Flex Your PCD Mettle:

[Pete Schumacher]

Re: Flex Your PCD Mettle:

That's gonna work, looks like. Get the system up off the floor for your measurements. As you see in the ZilchLab pics, I have the mic and axis of device under test at ~1/2 ceiling height to minimize reflections from the floor and ceiling, and a similar distance away from other objects and boundaries in the space. For convenience, that means inverting the speaker on my relatively high test stand, and thinking "upside down."

From my own experience, you have too much overlap of the drivers in the crossover region. Look back at the final crossover design plots of the projects completed earlier in this thread to get more of a feel for this.

Since you have a wider center-to-center distance using a 15" driver than I typically show with 12s (10.5"), aim for the lowest crossover frequency that'll work to maximize the usable height of the forward lobe. That suggests moving your lowpass successively downward, or increasing its rolloff slope, leaving your highpass where it presently is for starters; the response hump in the crossover region should disappear when you have it "right."

Pete and others may have additional suggestions....

One thing about leaving the woofer near the floor is that baffle step is almost entirely eliminated. If you go with the measurements with the high mount, then just remember to ignore the drooping response of the bass. It will come right up when you put it back on the floor.

[Zilch]

EconoWave Altec 414Z:

[Zilch]

EconoWave Altec Addendum #1

Repeating work done several years ago, here is the same BMS 4555 on JBL PT-F95HF measured on-axis with Altec bridged-T compensation filter, in this case incorporated in a vintage Model 19 1.2 kHz crossover, HF at max, MF at min, with a 6 dB fixed L-pad attenuation to bring the combination into range to balance with a different woofer. Black is with the supplemental "spike killer" notch specified in the legend:




Here is the earlier work; note the date stamp:



That's four sample BMS 4555s measured on PT-F95HF using Altec bridged-T HF comp plus a notch at 20 kHz to kill the BMS spike. This level of performance has been my benchmark ever since, and it's rare that I achieve it. PCD just got us mighty close with EconoWave 414Z, supra.


Per Mayhem13 request, BMS 4550 on QSC 152i waveguide:



Here is the impedance curve:



Adding my standard L-pad at 1:00 raises the impedance and smooths it out, suggesting that if we don't do that, a gratuitous 20-Ohm resistor across the driver would simplify highpass filter design:



Yes, delicous.... ;)

[Zilch]

EconoWave Altec Addendum #2:

Adjustable bridged-T HF comp filter:



Yes, 6.2 uF is fine.

LP1 is the parallel section of an 8-Ohm L-pad, or a 30 - 40 Ohm wirewound pot (5W minimum) connected as a rheostat.

Notch filter (if used) goes after, in parallel with the driver.

The files:

[Pete Schumacher]

Re: EconoWave Altec 414Z:

That sure is one smooooooth response.

[Zilch]

Re: EconoWave Altec 414Z:

That sure is one smooooooth response.

Thank you, Pete!

As you can see, taming the BMS driver was somewhat of a challenge, but the result sounds especially good....

[Mayhem13]

Re: Flex Your PCD Mettle:

And from feedback from BMS advocates, i wouldn't have expected the need for such a complex filter. It is smooth though.

Did you get a chance to check the response on 152i?

[Zilch]

Re: Flex Your PCD Mettle:

And from feedback from BMS advocates, i wouldn't have expected the need for such a complex filter.

I'm one of those, of course. The others need to step up with some comparable data. I'll be showing another approach in the addenda shortly.

Did you get a chance to check the response on 152i?

Nah, I'm still dorkin' with the big Screen Arrays for AVS forum right now.... ;)

http://www.avsforum.com/avs-vb/showthread.php?p=19254917#post19254917

Edit: BMS 4550 on QSC 152i is now posted:

http://techtalk.parts-express.com/showthread.php?p=1676614#post1676614

[Big Stogie]

Re: Flex Your PCD Mettle:

Cabinets, Waveguides, drivers and woofers ordered for SR Compact today.
Will start build thread soon have a few crossover and porting questions too
THANKS!
Mike

[Zilch]

Re: Flex Your PCD Mettle:

We'll want PICS, remember.... :D

55063/833=66.1020

[Big Stogie]

Re: Flex Your PCD Mettle:

No problem I will be running the TT's and the E-Waves with a pair if Crown XLS602's and a Behringer active crossover. I am pretty pumped
Mike

[bruson]

Re: Flex Your PCD Mettle:



All black round overs. Looks better.
Pipe foam with double stick tape on it, they come that way, Home Depot.

No measurements, buuuut the older yellow foam roundover sounds better on the WG. I don't know why.
The smaller radius black closed foam sounds annoying. May be accenting a frequency in the 8-12K hz range??

What kind of paint would adhere to closed cell foam? I think I'll paint the yellow foam black.

[Big Stogie]

Re: Flex Your PCD Mettle:

For my SR Compact's-
The center to center from the woofer to wave guide is 10.5" ? Or?

I am coming up with 2 2" ports 2.62" long for 50HZ tuning in the PE trap box, ports in the rear. What are other doing for porting in that box with the Dayton PA-310?

I will be using 2 BFM Table tuba's loaded with emininence HL10C's with and active crossover (80-100 I guess) powered by a pair of XLS602 Crown amps

thanks,
Mike

[Zilch]

Questions From A Builder:

I am building some SR Compact so if you could help me out that would be much appreciated. I am goign to rear mount the woofers to the baffle should I use some kind of insets to attach or just screws? I do not want the hardware to show in the front. How did you port the trap cabinets, meaning what size tube and how long? Using the stated dimensions I cannot get the same volume listed by PE. Front or rear firing ports?

The PE KD Trap cab kit is more like 1.65 cuft. when built according to instructions. It approaches 2.0 cuft. with the baffle moved full forward. My ports are on the rear, a pair of them, 2" diameter; 3" would likely be a better choice. The recommended tuning seems to be in the range of 35 Hz, but you should post that question in the thread once you finalize your design. I'm still at ~32 Hz in my prototypes, which have basically all used the same pair of cabs, and need to do more refinement of this, myself.

I'm just rear-mounting the woofers with wood screws presently; you can see them poking through in some of the pics. While I suppose short ones at all 8 mounting hole locations might suffice, once we start wanting to also round over the opening, a better option would be to install with clamps using blocks incorporating T-nuts or a speaker ring glued to the rear of the baffle. 3/8" or 1/2" thick ply would do it, depending upon the height of the T-nuts used.

For my SR Compact's-
The center to center from the woofer to wave guide is 10.5" ?

Yes, that was my "standard" for all of the KDT kit builds here, established early on by the minimum distance I could achieve using the QSC 152i waveguide. Aesthetically, it worked out well with the smaller-format 12" x 6.5" waveguides. As long as the crossover frequency is in the range of 1.5 kHz, I end up with good forward lobe height. If you move the woofer and waveguide closer together, the lobe height will expand somewhat. Rear-mounting the woofer in SR will move the forward axis down; PCD should reveal how much....

[Big Stogie]

Re: Questions From A Builder:

The PE KD Trap cab kit is more like 1.65 cuft. when built according to instructions. It approaches 2.0 cuft. with the baffle moved full forward. My ports are on the rear, a pair of them, 2" diameter; 3" would likely be a better choice. The recommended tuning seems to be in the range of 35 Hz, but you should post that question in the thread once you finalize your design. I'm still at ~32 Hz in my prototypes, which have basically all used the same pair of cabs, and need to do more refinement of this, myself.

I'm just rear-mounting the woofers with wood screws presently; you can see them poking through in some of the pics. While I suppose short ones at all 8 mounting hole locations might suffice, once we start wanting to also round over the opening, a better option would be to install with clamps using blocks incorporating T-nuts or a speaker ring glued to the rear of the baffle. 3/8" or 1/2" thick ply would do it, depending upon the height of the T-nuts used.....

So moving the woofer back say 1/2" with a plywood woofer ring to build a mount will be the option for me, I will use a big roundover and try to keep it out of the waveguide> I am going to leave it at 1.65cu/ft and try to fit a couple 3" ports in

Yes, that was my "standard" for all of the KDT kit builds here, established early on by the minimum distance I could achieve using the QSC 152i waveguide. Aesthetically, it worked out well with the smaller-format 12" x 6.5" waveguides. As long as the crossover frequency is in the range of 1.5 kHz, I end up with good forward lobe height. If you move the woofer and waveguide closer together, the lobe height will expand somewhat. Rear-mounting the woofer in SR will move the forward axis down; PCD should reveal how much....

I will get my final CC distance down and rear mount the woof, I am going to need some help with PCD I just started dow this road. I am going to kill the lip in front of the baffle too and roundover the edges. And yes I am taking some pictures
thanks for all the help Zilch and everyone!
Mike