cab question

[jeremyo83]

when choosing speakers for a 4x12 cab i am building, how should I consider the wattage?

I am planning an 8ohm 4x12 cab using 4 8ohm speakers (top 2 in parallel, bottom 2 in parallel, and top and bottom groups in series = 8ohms).. correct me if i'm wrong.

i'm looking at 2 speakers..
eminence red fang - www.eminence.com/pdf/redfang.pdf
eminence private jack - www.eminence.com/pdf/privatejack.pdf

The red fang is 30W, and the private jack is 50W.
If I have a 50W Traynor, will it be too much for the 30W speakers, or do the speakers in parallel/series as they will be add up how much wattage they can take? (ie: 2 groups in series of 2x30W speakers in parallel = a 30 watt capacity, a 60 watt capacity, a 120W capacity?) I'm not quite sure how to figure this out, or if it really even matters.

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I was also considering instead of a 4x12, seeing if I could do a 2x12+15. (?) -> 2 12" speakers, and a 15" for some extra low end. I know some people say that 15" speakers muddy things up, but I play a lot of rhythm and like a full bottom end. any thoughts comments or suggestions on this? ... sidenote - the eminence 15" speaker (big ben) is rated at 225W.. would this throw a big monkey wrench in the plans?

Thanks!

[vonFrenchie]

wiring 4 8 ohm speakers in ser/par will end up being 8 ohms

If you have four 30 watt speakers hooked up to a 50 watt amp each speaker will get 12.5 watts. 30 watt speakers can handle (roughly) a 60 watt peak.That was my main concern when I built my 2x12 cab. I chose eminence man-o-war speakers (125 watt rated) for my 210 watt head. Awesome speakers for the price. If you want you can buy two of the private jacks and two red fangs for a truely unique sound.

So you know, cabs are rated by the lowest speaker wattage times number of speakers. Most cab manufacturers use one speaker type per cab. If you do mix and match take the lowest watt rated speaker and calculate if all other speakers had that wattage. If you have two 30 watt speakers and two 100 watt speakers with a 200 watt head those 30 watt speakers probably couldnt take 50 watts running to them for an extended period of time.

Using three speakers will only change the calculations. Then you would need all of your speakers to have a 17 watt rating in your case. The only monkey wrench it will put in your plans is the design. It would be an odd layout and some careful engineering would be needed to gain the best sound possible.

My Man-O-War's have plenty of low end. I play my friends bass head through those and it works fine.

[ChrisK]

The red fang is 30W, and the private jack is 50W.
If I have a 50W Traynor, will it be too much for the 30W speakers, or do the speakers in parallel/series as they will be add up how much wattage they can take? (ie: 2 groups in series of 2x30W speakers in parallel = a 30 watt capacity, a 60 watt capacity, a 120W capacity?) I'm not quite sure how to figure this out, or if it really even matters.

Yeah, it matters.

The simplest way (assuming that all of the speakers have equal impedance) is to use the lowest rating of any for all. If you have If you have two in parallel, in series with two others in parallel (four 8 Ohm speakers resulting in 8 Ohms), and the lowest rating is 30 Watts, your cabinet can handle 120 Watts minimum. It may be higher (the math rules).

If you have two speakers (or <sub>groups thereof) in parallel, the resulting impedance is (A*B)/(A+B). In series it's A+B.

For the two 12" and one 15" example (and the fact that you like big bottom sound), you could put the one 15" (with an 8 Ohm coil) in series with the two 12" ones (with 16 Ohm coils) for a resulting 16 Ohm load.

So, A||B means in parallel, A+B means in series.
A[8] means A is 8 Ohms.

A, B are 12" and C is 15" (or, whatever anyway).

(A[8] || B[8]) + C[4] = 8 Ohm load;
A, B each dissipate 1/4 of the power and C dissipates 1/2 of the power.

(A[8] + B[8]) || C[16] = 8 Ohm load;
A, B each dissipate 1/4 of the power and C dissipates 1/2 of the power.

So, if A, B are rated for 30 Watts, or
A, B are rated for 50 Watts, and
C is rated for 225 Watts.

The maximum structure power dissipation is:
Based on A,B 30/(1/4) = 120 Watts,
Based on A, B, 50/(1/4) = 200 Watts,
Based on C, 225/(1/2) = 450 Watts,

The lessor of all calculations, or 120 Watts if the Red Fang is used, or 200 Watts if the Private Jack is used with the Big Ben.


Now, let's get cute with it.
(A[8] || B[4]) + (C[8] || D[4]) = 5.333 Ohm load (plug it into the 4 Ohm jack);
A, C each dissipate 1/6 of the power and B, D each dissipate 1/3 of the power.

So, if A is rated for 30 Watts,
B is rated for 50 Watts,
C is rated for 60 Watts, and
D is rated for 90 Watts;

The maximum structure power dissipation is:
Based on A, 30/(1/6) = 180 Watts,
Based on B, 50/(1/3) = 150 Watts,
Based on C, 60/(1/6) = 360 Watts,
Based on D, 90/(1/3) = 270 Watts,

The lessor of all calculations, or 150 Watts.


Cuter yet.
(A[8] || B[4]) + (C[16] || D[8]) = 8 Ohm load ;
A dissipates 1/9 of the power,
B dissipates 2/9 of the power,
C dissipates 2/9 of the power, and
D dissipates 4/9 of the power.

So, if A is rated for 30 Watts,
B is rated for 50 Watts,
C is rated for 60 Watts, and
D is rated for 90 Watts;

The maximum structure power dissipation is:
Based on A, 30/(1/9) = 270 Watts,
Based on B, 50/(2/9) = 225 Watts,
Based on C, 60/(2/9) = 270 Watts,
Based on D, 90/(4/9) = 202.5 Watts,

The lessor of all calculations, or 202.5 Watts.

And on and on...................</sub>

[jeremyo83]

thanks, both of you. that helps out greatly.

vonFrenchie, where did you buy your man-o-wars? online or at a local store? if online, where?

anyone know where to get them cheap? i know the red fangs are relatively expensive compared to the other eminence speakers, so I want to keep my eye out for a deal.

[ChrisK]

allenamps.com sells Eminence and often have a deal on particular units.

musiciansfriend.com