Dear Editor (Apr. 1976)

Ride-A-Rama!?!

Dear sir:

I have noticed lately in certain curious articles printed in your April issues, Professor I. Lirpa, whom these articles concern, usually discusses some radical ideas for sound reproduction. In 1973 he conceived the idea of producing records to play the inside of the disc first and finishing at the outside (clever yes, but hardly new; some of my friends had their turntables playing in reverse for years, for reasons you wouldn't understand if you're usually "straight" or sober!). My present line of thought is on the subject of sound separation and isolation, which is part of the original "realism" formula for ultimate high fidelity in the home.

Commercially speaking, there is no pure separation or isolation of non related sounds, even with discrete stereo or quadraphonic signals because they are both essentially mixes.

Their gain over synthesized multichannel systems is the fact that all their channels are individual and do not depend on each other. All these systems can be very satisfying as far as music is concerned, but many people (including myself) are frustrated with trying to locate the individual sounds.

Professor Lirpa's alternative to this, of course, was the basis to your "Converting To Mono" article. That article deserves a belated round of (monophonic) applause for preserving the sanity of those thousands who tried their utmost (budget permitting) to keep each sound separate.

Never-the-less, we "Isolationists" dream on.... One dreamer, a close friend of Dr. Lipra as it turns out, owns and operates a local hi-fi business and is known for his friendliness and fairness when making a sale. He is a modest man and had asked me not to mention his name. Therefore, I will refer to him by "Mr. Jones," a false name.

Mr. Jones, I have discovered, has been long displeased with the state of high fidelity and its lack of separation.

He was there like a trooper when audiomania first hit; with woofers, tweeters, and mid-ranges that would fill a store (which it did-his!). He had sounds like you would not believe...but only frequencies were discrete and he grew weary of whole orchestras getting up and running from one speaker to another, depending on their note and octave! Stereo was next. He quickly doubled his system, speakers and all, to grasp its full effect. Suddenly, voices and instruments would walk from channel to channel. For once an actual separation of sounds took place.

Still things seemed crowded. Sometimes two different sounds would occupy the same space at the same time.

Often, I would hear Mr. Jones angrily yell, "WHAT'S THAT !l@%#&tt GUITAR DOING IN THE SINGER'S MOUTH?"

He finally realized you could only do so much with stereo, just as you could only tie so many knots in a piece of string before tying double knots.

Quadraphony was no better, except that he was no longer making double knots, but square knots.

The result of these phases provoked Mr. Jones into devising what Dr. Lirpa considers the future of, and perhaps the ultimate in high fidelity. For the past several months he has been designing a system which he has termed "RAR/64," or more explicitly, "Sixty-four channel RIDE-A-RAMA." As the first part of the title suggests the system consists of 64 separate, discrete channels. Each of these channels drives a full audio-range speaker set (containing as many drivers and crossovers as desired). The speaker units are placed in an empty room so that they completely cover all four walls.

In the center of the room's floor would sit the system's nervous center.

Basically, it is a super-quiet, hydraulically lifted chair which contains inside all electronics necessary to control each channel as well as movement of the chair. As Mr. Jones puts it, "Why make the sound come to you, why not go directly to the sound?" The chair not only serves the owner with a comfortable seat, it also increases listening pleasure by taking the operator to any specific speaker he desires. Incidentally, this also eliminates those little knobs and joysticks known as "balance controls." Mr. Jones informs me that more than one chair could be attached to the lift. (Personally I think a love seat would be excellent for dating purposes!) Presently the RAR/64 has one holdback that is preventing it from becoming a reality: sixty-four channel program sources do not as yet exist. Jones says this can easily be worked out and expects to have an RAR/64 by 1984, possibly sooner.

So there you have it. Someday soon you may be riding on your very own personal Ride-A-Rama. If you are like me, 1984 can't come soon enough! I hope you are as excited about this as Mr. Jones, Dr. Lirpa, and I. We'll be keeping our expectations high, and writing to you frequently to inform you of further developments.

I almost forgot! If you think 64 channels are not enough, remember that 128 are next.

George Atwell Beazy; Horse's Breath, Montana

Low TIM Amp Addendum

Dear Sir:

Those readers who are building the low TIM amplifier which I described in the February issue of Audio should be aware of a potential problem with the specified heat sinks. Unlike the heat sinks used on my two prototypes, those specified in the parts list for the amplifier are anodized. Thus, they have an insulated coating which may make ground contact through the four mounting screws on each circuit board impossible.

To remedy this, the anodized coating should be scraped away from the areas where all four nuts on the circuit board mounting screws make contact with the flanged edges of each heat sink. The same should be done under all nuts on the screws which attach the L-shaped mounting brackets to the heat sinks.

An alternate solution would be to run ground wires of No. 18 stranded wire from circuit board grounds to the chassis. However, the method described above is preferred for minimum hum.

W. Marshall Leach

Georgia Tech–EE

Atlanta, Ga. 30332

EDITOR'S NOTE:

The last two paragraphs of "Build A Low TIM Amplifier" by W. Marshall Leach in the February issue were inadvertently left out. They are: Once R25 has been adjusted for both channels, the bias potentiometers should be marked with a fiber tip pen so they can be reset if they are accidentally misadjusted. Preferably, they should be sealed with wax so that this cannot occur. After this is done, the amplifier is ready for use.

Several precautions should be observed when using the amplifier. Never test it with a capacitor for a load, for the fused emitter resistors R29 and R30 will blow. Never attempt to connect or disconnect either the input or output leads with the amplifier on. Instead, turn it off and wait for the filter capacitors to discharge. They will discharge much more quickly if the amplifier is turned off without reducing the input signal level. When this is done, the amplifier will continue to operate several seconds until the filter capacitors are discharged. With the amplifier turned off, carefully check the speaker leads to insure that they cannot short together. Never drive a load of less than 4 ohms. And never place the amplifier where the air cannot circulate freely over the heat sinks. Happy listening!! More on AM Sound Dear Sir: Around 16 years ago, I was chief engineer for a low-power, college AM broadcasting station. This was, as far as we could make it, a high-fidelity operation, from the choice of the same moving-coil pickups as enthusiasts used at home, through studio equipment carefully designed with judicious use of feedback, to use of modulators in class AB instead of the usual class B. We did allow the telephone lines to introduce a gradual rolloff to-5 dB or so at 10 kHz, which was probably just as well considering what the mechanical impedance of the pickup styli was doing to the treble sound, but we discouraged gain-riding and never used compressors, peak limiters or other music homogenizers, which is more than some "quality" classical FM stations can honestly boast today.

At first I had the same skepticism as Paul Swartzendruber expressed in your January "letters" column, that these perfectionist efforts (largely my predecessor's) would be vitiated by the mediocrity of our listener's table radios. I was wrong. Aside from the mostly classical content and often callow announcing, this station was identifiable by an easy clarity of sound not found anywhere else on the dial, if the radio was one getting adequate signal strength.

Unless broadcasting stations are very much better, or radios much worse, than in those days, the limitation on the sound quality of AM is not truly at the receiving end.

-Jack Reed Chicago, Ill.

TV Sound

Dear Sir:

After reading Paul Swartzendruber's letter about AM receivers (Jan. 76), I felt compelled to comment on the current state of audio in television broadcasting. While Mr. Swartzendruber complains of poor quality only at the receiving end, television audio suffers at the home receiver, as it passes through network leased transmission facilities, and at the point of origination.

Television utilizes frequency modulation (FM) to transmit the aural portion of its programming and is capable of essentially flat response between 30 Hz and 15 kHz. The only receivers I have ever seen which could reproduce this kind of bandwidth were old monochrome sets with big cabinets and multiple speakers or sets that were combined with a stereo system in one huge console. The trend today is toward smaller television receivers which necessitates smaller speakers, but even large consoles are being equipped with tiny speaker systems.

Most commercial television stations are affiliated with one of the three major networks (ABC, CBS, and NBC) and as a result receive a large portion of their programming from the network control center in New York City.

The visual portion of the signal is routed to the station on AT&T microwave facilities leased by the network, while the aural portion arrives on a 5 kHz audio loop also leased from AT&T by the network. The visual signal travels through an essentially transparent medium, but the aural signal suffers considerable degradation as it passes through the reduced bandwidth audio loop. A typical specification for one of these loops is plus or minus 3 dB from 100 Hz to 5000 Hz with harmonic distortion less than 3% and noise at least 46 dB below normal program level.

This may all seem pretty gruesome until one realizes that the greater part of network audio is primarily vocal in nature. Most of the music we hear is in the background and not meant to be listened to solely for its entertainment value. Musical variety shows suffer the most from poor transmission facilities and small speakers in home receivers. The audio tracks of these shows are very good; usually having been recorded on multitrack machines, mixed down to mono, and then added to the videotape master after editing is completed. Feature films suffer somewhat less than the musical shows due to film's inherently poorer audio response. The optical sound tracks on 35 mm movie prints (the most common format for the networks) are only capable of response to about 8 kHz. Movies shown by local stations are primarily in 16 mm format. The optical sound tracks on 16 mm film are only capable of response up to about 5 kHz.

The end result of all this is a vicious circle in which the home viewer is the ultimate loser. The receiver manufacturers are not willing to add better and more expensive audio sections to their products because the quality of most of the audio being transmitted doesn't warrant it. The networks, on the other hand, are not too enthusiastic about upgrading their audio facilities because no one at home could hear the difference. An underlying factor here is whether or not AT&T could provide wideband audio facilities at a reasonable cost to hundreds of television stations.

All of what I have just said applies only to network programs broadcast by a particular local station. Anything a station broadcasts locally is limited in bandwidth only by the transmitter and whatever audio processing equipment the station has. If a station could obtain a videotape copy of a particular network show and play it back locally, the audio would not have to pass through miles of telephone cable and would suffer none of the resulting degradation. Unfortunately, this luxury is rarely if ever afforded to a local station.

There is one exception I know of to the network audio problem and that occurs in New York city. Each of the networks owns a commercial television station in New York city. The individual network control centers and their associated stations are, for all practical purposes, one in the same.

Since no telephone lines are necessary to connect the station to the network, the audio information is passed on to the transmitter and finally the viewing public without first having its lows and highs chopped off. I've listened to the New York stations when visiting friends, and even on a television receiver with a small speaker the difference is amazing to say the least.

I personally do not feel that television audio is going to improve in the near future. Neither the networks nor the receiver manufacturers want to make the first move and the stalemate could continue for a long time. Major improvements in television audio will not come about until the consumer decides that he is ready for them and is also willing to pay for them. Until that time comes, we die-hards who would like better sound from our television sets can either move to New York City or jump on the bandwagon for better TV sound and convince the industry to get with it!

-Richard P. Markey; Lebanon, Penna.

(adapted from Audio magazine)

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