• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Crazy PA Coaxials for Hifi

ernestcarl

Major Contributor
Joined
Sep 4, 2019
Messages
2,404
Likes
1,753
Location
Canada
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.

I do agree there are compromises made and directivity isn't perfect even at xo region. But if you think about it, many successful "hifi" speakers don't even measure this good despite having plastered the word hifi all over their name.
 
OP
voodooless

voodooless

Master Contributor
Forum Donor
Joined
Jun 16, 2020
Messages
6,210
Likes
10,300
Location
Netherlands
I do agree there are compromises made and directivity isn't perfect even at xo region.
Everything is a compromise. The question is just: is it the right one? When it comes to horns in coaxes, I'm not so sure yet. I'd love to see a comparison of IMD measurements of a coaxial with and without a horn. Some brands offer the same model in both options.
But if you think about it, many successful "hifi" speakers don't even measure this good despite having plastered the word hifi all over their name.
Well, there is almost nothing a good marketing marketing department can't fix ;)
 

ernestcarl

Major Contributor
Joined
Sep 4, 2019
Messages
2,404
Likes
1,753
Location
Canada
Everything is a compromise. The question is just: is it the right one? When it comes to horns in coaxes, I'm not so sure yet. I'd love to see a comparison of IMD measurements of a coaxial with and without a horn. Some brands offer the same model in both options.

It depends on who you ask... Earl Geddes thinks the higher order modes in these type of horn is an audible issue. Objectively, this can be seen in the measurements. Does it sound subjectively, offensively bad, though? Personally, I highly doubt it. A well practiced listener and speaker reviewer may be able to characterize a certain quality to the sound that's particularly unique to this speaker. Whether that is grounds to dismiss it as "hifi"... eh, again, is mostly a subjective matter.

With regards to IMD, while I have not seen measurements of this in any of their coaxes, I quite frankly seriously doubt that it's even a real practical issue here. The baked-in sound of the horn driver is the likelier thing or topic to arise from certain listeners.
 

dualazmak

Major Contributor
Forum Donor
Joined
Feb 29, 2020
Messages
1,873
Likes
2,013
Location
Ichihara City, Chiba Prefecture, Japan
The coax effect should be most dramatic up high, so a tweeter/mid-coaxial would make more sense.

Yes, I essentially agree with you.

You would please let me having a little bit off-topic issue. In case if we would have slight to considerable offset between tweeter/super-tweeter and midrange, to which our ears and brain would be more sensitive between right-left offset and up-down offset?

I assume you would agree with my thoughts that our ears are located left and right of our head, and hence we are rather sensitive for left-right sound image/allocation. On the other hand, our ears and brain would be relatively gullible with up-and-down sound staging, if both of the drivers are completely time-aligned (phase-matched). I recently discussed this here in terms of extent of "speaker disappearance".

Just for your reference, as I shared here, my tweeter and super-tweeter (singing together over 8,200 Hz, but tweeter tends to drop over 14 kHz; see here) are intentionally allocated uniquely far away up and down; I have my super-tweeter under the woofer which is/was found to be the best (magical for me) position through my intensive evaluation of 8 different positions around the main SP cabinet. In that physical alignment, midrange and woofer are sandwiched by tweeter and super-tweeter from up and down, respectively. All the SP drivers are fully time-aligned in 0.1 msec precision as shared/summarized here and here.

Very interestingly, at least in my fully time-aligned (0.1 msec precision) system, this positioning of tweeter (up) plus super-tweeter (down) (singing together at 8,200 Hz to 20,000 Hz) enables very nice "wider/natural" pseud-coaxial (or quasi-coaxial) sound image/stage with almost complete SP disappearance. I may express it would be "planar coaxial sound image" rather than "point coaxial sound image".

Maybe, I am going out of the topic of this thread which is "pure coaxial PA SPs". If needed I will continue this discussion on my project thread.
 
Last edited:

Geert

Major Contributor
Joined
Mar 20, 2020
Messages
1,395
Likes
2,254
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".
The horizontal directivity of these speakers is a bit strange, in the high ends it decreases again. It's most obvious for the RM28:
Screenshot_20221115_115343.jpg

It depends on who you ask... Earl Geddes thinks the higher order modes in these type of horn is an audible issue. Objectively, this can be seen in the measurements. Does it sound subjectively, offensively bad, though?
A lot of PA horns don't sound nice, especially when using drivers with larger diafragms like the 1.7" in the RM28. Often to much a compromise aimed at low Fres and maximum SPL (confirmed by RM28 product description: "high output capability"). Even after using using eq to flatten the frequency response you feel they need more eq. At that point you're probably eq-ing out distortion. Unfortunately distortion measurements are often not available.

Just saying I would never buy a PA horn/driver without having a listen first. I take all these stories of DIY-ers slamming a PA coax in a box and claiming they've build the ultimate speaker with a serious grain of salt.
 

Geert

Major Contributor
Joined
Mar 20, 2020
Messages
1,395
Likes
2,254
Very interestingly, at least in my fully time-aligned (0.1 msec precision) system, this positioning of tweeter (up) plus super-tweeter (down) (singing together at 8,800 kHz to 20,000 Hz) enables very nice "wider/natural" pseud-coaxial (or quasi-coaxial) sound image/stage with almost complete SP disappearance. I may express it would be "planar coaxial image" rather than "point coaxial image".

However, your vertical time alignment will only work for 1 fixed listening position. Move it up or down, or back or forth a few inches and time-alignment is lost (altough I don't expect it to be really dramatic for >8kHz content). That's the big difference with real coax speakers.
 

dualazmak

Major Contributor
Forum Donor
Joined
Feb 29, 2020
Messages
1,873
Likes
2,013
Location
Ichihara City, Chiba Prefecture, Japan
That's the big difference with real coax speakers.

Yes, theoretically you are right and I agree with you.

It is very interesting and fortunate for me, however, at least in my setup (LP is 3.3 m from SPs, L-to-R is 2 m), the nice sound perspectives as well as the "perfect disappearance of SPs" remain unchanged even if I move within about 80 cm 3D from my usual listening position; left-to-right, up-and-down, front-to-back. I confirmed it through my intensive comparative audition of real coax SP Fyne Audio's F1-12S. Of course, I know and understand that the coaxial (and/or pseud coaxial) effect would also greatly dependent on our listening room environments like I shared here.

I assume it would be better to stop my above discussion on this thread. In any way, I thank you for your kind attention on my above post.
 

ernestcarl

Major Contributor
Joined
Sep 4, 2019
Messages
2,404
Likes
1,753
Location
Canada
The horizontal directivity of these speakers is a bit strange, in the high ends it decreases again. It's most obvious for the RM28:
View attachment 243476

A lot of PA horns don't sound nice, especially when using drivers with larger diafragms like the 1.7" in the RM28. Often to much a compromise aimed at low Fres and maximum SPL (confirmed by RM28 product description: "high output capability"). Even after using using eq to flatten the frequency response you feel they need more eq. At that point you're probably eq-ing out distortion. Unfortunately distortion measurements are often not available.

Just saying I would never buy a PA horn/driver without having a listen first. I take all these stories of DIY-ers slamming a PA coax in a box and claiming they've build the ultimate speaker with a serious grain of salt.

There are a number of reasons why the HF from a horn may not sound “nice” to someone. It’s not necessarily going to be distortion that’s the cause… there is the remaining diffraction that’s quite variable with angle and maybe even the characteristic decay profile in the upper HF section. Looking at the axial sensitivity graphs, most of the egregious ugliness in the unprocessed response would have already been sufficiently tamed by their FIR equalization — I presume much of the time domain issues caused by a larger diaphragm being pushed into a tiny exit have also been largely tamed. Many coaxes that use compression drivers don’t even bother and leave EQ to the speaker designer or consumer.

Then again, even I find I like to EQ the HF section of my JBL LSR305 and Neumann KH120 monitors… actually, just about all of my studio monitors I manually equalize full-range to fit my personal taste anyways.

I would reserve judgment on these coaxes sounding not so good compared to other designs because they have higher SPL capabilities and are designed by a PA company, or come from a different design philosophy. If you’ve heard these or know someone who think they sound bad compared to another coax that’s aimed or geared towards hifi for the home, then I’d be most interested on hearing details of the account.
 

Geert

Major Contributor
Joined
Mar 20, 2020
Messages
1,395
Likes
2,254
I would reserve judgment on these coaxes sounding not so good compared to other designs because they have higher SPL capabilities and are designed by a PA company, or come from a different design philosophy. If you’ve heard these or know someone who think they sound bad compared to another coax that’s aimed or geared towards hifi for the home, then I’d be most interested on hearing details of the account.
Note that my comments about the sound of horns are not targeted at the Fulcrum Acoustic's, I have no clue how they sound. But I've heard hundreds of other compression drivers in my life.
 

Duke

Major Contributor
Manufacturer
Forum Donor
Joined
Apr 22, 2016
Messages
1,099
Likes
2,643
Location
Princeton, Texas
I got turned off of the idea by the messy response in the specs, and an apparently better approach to use an ~ 600 hz horn and compression driver.

This is the conclusion I have come to as well... I really like the elegant symmetry of a coaxial, but have never been able to get a coaxial to sound as good as using a separate high-quality horn.

One of the BMS coaxes has a nice soft edge on the horn, possibly to get a smoother transition?
View attachment 216807

Not only is that edge an issue for the horn, there will be frequencies where the cone's reflection off the back of the horn causes anomalies. I would choose the tradeoffs involved in using the woofer's cone as the horn for modest SPLs, but for high SPL applications the separate horn might be better because it precludes modulation distortion caused by the cone's movement.

Do diamonds shine on the dark side of the moon?

Only the crazy ones.
 
Last edited:

ernestcarl

Major Contributor
Joined
Sep 4, 2019
Messages
2,404
Likes
1,753
Location
Canada
Note that my comments about the sound of horns are not targeted at the Fulcrum Acoustic's, I have no clue how they sound. But I've heard hundreds of other compression drivers in my life.

Yeah, I really don’t mind if someone finds this kind of design flawed despite all the effort with equalization to fix the compression configuration’s imperfections.

But I am genuinely interested how worse or far off the mark the sound quality could be subjectively when listening blind, side-by-side in comparison to another.
 

behappybevegan

Active Member
Joined
Jun 8, 2022
Messages
138
Likes
136
I've stumbled on a 'coax' PA speaker that I find interesting.

LD Systems ICOA 15 A
dsp active
crossover 2000 Hz (?!)
horn loaded woofer (a cheap one)
horn tweeter with small horn
925 euro a pair


lig.jpg

333.jpg

Looks > zero points
It will need pimping or even a complete rebuild for better looks and sound.
Stuffing for starters.

If, and that's a big if, this test is to be trusted it has a very good frequency graph.


gr.jpg
 
Last edited:

test1223

Senior Member
Joined
Jan 10, 2020
Messages
338
Likes
351
I've stumbled on a 'coax' PA speaker that I find interesting.

LD Systems ICOA 15 A
dsp active
crossover 2000 Hz (?!)
horn loaded woofer (a cheap one)
horn tweeter with small horn
925 euro a pair


View attachment 248342
View attachment 248345
Looks > zero points
It will need pimping or even a complete rebuild for better looks and sound.
Stuffing for starters.

If, and that's a big if, this test is to be trusted it has a very good frequency graph.


View attachment 248343
This frequency response is smoothed a lot. You shouldn't compare these measurements with typical measurements with higher resolution.
 
OP
voodooless

voodooless

Master Contributor
Forum Donor
Joined
Jun 16, 2020
Messages
6,210
Likes
10,300
Location
Netherlands

gino1961

Senior Member
Joined
Dec 19, 2018
Messages
387
Likes
120
i guess you will not consider a smaller coax (8-10") above a big woofer (15") combination ?
 

Wolf

Senior Member
Joined
Nov 21, 2020
Messages
436
Likes
458
Location
Indiana
1800 euros a pop :eek: No off-axis response data either. That horn looks to be a bit small-ish for a 1.5 kHz crossover point as well.

You basically have just a very narrow window for the crossover:
23_15_05_360_6eGnGfep.jpg

Steep filters will help a lot here. The recommended crossover is 1.2 Khz, so right next to a major response dip. I would actually argue to stay below 900 Hz. For HiFi that is probably still fine.
There is plenty of CD output to burn there too. I don't think steep slopes would be a necessity, because the CD has bandwidth below 900 even if it is at -10dB. A shelving contour can help there. Once you tilt the woofer down to match and leaving the dip above unattenuated, 1kHz would be easy. I bet 700-1.2k is relatively of no consequence if the HD of the drivers does not go awry anywhere therein.
 

Wolf

Senior Member
Joined
Nov 21, 2020
Messages
436
Likes
458
Location
Indiana
The same horn on a flat baffle would yield a much smoother response. Seems like the abrupt edge and gap to the woofer edge have a big influence?

One of the BMS coaxes has a nice soft edge on the horn, possibly to get a smoother transition?
View attachment 216807
The soft edge reduces the diffraction off the edge of the flare. Lots of full range driver enthusiasts do this to the whizzer cones on them.
 
OP
voodooless

voodooless

Master Contributor
Forum Donor
Joined
Jun 16, 2020
Messages
6,210
Likes
10,300
Location
Netherlands
So, looks like @Juhazi has been quite busy the past few weeks with a crazy PA coax project, and he didn't tell us ;)


Great effort @Juhazi! Finally somebody that dared to buy one of those things and do some proper experimenting on them. It's a great wealth of information about horn loaded coaxes!
 
Top Bottom