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Hey all, long time lurker, been using the Skram for about 2 years now and decided it's finally time to post some proper calibrated measurements. I’m an acoustical engineer at QSC, and run my own custom rig as a side hobby. I've only been in acoustics for 2 years, before that I was an amplifier engineer so I'm still learning some of this stuff. Been meaning to get this info for a while and finally had some outdoor measurements to make for work, so while I had things set up, I thought I would go ahead and get some comprehensive measurements for this build. I’m currently running them with the 21SW152-8, but we’ll be getting our hands on the new cost-effective Celestion TSQ2145 for evaluation soon, at which point I’ll get another indoor groundplane & impedance measurement. I haven’t added fiber fill/acoustic foam to mine yet, so that could be another interesting data point. Indoor ground plane measurements are done with our 1/4th space calibrated, scaled, & windowed measurement sequence that we use for all product qualification. Also got some measurements of THD and harmonics at 10v. The one downside is that the signal path has >100ms latency for phase response and there are minor reflections even with the windowing of the impulse response. Unfortunately I can’t post pictures of this setup due to product confidentiality. 1w1m looks to be about 94dB SPL. I am a bit surprised how different the "knee" at 30 hz looks compared to previous measurements in this thread, I'm not sure where that difference is coming from... Earthworks M30 measurement microphone used for all data. ARTA outdoor setup, 22C, 30%humidity: RME Fireface UCX QSC PL-380 Q-SYS Core250i Outline ET series turntable Indoor measurement data: Audio Precision AP2700 for impedance response Lynx Aurora(n) audio interface Grace m801mk2 mic preamp Measured with SoundCheck 15 Outdoor setup has hard walls ~16 meters on either side, so spatial IR responses are windowed to 90mS (2x 16m). Turntable setup to rotate about the physical center of enclosure. Outdoor SPL scaled to match calibrated indoor measurement. I took 2 polar data sets, one with the enclosure vertical, with ports at the bottom, and one on its side, and you can see the slightly asymmetric polar response. I’ve attached a .vacs file with all of the measurements, and I can provide all of the outdoor .pir files if someone was interested. This is an amazing subwoofer, many thanks to @Ricci for his work. Hopefully this information will be useful to you, let me know if there’s anything else you would like to see, or clarification, and I’ll do my best to provide. Skram Data.vacs

I modeled a CNCable version of the SKRAM fit exactly to the detailed plans provided by Ricci in post #1. Feel free to use them as a base. These are meant to be used with Adam Hall 3402 and Neutrik NL4MPRXX, so you might want to adjust the respective pockets and cutouts. I did not yet include pockets/holes for wheels. SKRAM 3D.step Assembled enclosure SKRAM PARALEL CAM.f3d - Fusion 360 File including programmed toolpaths. 12mm Sheet 1.step 12mm Bracings as optimized flatpack 18mm Sheet 1.step18mm Sheet 2.step18mm Sheet 3.step 18mm Parts as optimized flatpacks. SKRAM Individual Parts.zipIndividual Parts

Jami, Thanks for the cnc files and sharing them! I'm sure it will be a huge help to some other builders. I know it probably took some time to put those together.

Hey Father Francis. Heat happens for sure, on gruelling bass music shows I can feel the heat on the metal of the hatch handles, and if you put your hands in the vents you can feel the warmth coming off the drivers. I've rolled mine out to the trailer in cold Canadian winter nights and seen heat causing a bit of fog to come out the vents haha. There was some mention in previous pages regarding the potential for heat to be a problem for this cabinet. While you should be careful with your limiters, in real life I don't think its turned out to be as big of a concern as was warned against. I've been using a pair of thermocouplers to pull temperature data off the magnet, if I'm working them hard I can get temps up close to 70-80 degrees or so when I'm tickling my limiters during heavy bass music shows. Bennett Prescott from B&C stated that the 21sw152 should survive 100 degree magnet temps reliably, but I've made it a point not to run them that hot. I only really see that high of temps for dubstep or modern bass music shows, for most everything else temps never seem to build up when I push them to the verge of limiting. I've actually found this a bit interesting, as it was stated earlier in this thread that one should avoid pounding techno with this cabinet but that hasn't been my experience at all. I specifically use this guide to set my limiters and I haven't burnt one up yet, its written by XTA but can be applied to any amplifier. Start at page 5 and follow the instructions closely. https://www.xta.co.uk/wp-content/uploads/2018/05/XTA-Application-Note-DPA-Amps-Limiter-Settings.doc.pdf

I should have Dune pt1 measured next week. JSS

Hello Andyman3k. Nice work and thanks for the measurements. QSC eh? I've used my share of QSC amps and speakers over the years. The impedance plot suggests that the tuning of the vents is near 30hz or so. That's right about where it should be. The corner drooping a little is probably due to the 8 ohm 21sw152 having a little lower motor force than some of the other drivers used. That's one effect is that the vents aren't loaded as aggressively which results in a little bit of a roll off before the tuning. Not the end of the world in the scheme of things. In general you'll get a sharper more aggressive low corner with drivers having more motor force ( BL^2/Re) / lower qts. My cabs are usually a bit undersized vs extension and thus require extra energetic drivers. That indoor measurement rig sounds intriguing. Too bad it's not for public consumption. Am I correct that the polar work was conducted outside but the FR and Imp were on the inside rig? Nice measurement rig. Again thanks for sharing your info. More data is always welcome.

My first exposure to DataBass and I can honestly tell you this thread is a game changer! Thank you!

JAMI, you rock !! thanks for sharing your CNC work with us! For convenience I packed al your CNC files on a rar archive (for the couch potatoes like me ) SKRAMCNC_JAMIPACK.rar

So.. here are some measurements with front plate installed and up to 3 ports blocked with grain sacks (quite tightly) Measurements were done in an mostly open area, the speaker was sat on a few tonnes mill stone on some paper bags to make it very stabil. The cobble stones were too uneven. there is a highway nearby but during spl calibration the noise of the cars didnt surpasse 68 dB. the microphone was sat 360cm from te center of the cabinet. It was sat close to ten meters away from the building wich is round so we felt that maybe it would be less visible in the measurements. Please comment on the plots so i know what to look at. And thanks again to Josh Ricci for sharing these plans Regards Lex ckram Dec 30 molen meting volledig.mdat

Using economy style plywood and some scraps for the 12mm parts i started construction here are some pictures of the process. First off thank you Josh the drawings are flawless! Sadly upon reaching this point my work shift starts again so will continue with the circular bit once i get back home. sofar everything is up to the millimeter exactly as drawn. Upon completion i would like to submit measurements. I think i have everything (software, calib. mic., mic, stand etc) Could anyone point me in the right directions on a step by step measurement process? I know theres a big chance this thread is dead, no one will be reading this but im trying anyway and like to thank Josh again for the nice drawings. Greetings Lex Breijs.

OK. I'm Now decided to build the amazing SKRAM. Like always you're so helpful Ricci, Many thanks Mr. designer speaker genius. 😉