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Crazy PA Coaxials for Hifi

gnarly

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Do you have in space measurements you could share by any chance? A sort of comparison between the datasheet and actual real-world performance?

Here's a set of indoor ground plane measurements. Never got outside with this one....
Blue and red are the two sections raw measurements, and green is processed.

15cxn88 indoor ground plane.JPG

Also, can you see some kind of horn structure under the dustcap? If so, does it seem to protrude out beyond the woofer cone or does it transition to the woofer cone?
(obviously not asking you to tear apart your speakers lol, just any visual observations would be appreciated as I try to identify the source of potentially jagged response - the sort which seems to be lacking in that B&C driver...)

Whatever horn structure there is is fully behind the dustcap, so sorry I don't really know much about it.

I didn't spend a lot of time on this build, because I dunno, it sounds fine, but sounds like PA. Not like the hi-fi sound I'd been getting from more typical CD+ horn + separate cone driver builds. It has a lot a small ripple like TimVG mentioned with his build, which simply can't be filtered out.
 

hex168

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I'm not sure if these are still available but the 15" in particular looks spectacular:
 
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voodooless

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Basically, it illustrates that prosound coaxials can have massive output especially in the bass department...
Actually, the main point is that excursion is low for a given SPL compared to the small units, and secondly, that a BR alignment is hugely beneficial in keeping excursion down even further for full-range usage, meaning less IMD than a closed box design.
 
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voodooless

voodooless

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What do you guys think is the better trade-off?
1. coaxial with horn:
+ possibly better directivity control
+ lower IMD due to less woofer interaction
- from the examples I’ve seen they have a more ragged frequency response
- usually directivity is narrower, but this can be a + in some situations as well..

2. coaxial without horn:
+ possibly smoother frequency response
+ bigger “horn” should have lower pattern control for HF
+ wider directivity
- worse IMD
 

AwesomeSauce2015

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What do you guys think is the better trade-off?
As long as the horn coaxial driver can be EQed reasonably flat and doesn't have other colorations; I'd take it because of the output capacity. Dome tweeters just don't do it for me.
Having a "lifelike" sound doesn't require super clean HF response in my experience. As long as it's close enough our brain will correct & perceive it as sounding fine. Having low distortion and high dynamic capability, on the other hand, is quite important to replicating a live experience.

Edit: But I'm sure y'all already knew my opinion lol!


Edit 2: I did a dumb. @voodooless was referencing whether we prefer coaxials with a horn assembly or ones which use the woofer as the waveguide. I would probably take one without a separate horn structure, as long as the woofer cone actually is the horn. (No just simply hiding a horn structure under the dustcap). I would address any major IMD issues with a separate bass driver.
 
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voodooless

voodooless

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As long as the horn coaxial driver can be EQed reasonably flat and doesn't have other colorations; I'd take it because of the output capacity. Dome tweeters just don't do it for me.
There is no output difference. All of these PA coaxes have compression drivers. Some things can be EQ’ed obviously, some things cannot. I will illustrate this a bit later.
 

Ericglo

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This is the PA coax that I would use if I were building a HT system.
 

Plcamp

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Ericglo

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Interesting to hear him say that the crossover wasn't hard. I wonder if anyone has tried to go active with them. I realize they are expensive drivers, but in the context of something like a JBL Synthesis....
 
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voodooless

voodooless

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This is the PA coax that I would use if I were building a HT system.
It’s not full range though.. that would disqualify it for the purpose of this thread. It is a nice driver! Needs a massive horn to work down low.
 
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voodooless

voodooless

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Some things can be EQ’ed obviously, some things cannot. I will illustrate this a bit later.
Well, we have some fine examples here posted by a few members, so let's go through them.

First, the horn-loaded example from @TimVG:

1657265276424.png


Here we see various anomalies remaining:
A: Looking at the power response, this should be fixable with EQ without too many issues
B: Here we seem to have a directivity mismatch between woofer and horn. This might be a common thing for these horn-loaded coaxial? A lower-order filter may smooth this a bit, but that would probably give other issues looking at the individual frequency responses, so it's a trade-off. Also, this seems to be mainly an on-axis issue. Off-axis much less pronounced.
C: Looks like mainly an on-axis issue. EQ for the off-axis will mostly fix this issue.
D: Not too much worried about that. Also here off-axis the issues are less problematic. It's past 10 kHz anyway...

@hex168 shared the Vortex kit. It looks like a derivative of an Eminence woofer:
1657266923263.png

Looks pretty good overall specially for a passice design. Biggest issues are past 10 kHz. Also here as expected, a bit off-axis is the best bet for smoothing whatever wiggles are left.
 

TimVG

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A: Looking at the power response, this should be fixable with EQ without too many issues
Since I've been updating my measurement rig I haven't had to the time to fully verify, but I strongly suspect this region is being affected by a port resonance.
The goal of this speaker is not only playback, but also live amplification from time to time. I did not build the enclosure, and while I did specify a certain port it came out larger than I had asked, luckily the tuning ended up alright for this driver.
B: Here we seem to have a directivity mismatch between woofer and horn. This might be a common thing for these horn-loaded coaxial? A lower-order filter may smooth this a bit, but that would probably give other issues looking at the individual frequency responses, so it's a trade-off. Also, this seems to be mainly an on-axis issue. Off-axis much less pronounced.

Matching the directivity is possible in theory, but since the horn covers a large part of the driver, it introduces other, even more undesireable issues.
C: Looks like mainly an on-axis issue. EQ for the off-axis will mostly fix this issue.

Diffraction issue inherent to this driver



Some general comments

-I don't smooth my measurements a lot, as you can see, so you can see all of the defects in full glory.
-The Dayton plate amp which I used (there wasn't a whole lot of money) features the worst DSP interface I've ever come across - which sort of limits what can be done.
-Despite the warts, it really doesn't sound half bad. In a large not-too-treated room it images incredibly well.
-I do believe most people would be better off with a standard non-coaxial 2-way system - although I haven't had the chance to do a side by side test. It'll certainly look prettier on paper. Since from time to time these are used for live amplification in a rehearsal setting, a clean and wider vertical window is desirable though.
 
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voodooless

voodooless

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Since I've been updating my measurement rig I haven't had to the time to fully verify, but I strongly suspect this region is being affected by a port resonance.
Ah, interesting! I was wondering about the source of this anomaly :)
Matching the directivity is possible in theory, but since the horn covers a large part of the driver, it introduces other, even more undesireable issues.
Isn't that inherent to these horn-loaded coaxes? They always seem to have issues with the transition area from the horn to the woofer. The problem is that the issues are always within the crossover region, so basically they are unavoidable.
Some general comments

-I don't smooth my measurements a lot, as you can see, so you can see all of the defects in full glory.
Yeah, I like that! Please don't see my analysis as a critique of the design. It was more about the inherent properties of these units, and how to possibly deal with them (or not).
-The Dayton plate amp which I used (there wasn't a whole lot of money) features the worst DSP interface I've ever come across - which sort of limits what can be done.
Remind me to not buy a Daton DSP amp then ;)
-Despite the warts, it really doesn't sound half bad. In a large not-too-treated room it images incredibly well.
That doesn't surprise me at all. It actually looks very decent.
 
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voodooless

voodooless

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@gnarly, do you have any off-axis measurements? It looks really good with about 2dB accuracy overall!
 

TimVG

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Please don't see my analysis as a critique of the design. It was more about the inherent properties of these units, and how to possibly deal with them (or not).
Not at all! In fact I agree completely. I just like to point that out for other members that sometimes the devil is in the details :)
 

gnarly

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@gnarly, do you have any off-axis measurements? It looks really good with about 2dB accuracy overall!
Hi, sorry I don't. I really didn't spend much time, or give the driver a real fair shot with the build i put together.
My ears (and measurements) told me it that at best it would make for decent hi-fi, but not in the same league as other builds I was doing with CD's on commercial horns and synergies. (Using the DCX464 mentioned above, for example)
 
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