After listening to your favorite music CD to determine whether you like the speaker under consideration?s bass response and treble smoothness, ask the salesman to play a movie soundtrack wherein voices and music are at equal levels.
A Few Tips on Choosing Home Theater Speakers
Albert Von Schweikert | Von Schweikert Audio
A Few Tips on Choosing Home Theater
Due to recent advances in technology, audiophiles are now able to enjoy audio/video equipment at home that is visually and sonically superior to the local cinemaplex. Indeed, the cost of high-end equipment is dropping every few months, enabling consumers on a modest budget to access a level of quality not imaginable a few years ago. As technology forces the prices downwards, technology also expands the choice of devices, making a buying decision ever more complex. In order to make a short-list of equipment to evaluate, here is a primer on how to go about choosing a suitable speaker system for your dream system.
First, choose the speaker style based on room size and placement considerations (see below). Next, choose the price range, and then begin to audition various brands within your price range. Note that within your price and style range, there will be significant differences in the actual sound quality between different manufacturer's systems. And since there are no standards for "tone" quality, you will have to do some comparative listening to determine what type of sound you will like best if two-channel music listening is a priority. Take your favorite music CD's to the store and listen for accurate tonal rendition; if the speakers sound good on music, they most likely will sound good on movie soundtracks, as long as the midrange frequency band is not pushed back in the frequency range balance.
PERSONAL SOUND TESTING
Taken for granted, of course, is that the manufacturer has the expertise to "voice" all of their different speaker models in the surround system with equal sound; this is called timbre matching. Test for this by having the salesman use the pink noise generator in the A/V processor; listen to uniform sound as the test tones sweep from speaker to speaker. If all of the speakers in the surround system sound identical, you have found a superior speaker system and you'll hear the best coherence of the sound field in a complex movie sound track - depending on how clear the speaker is in the midrange, of course!
Even though "flat frequency response" (a level balance between all musical tones) is an oft-stated goal of most manufacturers, it is surprising to see magazine test reports showing wide variations in volume levels between bass, midrange, and treble frequencies. (One high-end speaker system that won "Product Of The Year" at a famous magazine had a 9dB hole in the critical midrange frequency band, smack dab in the middle of the vocal range! Indeed, the manufacturer boasted about the "depth" of their soundstage, when in truth, the midrange was devoid of presence and clarity, as noted by the editor in charge of measurements).
After listening to your favorite music CD to determine whether you like the speaker under consideration's bass response and treble smoothness, ask the salesman to play a movie soundtrack wherein voices and music are at equal levels. For this test, have the salesman turn on the entire surround system if your listening was done with only the main speakers. Sadly, there are quite a few speaker companies that have not optimized their center channel dialog speaker for vocal intelligibility. If the voices are not clearly understood during loud music passages, try another speaker brand.
When making an assessment of vocal clarity, you may wonder how there could possibly be such a wide range of quality and/or clarity in the all-important midrange frequency band. Although the answer is complex, the main reason is based on distortion inherent in the materials used to build the cone, motor, cabinet, and crossover. When the level of distortion (caused by cone flex, cabinet wall resonances, and improper crossover design) reaches a certain level, the speaker system is no longer able to resolve low level detail and sounds "veiled." This is the cause of the lack of vocal intelligibility found in so many speaker systems found in the mass market electronics stores. By contrast, speakers designed by audiophile-oriented engineers utilize exotic materials to increase the level of vocal intelligibility; these types of speakers are most often found at the specialist hi-fi dealers that have lately gone into home theater and multi-channel audio.
BASS RESPONSE TUNING
In order to provide satisfying bass response in two-channel music reproduction, many speaker designers use a bass reflex ported enclosure. However, ported speakers often sound "boomy" due to undamped cavity resonances found in this type of design. Since the vocal intelligibility is greatly diminished by any type of boom or resonance in the lower range of the speaking voice, avoid the mistuned bass reflex designs at all cost and seek out either sealed systems or the legendary transmission line designs.
The "transmission line" design also uses a port to extend the bass response; however, this type of ported speaker is "non resonant" and has far tighter bass due to the extensive use of internal damping materials. Bass reflex design = hollow box with port. Transmission line: ported box completely filled with stuffing (fiberglass, wool, or Dacron).
If you have been looking at speaker systems for a while, you have noticed the wide variety of tweeter designs available: dome materials range from soft materials such as fabric, to hard materials such as metal. Although the hard materials have a sharper response and sound good on transients, many times their excessive response becomes fatiguing, making a soft dome easier to listen to over extended periods of time. Although a few years ago soft dome tweeters were criticized for their lack of sharpness on transients, this is no longer true. A few modern soft dome tweeters utilize a stiffening coating of a synthetic material to bridge the gap between a purely hard or soft sound quality.
ROOM SIZE CONSIDERATIONS
First, choose your video monitor based on your room size and layout; the video monitor choice may dictate a speaker system type. At the lowest price range of high definition video monitors ($800 to $1,500), a tube monitor of 36" on a table stand or a rear CRT projector with 40" to 50" screen will fit into a small room. For this application, there are several speaker choices that make sense:
The second video monitor choice in a small room would be the wall mounted plasma or LCD flat screen set. As the prices continue to fall, this choice is now affordable for most families; last weekend, I saw a 42" plasma screen advertised for less than $2,000! To go with the wall-mounted video monitor, it makes sense to use either on-wall or in-wall speakers.
In a larger room, the video monitor choices expand, with a separate screen/projector being the purist's choice if a larger budget allows. For a medium priced system, a 50" to70" rear projection set will offer a very high value for the expenditure, making this the most popular type of home theater video monitor. Along with rear-firing CRT projectors, thin-chassis DLP and LCD sets are becoming popular as their prices continue to drop. Your buying decision for the video monitor will probably be based on the actual store demo; there are plenty of tradeoffs regarding the various technologies on the market. Just remember that where you place your monitor will in some way dictate where you will need to place the speakers, at least in a cosmetic sense.
For this large system, tower speakers make the most sense if the room is a dedicated home theater and not part of the general living space, where size becomes an issue. When based on purely sonic considerations, tower speakers are the way to go, here's why:
Many industry experts recommend using identical speakers in all locations for best timbre matching. Gary Reber of Wide Screen Review has been extolling the virtues of his seven channel "clock" placement, using the same speaker model in all seven positions. Indeed, if you have the space and inclination, this is the state-of-the-art in system design! Simply choose a tower speaker with exemplary frequency response, wide bandwidth, and low distortion, making certain that the vocal intelligibility is exceptional. Next, using a tape measure, determine an equal distance for all of the five, six, or seven channels, using the listening/viewing chair as the center of the clock. Ideally, you will be equidistant from each of the channels/towers, as they are placed in a circle around you. Having personally experienced this placement scheme in the WideScreen Review laboratory, I can attest to its state-of-the-art sound quality: simply breathtaking! In effect, this is near-field listening, with the speaker response overshadowing (and reducing) the audible room coloration.
If this type of speaker system location is not optimum for your room considerations, your next "best bet" is to find a manufacturer whose speaker systems are constructed with the same drive units and crossover design, from the left/right mains, to the center channel and surrounds. Although there will be minor discrepancies in the timbre matching due to differing cabinet volumes and shapes, the sound field errors will be negligible, as they will be swamped by the program material differences between the channels.
SURROUND SPEAKER DESIGN
In the event that matching tower speakers cannot be used all the way around the room due to size or living conditions, the next best type of design will utilize matching drive units and crossovers from front to rear. Although the enclosure shapes and sizes will differ depending on the placement scheme, a good timbre match will be achieved by the careful designer. Many rooms that will contain a tower speaker at the front may have the listening position placed directly at the rear wall, dictating that a wall mounted type of surround cabinet to be utilized. That's fine, but do you want a monopole or dipole response pattern of directivity behind you? The choice is not clear cut, as it depends on the type of program material being played! Just what is a monopole/dipole, anyway?
Monopole: a speaker design where the sound is radiated from the front of the cabinet in a forward-facing direction, with all frequencies in phase with each other, i.e., the normal box speaker design. Devotees of the DTS (digital theater sound) encoding system believe that monopole speakers have a superior ability to image a pinpoint source location of the original sound field event; most engineers believe this to be true, IF the program material calls for directional cues, such as multi-channel music reproduction (not a film track).
Dipole: a speaker design where the sound is radiated by front and rear arrays, or side by side arrays; the critical design element is that the two arrays are driven out of phase with each other. Note that planar or open-back speakers are automatically dipolar in nature, without resorting to two separate drive systems, since the rear wave is automatically out of phase with the front wave. The "null," located at the junction of the arrays, is caused by the phase cancellation, where the positive and negative waves meet and cancel each other. This "null" is aimed at the listeners, so that the actual physical location of the speaker enclosure is not audible, or "localizable" as it is termed by psychoacousticians. This type of design does indeed wash the room with ambience and creates the desired lack of localization; and when this type of ambience is expected from the source material, such as rain, crowd noise, the scattered din of a battle, it is highly enjoyable.
Although the dipole design is fantastic with movie effects, it is not a good choice when playing multi channel music selections, where rear channel steering and localization IS desired. The THX company, once a division of Lucasfilm, patented the dipole design and mandates that the dipole design be used for rear/side surrounds to be qualified as a licensed THX system.
What if you want to watch a movie that will sound best with a dipole speaker, then later listen to a multi-channel music selection where you will want to use a monopole? The answer is: buy a surround speaker that is switchable between the two radiation patterns. One such design is the Von Schweikert TS-150, a small wedge shaped enclosure with two 5" woofers and two 1" tweeters. Located on the side of the enclosure is a push button switch that enables the simple conversion between monopole and dipole. This speaker system can be mounted at ear level on stands, behind or to the side of the listener, or alternately, up on the wall; mounting brackets are provided.
A decade ago, when home theater was coming into popularity, the Lucasfilm company designed a set of standards that they believed were necessary to standardize quality reproduction in both commercial and home theaters. Although sound quality per se was not one of the elements in this set of standards, at the time the THX requirements set a benchmark in some regards. The dipole surround speaker, timbre matching, and low distortion levels were some of the best aspects of the THX standards. However, not everyone agreed that these standards should be universally accepted.
One of the most controversial aspects of the TXH design was the multiple tweeter array, designed to promote a highly directional dispersion pattern in the vertical plane. This feature directed the high frequencies towards the listener's ears, greatly reducing reflections from the floor and ceiling. In a commercial movie theater, where reverberation is a huge problem, the controlled directivity did indeed promote better vocal intelligibility in the treble frequency range. However, many critics of the THX home theater speakers noted that the increased vertical dispersion pattern ruined the sound for music listening, feeling that the sound was too overbearing in the treble.
Today, the THX company has relaxed their insistence that THX certified speakers MUST use multiple tweeters to achieve the desired effect, and other tweeter designs are now allowed. Should you invest in a THX-certified speaker system? The answer is: listen to one and determine whether you like the sound you hear; many companies offer this design, although the controversy is not over.
SUBWOOFER DESIGN TRADE-OFFS
Although many listeners choose a subwoofer based on size and price, accurate transient response is often overlooked; however, the transient response (erroneously called "speed") IS extremely important when reproducing music. Although a loud and boomy response is sometimes desired by neophytes when action movies are screened, this type of sound becomes quite annoying when music is bogged down by the slow "one note bass." Ported subwoofers, along with subs using passive radiators (another form of bass reflex loading), can often sound like they are lagging far behind the main speaker; this time lag is caused by the under-damped nature of most bass reflex designs. In addition, mistuned ports have high levels of wind/port turbulence, making the bass notes sound "chuffy."
A superior subwoofer design is the sealed system, which necessitates a built-in equalizer to generate the deepest bass notes, especially when a small enclosure is required. Although more expensive than simple ported boxes, the new breed of equalized sealed subwoofers will enable you to listen to music without the dreaded loss of rhythm and pace. You can recognize this type by the small size and lack of port.
ENGINEERING FOR CLARITY
Speaker design has come a very long way from the crude acoustic horns of the beginning of the century. Twenty years ago, the electrostatic speaker was king of the audiophile mountain due to the lack of enclosure resonance distortion and lack of cone/crossover anomalies. However, the lack of bass extension and total lack of power handling caused system designers to focus their attention on improving on the lowly cone design. Today, many manufacturers of cone (sometimes called "dynamic") speakers have achieved a level of clarity and coherence that surpasses the electrostic/ribbon/planar type of speaker design, as hard as this may be to believe. Improvements in cone materials, lowered distortion in the "motor" structure (voice coil and magnet), and improved cabinet/crossover design has propelled the basic cone speaker to the head of the class when measurements and the listening experience are used to verify "realism" or accuracy to the input source. Look for midrange cones made from Aerogel and "low distortion motors" if you seek the very highest level of midrange clarity available.
CREDIBILITY OF ENGINEERING
When choosing your next home theater speaker system, do some basic research on how the company designs their products. Far too many so-called "audiophile" speaker companies design their products by ear and do not even own a proper laboratory. Although many of these "cult" brands have a following due to the esoteric nature of their products, their designs are not based on hard science and may fail the acid test of measurement accuracy or "faithfulness to the signal." If accuracy is your goal, along with long term satisfaction, try to find a company that has an engineering staff and a good laboratory. Although there are a few large companies with these basic requirements that do not make "good" sounding speakers due to their obsession with corporate profit, there are a handful of audiophile speaker companies that not only use the best test equipment and scientific design, but also use "golden ear" auditioners and live musical instruments to compare their designs.
One of these companies is Von Schweikert Audio, started in 1976 by a bunch of lab nerds from California's Institute of Technology, home of Jet Propulsion Labs and NASA's Apollo 12 successful lunar flights. Many of the engineering aspects noted in the above article are used by Von Schweikert Audio in their award-winning line of two channel and multi-channel speaker systems. To see VSA's products and learn more about the ultimate speaker engineering on the planet, please visit www.vonschweikert.com for further information.
Copyright 2005 by Albert Von Schweikert and VSA.
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