The umpteenth large format coaxial driver thread

[bonzo75]

Hi all, I have exposure to modern Tannoys and vintage Tannoy MG15 and HPD 315a (latter two which I like). Is there anyone here with more MG15, Reds, or Silvers?

I hope to listen to Radian coax at some point, and to a good Altec 604.

Are there any other coax people are running here with low wattage tube amps?

Thanks

 

[camplo]

2.5-way MINIMUM to maintain good efficiency.

_ I was just thinking about how a large diameter 2.5way is actually better than a 3 way.......

Best practice is to have your co-axial from about 450 Hz up, and 2 mid-bass drivers below it to minimize floor bounce.

_ Why 450hz? Why not 250hz? or maybe slightly lower even?

 

[ScottG]

In a typical listening setup the coaxial is far enough off of the floor to avoid the 1st reflection of the floor - at least within its pass-band.

It of course depends on many factors, but assuming a traditional listening height and a coaxial near that same height - then it's all about how far you listen from the loudspeaker. The further out, the higher the freq. for that first reflection. (..the closer you get, the lower the freq.). Lower is better, higher in freq. puts it into the range of the driver's pass-band. The higher the coaxial is off of the floor the lower the first reflection from the floor. You could enhance this by designing a fair bit higher than the listener's intended listening height and aiming the driver very slightly down to the listener (standup/sitdown pressure losses would become much worse though).

 

[ScottG]

Floor/Ceiling Reflection Calculator

I estimate 84-89 cm (33-35 inches) for the listener's ear height (as an average) and the height of the tweeter (center) in the coaxial to match that.

With the calculator you can see how the reflection moves up and down in freq. relative to listener distance from the loudspeaker.

 

[druif]

Hi all,

Thanks to AC for sharing this project....

Is the schematic suitable for the B&C 15FCX76 8+8 ohm or the 8+16 ohm?

Are there people who build this speaker?

Thanks in advance

A 15-inch two-way coaxial speaker - the ingredients and the crossover

Okay. So, back when I started this thread, my goal was a two-way speaker that could hit the mark of producing the lowest notes of a bass guitar with aplomb. And I'm quite happy to report that this mark was met, and even exceeded, though slightly depending on your room.

And of course I wanted this goal to be met with a coaxial driver. Not an easy task, mind you. With these goals and driver sizes we've nothing to utilize but PA-drivers, and most of these are unusable for Hi-Fi use. Most, but not all of them, mind you.

I think it was "ScottG" here at diyaudio.com, who pointed me to take a look at B&C's quite recent 15FCX76 drivers. And this was luckily no dead end. They do however need some space to thrive, when it comes to the enclosure. A hundred liters isn't enough, but 170-180 liters is nearer the optimum. Now, these speakers do rely on some room enforcement in the lowest octaves, but that seems to be normal with most high efficiency designs. What you end up with is something like 95dB/W/m efficiency and a response that goes straight down to 20-40Hz depending on your room. Not that bad for a two-way design? It took me quite a while to finalize the crossover, though. These large PA-coaxials are just that much harder to work with. Not because of their response, but more because of their directivity. They're not pointy, as some panels are, but they nonetheless have a very different directivity pattern to most "normal" loudspeakers (read: 6,5" 'bass' and a dome tweet...). This means you have to voice them very differently. A completely straight response isn't what you're aiming for, lest you want to feel the listening fatigue...

So, thus far we have the first two prime ingredients, the driver and the crossover. The crossover is in the file attached, though feel free to ask me for more info if you feel like it.

Though the crossover seems to be electrically of the second order, it's actually closer to third order acoustically. Considering components, use the best quality polypropylene caps you can afford. The first coil on the bass hand of the X-O should be one with a low resistance. The coil on the tweet side can be an air cored one with higher resistance, doesn't matter that much here. Considering resistors, I've tried some more 'high end' ones, and for me they've been no revelation. They should nonetheless be of 10 watt variants, and use the best quality you can afford. The quality of the resistors - at least for me - makes not much of a difference. I use Jantzen wirewounds here, since they're not ridiculously expensive.

I'll try to post the specifics of the cabinetry as soon as I can. As stated, I'm currently piled up with fun (=projects), so this may take some time.

 

[druif]

this schematic...