Members Mind Riot Posted July 19, 2006 Members Share Posted July 19, 2006 Hello all, I have a few dumb questions that no doubt everybody already knows the answer to but me. I'm using a Carvin DCM150 stereo power amp to power my studio monitors. Recently, I've also impressed it into service powering my 4x12 guitar cab I just got. Unfortunately, it turns out that one of the drivers in the cab is blown. They're 16 ohm speakers currently wired in parallel for a mono 4 ohm load. Until I get a replacement I have a few questions about how I can continue to use this cab. I could leave the blown speaker in the cab disconnected, or take it out and leave the hole. I'm curious as to if there would be any benefit either way, or if it doesn't matter in the slightest. I realize if I left it in it would be functioning as a passive radiator, but I don't know if that means anything with guitar cabs or not. As far as wiring, I could wire two of the remaining speakers in parallel for an 8 ohm load and power them with one channel of the Carvin. Then I could use the other jack in the cab to wire up the third speaker, which would be 16 ohms by itself. So what I'm wondering is, would running the two channels of the power amp at different ohm loads be a bad idea? Or are they independent, and it doesn't really matter? The other question I had was about wiring all three of them together. I know that a lot of the time speakers don't exactly hit their specified ohm rating, and an 8 ohm speaker may in fact be more around 6 something ohms. So if I wired all three of the remaining drivers in parallel for something like 6 ohms, would it be safe given the fact that the amp is safe running into 4 ohms? Or does it have to be right at or around 4 or 8 or whatever else the amp specifies? Also, will it hurt an amp to run at 16 ohms if the technical specs only mention 4 and 8 ohm loads? I'm talking a solid state power amp. Thanks in advance for any information regarding my dumb questions! Link to comment Share on other sites More sharing options...
Members Gregidon Posted July 19, 2006 Members Share Posted July 19, 2006 If all the speakers are wired in parrellel like you say simply disconnecting the broken one will result in a overall impedance of roughtly 5.3 ohms. It looks to me like the Carvin DCM150 can only be safely bridged into loads greater than 8 ohms. Therefore, you simply disconnect the broken speaker and run the cab off one side of the amp. However, the cab is not going to sound the same with a broken driver. Why not simply repair/replace the broken driver? -greg- Edit: It looks like you can bridge this amp into a 4 ohm load, but unless you really need the power this is really rough on the amp. Link to comment Share on other sites More sharing options...
Members Mind Riot Posted July 19, 2006 Author Members Share Posted July 19, 2006 Originally posted by Gregidon If all the speakers are wired in parrellel like you say simply disconnecting the broken one will result in a overall impedance of roughtly 5.3 ohms. It looks to me like the Carvin DCM150 can only be safely bridged into loads greater than 8 ohms. Therefore, you simply disconnect the broken speaker and run the cab off one side of the amp.However, the cab is not going to sound the same with a broken driver. Why not simply repair/replace the broken driver?-greg-Edit: It looks like you can bridge this amp into a 4 ohm load, but unless you really need the power this is really rough on the amp. Right, I wasn't going to bridge it, I was just going to use one side. I will most likely get a replacement sometime soon, but I need the cab now so I need to rig it up somehow for use. So it will be safe to run one side of the amp at 5.3 ohms? And are there any other thoughts about leaving the disconnected speaker in versus removing it? Link to comment Share on other sites More sharing options...
Members Gregidon Posted July 19, 2006 Members Share Posted July 19, 2006 First, yes it's more than okay to run a load with a impedance higher. At least on a solid state (read transistor based amp. It's going lower that's a problem. The issue is that a lower impedance draws more current and can damage components, 'cause overheating etc. So, yes it's fine. A tube amp needs an impedance matched to the load, but that's not an issue with this solid state amp. I'm not sure about the whole removing, vs. leaving speaker in the cab thing. I would assume that it would be better to leave it in as a passive radiator than to add a huge port by removing it. Other opinions?-greg- Link to comment Share on other sites More sharing options...
Members Mind Riot Posted July 19, 2006 Author Members Share Posted July 19, 2006 Originally posted by Gregidon First, yes it's more than okay to run a load with a impedance higher. At least on a solid state (read transistor based amp. It's going lower that's a problem. The issue is that a lower impedance draws more current and can damage components, 'cause overheating etc. So, yes it's fine. A tube amp needs an impedance matched to the load, but that's not an issue with this solid state amp. I'm not sure about the whole removing, vs. leaving speaker in the cab thing. I would assume that it would be better to leave it in as a passive radiator than to add a huge port by removing it. Other opinions? -greg- Thank you very much for your information, it really puts my mind at ease. I'm curious to see what anyone else has to say about the passive radiator possibility before I start putting the cab back together. I kind of get the feeling that it's not going to matter a whole heck of a lot one way or the other, guitar cabs aren't designed with volume or acoustics concerns in mind anyway. But hey, if one way or the other will give a bit more bass response, then why not? Thanks again Greg, I appreciate it. Link to comment Share on other sites More sharing options...
Members Dogoth Posted July 19, 2006 Members Share Posted July 19, 2006 Originally posted by Mind Riot I'm curious to see what anyone else has to say about the passive radiator possibility before I start putting the cab back together. I kind of get the feeling that it's not going to matter a whole heck of a lot one way or the other, guitar cabs aren't designed with volume or acoustics concerns in mind anyway. But hey, if one way or the other will give a bit more bass response, then why not? Thanks again Greg, I appreciate it. Speaker cabs are tuned somewhat (maby not tuned in the traditional sense like a studio monitor but tuned for a specific sound none the less). Leaving the driver in probably would be the best option. I think that opening up a giant port would cause you to loose a lot of low end due to out of phase back wash coming through the hole. unless it's a sealed cabinet I don't think that the passive radiator idea will have much effect but yes I'd leave the speaker in the hole until you can get it replaced or reconed. Link to comment Share on other sites More sharing options...
Members Mind Riot Posted July 19, 2006 Author Members Share Posted July 19, 2006 Originally posted by JRBLE Speaker cabs are tuned somewhat (maby not tuned in the traditional sense like a studio monitor but tuned for a specific sound none the less). Leaving the driver in probably would be the best option. I think that opening up a giant port would cause you to loose a lot of low end due to out of phase back wash coming through the hole. unless it's a sealed cabinet I don't think that the passive radiator idea will have much effect but yes I'd leave the speaker in the hole until you can get it replaced or reconed. Well it doesn't have any ports or anything, but I doubt it's a truly sealed cab. In any case, I guess I'll just run the remaining three in parallel and bolt the fourth back in until I can get a replacement. Thanks again, I really appreciate you both chiming in, made my life a lot easier. Link to comment Share on other sites More sharing options...
Members Keyrick Posted July 19, 2006 Members Share Posted July 19, 2006 Mind Riot, If it is a closed back cab, then I would leave it in until you get a replacement, assuming that all of the speakers are on the same baffle and they are not seperated into their own compartments. If you take it out you will just leave a big port. A closed back cabinet design takes into account which speakers are loaded in it. Since the cabinet is closed, or sealed, it will limit the excursion of the rest of the drivers when you are performing . If you take out the bad speaker and leave a big hole, you take away that ability to limit the cone travel. It's not a big deal if you aren't playing to loud, but since there is a blown driver, well! Go ahead and disconnect the bad speaker, but leave it in to keep the cabinet sealed, to be on the safe side. Good luck. Rick Link to comment Share on other sites More sharing options...
Members Gregidon Posted July 19, 2006 Members Share Posted July 19, 2006 Originally posted by Mind Riot Thank you very much for your information, it really puts my mind at ease. .... Thanks again Greg, I appreciate it. It's always awesome to feel appreciated! -greg- Link to comment Share on other sites More sharing options...
Members mparsons Posted July 19, 2006 Members Share Posted July 19, 2006 Unfortunately, it turns out that one of the drivers in the cab is blown. You need more watts. Look into the DCM4000. Should be what you're looking for. Link to comment Share on other sites More sharing options...
Members Gregidon Posted July 19, 2006 Members Share Posted July 19, 2006 Originally posted by mparsons You need more watts. Look into the DCM4000. Should be what you're looking for. What kind of cabinet is it? What kind of music do you play? These are all questions to ask. 75 Watts may be overkill Also, not to start a Carvin debate (please for the love of God, don't start a Carvin debate), there are better amps out there in that price range if you decide that you need more power. -greg- Link to comment Share on other sites More sharing options...
Members mparsons Posted July 19, 2006 Members Share Posted July 19, 2006 In all seriousness, 75W of solid state power is probably barely cutting it if he has to compete with drums and any kind of stage volume. Link to comment Share on other sites More sharing options...
Members where02190 Posted July 19, 2006 Members Share Posted July 19, 2006 Speaker cabs are tuned somewhat (maby not tuned in the traditional sense like a studio monitor but tuned for a specific sound none the less). Actually they are tuned exactly the same way. It's all the same mathematics whether it's a guitar cab or a studio monitor. Wire them for leave them wired as is, do not remove the blown speaker, and you'll be fine. It won't sound exactly the same, but it'll be close. 75w is more than enough power to push a 4x12, or in this case a 3x12 to a very loud volume. Link to comment Share on other sites More sharing options...
Members Gregidon Posted July 19, 2006 Members Share Posted July 19, 2006 Originally posted by mparsons In all seriousness, 75W of solid state power is probably barely cutting it if he has to compete with drums and any kind of stage volume. Also, he didn't really mention needing more power... just saying... to stay on the origional question....-greg- Link to comment Share on other sites More sharing options...
Members Mind Riot Posted July 19, 2006 Author Members Share Posted July 19, 2006 I'm not sure if I'll need more power. I just got this cab used a few days ago, and the driver was blown when it arrived. I don't think I've ever personally blown a speaker myself. I don't want to get into a Carvin debate either, I've just had this amp for a few years and it's served me well. But if I ever end up needing a new amp, I'm going to go for something from the QSC RMX line. I'm kind of optimistic that it will provide enough volume, but I'll just have to see when I jam with a drummer friend this weekend. The speakers are Eminence Legend M12's, which are among the more efficient guitar drivers out there. 102 db at 1w/1m. I have to say, they seem quite absurdly loud with very little power. I play hard rock and metal with a seven string, but I don't use as much bottom end as a lot of guitarists seem to. I come from more of a recording background, so I'm not the type to use a scooped EQ curve. It's all mids, with a bit of tight low end. Unfortunately, since I last posted I was working on the wiring in the cab and it seems that leaving the blown driver in there might not work. The cab came wired with some quite thin solid copper wire, and I noticed it was shorting in spots when I had the back off of it. So I rewired the cab with 14 guage stranded speaker wire and crimp on connectors. I then clamped the blown driver back in and put the back panel back on without screwing it in (it's a tight fit and stays put just fine). I played through the cab, and even at low volume the blown driver makes a nasty buzzing noise, I assume in sympathetic vibration with the other drivers. I do have a Celestion G12H-80 laying around that I could throw in there unconnected until I get a replacement, and that may be what I end up having to do until I get another M12. Link to comment Share on other sites More sharing options...
Members Gregidon Posted July 19, 2006 Members Share Posted July 19, 2006 Originally posted by Mind Riot Unfortunately, since I last posted I was working on the wiring in the cab and it seems that leaving the blown driver in there might not work. The cab came wired with some quite thin solid copper wire, and I noticed it was shorting in spots when I had the back off of it. So I rewired the cab with 14 guage stranded speaker wire and crimp on connectors. I then clamped the blown driver back in and put the back panel back on without screwing it in (it's a tight fit and stays put just fine). I played through the cab, and even at low volume the blown driver makes a nasty buzzing noise, I assume in sympathetic vibration with the other drivers. I do have a Celestion G12H-80 laying around that I could throw in there unconnected until I get a replacement, and that may be what I end up having to do until I get another M12. That's rough, let us know how it works out!-greg- Link to comment Share on other sites More sharing options...
Members mparsons Posted July 19, 2006 Members Share Posted July 19, 2006 With speaker sensitivity like that you're going to be good to go. Is the G12H-80 a Classic Lead 80? If so, those are my favorite guitar speaker. Very clear, punchy, and articulate. Good to see another metalhead too Link to comment Share on other sites More sharing options...
Members where02190 Posted July 19, 2006 Members Share Posted July 19, 2006 The cone is propably separated from the surround, and is rattling. Since the speaker is trashed anyway, simply put some gaff tape where they are separated to keep it from rattling. Link to comment Share on other sites More sharing options...
Members agedhorse Posted July 19, 2006 Members Share Posted July 19, 2006 Thin looking wire is NOT a problem for a guitar cabinet. It's a low power application and if you look at the wire of the VC, it's probably around awg 32 or so!!! 18 gauge is overkill. Link to comment Share on other sites More sharing options...
Members Mind Riot Posted July 19, 2006 Author Members Share Posted July 19, 2006 Originally posted by where02190 The cone is propably separated from the surround, and is rattling. Since the speaker is trashed anyway, simply put some gaff tape where they are separated to keep it from rattling. It doesn't seem to be, the buzzing seems to be coming from the voice coil. I think I might just stuff some foam into the basket to keep the cone from moving at all, at least then the cab will still be sealed. I'm going to try it today, I'll post again with some results. Link to comment Share on other sites More sharing options...
Members Mind Riot Posted July 19, 2006 Author Members Share Posted July 19, 2006 Originally posted by mparsons With speaker sensitivity like that you're going to be good to go. Is the G12H-80 a Classic Lead 80? If so, those are my favorite guitar speaker. Very clear, punchy, and articulate. Good to see another metalhead too They say it's very similar to the CL80, with slightly less bass and a bit of extended high end. I had it in a 2x12 cab with the other stock speaker for a while, then gave the cab to a friend but pulled the G12H-80. It was a great speaker, sounded fantastic. Now it's been sitting in my closet for over two years. But I think I'll try the foam and see how that works. The G12H-80 has a sensitivity rating of 99 db at 1w/1m, so unless I wired it up to the second jack all by itself it would always be lagging 3 db behind the other drivers. I may just have to sell it one of these days. Link to comment Share on other sites More sharing options...
Members Mind Riot Posted July 19, 2006 Author Members Share Posted July 19, 2006 Originally posted by agedhorse Thin looking wire is NOT a problem for a guitar cabinet. It's a low power application and if you look at the wire of the VC, it's probably around awg 32 or so!!! 18 gauge is overkill. Ironically enough, the short I was hearing turned out to be one bad solder joint that had come loose at the input jack. The solid core wire was still hooked through the hole in the terminal, but it was just loose and moving around in there. In any case, it's done now, I already rewired it. Makes me feel more comfortable in any case, the wire that came with it was pretty brittle and old looking. Link to comment Share on other sites More sharing options...
Members Mind Riot Posted July 19, 2006 Author Members Share Posted July 19, 2006 Just in case anyone was curious about what this thing looks like, here are some pics. It's butt ugly and beat up, but I did get it off ebay for $76. Shipping and insurance was a bit more than the actual price, but even so the grand total was only $157.50 so I'm not complaining even with the problems I'm having. You can't even get a good empty cab for that much, and this one still has three good drivers. Anyway, here's the cab by itself, with my guitar in front, and with my cat Gabby licking herself and posing on top of it. Here's the old wire from the cab, and the new wiring I did. It may be overkill, but I've had the wire sitting around for a long time, thought I'd use it. Link to comment Share on other sites More sharing options...
Members Mind Riot Posted July 19, 2006 Author Members Share Posted July 19, 2006 UPDATE: Well, I stuffed some seat cushion foam into the basket of the bad driver in an effort to keep the cone from moving, and it was still noisy in the cab. Rather than use tape, foam, Saran Wrap and all other manner of methods to keep the damn thing from buzzing I just decided to yank it out and put in the Celestion G12H-80. I was originally thinking of just leaving it in there unconnected to fill the hole, but once I bolted it in I was sitting there looking at it and thinking it really was a shame to just have it sitting there doing nothing. If I wired it in parallel with the other three speakers it would put the overall impedance of the cab below 4 ohms. If I wired two of the original drivers together and the Celestion and one of the original three, I'd have a stereo cab with one 8 ohm side and one what, 6 ohm side (16 ohm original in parallel with the 8 ohm Celestion)? But even if that would work, the difference in efficiency between the drivers would mean that the Celestion would always be 3 db quieter than the Eminence drivers, regardless of input power. So I decided that since the Celestion is the anomaly in the cab, I might as well set things up to where I can control it separately from all the rest. The cab has two jacks, which I just connected typically for daisy chaining, but honestly I don't see myself needing more than one 4x12 cab anytime soon. So I spliced the wire from the second jack to another bit of wire to connect it to the Celestion only. (I decided not to resolder the jack terminals since I don't have a solder sucker and I looped the strands through the holes for a stronger mechanical connection; it would be a nightmare to unsolder it.) I sealed the splicing with heat shrink tubing and used crimp connectors again to connect to the Celestion. So now I have the three original drivers connected in parallel to one jack for a 5.3 ohm load, and the Celestion connected to the other jack for an 8 ohm load. I can use both channels of my power amp to balance them out, and if I want to do some recording or just jam a little more quietly I can just use the Celestion by itself. (But just to be sure, it is okay to run the two channels of the power amp into different ohm loads, isn't it?) Thanks for everybody's help and advice, the cab sounds great now and there's no more annoying buzzing from the bad driver. I snapped a quick pic of what I hope is the final wiring setup for now. Link to comment Share on other sites More sharing options...
Members agedhorse Posted July 20, 2006 Members Share Posted July 20, 2006 Beware thatthe heavy wire doesn't put too much pressure on the terminal boards, it can break the boards, or twist the board atthe rivet causing damage to the drivers. The yellow spades are for #12-#10 gauge wire, look at some blue ones if you are going to stick with 14. Link to comment Share on other sites More sharing options...
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