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Time alignment, important? long

Sound wave certainly does not travel at the same speed for all frequencies, but music recording and reproduction often neglect this fact. Take recording for example, distance of a microphone will have strong effect on how the sound will emerge and be recorded. Say standing one meter from a jazz band vs. 5 meters from the band, you do expect bass to show up slightly slower when standing further from the band much like lightening appears much earlier than thunder. Since not too many recording is done with single microphone, the recording engineer further complicates this result.

One group of speaker designers stresses this issue by “time align” the drivers, this is usually done by tilting the face back (Thiel, Meadowlark) or move the higher freq drivers back in vertical plane (Dunlavy, Vandersteen). Consider a speaker driver generates a range of frequency, moving the higher freq drivers back in vertical plane does NOT align in time domain since 3000 Hz sound will still arrive at your ear earlier than 100 Hz which is generated by the same midrange driver. So that leaves tilting the face as the only viable solution to correctly time align drivers. However, how many speakers actually have identical tilt angle? In theory, delay vs. freq should be a constant value and all speakers that claim to be time aligned SHOULD have the same tilt angle.

Now come the bigger questions. I hear people praising Merlin, Dynaudio, and Maggie constantly, I have first hand experience with most of them and could not agree more, but none of them is time aligned! Music recording is not done in time align fashion whether single or multi microphones are used. On top, every instrument generates not one single freq, but a range of freq, so microphone actually is receiving the sound with time delay in all instances.

Is that a coincidence the aforementioned brands are well received because they PURPOSELY do not time align their speakers to properly reproduce the time difference captured by recording or they sound great because of other factors? Will they sound better if they were tilted back at an exact angle to time align the drivers? If so, why haven’t any owner done that. Or better yet, why haven’t the manufactures done that?

What's your take on this time alignment theory?
semi
semi OP
649 posts
 
Guess I was thinking about about the temp effect of ground vs. air which caused sound to propagate either upward or downward, depending on the temp gradient.

So with that straighten and put aside, I still have questions. If tilting the speaker back is simply to line up the voice coil of different drivers, that will be very simple and effective without moving the drivers back in vertical plane like Dunlavy which is the alternative method. I know x-over will introduce phase shift, I better since I am an MS EE graduate. A driver can potentially have a wide range of phase shift to reproduce especially woofer, but phase range decreases as we move up the freq in a 1st order x-over design. By tilting the speaker back by a few degrees, midrange driver which has less phase shift would actually either lead or lag behind on part of freq spectrum.

Take the Dynaudio Contour 3.3 measurement as an example:

http://www.stereophile.com/loudspeakerreviews/262/index6.html

Where x-over freq is at 350 Hz. Time alignment should only be done on the woofer, not midrange or tweeter. But Thiel, a big proponent of time and phase alignment, tilt the whole speaker back, which in theory can create more problem than solving it.

Who is right?
theaudiotweak
2,801 posts
 
As my memory is restored, Ed Long who owned the trade mark for TA or time aligned speakers back in the late 70's had a speaker brand he enginnered that was not 1st order and it did have staggered drivers for time compensation.Hales speakers of the early and mid 90's had multi order crossovers and sloped baffle cabinets designed by Tom Thiel..Peter Snell the original, had a couple of multi order designs in the mid and late 80's that had time compensation and diffraction adjusted baffles. Peter Snell had U.S patents on baffle and room interaction designs dating back to the early 70's. The original Jon Dahlquist Dq10 was a phased array but may not have been of of 1st order design. These are examples of speakers with voice coils aligned that may not have been of true phase coherency, none the less, some were ground breaking in theory and design..Tom
twl
3,251 posts
 
I prefer single-driver speakers.

An old engineer once said,"The fewer holes you poke in your boat, the less bailing you have to do." :^)
gregm
3,408 posts
 
Duke (Audio"movement") covered lots of ground.
Yes, tilting the mid-tweet baffle (which unfortunately means that the drivers fire at the ceiling) is a way of geometrically aligning the drivers so the pathlength from their reference point to our ears is the same.

I don't know if the woofer presents much of a problem if it enters @~200 or lower; wavelengths are longer there and our ears weaker... so, a few mm difference would not be AS critical vs the wavelength as, say, at 3kHz (lambda=~11 cm). I would try to be more careful in the critical region 300-5kHz where our ear is most sensitive. Maybe that's the region Dynaudio was worried about?

{However, geometrical alignment isn't enough for a linear phase system; the crossover also plays its ugly role and, as Duke notes, a good contender here could be a first order Butterworth...}

OTOH, with drivers on the same plane one can achieve flat AMPLITUDE response -- maybe what the designers of such speakers intended in the first place??
bombaywalla's avatar
bombaywalla
1,958 posts
 
Well, I really dug back into this Audiogon forum to extract this thread for you (somebody last posted on 9/9/03!). Do yourself a favour & read this thread. Somewhere in the middle Roy Johnson of Green Mountain Audio pipes in & gives us some incredibly good info on this subject. Every bit worth reading to educate yourself.

http://forum.audiogon.com/cgi-bin/fr.pl?cspkr&1032037028&read&3&4&

Hope that this helps.
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