Horatio
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Posts posted by Horatio
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Please post again when you've had some experience with it.
I have a pair of EV HR9040A's that I have decided to keep around (even though they are huge), because I have a pair of self-made University Classic bass horns for which these fit very nicely on top. I need to biamp these, and of course, equalize them, and I am buying a second miniDSP (but this one 'in the box'; how do you beat that for $125?!) to do that.
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Moray:
I will try to get some pictures of my setup, which I have promised some time ago, this weekend, and I will post them on this thread.
As you may recall from earlier posts in other threads, I am running EV HR6040's on top of Khorn bottoms. These just fit, width-wise, and the overall depth, with driver, fits the corner envelope nicely. It does make for a tall cabinet, but it looks (IMHO) not unreasonable. My wife can accept it, so that says something, I guess.
Right now, I am driving these with EV DH1012's, a 1.3" driver, but these don't go really high, but they do well enough that this makes for a very credible 2-way. Must be equalized, and so I am using a miniDSP to do this, and the crossover work.
I have *just* scored a pair of Altec 288-8K's, and these, being 1.4" throats, work with the 1.3" EV HR-series horns. The 288's should give performance to 15K, and that's good enough for me, for a two-way. The 288's can be driven down to 300 Hz, but one must mind the power at these frequencies. Since this is a home setup, and my upper end amp can't deliver much above a handful of watts anyway, I think this will be fine. The HR6040 can be used down to 300-350 Hz, so, this should be a good match. Really helps to deal with the 400 Hz region of the bass horn.
Right now, I drive the bottoms with monoblock MOSFET amps, 100W per, and I am using a T-amp for the top. I am constructing an SE84C-style SET amp, 2W, using the DECWARE ZKIT1 board, and this will replace the T-amp I am using, hopefully later this month.
This pretty much represents the end point for me, and is the result of a very long history of thought on the klipshorn, its problems, and their solution. I had tried several of the HR-series horns, trying to find the magic combination: the HR9040's are glorious, but positively epic in size. You've seen the pix; really hard to integrate these in any kind of esthetically pleasing way. The little brother HR90's just won't go low enough, but it you have a system that can be crossed in a 500Hz, they deserve a serious listen. The HR6040 enabled a reasonable solution in terms of packaging, and provide sonics the equal of the 9040's. In some ways, the HR6040's are to be preferred, as they increase the direct vs. reflected component in most rooms.
The thing that made this approach really doable is the advent of low-cost, high quality digital signal processing. This really makes the problem of crossover design, equalization and room-based adjustment vastly simpler. With adjustable digital delay capability, it really brings this all-horn setup into the 21st century in overall performance.
The runner up approach for me would have been an Altec 311-90, which is a horn of roughly the similar dimensions (the HR6040 being a few inches wider, a bit deeper, and several inches taller), and is a very well designed midrange horn. But, it is not suitable for a two-way design because of the exponential horn's beaminess at the upper reaches. So, this approach was less satisfying (not to mention much more expensive- those 311-90' may as well be cast of gold, these days).
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AFAIK, the original Keele-based HR series from the 1970's are not diffraction horns at all. This horn family is a mergence of three flares: a hypex throat, a conical central expansion, and a rapidly flaring bell mouth. I have always thought that this family of horns could probably have been improved by using a smoothing polynomial to connect the hypex throat to the flared mouth; you'd have a mild deviation away from conical expansion, but you'd do away with the reasonably abrupt changes of expansion rate. Nature abhors discontinuities. More or less, the horn families that came after this design from competing manufacturers strove to find ways around the EV patent, while acheiving the same directivity performance. Diffraction slot designs were yet another way to try to do this.
To my understanding, diffraction horns generally have a very narrow slot in one plane (uusually the vertical plane) and a flaring of one sort or another in the orthogonal plane.
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Ah, forgot to paste in the title to google on: Horns_measurements_ETF2010d. This is a pdf on several sites.
-M
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I don't know what the comparative sound is of these diffraction style CD horns is. The original CD horns, the HR series of EV, are a classic design that has withstood the test of time in terms of sonic performance, though. They are large, and difficult to mount into any kind of standard format (e.g., rectangular flat faced openings). On the other hand, they sound fabulous (to my ear anyway).
Here's something worth looking at: 'Measurements performed on 16 horns' by Jean-Michel Le Cleac 'h. Here is the name of the pdf, google it and you will find a few locations from which to download. In this series of measurements, the very latest enthusiast horns are tested with a variety of drivers... among these is an HR6040 (I think this is actually an 'A' series, as in HR6040A, and not the first production HR6040- I don't see evidence of the mating of the top and bottom halves as the first production models were done). This is tested with an Altec 288-8K. This combination appears to hold up quite well in the stack up of results: considering the level of main reflection and diffraction, the 16 horn/driver combos were sorted into 5 classes, 1 being best, 5 being worst. The HR6040/288 was ranked in the number 2 group. Not bad for a 35 year old design.None of the horn/driver combinations in this series contained a diffraction design, though.
-M
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I can understand this, to a degree, as my experience with miniDSP led to a similar result.
That is, I initially set up the miniDSP with L-R filters, at 400 Hz, and I set the delay for the HR6040 horn. This resulted in a remarkably good sounding setup, relative to the K400+T35 going though a Type A or AA filter network. I think there are several reasons for this improvement: the HR6040 is very stable in terms of its polar response, the DH1012 is head and shoulders above the K400, and getting an accounting of the driver spacing via delays made a very noticeable difference when A-B'ing the setup.
I then moved to the Le Clea'ch topology, and this seemed to improve the sound stage a bit more- wider, deeper. Not as dramatic an effect as moving from passive to active, but noticeable: I had pretty much given up on the notion that an all-horn setup could image; this one is quite good, as presently set up.
The benefits I see in the LeClea'ch approach are: 1) this noticeable improvement in the sound stage (which I would hope could be captured via measurements of the impulse response) and 2) the approach enables one to move the cross point of the bass horn down to 305 Hz, while keeping a 400 Hz -3db point for the mid/upper end. This part, I think, is most valuable, as it enables to sidestep the more troublesome response region of the basshorn; it's working pretty hard for anything above 300 Hz, and what it does yield is pretty raspy. Being able to sidestep that is a decided advantage, in my opinion. After all, the whole point of the 'Jub was to be able to solidly reach through and beyond 400 Hz, to enable a two-way configuration. If we can get this with a stock K horn and some digital magic, I am quite happy to have that result.
Now to move to the next step: replacing the T-amp driving the top with a single-ended triode (SET) tube amp; I have my eye on that little 2 watt wonder, the Zkit1 version of Decware's SE84C. With a good hefty mosfet solid state amp on the bass horn, this SET 2W amp ought to be more than enough for handling the top end alone.
The biggest problem I have run into in any of the active approaches I have taken has to do with more prosaic problems: depending on how complex the equipment, one needs a 'take-off and landing checklist' for how to power the system on and off. This is fine for the enthusiast, but my wife complains loudly. Gotta find a simpler way.
-M
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Sorry to be late on this response, I am traveling on business this week.
I think I misspoke on the filter type: I am using Butterworth, not Bessel, as I originally wrote.
With regard to the crossover frequency, yes, down .022F I believe is correct. When you do this with the original Klipschorns' crossover frequency of 400 Hz, you are effectivey raising the Fc of the midrange and lowering the Fc of the bass such that at 400 Hz, you are 5 db down. What I did was to KEEP the midrange's -3db down point at 400 Hz...this means I moved the Fc of the bass horn down even more...I don't have the notes in front of me, but I think the -5db point on my system is 350 Hz, which lets the midrange run with a -3db 400 Hz point, and makes the bass horn run with a -3db point of 305(?- again, don't have my notes with me) Hz. Bottom line, is, it's the Le Clea'ch topology, but I have effectively chosen a different (lower) crossover frequency than 400 Hz, but I am still running the midrange such that it retains its -3db point at 400 Hz.
I had questions, too, about how to use the basic Le Clea'ch scheme with a two-way, as this is what I am running. The spreadsheets and notes do not provide clear instruction about this. A bit of googling returned a thread on this that I eventually used to guide my setup:
http://www.diyaudio.com/forums/multi-way/131660-dxc2496-lecleach-setup-2.html
Jean-Michel addresses this 2-way question directly.
For those who've asked about circuit diagrams: I don't use analog filters for this...all done digitally.
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Have a look here:
http://www.diyaudio.com/forums/multi-way/121175-lecleach-paper-crossovers.html
There is a reasonably good discussion of this crossover in this thread, and at least as of this writing, the links still work. The main feature of the crossover is the relatively minimal phase distortion. This, to my ear, results in very audible consequences. I was leary of setting the crossover point at what becomes a 5 db down point, but, the proof, as they say, is in the tasting.
One thing to watch out for: nearly everyone, it seems, messes up the delay. The delay specified by the spreadsheets is to be added to any delay already dialed in to acheive acoustical alignment. So, if all drivers are physically aligned, there is no delay other than that from the Le Clea'ch calculations. If you have delay(s) dialed in to 'time-align' already, the spreadsheet values are IN ADDITION to these. Read it through a few times, and try it.
The other thing that tends to throw people is the need to invert the polarity on the mid range. It all comes out in the wash, due to the delay that's added, and the bessel response, set up at 5 db down.
Take a look at page 53 of the powerpoint (in pdf) presentation, and compare to p. 50's.
-M
I have not *measured* to see how this performs, but my *ear* tells me it's pretty decent.
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Thus far, I'd have to rate the sound quality as outstanding, although I would also say that I have no comparative experience with another digital crossover. I am using the analog in/out facility, so, I rely on the quality of the A/D that is on the board. I have purchased the digital input module also, as well as the digital amp module, but have not yet tried these out.
I front end this with a Hafler preamp, and the sources are all analog (tuner, CD, etc.) thus far, although I am intending to eventually set this up as pure digital from the CD forward, and simply switch in analog content as I change sources.
The output section is very quiet. Presently, I get a very faint noise signature from the upper horn, but I suspect this has more to do with getting the gains set well (e.g., I have the gain on the amp for the upper horns set rather high, before the miniDSP hits it) than anything else. I can say this, however: having used a Rane AC23 and a McClelland CX series through the same amps, the miniDSP is substantially quieter, regardless how one sets gains. I could never get those units to quiet down, no matter what I did with the gains. On the miniDSP, I would suspect that with the gain issue sorted a bit further, the noise that I very faintly hear between tracks (and I have to stand in front to hear it) will likely disappear into the background of my listening room.
Don't be put off by the low price (I know I had concerns about audio quality at this price point before I got it); this thing hits much harder than the price would indicate.
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The miniDSP is very easy to set up and work with. I got the miniDSP and the digital input board, and the digital amp board. These can get stacked, and used in a variety of ways, and getting it configured can be a bit daunting. This is why I began with just the miniDSP first. That part was really easy.
The thing that convinced me to look into this approach was this:
http://www.hifizine.com/2011/09/digital-direct-minidsp-stack/
As for pictures; I will try to take a couple and post them when I return from travel. That may take a couple of weeks, unfortunately.
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I have been messing around with a miniDSP active crossover that I am using on my Khorn bottom and DH1012/EVHR6040 top.
I initially set this up with Linkwitz-Reilly 48 db/octave filters, at 400 Hz, with some eq dialed in for the HR6040 horn, which is a CD horn. I also dialed in 6.5 ms of delay for the top, based on the Heyser article values, just as a starting point. Set levels by ear. This all sounded quite nice, even though it was rather quickly set up.
I have not yet verified the goodness of the 6.5 ms value, and will get to that during later testing.
I implemented the Le Cleac'h crossover in about 5 minutes with the miniDSP, and this is basically done by moving to 3rd order Bessel filters, setting the cutoff frequencies shifted up and down from the original Fc (down for the bass, up for the midrange/tweeter) by about 0.87 (bass cutoff), and 1.14 for the mid/upper. Then, you dial in an additional .22Fc(wavelength basis) of delay for the mid. One other detail: you need to invert the polarity on the midrange, too, in this crossover topology. This is for a two-way configuration, mind you.
The advantages are purported to be a more uniform phase response, manifesting in a broader sound stage.
I did this, but I did one other thing, which is why I am posting about this: instead of using 400 Hz as the crossover, and shifting up from there for the mid-range, and down for the bass, I MOVED THE CROSSOVER frequency DOWN, so that the mid was still being crossed at 400 Hz, -3db. This means that the bass, in the Le Cleac'h setup, is crossed out at something like 305 Hz(!) This bypasses the ragged response of the bass horn that is present from 300 Hz up. The kick to the delay was not much, compared to the 6.5 already dialed in, but, it's there.
The result is stunning. I have not heard a full-on horn system image like this. Moreover, I have never heard the kick drum thwack with a Klipschorn (not, say, like you get from an Altec VOT) until now.
So, doing this crossover resulted in two advantages!
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minidsp.com
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That was one of the things that attracted me to the miniDSP: you *don't* have to stay connected by USB to control volume. The board has a three-wire jumper to which a 10K pot can be fitted which provides the volume control. Once the board is set with what you want, in terms of levels, crossovers, EQ's, etc., etc., you just disconnect the USB and power it up like any other piece of equipment. The pot is there to adjust volume (as long as you've configured the board to do volume this way, and not by USB). This pot adjusts all outputs uniformly (although each output can be level adjusted individually to trim the drive levels; the pot applies the overall adjustment to all outputs, regardless their level offsets).
Right now, I am using a set of monoblock MOSFET amps of English make to drive the bass horns, and I am using a (rediculously cheap and just as rediculously good sounding) T-amp for the top end. The T-amp has volume adjust, also, so I level adjust the top end with this, and leave everything else alone.
The main remaining problem is devising a decent way to sequence power on and power off to this whole chain so that it is quiet and transient free.
Another thing I've learned: messing around with the connections must be done very carefully with active systems, even when channels are muted. I found this out the hard way, with one side of this system issuing such a bark that it shook windows and collapsed picture frames sitting on tables (!). Powering down to make changes is the only safe way.
-M
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I have been diddling, on and off, with the exercise of active crossovers for my Speakerlab K's, which have K33E woofers in them, and for which I have been using a Type AA crossover for quite a while (in other words, they're the Klipsch sound) for a few years, now.
Like others, I have sought to improve the midrange performance, and have felt that the real answer lay in a different direction...CD horns. But not the commonly understood CD horns as most know them. I am referring to the original Keele designs from the 1970's.
There are at least two problems with this. First, the HR-series horns that provide response to 350-400 Hz are BIG. Really big. EV made another, smaller HR series, but these can't really be used below 500 Hz, and part of what I was trying to do was to get down under what I percieve to be the 400Hz raspiness of the bass horn.
I acquired a set of HR9040A's and EV DH1012 drivers for these; they sounded glorious, but were unbelievable in a livingroom. I then acquired a set of HR90's (the smaller brotheren of the Great Whites), and those sound good, could be integrated without a thought, cosmetically, but again, it's the bottom end I was after. And, those HR90's, A/B'd against the HR9040A's (both with the same driver) just couldn't keep up with the HR9040's. Those stole the show.
The solution emerged: there were three horn models in the original EV CD horn offerings: the HR9040, the HR6040 and the HR4020. the HR6040's would *just* fit the top of the bass horn cabinets. Sure, the overall stack is taller, but at least they fit in terms of width. So, I scoured around and acquired a set of HR9040's (these are the first generation production models, not the later 'A' suffix models, but that's another story). The other compelling reason for choosing these over the HR9040s had to do with the coverage angle being a bit narrower (60 vs 90 degress), and published observations on other horn tests that suggested that narrower coverage angle probably results in better overall listenability in a reasonable room, once reflections are considered.
The second problem, once the size issue is sorted, is driving these; CD horns require equalization. So, it makes no sense to even consider using these horns unless you are also willing to go active.
Toward that end, I have played with a Rane AC23 and a McClelland 4-way, both of which have CD equalization, and these showed promise, in terms of being able to dial in the crossover frequency and provide adequate equalization for the HR horns, but, I could never get the hiss and noise problems sorted to my satisfaction, this being pro-sound gear, and the rest of my stuff being consumer gear. Another thing I wanted was programmable delay, but that's not easily done with analog gear.
For a long while, I considered Behringer stuff (cost being a driver; sure, we all would like Ashleys, but there comes a point...). The problems with this path were several: there's a lot of hotrodding that goes on with Behringer DEQ, and DCX, to get the power supplies quiet, replace output capacitors, stablizing clock jitter, and on and on. It's meant for professional output level gear, and that can be an issue, although it appears to work with consumer gear, from what I have gathered (here and elsewhere). And, there's the problem of needing to have a single volume control....
Then I stumbled upon miniDSP modules. Here, I could get the main things I was after: all the crossover control, CD equalization, and, when used with REW, you can feed it the parameters to do a bit of room-based tuning. So, this looked like it would replace the DCX and DEQ need. Moreover, additional boards were available to do direct digital feed, and there was even a digital amp. The price made it a reasonable risk for me. And, it has a single volume control that acts on all outputs, once you've tarted things up the way you wish.
I acquired this stuff last fall, and have just gotten around to playing with it, and just finished an initial tuning of this system.
VERY pleased! The HR6040's sound as nice as I recalled the HR9040A's sounding. And, I could adjust the delay for the HR horn, dialing this in at 6.5ms, at least for now. A funny thing happened when I did that, though: alot of the woodiness I have disliked in the original configuration pretty much disappeared. I have the crossovers set for 350Hz, as the HR6040 will get there, and the DH1012 can easily do this (I don't have to worry about long term high power use, you know!), and so part of the improvement may be there.
But the major element of the improvement is this: with the HR6040 on top, this is a formidable 2-way system. With a time-aligned top end, it gets very nice indeed.
I am not affliated in any way with the miniDSP folks, but, if there's anyone on the fence on these lists considering one of these, you really ought to give it a try.
The next several weeks will undoubtedly include some measurements (using REW), and I will try to do some followup posts of this work, as I get time.
-M
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288 indeed. Had a bit of a synaptic failure there!
Thanks for the tip on the microphone height- I am using REW to make the measurements, and I am finding the room sensitivities part of this quite interesting. The microphone I'm using (basic RS SPL meter, which seems credible enough for low end work) will limit decent upper end measurements, but we'll see how it goes.
The shape of the HR9040/series was their undoing, almost for sure. Who can deal with the shape? I found that I could incorporate the HR6040 into a tophat that looks like it actually fits the Khorn, in terms of styling. But, it's alot like the 1950's klipschorn design, except for the size differences in the tweeter horns.
-M
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Greg:
Thanks for the link- those HR9040A's are lovely, aren't they? I have a pair of those, too, and think they are just fabulous. Problem is, they are enormous! I could not find a way to integrate them into the top section of a Khorn- just too wide. The HR6040's I have fit just perfect, width-wise, are are of the saem overall height at the HR9040's. They are a bit deeper than than HR9040's, and so fitting the driver and ensuring this will tuck into the corner can be a bit a of a trick- the DH1012 will make it, but I am not sure if say, a 488 would!
I think Jim's advice on setting the delay makes the most sense, anyway, because one does it empirically, to ear, and the adjustment ought to be fairly sensitive. In the end, we want the result to sound good, not just be tuned to theory.
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Folks:
I have appreciated the comments and will take these into consideration as I tune this system. Right now, I am converting from the original three-way based K400/T35 type tophat to a two-way using a large format compression driver behind an EV HR6040 CD horn (one of the type that Keele designed in the 1970's). So, the delay I must dial in is that between the bass and the HR6040.
The procedure I'm inclined to follow is the one outlined by Jim Long in Sound Practices #13: Set SPL of bass and tweeter (in this two way system) to be equal at the crossover frequency, then, invert the polarity of one driver and begin advancing the delay until the sound level at the listener begins to drop and then increases again. At null, the signals are exactly 180 degrees out of phase and cancel. So, once you are there, flip the polarity back, and viola, you have it. I will report the number I find, together with the length of the HR9040, so that was can deduce the effective bass horn length.
-M
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Thanks- like most things Khorn, you get a variety of answers. It appears to lie somewhere between 1 and 2.2 meters or so!
I am messing around with a MiniDSP setup, and I have an EV HR6040/ EV DH1012 fitted to the top side. So, I am beginning to get it dialed in.
Thanks,
M
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This should be easy to find, but I have not been able to nail it down.
I am looking for the path length of the Klipschorn corner horn unit. I am going active, and want to adjust the delay(s) as I move through the drivers. Anyone know this path length?
Thanks!
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Loud one's, indeed!
Greg: you hit it on the head. I just got an email from Jim Long, confirming those H11's, and Newman's sketches of same. The drivers are probably TAD 2001's. I think Jim eventually settled on those, and I think those are 1" throats, so, it all makes sense- he only needed them to cover to 500 hz.
Cool thing about those H11 bass horns is that they showed, in the 1990's, what Delgado and Klipsch found with the Jubilee- that folding in a single plane and splay angle makes all the difference in how high you can get 'em to go.
Thanks!
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One other thing: I just noticed that the EV horns on top appear to have either Altec or JBL drivers on them, with what appears to be some sort of throat adapter. Anyone recognize those drivers?
-M
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Hello all:
I recently had a short correspondence with Don Keele, the designer of the first of the Constant Directivity horns, the HR series that EV produced in the 1970's. I had recently acquired a pair of HR6040's for Khorn use, and had a question about the early production versions. I have a pair of HR9040A's that I think are really very nice, albeit quite large. Anyway, Keele did not know the answer to my question, as he had left EV during that time, but referred me to a fellow by the name of Jim Long, and sent the following picture, showing Jim's setup:
My question to this forum is: what type of bass horn is this? It appears that the sides are tappered, and that there _may_ be a slot vent in front. Anyway, I can't quite figure this one's heritage. Anyone on this list ever seen this type of bass horn?
Here's a better shot of the overall setup:
Thanks,
Mike
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Thanks for the reply- went to the site to see what it was you were speaking of- right- a 'Jube-like set of fletchings on the sides of the K. I looked at my Speakerlab-built bass boxes, and they have the basic template (top plate and bottom floor plate) that scope out these extensions, as one would need to do them. Would need to look at that vertical piece, as shown in the link. Pretty cool idea. I need to refinish these anyway, and this is probably something I will include when this is done.
On the mid ideas and your '2496 DSP: Yeah, I played around a little bit with a biamp setup using a Rane 23, where I could diddle the frequencies, but not the roll-off, and I liked being able to bring that turnover point down when the HR9040's were sitting on top.
This is probably a question best addressed off-line, but, I'd really like to know the details of how you're using that '2496. For what I have in mind, the usual flexibilities are needed (variable frequency, variable roll-off, adjustable gain for each section), but I would potentially need CD compensation if I eventually chose to keep the HR horns on top, and I'd need time delays. Moreover, I'd really like some flexible parametric controls on at least the bottom end, so that I can fiddle about tuning/compensating for the Khorn's response as it approaches the mid section. Can this thing do all of that?
Finally, what I am enjoying about all of this, is the challenge of the struggle to get that mid section right. PWK evidently struggled with this, and the 'Jube was I suppose, the final statement on that. But, there are the constraints we work with; as a manufacturer, one typically wants a product that can be cost-effectively produced, and which meets certain size envelope and price targets, for a given performance, let's say. As a hobbyist, we are a bit more free, as we can play with the price a bit more (e.g., appeal to more and different compression drivers, for example, and the use of digital crossovers and separate amps, etc.) and maybe, depending on the domestic situation, the size envelope.
The thought that keeps running around in my head, is, suppose we bandwidth limit the bass sections, and then stack these both away into one corner (OK, I have place I can do this with). We keep the upper end low enough that it is below the limits of humans to use for sound localization purposes. Then, we build 'satellites' that are fully horn loaded, and take up the rest. The midbass would be a challenge to get right. They are going to be big, too, I would guess, but smaller than if we had to pull the bass unit into the same package.
Thanks!
Mike
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I use a DH1012, which has a 1.4" throat. The DH1a's are 2" as I recall. I can vouch for your experiences on the HR90's, and as good as those sound, the 9040's are that much better.
Thanks for the info on the JBL setup: I'll have to get the dimensions on this beast. Like most others who've been questing for this grail, the package size is the issue.
-M
Horn Types, how do they sound?
in Technical/Restorations
Posted
I promised this to a few on this forum, and to others, I thought you may be interested in some of this.
I have a set of HR6040 horns (with DH1012 drivers) integrated onto my Klipsch-style bass horns (Speakerlab factory builds, with K33E's in them). The HR6040 will *just* fit on top of the bass horn, and while the whole stack is rather tall. I have had custom cabinets made for the replacement top sections, by some Amish craftsmen I've dealt with for many years. They also made a replacement front panel and kickplate for the basshorn. This is all done in solid cherry, finished to my specification.
I have focused on showing the top hat assembly. I have not yet fabricated the grill assemblies, but that is coming. As you can see from the top hat design, the grills will wrap around in the style of the classic Klipsch manner. The top hat was designed after studying pictures of the 1950's series top hats, in which much larger midrange horns had been used.
As for the HR6040's: these are first or early production run versions. This can be seen from the molding lines reflecting the mating of the lower and upper halves during manufacture.
I have had a pleasant correspondence with Jim Long, who filled me in on some of the history of this remarkable horn design, and I thought I'd share an excerpt from Jim's response, together with some observations on another audio site:
I came across a series of posts by a 'gibber' in AudioKarma. Anyway, in these posts, some interesting pix and measurements were shown regarding the HR9040 and the HR9040A. I have a set of the HR9040A's, and I also have a set of the HR6040's. I noticed that the 6040's were manufactured differently, being the joining up an upper and lower half of the horn. I also noticed that the throats were 'slotted' just inside the driver entry hole. I went back the Keele paper, and sure enough, I saw the slot in the drawings of this paper. This is not a diffraction slot, per se, but rather, appears in order to satisfy the area expansion relationship.
However, the HR9040A's did not have this.
As indicated, some time back, I corresponded with Jim Long, who's written of these magnificent horns, and he sent me a short document he had written, trying to capture the developments in the HR series production: the early horns were produced using this two halves process, while the 'A' series had two variations: an early 'A' and a later 'A'. Both the original production (non A) and the early A horns featured the vertical support in the mouth of the horn. The later A's did away with this support, and instead, used several contour following slats on the outside of the horn, to provide the needed stiffness. If you look around for a pix of Jim's home setup, you will see a set of these late 'A' models.
The most interesting thing Jim said, though, in his writeup is this:
" There were three versions of the large-format EV HR horns. I will use the 90° x 40° HR9040 as an example. The HR9040 had both a vertical fin in the center of its mouth and a more complicated throat expansion than the later HR9040A’s. The copies of the original drawings I have show this—when traveling in the vertical cross section from the horn entrance toward the mouth, the HR9040’s profile “necks down” before finally blending into the main, 40° conical section that contributes most to the constant directivity. I recall Ray telling me that this provided a more truly exponential expansion in the initial part of the horn but also produced a more complicated molding process. The vertical fin was a stiffener to stabilize the rather wide top and bottom parts of the horn.
The first HR9040A simplified the throat expansion but still had the vertical fin. I recall Ray Newman telling me that the simplified expansion had the serendipitous effect of smoothing the response above about 8 kHz, due to the elimination of a standing-wave situation. None of the measurements made to illustrate this have survived in my possession. Old spec sheets in my archive may yield some info but a cursory look suggests that there is nothing as nice as driver x on both an HRxxxx and an HRxxxxA horn.
The final HR9040A eliminated the vertical fin and replaced it with three long front-to-back fins, with a maximum height of about 1.5 inches, running radially on the outside of both the top and bottom of the horn. These are the horns in my home stereo. I have added Sorbothane rectangles, about 0.25 in. x 1 in. x 2 in. in size, to the top and bottom of my horns.1 I recall that this further smoothed the already smooth impedance curves of the HR horns by a small amount.2
All of the above physical changes in HR horn design were driven by manufacturing cost.
Regarding audible differences:
1.
VHF smoothness improvement of the “A” versions. I have not had the opportunity to compare the old and new (I don’t have an original HR9040).
2.
The two fin approaches. I can’t evaluate this difference either, but I suspect they are not significant.
1 These were leftover items in the EV service department, used to dampen mechanical resonances in another EV horn. The current Sorbothane Web site is http://sorbothane.com.
2 This was ascertained, as I recall, when impedance curves were being run in the large EV anechoic chamber. Clamping the vertical horn mouth produced a slightly smoother impedance curve (small ripples gone). (More radical constant-directivity designs, which came later, such as the Altec Mantaray horns, have huge impedance swings with frequency. This is evidence of mouth reflections, which contribute/produce an unpleasant sound quality.)"
So there you have it: evidently there was some sort of defect in the response of the first series, which was (accidentally?) solved in the later series as a result of manufacturability concerns! I think the early series load a bit lower, and the trade evidently was in this 8 Khz+ response anomaly.
FYI.
OK. I just finished wrestling with this editor, attempting to find a way to load images, no joy. I will make another pass at this when I have figured this out.
-M