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I just had a stupid idea


mustang guy

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I have a pair of KPT-684 subs. Those things are beasts. They have pretty new Dayton drivers too. The problem with them is the lack of LF extension of the KPT-684 in it's stock configuration.

 

What if I yanked the current 18"s out, braced things up a little better, changed the tuning some, and put a pair of high excursion drivers in each? After all, this is a simple enclosure just like any other reflex enclosure. I bet I can get these flat to 20Hz without eq with the right drivers and tune.

 

 

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I have them too.  In fact 4 of them.
 
They are tuned to 28Hz with a "bent knee". 
 
If you want to put crazy big sub drivers in there, place a 3/4" circle plywood over the top woofer cutout. 
 
Add extensions to the two ports....you know....triangular....  Just remember to leave maybe 3-5" of "port space" from the back wall of the cab.
 
You can add with extensions by sanding off the paint from the back of the existing port (triangular piece) and the strip of sidewall and bottom cabinet panels where the new extension with glue.

Then install insane subwoofer driver.  You may need to reinforce the panels….is your 1” or ¾” front baffle?

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I just did some comparisons between the current Sigma PRO 18's currently in the 684's and Dayton UM18-22's, and there is a stark difference in every way. The Dayton wins hands down with one exception, efficiency. Here is what I've learned:

 

Dayton UM18-22 / Eminence Sigma PRO 18

 

-3db: 18.25 Hz / 36 Hz

hipass 4th O: 15 Hz / 20 Hz

excursion limit watts: 2500 watts / 200 watts

amp needed: big / small

efficiency: 89db / 100 db

rms max spl 250Hz: 123db / 123db

rms max spl 25 Hz: 123.5db 116db

rms max spl 20 Hz: 121db 101db

rms max spl 15 Hz:  115db 84db

 

edit: All this based on 17.5 cu ft enclosure. The tuning for the Dayton would be 15 Hz which makes for a beautiful curve for those Daytons..

 

Transfer Function Magnitude graph. White is Dayton and Pink is Eminence:

0CIJVpN.png

 

Impedance Curves:

fF33n8F.png

Edited by mustang guy
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What does the BC 18PS100 model in comparison?

 

Also....did your Dayton just screw right in?  Looked to me like the screw holes were different.

I haven't actually screwed anything in anything yet. I'm just thinking out loud.

 

Orange is B&C

CHErkuf.png

 

The B&C models well in the enclosure. It seems to be a better match for the 684 than the Eminence. Is still can't come close to the Dayton if you have the amplifier for it. 

 

If I do this, I will need to throw down some coin for another Yammy P7000S.

Edited by mustang guy
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Look at this thread and scroll down to the KPT684.PDF (not the Z).

 

https://community.klipsch.com/index.php?/topic/81011-raw-curves-on-roys-cinema-products/?hl=%2Broy+%2Bcurves

 

Look how the stock woofers start to show a loss at 40Hz eventhough the cabinet is tuned lower.

 

This is why......I suggested the one driver conversion with port extension.  You will lose the SPL as a trade off.  Depends on what u want. 

 

I don't need frequencies that low......mine are 99% for music.

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That's a nice thread.

 

If you change to a single stock driver, you will take the -3db from 36Hz to 26Hz and lose about 4db efficiency. With dual Dayton's you take the -3db to 18Hz and lose another 7db (-11db overall) efficiency. However, in the end, and considering HPF and excursion limits, the dual Dayton tops a dual or a single stock driver at all outputs below 250Hz in a KPT-684 enclosure if you pump 2,000 watts into them. They can handle 2,500 no problem. The stock drivers struggle with excursion at as little as 200 watts.

 

These could truly be amazing HT subs for LFE.

 

Look at these numbers:

 

rms max spl 25 Hz: 123.5db

rms max spl 20 Hz: 121db

rms max spl 15 Hz:  115db

 

Those are GJALLARHORN like numbers!

Edited by mustang guy
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Those are some big boxes, and the drivers are nucking futz.

 

34mm xmax 21 inch-ers!

 

Still, that big 25cuft sub isn't way off from the kpt-685 with the Dayton UM18-22's in em. Sadly, PE won't be getting more in until July. They are probably on a boat from China...

Edited by mustang guy
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Just a suggestion but you may want to go with flared ports, a high x-max 18" will tend to have port noise without.

 

Maybe you could find a passive with enough x-max for the design, just a thought anyways.

I agree with all of the above. I hadn't even thought of how to do the ports. It would be nice to somehow utilize existing corner ports. I don't even know what those port sizes are.  I need to take some measurements when I get down there. 

 

The existing ports will need to be smaller and longer and flared. Perhaps that can be done with wood if I can make a triangle and slide it right into the existing corner port. The flare could be done with 45 deg cuts and a some sanding.... I'm kinda thinking as I type this... If I transition the current port inside the enclosure to make it longer, I could use the existing port which is big enough to reduce chuffing...

Edited by mustang guy
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Sadly, PE won't be getting more in until July. They are probably on a boat from China...

 

 

Significant quality control issues, they're having to change things up where every single driver gets checked.  Probably had to send an entire batch back or something.  They've been out since early February.  

Edited by MetropolisLakeOutfitters
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Sadly, PE won't be getting more in until July. They are probably on a boat from China...

 

 

Significant quality control issues, they're having to change things up where every single driver gets checked.  Probably had to send an entire batch back or something.  They've been out since early February.  

 

 

It's crazy how countries so near eachother have such differing views on quality. In Japan they are fastidious, while in China they are indifferent. This is a generalized statement I know, but it doesn't come out of nowhere. There is plenty of evidence to back this up. 

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