peniku8

Whoa those edges look rough. No compression bit used here?

I typically like to grab the HR sim and use the filter wizard so that the maximum excursion below tuning doesn't exceed the maximum excursion above it. With a 4th order Butterworth that typically lands a few Hz below the tuning point, which is around the same point as you suggest, for this cab's native tuning of 30Hz.

Draw a 1:1 sketch onto the wood (optional but helpful). Then make a 6° jig for the table saw and cut it where it needs to be cut

I couldn't help myself...

Here is a small guide of what you need to obtain accurate measurements of a subwoofer: Equipment: Microphone with a known frequency response (ideally an omnidirectional mic, something like a UMIK for example, but technically for this purpose any microphone with a calibration file for on-axis (free-field) sound will work) Audio interface Amplifier DUT (Subwoofer) A computer with REW, ideally something portable Measurement process: Calibrate your electrical chain (I'd personally not recommend this step to beginners as it's possible that you'll be making things worse. So if you don't know how to do this you can omit this step, since it's likely not gonna make a huge differency anyways if you have decent gear) SPL calibrate your mic (not needed if you just care about frequency response) Find a suitable open space to obtain your half-space measurements in. This means outside on a flat surface with no objects within a certain distance to your DUT (say ~10m or 30ft; parking lot for example or your backyard if it's large enough Place the subwoofer in the intended configuration with the radiating source (aka reference axis) towards the microphone Place the microphone one the ground and at least 4 times the widest dimension of the baffle/frontal area (typically diagonal) away from the cab, which would be about 4m in your case Take a measurement sweep in REW. Start with a low level to avoid mishaps and define a sensible sweep range (for example starting two octaves below the expected tuning point and ending two octaves above the intended maximum usable frequency, which would be something like 10Hz-500Hz in this case) Interpreting sweeps is an entirely different topic, but I hope I didn't forget anything here so you can obtain some high quality data!

no, go for it.

I mean, these are all problems that can be solved. If you pay me a bit extra I'll modify the cab to your liking and then you can compare my price to the CNC quote you get Shipping would be around 100€, looking at a quick google search. I would just prefer to not have to paint it (the vinyl wrap can just be ripped off). But you'll have to get yours painted too, so either way you'll have to figure that out.

Wait, you're in Germany? I'm selling my Skhorn, without the drivers. I'm in Germany too, hit me up if you want it

Well just think about it.. the port is how wide? 600mm? Now you increase bracing thickness by 18mm total (three braces iirc). So you lose 18mm of port width from your 600mm which is 3%. Make your port area 3% smaller in hornresp and see how much the response changes (hint: no).

As the title says, I'm selling my Skhorn. I took the drivers out and built single driver subs with handles for PA use, because I don't have space for a subwoofer anymore after moving. As such, I'm just selling the cabinet without the drivers. The port blocks are still installed. Plenty of pics here: https://www.avsforum.com/threads/skhorn-build.3037204/ Asking for 1000€, that's about its plywood cost atm (18mm BB). Fixed price, for anything less I'll rather keep it. I live in Germany near Luxembourg. No shipping, unless you handle everything. I have an epal pallet which I could put it onto. Would charge 50€ extra for that. I can not transport it either, so it must be a local pickup. Has 4 wheels installed on its back currently to move it around easily.

Heya, I wanted to update this thread with my recent findings comparing straight ports with shaped ones from two 21" subs. I build two cabs of identical size and tuning loaded with 21DS115-8 drivers, where one cab has a straight port and the other one has a port with continuously changing area. The shaped port has a moderate ratio of 2.5 (largest to smallest area). I put both cabs up for compression sweeps at 2m half space and the results are quite interesting. Port compression is visible at around 20V for both cabs, but I don't care much for fractions of a dB of compression. It starts getting interesting at 64V, where the shaped port went 0.5dB into compression and the straight port was at 1.5. The difference remains 1dB at 90V, but now we see power compression starting to kick in as well, centered at around 75Hz. Here are both cabs at 128Vrms input: The difference is still around 1dB at tuning, but now we see a stark difference of around 2dB near 70Hz. The cab with the shaped port behaves much better overall producing a smooth curve, which would still sound excellent at those levels, while the straight ported one starts being kinda all over the place. The difference at tuning is easily explained: the aerodynamic port reduces 'air resistance' so the cab is more efficient there. The expansion at 45Hz I can explain too, or at least speculate: This is where impedance and particle velocity is high, which means no power compresison in this region and vortices forming along the surface, reducing friction with the cabinet walls. The dramatic difference at 70Hz I have no clue. The port does nothing at that frequency... Interestingly, the sweeps at 181V look similar, because both drivers are heavily into power compression at that point, but the shaped port wins out by 1dB on average. Distortion looks pretty similar across all levels, except for the 128V sweep, where the cab with less compression also has quite a bit less distortion (around that 70Hz). So, conculusions.. It looks like overall a shaped port can extract 1-2dB more out of a subwoofer of a given volume, depending on which frequencies you need for your application. The cab with the straight port performed almost identically from 40-60Hz, but for other frequencies, it might be the difference of bringing 6 to bringing 8 cabs to a show. On another note: hornresp predicted this subwoofer's max output at 44Hz to be 124dB (1m full space), limited by Xmax. But I measured 129dB (2m half space) with just 7% THD... 5dB is a pretty big difference, especially since hornresp doesn't factor in any sort of compression...

Randomly came across this old topic and I thought I'd elaborate on what (probably) happened here, in case someone comes across this in the future: Some amps have their 2nd channel running double reversed. Their input phase is flipped and then the output wiring is also reversed, flipping the phase back. This seems to make it easier on the power supply, since one channel generates a positive voltage swing, while the other goes negative, creating an overall balanced load on the PSU. It's kinda like running bridged. Since the output wiring is flipped on channel two, 2+ will be neutral. And since both channels are running on the same PSU, ch1 and ch2 have a shared neutral, which means you're running 1+ and neutral, essentially the same as 1+ and 1-. If you hook up 1+ and 2- while feeding both channels the same input, you're running bridged (differential) automatically.

I was under the impression that the variable input voltage thing was a doing of the SMPS itself, not PFC. Are you sure these amps have PFC? I got an email from them announcing the D-3004 with 4x8600W@2Ohm but in the follow up mail their rep said that the amp isn't really 2Ohm stable lol. But if it really performs up to spec, you could run 3 Skrams per channel for a total of 12 cabs off of a 1U amp, which would be pretty sick. But of course pushing the amp pretty hard.

Nice endfire setup! I'm in the process of building a 4th sub (not Skram but also 21") and will bring all 4 to a wedding next month. I also got a mail from CVR that they released a new 35KW 1U amp. Would love to test it but can't really justify buying stuff just for fun yet lol!

Nice! Now you just need to get appropriate amping and the setup will slay. Btw, it's called "infrasonic" (sound), not "subsonic" (speed)