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Barefaced selectable ohms.

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Evening all.

I see the barefaced two10s has a selectable switch for 12 or 4 ohms.

So,

1. select 4ohm if using one cab.

2. select 12ohm if using three cabs.

But was does running 2 cabs at 12 ohm do? (6ohm?) Will that be fine for running say any class d and class a/b amp? (Ashdown abm600 and rm500).

 

 

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Posted (edited)

It will be absolutely fine yes :)

Most solid state Ashdown heads (ie the ABM and RM ranges you mentioned, not the valve range) have a minimum impedance of 4 ohms, so a pair at 6ohms is perfectly fine.

Edited by Merton
Clarification on the amps

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PS if this is related to the one FS in the classifieds then, damn you. I was out at the pub and missed it 😂 

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If the amp is able to push power into 2 channels of 4 ohm loads (total of 2 ohms), go ahead. If the amp says 8 ohm per cab, you can try the 12 ohm setting. The impedance described in a single number is always an approximation, as it changes over the frequency range.

In theory the bigger impedance is easier for the transistor amp. If your amp is a tube/valve unit, it is recommended to match the amp's output transformer to the cab(s). 8 to 8, or 4 to 4. When in doubt, 8 is a good guess, and avoid driving the amp to its limit.

Usually the temp of the amp tells something about the matching, as hotter equals worse match:

1) Lower impedance requires more amps (A) from the transistor amp(lifier) and the head will be hotter.

2) Impedance mismatch in the tube amp drives the output transformer harder and the excessive heat may melt it.

These are generalizations.

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It won't hurt the amps. It'll just be a bit louder than a single 8 ohm cab and not quite as loud as a 4ohm setup at a given master volume . Although barely noticeable i would think. 

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Running the two cabs at 12 ohms will give you a significant increase in volume. You've doubled the radiating area of the speakers increasing their efficiency by 3dB as well as the maximum output and power handling. If you operate them at the same volume as a single cab you will have reduced excursion and the heating of the voice coils as well as the velocity of air in the ports and will have reduced distortion as a result plus you will have raised one cab up to ear level and will hear yourself better.

As far as the amp is concerned, well it depends upon the amp. Two things limit amps output; the voltage they can drive into the speaker without distorting, and the current the power supply can maintain. Trace watts for example are a myth but based on the reality that Trace amps tended to have really beefy power supplies. It's a rule of thumb that it'll be the voltage limit that determines the power output at 8ohms and above but the current limit that operates at 4ohms. So, whilst an amp ought to double it's output into 4 ohms you get a lot of amps that do 300W into 8 and 500W into 4. The probability is that you'd get 400W going into 6ohms from most amps and an extra 4dB increase in total output. Just running a single 4 ohm speaker would give you roughly 2dB extra output compared with an 8 ohm speaker so using both at 6 ohms is going to give you a small but noticeable improvement in levels over a single speaker as well as a potential reduction in distortion.

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