tuxedocivic Posted November 29, 2014 Report Share Posted November 29, 2014 Ok, so I accidentally had the drivers out of phase in one of my dual opposed cabs, after rearranging some things. I thought it was a little quiter than normal, but just shrugged it off. Was watching A Good Day to Die Hard and had about 6 or 7 clanks. Pretty hard! Then I began to check things out and found the polarity issue. Basically there was no air spring and they crashed. So I corrected the problem and tried them out. The other DO cabs are totally vibration free, but the problem sub has vibration. On top of that, if I place my fingers on the surrounds, it physically feels like they're moving in the same direction, rather than opposing. So I ran some impedance sweeps. All the drivers measure the same (but look like a passive radiator is in the box, no surprise there) and the DCR resistance is 4.2 on all of them (a little higher than most 4ohm subs, but could be my cheesy multimeter as well). BUT, when I measure both drivers in parralel, they look different. Below is one cab compared to the busted cab. Blue is the busted cab and has an Fb very close to what it would be if there was only one driver in the cab. Orange is the working cab and makes sense for the small size of cab both drivers are in. I can pull the drivers to see what's up. But looking for some feedback before I go through that kind of hassle. Oh and it sounds fine, but I haven't really dug into how it sounds as low frequencies. It may be active like a passive radiator box right now, which makes it sound fine on music. Sorry about the long post. Link to comment Share on other sites More sharing options...
Shredhead Posted November 29, 2014 Report Share Posted November 29, 2014 Oh no! If it was me, I'd take at least one of the drivers out first. It's a good sign that they read the same on the meter but to feel good about them you have to see if they have free range of motion and the bottom of the coil didn't get bent up from bottoming out. While you have one out and can get to them, I'd go ahead and disconnect all the leads and verify that both coils on each driver give the same reading (anal retentive, whatever). I would then connect each driver separately to an amp and use REW's sine wave generator to get the cone moving close to xmax in free air with 10Hz. Needless to say be careful, slowly ramp up the volume. If there is damage causing your "vibration" this will expose the offender(s). When you put them back together, get a 1.5V battery and put positive to positive, negative to negative and verify that both drivers are moving outward when you make contact. I hope they are fine. What kind of drivers are they? Link to comment Share on other sites More sharing options...
tuxedocivic Posted November 30, 2014 Author Report Share Posted November 30, 2014 Hey shred head. I think you're right, just gotta yank them. What bugs me the most, is I can't tell what I've broken on them. I don't hear any rub, but I can't tell very well in the box. I did the battery test and both popped out nice. But I'll try your other suggestions. They're single VC creative sound Trio 12 subs. So getting older and weren't very expensive. If I can find a replacement that's what I'll do, otherwise maybe I'll just go for a couple 18s and start getting serious. 6x 12" does it for me though, so I'm in no hurry to spend lots of money upgrading. Link to comment Share on other sites More sharing options...
tuxedocivic Posted November 30, 2014 Author Report Share Posted November 30, 2014 Ok I think I may have panicked. The vibration was probably me being overly sensitive. Everything measures good. Everything sounds fine. Everything is smooth when I compress the cone. I'll watch some deep bass and check some response measurements. Only thing I can't explain is the difference in impedance when both are hooked up. But I think it may have been an air leak. So I've put some silicone under the driver now and I'll remeasure. Hopefully I've just over reacted, but I'll forever wonder if I did some light damage during those bottom out hits. Link to comment Share on other sites More sharing options...
Shredhead Posted November 30, 2014 Report Share Posted November 30, 2014 Hopefully I've just over reacted, but I'll forever wonder if I did some light damage during those bottom out hits. Sounds like you need to check em'. At least pull the cone up all the way to check and see if the bottom of the coil clears everything. Link to comment Share on other sites More sharing options...
tuxedocivic Posted November 30, 2014 Author Report Share Posted November 30, 2014 Ya I did. They seem fine now that I've pulled them and sealed them better. But I need to run some more tests for sure. Link to comment Share on other sites More sharing options...
MemX Posted November 30, 2014 Report Share Posted November 30, 2014 It just makes you paranoid once you've had a slight issue! Link to comment Share on other sites More sharing options...
tuxedocivic Posted December 1, 2014 Author Report Share Posted December 1, 2014 Exactly. Link to comment Share on other sites More sharing options...
maxmercy Posted December 1, 2014 Report Share Posted December 1, 2014 I know exactly what you mean. Not sure if I had parts just touch or had the MiniDSP clip, but had a similar experience last week testing the system's limits.....scary. You almost start thinking you are smelling 'smoke'. JSS Link to comment Share on other sites More sharing options...
Ricci Posted December 1, 2014 Report Share Posted December 1, 2014 The impedance check is odd. If one driver was blown or not being measured the impedance would look like a PR or vented system with a saddle and second peak but that is not happening. I assume the drivers see a common airspace? One thought that comes to mind is perhaps the triple joint got damaged and the spider has come loose from the former. That would cause the FS to drop on the driver/s substantially since the spider compliance would be removed or diminished at the least. Of course this should also sound bad or at least noticeable though. Might still be worth pulling a driver and investigating. Link to comment Share on other sites More sharing options...
tuxedocivic Posted December 1, 2014 Author Report Share Posted December 1, 2014 Hi Ricci, I appreciate your input. I don't think I explained my results very well. Those impedance plots were two drivers in parallel, blue was the cab I was worried about, orange was a cab I knew to be ok. When I measured both drivers individually, they did have the passive radiator saddle between the peaks. But I didn't post them. I did 4 drivers and they were all similar. I think now that's I've sealed up the cab better and checked everything over, the blue will now measure like the orange. I just have to do it. Maybe tonight if I have time. So what I think happened was: I had the polarity wrong and clanked them. Started trouble shooting and pulled the driver. Reinstalled it with sealant. Found it now sounds right and there's no vibration. I was moving them around and stuff, plus my baffle is only 3/4" mdf and I've had sealing issues in the past. I've now reinforced that baffle so hopefully it'll stay sealed. Admittedly, I didn't build these cabs very well. I'll post the updated impedance results. Tonight I'm watching edge of tomorrow (again) with some friends. Hopefully the bass will be better since one sub was down last time Link to comment Share on other sites More sharing options...
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