Sloped baffle

06-22-14: Bombaywalla
Why the differences? Because the Vandy 7 is time-coherent & the Revel2 is not!
Bifwynne, if you click on the link provided by Tls49, you will see exactly why as you read the text there. Scroll down where Roy J talks about time-domain response & he shows how a step response looks when the speaker is time-coherent & when it is not.
The Revel2 are clearly not time-coherent.

I agree.

Bruce, taking the Magico Q5 as an example, whose measurements you also linked to, note that the frequencies of each of the four up and down oscillations that are shown in the step response figure become progressively lower (i.e., their periods/durations become progressively longer). That is because the first peak primarily represents sound arrival at the measurement mic from the highest frequency driver; the second peak primarily represents sound arrival at the measurement mic from the next highest frequency driver, and so on.

So it can be inferred that the amount of delay between the start of the arrival of the sounds from each of those drivers and the occurrence of the step in the signal that is sent into the speaker are significantly different, and become progressively longer for progressively lower frequency drivers. While with the Vandersteen 7 they are not significantly different, resulting in the outputs of each of its drivers summing (at the position of the measurement microphone, at least) to a much closer approximation of an ideal step response.

Best,
-- Al

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.