Ara has recently started a new hobby of building his own speakers at home. In the course of building them, talking about them and creating videos to show how he does it, we realized there quite a few speaker terms and some tech jargon we may throw around that not everyone is familiar with. Some of you may know this inside and out, for others it’ll be a refresher and for some, parts of this may be brand new, but we’ve compiled a glossary of sorts, based on some prior episodes and some new stuff, to make sure we’re all in on the conversation when talking about speakers.
Measures the range of audible frequencies a speaker reproduces across the entire audio spectrum. This spec helps you assemble a set of speakers that allow you to hear everything you’re supposed to. The general rule of thumb is that we humans, with young, undamaged eardrums, can hear really low sounds down to 20 Hz all the way up to really high-pitch, piercing sound at 20 kHz. Many argue that the highest and lowest frequencies are less important because the human ear doesn’t hear them as well – and for some of us, not at all. But for the lower range, it may not be as important to hear it as it is to feel it.
The scientific name for a speaker, or a loudspeaker, is an electroacoustic transducer. The transducer converts an electrical signal into the sound you hear when watching movies or listening to music. The individual transducers themselves are often referred to as drivers. The term speaker and driver can sometimes be used interchangeably. The word speaker is also used to describe a set of drivers in an enclosure – the speakers you buy at the store, online or in some cases, build at home. There are three basic types of drivers: tweeter, midrange and woofer.
Larger speakers tend to cover a wider range of frequencies, which is why you typically want larger speakers for your front and center channels. You can get away with smaller speakers in the surround channels because the sound there doesn’t tend to be as dynamic as the front of the room. Although some very large speakers will cover the lowest end of the spectrum, down to 20 Hz, most home theater speakers don’t go that low, so you need a subwoofer to fill that gap. Without the really the low end frequencies, a home theater tends to lack punch and the audio doesn’t feel as full.
The Crossover is an electrical filter that could be a high-pass, low-pass or band-pass filter. It is used to divide the audible frequency spectrum (20 Hz – 20 kHz). Since most loudspeaker drivers are incapable of reproducing the entire audio spectrum, the crossover is used to make sure the correct frequencies are sent to the drivers that are built to reproduce a particular sound range. Without a crossover every driver would be sent the entire frequency range, resulting in muddied and sub-optimal audio experience.
A port in a speaker cabinet is a hole or vent that allows air to escape from inside the enclosure. A speaker without a port is referred to as a sealed enclosure, where no air is supposed to escape from inside. This design yields a more accurate response and produces a speaker with a bit more punch. A ported enclosure is more difficult to design, it requires a more scientific approach, and they tend to be larger than sealed cabinets. But a ported subwoofer allows for extended bass response, resulting in deeper bass and a stronger physical impact: you can feel the rumble. Ported speakers are also more efficient. They increase the bass output of a speaker by around 3 dB, and that cuts the power requirements for your amplifier in half. More on that in a moment…
Decibels, or dBs, are a measurement of sound level. Our ears detect changes in volume in a non-linear fashion. A decibel is a logarithmic scale of loudness. A difference of 1 decibel is an almost imperceptible change in volume. It takes about 3 dB for most humans to hear a difference and 10 decibels is perceived by the listener as a doubling of volume. On your receiver or amplifier when you go from -15 dB to -5 dB the sound volume hitting your ears is doubled. As a side note, it takes a doubling of wattage in your amp for an increase of 3 dB. That’s why paying an extra $200 for the next model up just because it is 125W instead of 100W is a waste of money. Provided, of course, that’s the only additional feature.
This is the spec we use routinely to rank speakers when purley going by paper, not by sound. If you’re doing your homework on Amazon or another online retailer, keep an eye out for sensitivity. It gives you an idea of how efficient a speaker is; in other words, how hard it is going to make your receiver or amplifier work to play back those explosions you want to hear louder than you probably should. What it really measures is how loud the speaker will play when given a standard test input and measured at a specific distance, typically 1 meter.
As you can imagine, when fed the same test signal, the louder a speaker will play, the more efficient it is. So sensitivity is a measure of the speaker’s volume, expressed (as volume often is) in decibels. The higher the number, the higher the efficiency and the better your speaker will perform. Your receiver or amplifier won’t have to work as hard to produce the same volume level. Typical numbers are in the mid to high 80s; anything over 90 is considered excellent. Sensitivity won’t tell you how good a speaker sounds, but it will tell you how easy it will be to crank it up.
This is another measurement, like sensitivity, that is of no value when it comes to the pure audio quality of the speaker, but it can help guide some buying decisions. Where sensitivity tells you how hard the amplifier needs to work to produce a particular volume level, impedance tells you how much strain the speaker itself puts on your amplifier. Most speakers are rated at 8 ohms, and most receiver specs are quoted assuming an 8 ohm speaker load. The lower the impedance number, the more strain, so if you come across a sweet pair of 4 or 6 ohm speakers, you’ll need to make sure your receiver can handle them.
Also keep in mind that impedance is something you can influence if you decide to add more speakers to your home theater. You can’t simply add more speakers to the same channel. When you do, you change the overall load or impedance for that amplifier channel. Adding a second speaker to a channel, when connected in parallel, will actually cut the impedance in half, so instead of the amplifier working to run one 8 ohm speaker, it now has to work as if it is connected to one 4 ohm speaker. This could have a negative impact on your amp. Connecting speakers in series, however, actually has the opposite impact, but that may be too deep a discussion for this episode. Bottom line, make sure you know what you’re doing if you decide to add multiple speakers to the same surround sound channel.
This tells you the maximum amount of power you can run into a speaker without damaging it. To be honest, the spec is somewhat useless. A 200 watt per channel amplifier will rarely, if ever, run at the full 200 watts to each channel. If you tried it, you’d probably have blood coming from your ears before your speakers, that may be rated for 100 or 125 max watts per channel, would give out or blow. The 180 watt or 200 watt receiver is probably going to be a higher quality item than a 50 or 80 watt unit, so even though the smaller ones will never have the chance to ruin your speakers, they won’t sound as good either. Use common sense and you should be just fine.
Posted by The HT Guys, March 19, 2015 11:45 PM
About The HT GuysThe HT Guys, Ara Derderian and Braden Russell, are Engineers who formerly worked for the Advanced Digital Systems Group (ADSG) of Sony Pictures Entertainment. ADSG was the R&D unit of the sound department producing products for movie theaters and movie studios.
Two of the products they worked on include the DCP-1000 and DADR-5000. The DCP is a digital cinema processor used in movie theaters around the world. The DADR-5000 is a disk-based audio dubber used on Hollywood sound stages.
ADSG was awarded a Technical Academy Award by the Academy of Motion Picture Arts and Sciences in 2000 for the development of the DADR-5000. Ara holds three patents for his development work in Digital Cinema and Digital Audio Recording.
Every week they put together a podcast about High Definition TV and Home Theater. Each episode brings news from the A/V world, helpful product reviews and insights and help in demystifying and simplifying HDTV and home theater.