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| EMagazine Volume 6 Issue 2 Apr/May 2001 |
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This article
describes a novel approach to whole house music distribution. A brief
review of the traditional approach is presented and its problems and
limitations are identified. A novel approach that provides higher
performance at lower cost is described in detail. The benefits and
advantages of this novel approach are also explained. |
Introduction
Music is an essential and integral part of life and living. Ever since the early days of phonographs, people have devised many a schemes to fill their homes and lives with music. Technology has facilitated these desires by radio transmission of music via AM, FM, satellite and now Internet broadcast of the music. The inventions of audio cassettes, compact disc digital audio players and now MP3 players have enabled people to take their favorite music everywhere they go. Yet a simple distribution of high fidelity music to every room in the house has been a real challenge. Technology has made phenomenal gains in the quality and fidelity of music but it seems that the distribution methods have still remained archaic. Most consumers rely on the professional installers of audio/video and home theater systems, but due to the lack of innovative products in this area some of these installers still have to use the same antiquated approach to music distribution in the house that they have used for decades. It is a perfect way to take compact disc quality music and turn it into a radio station quality. It is an irony that consumers may end up spending tens of thousands of dollars with some of the professional installers, yet may end up with state-of-the-art technology of the 1960s in this 21st century. The professional installers can not be blamed for the lack of innovation in this area. A very small percentage of the installers have gingerly embraced new technologies for the music distribution system in the last few years, and some are already reaping the benefits of the novel approach described here. In order to solve the problems with the distribution of music in the house, it is important to understand the physics behind the methods being currently deployed.
Basics of the whole house music system
The traditional approach in the 20th century for music distribution in the house has been based on the use of high-powered amplifiers at a central location and running speaker cables from that location to every room. In the remote room, normally the speaker level signals run through a volume control (transformer based or L-pad based) to the in-wall speakers. Figure 1 shows a typical such signal path from the multi-channel power amplifier at the central location to the remote room.
Figure 1
In a typical 2500 sq. ft. house, the average length of the speaker cable will be about 125 ft. This may seem a bit long to some, but when one considers that the speaker wires have to be snaked around the house to avoid noise coupling from electrical wiring it will be long. Some speaker cable runs can be much shorter and a few may be longer than the average length. It is acknowledged that about 20 to 25 watts per channel is more than adequate power to drive average efficiency in-wall speakers. Typically only 10 to 12 watts of power is sufficient for music but having an extra 10 watts of power will help with the loud passages in the music. So in order to deliver this power to the speakers in the remote rooms, the amplifier must also account for the losses in the cable runs and any losses in the volume control units. A 16 gauge (16AWG) wire of 125ft. length will be about 1.4 ohms in resistance. If 8 ohms speakers are being used in the room, this wire resistance is about 18% of the load impedance. This means, 18% of power is lost on the speaker cables. The volume control units can also have typical losses of about 15% to 20% as well. So the amplifier needs to provide about 50% more power than what is required in the room as shown in Figure 1. Thus to deliver 23 watts per channel in a remote room, the power amplifier needs to be about 35 watts per channel at the head-end. This amounts to a power transfer efficiency of less than 66%. If a 12-channel amplifier is considered at the head-end for six rooms in a home, the central amplifier has to provide an output of about 420 watts. These amplifiers are typically class A-B type with about 40% efficiency. Therefore to deliver 420 watts of total power at the output, the input power to the amplifier is more than 1050 watts! And not to mention that up to 630 watts is dissipated in a heat sink.
Power losses and inefficiency are only part of the problem. As the long speaker cable snakes around the house to get to the remote room, it is also susceptible to noise pick from the house electrical wiring. So the speakers in the room end up with some electrical noise picked up from fans, household appliances and low level 60Hz or 120 Hz buzz!
The volume control units are also known to ruin the frequency response of the signal, both at the low frequencies as well as the high frequencies of the music. The loss at low frequencies can be of limited concerns because most in-wall speakers are not capable of reproducing signals below 85 Hz anyway. But the losses at higher frequencies will affect the fidelity of the signal. Thus a Compact Disc quality signal at the central location sounds more like an average FM stereo signal in the room.
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In summary, it can be seen that the traditional method has the following limitations:
- Thicker and more expensive cables are required
- Thicker cables are more labor intensive and expensive to install
- Losses on the cables are compensated by larger and more expensive power amplifiers
- Transformer or L-pad based volume control units in the room impact the audio fidelity
- Speaker cables are susceptible to power line noise pick up in the house
- Signal fidelity is diminished due to longer cable runs and volume control units
- Lower efficiency of the system raises overall cost of ownership
In order to address these limitations posed by the age old methods of music distribution, new technologies should be utilized that enable use of thinner and more flexible cables that are inexpensive, have improved volume control capabilities, and do not sacrifice the high fidelity of the music signals. In simple terms, there needs to be a better and cost effective alternative to maintain the same quality of signal from the source to the remote room. There are a few ways to achieve these goals. One of them is quite appropriate and is described here in the following section.
Design overview
The rapid growth in data communications and networking industry over the last two decades has led to the availability of very high performance and inexpensive category 5 twisted pair cables. The phenomenal growth and development in the semiconductors and integrated circuit technology has yielded very powerful Digital Signal Processing (DSP) circuits, low noise / high performance linear pre-amplifiers and advanced high efficiency power amplifier designs. These advances in technologies have culminated in the design of DMS™ (Distributed Music System) based on the TPA™ (Twisted Pair Audio) and SAA™ (Stereo Audio Amplifier) components with pre-amplifier volume control. A simple implementation for music distribution is shown in Figure 2.
Figure 2
Using the TPA™ line-level stereo audio transmitter, signals are transmitted over standard category 5 cables to the remote room. The SuperTranZ™ circuit incorporated in the TPA™ transmitters and receivers eliminates ground loops and noise pick up, and provides a clean signal in the remote room. The signal level is also independent of the cable length. Hence, regardless of the distance from the central unit, the high fidelity of music is maintained. Also since the number of receivers connected to the category 5 cable do not impact the signal level, many rooms can be daisy chained or connected in a star configuration to the central location. Noise generated on the house electrical wiring will not affect the signals in this system. The signals in remote rooms will have a signal-to-noise ratio in excess of 96 dB and a 20Khz bandwidth. Thus the compact disc quality signal is maintained throughout the installation.
The electronic volume control is embedded into the remote receiver pre-amplifier design and does not adversely affect the music fidelity. It also does not contribute to any losses to the signal. This type of volume control does not adversely affect the low frequency and high frequency signals of music and so the high fidelity of music is maintained.
The DSP based high performance and high efficiency amplifiers in the room produce big luxurious sound, yet fit into a standard size junction box! The small, powerful package delivers true high fidelity performance that actually rivals the sound quality of large amplifiers. It consists of two separate mono-block amplifiers that provide extremely clean state-of-the-art power producing unexpected sound depth and musical clarity. The advanced protection circuitry of the amplifiers guards against system damage from overload, over-temperature, or short circuits. This makes them almost indestructible. The amplifiers provide clean 24 watts per channel with a power bandwidth of 100KHz and distortion less than 0.02% in the listening range. These amplifiers also sport greater than 85% efficiency and do not generate much heat in the unit. For an output of 24 watts, the amplifier takes in about 28 watts and only 4 watts is dissipated in heat. For 12 such amplifiers in the six rooms, total power consumption is only about 336 watts! This is significantly less than the Kilowatt needed with the traditional approach. Also the 12 amplifiers will dissipate a total of 48 watts in heat compared to 630 watts of heat in the traditional approach.
The only loss of signal power occurs on the short speaker runs from the power amplifiers to the speakers in the room. Since these are typically less than 40 ft., no more than 5% of the power is lost on them. Using this concept, 24 watts of power amplifier yields 23 watts of power delivered to the speakers, or about 96% transfer efficiency compared to 66% transfer efficiency with the traditional approach as shown earlier, and that too without any loss in the music quality.
Besides these salient features of the DMS™ system discussed here, it is possible to upgrade the implementation to include full DVD quality video and Infra-red remote control communications on the same category 5 cable using the advanced CATS™ products which are not discussed here. It can be envisioned that in the future the same category 5 cable can be used to carry Dolby Digital™ , DTS™ or other multi-channel formats. More information can be obtained from the web site www.wireless-experts.com .
In summary, it can be seen that the new approach has the following benefits:
- Flexible and low cost category 5 wires can be used to distribute music
- Flexible cables are less labor intensive and inexpensive to install
- Only short speaker cables are needed in every room
- Electronic volume control maintains high fidelity of music
- System is not susceptible to power line noise in the house
- High system performance is maintained regardless of cable lengths
- Higher efficiency of the system lowers overall cost of ownership
- Easy to upgrade in future with the advanced system architecture
The plug-and-play simplicity of the DMS™, not only benefits the professional installers in completing their installations with speed and performance but also enables the do-it-yourselfers to have a high quality music distribution system installed by themselves without any problems. Also the new homeowners in recent years who have been lucky enough to have their homes pre-wired with structured wiring can benefit from the ease and simplicity of this design. They can add high quality of music to their homes without any additional wiring.
Figure 3
The first generation of DMS™ is available with up to four sources and four zones. The basic DMS2.1™ shown here in Figure 3 will take two sources and send either one of them throughout the house to create a whole house distributed music system. A more advanced DMS4.4™ will take four sources and create four different zones in the house where each zone can listen to a different source at the same time independently.
Figure 4
Figure 4 and Figure 5 show two different wiring topologies supported by the system. It is recommended that a star wiring topology as shown in Figure 5 be utilized for maximum future expansion possibilities in the home.
Figure 5
Conclusion
The DMS™ represents a major breakthrough in high quality music distribution. It solves problems that have not been addressed by the traditional methods for over four decades. The superior signal quality level, the versatility of the system, and the complete avoidance of problems which plague traditional methods, make DMS™ the best overall approach to whole house music distribution.
The DMS™ has been successfully installed in a variety of commercial applications including music distribution at a resort and also residential applications involving connections of MP3 music from a personal computer in the home office to the main audio system in the family room.
About the Company
Pragmatic Communications Systems, Inc., is a Silicon valley based company established in 1994 to design, develop, and produce a variety of innovative products for wireless audio, video, and data communications. The majority of company's products until 1997 were primarily designed for industrial and commercial applications. The success of these products has led to a strong and dynamic technology base, which has been applied to new generation of products such as the DMSTM as described in this article and others like the CATS™, TrueMusic™ wireless hi-fi system and TrueView™ wireless video system. The company's philosophy is to use its technologies to solve problems that have gone unresolved for decades.
For more information:
Pragmatic Communications Systems, Inc.
544 E. Weddell Drive, Unit 8
Sunnyvale, CA 94089 USA
Tel. (408) 542 0330 Fax (408) 542 0339
Email: sales@wireless-experts.com
Web: www.wireless-experts.com
Author's biography
Prasanna M. Shah is the Chief Pragmatist and Thinker at Pragmatic Communications Systems, Inc. He earned his M.S. degree in Electrical Engineering from Stanford University and B.S. degree in Electrical Engineering from Santa Clara University, Santa Clara, CA. He has more than two decades of experience working on semiconductors for analog and digital audio, video, cellular telephones, wireless communications, fiber optic communications, data communications, data acquisition and industrial controls in the Silicon Valley. He holds one patent on power line communications and several patents pending on audio, video and wireless multimedia systems. An avid audiophile and music lover, in his free time, he likes to apply his pragmatic thinking to solve complex problems.
DMS™, SAA™, TPA™, SuperTranZ™, TrueView™, TrueMusic™ and CATS™ are trademarks of Pragmatic Communications Systems, Inc.
