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Jamesemt

Running 8ohm cabs with 2x4ohm amp??

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Hi guys, I currently own a Superfly and am looking to upgrade the rig slowly (ie cabs first).

The Superfly is 2x250watts at 4ohms. Is there any way for me to run both inputs to one cab?

I fancy a 1x12 cab for portability (or maybe 2x12 - GK Neos are on my list...), but what I am looking at is 8ohms and I have a feeling it wont be loud enough.

I can't really afford to buy a new amp at the same time...

FWIW the amp is currently running into a 115 Peavey (which sounds good, but way too heavy). Obviously running just one side of the amp.


PS sorry for the barrage of posts in this section :)

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You won't be able to run both outputs into one cab as it'd likely blow it up. Getting 2 x 4ohm cabs looks like your best bet since it's dual channel.

I'm not 100% on this but if you email Guy at Ashdown he can tell you for sure :)

[url="http://www.ashdownmusic.com/tech/tech_service.asp"]http://www.ashdownmusic.com/tech/tech_service.asp[/url]

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I'm not quite sure what you are getting at here, I'm not sure if it's even possible to run two channels into one cab, but surely tw 4 ohm channels would take it down to 2ohms, rather than up to 8?

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You can't run two amp channels into one cab [i][b]unless[/i][/b] there are two or more speakers in the cab that have been wired up independently of each other (so you're effictively connecting to separate speakers that happen to be in the same enclosure).

Don't be misled into thinking there's a direct relationship between amp power and loudness - it's really not as simple as that.

An efficient speaker with a high Sound Pressure Level (SPL) will be louder than one with a lower SPL even if you put more power into the less efficient one.

As a general guide, you need approximately 10 times (yes TEN) the amplifier power to get twice the volume. So, for example, changing from a 250 W amp to a 350 W amp is not going to make a huge difference.

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[quote name='BOD2' post='137188' date='Feb 9 2008, 05:54 PM']You can't run two amp channels into one cab [i][b]unless[/i][/b] there are two or more speakers in the cab that have been wired up independently of each other (so you're effictively connecting to separate speakers that happen to be in the same enclosure).[/quote]

+1.



Ashdown make a Neo cab which is a single cabinet with 4x 8 speakers in. They are wired in separate pairs (ie two sets of two). The cab has two inputs, esp for use with the SF amp. Its effectively two 2x 8 cabs but in one box.

About £400 IIRC.


Edited by neilb

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[quote name='neilb' post='137237' date='Feb 9 2008, 07:01 PM']+1.



Ashdown make a Neo cab which is a single cabinet with 4x 8 speakers in. They are wired in separate pairs (ie two sets of two). The cab has two inputs, esp for use with the SF amp. Its effectively two 2x 8 cabs but in one box.

About £400 IIRC.


[/quote]

Cheers Neil - I think Ashdown have already discontinued them..and was thinking long term, when I upgrade to a better head, would the Superfly cabs be suitable?

On the soundcontrol website are a few Superfly specific cabs, but all I was wondering was if I buy two cabs (and spend around £800) is it going to sound as good as any other £1k rig? As the Superfly is really my first ever head, I've always thought of it as being a bit budget (but capable...). Am I way off?

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[quote name='Jamesemt' post='137159' date='Feb 9 2008, 04:50 PM']Hi guys, I currently own a Superfly and am looking to upgrade the rig slowly (ie cabs first).

The Superfly is 2x250watts at 4ohms. Is there any way for me to run both inputs to one cab?[/quote]
Yes. You need more than one speaker and the ability to do a bit of rewiring (of the speaker, not the amp) though.

I've got a Superfly which I'm running into a homebrew 2x10". I've wired two jack sockets on the cab so that I can either run into one socket and have the speakers in parallel at 4 ohms, or run a separate channel into each of the 8 ohm speakers.

You could do something similar with a 4x10" - if it's an 8 ohm 4x10, it would almost certainly be 4 8 ohm speakers, which could be wired up to give you two separate pairs of 4 ohm speakers.

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[quote name='BOD2' post='137188' date='Feb 9 2008, 05:54 PM']You can't run two amp channels into one cab [i][b]unless[/i][/b] there are two or more speakers in the cab that have been wired up independently of each other (so you're effictively connecting to separate speakers that happen to be in the same enclosure).

Don't be misled into thinking there's a direct relationship between amp power and loudness - it's really not as simple as that.

An efficient speaker with a high Sound Pressure Level (SPL) will be louder than one with a lower SPL even if you put more power into the less efficient one.

As a general guide, you need approximately 10 times (yes TEN) the amplifier power to get twice the volume. So, for example, changing from a 250 W amp to a 350 W amp is not going to make a huge difference.[/quote]

All that is true; it is also true that an amp designed to give full power into 4 ohms will nearly always give much more than half its rated power into 8 ohms.

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[quote name='tauzero' post='138090' date='Feb 11 2008, 12:07 PM']I've got a Superfly which I'm running into a homebrew 2x10". I've wired two jack sockets on the cab so that I can either run into one socket and have the speakers in parallel at 4 ohms, or run a separate channel into each of the 8 ohm speakers.[/quote]

Is there much difference in volume - comparing 2x8ohm to 1x4ohm? As 8ohm cabs seem to be cheaper...not to mention more futureproof.

Edited by Jamesemt

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[quote name='Jamesemt' post='138132' date='Feb 11 2008, 01:15 PM']Is there much difference in volume - comparing 2x8ohm to 1x4ohm? As 8ohm cabs seem to be cheaper...not to mention more futureproof.[/quote]
Haven't tried the experiment yet, and it's a bit impractical to do it here (at least at significant volume). My reasoning was that 250W into 4 ohms would most likely give around 200W into 8, so I'd be powering the 200W speakers to their optimum effect. They're not terribly efficient drivers either. I've got a couple of 8" speakers too, so I may knock up a smallish 2x8 to go with the other cab. Long term I want to build a couple of Omni 10.5s, which I'll quite happily put 8 ohm speakers into.

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I thought I might as well check whether my reasoning was correct, so I emailed those nice people at Ashdown, and this is what they said:

"If you've just got two 8 Ohm cabs, you'd be better off running one from each channel as you would obtain 2/3rds of the available power from each 250 watt amp (roughly about 160 Watts from each cab) as opposed to running the cabs in parallel on just one output when you would get 250Watts split equally between the two...."

So I was a little optimistic in what I thought I'd get per channel but the reasoning is sound.

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