Dumb, stupid, idiot question alert!

[Moos3h]

Here's one for you!

If a bass amp puts out 300w at 4 ohms, but is fitted with an 8 ohm speaker - is there any way of wiring something in series/parallel with the internal speaker to make the amp 'see' 4 ohms and thus put the full welly through the one speaker?

I'm SURE there must be a reason why this can't be done?

Cheers,
James

[Bloodaxe]

[quote name='Moos3h' post='1034209' date='Nov 23 2010, 06:48 PM']Here's one for you!

If a bass amp puts out 300w at 4 ohms, but is fitted with an 8 ohm speaker - is there any way of wiring something in series/parallel with the internal speaker to make the amp 'see' 4 ohms and thus put the full welly through the one speaker?

I'm SURE there must be a reason why this can't be done?

Cheers,
James[/quote]
No.

You [i]could [/i]wire a [b]very[/b] chunky 8Ω wirewound resistor in parallel with the speaker so that the amp would think it was driving a 4Ω cab, but it'd be a fairly pointless excercise as the 'extra' 150W would just make the resistor very hot.

If you want the extra 150W to be audible you either need to get an 8Ω extension cab or recone/replace the existing speaker with a 4Ω equivalent.

Extension cab FTW.

Pete.

[thebassman]

[quote name='Moos3h' post='1034209' date='Nov 23 2010, 06:48 PM']Here's one for you!

If a bass amp puts out 300w at 4 ohms, but is fitted with an 8 ohm speaker - is there any way of wiring something in series/parallel with the internal speaker to make the amp 'see' 4 ohms and thus put the full welly through the one speaker?

I'm SURE there must be a reason why this can't be done?

Cheers,
James[/quote]

The internal speaker is probably not rated for the full power output.
It's a way of keeping the cost down.
You can probably just change it to a higher output speaker. It would need re-wiring though to 4ohms. Someone else more knowledgeable than me could tell you how.

[warwickhunt]

I assume you are talking about a combo with a single internal driver that is 8ohm, if so you really only have 2 choices as a dummy load would be pointless;

1) A second 8ohm cab

2) Replacement speaker rated at 4ohms (200/300/400/500w wouldn't worry me personally but for your peace of mind the higher the better) but to ensure you retain a similar tone you'd need to research that the new driver was correctly spec'd for the size of the box... saying that, just chucking in a decent 4 ohm driver has 'the potential' to work equally well or better!

[xgsjx]

If you're planning on replacing the speaker then I'd still put an 8 ohm one in, just get a higher sensitivity driver & it will still leave you the opton of adding an ext cab in the future if needed.
The extra watts put to one 4 ohm driver will be barely noticable.

[warwickhunt]

[quote name='xgsjx' post='1034266' date='Nov 23 2010, 07:27 PM']If you're planning on replacing the speaker then I'd still put an 8 ohm one in, just get a higher sensitivity driver & it will still leave you the opton of adding an ext cab in the future if needed.
The extra watts put to one 4 ohm driver will be barely noticable.[/quote]

Good point!

[icastle]

[quote name='Moos3h' post='1034209' date='Nov 23 2010, 06:48 PM']Here's one for you!

If a bass amp puts out 300w at 4 ohms, but is fitted with an 8 ohm speaker - is there any way of wiring something in series/parallel with the internal speaker to make the amp 'see' 4 ohms and thus put the full welly through the one speaker?

I'm SURE there must be a reason why this can't be done?

Cheers,
James[/quote]

It can be done.
You just need to wire another 300W 8Ω speaker in parallel with the first one

[xgsjx]

[quote name='warwickhunt' post='1034426' date='Nov 23 2010, 08:53 PM']Good point! [/quote]
Haha, takes me that ling to type a post at work between doing things that there's been multiple responses before I finish!

[ThomBassmonkey]

If you put in an 8 Ohm resistor, would that not actually lower the power going to the speaker?

Just trying to find out, don't know (hence asking instead of stating) but if you have a 300w into 4 Ohm amp, due to the nature of the beast and because it's not as efficient at 4 Ohms, wouldn't it run at about 200w into 8 Ohm? So into one 8 Ohm speaker you'd get (guesstimate) 200w, but if you added an 8 Ohm resistor, you'd get 300w split in two, meaning the speaker would only get 150w?

That's just my logic speaking, it could be complete crap, just curious.

[icastle]

[quote name='ThomBassmonkey' post='1034574' date='Nov 23 2010, 11:18 PM']If you put in an 8 Ohm resistor, would that not actually lower the power going to the speaker?

Just trying to find out, don't know (hence asking instead of stating) but if you have a 300w into 4 Ohm amp, due to the nature of the beast and because it's not as efficient at 4 Ohms, wouldn't it run at about 200w into 8 Ohm? So into one 8 Ohm speaker you'd get (guesstimate) 200w, but if you added an 8 Ohm resistor, you'd get 300w split in two, meaning the speaker would only get 150w?

That's just my logic speaking, it could be complete crap, just curious. [/quote]

The biggest problem with using a resistor in place of a speaker is that there is nowhere for the power to go and therefore it becomes heat.
The resistor would need to be something capable of handling 300W or it would just burn out - to give you an indication of the sizes involved, the standard resistors that you see most frequently in amplifiers, effects pedals etc are usually rated at 1/4W.

I have an A4 sized board hanging on the wall in my little workshop which is covered with rows of big wirewound resistors which allow me to dissipate just over 300W into an 8Ω load and it gets hot enough to make touching it impossible.

Speakers dissipate this power mostly by moving the cone so stay a lot cooler.

[ThomBassmonkey]

[quote name='icastle' post='1034590' date='Nov 23 2010, 11:34 PM']The biggest problem with using a resistor in place of a speaker is that there is nowhere for the power to go and therefore it becomes heat.
The resistor would need to be something capable of handling 300W or it would just burn out - to give you an indication of the sizes involved, the standard resistors that you see most frequently in amplifiers, effects pedals etc are usually rated at 1/4W.

I have an A4 sized board hanging on the wall in my little workshop which is covered with rows of big wirewound resistors which allow me to dissipate just over 300W into an 8Ω load and it gets hot enough to make touching it impossible.

Speakers dissipate this power mostly by moving the cone so stay a lot cooler.[/quote]

Thanks for the explanation, but I was talking hypothetically, I realise 150w is a lot of heat to dispose of if that's it's only power sink.

[Bill Fitzmaurice]

[quote name='Moos3h' post='1034209' date='Nov 23 2010, 01:48 PM']I'm SURE there must be a reason why this can't be done?[/quote]
The same reason one doesn't fill the boot of their auto with concrete so that they might get all of the horsepower out of their engine. You'll use a lot more gas but you won't go any faster.
I believe the subject is addressed in the FAQ.

[chris_b]

[quote name='Moos3h' post='1034209' date='Nov 23 2010, 06:48 PM']....If a bass amp puts out 300w at 4 ohms, but is fitted with an 8 ohm speaker - is there any way of wiring something in series/parallel with the internal speaker to make the amp 'see' 4 ohms and thus put the full welly through the one speaker?....[/quote]
Don't bother getting the tools out.

Just get another 8 ohm cab. 2 8 ohm cabs will be louder than 1 4 ohm cab, will give you better tone, as 2 speakers won't be working as hard and you'll have the noise nearer your ears, so you'll think you're louder!