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Old 3rd December 2011, 06:47 PM   #231
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Quote:
Originally Posted by CRESCENDO View Post
I'm so indecisive...
That is why you should build it and experiment with the port length, you can decide which works best for the music you like.
The box will work with a wide range of Fb, and with the 4" wide port you can experiment all the way from a too high Fb (no duct) to way too low, which will act like a sealed cabinet.

None are "wrong", none are "right" (though one Fb will result in the flattest response in a given box volume), the varying alignments are a continuum.

If you want to add to your indecision, consider making a push pull Keystone tapped horn enclosure, slightly larger size (would need to be about 32.5 wide) than your present box idea, but will be about 6 dB louder.

Art

Last edited by weltersys; 3rd December 2011 at 06:55 PM.
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Old 5th December 2011, 02:46 AM   #232
djk is offline djk
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My first prototypes were particle-board, that's OK for a fixed install.
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Old 5th December 2011, 02:54 AM   #233
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Originally Posted by Djim View Post
Donít let the fun turn into frustration, itís not worth. Just look to what you have accomplished so far (no, didnít mean that sarcastic this time). You seem to dig into all details just because you cannot accept data without understanding, nothing wrong with that. Maybe itís just time to build something, even if it is made from cheap chipboard. Just get the adrenaline rush from your first build: cutting wood, smelling glue & dust and getting thrilled by its first sound (even itís not perfect). It will empty your head!
Hi Djim,

I'm not getting frustrated I just can't decide whether to build somethin with these 2 new 3015LF's or to sell them and go with a 30 Hz TH (with a higher quality driver - less pwr compression, etc) I've been eyeballing. I'm working on low funds at the moment, so I'm trying to be careful w/my decisions.The PPSL I posted was a 37 Hz cab and I don't know if they'd be ideal for PA, but according to the sim it would be 3-5dB louder @ 30 Hz than the 2 SS15's I have. I know what you mean though - I could've built one by now and got it out of my system.

Do BR6 enclosures raise the low corner when stacked (unlike TH's)?

Quote:
Originally Posted by weltersys View Post
If you want to add to your indecision, consider making a push pull Keystone tapped horn enclosure, slightly larger size (would need to be about 32.5 wide) than your present box idea, but will be about 6 dB louder.

Art
Hi Art,

I'd love to. Do you have any pics, plots, design ideas, etc for an enclosure? I've seen your Keystone thread, but didn't see any design models. Maybe I missed it..??
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Old 5th December 2011, 07:29 PM   #234
Djim is offline Djim  Netherlands
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Hi Crescendo, just build some cabs for the 3015LF’s and see how they work out. Afterwards you still can decide to sell them or not. Used or not, second handed is second handed, so would it matter for the value of your drivers?
Just don’t focus too much on the 30Hz output because 15 inch PA drivers are not built for that range. Roughly, the -3dB point for LF PA drivers (with a stiff suspension):

50/55Hz for 12inch
40/45Hz for 15inch
35/40Hz for 18inch

For so called extended LF drivers that would be approx 5 Hz lower. Although you can force them to play lower, it will be at cost of SPL and max power. In my view the 1/3WL of a TH should be on or above the Fs of the driver to get decent efficiency. Designing TH’s lower will roughly cost you 0.7dB for every Hertz.

If you are tight on the budget make sure your system at least delivers the efficiency needed in your case. Even if you can design a system with that extra octave lower, there is nothing more frustrating (and costly) as running out power/headroom. Also keep in mind you always can trick the minds of your audience by suggesting there is much more low end than there really is. A little eq or even better an extra filter + parallel compression of just the lower part of the sub range (40 to 60Hz for instance for JBell's SS15) gives more 'balls' than an extra half octave that is rolling off.


Click the image to open in full size.

Last edited by Djim; 5th December 2011 at 07:35 PM.
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Old 5th December 2011, 08:02 PM   #235
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Hi Djim,

I guess since they are New In Box, I was thinking I could get an easier sale for more $ than if they were used.

Since I have upgraded my power amp recently, I do have a bit of headroom. But, with this PPSL, it requires +6dB of eq at the cut-off freq. 3015LF's are 450W rms/ea x2 drivers = 900w + 6dB = 3600W - so, my amp must be capable of 3600W, correct? That's 3dB more than the 3015LF's MAX pwr. Am I missing something?

Re: EQ & filters: I'm already crossing over my SS15's lower than many others since the filter begins to cut much higher than the set point. According to WinISD, I am still within xmax by doing so, even with some eq you recommended quite a while back in the SS15 thread The majority of my gigs are dubstep, so a lot of sweeping sine waves and I haven't heard any funny noises from the drivers (knock on wood) and they don't get very warm either. We're running 2 of them off 1 ch. of my PLX3402 (1100w/ch @ 4 ohms). On top of that, I am running a limiter (not too heavy) w/fast attack & release times.

Last edited by CRESCENDO; 5th December 2011 at 08:03 PM. Reason: clarification
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Old 5th December 2011, 08:45 PM   #236
Djim is offline Djim  Netherlands
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Hi Crescendo,

Yes, the SS15’s will lack efficiency in the low end needed for D&B, Dub(step) and some others. For that kind of music 18inches (or even bigger) are actually a must! Putting the 3015LF’s in a low tuned PPSL will give you a more flat response down low but you will miss the efficiency higher up. Indeed, don’t feed your 3015LF’s with 1800W per cab because it will kill them. Also it wouldn’t work in practice anyway because the last 1000 watts would almost get lost by power compression. So that’s not a realistic solution.

About parallel compression, that is something different from what you have done and will therefore sound very different. The trick of parallel compression is that you feed two signals to the sub amp; one directly signal from the crossover as normal, the other one trough another processing stage. That processing stage needs to be squeezed totally by a compressor and use the output gain on the compressor to mix the processed signal together with the 'untouched' signals into the sub amp. This way you can pump up the rms signal of the low end while keeping the peaks (dynamics) from the ‘untouched’ signal. It will make subs sound larger then life. To set out the filter frequency for the processing stage you can take the 3rd knee point in the response of the TH.
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Old 5th December 2011, 09:16 PM   #237
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Hi Djim,

That's what I was thinking - didn't sound healthy.

For parallel compression, if I use the compressor inside my dbx DR260 on the sub channels, would it work similarly?
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Old 5th December 2011, 10:46 PM   #238
Djim is offline Djim  Netherlands
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Hi Crescendo, parallel compression is not available in (any?) digital crossover systems. Also, using compression in digital crossovers means you compress the whole bandwidth of the sub (including the peaks/transients). So the end result is different from parallel compression. Compressing the whole signal (blue signal in the graph), like all digital crossovers do, will sound much more processed/unnatural and destroys the dynamics at higher compression levels. It will also lead to more suppression of the lowest part of the sub range since the attack of kicks triggers the compressor.

Click the image to open in full size.

You can higher or lower the amount of the parallel compressed signal by using the output gain of the compressor.
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Old 5th December 2011, 11:12 PM   #239
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Quote:
Originally Posted by CRESCENDO View Post
Hi Djim,

I'm not getting frustrated I just can't decide whether to build somethin with these 2 new 3015LF's or to sell them and go with a 30 Hz TH (with a higher quality driver - less pwr compression, etc) I've been eyeballing. I'm working on low funds at the moment, so I'm trying to be careful w/my decisions.The PPSL I posted was a 37 Hz cab and I don't know if they'd be ideal for PA, but according to the sim it would be 3-5dB louder @ 30 Hz than the 2 SS15's I have. I know what you mean though - I could've built one by now and got it out of my system.

Do BR6 enclosures raise the low corner when stacked (unlike TH's)?



Hi Art,

I'd love to. Do you have any pics, plots, design ideas, etc for an enclosure? I've seen your Keystone thread, but didn't see any design models. Maybe I missed it..??
Yes, you missed the plans, they are in there.
A PP dual 15 could be made easily by widening the cabinet to fit them, and adding a standoff to the reversed cone adequate to account for the magnet depth.
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Old 4th January 2012, 09:27 PM   #240
Scott L is offline Scott L  United States
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Default compression ratios of the ppsl ??

Quote:
Originally Posted by djk View Post
I don't worry to much about trying to model it, I designed it BC (before computers) with a four function calculator and 6th order formulas from Keele.

The first dual 15 PPSL had an exit of 16.5"x5" (3.3:1) and I was concerned about the intense pressure it had. Subsequently I changed it to 22.5"x7" (1.7:1) and feel a lot more comfortable with the pressure. A Klipschorn runs a 13"x3" (3.4:1) in the throat.

The main thrust to minimizing plenum volume is to extend the midrange and minimize cavity resonances. The depth is the main issue, and yes, blocking off the back corners helps.

I have measured an organ pipe resonance out of one of the systems (where I had made a very deep plenum for no good reason), up around 800hz, but that is so far beyond the intended crossover point that I didn't care about it.
Yep, Me again. Am trying a different plenum, much smaller this time, and wanted to ask if my calculations with respect to the compression ratios agree with how you figure yours (?) I'm using a 12 inch driver; the approx SD is about 90 square inches and my plenum exit is also 90 sq inches, so is that a 2:1 ? (or does the volume of said plenum come into play somehow?)

Thanks in advance that you (djk) or anyone else may offer.
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