Ask the expert – impact of downgrading to smaller speakers

Steve Edwards writes:

I’m running two (large) 300w speakers from a 600w stereo amp (300w per channel). If I downgrade to (physically smaller) 250w speakers am I right in thinking that it’ll take less drive from the amp to get my current sound levels from the 250w speakers? Also, will the bass response be lower on the smaller speakers, (currently 15inch woofers – the smaller speakers would have 12inch woofers.) I’m not currently using subs, and I’d like to keep it that way.

Geoff Boswell, Sound Consultant, B&H Syscom Ltd replies:

This is a big one and quite complicated. Much of this is governed by ‘impedance’ both of speakers and what the amp is designed to work with. Different amps are designed in different ways to react to the impedance of a load [the speaker] presented to it.  Take a look at the spec of your speakers and the spec of the amp driving them and then it will be much easier to guide you. As a rule of thumb there is no rule of thumb!!  You really need to know the following:

SPEAKER – Impedance on ohms. Power handing rating in watts [peak, RMS, music, average]. Sensitivity in decibels at a certain distance [usually 1 metre] and frequency response and how it is measured.

AMP – what power it will deliver into a certain impedance speaker.

ANY FINALLY in the section  you need to know the length of speaker cables you plan to use and what size they are [cross sectional area normally in millimetres]. Ie 1mm 1.5mm 2.5mm 4mm  ….

NOTE OF CAUTION

If you have none of this info then the cautionary approach is to never NEVER stress the amp and run it a full wack. Use about 75% of the amps power and don’t push it. Doing this will hopefully mean that you never deliver harmful distortion to the speaker !  Always better to have a more powerful amp driving lesser rated speakers  – I guess that is a rule of thumb!

Re size of speakers. Size is not everything but cabinet design is. You can get more subsonic bass from a well tuned 10” sub than you can from a 15” in a simple box.