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Speaker Cab Question

Discussion in 'Recording' started by Guitarfreak, Oct 11, 2009.

  1. Guitarfreak

    Guitarfreak Well-Known Member

    I either just had an epiphany or an incredibly stupid thought, you decide. The premise is the reason which sparked the thought so read that for understanding first.

    Premise: When running a tube head into a cab, the speaker wattages must ADD UP to at least the output RMS wattage of the head itself.

    So at this point we can see that there is some kind of summing factor where it is not the individual speakers that matters but the combined total. And this may also mean that each individual speaker is somehow affected by the ones around it in a passive way.


    Question: If you had a 4x12 cab loaded with Vintage 30 speakers, would the individual speakers sound or respond differently than if you had the same 4x12 cab with two Vintage 30's and two of a different kind of speaker? Say for example the G12T75, which is a 75 watt speaker with a different frequency response curve.
     
  2. MrEase

    MrEase Active Member

    Once you start mixing up speakers you will certainly change the overall sound but you should also be aware your initial premise is not correct. It only works if all the speakers have the same power handling.

    To take your example and let's assume all the speakers are 8 Ohm. If you wire the two G12T75's in series and the two Vintage 30's in series (each brach is 16 Ohm) you would then parallel them to get the correct 8 Ohm overall impedance. Power handling would be 4 times the lowest rated speaker though. Why? Well in this case the two Vintage 30's could handle 30 watts each, in series, they can handle 60 watts. The G12T75's could handle 150 watts BUT at the voltage required to do that, you will be substantially overdriving (i.e. blowing up) the Vintage 30's.

    So power handling of 4 Vintage 30's is 120W (your head should not really be much more powerful than this) BUT the power handling of 2 Vintage 30's and 2 G12T75's is ALSO 120W.

    Things are even more complex if the speaker impedances are not all the same!

    Things do not improve whatever wiring you do i.e. wiring one vintage 30 in series with a G12T75. In fact this may change the sound yet again as speakers do not have a constant impedance with frequency so you may get some odd (but maybe desireable!) colouration by doing this.
     
  3. Guitarfreak

    Guitarfreak Well-Known Member

    That's a lot to think about. I thought Vintage 30's could handle 60w of power, this is quoting the Celestion website.

    http://professional.celestion.com/guitar/products/classic/spec.asp?ID=4

    Also, I meant would the V30's sound different if they were close miked (nothing more than the slight variations from speaker to speaker right?). What I got from your post was that as long as we are saying 'X' is two V30's wired in series and 'Y' is two G12T-75's wired in series and 'X' and 'Y' were wired in parallel then there should be no difference. Correct?
     
  4. Davedog

    Davedog Distinguished Member

    Its not as simple as stating that one speakers impedance is the same as anothers speakers impedance even though the label says they are the same. The same applies to load handling.

    A speakers impedance is not a constant when its being used. Different frequencies cause the impedance to change. Different speakers 'move' or extrude during usage and this also causes changes in the impedance as well as the abilty to handle wattage. What happens in most cases, one speaker....say a 30 watt rated speaker will move through the coil a certain amount at certain frequencies for a certain amount of time. There is, unfortunately, no standard for the manufacturers to adhere to to arrive at these values, so one mans 30 watter is another mans 60 watter. Higher rated speakers tend to be coned a little tighter and have a few more winds in the voice coil. Some will arrive at the rating simply by the type of magnetic material and its ability to shunt heat.

    One thing you need to be aware of when mixing speakers is the speed of their rection to signal. Some are a bit slower and when mixed with a 'fast' speaker can either sound a bit blurry, or give you the best sound you've ever heard simply by chance. But similar is always best.
     
  5. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    Usually the lower power rated speaker may tend to sound louder than the higher power one. For instance, a pair of 25W Greenbacks may be screaming at the top of their lungs while a pair of paralleled 60W V30s may be cruising in its middle ground. Since four Greenbacks are often used in 100W Marshall cabs, you should be OK, since part of that power is going to the V30's, instead of to a couple other Greenbacks. (25W x 4 =100W). You definitely do NOT want to put any lesser rated speakers that combine to much less power handling than than the head you are pumping into them...unless you are really careful. You may not want to run a Marshall Major into one 100W cab.

    The speaker types' efficiencies must also be taken into account when deciding which will stand out more..

    There will definitely be a different sound when mixing different speakers. Some amps even come with dissimilar speakers. Experiment and see. Just be careful with the wiring, and check, and doublecheck....and then check again...the wiring and impedance before connecting to some heads, especially Marshalls. They do NOT like wrong impedance settings.

    Kapt.Krunch
     
  6. Guitarfreak

    Guitarfreak Well-Known Member

    I've been kind of turned off to the idea of mixing speakers. I was liking the idea of a Marshall 1960AV 4x12 which has 4 Vintage 30's but it's so damn expensive. I may go with an Avatar 2x12 with two V30's. The wattage adds up to a perfect 120w which is what the head I am looking at is, so that's an added bonus. It'll only run me a good $429 + shipping as opposed to $949 for the Marshall cab.

    Now the next part is up to personal preference as far as I know, but I have no preference really. The head that I am ultimately going to get is going to be the Peavey 6505+ and it has switchable 4/8/16 impedance so that opens me up to a few possibilities. The V30's come in either 8Ohm or 16Ohm.

    I can have them wired parallel:

    2 8Ohm speakers = 4Ohms so I'd run the amp at 4
    2 16Ohm speakers = 8Ohms so I'd run the amp at 8

    Or I can have them wired in series:

    2 8Ohm speakers = 16 Ohms so I'd run the amp at 16

    At this point I think I would rather have them wired in parallel to keep each channel separate. I will most likely go with 16 Ohm speakers, no reason really, but I'd rather run the amp at 8 vs 4 since I've got the choice anyway right? Unless there is a good reason to run it at 4.
     
  7. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Some of the BEST tones have come from 2 different speakers mounted in 1 cab, don't let that spook you. That's why Avatar offers that option. If you go with 1 of their cabs, be sure not to get the less-expensive "traditional" model; pop for the Vintage or Contemporary. They both use 'T'-nuts to mount the speakers (rather than simple screws), and this will facilitate things if and when you want to experiment with swapping out speakers.
    Also, be careful choosing a Peavey amp. They had QC issues when they were made in the States (I used to work for them as well as for a dealer), and now they're made in China.
     
  8. Guitarfreak

    Guitarfreak Well-Known Member

    :D Thanks man. I guess I wouldn't mind putting two different speakers in there. The main reason for wanting to do this in the first place is to get a few different recorded sounds. I think the G12T-75 would sound great mic'd with my SM57 and the Vintage 30 would sound just lovely mic'd with my Audix i5. Same price so what the hell why not :cool:

    I actually had the Contemporary cab in mind. Thicker woods and better construction supposedly. I'm up for a gimmick as much as the next guy :D

    As for the Peavey amps, like what do you mean QC issues. Are we talking about bad tubes or scratch & dent or something more serious. And how would one know if there was a problem. Would it be a pretty obvious problem or something that only the meters from the guys at QA would detect? Not that it matters, I trust you either way. I'd assume it would be covered under warranty correct?
     
  9. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    Yep, kinda hard to find deals in pawnshops anymore like we used to. I found a vertical input early 80's JCM800 2203 100W w/6550's in one about 8 years ago for $325. It's my main amp, now...and I play funky-bluesy-rock.

    Then I went in a few months later to the same pawn shop, and they had a pair of Marshall cabs. A mint 1960AV with the V30's, and an old battered to death one with the Greenbacks. They wanted $350 for the Greenback one, and $275 for the 1960AV one. I bought the 1960AV.

    But, I can't seem to get that cab to sound good with what I'm playing. There's nothing wrong with it, it's like new. It just doesn't seem to get any bite, and sounds kinda dark. I've heard that about V30's, and the amp having 6550's instead of EL34's may have something to do with it also. That cab actually sounds better with my BF Bandmaster for some reason.

    So, I'm now using a vertical 2x12 Mesa Boogie cab with a pair of EVM12L speakers. I got that one cheap, also, and another pawn shop in Denver had no idea what they had. All I had to do was look at the cab, see the "EV" on the speakers, and I knew it was worth $85. Some kid had painted the wire grill with green, brown and black paint to look like camouflage. Then, they took black and white paint to the nameplate to spell "Messy Booger". A good washing in the tub took that paint right off, right down to the "Mesa Boogie", and then I repainted the grill black. A good deal, I think. I believe that cab's EV speakers put some sparkle in that the Marshall's V30's were lacking.

    Anyway, back to the subject...I agree with Monnbaby. Nuthin' wrong with trying dissimilar speakers as long as you pay attention to impedances and total power ratings vs. the amp power.

    And about 4,8, or 16 ohm total load? 8 would be a good all-around useful total load, because a LOT of amps will use 8. You may want to avoid 16 ohm total, because that may cut your amp choice, and I find 16 sounds a bit "stiffer" anyway. 4 Ohms may be alright, also. The less the total load an amp is capable of, the more the amp will put through of its useful power if you use that. It depends on the amps you plan to use, and/or may want to acquire soon.

    Just know what you're doing...or find out. :wink:

    Kapt.Krunch
     
  10. Guitarfreak

    Guitarfreak Well-Known Member

    So operating at lower resistance levels would actually have an effect on the tone of the amp? Or at least theoretically? I have heard of this theory a few times but haven't the first hand experience yet to back it up.

    I was just brainstorming on the situation again and I think this is a good idea. Avatar 2x12 - 1x Vintage 30, 1x G12T-75, both 8 Ohm.

    I could use both of them wired in parallel and set to operate at 4 Ohm or disconnect one speaker and operate at 8 Ohm and see if there is any audible difference on record when close miked. Solid idea right? Short of the fact that having a 120w amp pounding through a single 60w or 75w speaker is a little shoddy in theory (at least to some).
     
  11. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    Resistance is a component of impedance. Lower impedance will allow more current from the amp. So, yes, it'll change the characteristics of the amp, which will cause a difference in sound. Be careful. Too low for any particular amp can cause trouble.

    You can run a higher-powered amp through a lower-rated speaker. You just have to be careful. I wouldn't do it for a regular, every day setup, because it leaves too much chance that eventually, something will mistakenly get cranked too much and blow the speaker, the amp...or both.
    Being cognizant of the setup while in a recording situation, and vigilant in keeping others from messing with the thing may be OK, but I wouldn't leave it plugged in afterward.

    Kapt.Krunch
     
  12. MrEase

    MrEase Active Member

    While that is true if you use say a solid state amp. if you are using a valve (sorry, tube) amp so long as you set the transformer output impedance correctly it is only the load on the transformer that varies. The valves (tubes) will have (almost) the same loading so tone should not be greatly affected as it is only a function of the transformer.

    BTW: Sorry I stated 30 Watts for the V30's - I was running from an erratic memory!
     
  13. jg49

    jg49 Well-Known Member

    Mrease "BTW: Sorry I stated 30 Watts for the V30's - I was running from an erratic memory!"

    Run chkdsc and defrag, then reboot, should straighten out something.
     
  14. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    And then the transformer acts a bit differently depending on the impedance settings, if it has any. A Marshall has a 4/8/16 ohm switch to choose which secondary coil tap of the OT to use. 16 ohms has more windings than 8, which has more than 4. Just a different setting may cause a bit of a difference, even if there were such a thing as a certain type speaker offered in different impedances that would sound exactly the same just by switching the impedance switch to match each's impedance. So, the OT will probably react differently, and may "sag" earlier at one setting than another even given those hypothetical perfectly-matched at different impedance speakers.

    On some amps with no impedance switch, you may be able to safely go one step up or down on say, and 8-ohm amp. (HUH? An "Extension Speaker" jack...and no impedance switch?) You don't want to put 2 ohms on a 4 ohm output, normally, unless it was designed to. So, 16 or 4 may even work OK, and it will sound different. Some amps can take a bit of that. Marshalls don't like it at all.

    So, mismatching some amps that are able to do so will change the characteristics, and changing the impedance switch will change the characteristics of the OT. Even if it didn't, just having a different speaker will change the sound a bit.

    Anything that changes anything else will change the sound in some way.

    Kapt.Krunch
     
  15. Guitarfreak

    Guitarfreak Well-Known Member

    The only thing I am worried about is if there is some weirdness to the sound like being out of phase with eachother. I don't know much about speaker physics, but you know how speakers of different wattages will equalize and sum at the lowest wattage? Does this go for speaker cycle time too (not sure what to call it, the time it takes for the speaker to complete one back and forth motion).

    Take this hypothetical situation. You have one speaker that cycles at a rate of 1KHz and the other cycles at 2KHz. There are two things that can happen. Either the faster speaker equalizes with the slower speaker and they complete their cycles in unison summing eachother without cancelling any frequencies. OR. The faster speaker would continue to cycle at 2KHz and there would be some audible phase cancellation.

    I am still waiting for Celestion to get back to me, but if there is going to be any sort of problem like the one described above then I might have to reconsider the finer details.
     
  16. Kapt.Krunch

    Kapt.Krunch Well-Known Member

    Guitar speakers are fairly stiff, unlike PA or bass speakers which have a lot of excursion.

    1KHz going to one should be the same 1KHz going to the other. As long as they are connected in the proper polarity, they shouldn't really phase. Even with a bit of difference, the differences may just cause more smoothness at the frequencies of a guitar. They make amps with 10" and 12" speakers connected. The natural responses of each compliment each other. Electric guitars are usually not supposed to be pristine, hi-fi. Even clean country twang can benefit from a bit of intended "roundness".

    Kapt.Krunch
     
  17. MrEase

    MrEase Active Member

    I fully understand what you are saying here but I'm not sure you appreciated what I was trying to say. I did say that provided the output tapping is correctly matched to the speaker, any sound change "is only a function of the transformer". In other words the load on the output valves will not change significantly and this would be a MUCH larger factor on the "sound".

    Changing the output taps to accomodate various speaker loads (to maintain the anode loads on the output valves) will NOT have a great impact on the tone as the predominant factor in the output transformer "tone" is the primary winding and the interwinding capacitance which do not change with the tap selected. This is not to say that the characteristic of the speakers themselves won't be different as the voice coil inductances and capacitance will be different for the same speaker design with 4, 8 or 16 Ohm windings.

    Loading on solid state amplifiers is another issue altogether but suffice to say the vast majority of bipolar transistor designs will not even drive 4 Ohms well unless they are paralleled as their gain droops at high current and consequently overload the driver stages. An output stage designed properly to drive 4 Ohms will handle a 2 Ohm load just as well as a stage designed to drive 8 will drive 4.
     

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