Loud Speakers! How Loud Is Your LoudSpeaker?

by Andrew Bishop

Watt's it all about, Andrew?

Firstly, in my ears, it's about the quality of sound and not quantity as I want to protect my hearing!

One of the biggest mistakes buyers of audio equipment face falling into the 'loudness trap'. The loudness trap? It's where someone (a manufacturer, a retailer or even a friend who 'knows about these things') tells you that the loudness of a piece of equipment is measured in Watts!

You're offered what is claimed to be a 100 Watt amplifier and told it will sound just as loud as any other 100 Watt amplifier and from that you assume, or might even be told, that a 200 Watt version would be twice as loud. Neither is true!

Wattage is simply a measure of the amount of output voltage an amplifier delivers to a speaker - and even that can be misleading, especially is if someone has set out to make it so! The output of an amplifier is usually quoted in one of three ways: Watts RMS, Watts Peak or Watts Progam - but they are three very different things!

The most honest of the three is the RMS figure. Think of it as the average output of an amplifier. Program power is a slightly more misleading figure and is usually double the amplifier's RMS rating, while Peak power is just what it says - even if the amplifier can only hit that output for a millisecond!

Using these various methods, an unscrupulous advertiser can pretend his 100 Watt RMS amplifier is a lot more powerful than it really is. An amplifier rated at 100 Watts RMS will deliver a lot more power than one that produces only 100 Watts peak!!

To make matters even more complicated, even if you have comparable figures in Watts, it doesn't relate to how loud the eventual sound will be!  a 100 Watt amplifier feeds a loudspeaker or loudspeakers plural, and what determines the loudness you hear is the efficiency of those speakers and the design of the enclosure they are housed in. The sound that comes out of them isn't measured in Watts, it is known as the Sound Pressure Level (SPL for short) and is measured (in a regrettably complicated logarithmic scale) in Decibels - dBs for short.

For a fuller explanation of these terms, we have just published a detailed article on the subject in our How-To Guides (look under Support on our front page) which explains everything you ever wanted to know about the subject - and possibly a good bit more!

What the buyer looking for a replacement speaker needs to know how much power it will handle as input (quoted in Watts) and, vitally, how much of that energy it turns into sound, which is its SPL and quoted in dB,s. Bear in mind, also, that because decibels are measured in a logarithmic scale, double the loudness is just 3dB!

So what amplifier should you buy? As a rule of thumb, I always say an amplifier should be capable of delivering 1.5 to 2 times the power of the speaker(s) you connect to it. That way you won't run the amplifier flat-out into 'clipping' distortion - the consequence if you do, often being a fried loudspeaker!

When buying bare speakers, perhaps to replace a speaker in an old enclosure, you need to know the power in Watts they can handle and the SPL they will deliver, which should be quoted in dBs.

Not all loudspeakers are created equal! When buying speakers already in enclosures, if they are passive, you need to know the same things - how much to put in, measured in Watts, and what you can expect to get out of them - the SPL in dBs.

How loud is loud?

And if all this seems like too much of a hassle you can get avoid all these complications by buying an active system, where the enclosures house not just speakers but the amplifiers too. All BishopSound active speakers are carefully designed and matched to deliver optimum performance and will deliver the sound pressure levels we quote.  And if you have the slightest doubt, or any questions at all just give me (Andrew) a ring and I will help you!