4 / 8 ohm switch

[petetexas]

How does a 4 or 8 ohm switch work on the back of a cab , when you only have one speaker of 4 or 8 ohms in the cab ?

[Baloney Balderdash]

Passive transformer?

 

Just a wild guess, I am not exactly an electronics expert.

Edited February 15, 2023 by Baloney Balderdash

[BigRedX]

Anything that doesn't involve tapping the speaker coil is going to be wildly inefficient and wasteful of energy.

[basstone]

How odd. Multi speaker cabs often have the capability to switch between series and parallel connection to match to the amp. If there is only one driver speaker the switch possibly adds a series or parallel resistor which only makes any sense if connecting to a valve amp?  It might be worth opening up the cab to see what the switch does

[petetexas]

Hi ,

The Hartke HD112 cab is a 1x12 cab , and has a switch on the back for 4 ohms or 8 ohms ,

Pete

[wateroftyne]

Did someone say 'Accuswitch'? 😄

[Woodinblack]

  On 16/02/2023 at 21:01, basstone said:

 If there is only one driver speaker the switch possibly adds a series or parallel resistor which only makes any sense if connecting to a valve amp? 

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It doesn't make any sense regardless of the type of amp it is connected to, your resistor would have to match the wattage of any speaker it was connected to as half of your power would be going to heat up the resistor, which means it needs to be very big and bolted to some metal to get rid of the heat and you are wasting half of your power.

 

So if you have a valve amp, connect it to the correct impedance output, and if you have a solid state amp, you can put more power into the speaker, and use more power, just to throw away that power heating a resistor, giving you the same volume if you had connected it without the resistor.

 

The Harkte has a dual voice coil apparently, so I guess you are only using half of it in one of the modes.

[basstone]

  On 16/02/2023 at 23:21, Woodinblack said:

 

It doesn't make any sense regardless of the type of amp it is connected to, your resistor would have to match the wattage of any speaker it was connected to as half of your power would be going to heat up the resistor, which means it needs to be very big and bolted to some metal to get rid of the heat and you are wasting half of your power.

 

So if you have a valve amp, connect it to the correct impedance output, and if you have a solid state amp, you can put more power into the speaker, and use more power, just to throw away that power heating a resistor, giving you the same volume if you had connected it without the resistor.

 

The Harkte has a dual voice coil apparently, so I guess you are only using half of it in one of the modes.

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Totally agree with you, but if the switch is there just thinking out loud really.  I didn't know about the Hartke speaker with the dual voice coil.  It would be good to hear what it is actually doing but opening up the cab 🙂

 

[warwickhunt]

Tech Soundsystems did a 1x15 that had a 2/4/8 ohm switch; I remember opening it up and I'm sure it was dual coil.  

[Baloney Balderdash]

  On 16/02/2023 at 23:21, Woodinblack said:

 

It doesn't make any sense regardless of the type of amp it is connected to, your resistor would have to match the wattage of any speaker it was connected to as half of your power would be going to heat up the resistor, which means it needs to be very big and bolted to some metal to get rid of the heat and you are wasting half of your power.

 

So if you have a valve amp, connect it to the correct impedance output, and if you have a solid state amp, you can put more power into the speaker, and use more power, just to throw away that power heating a resistor, giving you the same volume if you had connected it without the resistor.

 

The Harkte has a dual voice coil apparently, so I guess you are only using half of it in one of the modes.

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Rather than only using half of the dual voice coil couldn't it be a case of either using the dual coil in respectively parallel and series mode of the two coils, seems to make the most sense to me?

Edited February 21, 2023 by Baloney Balderdash

[Downunderwonder]

  On 21/02/2023 at 06:42, Baloney Balderdash said:

Rather than only using half of the dual voice coil couldn't it be a case of either using the dual coil in respectively parallel and series mode of the two coils, seems to make the most sense to me?

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There is simply no way to swap equal loads series to parallel and achieve a factor of 2 change.

 

2X in series

0.5X in parallel.

 

In the same way a 4 ohm 410 can't be rewired to be 8ohm.

[wateroftyne]

Re: my slightly vague ‘AccuSwitch’ reference earlier, this was a minor scandal about 20 years(!) ago, in which respected cab builder Accugroove added a mysterious sealed black box to their cabs which they claimed offered switchable impedance. It was swiftly identified as snake oil. A very strange move.

 

I’m sure @Bill Fitzmaurice remembers that one!

[Baloney Balderdash]

  On 21/02/2023 at 07:12, Downunderwonder said:

There is simply no way to swap equal loads series to parallel and achieve a factor of 2 change.

 

2X in series

0.5X in parallel.

 

In the same way a 4 ohm 410 can't be rewired to be 8ohm.

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Right, I wasn't thinking that properly through. 

 

Thanks for correcting me. 

[Dood]

  On 21/02/2023 at 07:35, wateroftyne said:

Re: my slightly vague ‘AccuSwitch’ reference earlier, this was a minor scandal about 20 years(!) ago, in which respected cab builder Accugroove added a mysterious sealed black box to their cabs which they claimed offered switchable impedance. It was swiftly identified as snake oil. A very strange move.

 

I’m sure @Bill Fitzmaurice remembers that one!

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I do! I remember that well! 

[Dood]

Hartke’s cabinets (112) did indeed use a driver with two coils and a switch to select 8 or 4 ohms operation. It wasn’t a dummy or resistive load.

[Downunderwonder]

  On 21/02/2023 at 20:33, Dood said:

Hartke’s cabinets (112) did indeed use a driver with two coils and a switch to select 8 or 4 ohms operation. It wasn’t a dummy or resistive load.

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Adds up to only one coil used in 8 ohm operation, other coil becoming dead weight.

[warwickhunt]

  On 22/02/2023 at 01:15, Downunderwonder said:

Adds up to only one coil used in 8 ohm operation, other coil becoming dead weight.

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Indeed. 
 

IIRC the Tech Soundsystems 115 used a light weight Sica driver (spelling could be wrong) which made the cab a very reasonable weight.