I believe the "coherent" term describes what I referred to in my last answer as a monotonically decreasing sound power output response - that is where distinct nulls from phase cancellation are evident.
It is also worth mentioning that wide baffles (or soffit mounted loudspeakers at the extreme) consistently generate the best audible results. The constant push for narrow baffles to try and deliver 4pi radiation is a formidable challenge that wide baffles circumvent (albeit when well implemented, since wide baffles can also be badly implemented too). The incentive for narrow baffles appears to be promoted by factors such as domestic acceptability and costs, rather than for audio performance.
In the days when only analogue active filters were available, high order crossover filters were employed largely without compensation for the inherent driver roll-offs. Employing such 'dominant' roll-offs circumvented accommodating issues of less well-controllable driver manufacturing tolerances - of which 75mm dome damping at HF is a good example. Lower order passive crossovers don't generally permit such an approach.
Also to note is that active LR4 (or other) phase matched crossovers commonly employ first-order all pass sections too, as detailed in another of SL's JAES papers. These were used to align the main radiating lobes of the different drivers at some nominal listening position.
That 2,3kHz dip is pretty bad. -6dB and very narrow ... and exactly in the crossover area. That's a pain.
any one have built a speaker with 3 inch soft dome Bliesma MP74S ; i'm tented to build a 3 way with a fast 8 or 10 inch bass driver and a 1 inch T25S Bliesma tweeter..🙂
You cross to a 1" membrane which shows super wide radiation at 3,5kHz! That's not a speaker I would build ...
Neither would I. But remember also that the larger monitors employed a 34mm dome which softened the transition somewhat. The loudspeakers were also intended for use in relatively acoustically dead environments too, not reflective domestic situations where any such compromises can be more pronounced.
Well, out of curiosity, I modelled the on-axis response of the Volt VM752 with the OSMC baffle and crossover in Basta. (It's not an easy crossover to enter!) It's just a model, but I'm rather impressed:
is there a beginners guide to employing this current drive method that your talking about sound really interesting
There is plenty of information on this forum - even some that I contributed several years ago. Further discussion of magnetic non-linearities and coil current dependent distortion is perhaps best left to those threads. But I will say that many people get hung up on current drive re its reduction in displacement dependent non-linearities at low frequencies. I would advise ignoring this and listening instead to the improvement in the mid-range.
there is many decent speaker with 1" dome and 3inch medium tweeter , Dynaudio, Atc , Cello etc.. do you think they have all done wrong ?
thanks it seems great for a start , 30L box sealed with 8 inch purifi woofer , i would try it with active crossover first to keep it simple to tweak 🙂
I suppose "decent" is not something that @IamJF would consider enough for one of his projects ... ;-)
I helped a fellow forum member with a waveguide to match a T25B and an M74B at 3K. He had tried an augerpro elliptical waveguide and it created too much tweeter directivity lower down and did not match the M74B very well. To get a good match the waveguide ended up only being 5mm deep. This was for a rectangular baffle for dual 8" woofers, central placement of all drivers.
There is no problem with the Bliesma mid dome itself being in the middle of the baffle on a design like that, if there is the right amount of vertical baffle. Naked tweeters are quite different and rarely work well with that placement. If the tweeter needs to be offset then the mid has to go with it otherwise you get some pretty twisted lobes forming.
reminds me of a speaker i liked in my young days with de-centred drivers
