This worked out well ( BMS tweeters / DDS Waveguides )

[Branwell]

Hi,

Thought I’d share on a recent acquisition.

A pair of BMS 4540ND ( Compression tweeters )

http://www.assistanceaudio.com/02_bms.html

A pair of DDS ENG 1-90 ( 10.5” Waveguides )

http://www.ddshorns.com/catalog.php?page=ENG190Pro

I inserted these into an active system replacing 1” dome tweeters I’d been using. The system’s comprised of:

Morel 110 tweeters ( 1” Domes ), replaced by the wave guide / BMS.
PHL 1340 ( 6” Bass Midrange )
Eminence Kappa Pro 15lf ( 15” Bass )

The crossover is a DEQX.

The amps are UcD180ADs on the tweeters and UcD 400ADs on the mids and bass.

Couple quick comments related to the BMS / DDS Waveguides.

Very efficient.
No nastiest.
No harshness at all ( smoother than the 1” domes ).
Makes 1” domes sound SPL and dynamically challenged.
Relitive to the domes, they dont get congested sounding with complex music.
Very big 3D sound stage that does not loose focus on complex music.
Adds a sense of ease to the sound.

Overall I am really surprised by these tweeters. The only compression drivers I’ve heard have been at live events and to be honest, none of them sounded worthy of a home system. Given this, getting these was more of a leap of faith, but even not run in, they are showing surprising performance.

My plan is to let them run for a week and if all is well, build proper cabinets for them.

While I am doing that ( cabinets ) was thinking JonMarsh might like to test / try them. Any interest ?.

Branwell

[Rudy Jakubin]

Do you think that waveguide also helped improve the sound?
Is it similar to the Dayton 10" waveguide;

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=270-310

I was thinking of getting a pair next week.

Thanks for the link. The drivers are a little pricey for me right now, but maybe later...

[cotdt]

what is directivity factor?

[Dennis H]

Interesting! What XO frequency are you using?

[JoshK]

what is directivity factor?

I think 90º iirc. My quick glances at the website made me think they were using a smaller version of the Geddes type WG.

When I heard Geddes' system I thought the highs were the best part of the system and were as good as anything I've ever heard to date. I heard 0 nasties, which says to my leyman mind that his theory works in practice.

Basically I am not surprised you like them, and thanks for sharing because I have been interested in pursuing this at some point. I'd be really interested if Jon was willing to measure them in WG with his setup. But he has an overflowing plate as is, so you can only ask really nicely and hope he is kind. :W

[Mark Seaton]

The BMS compression drivers are quite nice, especially for home use. They also tend to have a lot of LF strength, and actually have a small amount of travel vs. the quiver that most compression drivers offer. What that means is that they are a little easier to push a bit lower in frequency, which comes into play with one of the two usual points of failure for horn systems. The crossover to the mid has a few more pitfalls. The other issue is simply the frequency response (i.e. magnitude). If the horn is more or less CD, getting flat response on axis is a very important factor. This is much easier to do actively for the DIYer. Passively you must be careful in designing the crossover with good impedance measurements for your model. If you want to very closely match the response, you usually at minimum need some form of high pass along with two tank circuits for "sculpting." Note that the impedance is in fact rising where the horn is strongest, so in effect it's fighting against you in terms of designing your crossover.

Nice job Branwell.

The unfortunate "gotcha" here is that I know of a few people who have noted that they have not received communication from either DDS or Assistance Audio for a while. It would be interesting to see how some of the newer offerings from PE work out.

[Branwell]

Rudy,

The BMS tweeter is a compression tweeter designed to work in a guide or horn. Given this, I’m not sure it would work without it, but might be interesting to try.
As to the DDS guide. While the diameter is about the same as the Dayton, I don’t know if the inner profile is the same so don’t know if they behave the same.


Dennis,

I've tried 1500, 1700 and 2100 using 96db slopes. I’ve not tried less then 1500 as the FR is going away so fast, it would need too much EQ to hold a flat response.
In comparing the 3 frequencies I tried, the lower one goes, the more detail is heard, but unlike 1” domes where you start to get into compression, distortion and SPL limitations, the BMS doesn’t seem to suffer.


Mark,

The DEQX has no problems creating a totally flat response curve from the BMS / DDS pair, but to your point………

I ran some partial tests today to see what it would take to get the thing flat with passives.
Looking at the FR and Impedance plots, inserting a 3uf cap should take out most if not all the Horn gain.

I tried it and indeed, from 5K to 17K went flat as a board.

Above 17K, there is a 5db hump to 22K. I need to do some off axes measurements to see if the bump remains but if it does, a trap would take care of the bump.

Between 1700hz and 5K, there is a bump of about 4 to 5db.
As you pointed out, this is an area where the impedance gets complex.
In the DDS wave guide, looks like a double hump right in that range.
One could use a trap to solve this bump, but I have a feeling you could solve it with a well implemented 12db electrical.

If I can ever figure out how to get SoundEasy to optimize Crossovers / Phase, I’ll have a go at a passive implementation.

In further listening / walking about the room, I am still fairly amazed by the performance. What’s interesting is a lot of what sounded like smear and garbage in “bad” recordings is resolving into listenable detail with this setup which really has me questioning this whole “most recordings are garbage” excuse many use for the poor performance of many exotic speakers.

Perhaps its not that most recordings are garbage, but that some recordings are simply not compatible with some speakers. Hmmmmm……..

Branwell

[dwk]

Very interesting indeed. I eyed that exact combo many times on the Assistance site, but never pulled the trigger. I hope the recent communication problems that Mark talks about are temporary. I have a plan on the drawing board that involves compression drivers, and the BMS were my planned units if it made it to 'production'. Maybe this post subconciously spurred me into action, as I actually started hacking things up on it yesterday.

The Dayton waveguides are NOT straight conical waveguides. There is a distinct curve in the flare. I have some of the 8" and 12" versions, although I haven't actually listened to them yet. They DO have a nice smooth transition to the mouth as suggested by Geddes, but it's not an oblate spheroidal curve either. Seems to be it's own beast; I suspect it may sound a bit more 'horney' than a pure conical due to the higher gain, but I'm guessing.

[JonMarsh]

Hi,

Thought I’d share on a recent acquisition.

A pair of BMS 4540ND ( Compression tweeters )

http://www.assistanceaudio.com/02_bms.html

A pair of DDS ENG 1-90 ( 10.5” Waveguides )

http://www.ddshorns.com/catalog.php?page=ENG190Pro

I inserted these into an active system replacing 1” dome tweeters I’d been using. The system’s comprised of:

Morel 110 tweeters ( 1” Domes ), replaced by the wave guide / BMS.
PHL 1340 ( 6” Bass Midrange )
Eminence Kappa Pro 15lf ( 15” Bass )

The crossover is a DEQX.

The amps are UcD180ADs on the tweeters and UcD 400ADs on the mids and bass.

Couple quick comments related to the BMS / DDS Waveguides.

Very efficient.
No nastiest.
No harshness at all ( smoother than the 1” domes ).
Makes 1” domes sound SPL and dynamically challenged.
Relitive to the domes, they dont get congested sounding with complex music.
Very big 3D sound stage that does not loose focus on complex music.
Adds a sense of ease to the sound.

Overall I am really surprised by these tweeters. The only compression drivers I’ve heard have been at live events and to be honest, none of them sounded worthy of a home system. Given this, getting these was more of a leap of faith, but even not run in, they are showing surprising performance.

My plan is to let them run for a week and if all is well, build proper cabinets for them.

While I am doing that ( cabinets ) was thinking JonMarsh might like to test / try them. Any interest ?.

Branwell

Interesting post, Branwell. I remember these coming up a month or two ago - the plots at assistance audio would indicate 2nd harmonic down ~ 50dB, and 3rd harmonic quie a bit lower- maybe as much as 70 dB down. I was skeptical becuase of the polyester diaphragm thing, but I might have to re-think that.

When did you order that waveguide? I hope that Mark's comments don't indicate there are business problems. Is BMS sold by anyone else in the US?

It would be interesting to get some detailed measurements of SPL vs frequency and impedance, and HD, espeically to establish what the issues might be doing a passive crossover. Looks like they might be usable in a passive application 2 kHz and above.

~Jon

[AJINFLA]

Hmm, I must be reading it wrong, but it looks more like 2nd (harmonic) is -30db and 3rd -50db, at least for the 4540ND (@ 110+db!).
I do like the coaxial driver, but way expensive to buy on a whim.

cheers,

AJ

[Mark Seaton]

When did you order that waveguide? I hope that Mark's comments don't indicate there are business problems. Is BMS sold by anyone else in the US?

It would be interesting to get some detailed measurements of SPL vs frequency and impedance, and HD, espeically to establish what the issues might be doing a passive crossover. Looks like they might be usable in a passive application 2 kHz and above.

~Jon

Hi Jon,

Knowing Jack Alexander of Assistance Audio, I'd be surprised if there was a problem with getting the BMS drivers in the future, but I'm not sure about DDS, as I know both DIYers and OEMs who haven't been able to get a hold o them, and no one was at NSCA last month. That would be a shame, as they make some very well crafted stuff.

There are some interesting options when using something like the BMS 4550 or its ND counterpart. The useful low end is greatly affected by the size of the waveguide being used. I, and others, have found these to generally have more sub 2-3kHz headroom than many other compression drivers. Once you have real impedance measurements and get a bit creative with something like LspCAD on hand, the crossover isn't as daunting. Like any other design choice, there are as many oppinions as options, but many look at the frequency response and look at the point where the low end starts diving as the lowest useful point. I would expect distortion to start to increase below this corner, but if you are looking at a passive crossover, especially for home playback levels, you can often put the drivers to use down to the frequency where the low end becomes equal with the response above 10kHz. Flat response isn't as simple, as it requires "scooping out" the range of highest efficiency, where there is typically a shallow bump in impedance. While you can get it to be ok with a single LCR notch, I have been finding a much better match to the shape when using a pair of notch circuits in conjuction.

The only other cautionary point would be to always be sure to work from a few measurements in the operating angle and not just on axis. There can often be artifacts directly on axis that dissappear quickly which really should not be addressed with the XO, but physical means.

[ThomasW]

I spoke with Tracy Sherwood of DDS a few minutes ago. I ordered a pair of the waveguides $64.50ea + shipping. He's in the middle of a waveguide build for Assistance Audio. He said mine should be completed by late this week. I'll update as I have more info.

The waveguides are available as either a thread-on or flat mount bolt on design.

[Mark Seaton]

Good to hear. My appologies to Tracy for any misinformation, but the reports were from 3 or more people recently.

[Dennis H]

Mark, as you have experience with DDS products and horns in general, which of the 1" horns/waveguides would be your first choice for a home system, say 15' to the main seats?

http://www.ddshorns.com/catalog.php?page=products

[ThomasW]

Branwell,

Do you have any pics of your latest project?

[AJINFLA]

Hi Thomas,

what tweeter are you planning to use with the DDS's? Whatever became of the MCM's you ordered? Enquiring minds want to know :B .
BTW, I'm well aware that the FR of the CD is dependent on the horn, but I would still like to see some off axis curves so I could at least see the behavior in the topmost octaves where the driver (presumably) has become too directional to be affected by the horn.
I'm not a fan of sharply decreasing directivity at high(est) frequencies and the resulting power response droop - like Zaph. The reason I chose the XT19 even though I also have XT25's. To me, off axis at the very top does matter and is audible, even to my aging ears :W

cheers,

AJ

[ThomasW]

The MCM waveguides are ready to go, just waiting for me to finish a new Arvo test baffle. Some domestic responsibilites have interferred with speaker building lately. However that should change next week....:T

I'm not sure about the tweeter for the DDS. Mark mentioned the BMS 4550, so I'm looking at that. I'll probably chat with Jon later today and see what he thinks. This isn't an area where I have much experience, as result I'll bow to those with more knowledge.

I may however do something weird and make this an MTM just for grims. The new Aura 10"/12" woofers that Jon's playing with might be just the ticket since they play pretty high....

[Dennis H]

AJ, the DDS site has polars for their horns - much appreciated. To me, the 630-16K horizontal response of the CFD 1-110 Pro looks very interesting. Of course the vertical dispersion is much more limited. Pinging Mark, have you tried this one?

http://www.ddshorns.com/catalog.php?page=CFD1110Pro

Edit: I just realized that the one above uses a different dB scale than the conical waveguide so the waveguide looks better than I thought.

[Branwell]

Hi,

Re Photos. Sorry. Old digital camera that doesn’t work. Need to get a new one……..

Re Assistance Audio. I had no problems at all. In fact, after talking with Jack, it crossed my mind that he was one of the more straightforward retailers I’ve spoken with in a while and based on my very limited experience with him, I’d definitely shop there again.

Branwell

[Paul W]

Mark,
The harmonic distortion measurements for many home audio tweeters look extremely good. On the other hand, distortion plots for many of the pro compression drivers don't look as good...even for the expensive ones. Of course the measurements are taken at wildly different output levels so it's an apples to oranges comparison.

So, I wonder, which do you believe stands the better chance of low HD in a low gain CD waveguide in a home environment...a good 1.75"/1" exit pro driver or a good 1" home audio driver? Is the distortion shown in the pro measurements caused only by the horns or is there an additional distortion mechanism inherent in the compression driver technology?

[Branwell]

Hi,

Re dispersion.

In my room, according to my ears, the wave guide is noticeably more directional than a 1” dome.

Is that a show stopper ?.
Wave guides have a different set of strengths and weaknesses then a traditional 1” or smaller dome tweeter. Given this, I’m not sure applying the criteria for conventional tweeters to a wave guide setup will result in satisfactory results.

I think if at all possible, one should listen and then decide on whether or not a driver is suitable.

Branwell

[Mark Seaton]

I may however do something weird and make this an MTM just for grims. The new Aura 10"/12" woofers that Jon's playing with might be just the ticket since they play pretty high....

While some may say it doesn't matter, I like symmetry. :T

I would again suggest not being too shy with the low end capability of the compression driver. Tom Danley crossed a 4550 below 1kHz in the Runt which gets startlingly loud for the small speaker it is. I won't say that an 800-900Hz crossover doesn't open up some possible problems, but I certainly wouldn't rule it out entirely. Of course those cases use rather large horns that provided more low end response and front-back directivity/gain.

The crossover to the woofer is after all the real stickler in a home application, and even in most pro-sound designs that may sound ok outdoors, and horrible indoors. Models I've played with to look at various interactions suggest that drivers with suitable bandwidth, allowing an overlapping, 2nd order filter are the holy-grail in overall integration. Of course making that work is rarely easy without compromises. That's along the lines of what I will be playing with in some high-octane home theater LCRs I hope to produce in the future. This would be a good situation for a DIYer to first validate such a design, components and target response with a DSP based crossover like the Behringer.

A steeper crossover like some of the eliptic sorts that Jon and others have been implementing could also be very appropriate here to minimize the range of interaction.

[AJINFLA]

Hi Dennis,

the DDS site, BMS etc have been on my radar screen for a while now, so yes I've seen those polars. My question is more about the BMS driver itself. What's the off axis (30,45) look like @ 15k when using a 110deg conical horn (round waveguide )? I've seen some (smaller) compression drivers that have really piqued my interest due to their very good off-axis.
Maybe the saddest part of all is that I've been sitting on a pair of P-audio coax's with compression drivers(!) for darn near a year now, without so much as a measurement. One's still unopened in the box . Thats what sucks about my current domicile :M .
I did offer it up for NP Dang (DIYMA) to test, but he was unable to squeeze it into his schedule.

Branwell,

I would certainly hope the waveguide is more directional, since that is what it's supposed to do! Or at least that's what I've been using them to do for years now:W . The question about dispersion is about the BMS unit itself, not the WG. How directional does it become at HF? That is the possible show stopper - for me.

cheers,

AJ

[Branwell]

Hay AJ,

I'll run some measurments to find out :-)
Do these need to be in the guides or out of it ?.

Branwell

[Mark Seaton]

AJ, the DDS site has polars for their horns - much appreciated. To me, the 630-16K horizontal response of the CFD 1-110 Pro looks very interesting. Of course the vertical dispersion is much more limited. Pinging Mark, have you tried this one?

Hi Dennis,

I haven't tried that one, and only have second hand information on most of their lenses, having seen some measurements, and knowing people using them. I have talked with them about custom work, and inspected the products. They do very nice work, and they actually provide real measurements of what the horns might do. I would note that on occasion there can be variances between different drivers on different horns. Depending on the angle of the horn, a good bit of the effective part of the "horn" exists in side the compression driver. The transition at the throat will be a little different for two drivers. Especially for wider angle horns, you shouldn't be surprised if you see some differences spacially between drivers. No huge, but some drivers are a little more tempramental with irregularities in the horn.

Radian also makes some very good compression drivers with good high frequency response, but on the pro side they haven't been viewed as durable as say BMS and B&C. I'm not sure it would matter for home use. Note that the BMS drivers are of a different geometry than most compression drivers where they are effectively a ring radiator.

In regards to the horn you link to, I would look for a more symmetrical design. I would look to have a horizontal and vertical angle that make for less than a 2:1 ratio. You could get really creative with shading drivers and such to get a smoother transition to the narrow vertical, but the short answer is that the dimensions are almost aways too short for the narrow angle. A symmetrical horn will be easier, and a round one even more so. The problem with symmetrical horns is that any issues or reflections all happen at the same place or frequency. Slight differences in the two angles and dimensions spread issues out some.

Of the asymmetric horns, the 60/80 or 70/90-ish degree horns would probably be best suited for home use IMO. Note that for a 1" exit/diameter driver, at 20kHz you can't get more than ~90 deg of dispersion. The trade off you have to juggle is that the larger the mouth area of the horn, the better pattern control and LF loading you will get on a compression driver while also pushing the woofers further from the tweeter. The DDS horn I might try and play with first would be the CFD 1-70 Pro. It would also seem logical in crossing to a pair of 10-12" drivers. I would tend to stay away from designs with lots of sharp transitions at the mouth or throat.

[AJINFLA]

Hmm, Branwell, I'd probably try it with the horn and without. Without might be problematic with diffraction effects,etc. As I suggested (and Mark S) the dispersion at 20k could be mostly limited by the angle of the horn.
But strongish output @ 45deg off @ 20k would be just dandy anyway :T .

Mark, do you have any experience with any eighteensound units? My exposure to pro stuff is limited to occasional setups, so I have some , but not enough!
Here's some that might be of interest: http://www.eighteensound.it/index.as...roduct&pid=179

http://www.eighteensound.it/index.aspx?mainMenu=view_product&pid=178

What are your thoughts about good ol' JBL? I don't hardly see anything that some of these sexy european brands are doing that JBL hasn't done before.
B&C's gap cooling, BMS ring radiators, (magnetic) shorting rings,etc,etc. Are they just refining what JBL has already lead the way to?
For example, I don't see anything that B&C,BMS or Eighteensound makes that can come close to the JBL 2268H, do you?

cheers,

AJ (Pro audio pseudo-amateur :W )

[tg3]

What does it mean that the ENG 1-90 are rated at 112 dB sensitivity?

[AJINFLA]

Not much. Unless they use the same CD for each horn so that you can compare them relative to each other.

cheers,

AJ

[Ludvig]

Off axis behaviour

How does the ENG 1-90 Pro perform off axis? Since it's not called a CD waveguide I suppose it is not CD So what is the off axis characteristics?

[noah katz]

These results are *very* encouraging. I'm going to build WG LCR's, using the Eighteensound XT1086.

A guy at High Efficiency Asylum tried a BMS compression driver on the XT1086 and got apparently similar excellent results.

http://db.audioasylum.com/cgi/m.mpl?forum=hug&n=98095&highlight=eighteensound&session=

Here's the response he got at 10 deg intervals

http://lscon.tripod.com/xt1086/SPL.jpg

"How does the ENG 1-90 Pro perform off axis? "

The web site gives that info.

[JoshK]

What woofers are you going to mate them with?

[Ludvig]

The web site gives that info.

Yes, they do, but their way to present the data is very difficult to use. You can see what the maximum and minimum dispersion is between 600 and 16000 Hz, but you can't tell wich frequency that belongs to which curve. So one can't see if the response are smooth falling between the two extremes, or if it ripples back and fourth. Their plots would look similair in either case.

I see that you have studied the XT1086 data, and look at the curves in it's datasheet, they are exemplary presented!

[noah katz]

"What woofers are you going to mate them with?"

They have lots of nice drivers, but today's frontrunner is the 12ND710.

http://www.eighteensound.com/index.aspx?mainMenu=view_product&pid=238

Dual shorting rings, 101 dB 1W/1m, 5 mm xmax, low power compression.

WinISD says that in 2.5 cu ft tuned to 55 Hz, 150 W will give 117 dB/1 m from 60 Hz on up.

Actually only about half that makes it to the driver; it takes 2.5 ohms series resistance to tame down the damping from the very low Qe. Without it there's a several dB trough centered around 90 Hz.

I know that sounds unpalatable, but it costs only 1 dB reference efficiency, and it allows the use of cheaper air coil inductors with higher DCR.

This last weekend on a plane flight I happened to sit next to a speaker designer for Tymphany (somebody Weatherby IIRC), and he said there's nothing the matter with doing that.

Power compression will be esentially nil; it's spec'd at 0.6/2.0/2.8 dB at 35/175/350 W, and average running power even when played very loudly will be a few watts.

[AJINFLA]

(somebody Weatherby IIRC)

Engineered the Mackie HR824. Likes waveguides. Unlike Ken Kantor's accountants.

cheers,

AJ

[noah katz]

"Engineered the Mackie HR824"

Yes, that's the guy.

[JoshK]

Noah,

Sounds very cool! Maybe I'll have to build that one too, if you are up for sharing. I've been thinking about doing such a speaker ever since hearing Dr. Geddes' summas.

[noah katz]

Josh,

Actually, I was hoping for some sharing, too

If I can't interest someone in designing a XO (a Cauer elliptic would be nice, I think), I'll just substitute the 12ND710 for one of the shorting ring-less drivers specified in the Eighteensound 12" kit with its 1.6kHz XO and hope for the best.

Their kits are here

http://www.eighteensound.com/index.aspx?pid=238&mainMenu=kits

I'll start a thread on my project when I get it more fleshed out.

[Hdale85]

Is it just me or are their subwoofer kits horrible? See the Frequency slopes for the 18? drops below 100db at like 200hz.

[dwk]

Noah, where are you sourcing the 18sound stuff? usspeakers has some of it, but I never saw the XT1086 on their site.

The main shortcoming of Noahs project when compared to the Summa is that the waveguide is too small- the same problem the Ciare/BMS kits at Assistance have. You need a pretty big waveguide to allow the lower 900-1kHz xover that would be ideal, without it you are asking the woofer to play that much higher. If they made a larger version of the XT1086, it would be great. Still, I agree that it's an interesting path, and am looking forward to more repors as it matures.

I wonder how big a run DDS would need for a custom OS waveguide for the BMS driver? IMHO if you can get a ~1kHz xover you also open up interesting options like mating with say a W22 (actively no doubt, due to the efficiency differences). As I mention in the RS52 thread my current experiment is along these lines - the RS52 dome mid in a waveguide crossed at 500-600 to an L26. I'll cross the RS52 at 4-5kHz to something - tentatively a Dayton neo in a mini waveguide, but that's only because that's what I have.

[noah katz]

Couple of things:

These are for PA, not HT. And 96 dB/1W/1m at 35 Hz is pretty impressive.

Also, I think they make their measurements in full space.

If you plug the data into WinISD or somesuch and then compare w/other drivers/designs, it will look much better.

[JoshK]

dwk,

I see your point, but I was thinking (and not saying) that I would take noah's idea and shoehorn a PHL 1120 in between the WG & 12". Harder to cross, but less problematic for the WG & 12.

[noah katz]

"Noah, where are you sourcing the 18sound stuff? usspeakers has some of it, but I never saw the XT1086 on their site."

I called USS the Friday before last and the guy said he'd get back to me w/quotes, but I haven't heard from him yet.

"The main shortcoming of Noahs project when compared to the Summa is that the waveguide is too small..."

Pick your poison. The main shortcoming of the Summa or any 15"/appropriate WG combo is it won't fit in the space I have for it.

Earl himself speculated that a 12" version of the Summa would likely give a large measure of its performance.

"If they made a larger version of the XT1086..."

They do:

http://www.eighteensound.com/index.aspx?mainMenu=view_product&pid=177

But again, too big for me. Also, it's pretty deep so time alignment is an issue unless you have a XO w/delay.

[AJINFLA]

You can buy 18sound here also: http://www.loudspeakersplus.com/html/18sound.html
Give them a call if you don't see what you need.
18sound drivers are of very high quality.
I had no problems with my previous transactions with USS.

Cheers,

AJ

[noah katz]

Glad to have another source!

Thanks for the link, AJ.

[dwk]

"The main shortcoming of Noahs project when compared to the Summa is that the waveguide is too small..."

Pick your poison. The main shortcoming of the Summa or any 15"/appropriate WG combo is it won't fit in the space I have for it.

Earl himself speculated that a 12" version of the Summa would likely give a large measure of its performance.

Yeah, size is a definate problem. I have the luxury/constraint/problem of needing to build my speakers into the corners of my room, and so have a bit of wiggle room.

A 12" summa-lite should work pretty well. Looking at the 18sound plots, it wouldn't surprise me if you could get away with a 1.2k or even 1k xover if you went active and steep. Not sure how hard a passive xover would be - not my forte (I'm using Jan's PC xover stuff, so my life is 'easy':-)). The proof is in the pudding, though.

"If they made a larger version of the XT1086..."

They do:

http://www.eighteensound.com/index.aspx?mainMenu=view_product&pid=177

But again, too big for me. Also, it's pretty deep so time alignment is an issue unless you have a XO w/delay.

Argh. Damn you. Didn't see this as I was looking only at the 1" units. The plots with the NSD1480 look pretty nice (it'd be nice if they had distortion plots though). You can certainly do 800Hz, and maybe even as low as 600 in a domestic setting. The ND drivers are awfully expensive, though, judging from the link AJ provided.

To add to that, turns out that BMS has a brand new 1.4" version of their coaxial compression driver. That might be very sweet indeed on the XT1464. I saw it on the BMS site - AssistanceAudio doesn't have any info yet.

I'm getting close to having a mono version of my RS52 experimental speaker running, though it will probably be after Memorial day. That will let me eval a ~600Hz xover to a waveguide to see how it does. I originally wanted to do a Unity concept to extend the horn/waveguide lower, but I'm debating the utility. If the mid will get me to 600 and the 1/4 wave resonance of my horn is 250 or so, it may not be worth trying to push it for an extra octave. I guess it depends on how bad the 1/4 wave resonance is and whether it can be dealt with in-band - if it can then there are more options.

Too many fun ideas out there.......