Domme

15 hours ago, lawbadman said:

IV now finished my first skram. It was a really tough build since I'm not a woodworking expert. My biggest mistakes are badly cut top, bottom and side panels. I need to find a way to accurately cut 4x8 plywood. Suggestions are welcome. The internal pieces were good as my table saw did the job just right.

Initial sound testing is ok so far with a brand new Lavoce SAN215.30. It seems the deep bass(35hz and lower) could only be heard right up close to the enclosure. 20 feet away and I heard nothing under 35hz. I figure multiple enclosures would solve this anomaly 🤷🏾‍♂️.

In any case it sounds good, I hope to paint it soon and then build a second enclosure by Easter. And I'm probably the first person in Jamaica to build a skram 😁 

Many thanks to Ricci for this project 👍🏾👍🏾👍🏾

 

btw would you guys mind sharing your EQ settings?

 

It is a super tough build if you've never done something similar before. Was my first speaker project and I'm glad I got a little assistance from a friend who is a carpenter master, even though I did most of it myself after he told me what to do.

Cutting huge plywood panels without a properly sized saw sucks. I am just building another pair of Skrams, this time alone and I also moved so I can't use the shop from my friend. This time the saw was too small though so I could not use the lateral fence. A real pain in the ass. Measure 10 times, cut once... next time I would probably just use a track saw with guiding rail instead. More work with measuring and drawing but probably a better quality after all. But there won't be a next time, 4 Skrams are enough for me to handle and transport :-O

The frequency response should improve after some time. You can also break the driver in with a white noise signal at moderate volumes for some hours.

Cheers,
Domme

On 11/3/2023 at 7:48 PM, Waipy said:

Would be any issue replacing the 12mm parts with 15mm apart from weight? 12mm is hard to find at good prices lately.

I am thinking about the bottom part and if the increased wood width reducing the volume will affect the output in any noticeable way.

While I don't have a comparison I made everything in 18mm because 12mm wasn't available from my supplier at the time. Does it sound bad? No. Does it sound worse? Can't tell.

I will do some measurements once I finish my second pair (also in full 18mm to match the existing ones).

On 10/27/2023 at 3:15 PM, Jjzamo said:

Thanks Domme! No CNC here so just trying to think about easier setup for myself.

I did those cuts with a jigsaw and manually routed the baffle (G) and the mouth braces (R) because they are visible in the finished construction. No CNC needed (although it would make things easier...)

Does anybody have experience with amps for an NSW6021-6 in a Skram? Or 4 Skrams to be exact? As I said I have 2 Skrams now and a Powersoft K20 and want to build 2 more. In theory I could put another 4 on the K20 (2R then) but I feel like they could use more headroom and I would also lose control on 2 Skrams for array operation. An X8 could easily drive 4 with enough headroom, but I could not add more because of bridged operation (only 4R rated) and the quite unusual driver impedance (6R). An X4L on the other hand would enable me to add more later (up to 12) but I would get diminishing returns in the headroom department. It would not be a real headroom benefit compared to the K20 if I should ever operate 6 Skrams and even with 4 it's not a lot of headroom gain compared to the K20, especially considering the high price (I could possibly get around 2-3 additonal K20s for the price). So right now I feel like an X8 would be the only true upgrade headroom-wise, it would offer me delay control on each individual cabinet, but would also limit me to 4 Skrams in total (probably not to bad because my back already says no anyway). A tough and expensive decision no matter which will be the result... I think I will first build and try my K20 on 4 Skrams and decide then but a nice little discussion on the amping topic would have my interest for sure.

Cheers,
Domme

20 hours ago, Jjzamo said:

Could the main brace (part L) be cut as a rectangle picture frame with three of the sides 50mm and the bottom 110.4? Or is there some sort of acoustic advantage to having the oval cut out and corner circles? Thank you!

Hi Jjzamo,

Acoustically it shouldn't matter. You sacrifice some stiffness because you have a little bit less material distant from the outer edge (area moment of inertia) but it really should be negligible. It would also make mounting the driver a bit easier.

The corner holes are for weight saving.

Cheers,
Domme

Two weeks ago I hosted my second public soundsystem show along with a friend. The pair of Skrams I built (loaded with NSW6021-6s and powered by a K20) played super loud and clean. We received a lot of gratitude from the crowd and other local soundsystem crews praised the clean sound of the system. Unfortunately we had power issues (to be exact, there was no power at all coming from the designated socket... ouch!) and after we fixed it there was not much time to do a proper soundcheck but you could easily tell that most of the bass was coming from the Skrams, and we're not even talking about low-end performance. It was such a difference when I went to a quite popular local techno club last weekend. I could have cried about what is thrown at you after you have to pay 15€ entrance fee...

I decided to upgrade to 4 Skrams this winter. That's all my van can handle and it will already be super cramped... my friend is selling his horns and wants to upgrade to Type O paraflex cabinets with 21" drivers. I tried to persuade him to bulid 4 Skrams instead but he prefers the more classic/roots look of the type Os. Anyway, once we are done building them I will drive on a field and compare them. Two cabinets, one measurement method.

It's no easy project at all. I have some woodworking experience, but not too much, and had some help from a friend master carpenter and it was still a PITA to get it all right. Without his help I probably would have messed up the glue step because you need to be quick! Those huge surfaces are not easy to move around once you apply glue and it's almost the last step and you can still mess everything up... you also need strong clamps and MANY of them.

I would probably order all parts CNC'ed next time because even though it was worth for the experience and learning, when you count man hours it wasn't worth spending hundreds of hours just to save a bit of money. Anyway, good luck!

@jay michael Wicked rig!

After a long winter break and moving to another city I finally finished my SKRAMs as well. Only two of them but super happy with them. Thanks for the design @Ricci Only thing that could have been better is my painting job. Gonna post some pictures later.

4 hours ago, DJimbo said:

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!!! 

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!

Hey everybody, I am wondering if and how you seal the area between your cabinet and handles, cable terminals and so on to minimize air leaks. I was thinking about using some 1mm neoprene sheet and was wondering if someone here has got experience with it or what you are using instead.

Cheers!

1 hour ago, rolo95 said:

Starving to see your construction pics   😻

hope you can share some audio measurements when you finish the cabs !!

Will do. Got some tolerant neighbours and a wide field in front of the house, but unfortunately my mic is only built for 128dB. Should be enough for those civilized measurements, but I will try my best to make it suffer 😉

2 hours ago, Tahoejmfc said:

I love how many people have built these subs! Also, I just love these subs as well. https://www.instagram.com/tv/CalY8Y1Bi6D/?igshid=YmMyMTA2M2Y=

 

I love this truck! I had it as wallpaper and all of a sudden he's wearing a custome 🤣

Just unloaded the wood for my 2 SKRAMs, starting the build on Thursday... oh boy 😻
Unfortunately I don't have access to a CNC router so I have go with lamellos instead. When it's finished I will probably reinforce some critical edges with glass fiber fabric & epoxy resin. That has to do for now...

@rolo95 For the moving sub problem I would recommend those anti-vibration rubber mats that you can put under washing machines. Cheap and effective. You can even cut them into smaller pieces to save cost. A washing machine is a hell of an unbalanced beast and still I've never seen one move (significantly) even after years of operation. Those mats also equalize uneven floors up to a certain degree and protect your subs from scratching. Or the floor itself if you're ever playing on parquet.

Hey everybody,

my system is growing slowly and steadily. Soon I'll be ready for summer! While getting used to the DSP software I was playing around with crossover setting. My cabinets are not finished yet but I was already wondering how everybody else feeds their Skrams? I will be using AE TD10Ms as mids with fs=40Hz so I should probably not go too low with them.

How high/low are you cutting your Skrams off?

Blessings,
Domme

@Ricci I think the stacking problem of your initial post has not been solved yet and I was just searching for corner protection and stumbled upon those

https://www.thomann.de/de/adam_hall_4071_cabinet_corner_plastic.htm

Me and my slight OCD find them much more elegant than trying to make stacking edges because they look much less asymmetrical, but if you want to go for them it should work as long as two neighboring edges have negative patterns, even if you rotate them. Just take a look at this very professional diagram that I made to understand the principle of those corners because my brain somehow refuses to think in transformation matrices.



 I hope  it will work without math but I hereby declare that I won't take any responsibility for resulting damages 😂

42 minutes ago, peniku8 said:

I assume he is not making Dado joints with a CNC, if he wants to use lamellos. I'd personally just use 18mm ply for the braces and leave everything else as is. The impact will be so small, it's nothing to be concerned about. If you make the entire cab wider, the tuning will drop too, in theory. Both options may lower the tuning by as little as 0.25Hz or so.

Thanks! He doesn't own a CNC router so we have to use lamellos instead or even do some manual routing of dado joints if unavoidable.

My carpenter friend is unhappy with using 12mm plywood for the vent section (parts "I") because he wants to use lamellos for easier assembly and thinks 12mm might be too thin for them. I assume that if we use 18mm plywood instead and just make the whole cabinet 18mm wider to preserve the vents' area it shouldn't be much of an issue in terms of tuning. Is this correct or am I missing something?

Best wishes for the weekend,
Domme

Thanks everybody for the input and interesting amp discussion. I'm gonna be using an original FP10kQ and I am considering to get another one. I think one on each side would be a good start with huge headroom for a 3-way system and I would still have enough capacity to double up at a later point or migrate to 4-way with another amp.

Anyway, cabinet building is coming closer and I am just studying the plans and converting the measurements to round metric numbers. Does anybody know why there is this 45° cut in the front panel C? I think it will get used as a handle in combination with the back-side hatch handles and now I am afraid that the sharp corner might break at some point and/or lead to injuries. I would prefer to use a rounded edge instead if it doesn't serve a meaningful purpose.

Cheers,
Domme

6 hours ago, peniku8 said:

Prices are identical between 4 and 8R versions and performance is very similar too. You're right that I recommended the 8R versions because of your upgrade plans in the future and the fact that 2R doesn't like long cable runs. You could also build one pair of 4R Skrams, put them on the 10kQ and then build another 4 with 8R when you get the FP14k and run 6 when needed.

Running 20m of 4mm² cables (typical length I bring to a medium sized gig) you end up with a damping factor of 12 into 2R, which isn't exactly great. To increase it to twice the value (over 20 is decent), you'll need to double the cable thickness (could run a 4x4mm² cable with two wires in parallel each to essentially get a 2x8mm² cable), halve the cable length (will you never need more than 10m?) or double the impedance. If your amps are always close to the subs go for it I guess. If you're not so sure about that, be aware of the issues running low impedance might cause.

The FP14k will pump out the most power into dual 2R, but more power is meaningless if your system sounds bad because the damping factor is nearing single digits.

I never considered the damping factor before, but did some research on it and tried to reproduce your numbers. I succeeded when using the following formula:



Is this the approach you took? If so, you most likely have forgotten to include the output resistance of the amplifier and much more important the voice coil. If we only consider these, we get the maximum possible damping factor (Re taken from 21DS115-4 TSP and halved because of parallel wiring):



If this model is correct then the damping factor can never get below this value. Even in 16R operation and with perfect cables we only get a DF of ~14. So it looks like cables only have a small impact on the damping factor unless they are extremely long or thin. Anyway, I was planning to use 4mm² cables. Not because of the damping factor but for current density and voltage drop reasons. Still, I see the benefits of using higher impedance drivers.

Sorry if I got a bit off-topic here. I promise to make up for it later by taking a lot of pictures 😘

24 minutes ago, peniku8 said:

@Dommewelcome to the forums, nice to see a fellow German here

I can imagine that a single 2x12" sub sounds a bit light on its feet in larger venues. I frequently do shows with only a pair of 12" subs (12BG100) when budget is tight and often wish for more, especially when it's outside. Two Skrams would be a night and day difference for sure. They're similar to the other pair of subs I own and the difference in output to even regular 18" subs is incredible. The Skrams are a fantastic choice, but remember to put big casters (100mm or bigger) on them if you have to roll them through uneven terrain.

About the Eminence, I think Ricci meant they're easier to drive compared to the 1Ohm Ipals (since that's its direct competitor, disregarding the whole IPAL system itself and disregarding the 2Ohm IPAL driver). Impedance wise, the SW152 is the highest. Efficiency wise, the DS115 is the best, by a small bit. The Eminence has a bit more excursion and slightly higher power handling, about two thirds of the way between DS/SW and IPAL. It's like +2db from them to the Emimence and +1 from the Eminence to the IPAL.

Amp wise, I currently run two 21DS115-4 off a 10kQ like you're planning on doing. It's damn loud. For the FP14k idea you'd be better off running two 8R cabs in parallel per channel. I would personally avoid running two 4R cabs in parallel, unless the cables are like max 10m and pretty thick (4mm² at least), or damping factor will come bite your ass.

For driver selection, I don't know what you paid for the SWs, but here are the cheapest prices I could find in Germany:

2 21DS115-8: 1074€ (my personal choice - I have 4 of them)

2 21SW152-8: 1194€ (not much of a difference to the DS)

2 NSW6021-6: 1958€ (~2dB more headroom)

2 21IPAL-1: 2072€ (~3dB more headroom, basically limited to plate amps or extremely short wire runs)

That makes the Eminence ~80% more expensive than the 21DS115.
If the 2dB higher headroom is worth that for you, then go for it.

@peniku8Thanks for your reply and summary of the drivers. I already cancelled the order earlier today because I decided to do additional research and get some input from more experienced people. Unfortunately, I will not be able to start working on the cabinets until somewhen in February anyway.

However, one thing confuses me: you are speaking about the 4R DS first, but in your comparison you listed the SW and DS in their 8R version, which the FP10k could not fully support, at least not in 4-channel mode. Did you recommend them because of my plans to maybe upgrade to 4 Skrams later with the damping factor in mind or was there another reason? Until now, I never noticed that there is no impedance recommendation on the SW/DS in the initial post. I must have thought it was 4R because it was still in my head from all the Othorn stuff I read earlier. And then I picked the FP10k to match it.

I can't wait to finally get started with building 🙂

Happy new year fellow bassheads,

I would like to introduce myself and announce that I am going to join the race for clean and low bass and decided to build myself a soundsystem that is going to include pair of Skrams (might double up later...). I am Domme from Germany, a DJ of Dub(step)/DnB/Jungle aka heavy bass music and very spoiled from my premium hifi sub (SVS PB12+/2), which hits the 20Hz mark cleanly and also quite loudly but of course lacks capacity for extended SPL-sessions in larger venues with its "only" 750W and 2*12" setup. It still is one of the cleanest bass I have ever heard so far, even at pretty high output levels, and I do miss the low frequencies a lot when I hear familiar tunes in commercial venues/festivals apart from a very few good DIY soundsystems. I love the culture and looks of the more traditional sound systems with their huge scoops and stuff but I don't think it is the cleanest and deepest bass, it's mostly loud. But I do want to deliver a clean and deep bass and not just loud one, at leas there is no war volume required right now. I am also very restricted with weight and dimensions since I only have a small crew, rather small vehicle and so on, especially because I don't exactly register my events in the current situation if you know what I mean so I have to hide in the woods where the floors are uneven and I would sometimes need to haul above roots and stuff... my initial plan was a pair of Othorns but when I worked through this thread and read about the Skram's benefits regarding weight and dimensions plans were changed quickly. Imagine someone building a Skram because he calls it "more mobile". I also prefer the driver to be hidden and protected from external sources of hazard like the audience, weather etc. Now I still have some questions on driver and amplifier. The Skrams might even replace the SVS in my home setup, where I would really like to have a pair and not just a single sub for increased tuning options and overall better room control.

Driver questions
I already ordered a pair of 21SW152-4s for the Othorns and at first I was glad that they can be used in the Skram as well. Then I read about Riccis recommendation to use the NSW6021-6. Could someone please explain to me why the NSW6021-6 is supposed to be easier to drive? Wouldn't it require a much stronger amp (wattage-wise) because of the higher impedance? The thing is that due to xmas/nye I can still return the 21SW152-4 because they have not been delivered yet (14 days return policy in Germany). Now I am very tempted to use the NSW6021-6 instead. Main reason is because I trust Ricci and the good reputation he has on several forums. More headroom sounds good to me so I would rather spend 50% more per driver than having to build and haul more cabinets. And ~45% increased driver cost is still better than having to buy a bigger van.

Amp questions
Closely related to the driver question is the amp question. For example, SME said that the NSW6021-6 is supposed to be easier to drive with common amps. Do you just mean easier because the load is lower? Because I would still need a bigger amp to deliver the power at 6 Ohms, right? And this is most likely not compensated by its 1dB increased sensitivity. Anyway, I am planning to use a Lab Gruppen FP10000Q for 2 subs and 2 tops. Do you think it's fine for them? In the (distant!!!) future I would probably upgrade to 4 Skrams and run all of them on a separate FP14000 and use the spare 2 channels on the FP10000 for kicks so the Skrams can fully concentrate on the frequencies below 80Hz. But as I said this is most likely not going to happen this year anyway.

Any advice would be greatly appreciated 🙂

Kind regards,
Domme