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Ricci's Skhorn Subwoofer & Files

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9 hours ago, SME said:

Assuming I understand the dimensional drawing, the ports are 3" (76 mm) wide, so adding 30 mm to each side would make the ports 140% bigger in cross-sectional area.  Vent tuning frequency scales with square root of port area, so tune will be ~118% or around 1/4 octave higher.  That's like 35 Hz vs. 30 Hz.  This assumes a pure vented alignment, and I'm not sure how the 6th order aspect will come into play.

So we did some calculations and think this should give pretty much the same response as the original.

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Depth and height of the cab will stay the same but the overall length will be 1440mm. We will also be using 18mm ply for the whole cab so we have taken that into consideration. Do you think this will work how we intend it too? 

27 minutes ago, radulescu_paul_mircea said:

Regarding limiters, for pro use, I suggest to make use of all of those limiters. The X-max limiter is excellent to be used when you force the system and you hit the peak limiter or maximum voltage quite hard. It will help you with keeping the high pass where it should be no matter what the input stage is doing.

Thats right, if a mic gets dropped on stage or someone unplugs something when they shouldn't it offers some protection but mainly its for protection against rubbish DJ's that like to have the mixer in constant clip. I regularly use the VX and Tmax limiters and I have never fried a driver and with the kind of events we do we get to really push the limits of our cabs. Here are some 44M20 logs from a 3 day festival we did last September, the first one is the whole device and the last 4 are the individual channels. we were driving 4 8r Beyma 18p1200nd per channel all channels driven with the same input/output settings.

68797386_Screenshot2019-03-12at15_04_56.thumb.png.5befc34d1ef36ac429cd6138c8653a09.png 

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I did some quick modeling and it looks like the tuning would come in at about 31.5 or 32Hz from the original 28 or 29Hz tune. A little more than I had guessed, but the response doesn't change much. It looks good. I'd say this modification would be barely noticeable if both were side by side and you have a little extra vent area. Go for it. 

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6 hours ago, radulescu_paul_mircea said:

 I managed to explode the final stage of one 44m10 playing my SKhorn XL version using Ipal driver squire fast , but the 20K is way more stable in 2 ohms. The problem was bus pumping from the very high back EMF.

I would suggest you to used 4 ohm drivers and use each sub on each channel instead of bridging it . This way you will use all the DSP capability of the amp and you can make more configurations like cardio and end-fire. The difference in stability is not big, a bridged class D amp will be a tad more stable at high reactive loads , but the back EMF will discharge in the endstage instead of the capacitors so for the same output power , more heat will be generated.

Ouch blown amp stages...I've had similar happen with unbridged smps amps. This is partly why I avoid running them like this for heavy duty bass now. It seems to shorten the life span quite a bit and induce more failures. 

 Most of the pro amps I've used seem to be fine on bass duty, half bridged until down around 25 to 30Hz with normal duty cycle music. Lower impedance loads / higher current requirements/ higher sustained power and especially very deep bass frequencies below 25Hz start to cause issues. With usual music primarily above 30Hz you may never notice. I go straight to bridged for subs anymore to avoid the possibility under demanding circumstances. YMMV. 

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1 hour ago, Ricci said:

I did some quick modeling and it looks like the tuning would come in at about 31.5 or 32Hz from the original 28 or 29Hz tune. A little more than I had guessed, but the response doesn't change much. It looks good. I'd say this modification would be barely noticeable if both were side by side and you have a little extra vent area. Go for it. 

Thanks Ricci, was this for the simple mod of making the vents wider or the latest mod I posted with wider and longer vents?

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The second option was a port width of 87mm and port length of 595. After replacing the 12mm ply for 18mm the last 35mm would be split between the rear chambers.

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Hmm. Man I think its splitting hairs. Should be fine. Your talking a couple hertz tuning difference if that. The vented chamber is relatively forgiving of small changes. Id say roll with it.

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54 minutes ago, Ricci said:

Hmm. Man I think its splitting hairs. Should be fine. Your talking a couple hertz tuning difference if that. The vented chamber is relatively forgiving of small changes. Id say roll with it.

We decided we are going to just make the vents wider. Going to start cutting at the weekend.  

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Making the vents longer will lower the tuning.  The rough scaling is square-root of 1 divided by length.  So increasing the length will counteract the effect of making the vent wider.  I doubt you'd be making them 1.4 times as long though, so its effect will probably be less than from widening the ports.

My guess is that shifting the tune up 1/4 octave or less around 30 Hz won't be noticeable most of the time, but I'm sure counterexamples can be found.  For example music with strong sustained tones at 27 Hz or something are probably going to sound quite a bit different.  I guess that could be a thing with some music genres.

On the plus side, I reckon the wider ports will give you another dB or so of low-end output without port compression.

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I have a question for you guys about sine sweep measurement pressure level. what does it really show? the SPL value is a peak one? 

Looking at the measurements for the SKhorn on the SP6000 amp, the CEA2010 values and the maximum swept values are within half a dB. From my tests, the crest factor of the sweep is 6 dB and the level it shows is 3 dB lower than the peak and 3 db over LZF. 

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Sine sweep SPL value is not a peak figure. None of the ones shown here are peak. Crest factor is 3dB.

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