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Coaxial Drivers


Retired Admin
What's the benefit of a coaxial driver?

I see the term "time alignment" mentioned frequently and now and then there's a further description that high and middle frequncies arrive at the same time. Is this noticeable (as in auidible) to the lay person or do you need to have a golden ear?
With a traditional speaker, the point where your brain perceives the tweeter's location and the point at where you perceive the midrange driver's location is slightly different - one is typically higher than the other. With a good coaxial (like KEF or Tannoy) that issue is eliminated and the sound of the tweeter and midrange originate from exactly the same location. Whether you are standing, sitting, or lying on the floor, the acoustic center of a coaxial driver remains identical. This acoustic center issue can also be resolved for a fixes vertical listening position with a MTM design, similar to my speakers. As long as you are seated such that your ears are directly between the midrange drivers in an MTM, the acoustic center will appear to be the tweeter in the middle. But if you stand up or lie on the floor that illusion falls apart.

Another issue is crossover design and driver output overlap. Again, it is all about dispersion into the room. You can tune a crossover perfectly for a fixed listening position where the tweeter and midrange are placed anywhere close to each other. You can even align the phase and such so they sound amazing together from that single fixed listening location. However, with traditional speakers with separate tweeters from midranges, moving from the ideal target listening position will cause all that tuning to be knocked out of alignment because the distance between the tweeter and your ear and the distance between the midrange and your ear will start to differ from each other, or the target ideal tuning distances. So, moving around the room will alter the sound and the acoustic reflections will not have the same timber in the crossover range. With a good coaxial like those from KEF and Tannoy you don't get that problem as you move around the room.

There are other benefits as well.

There are also some disadvantages to coaxials, such as the inability to easily mix and match midranges and tweeters and a redesign in the tweeter alone requires a redesign of the entire coaxial speaker. There are also some serious engineering and manufacturing complications with making high quality coaxials that can significant raise the costs. Also, with a dome based tweeter in a coaxial driver where the tweeter is deep in the cone of the midrange, the movement of the midrange cone can cause doppler distortion from the tweeter's acoustic output. The cone is acting like a wave guide for the tweeter - which also has its potential issues with off axis performance and such.
One of the best examples of a properly designed coaxial driver in conjuntion with time and phase alignment is Jim Thiel's CS3.7.



DIYer said:
Flint said:
I write about time alignment on the first page of this thread at S&V.
BTW, Flint, one more post there will make it 30K! :eek:

I know. That's why I stopped posting over there. I assume it drives everyone crazy that I won't make that one last post to put it over the top.
Here is a review of Thiel's less expensive coaxial speaker http://www.soundandvisionmag.com/articl ... r-speakers

I would like to hear a really good pair of coaxial speakers because of quotes like these, to compare their soundstage against my Magnepans.

The Thiel SCS4T perfectly captured Chesky’s carefully choreographed cacophony. Percussion percolated across the front of my room, while the ambience of the recording space enveloped my listening chair. I could even hear the echoes of a faint, high-pitched instrument — a bell tree or a tambourine, perhaps — coming from behind my listening chair. Rarely does one hear this combination of pinpoint imaging and an expansive soundstage.

Many other speakers, such as bipolar and electrostatic designs, produce a great sense of ambience, but their spatial qualities sometimes sound exaggerated.
Cabasse makes a 4-way coaxial speaker called La Sphere, too bad it looks like something from a 50's B Sci-fi movie, yep it's Fugly.

Vienna Acoustics makes also makes a coaxial with a flat midrange. http://www.vienna-acoustics.com/product ... e_kiss.php

Tannoy's Westminster, under their Prestige line. Is the Grandaddy of them all to me, I love all the woodwork on this speaker and I believe the is one Flint prefers for a coaxial. One day I will hear this speaker in person http://www.tannoy.com/ResidentialSummar ... dK1Hcut+xD
What prompted my query was the fact that I've been intrigued lately with KEF's new Q series, specifically their Q900 floorstander. I don't have much to go on other than manufacturer hyperbole but, that aside, these seem like incredible speakers for not a lot of money ($800/ea). Im fearful that this may be a case of if-it's-too-good-to-be-true...

Zing, I think it's time for you to step into diy speaker world. You can do the phase alignment physically or with active x-over.
That may be true but I can't build DIY speakers and active crossovers for $1600. The last time I compiled a parts list, I had $1900 in drivers, hadn't even considered cabinets yet and I certainly hadn't considered crossovers. Given my history and propensity, a DIY system would likely cost me $15,000.
Well they sure are lookers!! I suggest someone purchase some and report back...
$1,900 in drivers for a DIY build, if done properly, would result in a speaker on a similar level as a $5,000 retail speaker. You cannot assume spending $1,600 on retail is the same as spending $1,600 on DIY.
Zing said:
I can't build DIY speakers and active crossovers for $1600.
You sure can. Say, used active x-over (I did) and some less expensive but still decent drivers or used drivers rebuilt (I did).