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In Reply to: RE: The web blurb doesn't say they are time aligned... posted by krisjan on July 18, 2014 at 11:05:31
I love my Vandys, but they are old and failing, and they do not make a speaker that is ideally suited to my room. I felt the same way about the Theils.
From the designer:
“With regard to time coherency, the speakers are time coherent. Many stepped baffle loudspeakers are not time coherent. We use only a single air core copper coil and a single capacitor (a first-order or zero-order crossover) and unlike most loudspeakers both the tweeter and woofer are wired in the same positive polarity (most designs flip the polarity of the tweeter to gain better coherence). This indicates that the drivers are acoustically matched and the cabinet matches the parameters of the drivers very well. Keep in mind complex crossovers are meant to correct aberrations in the loudspeaker response and that you cannot get a flat frequency response with a first order, positive polarity design unless the drivers are time coherent.”
So the claim is clearly being made, and the relevancy of the frequency response in relation to the time coherence is mentioned. From what I read, time alignment is difficult because methods to determine the acoustic center of the driver are difficult and don’t apply across the frequency range.
Follow Ups:
You should probably check out the Gallo Ref. 3.1s and 3.5s. They are time/phase aligned and are virtually crossover-less. There are some great deals on them for $2500 and less on A'gon....
-RW-
I do find the language and thought process interesting which makes me wonder if the designer information matters. Remember the designer will talk up their design.
In the verbiage:
"and unlike most loudspeakers both the tweeter and woofer are wired in the same positive polarity (most designs flip the polarity of the tweeter to gain better coherence)."
I have not seen simple cap/coil designs (pseudo first order) flip tweeter phase. That is typically done when using a 2nd order electrical using a cap and coil on each driver.
Maybe everyone is just over thinking what this speaker is especially considering the price.
PeterZ
Only TRUE second-order designs, with both drivers -6dB at crossover frequency, and rolling off at 12dB/octave for at least an octave above and below that frequency, do that. Utterly unnecessary with first, third, or fourth-order crossovers.
Remember, we're talking acoustic crossover here, with slopes being the sum of the electrical transfer function of the filters and the natural unfiltered response curves of the drivers. Unless there is a VERY broad, flat overlap of the unfiltered driver responses, like four octaves, true first or second order acoustic slopes are really difficult to attain.
Ah, well maybe so. As a book designer living on fairly tight cash flow, the price is not small to me. I also chose to audition these based on the design goals. I think a measurement of step response will show what is really going on.
The acoustic suspension/transmission line bit struck me as odd from the beginning, but I assume the design uses a box with a small vent—small enough that the woofer gets some pressurized support, but less than an actual tuned, sealed box.
My biggest issue is one of not wanting to own a speaker sold on false pretenses. That means giving the designer several chances to respond to questions AND doing what measurement I can to satisfy myself.
For acoustic suspension, the box must be AIR Tight. There is no such thing as a small port. A TRUE acoustic suspension woofer wouldn't begin to work properly with any size opening. And to imply there is any relationship between acoustic suspension and transmission line is totally ignorant and says the writer either doesn't know what he is writing about or is spewing plain BS.
They claim they have a time-coherent (transient perfect) loudspeaker with a cap and coil for an MTM design with no baffle or driver offset. "Cap and coil" is a 1st order electric crossover. To get a first order acoustic response with a 1st order electrical crossover using just driver matching is, in my mind, quite a feat.But, according to theory you can't have a *true* transient accurate crossover unless you have a transient accurate acoustic response *and* drivers have their acoustic centers lined up. There are also other types of crossovers which can yield a transient accurate response, such as the B&O filler driver approach, or subtractive delays designs, or with group-delay correction in the DSP realm. In the DSP realm, anything is possible...
It's a simple matter of seeing this speaker's step response.
I'm skeptical, but if this speaker does have a transient accurate step response, I'd love to figure out how the heck they pulled it off. They may be guilty of taking a liberty with word usage "time coherent". A phase coherent speaker does not necessarily have constant group delay. The LR4 acoustic response is phase coherent but not time coherent, for example.
These terms sometimes mean different things to different people, depending on who you ask - and what you ask...
Cheers,
Presto
Edits: 07/18/14
I am skeptical as well. If all the claims are true, it IS something unusual. I am just looking for any rational idea.
I will ask again for an impedance curve and also a step response graph.
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