Hack #37 from Home Theater Hacks by Brett McLaughlin (O’Reilly Media).
Speakers are the most obvious features of any home theater, and they can turn even a lousy movie into an in-depth, surround sound experience. Learn how to choose the best speakers for your room.
Speakers will stand out in any theater, even if you’ve got the coolest HD set with all the toys. Ultimately, home theater means surround sound, and it’s your speakers that will bear the task of pushing out this sound. So, take some time to understand the technical issues, and then go forth and buy!
Understand Speaker Crossovers
A crossover is probably the most important part of a speaker. A bad crossover design can cause a speaker that uses the best drivers in the world to sound like junk. An extremely well executed crossover network, however, can enable some very inexpensive drivers to sound excellent. The intricacies of crossover design are way over my head (and certainly not all that helpful in a newbie document), but a basic understanding of what a crossover is and what it does can help immensely in understanding home theater and, in particular, subwoofers.
Crossover basics. In a loudspeaker (such as your home stereo speakers) you almost always have more than one driver. In a “two-way” speaker system, you have a tweeter (usually 0.75 inch or 1 inch in diameter) and a woofer (usually 4 to 8 inches in diameter). The tweeter covers the higher-frequency sounds while the mid/woofer covers the lower frequencies.
The crossover is what makes the tweeter get only high frequencies, and the mid/woofer get only low frequencies.
A crossover consists of two filters: a high-pass (HP) filter and a low-pass (LP) filter. When you combine the two, you have a crossover. An HP filter allows higher frequencies to pass through it, while attenuating lower frequencies, and is therefore connected to the tweeter.
This should make sense: a high-pass filter allows only high frequencies to pass through.
An LP filter allows lower frequencies to pass through it, while filtering away higher frequencies, and is therefore connected to the mid/woofer.
Digging into the technical details. To understand the finer points of a crossover, you need to know what an octave is. An octave, at its simplest, is a doubling of audio frequency. So, when you see someone complain about subwoofers not being able to play the first octave, they usually mean 16 Hz to 32 Hz. The next octave is 32 Hz to 64 Hz, the next is 64 Hz to 128 Hz, etc.
The order of the crossover is how steep the slope is; in other words, it is a measure of how quickly the crossover filters away audio. A first-order crossover filters the signal gradually as you move away from the crossover point, while a fourth-order crossover filters much more drastically.
For anyone interested in the specifics, a first-order filter attenuates the input signal 6dB/octave. A second-order filter attenuates at 12dB/octave, a third-order filter at 18dB/octave, a fourth-order filter at 24dB/octave, and so on.
It’s very important to understand that the chosen crossover point frequency mentioned earlier isn’t a brick-wall divider. Let’s say the chosen crossover point is 2,000 Hz. This doesn’t mean that the tweeter plays the frequencies from 2,001 Hz and up and the mid/woofer plays the frequencies below 2,000 Hz. What it does mean is that below 2,000 Hz, the HP filter starts to filter off the lower frequencies at a specific rate. The farther below 2,000 Hz you go, the more the signal is filtered away. The LP filter is the reverse. Above 2,000 Hz, the LP filter starts to attenuate the high-frequency signal at a specific rate. The farther above 2,000 Hz you go, the more the signal is attenuated.
The neat part is that, given how the dB scale works, when you have a tweeter with an HP filter and a mid/woofer with a comparable LP filter, the frequencies where the filters overlap (frequencies that both drivers are playing) will be filtered in such a way that you get an even level across the entire frequency range the two drivers are capable of!
So, that’s a two-way speaker. A three-way speaker just has two crossovers. It has an HP attached to a tweeter. An HP and an LP are attached to the midrange driver and an LP is attached to the woofer. There are also fourway speakers, and I’m sure some fool somewhere has designed higher-way speakers.
You might also have seen speakers listed as 2 1/2-way. This means you have a two-way speaker with an HP attached to a tweeter and an LP attached to a mid/woofer. But you also have a second mid/woofer — or just a woofer — with another LP filter. This second LP filter starts to attenuate higher frequencies at much lower frequency than the first LP filter. Your receiver also has a crossover in it over which you have some configuration options. The purpose of this crossover is to do the exact same thing a normal two-way speaker’s crossover does between the tweeter and mid/woofer. The receiver’s crossover just does it between your subwoofer and the other speakers.
Choose the Speakers with the Best Music Playback
Many of you might be balking at this hack already; isn’t this a book about home theater? Yes, but this advice is still warranted. When choosing speakers, it’s common to be able to quickly narrow down your speaker choices to just a few brands, and sometimes even to just a few specific models within the same brand. However, decisions at this level become harder to make, and too often, price becomes the only factor. Although price is important, add the musical listening experience to your thought process.
A DVD movie soundtrack is very empty and is highly compressed [Hack #26], at least compared to a typical music CD. Music is a much harder job for a speaker to reproduce; a few minutes with music will show you things about a speaker that a movie will not. This is one of the reasons there are many budget home theater systems that sound really good: speakers that have to serve in just a home theater environment don’t have to be highly accurate audiophile-grade units.
Along these lines, be sure to choose a good two-channel music CD. SACD (Super Audio CD) and DVD-Audio both provide multichannel music, and are great secondary choices for musical auditions of speakers. However, they still are going to focus sound in all speakers, and you want to really test those front two speakers (the front left and front right), as they will bear the brunt of the load in all your music and movie applications.
Five Mini-Speakers Trump Two Towers
We all love big speakers. Our fathers had them if we were lucky, and we grew up with the idea that a good music system had to include large speakers that resemble the monoliths from 2001: A Space Odyssey. But these music systems tried to fill the corners of several adjoining rooms with sound. A home theater speaker system has a very different mission.
A good home theater tries to surround a few chairs with a circle of speakers. You don’t care what it sounds like outside the circle, and you really don’t want the sound to go into the next room (waking the kids and ruining your evening). Big tower speakers can be a part of the speaker array, but they sometimes are overkill for even medium-size rooms. They take up the most room, are the most expensive, and if not properly matched with the rest of your speakers, can actually worsen the home theater experience.
Try to obtain five identical speakers in your home theater so that as special effects jump from speaker to speaker, those sounds don’t change tone and break the illusion of movement. It is a lot easier to set up monitor-style speakers; you are guaranteed a tone match, they have a higher SAF (Spousal Acceptance Factor), and they are usually about half the price of their taller siblings with identical inner workings.
Monitor speakers have another advantage: they don’t have woofers. The woofers in large speakers take up a lot of power. When you position the circle of speakers around your room, the locations are almost guaranteed to be bad for the low-frequency sounds that the woofer produces. With five monitor-style speakers, you are forced to add a self-powered subwoofer to your system. This external sub can now be put in a better location in the room for low-frequency sounds without disturbing the other speakers. Although towers are great if you have a big room and lots of bucks, consider getting smaller, matched speakers for most cases.
The Importance of Brand Matching
If at all possible, you should buy all of your speakers (front left, front right, center, surrounds, and rears) from the same manufacturer. This will ensure that they are tone-matched, allowing sound to move evenly and seamlessly from one to the other. Additionally, many manufacturers provide specific lines that go together; these speakers will work even better than mixing and matching speakers within different lines from the same manufacturer. Better yet, you often can get deals on buying a complete matched set at the same time.
In cases where you don’t have the budget to buy all at once, consider getting the front three speakers (front left, front right, and center) at the same time, in a matched set. Even if the surrounds and rears for that set change later, you’ve got the front of your theater, which drives most of the sound, perfectly matched.
However, subwoofers are an exception to this rule. A subwoofer produces a lot of indirect sound; this means the sound bounces off your walls, floors, and ceiling before it hits your ears. Human hearing is very poor at subwoofer frequencies. In fact, many of the better subwoofer manufacturers don’t even build speakers, and instead focus on just subwoofers. Don’t get the idea that you need to buy matching speakers and subwoofers. Sometimes they are sold in sets, but that’s just to make it easier on some people.
Concentrate on matching your speakers, and then pick the subwoofer you like the best, regardless of brand or manufacturer. — Brett McLaughlin and Robert McElfresh
This material has been adapted from Home Theater Hacks by Brett McLaughlin, published by O’Reilly Media, Inc. Copyright O’Reilly Media, Inc., 2005. All rights reserved.
A smart collection of insider tips and tricks, Home Theater Hacks covers home theater installation from start to finish, purchase to experience. Just imagine: no frustrating trial and error process and better yet, no expensive appointments with installation experts. Home Theater Hacks prevents both by imparting down-and-dirty technique not found anywhere else.