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MoJ

Ohm ratings

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Hi,
I just wanted to check something for my own benefit.
I understand ohmage in terms of matching cabs to heads etc (ie 2 x 8 ohms = 4, 2 x 4 ohms = 2 etc), but I wanted to make sure that running an 8 ohm cab with a 4 ohm cab won't be a problem (so long as the minimum rating is 2 ohms from the head, which mine is).
The way I see it is that would equal someting between 4 and 2 ohms, without knowing any specific equations for this sort of thing.

I stand ready with flame retardant material and gun above my foot (to shoot it with)....

Andy

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Assuming they're in parallel, it'll be 2.666 recurring.

The formula for parallel resistances is

1/R total = 1/R1 + 1/R2 + 1/R3 + ... + 1/Rn

Pete.

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The head may well be able to work down to 2-ohms however it will generate a lot more heat.

Another thing you might want to condiser is that the 4-ohm cab will probably be louder than the 8-ohm and tend to dominate. Much better to have two cabs of the same impedance and the same spl/watt if you can manage it.

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Exactly as OBBM said.... the 4ohm cab WILL get like 2 x the power of the 8ohm cab. Will work, Ive only done it with an ALL TUBE amp that was OK at 4 or 2 ohms & ran it on 2 ohm setting-as it equalled 2.67ohms.

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Cheers guy.
Thought it would work but I hadn't even considered the fact the 4 ohm cab would get more volume. Least I know in theory it works.
Anyone know of any 4 ohm 2 x 10's? :)

Andy

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[quote name='MoJ' post='36741' date='Jul 25 2007, 09:55 AM']Cheers guy.
Thought it would work but I hadn't even considered the fact the 4 ohm cab would get more volume. Least I know in theory it works.
Anyone know of any 4 ohm 2 x 10's? :huh:

Andy[/quote]

Yamaha used to make a 4ohm 2x10 - the BBT210s. 2x10 + horn, 250w, weighs 21kg. I bought 2 yesterday to use with my superfly and they sounded pretty good - I compared them with an Ashdown Mag 210 and they sounded good. I got mine from Sound Control and Rose Morris show them on their website : [url="http://www.proaudiostore.co.uk/proddet.php?id=3173"]Rose Morris Yamaha BBT210S[/url]

Andy :)

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Thanks for the help guys, though Im not persuing my original action now.

Basically Id seen an old Trace Elliot 1524 (2 x 15 4 ohm rating) which is pretty much what I really want and although the sale hadnt met the reserve and I wasnt the highest bidder the guy was prepared to offer it to me. I just wanted a light weight (compared to my 4 x 10 at least) option for the high end part of my tone whcih would also been closer to my ears fom stacking, I just needed to confirm I could do it despite the odd impedance the two cabs would create. I didnt know of anyone making 4 ohm 2 x 10s.

Just found out the cost of some repair work to my car so today and I doubt Ill be buying anything in the near future :)
Pains me to miss up a great oppurtunity.

Guess Ill just have to wait for some money, and Bill Fitzmaurice to release plans for the O15 Tallboy and have myself a self build :huh:
Andy

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[quote name='alexclaber' post='36962' date='Jul 25 2007, 06:15 PM']I cannot imagine any 4x10" being heavy enough to make a TE 2x15" appear light in comparison!

Alex[/quote]

Have you tried picking up a [url="http://peavey.com/products/browse.cfm/action/detail/item/116527/number/00584650/cat/14/begin/1/TVX+410+EX%3F+4+ohm.cfm"]Peavey TVX 4 x 10[/url]? Im assuming that weight is in lbs, which means it's about 30 lbs heavier (apparantly 30 bags of sugar!!) than my Trace 4 x 10. :) I borrowed one to try out my current head. Never again, though it was a great sound.
A 2 x 10 would make a rig comprising of a 2 x 15 lighter still.
The new TE 1528 is 77 lbs so is comparable. I wouldnt know if they've changed the construction though, thus making it lighter but I do note its 8 ohms not 4, and about £400 more than I was going to have pay, including shipping for the 1524.
Damn, I [i]knew[/i] I was going to regret declining it.
Really hope the plans for the O15 Tallboy come soon!

Alex, I need to ask you about the crossover built in to BFM designs like the O15, as being passive I understand that they will only handle a certain amount of wattage. Does that mean it has to be built super big? My Peavey Pro is 350w at 4 ohms (I assume the O15 is designed to be 4 ohms?). Is it just easier to wait for the plans, and wouldn't you be able to do a version, being as its your creation n all :huh:

Andy

Edited by MoJ

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[quote name='MoJ' post='37005' date='Jul 25 2007, 08:32 PM']The new TE 1528 is 77 lbs so is comparable.[/quote]

Ah, the old TE cabs were made of MDF and weighed a ton, easily as much as a 410TVX

[quote name='MoJ' post='37005' date='Jul 25 2007, 08:32 PM']Is it just easier to wait for the plans[/quote]

Definitely! All I did was bodge Bill's sketchup model into a new arrangement to illustrate my idea.

The series inductor in the woofer lowpass filter needs to be pretty heavy gauge - like this:

[url="http://www.partsexpress.com/pe/pshowdetl.cfm?&PartNumber=255-116"]http://www.partsexpress.com/pe/pshowdetl.c...tNumber=255-116[/url]

Alex

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[quote name='alexclaber' post='37017' date='Jul 25 2007, 09:25 PM']Ah, the old TE cabs were made of MDF and weighed a ton, easily as much as a 410TVX[/quote]

Then Im not surprised they were heavy! I was surprised after hearing about old TE stuff being heavy that the new 4 x 10 isn that bad.

[quote name='alexclaber' post='37017' date='Jul 25 2007, 09:25 PM']Definitely! All I did was bodge Bill's sketchup model into a new arrangement to illustrate my idea.

The series inductor in the woofer lowpass filter needs to be pretty heavy gauge - like this:

[url="http://www.partsexpress.com/pe/pshowdetl.cfm?&PartNumber=255-116"]http://www.partsexpress.com/pe/pshowdetl.c...tNumber=255-116[/url]

Alex[/quote]

Fair enough. Ill just wait it out for Bill's plans. Reeeally hope it doesnt take too long.

Thanks Alex
Andy

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[quote name='MoJ' post='36947' date='Jul 25 2007, 05:29 PM']Bill Fitzmaurice to release plans for the O15 Tallboy and have myself a self build :)
Andy[/quote]

Tallboy? [url="http://www.lancastermuseum.ca/s,tallboy.html"]eep.[/url]

Will it be followed up with a Grand Slam? [url="http://www.raf.mod.uk/bombercommand/grandslam.html"](bigger eep)[/url]

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[quote name='Bloodaxe' post='37039' date='Jul 25 2007, 10:10 PM']Tallboy? [url="http://www.lancastermuseum.ca/s,tallboy.html"]eep.[/url]

Will it be followed up with a Grand Slam? [url="http://www.raf.mod.uk/bombercommand/grandslam.html"](bigger eep)[/url][/quote]

I can only hope, looking at the spl charts for the standard O15 that the modded cab is the sonic equivalent!

Andy

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