... So, were going to talk coaxial again... Well, deal with it 
We all know that KEF and Genelec (and there are a few others out there as well) make the top end of HiFi coaxials. They can be best used in 3-way systems, but obviously, KEF also has 2-way's. Obviously, 3-way systems add complexity and also need the extra woofer. But the other thing is: they are small. The best ones are 5.25" at best. That's not going to give you bass extension and SPL for a larger room.
So in come the PA coaxials. You can get them in all kinds of sizes, up to 15". For a 2-way, this has some advantages, the main one is that it drastically lowers the need for excursion, leading to less modulation of the tweeter signal, and thus less IMD. To further help with that, I would recommend putting the 2-way PA Coaxial in a reflex enclosure. This will significantly lower excursion in the bass compared to a closed box. As an example a beast from FaitalPro, the brand new 15HX500. Let's have a look at the excursion at 40Hz at the same 106 dBSPL. For this, the closed box (both same volume of 100L) needs significantly more power, about 100W more, so 130W vs 30W for the reflex version:
That is a big difference. The BR advantage will be there all the way up to 200 Hz, so It is quite significant. Obviously, you'll need to control the excursion below 30 Hz, but that should be done anyway. So, that 2 mm movement will get you > 106dB from 40 Hz on. Pretty good! It also means this thing will go loud! > 112 dB > 30 Hz .
So these things seem to have some compelling arguments going for them. Obviously, the main question is: what about the dreaded coaxial frequency response and directivity issues? Well, here things get obscured quickly. Sadly one cannot find much information about this just about anywhere. You can find lots of people claiming they used a PA coaxial and that they sound great, but rarely does one find a frequency response, and even more rare is an off-axis frequency response
. The manufacturers aren't helping either with their (lack of data)-sheets...
So time to try to consolidate all the information we can find on these things so we can make some more sense out of it all!
There seem to be two notable groups of coaxial available:
But possibly this can be very well tamed? Once again, data is lacking... I just hear they seem to sound fantastic... Oh, did I mention it is really expensive?
The FaitalPro 12HX500 (the smaller brother of the earlier referenced 15" version), seems to sport quite a smooth directivity:
Obviously, this is highly smoothed.
This 14" B&C also:
I especially like the between 12" and 15" size.
Arguably better than a horn-loaded version of the same brand:
This horn-loaded 15" 18 Sound also doesn't look too bad:
This Beyma seems to be a popular one as well:
So, this is just a fairly random collection. I did find some DIY projects with some of these. But I'll need to compile some more links. And many are for PA wedge speakers or tops. Essentially that should not matter as long as the data is decent. I'll add some follow-up posts with a few links coming days. For now though, this might already be some food for thought and discussion.
We all know that KEF and Genelec (and there are a few others out there as well) make the top end of HiFi coaxials. They can be best used in 3-way systems, but obviously, KEF also has 2-way's. Obviously, 3-way systems add complexity and also need the extra woofer. But the other thing is: they are small. The best ones are 5.25" at best. That's not going to give you bass extension and SPL for a larger room.
So in come the PA coaxials. You can get them in all kinds of sizes, up to 15". For a 2-way, this has some advantages, the main one is that it drastically lowers the need for excursion, leading to less modulation of the tweeter signal, and thus less IMD. To further help with that, I would recommend putting the 2-way PA Coaxial in a reflex enclosure. This will significantly lower excursion in the bass compared to a closed box. As an example a beast from FaitalPro, the brand new 15HX500. Let's have a look at the excursion at 40Hz at the same 106 dBSPL. For this, the closed box (both same volume of 100L) needs significantly more power, about 100W more, so 130W vs 30W for the reflex version:
That is a big difference. The BR advantage will be there all the way up to 200 Hz, so It is quite significant. Obviously, you'll need to control the excursion below 30 Hz, but that should be done anyway. So, that 2 mm movement will get you > 106dB from 40 Hz on. Pretty good! It also means this thing will go loud! > 112 dB > 30 Hz
.So these things seem to have some compelling arguments going for them. Obviously, the main question is: what about the dreaded coaxial frequency response and directivity issues? Well, here things get obscured quickly. Sadly one cannot find much information about this just about anywhere. You can find lots of people claiming they used a PA coaxial and that they sound great, but rarely does one find a frequency response, and even more rare is an off-axis frequency response
. The manufacturers aren't helping either with their (lack of data)-sheets...So time to try to consolidate all the information we can find on these things so we can make some more sense out of it all!
There seem to be two notable groups of coaxial available:
- Coaxials without a horn. These usually have a smooth transition of compression driver throat to the woofer voice coil. The profile of the woofer is usually shaped as a waveguide to provide a better off-axis response.
- Coaxials with a horn. These use a horn for the HF part. The horn then covers most of the woofer cone. This leads to some difficulties regarding crossover design because of the profound effect on the woofer response this configuration has. Obviously, the horn will give a much better HF response and will yield lower IMD because there is far less chance of modulation. Some horns are symmetric, others are not. Dispertion is generally less wide than the coaxials without horn.
But possibly this can be very well tamed? Once again, data is lacking... I just hear they seem to sound fantastic... Oh, did I mention it is really expensive?
The FaitalPro 12HX500 (the smaller brother of the earlier referenced 15" version), seems to sport quite a smooth directivity:
Obviously, this is highly smoothed.
This 14" B&C also:
I especially like the between 12" and 15" size.
Arguably better than a horn-loaded version of the same brand:
This horn-loaded 15" 18 Sound also doesn't look too bad:
This Beyma seems to be a popular one as well:
So, this is just a fairly random collection. I did find some DIY projects with some of these. But I'll need to compile some more links. And many are for PA wedge speakers or tops. Essentially that should not matter as long as the data is decent. I'll add some follow-up posts with a few links coming days. For now though, this might already be some food for thought and discussion.
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