Quick & Dirty 4430-Inspired Two-Ways Part II

[Zilch]

At the risk of y'all thinking I'm makin' this up, here are the results of a simple test with the three 90° x 50° waveguides currently under evaluation.

Method: EQ flat 22.5° off axis, half of horizontal spec. Measure on axis. All with same 2431H driver.

This is how I normally EQ, mic in middle, aimed at speakers separately, left and right.

Note: RTA sensitivity is twice what I normally post. Here, 2.5 dB per dotted line.

1) 2332 flat off axis (Beautiful!)
2) 2332 on axis
3) SRX712 flat off axis
4) SRX712 on axis

ACK!!

[Zilch]

PT-H95, same two conditions. No wonder those aluminum horns sound "crispy." It may just be they need to be mounted and damped as suggested above, but I'm bettin' PT waveguides have directivity under substantially better control.

Admittedly, I'm cuttin' a fine line here: +/- 2.5 dB.

O.K., O.K., I'll mount 'em before I give up on them....

[Ian Mackenzie]

Zilch,

Nice work, it would appear the 2332 Di index narrows above 8 kerts.

Ian

[Zilch]

... it would appear the 2332 Di index narrows above 8 kerts.

Yup, and that may be the root of Sebackman's difficulties using it two-way in his HT. Looked good in measurements, but HF couldn't be successfully EQ'd. HF extension isn't worth a whit if it crashes off-axis in a constant-directivity system.

Which has led me to review the published beamwidth, DI, and HF polar plots of the various PT waveguides in acutal product. They are shown on the various spec sheets here:

http://www.jblpro.com/ae/index_B.html

PT-F1010 looks the best and flattest, I think, though JBL doesn't make a product using that one with 2431H for direct comparison, just 1" drivers with throat adapters.

It certainly speaks to the utility of these with 2418H-1, 2426, et.al., tho.

My avatar shows the 2431H/PT-F1010 combination for those new to this thread and wondering what the heck this is about.

Tech note regarding influence of DI here:

http://audioheritage.org/vbulletin/s...4269#post64269

"In general, a system with a relatively smooth on-axis DI can be equalized for flat power output over a wide frequency range. A system which has a rising on-axis DI cannot be successfully equalized, because the on-axis response will tend to rise at high frequencies."

As illustrated above, presumably.

What's the relevance? Flat DI is part of 4430's "magic" formula, as documented in the tech note. If you wanna play constant directivity, it must be uniform throughout the system frequency range....

[stevem]

Yup, and that may be the root of Sebackman's difficulties using it two-way in his HT. Looked good in measurements, but HF couldn't be successfully EQ'd. HF extension isn't worth a whit if it crashes off-axis in a constant-directivity system

Zilch,

I had mentioned that I got my pair of 2435s yesterday, and I tried them first on the 2332 horn. The response was very flat and then rolled off fast above (I think) about 8 or 10 khz, which I expected with a CD horn. When I tried to boost the highs as I do with my 2450SL, I couldn't get them flat, and they still exhibited a roll-off from about 12k hz (I'm going from memory here) on up. I mention this because I saw a pronounced notch in the HF somewhere around 10 or 12khz, and it looked a lot like the response you were getting with the 2431s on the 2332. The 2450SL, on the other hand, does not show any such notch, and is easily EQ'd out to 20khz with a simple shelving filter. When I put the 2435s on the 100x100 PT waveguides, I still could not EQ to 20Khz, but the notch disappeared and the roll-off was smooth. Do you think there is some type of incompatibility with the 2435/2431 drivers and the 2332 horn that doesn't exist with the PT waveguides? Do you have another 1.5" exit driver you can try with the 2332 to see if this is the case? I'm just curious.

[Zilch]

Hi, Steve,

I'm pleased to welcome another member to the PT/243x quest!

Regarding the notch, see http://audioheritage.org/vbulletin/s...514#post64514. 2332 is an "Optimized Aperture" horn, and may not work well with these other drivers, as you suggest: the phase plug might simply be wrong. 2431 and 2435 are the only 1.5" drivers I have here, so I can't check it out.

I get essentially the same response with SRX712 horn as well, though, and that one JBL uses with 2431H. They're kinda shy about publishing the beamwidth and DI data above about 12 kHz, tho, and the response curve reflects similar "problems."

http://www.jblpro.com/srx700/PDF/JBL.SRX712M.pdf

Same notch in the frequency response here:

http://www.jblpro.com/srx700/PDF/JBL.SRX715.pdf

I can get them flat, but not both on and off axis concurrently. These combinations are "kinky."

Look at the beamwidth and DI of DMS-1. Even with the proper driver, 2332 goes weird between 8 and 10 kHz. The recommended voltage drive for it reflects the requisite compensation.

You'll have some difficulty pushing the 2435 to 20 kHz, even on PT waveguides. It does not exhibit the HF extension 2431 does, perhaps because of the the ferrofluid. Allegedly, 2435 is "pistonic" out to 17kHz, a good feature, if real.

The rolloff is smooth, as you have seen, though, and passive EQ is easy with AM HF filter. Use active EQ on top of that, and it will push. I don't know what the quality of that response is, tho. It's not as if I can hear it up there....

[stevem]

What's the diifference betwen the 2431 and 2435? Is it the diaphram material? I can't see applying so much boost to try and get the top flat of the 2435. I'm going to try finding a suitable tweeter. Is the 045Be driver and horn available to us mere mortals? I'm going to check out the TAD ET703 as well. Any other suggestions?