unclej Posted February 16, 2005 Report Share Posted February 16, 2005 allright, one of the guitar instructors that teaches at my shop brought me a question that he thought i should be able to answer.. but i can't.. he's got a powered mixer that puts out a bazillion watts per channel at 4 ohms blah, blah, blah. he's using two 500w 8 ohm EV cabs and doesn't think they're loud enough. he wants to know what would happen if he changed the wiring from parallel to series or vice versa depending on how they're wired now. so during the discussion i finally said that i thought there were too many unknowns and too many variables for either of us to come up with an answer...so here's the hypothetical that i need to start with: take a 12", 50 watt, 4ohm speaker and plug it into the 4 ohm output of an amp with 4 and 8 ohm outputs..then take a 12", 50 watt 8 ohm speaker and plug it into the 8 ohm output of the same amp set on the same settings..which speaker is going to be the loudest? second question...will a 10", 75 watt, 8 ohm speaker be as loud as a 12", 75 watt, 8 ohm with similar magnets? Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 16, 2005 Report Share Posted February 16, 2005 The amp will put out more power when driving a lower impedance load, so if he can rewire his cabs to 4 ohms, he'll get a little more output - the problem is that doubling the wattage only produces a small change in perceived loudness, so he may not even notice. So far as comparing speakers by magnet size and diameter, fuggedaboudit! Depending on construction and materials, a 10" with a 16 oz magnet could easily be more efficient than a 12' with a 32 oz magnet. Rely on the manufacturer's published specs for efficiency and frequency response info. There are too many "sheep in wolves clothing" drivers out there that look massive but don't put out. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 16, 2005 Report Share Posted February 16, 2005 (edited) double post Edited February 17, 2005 by lovekraft Quote Link to comment Share on other sites More sharing options...
silvertonessuckbutigotone Posted February 16, 2005 Report Share Posted February 16, 2005 so a 3.5 inch speaker that can handle 150 watts would sounds as good as a 12 inch that could handle 150 watts at high volumes? Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 16, 2005 Report Share Posted February 16, 2005 (edited) First of all, "sounds as good as" is completely subjective - it's meaningless except in a personal context. A 3.5" speaker is going to tend to have less bass response than a 12" speaker simply because of the difference in cone area. It could, however, be more efficient and cleaner in it's midrange response. I get the feeling that question was posted simply to get a reply. But since only simpletons and mad geniuses are likely to be using a 3.5" speaker in a guitar amp, it's not really relevant to this discussion - let's confine ourselves to the common sizes used in commercial amps. In the range of 10", 12" and 15" speakers available, there's a wide spread in efficiency, power handling and frequency response. If you're playing a standard tuned guitar, the only frequencies that hold much interest are between 80Hz and about 6KHz (drop that range by about 25Hz if you're a Meshuggah tribute band ), so any specs outside of that range are at best unrelated, and too much treble response can make a speaker sound harsh or shrill. Since most well-built speakers in the size range specified perform at least toleraby over that frequency range, the efficiency becomes pretty important. A great-sounding speaker with a 96dBm efficiency simply will not compete with a 101dBm speaker with the same response, regardless of what size either speaker is. Edited February 16, 2005 by lovekraft Quote Link to comment Share on other sites More sharing options...
Jester700 Posted February 17, 2005 Report Share Posted February 17, 2005 lovekraft hit the nail on the head. The one spec you missed in the first post was the important one - efficiency. Basically, when you double the amp power into a speaker, you increase output by 3dB. So going from a 96dB speaker (usually measured on axis, 1 meter away, i watt input) to a 102dB one would be like quadrupling your amp power. As a rough guide, 10dB is usually considered "twice as loud", so that 6dB is a good bit of difference. Quote Link to comment Share on other sites More sharing options...
unclej Posted February 17, 2005 Author Report Share Posted February 17, 2005 The one spec you missed in the first post was the important one - efficiency. i didn't actually miss it so much as avoid it. i told the guy that i'm having this discussion with that there were too many variables to come up with a definitive answer so basically i was looking for what lk said at the beginning of his answer..re-wiring to 4 ohms will give a little more power which is what i thought except i forgot about the perceived loudness factor. my friend is a performing musician using a mackie 808m power mixer through two 8 ohm cabinets that didn't come with the mixer and he doesn't think they're loud enough. so my answer to him is going to be bring me a cabinet and let's look inside to see how they're wired. thanks as always for the input. Quote Link to comment Share on other sites More sharing options...
silvertonessuckbutigotone Posted February 18, 2005 Report Share Posted February 18, 2005 (edited) actually, I was kind of wanting to know the answer because i have seen speakers that are 3.5 inches wide and can handle 150 watts online, and it would be interesting to have a cabinet as loud as a fairly large combo amp, and the answer I was seeking (should have been more specific, I didn't mean AS GOOD i meant its response range) was answered and thats what I thought when I initially saw the speaker and it would be cool too have a small cab like that. btw, what is a good frequency responce range to look for in speakers (in Hz/kHz) Edited February 18, 2005 by silvertonessuckbutigotone Quote Link to comment Share on other sites More sharing options...
thomasteven Posted February 18, 2005 Report Share Posted February 18, 2005 I don't think that the 3.5 inch speakers would be as "loud" as a 4x12" because sound waves are from moving air, and a bigger speaker would move more air, right? Maybe a LOT of 3.5" speakers would be as "loud" as a 4x12" but I'd say that it would take a good few. The 12" speakers would also have a beefier basier tone than the 3.5 inch speakers, they would be good for the high frequencie range, but I wouldn't rely on them if your playing rhythm. Quote Link to comment Share on other sites More sharing options...
unclej Posted February 18, 2005 Author Report Share Posted February 18, 2005 have you ever looked into "hot spots" silvertone? they're small cabs with two speakers. i've got one that i use for a monitor in small venues when working solo or duet. not quite loud enough when you've got a full band but they have a pretty good frequency response. there are two 4" speakers with some big as*** magnets on them. if you're looking to use them as mains they might be a little wimpy. but hang tight. this employee i've been talking about is going to buy another one and then we're going to play with wiring them together and see what we get. i'll try to remember to let you all know the results. Quote Link to comment Share on other sites More sharing options...
Jester700 Posted February 18, 2005 Report Share Posted February 18, 2005 A 3.5" speaker will not handle 150W over the entire audio range. You feed a 150W 80Hz signal to that and it's toast. It was probably measured at 1k or some such single frequency, which means nothing. A guitar's low E is about 80Hz, so you want to cover that (and maybe lower). A 12" speaker does this well, and so can a 10" if it's designed to. Smaller than that and you usually start to get some rolloff. But it also greatly depends on the cabinet and how it's made - closed, open back, or ported. The highs are REALLY muted by all these speakers because there's no tweeter - just a relatively big woofer that doesn't reach very high. That's why one big effect of modelers' "cabinet sims" is to suck out a lot of highs. Even beyond amount of bass, small speakers & cabinets aren't generally as efficient as big ones. It sounds counterintuitive, but you can actually get by with SMALLER amps if you use big, efficient cabinets. As for rewiring cabs to decrease impedance & increase wattage: be careful. IF the amp isn't rated to drive the impedance you end up with, it can heat up beyond its design. That can trip thermal protection, blow fuses, or at worst toast the amp. So make sure the Mackie is OK with 4 ohms. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 18, 2005 Report Share Posted February 18, 2005 The caution about impedance is a good idea, and should be mentioned - that said, I've never seen a piece of Mackie power equipment that wouldn't handle a 4 ohm load. Most pro audio power amps are rated to at least 4, and often 2 ohms, simply because they're often asked to drive multiple cabinets in parallel. But definitely don't slap a 2 ohm load on your blackface Twin - it will fry! Quote Link to comment Share on other sites More sharing options...
silvertonessuckbutigotone Posted February 19, 2005 Report Share Posted February 19, 2005 as far as i understand you need a cabinet with the same/higher impedence as the amp? i think thats what it was. Quote Link to comment Share on other sites More sharing options...
Maiden69 Posted February 19, 2005 Report Share Posted February 19, 2005 One thing I think that was overlooked, (unless I overlooked it my self) is that your teacher 1st need to make sure that the mixer can handle the lower resistance. If it is rated at 8 ohms, and you run it at 4 it will get so hot you could fry eggs on it. I seen a few amps solder joints melt because of wrong impedance match, some guys running as low as 1 ohm on an 4 ohm rated amp. HTat said, all I usualy care or look for is that at the end the amp overpowers the speaker load, even if just by a bit, that will keep them in the sweet spot and the efficiency will be better, you won't be able to "move" a cone efficiently if you don't use enough power. Quote Link to comment Share on other sites More sharing options...
silvertonessuckbutigotone Posted February 19, 2005 Report Share Posted February 19, 2005 (edited) (unless I overlooked it my self) you did overlook it check post #12 of this thread: http://projectguitar.ibforums.com/index.ph...ndpost&p=172090 Edited February 19, 2005 by silvertonessuckbutigotone Quote Link to comment Share on other sites More sharing options...
unclej Posted February 19, 2005 Author Report Share Posted February 19, 2005 no, it definitely wasn't overlooked. it's rated at x number of watts at 4 ohms. now, since this thread hasn't died let me ask another question. i just ordered all of the parts to make my first tube amp. basically a champ with a couple of mods. the plans call for an 8" 4 ohm speaker. i've found that i can get two jenson alnico 8" 8 ohm speakers from one wholesaler for the same price that i would pay for the one 4 ohm at another. all of the speakers are from their vintage line..all with very, very similar specs: 25 watts rated power, same voice coil diameter, magnet weight very close, etc. so is there any reason not to put the two eights in running them parallel for the 4 ohm load and what would be the audible difference between the two setups? Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 19, 2005 Report Share Posted February 19, 2005 No reason whatsoever - it'll be a little louder, amd probably have a little more bass response, but just between you and me, I'd make the cabinet just a wee bit larger and use 10"s instead of those 8"s. To my ear, those Jensen 8"s have a serious Japanese portable transistor radio, ca. '64 vibe, and can make even great amps sound cheap and cheesy. Quote Link to comment Share on other sites More sharing options...
unclej Posted February 19, 2005 Author Report Share Posted February 19, 2005 will a little amp using a 6v6gt be able to push two tens ok? Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 19, 2005 Report Share Posted February 19, 2005 Yeah, no problem - heck, a push-pull 12AU7 will drive a Marshall 4-12 cabinet! You won't be beating them to death, but a Champ isn't exactly a fire-breathin' high-gain monster, so you don't want the speakers to break up much, even at full tilt blues crunch. BTW, unless you're absolutely sold on that Champ, take a look at the 5F2 Princeton project on Angela's website - it's dead simple, and loaded with old-school blues mojo! Quote Link to comment Share on other sites More sharing options...
Maiden69 Posted February 19, 2005 Report Share Posted February 19, 2005 Yes I did, can't belive this I usualy read all lovekraft replys and I completely over looked this one! Quote Link to comment Share on other sites More sharing options...
unclej Posted February 19, 2005 Author Report Share Posted February 19, 2005 yeah, i saw that one but i'm making this one at someone's request. if all goes well i'm actually thinking about making the super single-ended 6v6 on the angela site and then jump into a relatively simple push/pull project. depends on whether or not i have any sanity left after this first one. edited to say that the other reason for sticking with the champ is that all of the parts are already on the way. Quote Link to comment Share on other sites More sharing options...
silvertonessuckbutigotone Posted February 19, 2005 Report Share Posted February 19, 2005 isn't it possible to blow speakers if the wattage level is TOO much higher than what they can handle? Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 19, 2005 Report Share Posted February 19, 2005 (edited) Well, yeah!! However, you don't want to drive a 500 watt PA cabinet with a 50 watt amp, either - that has its own set of problems! In practice, if your amp is within a +5/-20% range of the speaker's rating, and you don't run the power amp into hard clipping, you're probably safe - start clipping the power amp regularly, and you should expect to replace speakers early and often. Edited February 19, 2005 by lovekraft Quote Link to comment Share on other sites More sharing options...
silvertonessuckbutigotone Posted February 19, 2005 Report Share Posted February 19, 2005 thats about the ratio that I was thinking but when maiden posted his comment at the end the amp overpowers the speaker load, even if just by a bit, and what confused me was the "EVEN if just by a bit" so i thought he meant that a lot over the speakers rating was preferable/acceptable. Thanks for clearing it up LK. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 20, 2005 Report Share Posted February 20, 2005 OK - I thought Maiden's post was pretty clear, but if that helped, that's great! Quote Link to comment Share on other sites More sharing options...
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