Speaker specifications: A consumer guide

I recently met with speaker designer Andrew Jones at the CNET office in NYC to discuss his latest project, the new Pioneer SP-SB23W Speaker Bar. And after we finished, I picked his brain about the value of speaker specifications.

My take is that most, but not all, are nearly useless for providing consumers with information that could lead to opting for one speaker over another. For example, what exactly does "power handling" mean? When a manufacturer claims its speaker has a 100-watt power handling rating, can it be safely used with a 200-watt-per-channel amplifier? Or a 500-watt amp? Yes, just don't play the speakers too loud, and if you start to hear distortion or the woofers are making thumping sounds, turn the volume down.

Right; too much power can damage speakers, but what about too little? Running a 50-watt-per-channel amp with the same 100-watt-rated speakers won't guarantee they won't be harmed by playing them too loud. Jones put it this way: "If they sound really, really bad, that should be an indication it's too loud; please stop."

Room size has to be taken into consideration when discussing loudness. For the purpose of this discussion we're referring to an average 12-by-18-foot room. If your room is two or more times larger than that, power requirements escalate. If you have a 20-by-30 room, don't expect a set of tiny speakers to play at rock concert levels. Here's a worst-case scenario -- play your 50-watt receiver really loud with 100-watt-rated speakers in your back yard, and there's a chance they won't survive the good times. So too little power can damage speakers when they're played too loud. If you want to really crank your tunes, even just once a year, buy big speakers and a really powerful amp or receiver.

At this point I reminded Jones that I'm trying to break these questions down so even the least technical readers can get useful information, and I asked if it's safe to assume a speaker with two woofers will always generate more bass than a similarly sized speaker with just one woofer. Jones just smiled and said, "You're asking an engineer, right? Two woofers in a tower speaker make it easier to reduce the standing waves inside the cabinet, and that's a clear advantage, but it's easier to engineer a longer throw in a larger driver."

OK, I followed up, "One 8-inch woofer will make more bass than two 6-inch woofers, right?" He said, yes, but there are always other factors in play; the number of woofers or woofer size may not be a reliable gauge of bass capability. Sure, large woofers in larger cabinets generally make more bass than smaller woofers in smaller boxes, but the quality and definition of the bass isn't something that specifications can predict.

Frequency response specifications can be misleading, and, as Jones reminded me, only trust ones that define the number with a "+ and -" tolerance, for example, "30Hz to 22KHz +/- 3 dB." The first number in that sequence refers to the speaker's lowest bass frequency, the second number the highest treble frequency, but if the spec doesn't also include a +/- tolerance, the spec is meaningless. With bass frequencies, the lower the number, 25Hz vs. 30Hz, the better; the lower number indicates that the bass will be deeper. There is one problem -- comparing one manufacturer's specs against another is next to impossible. There are too many variables involved to make the numbers meaningful. Jones said, "As a consumer you have no idea how realistic that performance spec is."

Speaker impedance confuses lots of buyers. Most mainstream consumer speakers are rated between 6 and 8 ohms; some higher-end speakers go lower, to 4 ohms or less. So the question is how does that relate to a receiver or amp's impedance requirements? Can you use a 4-ohm speaker with a receiver with 6- or 8-ohm power ratings? The short answer is yes you can, but the speakers will distort sooner than they would with an amp or receiver with a 4-ohm power spec, when the speakers are played loud. When in doubt about a low-impedance speaker's compatibility with a receiver, check with the speaker's and/or receiver's manufacturer. According to Jones, some receivers might not play at all with low-impedance speakers; again, check with the manufacturer. I'm using the 4-ohm speaker as a worst-case example; most consumer speakers have higher impedance. If your speakers are rated at 6 or 8 ohms, you never have to think about matching impedance.

Then I asked Jones, "Is there one spec that buyers can always count on to predict superior performance?" I proposed speaker weight -- the heavier speaker of two -- is more likely to have a better-built cabinet or drivers with larger magnets. It's a far from scientific approach, but most speaker specs don't predict sound quality either. Jones wasn't totally on board with my view, but he didn't have anything to say about it.

One spec I find useful is "sensitivity," which is sometimes referred to as efficiency. A higher-sensitivity speaker will play louder than a speaker with lower sensitivity with the same amount of watts. The variations in sensitivity from one speaker design to the next can be large, and sensitivity is unrelated to power handling. A speaker with a sensitivity spec of 90 dB/2.83 volts is considered moderate; one with a 94 dB/2.83 volts is higher. Sensitivity becomes an important spec to consider when you have a low-power (50 watts or less) receiver or amp, or you like to play music or movies really loud.

I'll cover speakers that can play loud in greater detail on tomorrow's Audiophiliac, and give a few specific recommendations.