Colt's Neck High School Graduation
Due to a number of unforeseen circumstances it was about a month before I had an opportunity to really take the M421s out again, and for that I apologize. Too many shows where I couldn't be there for the show, or where it was a corporate gig and we couldn't use anything that large. What I needed was an outdoor show, with real power and reasonably large PA, with plenty of setup time, and a band that would be happy whether or not I managed to get the subs to play as nicely as I'd like.
Enter Colt's Neck High School graduation. An event in the middle of a football field 200 yards from any major obstructions, 10 hours from access to the field to the show, top 100 country act playing one song, and power tapped right off a 480v transformer. Audience of about 2,000 spread out over about 200' of throw. 6 per side ADRaudio L2821 flown off lifts, simple 4 mix 5 wedge monitor rig, full analog FOH with all the toppings, beautiful sunny day... I couldn't have asked for a better setup.
While the fork lift was taking all the heavy stuff onto the field, I took apart the amp rack that McCauley had provided. Aside from a few loose-ish output terminals, everything checked out just fine. I took every connection apart, checked it, and put it back together. Then I took apart every NL8 cable (each driver gets its own line back to the amps, cable is 10/8, every pin soldered... this shit could be used to power your house) and checked every connection, all good. The Neutrik NLT8 is used since the sub can take, like, 195+ fucking volts.
While the arrays were going up, I started cabling FOH and getting power out to the deck. A dedicated L21-30 for the sub amps, and a line right out of the
DLP. If I was clever I would have run four lines and done all my verification myself, but we had plenty of time. Setup my Smaart rig, cast stones and read tea leaves to determine my measurement mic location, and I sent some noise down the line. Final check was to have Steve, on deck, turn up one amp channel at a time and make sure that all drivers in both subs measured identically. Never measured a rear isobaric driver alone before, it's kind of interesting, but that's for another thread. In any case, all amp channels and all drivers in both subs checked out 100% in frequency response and polarity. At this point I'm pretty sure it's impossible for me to be doing anything wrong, so I fired up the whole thing and got ready to take measurements to equalize and integrate the subwoofers.
The first step was to take several measurements to take a look at the raw acoustic response of the subwoofers. This is with no EQ or HPF/LPF, not even any delay (aside from that inherent in the DSP). I got a measurement at FOH, equidistant from both subs. One midway between the subs and FOH, slightly off axis. Another well off axis house left. Since all three measurements agreed extremely well I moved on to equalize the subs themselves. (A quick note: All these measurements were taken in Smaart 7 with MTW, 2 second averaging, 1/48 octave smoothing. The mic was at ear height for a seated audience member, except at FOH where it was at ear height for a standing FOH person.)
What may become apparent to you from looking at the measured response of both subs is... where's 20Hz? The spec sheet says 20Hz -3dB, 16Hz -10dB. Those are extreme low frequency numbers, there are very few boxes on the planet that will even do that and even fewer that are designed to be large scale PA subs. By fewer I mean, like, two that I can think of off the top of my head. According to my measurements, the frequency that is 3dB down from 40Hz is about 27Hz. That's, what, 1/3 octave above 20Hz? 20Hz itself is about 15dB down. Now, this potentially calls into question my measurement system, but I'm also not hearing or feeling extreme LF. To be doubly sure, however, I will bring my freshly calibrated B&K 4007 next time and check my field measurement mic against it, and re-measure the subs. My I/O passes a loopback test no problem, and I can see 20Hz on an RTA if I tap the mic, but I want to be absolutely positive before I go claiming that this is a 30Hz subwoofer, not a 20Hz subwoofer.
To rewind a little, after having been so dissatisfied after the SFN expo I called Mark Herman up and asked if he could put me in touch with someone who has experience processing these subs, someone who I could at least talk filters with and get an idea of what they were doing to get these monsters to play well with others. Mark got me in touch with Alex Moran of Spider Ranch Productions, who has a pack of M421s and uses them regularly. His advice was pretty similar to that given to me by McCauley, 8th order L-R at 25Hz and "shut 'em down hard" at 90Hz. "What about EQ? What do you do for EQ in and out of band?" I asked. Nothing. Nothing whatsoever, just high pass and low pass and you're good to go.
That just doesn't make sense to me. First of all, if the sub is -3dB at 20Hz you don't put a filter with a -6dB point at 25Hz. You put your overexcursion protection filter at, I don't know, like 15Hz or so. You want it to protect the drivers from getting blown out of the box, not cut out all that impressive low end. Furthermore, I'm plainly not imagining that 6dB boost at about 70Hz, nor the out of band spike near 200Hz. Neither of them is any cause for alarm, but they are not subtle and need to be equalized out if the subwoofer is expected to have reasonably flat response! I mean, I like a response that slopes up a little towards the low end, but not 6dB at 70Hz. The out of band thing may be why the extremely high order LPF has been suggested to me twice now. I'd rather just EQ it out and use a lower order filter (I mean, c'mon, 4th order L-R isn't exactly gentle either) so my phase traces line up better between my tops and subs.
That said, since this sub doesn't appear to have a -3dB point at 20Hz, I went ahead and put in the following processing:
- 25Hz 24dB/8ve Linkwitz-Riley HPF
- 30Hz Bell, 0.5 Octave, +3dB
- 70Hz Bell, 0.7 Octave, -6dB
- 193Hz Bell, 0.7 Octave, -8dB
- 90Hz 24dB/8ve Linkwitz-Riley LPF
You can see the final response of the sub, with (red) and without (tan) HPF/LPF, in the picture to the right. Not too bad, I might have put a small boost in around 100Hz and widened up the boost at 30Hz, but I hate to use little tweaky filters and that's totally excellent sub response. I chose to align the subs to my mains dead center at FOH (120' away), and all I needed was 3ms of delay and the phase traces lined up perfectly for over an octave on either side of the crossover point. A system integrator's dream.
I then went ahead and had my left hand man Austin run from the furthest audience position to the closest, and I finished equalizing my line array. Managed to get 14kHz to the back of the stands about 200' away, not at all shabby for 6 boxes hung at a mere 20'. Time for some music.
Good alignment, small power alley, these subs behave exactly as I'd expect. Level wise, these two are definitely enough for this crowd. At no point did I hear them working hard. It was too bright to see the meters on the Lab.Gruppen FP14000 amplifiers, so I have no idea where we were signal wise. Out of the DLP I was sending about as much level as I normally do for subs with 36dB of amp gain, and the Labs are set to 41 IIRC. That doesn't necessarily mean anything, so suffice it to say I had no problems getting plenty of output for the crowd. There is little doubt in my mind that these boxes are extremely loud. Whether that SPL is high relative to their size is something you'll have to decide for yourself, I certainly haven't pushed them hard enough yet to determine that for myself, and I haven't compared them to anything else. At this point I'd feel comfortable taking them out for almost any genre of music for maybe even 4,000 people outdoors, no question about 2K, save really really bass heavy stuff. That is indeed a monster of a sub with monster output.
Even with the enormous horn size, getting in front of these boxes is a visceral experience. They move a lot of air. There is a very small amount of chuffing from the mouth on very high SPL kick hits, certainly not enough that most people with their head 1' away would even notice it, but that should give you an idea of just how much air it moves. The cabinets sound solid, no squeaks or farts that I could hear with moderate abuse. The grille doesn't make any noise, which is a Big Deal™. A little bit of caster rattle but nothing serious, noticeable behind the sub but only a little in front, gone a few feet away. Not unexpected for such a high power box. I know a thing or two about isobaric designs and there is a
lot of pressure in that chamber, not to mention at the horn throat. This thing must be braced to high heaven.
Here's a little video I made of the sub making everything around it respond to the music, the LF is clipping the mic in my iPhone a bit but you can hear that it's pretty clean otherwise. When I bend down to get closer you can hear the AGC in the iPhone kick in and the kit totally goes away. I told my iPhone to upload this in HD, so if you select 720P at the bottom right of the video you can blow it up to full screen and get better audio and video quality. Not that this is exactly scientific!
During soundcheck, more power problems emerged. Midway through the last song of a quick 15 minute check (noise complaints already...) the amps popped their breaker on the PD. That's kind of troubling, since we were by no means pounding the snot out of anything. Each amp has a 30a cord on it, running down 150' of 10AWG wire, attached to a 30 amp breaker. Nothing else on that breaker. During the check you could see the analog voltage meters on the PD ducking on kick hits, and the two legs that had subs on them were drawing over 25 amps during kick hits, whereas the leg that just had monitors, FOH, line array, etc was drawing 5A. That's a lot of current. I normally see 25a per leg with a full monitor rig, twice as many boxes, 12 boxes of big subwoofer, FOH, monitor console, etc. Popping breakers for this kind of show is extremely unexpected, and makes me wonder if we can even drive these subwoofers to their maximum output. I will probably have to enable the peak voltage limiters on the amps next time I try and take these out, can't have them shutting their service down mid-show. Now, to be fair, if the PD meters were ducking on kick hits our power can't have been that solid. I would expect tying into a 480v transformer to be pretty good normally, but there was another 150' of 2/0 cams after that, and who knows how far the service had to travel before it hit the transformer. Another variable to eliminate next show.
I still feel like the sound that comes out of these boxes is a little flat. I've been trying to find a way to describe it, and I think compressed is the best way. It's definitely loud, has good punch, has reasonable definition, but seems like it was run through a mild compressor. Just a little dull, not the end of the world by any means and definitely a reasonable sounding box, but not going to win any awards for sound quality. Whether that matters in the face of bone crushing output is really up to you! Maybe I can get Steve or Jason, who were both with me and spent time making noise through these boxes, to comment on their impressions of the sound quality. I would certainly mix any show on them.
In wrapping up for now, I have no problems agreeing with McCauley that these subs have absolutely huge SPL output. Whether they really do 155dB at 1m is a different matter, I would say they are probably close, verifying that number for real is something I'm not really set up to do. Basing it off other subwoofers I know I don't find it hard to believe.
For such a big box they are also reasonably easy to move around. If deploying them in larger numbers I would definitely want to keep amp racks close, since the speaker cable is enormous. Smaller diameter wire would probably be OK since each pair is only seeing a 4 ohm load with two subs, but it's a lot easier to run 10' of that big ass speaker level cable and an extra 50' of 10/5 attached to L21-30s than it is to run longer speaker cable runs.
As you have seen, however, I have doubts about the LF extension. The processing I ended up with to make them play well is not at all unreasonable, but you can't put in enough boost to make them meet spec. That would be crazy, and cost way too much headroom everywhere. Assuming I don't find out that my shit is all fucked up and my mic happens to take a 6th order dive at 27Hz (unlikely, but I'm open minded) I think the spec sheet does this sub a disservice. The state of the art today is a concert sub that can do a little below 30Hz. There is no doubt that the M421 can achieve that goal, with really only EQ to taste down low.
Claiming that it needs no processing gives it a bad rap, since obviously it needs more than just a HPF and a LPF. I have no problem with that, but being told all along that it didn't need EQ made me wonder if I was going crazy. Claiming such a low -3dB point also hurts the sub, since I was expecting to be absolutely blown away and I wasn't, making me doubt this box from the get go. If the -3dB point had been stated as 29Hz that would have been excellent LF extension regardless, easily verifiable in the field, and being able to do that at the box's claimed output capability is nothing short of impressive. The spec sheet for this product raised my expectations to the level that, when I encountered what is actually excellent in reality, I was disappointed. Change that one number and this becomes a great product in my mind. Yes, the sound quality isn't as good as a few other boxes I know, but it is not bad... just not stellar. How well it behaves even at high SPL is commendable, there are very few subs that can actually perform at high SPL. No qualms there.
Fortunately, it looks like there are plenty of shows coming up where I will be there the entire time, and where it would be appropriate to try this product. I am reasonably comfortable with it now, my only real worry is keeping it turned on under heavy use. Perhaps with the amps in the shade and more solid power to the PD everything will be copacetic. I hope so, because I'd really like to nail these suckers and see what they can do, and especially see if they remain well behaved into clip on the amps. So far I have been pleased with their behavior, they are easy to work with. Even with the unique design they behave just like a traditional front loaded sub, no tricks required. Plug 'em in, apply a little bit of EQ, and get going. I'm sure there will be plenty of interest in these boxes, and I hope to be able to pass them on to another interested party by the end of July so we can get more opinions during summer concert and festival season.
P.S. I think based on this post 16,000 characters is probably a reasonable message size limit from now on
P.P.S. If you want to Test Drive and you think it will be easy, the three posts I have in this thread took me about 5 hours to put together, and that was after taking extra measurements and photos in the field.
To familiarize you, the M421 is an approximately 23"x72"x44" cabinet weighing 486lbs. A beast to be sure, but I was promised it would be an easy two man move. Casters are attached to the rear of the enclosure, generous handles are provided all around, and the sides are covered in "interlocking skids" that appear to be teflon or some other slick composite material. The paint, they call it "weather and wear resistant ProCoat™ polyurea hybrid finish", is excellent... rough, but not so much it takes your skin off. The skids keep most of the wear off the paint, and the finish seems to take a lot of abuse. The damage from the box's trip up from Texas is all chunks of wood removed, not much finish damage.
:lol: 
