high, that's where the measurements came from. The sound is great, the SS8543 6.5" is extremely clean, the (cheap) Seas tweeter is never harsh etc.

So why change then?

- the woofers are older Vifas and though Q=0.5 at Fs 23 Hz they always seem a bit boomy to me - I suspect at higher excursions 2nd and 3rd harmonics might play a role in this. I'd guess new designs are cleaner, plus maybe a bit more Xmax.
- the system sounds extremely clean up to say 90-93 dB in-room. Beyond that distortions set in - be it power limitations (I use 3x LM3886 at 38V rails per side) or tweeter overexcursion, hard to tell. It would be nice to actually have a true 20 dB *headroom* at say 90 dB in-room SPL and that means, efficient (pro) drivers and horns.

Now initially I wanted to simply add a 15" pro woofer - the B&C15PS76 is available here, looks good, and is OK price wise. Better may exist but I'd rather save that USD250 on shipping.

Then I thought, why not take power demands off the fairly inefficient SS8543 on the low end and aim at crossing the 15" high, say 300 Hz.

Then I saw Earl Geddes' Summa design, which is a boxed 15" (he uses B&C15TBX100 crossed at 900 Hz into a horn of his design, oblate spheroid that is) which gave me the idea to just use a larger driver higher up. Ironically the Summa has practically identical dimensions to my baffle, except for a bit more depth. Nothing new on the planet. But higher than 1k is daring with a 15", even in dipole, and what if I don't like the horn. So I thought of a 10" or 12" taken beyond 1k, maybe leave the dome tweere for now, and keep the horn option. In dipole a single 12" might do down to 60-80 Hz with sizeable SPL capability, below that a closed box woofer naturally comes to mind - even allowing for experimenting mixing dipole and monople with a shallow slope, for a smooth dipole-cardioid-monopole gradient. Especially, considering that my measurements show my design isn't exactly dipole in the mids anyway.

And now my trade offs:

- how likely is one to be disappointed with the transparency (read, linear distortion performance) of a 12" pro midbass vs an excellent 6.5" hifi woofer
- is dipole -> monopole transition experimenting worth the added complexity of two 12"ers, one in dipole, one in monopole, add an x-o and amp channel..., compared to a simple 15" up to 300 Hz in dipole
- horn tweeter or not - even if the radiation patterns and power response are made to match, the highs will then be very directional. If anything I'd actually want more dispersion in mids and highs than I have now, for depth and naturalness. A horn tweeter would possibly turn out a clinical monitor sound, great for microscopy, not so great for the typical off axis listening around the house that I do. OTOH you can't get high SPL headroom from a dome tweeter... save for exotics made of unobtainium.

Not to threadjack, I just suspect we have similar thoughts and trade offs in mind, and ScottG sure has some ideas on this as well.

[Paul W]

BTW Paul what are your reasons for wanting a large diameter driver - in open baffle the dispersion is quite predictable anyway, to match with a compression driver... and a 10" or 12" might have a much less favorable linear distortion / decay behavior, especially considering you've had ribbons and line sources (didn't you have this gorgeous B&G line with Seas Excel at some point? I thought I saw this on this site somewhere).

I like the "boxless" sound of OB, but the dipole backwave bouncing off the front wall interferes with imaging. The furthest distance achievable in my room is about 6' from drivers to the front wall. (The room has been rotated 90 degrees from this photo...see avatar for current orientation.) So, with OBs, I always end up with felt behind the drivers to attenuate the backwave. (BTW, that is a DIY ribbon, not a BG driver!)



With felt across the backwave, the dipole figure-8 radiation pattern doesn't hold, especially on the top end of a drivers range. The felt will likely continue, so pattern control needs to come from the drivers front radiation. The Summa box and the felt loaded OBs are both monopole at xo...and that's why a large diameter driver to transition to a WG.

Your concerns about large pro-drivers are why I'm not as brave as Earl and will try a 10-12" rather than 15" like Summa. W26's would be great except that violent breakup is too close to a 1k-2k xo...and that's why the current search.

This system will be built as stackable modules until I find a combination that works at least as well as the Seas WTW pictured above...then "permanent" baffles will be built. The BMS1850 pictured up top is the woofer module. BTW, my excuse for this whole exercise is to find equal or better performance in a smaller package.

I find fewer room reflections help imaging, but a waveguide or horn may take directionality too far...just have to try it and live with it for a while to know for sure.
Paul