Flex Your PCD Mettle:

[Pete Schumacher]

Re: Flex Your PCD Mettle:

What is the advantage of that big, round waveguide? Wouldn't an elliptical style allow for a closer CTC?

[Zilch]

Re: Flex Your PCD Mettle:

http://techtalk.parts-express.com/showthread.php?p=1688887#post1688887

Read on.... ;)

[Erich H]

Re: Flex Your PCD Mettle:

Yes

Pete, I was looking at that a couple months ago, but it won't quite do what's needed. I spoke with the owner and he thought he could make it useful with some additional custom work to the machine, but I'm not convinced. It has to do with the depth, angles, and the actual hole on the bottom of the waveguides. Plus the width of the baffle. It would get you there I suppose, but it would take a decent amount of additional work once the machine did all it could do. And even at that point, the machine would be nearing $3000 with options and router.


The ones that would do the work properly (without a lot of additional labor) are $5000 on up, and even those need some custom work. The cheaper ones look good in photographs, but there are some things that need to be done that they can't really do perfectly. I did find one that should do everything, but it starts at nearly $11k. At that price point, a CNC is better. And once it gets over $5k, it makes more sense to try and build exactly what's needed anyway.

[Pete Schumacher]

Re: Flex Your PCD Mettle:

http://techtalk.parts-express.com/sh...87#post1688887

Read on.... ;)

What's to like?????

[Zilch]

Re: Flex Your PCD Mettle:

What's to like?????

Geddes's HOM theory, presumably, though nothing precludes doing it elliptically, as you suggest. The one in his earliest paper was that, so he has prior experience with the approach; there may be undisclosed compromises he's unwilling to make.

[Other than the cost of tooling, of course. :rolleyes: ]

The on-axis "notch of perfection" appears in the polars of his early elliptical, as well. We can bet that JBL engineering looked long and hard at oblate spheroid in larger scale than the ones they've been making for 20+ years. Clearly, that anomaly alone is a deal breaker in their market, and I suspect why they have pursued alternative means of achieving similar objectives, i.e., optimized aperture and progressive transition....

[penngray]

Re: Flex Your PCD Mettle:

What is the advantage of that big, round waveguide? Wouldn't an elliptical style allow for a closer CTC?

The advantage is that they are closest to what Geddes builds. Its not just a round waveguide but its an OS waveguide which according to Geddes is very important. It would match that of the Geddes Abbey speaker which has in all accounts sounds awesome and measures better the our stuff.

Besides that it looks a LOT better then all of our monkey confines with bad corners, seams, screws showing.

He does offer a large elliptical shaped horn called the IWATA. Not sure if it was OS though. I also agree that an Elliptical OS Waveguide would solve even more problems.

[jzagaja]

Re: Flex Your PCD Mettle:

Iwata-300 WH4 behaves like JMLC with cut off 350Hz. It's common OS waveguide sounds brighter and sharper than JMLC setup with tweeter horn and midrange horn as shown below (midrange compression driver is hard to beat by the cones).

[penngray]

Re: Flex Your PCD Mettle:

Thanks jzagaja!

Could you address the discussion about the CTC of the larger horns?

I know there are many, many users of larger horns that love their sound so how do people get around the CTC possible problem?

[jzagaja]

Re: Flex Your PCD Mettle:

No personal experience but my friend is using JMLC-350 with BMS 4590 and Onken bass. He told me better is when he increased CTC

[penngray]

Re: Flex Your PCD Mettle:

Thanks, nice pic!!!

[Zilch]

Re: Flex Your PCD Mettle:

No personal experience but my friend is using JMLC-350 with BMS 4590 and Onken bass. He told me better is when he increased CTC

A 350 Hz crossover changes the C/C game, of course.

May we see the vertical polars of the Abbey-esque Mummy cabs at a suitable crossover frequency (~1 kHz)? Five degree increments out to +/- 20° above and below the midpoint between woofer and waveguide should define it reasonably well.

What IS the actual C/C distance?

[jzagaja]

Re: Flex Your PCD Mettle:

Must build vertical turntable. CTC distance in Onken is 45cm.

[Zilch]

Re: Flex Your PCD Mettle:

Must build vertical turntable. CTC distance in Onken is 45cm.

No, not necessary. Just calculate the mic height differential at the measurement distance in 5° increments. It's 9 measurements total to map the forward lobe +/- 20° about the midpoint between drivers.

The Mummy C/C please....

[jzagaja]

Re: Flex Your PCD Mettle:

Mummy C/C = 35cm.

[Zilch]

Re: Flex Your PCD Mettle:

Perhaps we can talk Catapult into simming the forward lobe across a suitable range of crossover frequencies with that information....