Speaker Designers Needed.

[diyaudio]

I really don't understand lobing but understand it can be controlled by having a low crossover and sandwiching the tweeter as close to the midranges as possible. It also depends on careful driver matching to get the best result.

It needs a crossover so low that the tweeter cant handle it

 

[diyaudio]

Just pointing out that most ultra expensive speakers seem to be designed symetrically with a WMTMW layout, or a MTM sandwich somewhere in the design.

Must be a reason for it.

There is no relation between ultra expensive speakers and MTM. MTM looks good and ultra expensive speakers cater to a different public, the speakers are designed for aesthetics first and acoustics take aback seat. There is a lot of marketing hype and snake oil theories. There is no scientific data to support the high price. There will always be a market for it as the buyer belongs to a niche group.

I am not against MTM, I may be building next project with MTM myself as my primary listening position is sitting at one place on sofa.
I just wanted to tell the problems with it. Coax solve these problems and OP is already inclined to use it.

Do these ultra expensive speakers give distortion graphs, polar charts, power compression at full power etc? No they dont.
One of the reasons I like DIY is because I know with DIY we can trump these so called ultra expensive speakers which can be very rewarding in itself

 

[grindstone]

Yeah, as they will be active, all that's really necessary to aid the OP is to specifically identify the two drivers. Then, speaker designs can fall out of the Aether. If you know where he might source reputable coaxes from trustworthy manufacturers, it may be helpful for you to choose an example 6 or 8.

BTW, MTM were popular in the 60's for a bit but it's only after Joe d' Appolito figured our some filtering maybe 30 years ago that the vertical polars really got "fixed". Then, of course, everyone had to build them for a spell, like any other speaker topology fad.

Re the "lobing" in this vernacular: Drivers narrow their dispersion as frequency increases (aka their beamwidth narrows or they "beam"). At low freqs (long wavelength relative to source size), radiation is hemispherical blob. Increasing frequency, the blob narrows to a sort of teardrop. Increasing frequency further, it begins to form side "lobes" (sic). Reality is revolved 3-D for pistonic sources.



That's one part of it. Now, add a second source. The distance from each to a given receiving positon will be different. What happens is frequency-dependent constructive and destructive interference. Like throwing two rocks in the water--some spots have wave peaks, some spots have troughs. It you keep the two radiation sources within a distance of say 1/4 wavelength at crossover, they combine as a single source to make a single forward lobe. Fore- or aft- positioning of each relative to the other will then begin to "tilt" or rotate their main lobe (and pattern) when viewing the vertical plane from the side.



Filters mess with phase and can thus move/rotate the radiation pattern as well. By inspection, then, the choice for axis of measurement relative to forward lobe axis matters. This can show as "polar problem". Just jockey things so that you can sit in the big fat forward lobe, and all is well, basically. Aim the vertical nulls at that ceiling reflection and floor bounce and your spectral balance is more forward lobe and less reflection, etc. Of course nothing is quite that simple when considering breakup modes and non-ideal drivers and no speakers are perfect. The OP need not think about any of this and in a way, the coax choice can make everything easier.