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Advice for a Friend


Edgar

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I have a friend who loves electrostatic loudspeakers (ESLs), and who also dabbles in electronics and loudspeaker construction. He just designed and built his own flea-watt amplifier, knowing ahead of time that it would not be able to power his ESLs. So he has been asking me for advice on horns and drivers.

 

To make a long story short, our discussions have led him to obtain some B&C DCX464 compression drivers and Eighteen Sound XT1464 horns. These items are fine examples of modern compression driver and horn design, so he should have a first-rate system. However, he complains that, "It does sound a bit like it is talking through a plastic cone," that he likes the sound of the driver without the horn better than with the horn, and that the system is "noisy".

 

How can I convince him that he is falling prey to his own preconceived notions about horns? Or should I just advise him not to even bother with horns, and stick with ESLs and high-power amps?

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10 minutes ago, Chris A said:

Is he dialing in the B&C driver on that horn using a DSP crossover and a calibrated microphone/measurement app?

 

No, at this point he is just listening ... with great skepticism.

 

He does not like DSP crossovers, commenting that good passives sound better.

 

BTW, the B&C driver was his choice, not mine. I recommended the BMS 4592Nd. He wanted something that could reliably operate well below 500 Hz.

 

EDIT: Yes, the 4592 is a 2" driver and the 1464 is a 1.4" horn. Had he chosen the 4592 I would have suggested a different horn.

Edited by Edgar
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12 minutes ago, Edgar said:

He does not like DSP crossovers, commenting that good passives sound better.

I think this is your problem, but you already know this...

 

12 minutes ago, Edgar said:

I recommended the BMS 4592Nd. He wanted something that could reliably operate well below 500 Hz.

Well, I lost my BMS 4592ND raw measurements on a K-402 horn last April when my external HD hit the floor to show you the performance of that driver--which he apparently rejected.  Too bad...he paid more than the price of a BMS 4592ND for those.

 

What you're going to find is that all of these full range 1.4"-->2" drivers show a drop off of about 7-10 dB from 500 Hz down to 300 Hz--even the Celestion AXI2050, which has a huge diameter--just like an old EV DH1A driver.  So the BMS 4592ND also can go down there, but not without a horn that controls its polars down to that point (i.e., it's probably bigger than the horn he's using--it needs to have mouth dimensions on the order of 23 inches in each direction, at least--a half wavelength at 300 Hz), and he will definitely have to use a DSP crossover to boost SPL below 550 Hz--on all horns--or a significant attenuation using ramping filters that will pull down almost everything quite a bit--maybe below the SPL of the bass bin--whatever he's using.

 

Chris

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2 hours ago, Edgar said:

I have a friend who loves electrostatic loudspeakers (ESLs), and who also dabbles in electronics and loudspeaker construction. He just designed and built his own flea-watt amplifier, knowing ahead of time that it would not be able to power his ESLs. So he has been asking me for advice on horns and drivers.

 

To make a long story short, our discussions have led him to obtain some B&C DCX464 compression drivers and Eighteen Sound XT1464 horns. These items are fine examples of modern compression driver and horn design, so he should have a first-rate system. However, he complains that, "It does sound a bit like it is talking through a plastic cone," that he likes the sound of the driver without the horn better than with the horn, and that the system is "noisy".

 

How can I convince him that he is falling prey to his own preconceived notions about horns? Or should I just advise him not to even bother with horns, and stick with ESLs and high-power amps?

Have him go back to electrostats.  One and done.

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Some interesting measurements here show that both drivers make it down to just above 400 Hz with the XT1464 horn, probably showing that to be the intrinsic cutoff of the horn itself. (Though how they're mating a 2" driver to a 1.4" horn is mysterious to me. Perhaps they explain but I do not understand German.) So the driver/horn combo satisfies his LF extension requirement. It's the sound quality that he is complaining about.

 

Some people just don't like horns. I may be up against that.

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9 minutes ago, moray james said:

a layer of dynamat on the back side of the horn will help with horn lens vibration. High efficiency horns will show up amplifier noise so don't blame the messenger.

I agree, but how do you explain this?

 

"he likes the sound of the driver without the horn better than with the horn, and that the system is "noisy". "

 

It sounds like he has a preconceived opinion about horns.  He likes elecrostats because the driver is out in the air and thinks that a compression driver is the same, so better with no horn.  Hard to get past that hill. 

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I am not sure, but I think that horn is a CD (controlled dispersion).

If that is the case, it will need some high end boost (it is in the physics and shared by all CD horns). This is why I get concerned about folks tossing pieces together without doing the necessary crossover / balancing chores. I hope he takes the time to do a proper job.

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11 minutes ago, moray james said:

a layer of dynamat on the back side of the horn will help with horn lens vibration.

We're not talking about horn lenses here (...but Roy might be with the new Jubilee)...

 

D29178D3-8E4F-4270-B03C-85B841F95718.png

 

What's needed is something to EQ the horn and driver to flat SPL and phase response.  That's what the root issue apparently is.  And it's a big one.  A big low-Q notch to compensate for the rise in response at a 1.5 kHz (approx.), band limited to ~600 Hz --> 10kHz would pull everything down in terms of sensitivity.

 

Additionally, going below ~500-600 Hz with his present horn is another issue.  He'll have to build horn wall extensions or use a bigger horn to address that issue.

 

Chris

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1 hour ago, moray james said:

a layer of dynamat on the back side of the horn will help with horn lens vibration.

 

If that was actually the problem, then this would be true. All of the reviews of the XT1464 that I have read have been overwhelmingly positive, and not one has ever mentioned a mechanical resonance problem with the horn. Presumably this has been addressed in its basic design.

 

Quote

High efficiency horns will show up amplifier noise so don't blame the messenger.

 

He seemed surprised by that. I wasn't.

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49 minutes ago, Chris A said:

What's needed is something to EQ the horn and driver to flat SPL and phase response.  That's what the root issue apparently is.  And it's a big one.  A big low-Q notch to compensate for the rise in response at a 1.5 kHz (approx.), band limited to ~600 Hz --> 10kHz would pull everything down in terms of sensitivity.

 

That's a good point. He may be interpreting that general rise around 1500 Hz as horn resonance, when it is really interaction between the driver and the horn. When he removes the horn and listens to the driver alone, there is no acoustical loading so the response falls off significantly as frequency is reduced.

 

Quote

Additionally, going below ~500-600 Hz with his present horn is another issue.  He'll have to build horn wall extensions or use a bigger horn to address that issue.

 

The FR plots show the cutoff just below 500 Hz, which is all he needs, I think. So it should be fine from that standpoint.

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7 minutes ago, grindstone said:

On the upside, you should have access to some really sweet drivers at a discount pretty soon...

 

Actually, I have a pair of Altec 288 drivers that would look very nice attached to those XT1464 horns.

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A little off-topic (but still related), Greg:

 

One of the things that is happening with the selling of compression drivers that can go down to 300 Hz is that it's forcing the issue of larger horn mouths to those that "don't want things to change...".  This has two positive benefits, at least from my knothole:

  1. Actually eliminating the midrange driver in horn-loaded HF loudspeakers (at least) requires a single horn that has K-402- or K-510-like shapes (straight-sided throats to spread the HF coverage out, with tractrix/straight/exponential mouth flares to avoid coverage waist-banding at lower frequencies, and a minimum horn mouth size that is based on the lowest frequencies that the compression driver can attain).  For 300 Hz, the minimum horn mouth dimension is 23 inches.  For 600 Hz, that is still 11.5 inches square or diameter (still pretty large).  Otherwise, loss of directivity will occur and correspondingly, loss of on-axis SPL below the mouth loss-of-directivity frequency.
     
  2. By going to a single large mouth horn, using a multiple entry horn approach becomes much more attractive, from a directivity, time alignment and point source perspective, and from a cost to build perspective.  It's actually quite easy to put a grill over the horn to make it look like a Cornwall, etc. (and that's about the size of a horn mouth that it will be in order to support a 300 Hz crossover frequency).  The type of horns that Danley uses (dual-flare straight sided) out of plywood is easy and cheap to fabricate using jigs/fixtures to hold the parts for gluing and stapling.

 

Both of these developments are being driven by the advance of compression driver technology--in the 1.4-->2 inch exit diameter categories. The subjective listening results speak for themselves.  Using DSP is now becoming a technology enabler.

 

Chris

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4 minutes ago, Chris A said:

One of the things that is happening with the selling of compression drivers that can go down to 300 Hz is that it's forcing the issue of larger horn mouths to those that "don't want things to change...". 

 

Can't break the laws of physics. Can't even bend them.

 

Quote

For 300 Hz, the min. horn mouth dimension is 23 inches.  For 600 Hz, that is still 11.5 inches (still pretty large).  Otherwise, loss of directivity will occur and correspondingly, loss of on-axis SPL blow the mouth loss-of-directivity frequency.

 

The XT1464 is 16" wide. That 16" dimension puts it right at 431 Hz, which agrees rather well with the response curves cited earlier.

 

Math works.

 

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By going to a single large mouth horn, using a multiple entry horn approach becomes much more attractive, from a directivity and point source perspective, and from a cost to build perspective. 

 

My friend has mentioned an interest in bulding a MEH, but frankly if he intrisically doesn't like horns then I doubt that he will like multiple entry horns.

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I think a lot of the "audiophile mindset" constraints on loudspeaker design are going to go by the wayside--and probably sooner rather than later. 

 

Now that the original patent is expired (US6411718), I think it's something that KGI has to look at at some point (and sooner rather than later).  The competition is necessarily coalescing in the home hi-fi business with the demise of theater and PA marketplaces, i.e.,

 

 

Don't know yet what brand "X" is going to do, but I wouldn't bet that it's going to be something that this company and others are going to be able to ignore.  I've learned that it's best to jump on the bandwagon early--in order to keep it from being yet another case of "disruptive innovation" eventually overturning the players in the marketplace.

 

Disruptivetechnology.png

 

I think of the early loudspeaker marketplace of the 1940s-50s, and the players adopted formerly patented technology--and quite rapidly to stay in business...

 

JMTC. 😐

 

Chris

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