Flex Your PCD Mettle:

[dantheman]

Re: Flex Your PCD Mettle:

ok, I think it's easier to see more smoothed as before. Thanks for the effort. Much appreciated.

Dan

[Zilch]

Re: Flex Your PCD Mettle:

It's clear a 1.5" throat can't hold a wide pattern in the last octave; that's three different drivers we've tried with this waveguide.

[Who told us that...? :D ]

[donprice]

Re: Flex Your PCD Mettle:

Now all we need is an econo ($15) version of the 1.5" $113 waveguide :D

[Zilch]

Re: Flex Your PCD Mettle:

Will the circle be unbroken?

It's the standard thread-on eWaveguide, of course.

[SO, who's gonna run BMS drivers on 152i and XT1086? ]

[edlafontaine]

Re: Flex Your PCD Mettle:

The posts of Lynn Olson, # 7306 & 7308 are of particular interest...

http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-366.html#post2300249

[Zilch]

Re: Flex Your PCD Mettle:

I've been working through the power response thing for several years now, but can't say I have a firm grasp of it yet. This we know: flat power response is perceived as being overly bright, and thus, undesirable. Just as Geddes teaches, a throat diameter larger than 1" cannot directly support wide dispersion in the top octave; it behaves like a dome tweeter up there, but with a smoother transition in directivity than occurs with actually using one.

My take (for now) is that Linkwitz is employing shelving EQ to smooth this transition between his relatively wide (120+°) "controlled" directivity and a substantially narrower top octave to achieve a desired (non-flat) power response suited to simulation of concert hall acoustics in a small listening space. That specific objective aside, unless the directivity is constant through the top octave, the power response suffers from non-uniformity, and the better approach to achieving room independence is maintaining that, instead.

I certainly agree with Olson that getting the direct field "right" is primary, but the same applies to power response, despite it being secondary, as well.

So the main purpose of a supertweeter (any tweeter working at 7 kHz or above is a supertweeter) is to improve the sensation of spaciousness - to "open up" the soundstage. This works hand-in-hand with the narrowing directivity of the T= 0.707 LeCleac'h horn and the 1.4" throat size of the large-format driver. Unlike a small-format horn which aims at reaching 15 kHz or above, this horn gives up the top octave in return for another octave at the bottom of the range. The diaphragm of a large-format driver is twice as large as a small-format driver, and that's the tradeoff.

You wouldn't expect a 15" bass driver to behave in the same way as a 7" midbass; they cover different frequency ranges, and have different power-handling characteristics. Similarly, the large and small-format drivers do different tasks.

We further concur regarding the narrowing directivity in the top octave, but that would appear to be less a function of whether the driver is large vs. small format than the size of the exit/throat diameter. We've clearly demonstrated that suitably designed large (4" diaphragm) and medium (3" diaphragm) format drivers can play to/through 20 kHz; the 3" JBL 2435HPL is pistonic out to 18 kHz. As with these larger diaphragm drivers, however, the small format (1.75" diaphragm) BMS 4555 cannot hold a wide dispersion pattern in the top octave with this 1.5" throat, either:

4": http://techtalk.parts-express.com/at...5&d=1281575907

3": http://techtalk.parts-express.com/at...3&d=1282091893

1.75": http://techtalk.parts-express.com/at...1&d=1284343086

[We obviously disagree on the answer, tho.... ;) ]

[stgdz]

Re: Flex Your PCD Mettle:

Zilch,

Can I use the L-pad used in the econowaves to lower the response of my HF section in my QSC-2150 clone?



It gets pretty bright at the upper end but this measurement was using a rat shack meter and HTshack's room eq program in my room at 1m.

[Zilch]

Re: Flex Your PCD Mettle:

I'd suggest R/S measurements in the top octave may not be particularly reliable, but if you perceive them as having too much "sizzle" or "air," then, yes, you can dial down the VHF with an L-pad. That's not going to alter the rising response up there, if it's real, but you may be able to strike a more pleasing balance....


Footnote: If you review my research on JBL Screen Array, I believe you'll see that a similar on-axis peak in the top octave is a response characteristic of speakers designed for deployment behind a perforated screen. Again, if "real," that would not be a mistake on QSC's part:

http://www.audioheritage.org/vbulletin/showthread.php?23546-Screen-Array

Thinking more: Measure at 30° off axis. If the peak remains, and you intend NOT to use them behind a perfed screen, EQ it out. If the peak is gone there, either mitigate it on-axis with sunshade or equivalent grilles, or don't toe them in.

50020/801=62.4469

[Big Stogie]

Re: Flex Your PCD Mettle:

OK I read this thread and as much of the AK thread as I could without meltdown and I am goign to build a set of SR's but I have some questions.
Do the SR or SP Compacts sound much different?
Are these ported? I did not see anything about that?
Should the baffle be moved forward or cut back with a router? more for looks for me, will it hurt? Which way is better?
Should the woofer hole be rounded over since the woofer is back mounted?
Zilch, do you sell a circuit board for the crossover? seeems like the least we can do for all the work you have done. Thanks!!
I am going to use these with a subwoofer, one of the BMF horns.
Mike

[Zilch]

Re: Flex Your PCD Mettle:

Do the SR or SR Compacts sound much different?

They sound quite similar.

Are these ported? I did not see anything about that?

They are ported. I'm running at ~32 Hz tuning, but consensus among others running the numbers here seems to indicate somewhat higher would be better when used with sub(s). Finalize your cabinet volume, and we can nail that down.

Should the baffle be moved forward or cut back with a router? more for looks for me, will it hurt? Which way is better?

The evidence in this thread suggests that eliminating the edge overhangs is beneficial, particularly when using the smaller waveguide. The two perform about the same, but the larger QSC has an integral mouth roundover, and apparently less diffraction at the baffle transition.

I favor moving the baffle forward, as it increases the internal volume, but that also leaves a gap at the sides which must be filled for "finishing." Doing that with a contrasting wood or vinyl bead might make for an attractive pinstripe there, though.

I haven't progressed to rounding over the edges like Brandon's No Quarters yet, but I can envision that the 10° taper of the PE trap cabs will add some visual character and interest there.

Should the woofer hole be rounded over since the woofer is back mounted?

The improvement in performance is measurably minor, but I believe it confers a major aesthetic benefit. Though I haven't tried it yet, it appears that with the QSC waveguide recessed flush with the baffle face, the woofer roundover (3/4") might incorporate the waveguide flange at the center, as well. All of this is using the stock baffle and woofer location that comes with the cab kit. If you make your own baffle, there are other options, but I would not increase the center distance between woofer and waveguide by much, as that will degrade the vertical polar performance.

Zilch, do you sell a circuit board for the crossover? seeems like the least we can do for all the work you have done. Thanks!!

Yes, I stock a PC board for the original generic EconoWave crossover design, which may be suitably adapted for use with most of the more refined custom crossovers in this thread. SR adds an external notch filter, R4/C4/L3, and SR Compact, two external notch filters. They are $10 apiece postpaid in the USA; PM me for the PayPal address....

[Zilch]

The Bloom

Is all but gone after moving the baffle flush front:



Toggle:

Original: http://techtalk.parts-express.com/at...6&d=1281474687 (different drivers, stock recess)

Later: http://techtalk.parts-express.com/at...1&d=1284678488 (these drivers, baffle 3/4" forward)

Before: http://techtalk.parts-express.com/at...1&d=1284343086 (these drivers, baffle 3/4" forward w/ woofer roundover)

After: http://techtalk.parts-express.com/at...1&d=1284623314 (baffle 1/16" proud of flush)

[Big Stogie]

Re: Flex Your PCD Mettle:

Thanks for the info, I will get some cabinets and waveguides on the way from PE and get to work on them. Moving the baffle and the rest.
Mike

[Mayhem13]

Re: Flex Your PCD Mettle:

Nice Job Zilch. The advantage of the 1.5" throat are clearly evident here as the system maintains directivity to the 500 hz.

[Skywave-Rider]

Re: The Bloom

More proof diffraction off of the baffle edge affects both woofers and tweeters. In this case, the woofer especially. (Move those KDT baffles forward guys.) The directivity is getting so progressive and smooth throughout the frequency range... what remains to be done?

Is all but gone after moving the baffle flush front:



Toggle:

Before: http://techtalk.parts-express.com/at...1&d=1284343086

After: http://techtalk.parts-express.com/at...1&d=1284623314

[Skywave-Rider]

Re: Flex Your PCD Mettle:

Oh...verticals.