thrashncrust Posted December 31, 2004 Report Share Posted December 31, 2004 ok, im about to start building my cabinet , i have 3 speakers, 1x15 and 2x12's all 8 ohms. if i wire this all in parallel how many ohms will i have? Quote Link to comment Share on other sites More sharing options...
Drak Posted December 31, 2004 Report Share Posted December 31, 2004 2 ohms and some change. Just divide 3 into 8. Quote Link to comment Share on other sites More sharing options...
thrashncrust Posted December 31, 2004 Author Report Share Posted December 31, 2004 what if i do the 12's in paralell and the 15 in series Quote Link to comment Share on other sites More sharing options...
Drak Posted December 31, 2004 Report Share Posted December 31, 2004 How did I know you were going to ask that next? I must have ESP. Once you start down that road, you'll be sending different amounts of power to different speakers, you may wind up not hearing that 15 at all. You can do such things, but you need to be aware of a lot of different parameters, such as: 1) the efficiency rating of each speaker 2) the ohms of each speaker 3) the power handling of each speaker (but the efficiency is more important, efficiency basically equals how loud it is at a given power input) 4) the sonic characteristics of each speaker. Like, I have an amp that calls for a 16 ohm load, puts out about 35W cathode biased, and I did a custom 3-10 setup on it. I bought 2 10's that were 4 ohms each and very efficient (Weber C10P's), and used an old 8 ohm CTS alnico out of an old Fender Super Reverb (some of my favorite speakers when juiced properly, but I don't like them just by themselves, they need help on the top and bottom) Now, that old CTS is rated for 15W max, AND it's old, so I didn't want to strain it too much, but I wanted it to have a good voice, so it went on top, the Webers on the bottom. The Webers have a great full spectrum sound, great bass and trebles and get all Britishy on ya when cranked, and the one thing that the CTS is good at is that fat thick gnarly midrange punch, so all bases are covered quite well, the total ohmage of all three wired in series is 16 ohms. And the speaker that's good in the mids (the CTS) is up top so you can hear it's voice predominently since mids punch thru more than bass, and it's not nearly as efficient as those Webers are, so it needed to go on top where it can be heard and it's projection range is up near our ears. So I thought that deal out pretty good, and I can hear all 3 speakers appropriately, and it's wired to make the amp happy. My recommendation to you is to go to WeberVST and spend a lot of time there, EVERYTHING you need to know is there, many different diagrams of different speaker hookups, just tons and tons of speaker information there, but you're going to have to put a little time into it if you want a 3-10 to sound good and you can hear all the speakers. They have a tremendous forum there too, very intelligent guys on the Weber 'boards. You can try out a lot of 3-speaker cab scenarios that are disasters tonally. You have to really think it thru for it to be really effective and tonally terrific. In the end, you may just want to cab the 15 separately, or do a 1-12/1-15 and leave the second 12 for something else. Quote Link to comment Share on other sites More sharing options...
thrashncrust Posted December 31, 2004 Author Report Share Posted December 31, 2004 the reason i was asking, is because i have a head that can switch from 8 to 16 ohms, and i need either an 8 or 16 ohm cab, and that 15 by itself isnt doing good enough. thanks for you help drak Quote Link to comment Share on other sites More sharing options...
lovekraft Posted December 31, 2004 Report Share Posted December 31, 2004 Resistances/impedances in series simply add, ie Xtotal = X1 + X2 +X3.... In parallel, the sum of the reciprocals is the reciprocal of the total, ie 1/Xtotal = 1/X1 + 1/X2 + 1/X3.... If you remember that, you can figure out any combination of speakers. Quote Link to comment Share on other sites More sharing options...
Engineer Posted January 1, 2005 Report Share Posted January 1, 2005 Resistances/impedances in series simply add, ie Xtotal = X1 + X2 +X3.... In parallel, the sum of the reciprocals is the reciprocal of the total, ie 1/Xtotal = 1/X1 + 1/X2 + 1/X3.... If you remember that, you can figure out any combination of speakers. The series explanation above is correct. But the parallel explanation is wrong. For parallel, the formula is R1 * R2 etc. divided by R1 + R2 etc. So, for 2- 8 ohm speakers in parallel, you would have (8*8)/(8+8) for a total of 4 ohms. Do a Google on Ohm's Law. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted January 1, 2005 Report Share Posted January 1, 2005 Nio, that's not going to fly! That formula is the most common way of calculating parallel resistances: http://www.tpub.com/neets/book1/chapter3/1-26.htm http://physics.bu.edu/py106/notes/Circuits.html http://hyperphysics.phy-astr.gsu.edu/hbase...c/resis.html#c3 Now, read this page, and maybe you'll understand that while your answer is technically correct, it complicates the issue and is still equivalent to the formula that you seem to object to. http://www.technologystudent.com/elec1/parress1.htm You see, X1*X2/X1+X2= 1/((1/X1)+(1/X2)) - so there's no difference, except that meaningful results are more difficult to get from the formula you seem to prefer, espceially when 3 or more resistors are included. And thanks for the Ohm's Law tutorial. I repeat, the sum of the reciprocals is the reciprocal of the total resistance. Quote Link to comment Share on other sites More sharing options...
G_urr_A Posted January 1, 2005 Report Share Posted January 1, 2005 The series explanation above is correct. But the parallel explanation is wrong. For parallel, the formula is R1 * R2 etc. divided by R1 + R2 etc. So, for 2- 8 ohm speakers in parallel, you would have (8*8)/(8+8) for a total of 4 ohms. Do a Google on Ohm's Law. lovekraft is right. Ohm's law doesn't directly concern resistances in series or parallel. U = R * I can only indirectly be used for that type of math (ie if you have the voltage and current through every component, you can find the total voltage and current, and thus the resistance, or vice versa). So Ohm's law is not what you want to google for in this case. And I don't understand how your (R1*R2)/(R1+R2) is derived from Ohm's law. Quote Link to comment Share on other sites More sharing options...
westhemann Posted January 1, 2005 Report Share Posted January 1, 2005 i thought that the simplest way to determine this on a set of speakers in parrallel was to divide the ohm rating of the speakers used by the # of speakers used? am i wrong?this is not my area... but it seems as if your way(lovekraft) takes into consideration the use of differently rated speakers in the same setup? math is not my strong point Quote Link to comment Share on other sites More sharing options...
G_urr_A Posted January 1, 2005 Report Share Posted January 1, 2005 wes, that works if they all have the same resistance (or as you say, Ohm rating). If you start getting into different resistances in the speakers, you need to get fancy with the math. Quote Link to comment Share on other sites More sharing options...
westhemann Posted January 1, 2005 Report Share Posted January 1, 2005 wes, that works if they all have the same resistance (or as you say, Ohm rating). If you start getting into different resistances in the speakers, you need to get fancy with the math. allright,cool...that makes sense Quote Link to comment Share on other sites More sharing options...
Engineer Posted January 2, 2005 Report Share Posted January 2, 2005 Sorry lovekraft, I misread your post and didn't see the 1/xtotal. I just read xtotal. Both resistance calculations Quote Link to comment Share on other sites More sharing options...
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