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Crazy PA Coaxials for Hifi

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voodooless

voodooless

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tmuikku

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^everyone should read all the purifi blog and papers and tech notes if not already familiar with driver distortion mechanisms :) Or any other resources, there ought to be plenty, its just easily accessible and very recent material so a fine resource, although a business website.

Driver electrical and mechanical parameters change with cone position and basically sound of whole pass band suffers the more there is excursion. Excursion is due to physics, volume displacement needs to 4x for every octave of bandwidth (down) with flat power response. Some drivers have motors and suspension that makes less difference, some more. Imagination to play, think time slowed down, loud 50Hz component keeps the cone say 5mm off center which can make different inductance compared to rest position for example, perhaps change in Sd if part of surround is not moving as being stretched. Now for example 500Hz component plays quite many cycles while the cone is at this extreme position, or between extreme positions. Basically the low frequencies keep the cone in move and all the high bandwidth output depends on what the low frequency content is, non-linear distortion.

Basically any particular driver can play louder before audible distortion the higher it is high passed and excursion reduced. Simple stuff in the end for loudspeaker system design perspective. Its good to know there are good drivers available, that can have quite dramatic excursion before bad sound, if a system needs to rely on high excursion. What is not obvious though how much distortion is audible and what is good enough for each listener and application.
 

fpitas

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For myself, every time I considered pro coaxes, the stumbling block was the titanium tweeter diaphragms. Titanium is indestructible, which is essential for pro audio, but reminds me of listening to a very musical trash can lid.
 
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voodooless

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For myself, every time I considered pro coaxes, the stumbling block was the titanium tweeter diaphragms. Titanium is indestructible, which is essential for pro audio, but reminds me of listening to a very musical trash can lid.
There are now plenty of non-titanium pro coaxes, for instance from FaitalPro, BMS, 18 sound, etc…
 

fpitas

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Jukka

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For myself, every time I considered pro coaxes, the stumbling block was the titanium tweeter diaphragms. Titanium is indestructible, which is essential for pro audio, but reminds me of listening to a very musical trash can lid.
The material alone is not very good indicator of sound quality. Example goes Eighteen sound NSD1095N has titanium diaphragm, but breakup nodes are beyond audible range and it's a very good driver overall.
 

fpitas

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The material alone is not very good indicator of sound quality. Example goes Eighteen sound NSD1095N has titanium diaphragm, but breakup nodes are beyond audible range and it's a very good driver overall.
Dunno. JBL used to go to great lengths to aquaplas their titanium in the attempt to tame the break-up. Maybe somebody has a different alloy now, or something.

In any event, titanium offers nothing for home use unless you listen at 120dB. Then the breakup may not matter a lot ;)
 
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voodooless

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I really like the PHL Coaxials. Especially the PHL X30-4590

You can choose your own compression driver but the BMS-4544 seems to work pretty well.
That's going to be my next project :) Paired with two 18" subs :)
That looks pretty good:
hh_test_phl-X30-4590_2.jpg

The high frequency response is quite smooth off-axis as well.
 

D!sco

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For all the potential value of a professional grade coaxial driver, I haven't seen the measured value of the woofer as a waveguide. Coaxial listening axis alone is valuable, but if the woofer isn't an effective acoustic horn, it only produces different kind of inaccurate directivity or distortion. With measurements as variable as they are on the commercial level, how can I even be sure the professional coaxial tweeter is measured inside the woofer, for example? It would be nice if there were some kind of industry standard, but it's hard to rely on either that or third party measurements. Frankly, most Pro Audio is still a matter of "it sounds good" but from different ears. "This pro coax sounds better than another" is just as valuable as most random hifiguide recommendations.
 

dualazmak

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I assume and do hope Geithain's RL 901K would not be "crazy"; I am now very much interested in this coaxial SP.
WS00004946.JPG


WS00004947.JPG


I am a little bit suspicious about the rather wide midrange panel over the woofer (may cause some distortions for low Fq sound??) and the heat treatments for the built-in amplifiers, though. I really would like to know about the possible "chamber" behind the midrange driver.

I know our ASR member @Berlin already has this SP in home listening room as he kindly shared here and here. I hope we can hear more from him or others about this interesting active coaxial SP hopefully with some measurement data at real home listening environment.
 
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voodooless

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I assume and do hope Geithain's RL 901K would not be "crazy"; I am now very much interested in this coaxial SP.
View attachment 243432

View attachment 243433

I am a little bit suspicious about the rather wide midrange panel over the woofer (may cause some distortions for low Fq sound??) and the heat treatments for the built-in amplifiers, though. I really would like to know about the possible "chamber" behind the midrange driver.
Technically, this is not a coaxial driver. The tweeter is offset. I’d love to see a full spin of this thing. Genelec also pulls of half covered drivers, so why not here as well.
 

dualazmak

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The tweeter is offset.

Thank you for the point. Yes, I know; I should better to say "pseudo coaxial" or "quasi coaxial", I assume.
We would better to hear at least 3 m away or more...

BTW, Fyne Audio 's F1-12S is similar "pseudo coaxial" or "quasi coaxial" since it has 360-degree bass reflex port at the bottom. I intensively auditioned it at Tokyo International Audio Show on October 28 (shared here), and I was much impressed with it.

Which do you prefer tweeter offset or very-low bass offset? Of course I assume here in this thread, all should be better to be completely coaxial.
 
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voodooless

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BTW, Fyne Audio 's F1-12S is similar "pseudo coaxial" or "quasi coaxial" since it has 360-degree bass reflex port at the bottom. I intensively auditioned it at Tokyo International Audio Show on October 28 (shared here), and I was much impressed with it.
I don't think the position of the reflex port makes it more or less a coax. The port will radiate omnidirectional, regardless of where it is installed.

As for the Geithain: It's more a space-saving thing than that it's technically useful. At a 550 Hz crossover point, you can get pretty good overlap even in a normal MW setup. The coax effect should be most dramatic up high, so a tweeter/mid-coaxial would make more sense.
 

ernestcarl

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Haven't seen too many coaxes with a horn waveguide. Missing in this list is Fulcrum Acoustic. Most of their models have multiple patterns to choose from... some of which maintain a more evenly flat response than others. I believe this is probably why their Reference monitor line now is only available in the narrower 90x60 degrees pattern which may be the best "compromise".

For home "hi-fi" use, I think it unlikely that one can go terribly wrong with something like the RM28 or RM22 -- other than a difference of personal preference/requirements e.g. dispersion width, space and aesthetic constraints, or if someone doesn't want the hassle of an external pro audio DSP amplifier. However, a big advantage of having a modifiable DSP amplifier in the chain is one can EQ the speaker to fit the sound closer to what one wants if the default EQ voicing presets are not entirely to one's liking.

from RM22 v5 spec sheet graph
1668528018068.png



from RM28 v1 spec sheet graph
1668527904342.png



Interestingly, the RM28 seems to have passively padded out the HF section. Below is the internally amplified RM28AC v4 spec sheet "axial sensitivity"


1668528522884.png

*either that... or it's a different driver version?
 
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voodooless

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Haven't seen too many coaxes with a horn waveguide. Missing in this list is Fulcrum Acoustic. Most of their models have multiple patterns to choose from... some of which maintain a more evenly flat response than others. I believe this is probably why their Reference monitor line now is only available in the narrower 90x60 degrees pattern which may be the best "compromise".
Horns are tricky. These Fulcrum horns are a bit small, therefore crossover point must be fairly high-ish. It also leads to some mismatch of directivity at around 1 kHz (and lower) for the RM22 and RM25, and 1.8 kHz for the RM28. It also has a pinched throat to make the horn a bit more effective for its size, which is not very hifi, but may not be too bad.
 
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