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Ricci's Skram Subwoofer & Files

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I know what you meant Scott. I am not exactly young myself. Kind of like schmuck being used anymore.

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For anyone who might find it helpful.  Attached are cut lists to build 2 skram cabinets.  I tried many combinations of 4x8 and 5x5 to find the route with the least leftover waste.  Factoring in cost of materials for me in Canada, $73 per 18mm 5x5, and $105 per 18mm 4x8, this was the cheapest route... your mileage may vary depending on material costs.  Will require 6x 5x5 of 18mm and 1x 5x5 of 12mm costing about $487 Canadian.  I used the Cutlist optimizer app.  All pieces are accounted for as rectangles, some finish cuts will be required after the fact

 

Skramcutlist18mm.pdf

skramcutlist12mm.pdf

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On ‎4‎/‎6‎/‎2019 at 8:49 PM, jay michael said:

If possible it would be great to see a sim for the 21sw152.  How high do you think this will play smoothly,  150hz? or perhaps even higher?  Compared to a Othorn it seems like one should expect a slightly higher output with more usable response up past 100hz?  For the people who have heard both the othorn and the skhorn, is there a difference between the type of sound between the two?  Curious about what to expect as far tightness, speed, musicality and felt impact on the dance floor between the two.  Having already built some Othorns would it be worth the effort to give the Skram a try?  Cheers

21SW152-4 models great in this cab. It's one of the smoother modeling drivers in it. All of the usual pro 21's should be a good match. 18Sound 21ID, 21NLW9601, B&C 21DS115, 21SW152, 21Ipal, RCF LF21N551 looks decent, Lavoce SAN214.50 and the new Eminence NSW6021-6. 

I'm hoping that it will be smooth up until 150Hz if needed. It should be. Actually I'm hoping it behaves similar to the Skhorn and is relatively smooth up until a bit past 200Hz allowing XO's well in excess of 120Hz if required and a predictable XO transition to the mains. Until I get finished cabs with drivers installed I won't know exactly but it should be close to the sims.

As far as sound of the cabs I actually preferred the Skhorn over the Othorn slightly, Skhorn seems a little bit cleaner at high output (lower THD) with a bit more oomph in the 60-120Hz octave, but both are still really good for loud music playback. I'd expect this cab to sound extremely similar to the Skhorn and perhaps a bit better in a Skram pair vs single Skhorn situation. Again I don't have Skram's done yet but that's what I expect. Unfortunately I got rid of my last pair of Othorns a while back so I no longer have those on hand for direct comparison. A lot of people are happy with them though.

Output and sensitivity between the 2 cabs isn't a whole lot different overall. Othorn is a larger cab, heavier cab that is 4" deeper, so it likely will have a bit more max output in the 25-35Hz area and a bit more sensitivity over that range too. HIL and all of that. The Skram will likely have a bit more from 35-70Hz or about that. This is with all of the Skram vents open. It is more flexible and can go deeper once the alternate vent tunings are factored in. Top end above 70Hz is a bit of a wash. When I say more output I mean in the neighborhood of a couple of dB or less while using the same drivers. Not huge differences. Once I get to test the real cabs I'll know for sure. I'd say it's more of a lateral move to something a bit different rather than an across the board improvement.

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Thanks for the great description Josh, really appreciate it. Pretty reasonable cost to build so I'm going to knock off a pair to compare.  Thanks for the posting the design!

 

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On ‎4‎/‎2‎/‎2019 at 10:29 PM, Ricci said:

I don't see myself doing many TH or FLH's in the future. FLH makes more sense for systems without size restrictions, looking to extract maximum from a single driver and those without the need to go very deep. I might employ it for 80-300Hz range or so in the future but it's doubtful I'd do a subwoofer. 30Hz extension is bare minimum for something I consider a "sub". FLH's can be bested in the lower register by smaller more output dense alignments. They can sound very good. TH's I've found that the limited bandwidth and limitations imposed by path length needs and folding options cause them to be difficult to design well. More importantly the harmonic resonances in the response are audible and can cause major issues with harmonic distortion and ringing. In order to keep this up out of the sub bandwidth, well damped and above the low pass filter it's difficult to get extension much lower than the Othorn IMHO. TH's are best with extension to the 30-40Hz range IMHO. When done right they can sound killer as well, but the driver is more exposed usually so they have a bit more operational noise than FLH's. Better driver cooling though. The hybrid BP's I've been doing can be smaller than TH's, much smaller than FLH's and can almost match the TH's output. They are still somewhat tricky to design well and package but easier than a TH and easier to build. The response can be made to lack the upper end response issues more easily. The driver is buried in the cab so mechanical and operational noises are diminished, which is a big deal to me, but the air exchange and cooling is a lot better than a FLH. They are a bit more tolerant of a wider range of drivers as well. The sound is definitely clean and visceral when done right. 

In summary I have heard excellent examples of all 3 sub types. I'm a big fan of burying the drivers in the cabinet. Reducing the direct operational noise of the drivers especially when operating at high excursion / high output scenarios makes a large difference to me. The tradeoff is it may be difficult to tell just how hard the driver is being worked. 

One of the benefits of tapped horns in regards to THD and power handling, from what I can understand, is that the driver has excursion minima at the tuning frequency, whereas FLH's have excursion maxima here. Does that mean that FLH's are loading the driver at higher frequencies and possibly even over a broader range compared to TH's, and does it therefore follow that FLH's have less excursion over the midbass area compared to TH's? Reading up on the subject it's not always clear to me whether a (fitting) driver used in a TH is totaling less or more excursion in its operating range compared to a driver in a FLH. Off the top of my head it seems having excursion minima at the tuning frequency will "bleed" - i.e. have similar influence into higher frequencies as well (contrary to frequencies below the tuning fs), though to a lesser degree. I'd therefore wager excursion control is more important at lower frequencies, where excursion demand is higher, and that TH's, overall, sport less excursion than drivers used in FLH's - is that correct? I'm assuming the Skram/SKhorn behaves similarly to a TH in regards to excursion characteristics at the tuning frequency?

Perhaps how the driver is loaded in a design is only of academic interest where overall performance envelope and sound quality goes, and that upper band limitation with TH's is a more significant marker in regards to THD when used close to the performance ceiling. In any case the SKhorn/Scram seems to be a very neat "compromise" combining fairly compact size, extension, SPL capabilities, and upper band cleanliness. 

Slightly off-topic perhaps: I've sometimes stumbled over the expression "enclosure interaction," and how horn variants that sport very little enclosure interaction are desirable. What's to be understood with 'enclosure interaction'?

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M_MS,

FLH's do indeed have their excursion maximum at the low frequency knee. This often means that their output is limited in that area first as the driver runs out of excursion. It makes their frequency response and extension a little bit misleading if they will be driven hard. Most other alignments such as ported, TH, BP6, BP8, Skhorn style hybrid, passive radiator etc, etc. have an excursion minimum near the low frequency knee.

Other than the above sealed OB and IB subs have no excursion notch, ported has a single notch and higher order alignments like TH, FLH and BP6, etc have 2 or more excursion notches. Beyond this it cannot really be said that one has less excursion, or THD than another. It depends so heavily on the individual design, drivers used etc...There is no simple blanket answer to a very complex set of interactions.

The absolute best way to learn this stuff is to download a program like HornResponse and start simulating different designs. Build, measure, listen, etc...

I have no idea the context of "enclosure interaction" or the intended meaning. All drivers interact with their enclosures. I'd actually say larger horns cause more interaction if anything. The response is being modified more greatly than the drivers free air behavior not less.

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15 hours ago, dsl1 said:

lXbkkZu.png

Finally had an afternoon to cut some stuff.

Quick work as usual...I imagine you'll be the first person to complete a Skram and fire it up.

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37 minutes ago, Ricci said:

Quick work as usual...I imagine you'll be the first person to complete a Skram and fire it up.

I wanted to get it done two weekends ago but the CNC was having issues :(

Everything is cut now except the reverse side handle cutouts and the feet/stacking situation for a pair. I still don't have a good plan there. 

 

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3 hours ago, dsl1 said:

I wanted to get it done two weekends ago but the CNC was having issues :(

Everything is cut now except the reverse side handle cutouts and the feet/stacking situation for a pair. I still don't have a good plan there. 

 

Me either...I got sidetracked back to working on content for the new website.

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Looking good Jesal.

I thought something looked a bit off but I remember now you were building them at 32 high x 36 deep instead. ;)

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It will be on it's sides, so had to shorten it a bit.

But it would still be a wall to wall bass, with 2 Skrams and a Skhorn up front.

A single Skram by the couch for nearfield impact, it should do the trick lol

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What's the best way to cut brace circles?

I tried router straight bits and hole saws, it's a pain in the butt.

So I just leave it solid... as I do everything manual, unfortunately no CNC.

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3 minutes ago, Jesal said:

What's the best way to cut brace circles?

I tried router straight bits and hole saws, it's a pain in the butt.

So I just leave it solid... as I do everything manual, unfortunately no CNC.

If it's sitting in a room, doesn't matter. Just cuts weight a bit. 

 

 

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2 minutes ago, dsl1 said:

If it's sitting in a room, doesn't matter. Just cuts weight a bit. 

 

 

Ok thanks, will go without the circles. Weight is not much of an issue.

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There are differences. Its a lot to go into from my phone and Ive posted about it in the Skhorn thread and other places. I'm not familiar with the linked subs or if there are measurements but its a vented sub that is smaller with what looks like less vent area and its a direct radiator. 

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Sure.  I haven't reread through the skhorn thread in a while so maybe I'll go read all those again.  I just came across the linked sub today so I'm not super familiar either.  I've been planning to tackle a skram build (or 2) with the Lavoce drivers so I've been digging into all the related builds with similar drivers lately and was just curious how they compared.  The size of the skram is seems to be pretty compact which is quite handy! 

I also came across another similar (albeit larger) design by LTD02 for these drivers called the Devastator.  Does anyone know if that would that be similar in performance, at least when accounting for the difference in overall size?

 

Devastator an LTD02 hybrid design https://www.avsforum.com/forum/showthread.php?t=3032394

 

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Looks great!

I have two all glued up and ready for round-overs + painting, but this weekend got away from me. Maybe tomorrow night. 

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