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Chris A

A K-402-Based Full-Range Multiple-Entry Horn

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That just means that the anomaly is minimum-phase, which isn't all that uncommon in the real world...reactance annulment really only applies to exponential horns, and even then doesn't necessarily give the most desirable response. Back chamber can be too small or too large, but there is a great deal of latitude in-between.

 

I figured that you knew all this, but I'd bet that there are about a dozen others out there saying, "...what a fool this Chris guy is...he doesn't know the rules..." 

 

In any case, I've learned the hard way to state goals and my view of the design space characteristics, sensitivities, and boundaries for those that may not be familiar with the design domain.

 

Chris

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I assume that you're talking about the insides of the box: the back of the box itself isn't very interesting. 

 

When I get it apart again, I'll take a shot or two. 

 

Chris

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This is very interesting and a cool idea. The walls on the 402s look pretty thick, or is that the mounting plate for the woofers showing?

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Don,

Somewhere in this he mentions some 3/4 inch mdf to mount the woofoers.

Bruce

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Ok, so nothing (other than the center driver) is mounted to the horn directly?  (no screws holding any driver to the sides like on the back)

 

They're all just 'pushed' or held in place?

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I'm using 3/4" MDF salvaged from an earlier piece of office furniture for each woofer mounting pad, with the woofers held in place by larger wood screws.  The mounting pads are screwed to the horns, also using 12 x 1 1/4 wood screws top and bottom.  That is a tricky part--tapping drill holes into the horn in the right places to anchor the screws.  The mounting surfaces on either side of the horn throat must be sanded flat--which is trivial except for a stiffening rib extending from the throat mounting plate toward the horn mouths--about 6.5 inches long--that must be sanded flush.  A belt sander made short work of that one detail.

 

The mounted woofers on their pads significantly increase the stiffness of the horn side walls when screwed down to the horn, but the top and bottom horn walls could use some extra stiffening.  (I have a solution in mind already.)  The horn mouth is already screwed down to the KPT-305 cabinet at 12 locations with long machine screws into threaded inserts located on the reverse side of the cabinet front face, so everything else on the horn is very firmly supported.  I'll post some pictures within the next few days.  Right now, I'm in the listening/evaluation stage. 

 

Ellis63 asked about the trade-offs.  As you might know, the Danley Synergy horns all begin to lose their on-axis horn gain below ~200 Hz, transitioning smoothly to direct radiator operation at some lower frequency.  All Synergy horns certainly have a large EQ boost below 200 Hz built into their passive crossovers.  Danley has never really talked about this openly to my knowledge.  This loss is really due to a more rapid widening of horn polars at fc and below, just like occurs on the Jubilee bass bin at about 110 Hz. This isn't a sudden loss of horn loading, rather just a widening of its polars.  The room itself becomes the last horn segment for these horn types. 

 

For this "New Center" horn, that final transition occurs between 175 Hz down to ~40 Hz, with decreasing on-axis SPL initially occurring due to the loss of polar control in this region, but not a sudden loss of horn loading altogether like you get with a hyperbolic or exponential horn profile.  The loss of on-axis SPL occurs a bit more more gradually, with some loading that remains below fc due to the conical horn profile (ref: Beranek for more information on this topic).  With the sizing of woofers on the New Center (twice the woofer area of any of the Heritage series designs), the extra surface area of the woofers can be brought to bear via EQ to compensate for this loss of on-axis SPL. It takes two shelving filters in the Dx38 crossover at or near 300 and 200 Hz, respectively, to compensate for this loss.

 

Below about 40 Hz, an additional loss of on-axis SPL occurs, just like the Jubilee bass bin.  A PEQ boost at 31 Hz adds another 10 or so Hz of low end at this point, limited only by the increase in harmonics (not xmax) of the woofers.  This is the trade off--again, just like the Jubilee bass bin.  Can you hear the increase in distortion (mainly modulation distortion) below 40 Hz or not? 

 

That's the choice that you get to make at listening time--remembering of course that my New Center is not in a corner, rather it is up against a wall--"Pi space".  If you've got good, low distortion horn-loaded subwoofers, then you'd probably just cross over about 40 Hz--just like I do in my room.  If you haven't got horn-loaded subs, your trade off is easy - add a little more boost below 40 Hz.  It's up to the person's taste.  Right now, I'm leaning toward less boost below 40 Hz and more subwoofer crossing at 40 Hz.  This is exactly like the corner-located Jubilee bass bins. 

 

The New Center in the mid-wall configuration has a great deal of "impactful" bass, but not "flubby bass" that I associate most with ported (bass reflex) cabinets-like the Cornwall  and the other KPT ported cabinets.  I associate the difference to the continued horn loading of the New-Center's bass that significantly reduces the woofer cone excursions for a given on-axis SPL.  If it were only radiating via DR mode, it would have an essentially flat SPL on-axis from 200 Hz to 40 Hz.  It doesn't have this frequency response profile.  The following frequency response (on-axis SPL) and phase response were recorded in the mid-wall center location--i.e., NOT in the corner of the room:

 

post-26262-0-32460000-1452522706_thumb.p

 

And here is the Hornresp simulation of the woofers+horn power response for mid-wall (quarter space or "pi space" in-room) loading:

 

post-26262-0-32460000-1452522979_thumb.g

 

I have yet to listen to the New Center located in the corner location.  I don't expect a great deal of difference in sound or in EQ used...but I could be surprised. 

 

Chris

Edited by Chris A
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I'm aware that I'm throwing a lot of info your way that's probably a bit difficult to digest in an integrated way.  If you've been a fan of Danley's designs, you may feel a bit crestfallen at this point, not realizing what he has been doing all along.  If you've been a student of exponential bass horn designs, all this may look very strange to you since the basic rules of horn length and reactance annulling are being violated--flagrantly.  What I've found is that it's the size of a horn's mouth--not the horn's length and flare rate--that determine its real low frequency potential, assuming of course that conical or tractrix expansion profile types are fair game.  Everything that I've learned about horns changed when Unity horns and the K-402 hit the scene.  They seem to violate the rules--and they do. 

 

If you've got questions on any of the above that's not making sense, feel free to ask--who knows, you may find a flaw in the logic.  Unlike many others that build loudspeakers, I hold less to Beranek's Law than you might guess.  I've built quite a few loudspeakers in my life and there is no magic in this particular case--just a design based off the designs of other guys: mainly Danley...but also Roy.  I make no excuses for their designs. ;)

 

Chris

Edited by Chris A
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I know you have lots more work to do on this project, but I was wondering if you were going to run any polars on this hybrid.

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Chris,

 

Thanks for taking the time to do this, this is awesome.  Just last week when I started looking at the unity/synergy horns.  I looked at my EV hp9040 and thought, man that looks like I could just drill some holes and add some mid drivers and I would then have a unity horn.  I think I would have problems with the diffraction slot, plus you beat me to it with the K402.  So now some of us have something to try when we have time and of course $$$. 

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Interesting stuff.  I'd like to see how you mounted the woofers to the horn.  Any chance of getting a look at that?

 

Seems like blasting a 15" woofer at the side of the plastic horn would vibrate the crap out of the horn.  Comments?

 

Do you have the woofers sealed, like in a can as done on the 305?  Or, are they open backed in the box?

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but I was wondering if you were going to run any polars on this hybrid.

 

 

That's on my list of things to do, albeit a fairly large item to do, since I've not run the type of detailed polar plots (many angles, a lot of data using ARTA), and I need to get a turntable set up in my grass-covered back lawn, plus all the cables required to hang out the window of my listening room. 

 

In the mean time, here are some polar plots that should be extremely close:

 

post-26262-0-18060000-1452530323_thumb.g

post-26262-0-28300000-1452530337_thumb.g

 

or if you prefer a different plotting style...

 

post-26262-0-85300000-1452530829_thumb.j

post-26262-0-66900000-1452530866_thumb.j

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Here are the polar plots for the Jubilee bass bin...

 

post-26262-0-99140000-1452530996_thumb.j

post-26262-0-44300000-1452531017_thumb.j

Edited by Chris A

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Mark, I believe all your questions are answered above except for the one about "blasting a 15" woofer against a plastic horn". I'm not sure that I've got an answer for that one.  I do have an answer for you on stiffening the horn: it's already stiff in the horizontal walls and mouth areas.  I plan to stiffen the top and bottom side walls.  I have a better long-term solution in mind, but I'm not ready to share that one yet.

 

Chris

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Chris,

 

After a reread..........all very impressive.  I just have a comment on woofer back loading.  You mentioned that changing the cabinet volume did not change the performance very much.  Did you notice if it changed the excursion on the woofers?  It could be a key to keeping them from moving a lot and vibrating the horn.

 

You know I have a pair of 305s so I can say that volume is very little loading on dual 15" woofers.

 

Curious why dual 15" and not dual 12" like the Jub?

 

Obviously, we all have a lot of questions............but I have to say this is pretty darn cool.  Nice job.   :)

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Those are good questions that I asked myself, too, Mark.  As it turned out, I did check the woofer excursion and it almost didn't change at all with changing the enclosure volume.  In fact, I was amazed to see that the woofer excursion predicted in Hornresp was actually the same as the Jubilee bass bin K31s, except these are 15" (note that we're talking equal output power, or perhaps slightly higher output power in the New Center case than the Jubilee bass bin). That gave me some confidence to move forward, even though in real life it may mean very little.

 

If that's the only price of going to multiple-entry horn over a dual-mouth "W" section Jubilee bass bin (using dual 15" woofers increases the price about $100 in driver costs alone)--I'll take it.  It saves several thousand dollars a pair in loudspeakers and potentially moves the Jubilee experience into many more households--if you catch my drift.  It's a much more palatable package that looks more like a "super La Scala II" in terms of its size and shape, and certainly lower in cost than a La Scala II. 

 

I tried dual 12" woofers within Hornresp: it wasn't enough.  It was very clear.  Even in the corners (0.5 pi space) the design needed more woofer drive area.  So I obliged.  I tried many 15" drivers. Lo and behold, on a lark I used the K-33 woofer values: everything just fell into place and I got about 4-5 dB more overall bass performance and flatter performance than using other "subwoofer" and regular woofers.  Perhaps there is a lot more to the K-33 design than initially meets the eye. 

 

I decided to go with Crites cast frames to ensure that there will be longevity in supply of these Eminence-produced K-33 replacement woofers, since there seemed to be a lot of turnover of 15" woofer models that looked applicable on Parts Express.  I got a little spooked by that--but I know Bob and Michael and I thought they were a much better bet for sourcing woofers vs. time...and overall quality/support.

 

Thanks for the encouragement.  I'm mildly enthusiastic at this point. :rolleyes:  I didn't expect success on the first try.

 

Chris

Edited by Chris A
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OK last 3 questions for the day, I promise.

 

How did you decide where to drill the throats for the woofers?  Why 2 holes per woofer?  How did you determine the size of the holes?

 

Done.

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With a little care you should be able to "plug" the 402 holes if you need to move them or drill more.  Just need to find the right glue and/or material.

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