DJimbo

Awesome shares yall.

I spoke with a rep of B&C about powering their drivers. Guy was insanely knowledgable. He said, "you want the absolute most powerful amps that are made to power these drivers properly"

He explained how power hungry these can be and how under-driving them is a bad idea. We discussed powersoft amps and Linea. He basically just shot down my dreams of being able to power these (6 or 8 SKRAMS) properly off of a 120v circuit, or even two circuits. Now I am a lamen when it comes to most of this so I am curious about yall's thoughts about this.

Like 21' drivers are sick obviously but if we are putting them in such a small box for their size we are cutting their balls off a bit. I guess I am stuck wondering if the LF extension of the skram is worth the extra amp expenses, powering issues, etc. when TH118XL's can be found used and are comparable in size and output (above low low freq's) according to previous posters. Id love to be enlightened on the skrams and anything I am missing here and I think our group here will find any reflections useful. Thanks!

Wow thanks so much Domme, Ricci, Tahoejmfc, and Jay!! I really appreciate your expertise.

Noted on the gluing order. Sounds like I will have to build an arsenal of clamps and see what happens!

The comments about the amps makes sense. I will try to find some arrangement that pushes 4k to each driver with the minimal amount of boxes. 

The notes re: air dynamics all make sense and help me understand. Its such a compact box for a 21 that I'm sure maximizing volume was challenging to say the least. 

Tahoe JMFC which camp were you with? I was with Lux elixirs (fairly small audio setup this year).

Jay I'm surprised to hear that the 6 SKRAMS that have trouble keeping up with the Danleys. I would have assumed it would be the other way around. I have listened to the 46's at about 80% capacity and they are loud but not quite as loud as you might guess. Which drivers do you have in your SKRAMs?

Blessings!!

13 hours ago, Domme said:

If you have a CNC at hand you can route some grooves which should help with assembling and gluing process. I did not have one so I used lamello joints for easier assembling and increased stability.

This was my gluing order:
1. Baffle and horn
2. Base with ports
3. Braces
4. Outer sides

It was a pain in the ass though. I am glad my friend -a master carpenter who owns the workshop- helped with the gluing and I never knew that you can get sore muscles in each and every finger. You are going to need a lot of large and strong vices, too! Gonna post some pictures later on how it went.

From the fluid mechanics perspective i would say that you are moving large amounts of air back and forth repeatedly in different frequencies all at once. There will be turbulence all over the place no matter what you try. Even though I was also tempted to round of "F" I ultimately went with the original design (well almost...)
 

Good luck!

4 hours ago, Ricci said:

Hello DJimbo and welcome. 

As far as assembling the cabs go. Clamps and more clamps are your friend. Other options that help are a brad nailer, or a pocket screw kit. 

If using the 21SW152 drivers best results will probably be with 2 to 4kw of amplifier rating per driver. Any more might get sketchy over long periods of time. Less would leave some of the dynamic capability on the table. I prefer to run fully bridged amp channels on bass when possible. 

Smoothing out the corners might help with airflow in an ideal scenario but it has drawbacks. It reduces the internal volume utilized by the driver. With bass size (air volume) is king. The Skram is a vented cab on the back side so it's a traditional ported arrangement there. Large flares and circular vents would be beneficial ideally but would greatly increase the size of the cab and its complexity. The front is a short horn/expanding slot. The same applies here. Ideally it would be a totally smooth, straight path, but packaging it into the cab dimensions requires compromises. At best these would be small gains in output / noise reduction, even if it was built ideally with a totally different (much uglier and unwieldy) form factor. I hope this explains why most bass cabs do not bother with dramatic smoothing of the air path. It comes with other tradeoffs. 

3 hours ago, Tahoejmfc said:

Welcome to the Rabbit hole of BASS! Correct me if I am wrong with any of this.......

I use the B&C 21SW152's at 4ohm with a QSC PL380 amp. This amp drives 2 SKRAMS, with room to melt the coil if you turn the clip limit switch off.(I know from accidental experience) I have thought about running 4 x 8 ohm drivers with this one amp in series as well, but figure that would be pushing the amp alot and I typically use the amp at Burning Man and it was %*&#^@ hot this year so it prolly would not be the best idea as the amp would be turned all the way up instead of running at 50-60% like I currently am. I pair the 2 SKRAMS with Meyer Sound UPJ's and run the tops at -6db for most outdoor venues and -10db for most indoor venues (unless it gets really crowded, then I go to -4db outdoors for the tops and -6db for indoor.... Otherwise the tops are Too Bright). I have Meyer Sound UPQ's on order and will need to double my SKRAMS to keep up with the UPQ's output so I plan on building 2 more of these unless I just go straight to the Powersoft 30" M-Force subs but they are 12,000$ a pair with amp and you have to wait a year to get the drivers.

If you are going with 6 SKRAMS you will need quite the tops to compete as these Bass Bins output some serious BASS!!! Jay on here has quite the system with I think it was Danley tops, he might be one to DM. 

I would always cut in the grooves to build these boxes, serious forces going on here and you need the cabs to be rock solid, make sure you use the best Baltic Birch you can find, PU Glue and lots of pre-drilled screws. One option if you do not have access to a CNC router is to find a local makers space that has one, I used the TRUCKEE ROUNDHOUSE shop bot to make mine. 

GOOD LUCK AND MAY THE BASS BE WITH YOU!

40 minutes ago, jay michael said:

My pair of Danley sh46 are a pretty good match for 6 skrams, but they still outrun them a bit. I think 8 skrams would be the perfect balance. I've got another pair of skrams in the cutting phase, and another pair of sh46 on the way. Lots of skrams popping up in my area, there will be 12 in my city pretty soon, as well as 8 or 10 on the island. Been some planning discussing how to get them all in the same place sometimes soon

I'm planning an after summer report soon, was hectic busy with lots of great gigs

Hi! Thank you all for a riveting 40 pages of juicy tips. Thank you Ricci for the fantastic design!! I am sold. I am pulling the trigger on building 6 of these and I have a few questions for yall. In advance, please forgive my ignorance regarding everything. 

1. I see in a lot of other designs the "rounding off" of corners and deep pockets in the cabs. In the fluid mechanics world, you get a lot of turbulence around sharp corners and pockets in pipes and vessels. The SKRAM obviously sounds great to a lot of experts but it seems to have pretty aggressive corners and sharp directional changes. Im sure Ricci thought about this but I would love to know the thinking from a design perspective specifically with air as it moves around panel F and 90* turns in the back of the cab. Does it not really matter with subs?

2. Any guidance from anyone who has built these how tf you go about gluing these together? Are there certain groups of parts you do in different groups? I saw the one poster a while back who kinda sent it all at once.. Id love to better understand how to approach the gluing process.

3. Im looking at using the B&C 21SW152's in 4 ohm. Which amps would yall recommend? I am powering my Danley's with Linea. Ideally Id like to power all the subs off one amp for simplicity's sake (Linea 44M20, 20,000wattsRMS) using three channels split to two subs each wired in parallel. The amp goes down to 2 ohm but output is 3,000wattsrms for the 4 ohm and 1,500wattsrms for the 8 ohm respectively. If I bridge them I can apparently get 10,000 watts RMS at 4 ohms from each pair.. I dont know enough about amps to know whether it would be better to run two skrams off on one output in series or parallel given the wattage rating changes. Any thoughts about this? I could always change the drivers to 8 ohm and run them in parallel but the 1500 watt rms rating seems undersized..?

4. I will try to take a lot of photos and post the build here. I promise some nice videos once were rumbling.

5. I plan to take Ricci's files and have them cut out of 4x8' sheets (13x18mm, 1x12mm) with a cnc my cousin has. It seems like the only cuts that might not be able to be made with the CNC are the angled cuts for panel F and the front panel which I can manage on a table saw. It seems fairly straightforward but am I being short-sighted? 

6. Im budgeting about 11,500 for the six with all costs. I anticipate it being 2,000 less, however, these types of projects have a way of creeping up on budgets ;). Still way cheaper than used TH118's I have been scoping for a long time.

Thanks in advance! I am so stoked!!!