Flex Your PCD Mettle:

[Zilch]

FLEX It, Round 2.2:

Deltalite II 2512 in Dayton KDT Kit Cabs with B&C DE250 on QSC 152i Waveguide.

While CLIO is in for a hardware update, can we do it with:

http://www.holmacoustics.com/holmimpulse.php

Plus these from our sponsor:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-801

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=245-8688

Here's the measurements in the files below, along with both together for determining the Z-axis offsets, all unsmoothed:

And here's the result of my first attempt:

These are all quasi-anechoic gated log sine sweeps except blue, just above, in-room full range, smoothed 1/6 octave. Dashed lines in the impulse response graphs show the gated window closing just before the first reflection. Dotted blue ones in the bottom impulse graph illustrate how the smoothing algorithm was applied to the in-room response. Measurements are referenced to the impulses in the time domain, so phase should be minimum. Well, roughly. ;)

C/c distance is 10.5", all measurements taken at midway between woofer and waveguide at a distance of 47"....

[Pete Schumacher]

Re: FLEX It, Round 2.2:

These are all quasi-anechoic gated log sine sweeps except blue, just above, in-room full range, smoothed 1/6 octave. Dashed lines in the impulse response graphs show the gated window closing just before the first reflection. Dotted blue ones in the bottom impulse graph illustrate how the smoothing algorithm was applied to the in-room response. Measurements are referenced to the impulses in the time domain, so phase should be minimum. Well, roughly. ;)

C/c distance is 10.5", all measurements taken at midway between woofer and waveguide at a distance of 47"....

Is is safe to assume from the position of the gating that baffle step is determined pretty much by that position? In other words, would the reference sensitivity be whatever the level is at 250Hz?

[Zilch]

Re: FLEX It, Round 2.2:

Is is safe to assume from the position of the gating that baffle step is determined pretty much by that position? In other words, would the reference sensitivity be whatever the level is at 250Hz?

No, "Gating" relates to the duration of the window between the impulse at time zero and where I have set it to close, just short of the first reflection, in this case, a bit under 4ms., and represents the frequency at which the resolution is one wavelength, i.e., 1/0.004s = 250 Hz. Below that frequency, it is not possible to resolve the SPL, and the results are indeterminate. If I let that reflection in, the high frequencies turn to hash. I'll illustrate, but first, here's my second attempt; I'd be sayin' "Done" but for the forward axis being too high @ +10.25°:

Here then are three gated sinusoidal sweeps (unsmoothed) of the actual performance of my second attempt design, each offset by 10 dB for visability, with the gate set to close at 2, 4, and 6 ms after the impulse at time zero, illustrating the effect of the choice:

Are the notches at 750 Hz and 3 kHz real or measurement artifacts?

HOLMImpulse also has a MLS option, which might answer this question....

[Pete Schumacher]

Re: FLEX It, Round 2.2:

No, "Gating" relates to the duration of the window between the impulse at time zero and where I have set it to close, just short of the first reflection, in this case, a bit under 4ms., and represents the frequency at which the resolution is one wavelength, i.e., 1/0.004s = 250 Hz. Below that frequency, it is not possible to resolve the SPL, and the results are indeterminate. If I let that reflection in, the high frequencies turn to hash. I'll illustrate, but first, here's my second try; I'd be sayin' "Done" but for the forward axis being too high:

I understand what gating is. What I was asking is that because the lowest frequency that can be considered an accurate data point, should we use it as the baseline sensitivity, since it's below the baffle step.

Looks good by the way. But I'd opt for less peaking in the tweeter transfer function and live with the slight dip in that region instead.

[Zilch]

Re: FLEX It, Round 2.2:

I understand what gating is. What I was asking is that because the lowest frequency that can be considered an accurate data point, should we use it as the baseline sensitivity, since it's below the baffle step.

Frankly, even using CLIO MLS under these same measurement conditions, I consider everything under 1 kHz an approximation. It takes big clear space to resolve these lower frequencies without the influence of reflections. Baffle step comp is thus somewhat of a crap shoot; some designers would advise it's also a bull shoot, particularly when working with baffles this wide @ 17".

Looks good by the way. But I'd opt for less peaking in the tweeter transfer function and live with the slight dip in that region instead.

Yes, I'll probably be letting the VHF roll down a bit. This is one of the newer DE250s in the evaluaton of multiples I posted earlier, and I have bumped it more up there than is warranted....

[Zilch]

Re: FLEX It, Round 2.2:

HOLMImpulse also has a MLS option, which might answer this question....

MLS, Grn, log sweep, Blu, and log chirp full range in-room, smoothed 1/6 octave, Red:

The trusty 1/6-octave RTA in Behringer DEQ2496 (also available from Parts Express ) says we're doing fine thus far:

If it weren't for the room node "hole" just above 100 Hz, looks like we'd be seeing the hump Dennis showed in his model in that region, magenta:

Where are we with respect to sensitivity? Deluxe 3012LF, Red, vs. Delite II 2512, Blu:

The same place, pretty much....

[Pete Schumacher]

Re: Flex Your PCD Mettle:

Those just look very, very good. :D

[Zilch]

Re: Flex Your PCD Mettle:

Those just look very, very good. :D

O.K., I've tweaked the forward axis down to +5.47°, so I'll draw it up and y'all can "streamline." ;)

Are the files usable? I had to preprocess by adding 120 dB to the SPLs in the HOLMImpulse FR text files and round the data to four decimal places to render them suitable for use as PCD FRDs before posting them here. Excel's "Paste special" made easy work of accomplishing that.

It's noteworthy that this minimalist $150 measurement setup and a couple of free software downloads can produce such a result....

HA! The inverse nulls are within 6 Hz of each other. :D

[Skywave-Rider]

Re: Flex Your PCD Mettle:

Impressive.
Maybe I missed it, but have you compared distortion measurements between the Kappalite and Deltalite?

[Pete Schumacher]

Re: Flex Your PCD Mettle:

O.K., I've tweaked the forward axis down to +5.47°, so I'll draw it up and y'all can "streamline." ;)

Are the files usable? I had to preprocess by adding 120 dB to the SPLs in the HOLMImpulse FR text files and round the data to four decimal places to render them suitable for use as PCD FRDs before posting them here. Excel's "Paste special" made easy work of accomplishing that.

It's noteworthy that this minimalist $150 measurement setup and a couple of free software downloads can produce such a result....

HA! The inverse nulls are within 6 Hz of each other. :D

Is it too late to offer a suggestion?

I set up the tweeter out of phase with the woofer, like in the LF version.

Tweeter XO: 5.6uF with Lpad of 3.3 Ohm and 3.3 Ohm.

Woofer XO: 3mH, 15uF + 2 Ohm, 1mH

[Zilch]

Re: Flex Your PCD Mettle:

Impressive.
Maybe I missed it, but have you compared distortion measurements between the Kappalite and Deltalite?

CLIO's down for hardware update, but I COULD push the "THD" button in HOLM, I guess. :rolleyes:

Is it too late to offer a suggestion?

NEVER too late, Pete; I'll fire that up tomorrow....

[Zilch]

Re: Flex Your PCD Mettle:

Zilch (+5 dB) = Blue
Schumacher = Grn
Inverse = Red

Forward axis is midway between woofer and waveguide, XO = 1453 Hz:

[Pete Schumacher]

Re: Flex Your PCD Mettle:

Zilch (+5 dB) = Blue
Schumacher = Grn
Inverse = Red

Forward axis is midway between woofer and waveguide, XO = 1453 Hz:

Wow, those are CLOSE!!!

[Zilch]

Re: Flex Your PCD Mettle:

Yours is sloped down a bit at the VHF; mine flattens that with HF comp. You have a little more phase interference between 2 & 3K, but that's likely coming from the different forward axes.

I'll play with it a bit in PCD and get you the numbers to find the forward axis and tweak that upward a few degrees, maybe....

[Pete Schumacher]

Re: Flex Your PCD Mettle:

Yours is sloped down a bit at the VHF; mine flattens that with HF comp. You have a little more phase interference between 2 & 3K, but that's likely coming from the different forward axes.

I'll play with it a bit in PCD and get you the numbers to find the forward axis and tweak that upward a few degrees, maybe....

OK, change the L-pad to 4.7 Ohm series and 4 Ohm shunt resistors, and bypass the series 4.7 Ohm with 2.2uF.

There's also the option of taming the impedance peak of the DE250. That will allow a bit less of a bump at 2KHz, but at the cost of 3 more components, 1mH (20ga), 8uF and 8 Ohm. If you do that, change the 5.6uF to 6.8uF. I like that particular configuration the best, mainly because the transfer functions for the tweeter and woofer seem to have the smoothest transfer functions.