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In the Forum: Horn-Loaded Speakers
In the Thread: "O Vitavox, Vitavox! Wherefore art thou Vitavox?"
Post Subject: Specs & speculationPosted by jessie.dazzle on: 7/1/2011
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Romy wrote:
"...jd, I cannot see any of PDF files, probably my current networks kills them..."
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"...The biggest thing that I wonder is how Mick made the Vitavox bass drivers to has 35Hz resonance. You can always use softer suspension and it will drive resonance down but it also make the excursion of the driver and much wider. Does the original Vitavox magnetic structure supports it? I do not know. On a different note Mike might make the gap a bit longer and use longer magma ring…?..."
The AK150 and 152 are not new creations dreamed up by Mike; they were made back in the day by Vitavox but nobody ever talks about them and I have never seen either. See the Unofficial Vitavox web site; AK150 = Catalog N° CN143; AK152 = Catalog N° CN327.
http://website.lineone.net/~empson/CN.html
My understanding is that all these drivers use a common chassis and magnet and that it is only the addition of a cone/voice coil that finally determines what they end up; if that is so, then presumably the original AK driver was designed with consideration for the lower Fs. I would hope the lower Fs were achieved via an additional pleat in the suspension. This would of course require additional tooling, so it is possible that the lower Fs were achieved via simple mass-loading of the membrane (i.e. making the cone thicker) which comes at a price.
"...I personally do not see a use of those drivers..."
20Hz bass horn anyone?
So you don't think the tail that starts 3KHz lower may be worth the fight it would take to get the Fs up high enough for use in a 40Hz horn? In any case, I'd share your concern regarding possible rear compression due to an ultra-small rear chamber volume. Assuming DSET or dedicated amps, driving an K15/40 or AK151 low enough and loud enough via a 40Hz horn should not be a problem; in this case, the potentially stronger low-frequency performance of the AK152 is not so much of interest. However, for those that do not give these horns their own dedicated amp, the stronger low end may be more of an enticement.
"...Since the AK157, AK151 and K15/40 become available (even with new diaphragm that no one knows what they are made from)..."
As with the S2, my understanding is that every attempt was made to be as faithful as possible to the older production units which would suggest simply continuing production of the parts unchanged. This in theory is possible, as I read a while ago that, along with the rights to produce the drivers, the original tooling was purchased and is presumably still being used (though it did require refurbishing). If so, the question then becomes one of availability of the materials and of course the know-how. In response to both of these issues, given the fact that this is all taking place in England (wonderfully resistant to change as it is!), there's a fair chance both are possible.
Paul S wrote:
"...it is my understanding that only one of these was meant for a horn; the other is a direct driver..."
In practice it is not necessary to abide by it (as Romy has proved) but the original intent and "official line" as seen on the old spec sheet was as follows: The 15 Ohm drivers were intended to be used as direct radiators and the 8 Ohm (really 7.5 Ohm) versions were intended to be horn-loaded. The reason for this is that in theory, the load the membrane sees as a result of firing into a horn where there's only one way out (down what starts off as a narrow tunnel), is greater than in the case of a direct radiator (which is free to diffuse its pressure over at least 180° hemisphere). The additional load translates to greater Z as seen by the amp and presumably brings it more into line with the 15 Ohm load presneted by the compression drivers which themselves, due to the frequencies involved (less excursion) and being semi-coupled to a far smaller and lighter column of air in the horn, are less prone to having their load upped by the presence of a horn.
"...IMO the "raw" S2 is too wild and too... raw. Like most drivers, this one needs an education and training..."
I use the S2s with the older metal suspended diaphragms which are known to be the most "raw and wild"; it is true, they are definitely live and with really correctly-mastered recordings, it is in part, exactly that live factor that pleasantly reminds me why I built my horns and continue to let them dictate my real estate options. What is also definitely true is that they make the really sub-par recordings (i.e. most all pop/rock etc, about half of jazz and around 15% of classical) unbearable, and I don't mean just a little. When its good, its extasy; when its bad, its painful. For those who listen mainly to classical, its a no-brainer; there is a sufficient number of correctly-enough mastered recordings to make the affair worth pursuing. If jazz is your thing, it will mean doing a bit more weeding but the results are very worth while. If pop/rock etc is your thing, definitely look elsewhere. The new production drivers are equipped with the more polite Mylar diaphragms (in theory, the same as the last production run of the older production drivers); I plan to give them a listen.
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