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Old 15th February 2014, 06:31 AM   #1
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Default PPSL Questions

Hello, my 1st post here! I have a few Q's about DJK's PPSL design for the Kappa Pro 15LF, hoping that he or someone who built it can chime in. I'm having 4 of them built for live sound, trying to make them as compact as possible.

1.) Based upon DJK's cut sheet, I calculated the NET volume to be 6.172 ft^3. Is that about right, or am I missing something?

2.) Assuming that the Sv is 54.375 in^2 with a brace down the center, a Keele equation gives an Lv of less than 13.5" for a 35Hz tuning (the driver's published Fs). Is there a particular reason why the Lv is 16.75"? Does splitting the vent with a brace make so much difference? Or, perhaps is the measured Fs of this driver lower than the published result?

3.) Is there any harm in building a smaller plenum? I'm thinking 16" square by 7.5" wide, internal. I can barely get my stubby digits around the back of the frame. Will that put too much pressure on the driver cone?

The concept of this design is appealing, like semi-horn loading with the LF extension of a vent. Thanks for any input!
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Old 20th February 2014, 03:21 AM   #2
Zero D is offline Zero D  United Kingdom
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Hi, sorry you havn't received any replys yet I think you might get a better response if you repost it in the Subwoofer section, where DJK is more likely to see it, amongst others

All the best
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Old 21st February 2014, 01:52 AM   #3
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In response to #2 - is there any particular reason that the cabinet should be tuned to the driver's Fs?
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Old 21st February 2014, 04:47 AM   #4
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I guess I think of the design for this driver as a PA subsystem. I suppose it should be reposted. One of DJK's guidelines in his old Speakerplans postings for a PPSL is tuning to the driver's Fs. I'm just curious about why his design for the 15LF seems to be tuned below the Fs. For any pro audio subwoofer, isn't that just added excursion?
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Old 22nd February 2014, 04:39 AM   #5
djk is offline djk
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The published plan for the dual 15 PPSL is based on the Kappa Pro 15LF-2.

http://www.eminence.com/pdf/Kappa_Pro_15LF2.pdf

"is there any particular reason that the cabinet should be tuned to the driver's Fs?"

As we see, the Fs=35hz. It is a perfect candidate for a B6 design. If the Qts were higher or lower the design would become a C6 with some ripple in the response.

A Qts=0.312 gives the perfect balance between efficiency, box size, and LF response. The PPSL is an SBB4 design (best transient response of all the vented alignments) with a high-pass filter with a Q=2 applied to make it a classic B6. Drivers with higher or lower Qts will work (with some re-design), and it will become a C6 with some ripple in the response.

A 2 cu ft 2nd order sealed box with an F3 of 30hz can only be 0.18% efficient (84.55dB).
A 2 cu ft 4th order vented box with an F3 of 30hz can only be 0.36% efficient (87.56dB).
A 2 cu ft 6th order vented box with an F3 of 30hz can only be 0.90% efficient (91.54dB).
(after Keele)

" Does splitting the vent with a brace make so much difference? "

The dimensions were generated by BassBox Pro v6.0 based on the actual size used in the box. Changing the aspect ratio, or going round, gives different dimensions.

"Is there any harm in building a smaller plenum?"

My original prototype boxes had the plenum 16.5" by only 5" wide, this required a removeable panel for access to mount the drivers. The outside dimensions were 36W x18H x 30D, and tuned to 34hz. In a good sized room in a home they measured flat to 31hz without the EQ of the filter they were designed for (room gain). For PA in a large room you will need to use the proper filter (most crossovers or equalizers have filters that can be modified with just two resistors).
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Last edited by djk; 22nd February 2014 at 04:54 AM.
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Old 23rd February 2014, 07:10 PM   #6
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Thanks for jumping in, DJK!

Right, I own 8 of the Kappa Pro 15LF-2 drivers. We use a DriveRack PA (I know, not the best) for processing; the subs are high-passed at 35Hz, tho' we're not doing the B6 alignment. (Is B6 a subwoofer vitamin? Sorry, couldn't resist.)

I rearranged the layout so that the vent is under the plenum with the same internal width of 7.5", so the vent is a single rectangular aperture of 7.5" x 7.25" without any divisor. This gives a taller box & fewer panel cuts. Both Keele & a very old LEAP program give an Lv of about 13.3" for a 35Hz tuning, unless I miscalculated the net volume. Internal dimensions are 24"H x 28"W x 21"D. As we're using 5' square 13-ply Baltic Birch panels, I wanted to limit the width to 29.5" exterior.

I'm surprised that there aren't more live sound DIY'ers building PPSL's for their systems. The benefits easily outweigh the added size & effort to build. Plus, they look cool!
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Old 2nd March 2014, 11:11 AM   #7
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djk,

You used to recommend the Martin/Eminence driver for your 30-ish-Hz boxes. I believe they're now discontinued...(?). What driver(s) do you like/are you now recommending instead?

Cheers
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Old 11th March 2014, 12:45 AM   #8
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I would have to have a batch of them custom made (I do have an OEM account with Eminence).

Is this for home or PA, and how many drivers are we talking about?
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Old 11th March 2014, 02:11 AM   #9
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PA.

If could better (extend the f3 by at least 5Hz w/o losing output) what I have now (four 18SW100 loaded TH-18s) by building some possible PPSL enclosures with two lower priced drivers that about equal the cost of one 18SW100, that could be what I'm looking for. According to BB6 Pro, it definitely seems possible, before losses.

Like you say, a qts of .312 is preferred, so I have been aiming for drivers near that specification.

I currently have two PLX3402 amplifiers to drive the low end. Though, I will be changing them in the near future, as these run hot and have hit thermal a few times (bridged), 6dB before limit light even (due to the low impedances of the paralleled TH18s, I'm almost certain).

*please forgive any errors as I'm typing from my cell.
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Old 11th March 2014, 01:12 PM   #10
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In my active vented designs in BB6 Pro, I was aiming for an f3 of 28-29Hz (f3 of my TH18s is 36-37Hz, I believe). 22.5 x 40-45 x 28-30" external were dimension ranges.
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