Friday, May 20, 2011

Choosing speakers to match your amplifiers


By UK Sound Base

Of all the equipment we use in our hi-fi and home theater systems, the thing that's changed the least over the past 20 years is the speaker. After all, there's only so many ways you can move air to produce sound. With that in mind, matching speakers to an amplifier should be easy, right? Well...it's not rocket science, but there are a few key specifications that affect their overall performance.

Impedance: Measured in ohms (?), typically 4, 6 or 8. The lower the impedance, the more demand the speakers place on the amplifier, which is why matching the impedance of your speakers to your amplifier is important. Most home theatre speakers will be 6 or 8?, as are most home theatre amplifiers. Hi-Fi (2 channel) amplifiers are often capable of handling impedances of anywhere from 8?, all the way down to 2?. Consequently, speakers designed for 2 channel systems come in a wider range of impedances.

A common complaint of people with mismatched speaker/amp combinations is that they shut down during loud action scenes in movies, or after 2-3 minutes of music at a moderate level. The amplifier/AV receiver often gets unfairly blamed in this scenario.

Power handling: An often misunderstood specification. Measured in watts, it is best represented by RMS (root means square.) This figure tells us how much power the speaker can comfortably handle for a sustained period of time. Also referred to as continuous, or nominal power.

Power handling doesn't necessarily translate as a speakers ability to produce sound as many would have you believe.

PMPO (peak music power output) is essentially the measure of the speaker operating at or near its absolute limits on the verge of serious damage. It is not a useful rating, and easy for manufacturers to inflate - so avoid it completely.

When power matching speakers to an amp, a good rule of thumb is to power them with a little more juice than they're designed to handle - around 10% should do it. That way the amplifier doesn't have to work as hard to drive the speakers to their full capacity, resulting in cleaner, more dynamic sound. Speakers are designed to handle fluctuations in power levels, so this extra bit of juice won't cause any issues.

Sensitivity: Sensitivity is a rating often listed for speakers but not terribly well understood. Measured in decibels (dB), it refers to the speakers ability to turn the power from the amplifier into sound. The higher the rating, the more efficient the speakers are. Anywhere from 87-93 dB is typical of most speakers, but anything 90 dB or above is a good rating.


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