[Michael V]

After some flirting with boxed speakers, I'm going to try another open baffle project.  I've acquired a pair of vintage Jensen P15LL woofers, but T/S specs seem nowhere to be found.  All I know for certain is that it has a great reputation - it was used in Jensen Imperials, Leslie 122 and 147 cabinets, as well as the Western Electric 753C loudspeaker.  The WE 753 is famous for its midrange, and crossed the P15 at 1khz, so it must be pretty smooth.

Some have claimed it has a Qts of 1.6 and Fs of 37hz.  I'm not sure I believe the Q #, since it was used in BLH's like the Imperials.

Any thoughts?

[nullspace]

I had a pair of F15LL, the field coil versions, at one time. Fs was ~37Hz, but it was definitely a low Qts driver -- somewhere between .2 and .35 depending on DC voltage.

I suspect the Weber dudes have more experience than anybody with the P15LL, and here's what they have: http://www.webervst.com/spkrcalc/p15ll.htm.

Regards,
John

[Michael V]

Many thanks, John.  I hadn't seen that.  Looks like a 6db/octave rise starting around 500hz; could be easily fixed in the LP filter.

What were your subjective impressions of the F15's?  I've heard the P15LL's in my local audio store (Deja Vu Audio in McLean, VA), and thought they were very impressive but not extended enough.  So, if I have to use a sub why not throw them on OB...

[nullspace]

I actually didn't end up listening to them much, but what I recall is that they were very nice and if I had thought that I'd ever have a use for them I would have hung on to them.

With a sub, they might be pretty decent on an OB; I would think bandwidth would be pretty limited, though. Maybe 1kHz down to 150Hz, and with the moderately low Fs and no xmax to speak of, you'd really need to think about a highpass. If you already have them, why not give it a whirl?

Any thoughts yet on >1kHz?

Regards,
John

[Michael V]

Good point about the limited xmax, that could be a problem.  They haven't even arrived yet, so I'm in pure speculation mode right now.

Above the Jensen, I'll be using an Altec 802 on a 550hz Azura horn.  I've used the horn + OB midbass combo before, and really liked the way it meshed together.  Apparently, the Jensen P15 is subjectively "fast" and keeps up well with horns.

For the low lows, I'm planning on an equalized U-frame woofer below the Jensen, driven separately.  I have a pair of Alpha 15's and Goldwood 1558 (?) on hand, both of which should reach 40-45hz.  Maybe this will be a chance to try Graham's bass circuit.

[nullspace]

Best of luck with the project. Let us know how it goes.

If you're biamping between bass and midbass/treble, then perhaps try a simple 1st-order RC filter ahead of the main amps to keep the excursion down on the P15LLs: PLLXO.

Regards,
John

[Michael V]

Thanks.  For the mains, I use a really small output coupling cap in my linestage (.033uf) which forms a HP with the input impedance of my power amp.  It's as close to a free lunch as it gets.

I'll post later once I make some progress.

[nullspace]

Even better. Less a free lunch and more a free dinner with drinks included...

Let us know how it goes.

Regards,
John