Flex Your PCD Mettle:

[Zilch]

Re: Flex Your PCD Mettle:

Zilch, is the inverse null at 1589 Hz?
And what is the forward measurement axis you are using?
Is that in-room response for the LF? Must be.
Looks great!

Yes, the XO frequency moved up a bit when I added the notch on the woofer. L-pad is at 3:00 for these measurements, which slides it and the forward axis around a bit. For the polars, the axis is as stated in the legend -- ~1° below the midpoint between woofer and waveguide. We'll see what the forward vertical lobe looks like in a bit here.

All measurements are gated thus far, so nothing below ~200 Hz is valid. It's a ported alignment, so I'd have to sum and stitch nearfield low frequency measurements to quantify the response down there. RTA tells me it's rolled off in-room, and requires assist to make 40 Hz; there's nobody home at 30. High-efficiency pro woofer requires sub(s) in this alignment.

[HT's usually got 'em.... ;) ]

[Skywave-Rider]

Re: Flex Your PCD Mettle:

I would think for SR, on a pole stand, that's what you want as far as forward axis goes. Sorry I saw the legend but thought it said 1"...need glasses, actually need to put them on.

It will be interesting to see the verticals. Amazing the horizontal looks so good with the overhanging panel edges. In my opinion, the edges are what you want for SR in this type of cab. They will ward off a lot of destruction from carting. Add the PE round metal grille over the woofer, naturally.
http://www.parts-express.com/pe/show...number=260-374

Yes, the XO frequency moved up a bit when I added the notch on the woofer. L-pad is at 3:00 for these measurements, which slides it and the forward axis around a bit. For the polars, the axis is as stated in the legend -- ~1° below the midpoint between woofer and waveguide. We'll see what the forward vertical lobe looks like in a bit here.

All measurements are gated thus far, so nothing below ~200 Hz is valid. It's a ported alignment, so I'd have to sum and stitch nearfield low frequency measurements to quantify the response down there. RTA tells me it's rolled off in-room, and requires assist to make 40 Hz; there's nobody home at 30. High-efficiency pro woofer requires sub(s) in this alignment.

[HT's usually got 'em.... ;) ]

[Zilch]

Re: Flex Your PCD Mettle:

As you see, Pcasper rounded the top and bottom of the PE KD trap kit, and cut back the sides a bit. He used round grilles on the woofers, but that won't work with the big QSC waveguide in there so well. Johnaec's curved perfed metal grilles (the first of that group of pics) sure would, though.

I'm building the next two, eWave SR Compact and eWave HP Pro (high power) in John's cabinets:

http://www.audioheritage.org/vbulletin/showthread.php?18577-New-Stage-Monitors-Finished&highlight=

[Zilch]

eWave SR Vertical Polar Response

An upwardly asymmetric forward lobe:

[Skywave-Rider]

Re: Flex Your PCD Mettle:

Zilch, in 3rd plot, purple and magenta are 15 and 20 deg down, respectively? Or up?
Down I guess...

[Zilch]

Re: Flex Your PCD Mettle:

Violet is 15° down, and Cyan 20°, the Zilch effect in living color action.

Black is 20° up.

Compare Deluxe, which was steered 3° higher:

http://techtalk.parts-express.com/attachment.php?attachmentid=7383&d=1267952898

[dantheman]

Re: Flex Your PCD Mettle:

Looking good Zilch/Pete! That's got to be the best one yet. Zilch, when it comes to the vertical polars, I have a little trouble reading your graphs. I prefer the way I've done it just showing one direction at a time. I still can't tell what your forward lobe is basically doing. Of course I couldn't tell you what color "cyan" is. I just know the basics ROYGBIV.

One other thing I'm curious about, "why haven't you done an EW with the PE WG?" By the measurements with the Selenium it's smoother than anything you've tried--well anything you've shown measurements of. Is there a reason you haven't tried it? Keep in mind I'm not trying to be antagonistic, just curious.

Again, Looking great!

Dan

[Zilch]

Re: Flex Your PCD Mettle:

You can tell the ups from the downs from where the null intrudes. Above crossover is down, below is up, and they progressively move toward the crossover frequency (marked by the cursor, usually,) as they get deeper; that's the Zilch effect. I use the same colors every time, with red being on the reference axis.

Which PE waveguide are you suggesting? The 10" round one? I used the 7" elliptical in KLH 17 with Selenium successfully some time back. The deal is center distance and crossover frequency vs. height of the forward lobe. We can work with loss of pattern control in the vertical, but not the horizontal.

A 10" axisymmetric round waveguide must be crossed at a higher frequency than an equivalent height asymmetric that's wider in both the horizontal in dimension and dispersion, and there's no downside to a narrower vertical dispersion pattern. Wayne Parham discusses this at length and in detail. Basically, you need a symmetric waveguide diameter equivalent in dimension (not counting mouth roundover) to the woofer mating with it for a directivity match. This imposes a constraint on the center distance between woofer and waveguide which, because of the vertical nulls, also limits the range of crossover frequencies which may suitably be used.

Geddes generally follows this guideline but refuses to publish his vertical polars. Wayne argues that an asymmetrical waveguide produces a better result. See Delite 10e in this thread; a 10" woofer with a 10" round waveguide functions at the minimum acceptable forward lobe height in this example:

http://techtalk.parts-express.com/showthread.php?p=1646965#post1646965

The color code is listed there.

[dantheman]

Re: Flex Your PCD Mettle:

Excellent Zilch! That's a heck of a post. When I was doing my design though I noticed that our C-C distance on whatever the variant you were doing at the time was nearly identical vs. frequency. They might be worth reinvestigating. I wish I had done verts on that design, but I never finished it. Once I heard these B2031Ps, I just said screw it.

I'll still have to figure out your color scheme. There's just a lot of tightly spaced lines and it's hard for me to interpret.

Anyway, nice job. I think this is your best looking design.

Dan

[SheldonD]

Re: Flex Your PCD Mettle:

Zilch & Pete;

I noticed that Pete has the tweeter to be B&C250 but Zilch is using 220ti

Is this OK? Or does it not matter?

SheldonD

[Zilch]

Re: Flex Your PCD Mettle:

I noticed that Pete has the tweeter to be B&C250 but Zilch is using 220ti

Is this OK? Or does it not matter?

Pete mentioned that the driver designations were from the Deluxe session file (which used the same cabinet, waveguide, and woofer sizes), and to ignore that. What matters is the actual .zma and .frd files used, which are loaded independently....

[Zilch]

Dayton KD Trapezoid Kit Cab Construction:

http://www.youtube.com/watch?v=K__fzfSZr0w&feature=related

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=245-325

Looks like quite a setup there. Nice fit for the cabinet, too, all the drivers and box almost look like they were made for each other.

I think this is your best looking design.

[dantheman]

Re: Flex Your PCD Mettle:

I mean graphically.:o

Dan

[Pete Schumacher]

Re: Flex Your PCD Mettle:

Pete mentioned that the driver designations were from the Deluxe session file (which used the same cabinet, waveguide, and woofer sizes), and to ignore that. What matters is the actual .zma and .frd files used, which are loaded independently....

Yeah, I simply loaded the Deluxe session for the offsets, etc, and went from there, importing the new FRD and ZMA files. I simply forgot to update the titles of the woofer and tweeter, apparently more than once . . . :o

[dantheman]

Re: Flex Your PCD Mettle:

Zilch, maybe a large part of the rough treble in your designs has to do with the diffraction of that lip. The B2031P has 2 ports on either side of the tweeter. Check out a sample polar response graph of that:

Then with some white cotton ***** stuffed in those ports:


I bet when Dr. Geddes measured these, he did it right between the woofer and tweeter where his forward axis is. There would be less port influence there as my first graph of these shows. Here's that graph:

Not as nice as the cotton balled one, but better than any of the others. Same goes for the impulse.

OK, let's also look at the cotton stuffed ports graph 1/3 oct smoothed vs. the added stuffing material's graph 1/3 octave smoothed:


Can you tell which is which? I know YOU can Zilch, but it's not obvious for me at first glance.

Cool stuff.

Dan