Flex Your PCD Mettle:

[Skywave-Rider]

Re: Flex Your PCD Mettle:

You're right, I looked up 8", not the correct piston diameter.

Standing by.

[edlafontaine]

Re: Flex Your PCD Mettle:

Hey Zilch,

My Delite x-overs are assembled. The drivers are playing sans cabinet on the floor. I'm getting a head start on the break-in. I plan to take these to The Mid-West Audio Fest

Does the DE250 break in? How sensitive is the driver response to diaphragm positioning? I'm aka "truth seeker" on your home court.

[Mayhem13]

Re: Flex Your PCD Mettle:

It's a 10" that'll behave to ~3 kHz that's needed to mate with the QSC 122i, looks like to me....

And would it be safe to say the 3012HO from Eminence might be a better candidate for the 122i........a bit late to the game but i really like the sound of this WG/CD combo. If a woofer upgrade is needed i'm all for it. You're pobobly going to point me away from the round WG anyways buy hey..it's worth a shot! There is a method to my madness with the 3012. Notice the wide open basket. Can you say Dipole?

[Pete Schumacher]

Re: Flex Your PCD Mettle:

And would it be safe to say the 3012HO from Eminence might be a better candidate for the 122i........a bit late to the game but i really like the sound of this WG/CD combo. If a woofer upgrade is needed i'm all for it. You're pobobly going to point me away from the round WG anyways buy hey..it's worth a shot! There is a method to my madness with the 3012. Notice the wide open basket. Can you say Dipole?

The Lambda TD10 Series is the optimal candidate for the 122i WG. It has the total displacement capacity of most pro 12" woofers, and if it has the well behaved response of its big brothers, then it should make the ideal candidate. The Lambda motors have some of the lowest THD and IM out there.

I will be doing a WG with woofer project, and the TD10H with the RS28F in a 122i profile might make a great near full range MT (40Hz on up). Or perhaps as a large format OB mid, (Orion on steroids) with the waveguide tweeter. After hearing DoubleTap's 8" OB with waveguide loaded ScanSpeak AirCirc, I want to do something similar.

[Zilch]

Re: Flex Your PCD Mettle:

Does the DE250 break in? How sensitive is the driver response to diaphragm positioning? I'm aka "truth seeker" on your home court.

I am not aware of any break-in effects with DE250, or any other compression driver, for that matter.

Diaphragm positioning in what sense? Throat adapter?

[edlafontaine]

Re: Flex Your PCD Mettle:

I hope I'm not in a battle with my own with windmills. I'll be ok. ;)

Diaphragm positioning in what sense? Throat adapter?

No, the centering of the cd on the throat I understand. These need a little work there.

There have been concerns that I've read about the centering of the diaphragm within the cd. "Proper" positioning will decrease HD.

These are my first cd's...pop a cherry...:D

[Zilch]

Re: Flex Your PCD Mettle:

With bolt-on drivers, there's a small amount of adjustability. I just look down the throat and center it by eye in the course of mounting the driver.

Thread-on, there's nothing to adjust; it is what it is. Some builders fill small discontinuities with modeling clay. I don't obsess about such unless there's a gap, or something I can easily smooth out by hand....

[Mayhem13]

Re: Flex Your PCD Mettle:

The Lambda TD10 Series is the optimal candidate for the 122i WG.

Unfortunately Pete, the AE drivers are a bit rich for my blood or fiscally unobtanium. I too am thinking about an OB design with the 122i WG but a CD instead to get the most out of a level match with a driver like the the 3012HO whose open back basket is screaming for an OB application IMO. I'd like to combine this with a sealed box RS315HF actively anchoring the whole thing. I have some 16"x24" x5/8 clear cellcast acrylic sheets that might just come in handy for the baffle.

[Pete Schumacher]

Re: Flex Your PCD Mettle:

Unfortunately Pete, the AE drivers are a bit rich for my blood or fiscally unobtanium. I too am thinking about an OB design with the 122i WG but a CD instead to get the most out of a level match with a driver like the the 3012HO whose open back basket is screaming for an OB application IMO. I'd like to combine this with a sealed box RS315HF actively anchoring the whole thing. I have some 16"x24" x5/8 clear cellcast acrylic sheets that might just come in handy for the baffle.

Sounds like an interesting concept. It's just that the 3012 isn't that well behaved above 1KHz. You'd be better off going with the larger QSC waveguide that allows for a lower XO point, Econo Deluxe OB.

[Mayhem13]

Re: Flex Your PCD Mettle:

I was pondering the larger QSC rectangular guide as it would make for a shorter enclosure and closer driver C to C spacing. I'd really like to hear an Ewave with it to see if i'd like the CD/Horn combo but all of the GTG's are far from the east coast. Maybe a post to locate any Ewave owners in my area would help.

[Zilch]

Re: Flex Your PCD Mettle:

It's all of $25 more to have both QSC waveguide types on hand to try....

[Zilch]

SpitWad Directivity Data

Here are the horizontal polar response measurements, 0° - 45° in 5° increments for both the waveguide (-10 dB) and woofer, taken at their respective axes, without filters. The waveguide has a 30uF protection cap in series with the driver:






Their normalized (to 0°) directivity maps indicate how they would perform were they successfully EQ'd flat on axis via their crossover filters:





The HF is familiar from earlier measurements; no surprises there. The LF begins narrowing at ~800 Hz, but is stable at 90° beamwidth (-6 dB, light blue on both plots,) between 1 kHz and 1.6 kHz, indicating that, from the woofer directivity perspective, a crossover to the waveguide anywhere in this region would be an optimum match.

[We may then look to the waveguide directivity and pick our poison.... ;) ]

[Zilch]

Fixing Directivity:

Indeed, here is the normalized system horizontal directivity map, crossed at 1.481 kHz:




The directivity waterfall illustrates the improvement:




The horizontal polar response curves from which the above are derived; I'm tempted to push it a bit higher to try and smooth out the remaining directivity issue at ~1.75 kHz:




The vertical polar response says we're good (-6dB) to +/- 15° about the forward axis, which is midway between the woofer and waveguide, presently:




The filters still need work, though; this was my quick attempt to determine if the remaining directivity issues were amenable to mitigation via crossover frequency selection; I used standard EconoWave topology plus a series notch on the LF:

[Zilch]

Fixing Directivity, Continued:

The normalized horizontal polar plot also shows it's much improved:




New PCD files below. The C/C distance is 8.8125", mic distance 44", and I find the HF offset at 151 mm. Is that plausible? Yes, this waveguide with D220Ti driver is 7.625" deep.

[Skywave-Rider]

Re: Flex Your PCD Mettle:

Zilch, stupid question from filter network fool:
Presumably the on axis response rise at about 1500 Hz is easily dealt with in filter summation?
(Referring to system response plots you posted...or is all that out the window..are you starting from scratch?)