Sloped baffle


Some great speakers have it, some don't. Is it an important feature?
psag
In speaker designs that I've only simulated for now, sloping the baffle 10 degrees allowed a slightly higher crossover with the same drivers, which is not so arbitrary. In a 3-way, it also allowed symmetric slope crossovers. In a 2-way, adjusted for BSC, it ended up asymmetric similar to the way I'ld do a flat baffle. Since a normal TM tends to lobe downwards, the sloped baffle tends to correct that and even allow a shorter height. The downside was that it was sensitive to listener height and distance.
There are time and phase coherent speakers that are
wonderful and there are those that are lackluster or worse.

There are speakers that are not both time and phase coherent
but are wonderful, and those that are lackluster or worse.

Time and phase coherency are two out of many attributes that
would be goals in designing a loudspeaker. But not having
it does not mean the speaker is not great, and having it
does not mean the speaker is great.

You have to listen.

Of my favorite speakers, one is and some others are not. It
does not bother me that some are not. I cannot detect the
effects of the lack of time and phase coherency of those
that are not. None of this means that it is not a valid
design goal, but it is only one of a very large number of
valid design goals.
Bombaywalla, did you or Tim mention that one mark of a phase coherent speaker is one which has a flat impedance and phase plot. Take a look at the Magico S5's specs. Is there anything else apparent from the NRC tests that permit inferences about phase coherence?
Bifwynne, don't know whether I or Timlub wrote this - I don't recall writing this in this thread. Maybe in some other thread you & I contributed to?
Anyway, looking at the Magico S5 measurements, even tho' the imp & ph plots are less bumpy than many others in the market, there is still quite a bit of phase shift. Plus, at 2KHz the speaker goes from positive phase angle (inductive) to negative phase angle (capacitative). This can be quite burdensome for the amp - the phase relationship between the current & voltage changes very suddenly & the amp has to react to that instantaneously. This is difficult to do.
Looking at these impedance & phase plots I cannot confirm whether or not this speaker model is time-coherent. Probably not as I've not seen Magico design any speaker thus far that has been time-coherent. Maybe the S5 is a departure from that norm - don't know - but if I'd have to guess, I'd say 'no'.

OTOH, for, say, Green Mtn Audio speaker I'm used to reading specs that look like this. For the C3 speaker model, for example:
Response +/- 0.75dB from 40Hz to 21kHz, -3dB at 35Hz and
23kHz, from 2.5 to 6m, on Soundfield Converged axis, on first arrival
tone bursts, across approx. 80dB dynamic window.

Phase shift +/- 3 degrees acoustically, from 160Hz to 8kHz.
Does not vary with loudness.

Impedance 6.5 Ohms, +/- 0.75 Ohms 150Hz to 20kHz. Does
not vary with loudness.

My brother owns the Callisto bookshelf models & their specs are:
Response Freefield at 2m: +/- 0.75dB from 55Hz
to 20kHz, -3dB at 47Hz and 21kHz. Typically -3dB
at 47Hz on 24” speaker stands at 8’ distant.

Phase shift +/- 2 degrees acoustically, from 200Hz to 8kHz
on listening axis. Does not vary with loudness.

Impedance 4.8 Ohms, +/- 0.75 Ohms 100Hz to
20kHz. Does not vary with loudness.

In both the Green Mtn Audio speaker specs, now, we are talking flat impedance & phase response. :-) Nothing like that in the Magico S5.
(Once again, I've experience with Green Mtn Audio speakers hence I bring them up time & again. If other members have similar specs for other time-coherent or phase-coherent speakers, please share those specs. Thanks.)
Gentlemen,

I am glad to know my previous writings were appreciated, and it's become easier to explain since then.

I can clarify some basic technical concepts above, without reference to our products, if you like.

Please let me know.

Thank you,
Roy Johnson
Just took a look at this thread; the title didn't obviously say "read me" so it took me a while to check it out.

Lowpass drivers lag behind highpass drivers in both time and phase, and a sloped baffle can introduce a limited amount of compensation for that, along with a tilting of the driver axes (which may be desirable in some cases). In and of itself, it's not enough compensation to make much difference, but could be part of a full-scale time-coherent effort such as Roy Johnson's magnificent speakers.

"Phase coherence" and other phase-based terms have been used loosely and don't necessarily mean what we think they mean. For instance, the woofer can lag the tweeter by 360 degrees at the crossover point, yet the system could be called "phase coherent".

Roy's designs are truly "time coherent", and that puts them in a different league; they're the real thing. His designs do everything we might have optimistically hoped for, such as waveform preservation, when we first came across the term "phase coherent".

As for how small manufacturers can do decent design work without access to an anechoic chamber, one answer is time-gating. That's a measurement technique wherein the microphone is turned on briefly to catch the direct sound from the speaker, and then turned off before the first reflection arrives. Time-gating has limitations relative to what can be done with a true anechoic chamber, but it sure costs a lot less.

Roy, I'd be very interested in reading any clarifications you care to post, and have zero problems with your making specific references to your products. The inherent rapid rolloff at the bottom end of the horns I use prevents me from ever doing what you do without totally changing directions (and going back to college), but that doesn't lessen my admiration for your work.

Duke
dealer/manufacturer
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