Flex Your PCD Mettle:

[Pete Schumacher]

Re: Flex Your PCD Mettle:

Thanks for the information. Planning on staying passive. Looking at the specs for the woofer it seems that a larger enclosure (maintaining the same baffle width) would be the way to go to extend the low end. I see the recommended enclosure volume is 1.3-3.0 cu.f.t; am I correct that the low end extends as you approach 3.0 cu. ft.?

If you enter the parameters into any number of box calculators, you can get an idea of the required dimensions to reach the low end you're after.

Does this change the upper frequencies of the woofer's response?

No, upper frequencies will be unaffected. Make sure that whatever you do, you add proper damping to the inside of the enclosure to minimize resonances and reflected energy.



Just as an aside, could another woofer be used as the L-pad can match the levels? (I am assuming NOT, but we all know what happens when you assume).

Yes, another woofer could be used, but the woofer crossover circuit would likely have to be modified.

Lastly, would an air core inductor (such as the Jantzen 4.5mH 18 AWG Air Core Inductor [Sku 255-282]) offer any sonic advantage over the ERSE I-core inductor? The cost differential for 2 isn't that much.

I don't see how you get any benefit by going air core, personally. You'll only suffer a slight loss in sensitivity due to the higher DCR of the air core, so a slight tweeter level reduction might be in order.

Thanks for the reply! Trying to minimize cost, while maximizing quality. I only upgrade speakers about once a decade, so I have to get it right when I do.

Have fun!!!

[Zilch]

Re: Flex Your PCD Mettle:

Did you port the cabinet?

Yes. Two 2" ports at ~9.5" tuning to ~30 Hz. I'm using a Q=2 assist at 30 Hz and a highpass just below there presently to augment the VLF in these "too-small" cabs. Sub(s) will work nicely, as well, of course.

Would a supertweeter help (due to the roll off over 15 kHz) or hurt the overall sound?

Try it, and see. On-axis, I measure -6 dB at more like 18+ kHz; see the attenuation plot, above.

It's the same driver and rolloff as in Geddes designs, for example. Has anyone found the UHF to require supplementation in those?

I'm saying it wouldn't hurt to add more "air" at the top, but I certainly would not lowpass the DE250 in the course of accomplishing that, and you'll need a wide dispersion supertweeter to match this system's 90° directivity up there....

[NWCgrad]

Re: Flex Your PCD Mettle:

Thank you for this information. Will stick with the driver and XO described in this thread.

[Zilch]

Re: Flex Your PCD Mettle:

Thank you for this information. Will stick with the driver and XO described in this thread.

I've added a pic of the crossovers I built yesterday at Post #72, above. It fits neatly on our standard EconoWave board without mods.

If there's enough of these being built eventually, I'll lay up a custom board for this "Deluxe" variant. For high continuous-duty SPL applications, in SR, for example, we should probably follow Wayne's lead and increase the thermal dissipation capacity of R1 and R2....

[NWCgrad]

Re: Flex Your PCD Mettle:

I tried to model in WinISD but it only goes up to 1 kHz. Modeled sealed and vented, 130 W @ 1 M. The program defaulted to vent length of 1.99" w/ a Vent Mach of 0.18 w/ a tuning freq of 40 Hz (provided the flattest curve). I would think I would require longer.

Attached a bitmap image of the resultant SPL plot, the sealed starts to roll of faster as expected, but the vented seems to be better.

I'm thinking this program is optimized for subwoofers, but I think it should suffice for my purposes. A 3 cu ft enclosure tuned to 40Hz should provide good bass down to the tuning frequency where it rapidly falls off. I would use my Onkyo 805 receiver at 80 Hz so this should not be an issue.

Am I correct? All this is rather strange territory for me. Again, I want to thank you both for your assistance!!!!

[Pete Schumacher]

Re: Flex Your PCD Mettle:

I tried to model in WinISD but it only goes up to 1 kHz. Modeled sealed and vented, 130 W @ 1 M. The program defaulted to vent length of 1.99" w/ a Vent Mach of 0.18 w/ a tuning freq of 40 Hz (provided the flattest curve). I would think I would require longer.

Attached a bitmap image of the resultant SPL plot, the sealed starts to roll of faster as expected, but the vented seems to be better.

I'm thinking this program is optimized for subwoofers, but I think it should suffice for my purposes. A 3 cu ft enclosure tuned to 40Hz should provide good bass down to the tuning frequency where it rapidly falls off. I would use my Onkyo 805 receiver at 80 Hz so this should not be an issue.

Am I correct? All this is rather strange territory for me. Again, I want to thank you both for your assistance!!!!

WinISD is only good for modeling around tuning.

If you intend to run this crossed actively at 80Hz to a sub via your HT receiver, then there's really no reason to build a vented box. I'd just go sealed.

[NWCgrad]

Re: Flex Your PCD Mettle:

WinISD is only good for modeling around tuning.

If you intend to run this crossed actively at 80Hz to a sub via your HT receiver, then there's really no reason to build a vented box. I'd just go sealed.

Thanks again . That would make it easier to build. Would you, or Zilch, recommend using a round over router bit on the baffle to minimize edge diffraction?

[Pete Schumacher]

Re: Flex Your PCD Mettle:

Thanks again . That would make it easier to build. Would you, or Zilch, recommend using a round over router bit on the baffle to minimize edge diffraction?

Edge diffraction will only affect the woofer, and since it's a large radiating surface, a roundover will have no effect on the sound.

At least, it won't have an effect on the tweeter if the baffle is flat, with no rising edges. Even then, with the controlled directivity, the impact will be minimal.

[NWCgrad]

Re: Flex Your PCD Mettle:

I ran box design program (UniBox) for 2 and 3 cu ft enclosure for the 3012LF. Looks better w/ 2 than 3 due to cone excursion passing the X-Max w/ the 3 cu ft box (at 450 W, which is unlikely). I've attached the frequency resp and cone exursion graphs. NOTE: I really don't know what I am doing - I just entered the parameters to the best of my limited ability.

SWN

[NWCgrad]

Re: Flex Your PCD Mettle:

I also calculated using a 15" passive radiator for comparison. These graphs look better than the sealed box design to me, suggests the speakers would be pretty nice w/o subwoofer support. The PR's cost $55/ea.

Specifications: Exodus Audio 15” Passive Radiator
Fs: 20 Hz
Qms: 6.0
Mms: 200g
Cms: 0.28 mm/N
Vas: 245L
Sd: 791 cm^2
Excursion: 32-35mm one-way

Seems like this may be the way to go, despite the additional cost. Am I missing something?

Thanks,

SWN

[Pete Schumacher]

Re: Flex Your PCD Mettle:

I also calculated using a 15" passive radiator for comparison. These graphs look better than the sealed box design to me, suggests the speakers would be pretty nice w/o subwoofer support. The PR's cost $55/ea.

Specifications: Exodus Audio 15” Passive Radiator
Fs: 20 Hz
Qms: 6.0
Mms: 200g
Cms: 0.28 mm/N
Vas: 245L
Sd: 791 cm^2
Excursion: 32-35mm one-way

Seems like this may be the way to go, despite the additional cost. Am I missing something?

Thanks,

SWN

Nothing wrong at all with using a PR. They have one advantage in that they don't let rear wave excitation out of the box like a port does.

[NWCgrad]

Re: Flex Your PCD Mettle:

I went back and modeled the 1.65 cu ft cabinet that Zilch used over on the PE forum (PE Sku 245-325) using Jeff Bagby's Woofer Box Model (Ver 4.5). I want to eventually build 7 of these speakers, so the additional cost of PR's really added up. This speaker project has been an iterative process, but I think I am getting close to the final design.

In this cabinet tuned at 45 Hz (Port: 4" dia, 7.17" length) the cone excursion does not surpass the Xmax at 450 W input (the rating for the driver). The vent air velocity reaches 5 m/s at ~85 Hz and 10 m/s at ~68 Hz. Freq response stays flat to 60 Hz (-3 dB = 48.38; - 6 dB = 41.61; - 10 dB = 35.8).

This cabinet tuned to 35 Hz (4" dia, 13.77" length) the cone excursion surpasses the Xmax at 450 W input at 70 Hz. The vent velocity is lower than the 45 Hz tuning, 5 m/s at ~68 Hz and 10 m/s at 50 Hz. Freq response stays flat to ~90 Hz (-3 dB = 59.14; -6 dB = 42.03; -10 dB = 32.05).

With 200 W input, neither excursion or vent air velocity appear to be a problem for either cabinet tuning. I plan on using a 130 W/ch Onkyo 805 receiver, with HPF set ~80 Hz, so I assume I not be able to hear port noise from my seat (13 ft away) or overdrive the woofer.

I am thinking the 45 Hz tuning looks better than the 35 Hz tuning (with 40 Hz stradeling the two). Am I missing anything important?

[NWCgrad]

Re: Flex Your PCD Mettle:

This cabinet tuned to 35 Hz (4" dia, 13.77" length) the cone excursion surpasses the Xmax at 450 W input at 70 Hz. The vent velocity is lower than the 45 Hz tuning, 5 m/s at ~68 Hz and 10 m/s at 50 Hz. Freq response stays flat to ~90 Hz (-3 dB = 59.14; -6 dB = 42.03; -10 dB = 32.05).

Data for the 35 Hz tuned enclosure.

[Pete Schumacher]

Re: Flex Your PCD Mettle:

I went back and modeled the 1.65 cu ft cabinet that Zilch used over on the PE forum (PE Sku 245-325) using Jeff Bagby's Woofer Box Model (Ver 4.5). I want to eventually build 7 of these speakers, so the additional cost of PR's really added up. This speaker project has been an iterative process, but I think I am getting close to the final design.

In this cabinet tuned at 45 Hz (Port: 4" dia, 7.17" length) the cone excursion does not surpass the Xmax at 450 W input (the rating for the driver). The vent air velocity reaches 5 m/s at ~85 Hz and 10 m/s at ~68 Hz. Freq response stays flat to 60 Hz (-3 dB = 48.38; - 6 dB = 41.61; - 10 dB = 35.8).

This cabinet tuned to 35 Hz (4" dia, 13.77" length) the cone excursion surpasses the Xmax at 450 W input at 70 Hz. The vent velocity is lower than the 45 Hz tuning, 5 m/s at ~68 Hz and 10 m/s at 50 Hz. Freq response stays flat to ~90 Hz (-3 dB = 59.14; -6 dB = 42.03; -10 dB = 32.05).

With 200 W input, neither excursion or vent air velocity appear to be a problem for either cabinet tuning. I plan on using a 130 W/ch Onkyo 805 receiver, with HPF set ~80 Hz, so I assume I not be able to hear port noise from my seat (13 ft away) or overdrive the woofer.

I am thinking the 45 Hz tuning looks better than the 35 Hz tuning (with 40 Hz stradeling the two). Am I missing anything important?

You could go with a much higher powered amp and still not have issues with Xmax under normal music conditions.

Music typically has a peak to average ratio in excess of 5:1. Well recorded works, 10:1 or higher.

In the "worst case" scenario, with the 5:1 ratio, a 130W amp will produce around 26W RMS, 13W or less with very dynamic recordings.

I don't think you'd have a problem with either alignment.

[NWCgrad]

Re: Flex Your PCD Mettle:

You could go with a much higher powered amp and still not have issues with Xmax under normal music conditions.

I can bi-amp the speakers with the 805 for 260 watts/channel or run them off an Adcom GFA-555 I am using to run my subwoofer once I upgrade to a pro amplifier for the sub (probably a Crest Audio CC-2800, 2800 W x 1 into 4 ohms).

Thanks again for your assistance on this project. The box tuned to 45 Hz seems to have the best freq response, the vent air velocity is the highest. Thus, I may elect to go with the 35 Hz tuning.

Best,

SWN