Amp power/speaker impedance

[jezzaboy]

This may be a stupid question but I know very little about ohms or amp power. My old Ashdown combo quoted a power output of 300w at 4 ohms but the internal speaker was valued at 8 ohms as most speakers seem to be. I realise you can get the full 300w by conecting a second cab and that brings it down to 4 ohms and you get full power. Correct?

Why don`t they just fit a speaker capable of running at 300w at 4 ohms? I guess there must be a sound reason for it?

Edited August 5, 2012 by jezzaboy

[RandomBass]

[quote name='jezzaboy' timestamp='1344164132' post='1760509']
This may be a stupid question but I know very little about ohms or amp power. My old Ashdown combo quoted a power output of 300w at 4 ohms but the internal speaker was valued at 8 ohms as most speakers seem to be. I realise you can get the full 300w by conecting a second cab and that brings it down to 4 ohms and you get full power. Correct?

[/quote]
Correct

They only fit an 8ohm internally to force you to buy another cab from them to get the full power. Sorry, I meant you can then upgrade with another cab to get more volume - moving more air.

Edited August 5, 2012 by RandomBass

[warwickhunt]

Many manufacturers do this for various reasons, inc' giving you the option of adding another cab to increase the dispersion through the addition of speakers. My old H&K Bassbase combo however was designed to be specifically used with the internal speakers and as such had no other speaker output, personally I think that shows a commitment to their design; would a combo with 2x15's or 6x10's have as great a market as say a 1x15 or 2x10 combo that you can (have to) add speakers to? The answer by the way is NO, so the main reason for external speaker outs to get full power etc. is 'marketing'!

[icastle]

[quote name='warwickhunt' timestamp='1344167189' post='1760578']
so the main reason for external speaker outs to get full power etc. is 'marketing'!
[/quote]

+1

A 'well marketed' combo will have a name like 'GTX300'.
The '300' part is 'obviously' showing its power and gives the impression that the combo is loud - a standard industry manipulation of a somewhat meaningless measurement.

If I was a manufacturer selling the GTX300, I'd want to sell more than just a combo - I'd sell an extension speaker to allow the amp to run at it's maximum.
Am I using dubious marketing?
Of course not, I'm adding [i]extra choice to allow our user base of talented, professional bass players to expand their amplification in a cost effective and truly modular format [/i]...

On a slightly more practical note, I wonder how reliable my GTX300 amp would be if it was stuck in a box with the whole 300W vibrating around it...

[Mr. Foxen]

Pretty much no chance of the internal speaker being able to use 300w anyway.

[Bill Fitzmaurice]

[quote name='jezzaboy' timestamp='1344164132' post='1760509']
Why don`t they just fit a speaker capable of running at 300w at 4 ohms? I guess there must be a sound reason for it?
[/quote]If they used a 4 ohm driver you couldn't add an extension. As for the power issue, few fifteens are capable of making use of even 150w, irrespective of the thermal power rating, so you'd need at least two to make use of 300w anyway.