Impedance change

[oldslapper]

I have recently bought a mark bass LMII, 300 watts at 8 ohm and 500 @ 4ohm.
I have 2x8 ohm "ashdown" mini cabs (4x8 @ 600 watt and 1x15 @ 300 watts).
I like both cabs, but had thought about just using the 4x8, which has a surprising spread.
It occured to me tho' that I'll never get the full whack out of the head using a single 8 ohm cab.
All 3 outfits I play in take a signal out from the backline and the cabs are for monitoring really and, to date, I've never had to have any of my amps (min 400 watts in the past) over half way output volume, and never needed to use 2 cabs of any description.
So, I could live with just one...but wondered if it was possible to convert drivers to 4 Ohm, so "just in case" I need to suck a bit more juice out of the amp. The 4x8 is 600 watt rated...?
Any advice?

Edited January 19, 2010 by oldslapper

[bumnote]

You cant

I have a mini 4x8 and 1 1x5 as well
I suspect the speakers are probably 8 ohm jobbies wired in series parralell to give a combined ohmage of 8 ohms. You can probably rewire the speakers to get 2 ohms or 32 ohms but not 4

To be honest its probably not worth it anyway, the difference in volume going to a 4 ohm and getting those extra watts is probably negligable. the fact you are putting in half as much power again into 1 small cabinet wont give you half as much volume again or anywhere near it.

iI changed out a 8 ohm 15 for a 4 ohm and there was little in it.

[phil.i.stein]

[url="http://wiki.basschat.co.uk/info:amps:impedance_and_wattage"]http://wiki.basschat.co.uk/info:amps:impedance_and_wattage[/url]

[Al Heeley]

esp. if the cabs are really for monitoring I'd very much doubt with your rig you'd have any problem not hearing them

[oldslapper]

[quote name='Al Heeley' post='713235' date='Jan 14 2010, 11:24 PM']esp. if the cabs are really for monitoring I'd very much doubt with your rig you'd have any problem not hearing them [/quote]

Thanks for the advice guys.
I probably don't need the full gas from the head, never have done to date and I'm never likely to play wembley , so I'll stick with what I've got from what you say.
I guess I could always get a 4 Ohm cab in future if The Who need me....in which case make that several 4 ohm cabs and heads.
Thanks again,
John

[oldslapper]

[quote name='phil.i.stein' post='713221' date='Jan 14 2010, 11:17 PM'][url="http://wiki.basschat.co.uk/info:amps:impedance_and_wattage"]http://wiki.basschat.co.uk/info:amps:impedance_and_wattage[/url][/quote]
Thanks for the link Phil....I'll use the wiki in future as a starting point.
John

[alexclaber]

Also bear in mind that it's highly unlikely that either of your cabs would play any louder when powered with 500W rather than 300W. Why? Because although the thermally limited power handling may be more than 300W the excursion (i.e. volume displacement) limited power handling is likely to be significantly lower.

With multi-driver cabs changing the wiring (and still maintaining equal power per driver) can only ever quadruple or quarter the impedance (depending on how they're originally wired), it can never double or halve the nominal impedance.

Alex

P.S. It's impedance, not ohmage!

[bumnote]

[quote name='alexclaber' post='713541' date='Jan 15 2010, 11:24 AM']P.S. It's impedance, not ohmage! [/quote]

OOPS

[oldslapper]

[quote name='alexclaber' post='713541' date='Jan 15 2010, 11:24 AM']Also bear in mind that it's highly unlikely that either of your cabs would play any louder when powered with 500W rather than 300W. Why? Because although the thermally limited power handling may be more than 300W the excursion (i.e. volume displacement) limited power handling is likely to be significantly lower.

With multi-driver cabs changing the wiring (and still maintaining equal power per driver) can only ever quadruple or quarter the impedance (depending on how they're originally wired), it can never double or halve the nominal impedance.

Alex

P.S. It's impedance, not ohmage! [/quote]
Ok thanks Alex.
So my 300 watt 15 mini cab, which is considerably lighter, wouldn't be a problem with 300 watts from the amp? If so, that gives me a bit more of a choice.
John

[Protium]

[quote name='alexclaber' post='713541' date='Jan 15 2010, 11:24 AM']P.S. It's impedance, not ohmage! [/quote]

Thank god someone finally pointed that out, it's almost as annoying as "cog"

[3below]

What's wrong with "cog" ? - still taught & examined in A level Physics, or "com" if you prefer - (not that A level Physics is a measure of anything these days)

[Protium]

[quote name='3below' post='714328' date='Jan 15 2010, 08:55 PM']What's wrong with "cog" ? - still taught & examined in A level Physics, or "com" if you prefer - (not that A level Physics is a measure of anything these days)

[/quote]

Using "cog" instead of "gear" I mean.

Edit: "Gear" as in part of a gearbox for example

Edited January 16, 2010 by Protium

[Merton]

[quote name='Protium' post='714387' date='Jan 15 2010, 09:51 PM']Using "cog" instead of "gear" I mean.[/quote]
You mean like this?

"My bass cog consists of a Hartke head, a Barefaced cab and some Status basses."

[oldslapper]

[quote name='Protium' post='714387' date='Jan 15 2010, 09:51 PM']Using "cog" instead of "gear" I mean.[/quote]
or...scored some cog?

[phil.i.stein]

[quote name='oldslapper' post='714737' date='Jan 16 2010, 12:28 PM']or...scored some cog?[/quote]
nice, that may well become new slang...

[Protium]

[quote name='Merton' post='714603' date='Jan 16 2010, 09:25 AM']You mean like this?

"My bass cog consists of a Hartke head, a Barefaced cab and some Status basses."



[/quote]

Yes that is exactly what I mean.

[stevie]

[quote name='Protium' post='713976' date='Jan 15 2010, 04:32 PM']Thank god someone finally pointed that out, it's almost as annoying as "cog" [/quote]
But not as annoying as deja vous.

[acidbass]

Or the word 'tube' when describing a thermionic valve this side of the Atlantic!

[/threadderailment]

[Dandelion]

A semi-automatic cog box.

[slobluesine]

so could i get a 2x12 8ohm cab down to 2ohms?

any point you ask? well my amp will go down to 2ohms apparently

[bumnote]

[quote name='slobluesine' post='747304' date='Feb 16 2010, 03:01 PM']so could i get a 2x12 8ohm cab down to 2ohms?

any point you ask? well my amp will go down to 2ohms apparently[/quote]


It depends on the impedance of the speakers in the box
2 16 ohm will give you 8 if wired in parallel or 32 if wired in series
2 4 ohms will give you 8 ohms wired in series and 2 if wired in parallel

I suspect your speakers are more likely to be 15 oms rather than 4 but you need to check them out.

Personally I wouldnt bother and I dont think you will notice much or any difference

[slobluesine]

asit appens my 2x12's are 4ohms, so i COULD get the cab down to 2ohms, are there ANY advantages?

better sound? more power? better for my amp?

[Uncle Balsamic]

If it's 4 ohm then you can't make it 2 ohm at all. Even if you could, it would probably be of little benefit.

Edit: Do you mean that the cab overall is a 4 ohm load or that each individual speaker is 4 ohm?

Edited February 17, 2010 by Uncle Balsamic

[slobluesine]

individual speakers are 4ohms

[Uncle Balsamic]

Oh right. Yeah you could do it. It's probably not worth it, but you never know.