[DaveC113]

So why isn't a whizzer a good solution? Its partially physically decoupled from the main cone forming a mechanical crossover. The ones I've heard maintain the "coherency" and other positive traits of a single driver, although I've heard some arguments against whizzers that may or may not have merit. Maybe like the excursion issue, it shouldn't work as well as it seems to, but the fact remains some of the best single driver speakers I've heard happen to use whizzers.... and higher than normal excursion. I suppose, theoretically... they shouldn't sound good. 

My guess is that the compromises involved with having higher excursion and a whizzer, which enable the driver to cover more of the audio spectrum, are worth it in some cases. I'd guess if the driver was designed to minimize the effect of these compromises, they might not be as big of a compromise as most might guess.

Ed, isn't that why you offer the model 2, and now 3? You decided to go the route of more drivers instead of bigger drivers, which involves its own set of compromises, no doubt...

[ejfud]

Wow this is starting to make sense to me. Thanks for sharing your knowledge gentlemen. I for one appreciate it.

I'd love to see the simple line article as well. Sounds like a fun quick project.

[Graham Maynard]

Hi Ed,

Variants of a transmission line can make good use of a decent transducer because the line 'tunes up' the LF.

However, once you recognise the family of reflections/suckouts from within a line enclosure it does not matter which driver you use, you cannot avoid hearing the line itself through the driver cone.
And if you damp the line to minimise these reflections/suckouts, which are higher in frequency than the fundamental line augmantation frequency, you end up overdamping the line and nullifying the LF output which was the original reason for using it.
To identify line characteristics, simply remove the driver, tape a few sheets of newspaper over the LS mounting aperture and then tap them as you would a LS cone.  (Ooops!)

Now as far as I am aware the 103 will do excellent mids and highs, and loudly too, but if you add mass it won't !

Far better to use the single driver as designed, and parallel up with another one (or more) running only as high as is necessary to lift the LF plus baffle step etc.  This can be a same type driver, or larger to achieve greater cone area with falling frequency and thus increased LF output without having to rely upon a recognisably tuned enclosure.

Cheers ........ Graham.

[DanTheMan]

Was there a specific case for a 10 gram 6" tweeter?  In other words, is there some magical significance or science to the choice of those numbers?

Thanks,

Dan

[Graham Maynard]

Not that I am aware of - merely illustrative.

[DanTheMan]

Thanks Graham!  I was thinking that perhaps there was an ideal weight/size ratio, but I guess not.

[Taterworks]

So, isn't the common thread here the fact that smaller drivers have significantly more magnet-to-cone-area ratio? And...overhung/evenhung motors (to add another wrinkle)?

If we imagine that a loudspeaker cone is theoretically perfectly rigid, we will still need to apply larger forces to get that mass to change direction rapidly. In the case of a dome tweeter, most ceramic-motor dome tweeters have a motor with 3-5 times the cross-sectional area that the diaphragm does (though one could easily use many smaller slugs and a deeper motor structure to fit the same amount of magnetic material in there). Yet in the case of ceramic-magnet Fostex full-range drivers, there's a much smaller force-to-cone-area ratio.

The answer here is that mass is the limiting factor, and the solution is to decouple as much of the cone's mass at high frequencies as possible. Look at Thiel's CS2.4 coherent source mid-hi driver, with an additional elastomeric suspension element functioning as a mechanical 'crossover' at the junction of the HF dome and the midrange cone. Why does this work as well as a tweeter? Because we've decoupled enough cone mass to allow the driver to continue to vibrate efficiently. If we had the ability to perform a similar decoupling act at the center of a Fostex FX120, for example, we'd enjoy greatly improved HF response from the driver. Looking back at the FX120, the driver has a rigid aluminum dome coupled to its voice coil, much like the Thiel driver, but there's no additional suspension element between the edge of the aluminum dome and the larger cone area. The rigid dome helps to improve very high-frequency performance because it continues to vibrate pistonically at high frequencies, while the cone itself is dancing chaotically with transverse and ring modes.

Back up a bit. Driver cones undergo a phenomenon known as 'doubling' -- the region of the cone that is stiff enough to continue to vibrate pistonically shrinks as the frequency being reproduced increases. Outside that region of pistonic vibration, however, the cone is still moving chaotically like a drum membrane, providing some output, but with plenty of ringing effects and 'cone cry'. The more rigid the cone material, the higher the frequencies where this sympathetic 'breakup' will occur. On an 8" full-range driver, at high frequencies there is quite a bit more of this chaotic dancing going on, because of imperfect 'doubling', and that contributes output through the upper midrange, but at the expense of transient response. What's more, the larger cone will produce a 'cavity effect' where it functions as a horn waveguide to the part of the cone that is still vibrating pistonically, giving the 'cupped hands' coloration that those who dislike large full-range drivers often cite. We add a small 'whizzer' cone to add more energy at higher frequencies to mask the cavity effect, but the whizzer cone radiates backwards just as much as forwards, and that rear radiation reflects off the cone and is re-radiated into the room with plenty of frequency-dependent phase shift.

The only practical answer to the problem of imperfect doubling is to develop a driver cone that decouples the outer parts of its diaphragm with increasing frequency, allowing the motor to continue to develop enough force to drive the diaphragm at high frequencies. I'd suggest a driver with a metal HF dome coupled directly to the voice coil, with a 3"-5" diameter metal diaphragm decoupled from the voice coil by a stiff elastomeric suspension, providing midrange response. Next, another elastomeric suspension member would decouple this from a 12"-diameter paper LF cone. With this design, you'd have a cone that radiates over a progressively smaller area with increasing frequency, with significant reduction in these other chaotic vibrating modes of the cone. (The other option is to develop a very rigid cone, and arm it with a proportionally large and unwieldly motor structure and high-power voice coil to get that mass moving. But then -- then you'd still need to deal with the fact that with air as a working fluid, your huge driver would still become very directional at higher frequencies. Still no go -- the 'mechanical crossover' driver wins this one.)

At the end of the day, it may be easier on our pocketbooks and our blood pressure to simply admit that full-range drivers as they exist now are simply a compromised technology, just like everything else in the world of loudspeaker designs, and those that opt for them simply choose them for the things they do well.

[planet10]

FX120 cap is attached to the cone not the voice coil.. the FF85 on the other hand is attached directly to the end of the vc.

dave