Flex Your PCD Mettle:

[kcburnes]

Re: Flex Your PCD Mettle:

Any thoughts on the waveguide being incorporated into the Tweak City Audio Pro-10 speaker, that has recently become available:

http://img.photobucket.com/albums/v5...367640x480.jpg

http://www.parts-express.com/pe/show...number=264-308

Also interested in their implementation of both vertical and horizontal placement options. As I understand, the horizontal alignment simply rotates the waveguide but otherwise uses the same driver placement in the same enclosure.

I would like to embark on a compact waveguide speaker to replace my aging PSB Alphas across the front L/C/R in my theater...and want to go DIY. I've built a sub that I'm very happy with, and now want to increase the dynamics in my other speakers.

Thanks so much!

[Zilch]

35079/557=62.98

[donprice]

Re: Flex Your PCD Mettle:

PCD for dummies, round 3

Kappalite 3015 QSC 152i/ B&C DE250

FRD files from HolmImpulse in-room measurements - measured at center of HF/LF at 44" on axis.

3015 ZMA from Jeff's response modeler
DE250 ZMA from 3012HO/DE250 posted previously - how can this be done better?

CSP file copied as text file...have not tried pasting into excel file, renaming as *.csp, and reloading. It should work - may have to copy over existing csp file to force recognition as CSP instead of workbook.

Will try to paste screen shots from PCD next.

[donprice]

Re: Flex Your PCD Mettle:

FRD measurements with grill cover in place (not shown) to catch diffraction effects. First attempt at XO design based on the 5 component XO for eWave Deluxe HO.

Any help would be appreciated. I really don't understand this stuff enough to tweak it.

Don

[Zilch]

Re: Flex Your PCD Mettle:

How did you measure the response of the DE250 QSC for its FRD? It looks like you did it with the highpass filter in place, maybe? The raw driver should be measured with no filter, though I use a 33uF - 47uF protection cap in series (which must be done if the test signal is not restricted to ~500 Hz and above), which produced this FRD, shown in the same scale as yours:



That file is in the ZIP here:

http://techtalk.parts-express.com/sh...28#post1624828

[Zilch]

Re: Flex Your PCD Mettle:

BAH!

Compare Post #552 , supra.

http://techtalk.parts-express.com/sh...79#post1661779

[Skywave-Rider]

Re: Flex Your PCD Mettle:

So the 2k horizontal problem is inherent in the HF and not due to interference from the woofer. Am I right? And does the same thing happen with the 2452H-SL driver?

[Zilch]

Re: Flex Your PCD Mettle:

So the 2k horizontal problem is inherent in the HF and not due to interference from the woofer. Am I right? And does the same thing happen with the 2452H-SL driver?

I don't know, which is why I'm bangin' my head here:



It's as if this waveguide has lost patten control down here at 1.367 kHz, but it's the same family as JBL is using in their product at 1.4 kHz. Without measuring, I think we know that 2 kHz is not going to work in the vertical at this 10.5" center distance.

My next suspect is the 1.25" overhang in the KDT cabs, but the QSC waveguide had exemplary horizontals in them. I can see a 1.5" throat having beamwidth "difficulties" in the top octave, but that should not impact the low end like this. Did SRC with its 0.25" deeper overhang in closer proximity have similar issues with the 1" throat version of the same waveguide crossed at 1.6 kHz? I guess I could argue it did:

http://techtalk.parts-express.com/sh...62#post1661262

[I'll stick 2452H-SL in and see what happens, though we're getting ahead of ourselves with trying that.... :p ]

Edit: Baffle opening's too small to fit the driver through, but once in, the same crossover plays it nicely, as we'll see in the polars.

[Skywave-Rider]

Re: Flex Your PCD Mettle:

Speculating that there's more edge diffraction on the PT waveguide, compared to the QSC, setting up the interference cancellation within the KDT's overhang. The QSC has a smoother profile at the mouth. I guess you could test the HF alone out of the cab, or on a baffle in a box w/o overhang.

Easy for me to say.

[Skywave-Rider]

Re: Flex Your PCD Mettle:

I don't see anything like that in the JBL horizontals of the 7212 system, but they are using the 2452H-SL in it.

[Zilch]

Re: Flex Your PCD Mettle:



Do we believe for a minute that BOTH woofer and waveguide are losing pattern control at the same frequency, where the family of curves is "pinched?"

[donprice]

Re: Flex Your PCD Mettle:

How did you measure the response of the DE250 QSC for its FRD? It looks like you did it with the highpass filter in place, maybe? The raw driver should be measured with no filter, though I use a 33uF - 47uF protection cap in series (which must be done if the test signal is not restricted to ~500 Hz and above), which produced this FRD, shown in the same scale as yours:

I used a 36 uF (3 x 12 uF in parallel) in series with the driver. Sweep from 500 to 40,000 Hz. I was only running about 30 dB above background noise (HTPC) due to caution with driver and unfamiliar software. Plots were normalized to 0 db (HOLMImpulse default?) and then I added 90 and 98 dB offsets to get them closer to published specs (100 and 108 dB/w/ @ 1m). The high-pass filter was bypassed. Also timing was based on "first pulse" - not sure if that is an issue with phase measurements.

What do I need to change when I re-run them?

I didn't test the drivers together (except with the standard eWave XO in place). I remember discussions about using the data for determining acoustic depth (and phase?). That will be part of the re-test phase.

Late for work, got to run. Thanks!

[Pete Schumacher]

Re: Flex Your PCD Mettle:

I cannot imagine damaging that driver with a 2.83V signal, regardless of frequency.

I routinely sweep dome tweeters with small signals well below their resonance. There is no problem doing so. The suspension limits excursion.

Ribbon tweeters connected via transformers need the coupling cap as protection for the amp.

[Pete Schumacher]

Re: Flex Your PCD Mettle:

How did you measure the response of the DE250 QSC for its FRD? It looks like you did it with the highpass filter in place, maybe? The raw driver should be measured with no filter, though I use a 33uF - 47uF protection cap in series (which must be done if the test signal is not restricted to ~500 Hz and above), which produced this FRD, shown in the same scale as yours:



That file is in the ZIP here:

http://techtalk.parts-express.com/sh...28#post1624828

When I see the response start dropping off at 2KHz in the unfiltered response, it's indicative to me that there is something going on. For directivity issues, shouldn't the response of the WG/tweeter combo continue rising to the intended cutoff? The natural response BEGS to be crossed at 2KHz.

[Zilch]

Re: Flex Your PCD Mettle:

Used with a true constant-directivity horn/waveguide, compression drivers behave as if on a Plane Wave Tube (PWT). Generally, they have rising response up to the region of mass breakpoint, then the familiar falling response (requiring high-frequency compensation) above there. See Fig.6 here:

http://www.audioheritage.org/vbullet...ume-1-Number-8


Since the original work of Keele, PWT response has been used as the baseline for assessment of the relative constant directivity "quality" of horns and waveguides:

http://www.xlrtechs.com/dbkeele.com/...xp%20Horns.pdf


With constant directivity flares, in addition to provisions for HF comp, the core highpass filter is typically underdamped to compensate for rising response in the region below mass breakpoint:

http://www.pispeakers.com/Speaker_Crossover.doc


When mating a horn or waveguide with a large woofer, limitations to the availability and quality of woofer higher frequency response and the influence of center-to-center distance between drivers upon the height of the usable forward vertical lobe mandate crossing over in this region. A primary advantage of compression drivers is that they provide the order of magnitude greater acoustical power output than conventional tweeters at these lower frequencies essential for sound reinforcement and home theater applications.

[And simply "cranking it" to live levels and beyond, occasionally, with hearing protection as required, as well.... :D ]