Subject: Center Speaker Recommendations for Main Horn Speakers

[ajant]

Your crossover designer might put a little bit of dippage in the on-axis response of the ME90 down near the crossover, in anticipation of the wider off-axis response filling in this region.

To thereby keep the ME90 from having a wider dispersion than the midwoofers?

 

[ajant]

Well, imo there are trade-offs either way.

800 Hz and 1200 Hz are effectively in two different categories, as far as available waveguides and suitable compression drivers.

For an 800 Hz crossover we'd have to use at least a 1.4" throat waveguide and then choose a suitable compression driver. I am not aware of any off-the-shelf 1" throat waveguides and horns suitable for an 800 Hz crossover.

For a 1200 Hz crossover there are a few off-the-shelf 1" throat waveguide/compression driver combinations that would work.

If we end up staying with the 90-degrees-ballpark radiation pattern width as our target, I'm thinking the 80-degree-pattern B&C ME90 looks the most promising for an 800 Hz crossover. The SEOS-15 and Pi Speakers H290C, both 90 degrees in the horizontal plane, look to me like viable options for a 1" throat compression driver with a 1200 Hz crossover.

Imo the advantage of an 800 Hz crossover is that we have a bit more of the overtone region covered by a single driver (which is imo desirable), and of course the power handling is higher, but the downside is that the radiation pattern will narrow somewhat in the top octave. Therefore top-octave coverage across the entire listening area will be less uniform than the coverage further down the spectrum. Also, there will be more of a radiation pattern discontinuity in the crossover region because the woofer's pattern will be wider than the waveguide's pattern.

Imo the advantage of a 1200 Hz crossover is that we can use a 1" throat compression driver which will give us more uniform coverage in the listening area in the top octave, along with better pattern-matching in the crossover region (assuming a 90-degrees-horizontal waveguide). The trade-off of course is that we don't get the benefits of an 800 Hz crossover.

These tradeoffs are driving me nuts!! But Earl Geddes recently mentioned that the smallest driver practical is best. https://www.diyaudio.com/community/threads/best-compression-drivers-today-2022.382609/post-8135700 But a 1" driver would rule out the M2 , ME90 and other waveguides but nominate which ones? And which are among the best performing 1" drivers? Or should I stick with the 3" or 4" drivers and the waveguides discussed?

 

[Duke LeJeune]

how and why could I know whether I would prefer your downward sloping response vs. the flat response which Rob and others like for direct sound

Certainty is a rare commodity in this sort of venture.

If I was in your situation (lacking a wide range of relevant personal knowledge and experience, but seeing that the majority prefers one thing and one random manufacturer prefers something else), I'd probably play it safe and go with the majority.

To thereby keep the ME90 from having a wider dispersion than the midwoofers?

The on-axis dippage I mentioned would be to compensate for the ME90's dispersion gradually widening south of about 1.5 kHz.

Because of this widening , there is a bit of a trade-off between good on-axis response and having a bit too much off-axis energy between 1.5 kHz and the 900 Hz crossover. My preference in situations like this is to "split the difference", and use a small on-axis dip to partially compensate for the excess off-axis energy.

These tradeoffs are driving me nuts!!

I totally sympathize!

"No compromise" is a marketing department term. Loudspeaker system design is all about the juggling trade-offs.

But Earl Geddes recently mentioned that the smallest driver practical is best. https://www.diyaudio.com/community/threads/best-compression-drivers-today-2022.382609/post-8135700 But a 1" driver would rule out the M2 , ME90 and other waveguides but nominate which ones? And which are among the best performing 1" drivers? Or should I stick with the 3" or 4" drivers and the waveguides discussed?

Imo a good 1" throat driver has this main advantages over a good 1.4" throat driver: Given a suitable waveguide-style horn (something Earl invented so it's a given for him), a 1" throat driver can give you good coverage across a 90 degree pattern width well up into the top octave. There will be some pattern-narrowing in the top half of the top octave.

Imo the 1.4" throat approach trades off wide pattern coverage up high in exchange for being able to cross over lower. Like, you can get away with 900 Hz or maybe even 800 Hz with the ME-90 because 1.4" throat drivers have more output down there and are more rugged, but with a similar-sized 1" throat horn you probably would not want to cross over below 1 kHz at the lowest. On the other hand the ME-90's pattern narrows in the top octave, and I think it's because the 1.4" diameter inevitably starts beaming (in the absence of a diffraction slot).

Earl used a 1" throat driver, the B&C DE25 and later the DE250, on a 15" 90-degree waveguide and crossed over around 1 kHz to a 15" B&C woofer. I think your Altecs would be perfectly fine crossing over at 1 kHz, but my understanding is that you would prefer to have a lower crossover frequency based on the Altec's distortion measurements.

Earl later lowered his crossover frequency to 900 Hz, still with the 15" waveguide, and I THINK this is when he started using the DE550. The DE550 is among the few 1" throat compression drivers that have a 2" diaphragm. The others are the DE550TN (titanium rather than polymer diaphragm); the Kartesian Cmp50_vPA-S (titanium diaphragm); and the Faital HF1000 (polymer diaphragm). The final version of his Summa used the DE550 on a big 18" waveguide with an 800 Hz crossover frequency.

I am pursuing the development of a commercial product in this general category (big woofer; big constant-directivity waveguide with a fairly wide pattern; 1" throat compression driver). I'd rather not post the specifics in your thread, but you can shoot me a message if you'd like, as some of it might be relevant to your project.