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3-15 B Cabinet (3x15') 4ohm or 8 ohm? [message #7512]

Fri, 15 September 2006 17:09

Vintage
Messages: 23
Registered: March 2006
Location: Montréal

Junior Member

Hi!
I have a Kustom 3x15' cabinet, model 3-15 B, �and I was wondering if it were a 4 or 8 ohm cabinet... I baught it used with a 250 head, both originals from 1970, and the head only have a 4 ohm output. So I guess that the cabinet is 4ohm too? How is it configured? 3x 8ohm speakers in paralell?
Thanks!
Smile

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Re: 3-15 B Cabinet (3x15') 4ohm or 8 ohm? [message #7519 is a reply to message #7512]

Sat, 16 September 2006 20:19

stevem
Messages: 4742
Registered: June 2004
Location: NY

Senior Member

Hi. you have 3 16 ohm drivers in parallel for a 5.3 ohm impeadance.
Close enough to 4 ohms for anyone!

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Re: 3-15 B Cabinet (3x15') 4ohm or 8 ohm? [message #7585 is a reply to message #7519]

Sat, 23 September 2006 11:40

Vintage
Messages: 23
Registered: March 2006
Location: Montréal

Junior Member

�Hi!
hmmm... I think it's 3x15" at 8ohm each, in parallel... What would be the total load?
Thanks!
Smile

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Re: 3-15 B Cabinet (3x15') 4ohm or 8 ohm? [message #7587 is a reply to message #7585]

Sat, 23 September 2006 12:57

Optyk
Messages: 125
Registered: August 2006
Location: Texas

Senior Member

If I remember my math correctly, the formula is

1/ohmage + 1/ohmage + 1/ohmage = 1/x (where x = the actual load in ohms)

Taking that further, with 16's, you'd get

1/16 + 1/16 + 1/16 = 3/16 = 1/5.33333 so x = 5.33333 ohms total load

With 8's, you'd have:

1/8 + 1/8 + 1/8 = 3/8 = 1/2.66667 so x = 2.66667 ohms total load. This would be too low of a load for your amp.

I just built my "Shure Thang" kustom/peavey/shure contraption. the speakers I put in it were two 10's at 16 ohms each and one 8 at 8 ohms. If I calculated correctly, then I'd get

1/16 + 1/16 + 1/8 = 1/16 + 1/16 + 2/16 = 4/16 = 1/4, so x = 4 ohms total load. If I'm out to lunch on all this, someone straighten me out quickly before I have a problem. So far, it's all worked perfectly. I haven't been running those internal speakers actually. I have a pair of Crate small PA speakers rated at 8 ohms each and that's what I'm actually running instead of the internals.

I guess I should also mention that all of the above pertains to speakers wired in parallel, not series. In series, I believe it's very simple, you simply total up the ohmage of the three speakers and that's your load. So, in my case, 16 + 16 + 8 = 40 ohms wired in series. Not a workable situation.

Rod

There's only two kinds of music. . . . blues and zippity doo dah.

[Updated on: Sun, 24 September 2006 15:06]

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Re: 3-15 B Cabinet (3x15') 4ohm or 8 ohm? [message #7590 is a reply to message #7512]

Mon, 25 September 2006 07:20

stevem
Messages: 4742
Registered: June 2004
Location: NY

Senior Member

A easyer way to figure dissimilar impeadance or resistance in parallel is this.
a 16 ohm and 4 ohm driver are being used.
16 X 4=64
16 + 4=20
64 DIVIDED BY 20= 3.2 OHm.
This works for how ever many drivers or resistors you have in parallel.

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Re: 3-15 B Cabinet (3x15') 4ohm or 8 ohm? [message #7597 is a reply to message #7590]

Mon, 25 September 2006 19:53

Optyk
Messages: 125
Registered: August 2006
Location: Texas

Senior Member

I had forgotten about that method, steve. Like I said, it's been a long time since I took some electronics and used those formulae on a day to day basis. Leave it to me to use the hard way. LOL

Rod

There's only two kinds of music. . . . blues and zippity doo dah.

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Re: 3-15 B Cabinet (3x15') 4ohm or 8 ohm? [message #7600 is a reply to message #7597]

Tue, 26 September 2006 00:16

Vintage
Messages: 23
Registered: March 2006
Location: Montréal

Junior Member

So if I have 3x8ohm spkrs in parallel, it would be:

8x8x8 / 8+8+8 = 512/24=21.3 ?

hmmm... Confused

I'm all messed uuuuuppppp Laughing

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Re: 3-15 B Cabinet (3x15') 4ohm or 8 ohm? [message #7601 is a reply to message #7600]

Tue, 26 September 2006 00:59

C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...

Senior Member

No, product over sum only works for 2 resistors. The impedance is 2.6666 ohms. The reciprocal method is used for more than 2. However you can group 2 and then group another 2 so 8X8/8+8=64/16=4 then 4x8/4+8=32/12=2.6666, That could work for any number.
Conrad

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Re: 3-15 B Cabinet (3x15') 4ohm or 8 ohm? [message #7603 is a reply to message #7512]

Tue, 26 September 2006 06:52

stevem
Messages: 4742
Registered: June 2004
Location: NY

Senior Member

Thanks Conrad, I should have went into more detail on that.
Sorry about that Vintage!

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