A time-aligned top end for the Khorn

[Guest " "]

I've had the BMS coaxial 4592ND compression drivers/V-Trac horns, in my Khorns for over a year now. Hardly a new idea.

My question to the forum is this. Has anyone here heard a pair of 2" outlet coaxial compression drivers in 2" throat midrange horns in a pair of Khorns?

Greg

around here anything goes. no different than how the patrician IV put horns inside horns. the more choices and options, the better. different products are just that....products don't always need to compete with each other.

I think that altas has a licl *** PA horn with coax drivers in it as well.

[Al Klappenberger]

Roberts,

I sure wasn't YOUR new idea! Now let's see you do a Linzwitz-Riley phase coherent network for it. You can bet I won't do it for you. You can just shove my Universal network in it being you have the remainder of the 10 sets you made under license from me sitting around. You lucked out since it's at 6 KHz. What are you going to do when those run out? Guess who will have to supply them then? Where do you put the attenuator? Does it need one? What impedance? I am not going to do that research for you either!

Fritz,

When you say "horns inside horns" I assume you mean mounting a tweeter like the T35 inside the mid-range horn mouth. The CDX50 is different. The two drivers are actually mounted such that the two diaphragms are the same distance from you, That means virtually the same propagation distance. I suspect you know that though. I just figured I would clarify the difference.

Al K

[djk]

"Has anyone here heard a pair of 2" outlet coaxial compression drivers in
2" throat midrange horns in a pair of Khorns? "

Yes, the BMS on First Octave Audio wood horns. These horns are really too big for a standard Klipschorn, Octave research sells a cornerhorn based on an 18 that has a 300hz crossover point to the Mid and HF.

Large Tractrix (or exponential) horns have very limited dispersion in the top octave. The rule-of-thumb for these types of horns is cross one octave above Fc, and cross again into the tweeter at one decade above this. This works out to a 500hz crossover for a 250hz Fc horn, and bring the tweeter in above 5Khz.

The initial expansion just off the throat is what controls the VHF dispersion. If you look at the K402 you will find this initial expansion looks to be conical, only changing to Tractrix near the mouth.

http://counseling-software.com/4way.html

[Nat Denkin]

Al,

Do you plan to make IM distortion measurements of coaxial drivers? Depending on crossover frequencies, nearly half the power would be in the same throat as the tweeter band so that I would expect IM to be higher for the tweeter band than if that band had its own horn.

Thanks,

nat

[Al Klappenberger]

Dennis,

"Yes, the BMS on First Octave Audio wood horns. These horns are really
too big for a standard Klipschorn, Octave research sells a cornerhorn
based on an 18 that has a 300hz crossover point to the Mid and HF"

Yes, I think the B&C DCX50 was "inspired" by the BMS coaxial. The 300 Hz low end is what I don't like about it. It is for larger systems than the Khorn. It just doesn't need respons down to 300 Hz and below. The B&C mid-ranges were designed for the 400 Hz of the Khorn.

----------------

" Large Tractrix (or exponential) horns have very limited dispersion in
the top octave. The rule-of-thumb for these types of horns is cross one
octave above Fc, and cross again into the tweeter at one decade above
this. This works out to a 500hz crossover for a 250hz Fc horn, and bring
the tweeter in above 5Khz."

This dispersion of highs is why I was so surprised to see the nice 30 deg off axis response the DCX50 tweeter was showing on Dave's horn. I expected the highs to come straight out like a flashlight beam! The crossover choice at 9 KHz is where B&C suggests it should be on its spec sheets. It looks like the right spot by the overlap in the responses of the two driver too.

------------------

"The initial expansion just off the throat is what controls the VHF
dispersion. If you look at the K402 you will find this initial e"xpansion
looks to be conical, only changing to Tractrix near the mouth. "

This is out of my area of expertise! Someone earlier mentioned the conical throat issue. All I can say is the horn is purely Tractrix expansion but it has a rectangular cross section. Could the conical thing have something to do with the cross-section being rectangular versus round? My UNeducated thought was of the JBL "Paragon" where the mid-range horns were aimed sideways at a curved front. The highs may be bouncing off the curved vertical sides of the horn in a similar fashion. ???? What do you think? I really have no other idea!

-----------------

Nat,

I had thought about doing distortion plots, but didn't. I did distortion testing on the DCM50 driver that is at the heart of the DCX50 and it was very clean. Only the tweeter would be in question. I found that the small round aperture in the Beyma CP25 caused distortion when you ran it up to unrealistic levels. The throat of the tweeter in the DCX50 is right small too. RATS, Now I guess I gotta go measure that!

Al K.

BTW: The Sonicaps came in for the network yesterday. I think the inductors are going to take a while yet. I need them to determine how I am going to handle one inductor that is less then the 0.1 mHy smallest inductor Solen makes of Litz wire. I am going to try gluing two .1 mHy inductors together, connecting them in parallel and using mutual inductance to adjust for the value. It's going to be fun to determine the correct spacing!

[Al Klappenberger]

Dennis,

Here's what I'm thinking on the high dispersion thing. The curve is the exact curve of the K2 horn, well, half of it anyway, looking down at the flat curved sides. It's the correct curve because it was drawn by a CADD program from a macro generated by my Trachorn.exe program used to design the K2 horn. The other lines were done by the seat of my pants trying to make the incidence and reflection angle equal as a sound might bounce off the curved side. I think the driver might be farther back than I have it shown though.

What do you think? Hair-brained?

Al K.

[djk]

"The initial expansion just off the throat is what controls the VHF
dispersion. If you look at the K402 you will find this initial
expansion
looks to be conical, only changing to Tractrix near the mouth. "

This
is out of my area of expertise! Someone earlier mentioned the conical
throat issue. All I can say is the horn is purely Tractrix expansion but
it has a rectangular cross section. Could the conical thing have
something to do with the cross-section being rectangular versus round?
My UNeducated thought was of the JBL "Paragon" where the mid-range
horns were aimed sideways at a curved front. The highs may be bouncing
off the curved vertical sides of the horn in a similar fashion. ????
What do you think? I really have no other idea!

-------------------------------------------------------------------------------------------------------------------

It'a confusing, as a conical expansion horn may have a rectangular cross-section. I think the only reason you have any off-axis HF is that it radiates only from the small inner stub inside the driver, and is not seeing the side walls of the horn for a ways. It would be interesting to do a TEF on the combo. With regular 2" drivers on a Traxtrix (or exponential) horn they may measure flat on axis but they don't sound right in the reverberant field in the room. I know two people that have TAD 400x drivers that later added supertweeters.

I couldn't get the BMS to sound 'right' and I sold them to a friend (who is still fiddling with the VHF crossover point), but Iwould like to try them again on some old Emilar 500hz horns that look like they should work with the BMS type driver. Bill Woods has done quite a bit of work with these type drivers and has given me some ideas to try.If you would like his data and network ideas (eight graphs, a schematic, and a couple of horn photos), shoot me your e-mail address.

[greg928gts]

dkj - I've heard that system that you included a picture of, all except for the Lecleache style tweeter horns. Those mid-bass cabinets were fantastic sounding. The 18" bass horns didn't sound good to me. I listened to the coax and then with a separate tweeter and I preferred the separate tweeter. But all in all the system was really good. The guy demostrating it for us also had a 10' screen projection system and we watched/listened to Pink! Wow, flexible is all I have to say on that subject!

Did you notice any beaming issues with the tweeter in the BMS coax driver on that system?

Greg

[Al Klappenberger]

Dennis,

I would like to see the data, but I'll bet it will be over my head. I really don't know much about horns. It's al_k@alkeng.com

When I get this network done and the other one built up, I plan to do some listening tests this time, which I usually don't do. I don't trust my ears, but if there a glaring difference between this and what I am used to, I should hear it.

There is yet another issue that bothers me. I wrote a little DOS program that takes the computed amplitude and phase data out of each of the channels of a crossover and sums them up. I have the option to invert one driver or add in a delay to one or the other. I found that the outputs add up flat as a pancake if the delay a zero, but add just 1/4 inch different propagation delay to on channel and it results in a 2 dB dip. More delay screws things up even more. This is why I have never attempted a Linkwitz-Riley network before. I don't know just how closely aligned the acoustic sources are in the DCX50. All I'm sure of that it's a lot closer than a separate tweeter and mid-range!

Al k.

[djk]

"I preferred the separate tweeter"

So do Dr Bruce Edgar, Bill Woods, and I.

"Did you notice any beaming issues with the tweeter in the BMS coax
driver on that system? "

It didn't sound quite right. Bill Woods says it tends to sound 'tizzy', and I would have to agree. It is especially noticeable on aplause and female vocals. Stuffing a small block of 30PPI foam (with a hole in the center) in the throat really helped.

[greg928gts]

"I preferred the separate tweeter"

So do Dr Bruce Edgar, Bill Woods, and I.

"Did you notice any beaming issues with the tweeter in the BMS coax driver on that system? "

It didn't sound quite right. Bill Woods says it tends to sound 'tizzy', and I would have to agree. It is especially noticeable on aplause and female vocals. Stuffing a small block of 30PPI foam in the throat really helped.

In my Khorns, the BMS coax sounds remarkably good at my seating position. I attenuate the tweeter 3db and it's probably still a little hotter than the average person likes, which happens to be the way I like tweeters. It's an average sounding compression tweeter, not nearly as nice sounding as the Beyma CP25 or the Ciare 1.26Nd.

In my system, at my listening position, the high frequencies are much more directional coming from the mids, which is not necessarily bad, just something I notice. I also notice that soundstage widens out and imaging is not as precise, which again, especially in my system, is not bad. I tend to get imaging that is too pinpoint at times, so a wider soundstage and imaging is nice.

The problem is, with music playing, when I stand up, I hear the tweeter sound change, and when I walk around the room, the tweeter comes in and out. It's quite obvious that the high frequencies are beaming out of the mid horn. It's just too deep a horn to properly disperse the high frequencies. This is the primary reason why I have not recommended using the coax in the V-Trac horn.

This is also why I asked if anyone had actually heard the recommended setup being discussed here. I think what we have here with these recommendations is an over-reaction to a perceived problem (time alignment) that ends up not sounding as good.

Greg

[djk]

The server ate a major post, what a PITA.

3D mapping of reflections and resonances:

http://forums.melaudia.net/attachment.php?aid=1760

Magenta = direct wave
Green = reflected wave (from mouth edge or zones of rapid variation of the profile)
Blue = diffracted wave (from the mouth edge or zones of rapid variation of the profile)
Orange = high order modes + breaking modes of the diaphragm + high frequency resonances of the driver

A good horn should provide the less amount of reflected waves,
diffracted waves and unwanted high order modes.

Round Tractrix horns #13, 14 (driver resonance around 10Khz), Rectangular Tractrix horn #16.

Be sure and see #9, flat from 300hz~20Khz, minimal reflections.

----------------------------------------------------------------------------------------

I bought some 500hz Emilar EH520 reciprocating flare horns that look like they should work well with the BMS and maybe some foam, I may buy another pair of the BMS.

It looks like a tweeter horn entering into a mid horn.

I was thinking of making a speaker like the LB-76 with the Emilar/BMS replacing the K500/K55V/K77 and using with a TH115 sub for a small kick-butt PA.

[Al Klappenberger]

Dennis,

I looked at that pdf. It's displays are a format I have never educated myself about. It's looks like it might be worth looking into. That Emilar horn does look interesting. It looks like a T35 sitting in it! With all the different types of horns that are made you would think there would be one that would stand out as overall best to everybody. The fact that so may exist says that there is just no "right" way to do it!

Al K.

[greg928gts]

http://forums.melaudia.net/attachment.php?aid=1760

Isn't that a terrific article? I was reading through it the other night, understanding about half of it. A lot of work went into that. I think it will be referenced for years and years.

Do you think a Le Cleac'h expansion could be built in the Edgar style and still have most of the benefits? How much is the round horn playing into it?

The Emilar horn looks interesting. What IS the purpose of the unusual throat? Is that splained somewhere?

Greg

[DrWho]

"The initial expansion just off the throat is what controls the VHF
dispersion. If you look at the K402 you will find this initial
expansion
looks to be conical, only changing to Tractrix near the mouth. "

This
is out of my area of expertise! Someone earlier mentioned the conical
throat issue. All I can say is the horn is purely Tractrix expansion but
it has a rectangular cross section. Could the conical thing have
something to do with the cross-section being rectangular versus round?
My UNeducated thought was of the JBL "Paragon" where the mid-range
horns were aimed sideways at a curved front. The highs may be bouncing
off the curved vertical sides of the horn in a similar fashion. ????
What do you think? I really have no other idea!

-------------------------------------------------------------------------------------------------------------------

It'a confusing, as a conical expansion horn may have a rectangular cross-section. I think the only reason you have any off-axis HF is that it radiates only from the small inner stub inside the driver, and is not seeing the side walls of the horn for a ways. It would be interesting to do a TEF on the combo. With regular 2" drivers on a Traxtrix (or exponential) horn they may measure flat on axis but they don't sound right in the reverberant field in the room. I know two people that have TAD 400x drivers that later added supertweeters.

I couldn't get the BMS to sound 'right' and I sold them to a friend (who is still fiddling with the VHF crossover point), but Iwould like to try them again on some old Emilar 500hz horns that look like they should work with the BMS type driver. Bill Woods has done quite a bit of work with these type drivers and has given me some ideas to try.If you would like his data and network ideas (eight graphs, a schematic, and a couple of horn photos), shoot me your e-mail address.

Do you mean a straight-walled section, or a true conical area expansion?

I believe that tizziness tends to be a common trait for ring radiators, which is the case for the MF section of the BMS.

[dkalsi]

Greg,

Were you not happy with the BMS Coax?

As I mentioned before - the Orphean system was the best system I have heard to date by a long shot. I have been to many "HiFi" stores as well as attended few fancy audiofests/shows - and nothing came close to the Orpheans.

Again - that is the reason why I sold every upgrade I had (Vtrac horns + ALK Universal and ES Crossovers). I want to save up my money for an Orphean system or hopefully Al's offering can be finalized soon enough and I can save for that.

I don't know how much the networks/mods that BD-Design provides for the BMS is helping the system. Based on your opinion of the BMS coax, it seems like a lot may have to do with the network design BD-Design provides. I am really hopping that AL can provide similar results with a more budget driver like the B&C.

[Al Klappenberger]

Dkalsi,

The time to get the network done will be pretty quick once I get the parts from Solen. Unfortunately, the first set is already spoken for though. It's up in the air as to how much of an improvement it will be over a separate tweeter with ES networks. How something sounds is so subjective that only time will tell. Even the unexpected high dispersion thing is unresolved! I can only hope that the Linkwitz-Riley network concept will solve whatever problems exists with coaxial drivers like this. I know so little about horns that I can't make any rationalizations based on theory about it. I can't see that type of network being useful for anything else but sub-woofers considering how much effect just a slight difference in propagation time mess up the summation!

Al K.

[Al Klappenberger]

Earlier djk said this about the high dispersion:

"I think the only reason you have any off-axis HF is that it radiates
only from the small inner stub inside the driver, and is not seeing the
side walls of the horn for a ways. "

I believe now that he's right. I set the other driver I have on the bench with no horn and the mike suspended above it on axis, 30 and 45 deg off axis. The dispersion is still there! It's the driver itself, NOT the horn!

[greg928gts]

Greg, Were you not happy with the BMS Coax? As I mentioned before - the Orphean system was the best system I have heard to date by a long shot. I have been to many "HiFi" stores as well as attended few fancy audiofests/shows - and nothing came close to the Orpheans. Again - that is the reason why I sold every upgrade I had (Vtrac horns + ALK Universal and ES Crossovers). I want to save up my money for an Orphean system or hopefully Al's offering can be finalized soon enough and I can save for that. I don't know how much the networks/mods that BD-Design provides for the BMS is helping the system. Based on your opinion of the BMS coax, it seems like a lot may have to do with the network design BD-Design provides. I am really hopping that AL can provide similar results with a more budget driver like the B&C.

The BMS coaxial drivers sound very good in my Khorns. I attenuate them 3db and they are still a bit hotter than most people would consider "normal". I notice the high frequencies are more directional, coming from right and then left, versus with the Beyma's, where the high frequencies are sort of mixed better and filling in the middle. But this is not objectionable to me, just something I notice. In my own system (and I'm sure it would be different for everyone), my soundstage widens out and I don't get the pinpoint imaging that I get with the Beymas'. Again, this is not a problem for me, since my system tends to pinpoint image a little too much sometimes. So all in all, it's pretty nice.

There are two problems I have, and they're the reason I don't use them much, or recommend them to my customers. First, when you stand up and walk around, you can hear the high frequencies change and come and go. So I don't think the dispersion is correct. From what I know of horn design, this makes sense, since a horn that is as deep, and with a throat as relatively constricted as the Fc260 Volti Audio horn, the high frequencies would tend to beam down the center of the horn. This is why tweeter horns are generally much shallower and with a wider splay to the sides. It's why the K402 can work so well to cover high frequencies, even though it is designed to also cover all the way down to 500Hz, it's relatively shallow and wide open.

Second, the tweeter that's built into the BMS coax just doesn't sound quite as good as the Beyma CP25 to me.

So in the end, having the choice, I would rather have the slight bit of time alignment issue (that I'm not convinced is even audible to me) rather than compromise the quality of sound of the high frequencies, or the dispersion of those high frequencies.

What Al is saying about the high frequencies coming from the driver and not interacting with the sides of the horn much, and dispersing, is very interesting. I suspect that is happening to some degree in my system, which is why it's not a total bust. What we need is a wider and shallower horn to fit the top of the Khorn. Without a tweeter in the Khorn top, the horn can grow quite a bit in width. That would be an interesting experiment to put on the long-term list. Too busy right now.

Greg

[crd97086]

My my, Al, you certainly are an overly sensitive person aren't you.