relder

I haven't been propositioned for white van speakers for several years (outside of a home depot.) But a guy I know was taken in this last week after leaving the ATM.

Why always a white van, why not mix it up with a red one or something?

They are a lot more sophisticated it seems now.

It might be fun to borrow his newly acquired $300 sound system and measure them, but I think I'd rather use my time on real audio projects.

Adding yet another variable (current vs. voltage driven) sure makes for a lot more measurements.

I survived figuring out Soundeasy's quirks once again with minimal bursts of cursing.

The following are the 3 driver's frequency response at varying levels of current drive vs. voltage.

For the woofer I'll clearly have to limit myself to more voltage drive given the peak at resonance, but for the mid tweet I can go current drive easily.

I'm not sure where I got the idea that current drive altered phase. The phase for the mid and tweet are identical for current vs. voltage and the woofer is close enough to measurement error.

Tony asked about the B1 active XO's. There's really not much to say. Any active filter that uses an opamp as a buffer (I.e. where output is directly tied to the '-' input) AND a cap blocks DC from the output to the feedback loop should be able to use a B1 like buffer. The circuits in sections 1, 2, 3 and 7 of SL's filter page all qualify, but the rest may be sketchy in my mind since the B1 can have some DC offset.

Attached is a rough drawing I scribbled last night for my own benefit, so it ain't pretty. An input buffer is something I'm still debating needing or not, but I'm leaving some room for it.

I'm going to let Soundeasy help me define the values, but the drivers are pretty well behaved in their desired bandwidth such that nearly textbook filters can be used.

I don't have enough JFETs of any one type for everything, so I'm going to have to mix types, probably LSK170s for the woofer and Toshi 2SK170s for the mid/tweet.

...

A main reason I'm active on this project is the event coming up on the 5th. For me there's nothing like a deadline to get me out in the garage.

A lot left to do:

• MLS measurements - on/off axis at varying output impedances for 3 drivers will make for quite a few measurements
• Figure out how to enclose the mid - I'm thinking open back at the moment
• Design the active crossovers in Soundeasy
• Build the active XOs - point to point likely using FirstWatt B1 type buffers (two JFETs isn't much more work than an opamp)
• Paint

Two weeks left!

Unlike the mid and woofer - the tweeter doesn't seem to show any gains under current drive.