Sloped baffle

Just a word of caution regarding some speaker measurements one might come across. In an effort to avoid room interactions skewing measurements, very often speaker measurements are taken closer to the speaker than where one would typically sit. Most speakers designed for time and phase integrity need to be taken further away to allow for driver integration (approximately 8'-12'), where listeners typically sit. Unless these further measurements are taken in an anechoic chamber, the room will now contribute more measurable distortions than if the same measurements were taken closer to the speaker. Most people don't listen to speakers at the distances many speaker measurements are taken. If speakers with time and phase integrity aspirations are measured at distance ranges other than where they were intended to be heard from; their square wave and step response, though probably still better than competing speakers without such design considerations, will have their ultimate measurable potential be compromised.

Bombaywalla, I'm somewhat familiar with NRC test facility. But I am not sure which of the NRC tests speaks to time and phase coherence.

Btw, I surmise that the reason many of the top speakers, like the Magico Q5, that have flat frequency response plots and probably use higher order cross overs is because the driver timing is tweaked at the cross over points to optimize wave cancellation and augmentation. But ... the drivers are not otherwise in phase outside of the cross over overlap region.

So ... even if the speaker specs well on the bench, it may very well be distorting complex sound patterns as Roy Johnson explains in his articles.

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?

http://www.soundstage.com/index.php?option=com_content&view=article&id=1043:nrc-measurements-magico-s5-loudspeakers&catid=77:loudspeaker-measurements&Itemid=153

Al, here's another Roy Johnson article I clipped. Perhaps if you get a chance to read his articles, please share comments and thoughts:

http://greenmountainaudio.com/speaker-time-phase-coherence/

Btw Al, you may find the square wave pics in the article to be of interest. It seems that using higher order cross overs creates an almost unsolvable electrical problem.

BIF

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.)