McIntosh Loudspeaker Division Part 1
A History (1952-1975)

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Listed by year plus these additional subjects:

Frank McIntosh and the F100

In 1952, Mr. McIntosh had attempted to market a speaker system called the F100. Harvey Radio advertised it in Audio Engineering for a few months, but only five or so were sold. It contained four special long-excursion woofers, an 8" mid-range, and four tweeters. Rudy Bozak made the drivers. It had an overall width of 43" and a front face width of 22-1/2". Height is 30". Power rating was 50 watts and impedance was 8 ohms. The advertised price was $374.50 in either blond or mahogany finish.

No further attempts were made to sell loudspeakers until I was hired. Mr. McIntosh gave me the photo at the left many years ago.

Here is a rare picture of an F100 system (right) owned by Bruce McIntosh (grandson). I think it is only one of two known F100 systems that still exist today.

That is a MAC1700 receiver sitting on the top of the system. Many thanks to Bruce for the picture.

 

1967
This year marks the beginning of the McIntosh Loudspeaker Division. I was hired in March to create a series of loudspeaker systems that would introduce an entirely new product line for McIntosh. This was an opportunity for me to continue with my fascination with sound and search for better ways to increase accuracy and expand the listening experience.

In a way, speakers are much more complex than amplifiers or preamplifiers. With electronics, you can put the unit on a bench and attach oscillators, meters, etc. and you have the performance pretty well tied down. In speaker design, there is not only an electrical system having resistance, capacitance and inductance but there is also mechanical and acoustical systems, each having equivalent reactive and resistance elements. What's more, these can interact with each other and the room. Due to the complexity of speakers and speaker systems, design turns out to be partly an art and partly a science.

The formal name for a speaker is an electro-mechanical transducer. This covers not only speakers but also other devices that convert energy from one system to another—such as microphones or phonograph cartridges. Good speaker designers are hard to find and conversely, jobs for these designers are also hard to find.

An addition to the main plant was completed early in the year for the acoustics lab. Although my first priority was to design the C26 Stereo preamplifier that was immediately needed to replace the C24 preamp, I also began planning procedures and assembling test equipment needed to run the speaker research and development.

Here I am happily involved with the first prototype design of the 12" ML woofer--either that or having magnetic shoulder therapy at a young age. The woofer weighed 14.5 lbs. and was easier to carry this way. Photo is courtesy of Dave O'Brien. This woofer is further described in my Drivers Page.

The acoustics lab consisted of a reverberant room and a small listening room. The reverberant room was made entirely of concrete, including the ceiling. The walls were coated with hard plaster and then painted with epoxy paint to be as reflective as possible. The dimensions of 16' by 13' and a 10' high ceiling were proportioned to give useful measurement down to 250 Hz. With the use of a calibration fan, I was able to measure even lower. The purpose of a reverberant room was to sum up the total energy that a speaker radiates regardless of its directional properties. The test could be used to measure acoustic power. The speaker and microphone could not be located near each other, however, for this to work properly.

The test equipment was made by General Radio and consisted of a 1564 sound and vibration analyzer, 1521-B chart recorder, 1304-B oscillator and 1900 wave analyzer. Although the GR test equipment I used back then could be thought of by today’s computers as antique, it was never-the-less just as accurate and even had some advantages. However, the time needed to run the tests was definitely longer. Bruel & Kjaer 4133 and 4134 microphones were used. The 4134 was a random incidence microphone used for the diffuse field measurements in the reverberant room. The 4133 was for free field measurements. Because the microphone response was flat beyond 20kHz within a few tenths of a dB, a correction curve for speaker measurements was not needed. Photo courtesy of Dave O’Brien.

While finishing up the C26 Preamp, several months were devoted to testing speaker systems that other speaker manufacturers were making. The listening test was first. I feet this might avoid any bias from measurements that were made later. I was able to borrow Vince Wallace from his normal production-testing job to run the hundreds of curves needed to make a thorough evaluation of the many different kinds of speaker systems we had bought or borrowed. Among these systems was the Ionophone (Ionovac).

1968

Because distortion, response and impedance curves were very time consuming to run. I was able to borrow Vince Wallace (above) from production now and then to make some of the tests. Here is Vince working on an MC3500 power amplifier in production. He seemed very quiet and reserved but at the company Christmas parties he was a very outgoing Santa Claus and handed out the presents.

Meanwhile, using some of the electronics from the C26, I created an equalization circuit that, when combined with an overdamped woofer, formed a complete speaker system. The first speaker system using this technology became the McIntosh ML-1C. The required matching electronics was called the MQ101 Environmental Equalizer.

Bob Campbell joins McIntosh

 

To confirm the low frequency measurements that I made in the listening room, I decided to make measurements outdoors as well. Bob dug a hole in the field about 50 feet from the main plant. The speaker was buried flush in the ground to simulate radiation into a solid angle of 180°. It was buried to avoid sound from reflecting from the ground and interfering with the direct radiation from the woofer.

We encountered a surprising amount of background noise from cars, insects and even beetles that managed to get on the woofer cone and rattle around. Open pore acoustic foam was wrapped around the microphone to prevent wind noise from interfering with the measurements. The microphone was located at various heights up to 10 feet.

 

 

 

Crossover Requirements

I designed my first elaborate speaker system at home back in the early 1960’s. This was while I was working at the Sonotone Corporation in Elmsford, NY. I had advised and assisted Phil Kantrowitz, a phonograph cartridge design engineer who worked there, in preparing his second Audio Engineering Society paper; Distortion Measurements of High-Frequency Loudspeakers presented at the Thirteenth Annual Convention in October 1961. We had found the AR-3 tweeter to have very low distortion. Ed Villchur at AR was very pleased with our findings. We also found the AR-3 woofer to also have very low distortion. I arranged with Ed to purchase two 5/8” excursion woofers for my own system and drove to 24 Thorndike Street in Cambridge to pick them up.

Because I was still enamored with the Lowther drivers at that time, I arranged with Donald Chave at Lowther in England to send me a pair of PM-4 drivers. The efficiency of the PM-4 was much higher than the AR woofer so I thought I would try an electronic crossover and separate amplifiers to drive each of the speakers. Although a Heathkit electronic crossover was available at that time, it did not roll off the speakers fast enough. The Lowthers were designed to cover a much wider frequency range than what I had in mind. I decided to use something with a sharper rolloff. This was the UTC Butterworth filters that roll off at 60 dB per octave. The crossover was at 500Hz and I used LMI-500 filters for the low pass and HMI-500 filters for the high pass.

The graphs I made look like the curves roll off straight down, but of course, no filter rolls off that fast. What I learned from this experiment is that a better and simpler crossover design can be used when the drivers have their own inherent passband characteristics. Ideally, the driver output increases, is flat through the desired passband and rolls off without any crossover at all. Of course, no driver is perfect and a supplementary one is still needed to trim the response. However, the number of elements and complexity of the network can be greatly reduced. The natural rolloff of the driver combined with only a moderate crossover rolloff is more than adequate and the more complicated and expensive 60dB/octave network is not needed.

1970
The ML-1C went into production. McIntosh, of course, manufactured the MQ101 and MQ102 equalizer. However, we were not able to manufacture or assemble the speaker systems at this time. It required extra space, personnel, magnetizer, etc. The ML-1C's were assembled by United Speaker Systems, 192 William Street, East Orange, NJ. They also made speakers for Fisher. We used a patented soft dome mid-range invented by Bill Hecht, The President of United. The soft dome upper mid-range, 8" lower mid-range, 12" woofer, and crossover network were all built by United to our specs. United Speakers is now known as Phase Technology in Jacksonville, FL. Bill's son, Ken, is now President.

The 1-1/2" soft dome "tweeter" did not extend response to 20kHz, particularly off axis. I decided a supplementary tweeter crossing over at 7kHz would solve the problem. The tweeter was made by Peerless of Denmark, formerly known as Royal Copenhagen. I had used the Royal MT-20 tweeter in my RM-1 system at Sonotone. Since then, a new Peerless MT225HFC tweeter had been introduced. It had much better response and directional characteristics. The thin 1/2" aluminum diaphragm in the center extended response to 20kHz.

Starting with the ML speakers, all response claims were for 20Hz to 20,000Hz. A tolerance of + or- so many dB was not given. I did not guarantee that a customer would get response within certain limits at any particular point in their listening room. This was particularly true at low frequencies. Room acoustics play a major role in the apparent response of a speaker. This is determined by room dimensions and construction. Different rooms, of course, will have a different influence on the same speaker system.

We supplied a Bruel & Kjaer 4712 Frequency Response Tracer, 4133 microphone, 2801 power supply and HP sweep oscillator to United to insure uniform response quality for the individual drivers and crossovers they made for us.

The cabinet appearance was created by Warren-Freidman, consulting designers, who also made designs for the Drexel furniture line. United Speaker Systems purchased the cabinets from Arnold Furniture in New Jersey.

This unique logo appeared on the first McIntosh loudspeaker system, the ML-1C. It was used only on the speaker systems and continued until 1992. The full name of McIntosh was used thereafter, starting with the XR290.

 

With the completion of the C26 preamplifier and addition of more engineers, I moved my desk and test equipment into the listening room. By this time, Sidney and I were looking for a bigger place to expand the speaker lab. Eventually, the listening room became the new computer room and the reverberant room was divided into two offices, one for Jean Filon and one for Mike Paiva.

Young engineer suffering from listener fatigue in a room with poor acoustics.

New Acoustics Lab

In the summer of 1970, the acoustics lab was moved from the main plant to a 10,000 square foot facility called plant 5 at 1290 Arterial Highway in Hillcrest. This was about 5 miles north of the main plant in a group of trucking terminal buildings. The building was rented by McIntosh. It was built by Cliff Signor, who owned the Albany-Binghamton trucking lines. The roof came from the old Arlington Hotel in Binghamton. The building was previously a storage facility and had been filled with thousands of gallon containers of Elmer’s glue. For McIntosh, it served as a warehouse where finished goods were stored and shipped plus our acoustics lab. Loading docks were at the other end of the building.

Shake (Blanen Baroa) was also transferred to plant 5 to handle the shipping of all finished goods. Jim Kane handled the fork lift but after he left, Jim Melody took over. All the units were placed on wooden skids and stacked floor to ceiling. Here are some ML-1Cs being stored. Placing the skids on the simple steel framework was a little tricky but the boys were good at it. The fork lift was very heavy.

I remember one time when Jim was driving the lift into a long trailer truck to pick up some skids, the front wheels went through the floor of the trailer. We had to wait for the company truck to bring over some long Johnson bars and all of us had to lean on them to pry the lift up and back to get it out of the trailer.

The building wasn’t much to look at from the outside but the lab rooms inside the building were all finished very nicely. There was a listening room, reverberant room, test room, office space and rest rooms. I couldn’t resist putting signs on the doors of the rest rooms. Instead of saying men and women, I put “woofers” and “tweeters.” This caused a little confusion with some of the visitors but at least it was educational.

I was the responsible manager for the building. This included making sure there was sufficient propane gas for the heaters in the winter. The main building was not well insulated and we went through 1500 gallons of LP gas every three days when temperature went below zero. We also had an alarm system that failed now and then and I sometimes needed to find the defect and temporarily bridge across it until the service man, Lou Stantz, could get there the next day. I also made sure Ed Fendick got there with his snow plow before noon time so the McIntosh truck could get to the loading dock. I was usually the one that shoveled out the entrance to the building in the morning so we could get our cars off the main road. I enjoyed having my own building to manage.

The listening room was improved over the one in the main plant. Here I am in the listening room with Dave Wheaton, who I hired later. The room was proportioned to distribute standing waves at low frequencies as evenly as possible throughout the spectrum. It measured 19'-6" by 25' and 7'-6" high. Although the walls defining the listening room were concrete block, interior walls were made using 2X4's spaced away from the block by one inch. Fiberglass insulation was put between the 2X4's and the walls were covered with sheet rock, making it very similar to home construction. This construction allowed the walls to move, absorb some of the energy, and greatly reduce the amplitude of the standing waves that remained. The ceiling was 2X12's covered with sheet rock. A plywood floor was added on top of the 2X12's and used for storage above the room. A durable carpet with foam rubber backing was installed on the floor.

The lab area contained all of the desks, work bench, test equipment and storage shelves. This is the view taken from my desk that was at one end. This area was almost as large as the entire engineering section at the main plant.

The reverberant room was identical to the one at the main plant. The test room was for quality control inspection and testing of the ML-1C's. A spray type humidifier system was added to keep the humidity in the rooms higher during the winter months. Without this, the difference in absorption could change the response in the reverberant room by as much as 5 dB at the higher frequencies. A water filter was used prior to the humidifier to remove calcium from the water. Otherwise a fine calcium dust would appear on everything in the lab and possibly get into the test equipment. An area out in the main building was used for wood cutting and prototype cabinet construction.

The new listening room was also used for lectures and demonstrations. Gordon Gow, or a McIntosh representative, often brought in a group of employees from various McIntosh dealers, reporters from various publications or customers for a tour of the acoustics lab. Occasionally there were groups of 20 to 30 from Europe or Asia. I showed them the various test rooms and equipment. I also set up a demonstration showing how the equalizer and speaker combined to produce flat response to 20 Hz. We had just purchased a $20,000 Bruel & Kjaer 3347 real time analyzer for this demonstration as well as for research. I also demonstrated our latest speaker designs. There was usually a question and answer period afterwards. Visitors were brought in about twice a week.

Jim Carroll arranged to rent some musical instruments for us to evaluate. The kettle drums didn’t go low enough in frequency to make a good demonstration. I decided to show the spectrum of a strike on our bass drum using a Bruel & Kjaer microphone and the B&K real time analyzer in the peak hold mode. Prior to the visitors arriving, I had tuned the drum for a 25Hz fundamental. Tuning was essential as the tension was greatly influenced by temperature and humidity. This established that real musical instruments do indeed have acoustic output at very low frequencies. Then, using pink noise, I showed the response of the ML-1C woofer using a close microphone technique without the equalizer and with it. Response was within 1 dB using the equalizer from 20 Hz up to 250 Hz where the woofer crossed over to the mid-range. With this kind of response, the drum strike could be reproduced very accurately. I also demonstrated our latest speaker designs. There was usually a question and answer period afterwards.

The ML-1C's sold very well. We were opening testing and re-packing 50 systems a week. It had become necessary for me to hire more personnel to handle and inspect the systems. Here are two of the system testers, Jim O'Dea and John Knapp.

Here is Jim Hill putting the final touches on the ML-1C systems. A form was filled out for each system that described any defects that were found in the systems. This information was sent back to United Speakers.

 In addition, there were quality control people from the main plant. By 1971 there were nine people working for me, including three in the research area. We also added the ML-2 and ML-4 floor standing systems, which were initially built by United Speaker systems. The floor systems were made in a contemporary style similar to the ML-1C. The ML-2C has two 12" woofers and the ML-4C has four 12" woofers. The floor systems were also made in a Mediterranean style, the ML-2M and the ML-4M. The Mediterranean systems were available with pleated red, green or gold cloth curtains behind the grilles. The equalizer was also required for these systems as well.

Equipment consoles of similar height and depth to the floor systems were also made in both styles.

The ML-4's were capable of handling large amounts of power with low distortion. The four 12" woofers were superior to two 15" woofers. The total moving cone area was greater and there were four voice coils to dissipate heat instead of two. A favorite demonstration of mine was to plug the ML-4 woofer section into the 120-volt wall outlet. This really captured the attention of visitors who questioned the power handling of the system, and it was also very loud. Although this demonstration was impressive, the actual power delivered to the woofers at 60Hz was not that great. The impedance of the system at that frequency was about 30 ohms and the current was only about 4 amps. Had the line frequency been at 120Hz where the impedance was 10 ohms, it could have burned out the woofers. I had also disconnected the mids and tweeters. The harmonics from the transient current might have damaged them when the system was first connected to the line.

1971

To introduce the new McIntosh speaker line, Gordon Gow presented several loudspeaker seminars at various dealers.

Perhaps this was a forerunner to column systems. Several people had suggested stacking three ML-1C’s for louder sound that takes less floor space. A special pair of white Formica cabinets were made for one of the shows where the ML-1C’c could be placed inside. It was a great demonstration with the new MC2300 power amplifier to drive them.

A grille with black cloth was provided and was leaning against the cabinet. Two such columns of ML-1C’s were donated to Roberson Center for arts and science in Binghamton for their auditorium. A power amplifier and preamplifier were also included in the donation. The auditorium featured a restored Link pipe organ.

 

1972
This year we started to assemble ML-2's and ML-4's at plant #5.

A more controlled environment was needed to do more accurate and repeatable tests for drivers. We were able to purchase an Eckel portable anechoic chamber that had a cube shaped internal useable space 45" on a side. The word anechoic meant without echo or reflection. Fiberglass wedges were used to absorb 99.9% of the sound striking them. The wedge dimensions determine the lowest frequency limit. The wedges are 12" long, which correspond to 1/4 wavelength, for a cutoff frequency of 250 Hz. It arrived in three sections that had to be bolted together. The whole chamber weighed 3000 lb. and rested on rubber shock mounts. It cost about $9000 at that time.

We also invested in some Bruel & Kjaer acoustic test equipment. Included in this was a 2305 chart recorder, 2607 measuring amplifier, 1022 oscillator and 2020 slave filter. The slave filter enabled us to make continuous harmonic distortion measurements. This was very important in loudspeaker work. In electronics you can measure distortion at 20 Hz, 1kHz and 20kHz. If it's low you can accurately infer all frequencies in between are equally low. In speakers this is almost never true. Resonances and breakup can occur at any frequency and not show up at others. Shortly after that we added a B&K 1901 tracking frequency multiplier. This unit enabled us to resolve the harmonic distortion measurements into continuous individual distortion curves--second, third, etc. This measurement technique was essential in the development of the LP/HP woofer by Carl Van Gelder in 1992.

About this time McIntosh began offering speaker clinics to a few selected dealers. Gordon Gow conducted them almost entirely. The tests were made on any speaker brought in to the clinic, regardless of manufacturer. There were three different measurements. The first was a distortion versus power test at a frequency of 25.7Hz, A4 on the music scale. Power measurements were made up to 100 watts, or until the speaker distortion exceeded 30%. The second was a low frequency response curve of the woofer from 25Hz to 500Hz. The third was an impedance curve from 20Hz to 20kHz.

When McIntosh speakers were tested, the required equalizer was used and response continued within 1 dB right down to 25Hz, the lower limit of the graph. No other system was able to do this. Many other brands went down to system resonance, typically 50Hz or higher, and then rolled off. Some systems didn't even reproduce that low and the 25.7Hz distortion reached 30% very quickly.

An impedance curve was made for each system from 20 to 20kHz. Impedance remained at 8 ohms or higher through most of the range. The lowest limit was 7.2 ohms. We found the manufacturers of a few systems incorrectly rated the impedance of their systems. The impedance of a few "8 ohm" systems could actually dip down as low as 2 ohms. Some amplifiers, including many McIntosh amplifiers, had multiple impedance taps. If the speaker is connected to the 8-ohm tap, the impedance mismatch could cause a power amplifiers to go into current limiting prematurely. The correct rating for that speaker should have been 2 ohms and should be connected to the 4 or 2 ohm tap.

1973
In January, Sidney Corderman and I went to visit the Rola-Jensen speaker manufacturing facilities in Punxsutawney and Dubois, PA to learn about their production facilities and consider them as a source for drivers. In June we also visited CTS in Paducah, KY, another potential source.

Carl Van Gelder Joins McIntosh

In September, I hired Carl Van Gelder as a technician to assist in the work on loudspeaker mechanism designs. He came to me through the Ethan Allen Employment Agency. Although Carl had a degree in earth sciences, I found he had a natural talent for speaker mechanisms and eventually he became an Acoustic Design Engineer. In 1992 he received an important patent for the design of the new McIntosh LD/HP driver assemblies. With this technology, he was able to reduce driver distortion by a factor of 10. This improvement was clearly audible, particularly in the voice range.

Over the years Carl and I spent considerable time doing research on acoustics, enclosures, drivers and listening tests. We developed many systems. A few never went into production for one reason or another. We also evaluated many other brands of systems.

 

 

 

 

 

Dave Wheaton joins McIntosh

In August I hired Dave Wheaton as an Engineering Assistant. He had almost completed a degree in electrical engineering at Cornell. Dave made prototype systems and did design work on the systems. He had a talent for conversation and sometimes conducted the seminars for the visitors in our listening room. That's him on the right portion of the picture. Dave stayed for 5 years and the three of us have a very enjoyable time during his stay. Then he decided to complete the requirements for his degree. After graduating, he went to work for Texas Instruments in Dallas, TX.

 

 

 

 

 

In November of 1973 I was made Director of Acoustic Research. This was the only business card for key employees that displayed the Mc logo. It corresponds to the logo used on the McIntosh speakers. The card artwork was changed many times over the years. The word Acoustical on my card was later changed to Acoustic.

The ML-10C was added to the line this year and had a 10" woofer. The cabinet style was contemporary.

 

 

We test electrostatic speakers.

Art Janszen had been a consultant for McIntosh for several years. He visited our acoustics lab about this time to test his new idea for spiral wrapping the electrodes for his electrostatic tweeter. Earlier versions were constructed using short parallel wires connected together.

Gordon Gow was interested in the Janszen tweeter as a possible high frequency speaker in a McIntosh system. He was also concerned about peak power levels needed to reproduce musical instruments at high frequencies. We set up a microphone at 1 meter and used tone bursts to see how the tweeter will handle short bursts of high frequency power. As the power level re: 8 ohms increased, the acoustic output increased by an equal amount, but at higher power the output began to decrease. We found that by blowing across the tweeter, the output would be temporarily restored. The reduced output was caused by ionized air. The electric stress in the air had exceeded 100V per mil. Ions were produced that in turn discharged the polarizing voltage and caused the output to decrease. By blowing away the ionized air, the polarizing voltage was restored until new ions were formed.

We then compared our dome mid-range at the same sound pressure level and were able to increase the driving power level by many dB above the Janszen while still remaining completely linear.

Gordon learned that the Dayton-Wright electrostatic speaker was enclosed in sulfur hexaflouride gas to eliminate this problem. The thin membrane that enclosed the gas was porous, however, and exhibited the osmotic process where the higher density gas molecules migrated through the membrane to the lower density air. The speakers needed to be periodically recharged with gas.

As a result of this research and other factors, Gordon decided not to pursue the electrostatic speaker as a viable product.

One day we came in to the building and found the floor covered with water. The office was flooded with about an inch and a half of water. I determined that the water came from a hose that had slipped from the water filter that supplied the humidifier. I called the main plant for help and Mike Stolowyk came over with a wet vacuum and long handled rubber push blades. Mike was the head of maintenance and by noon, he and his crew had things set in order again.

Plant 5 became the storage area for finished XR systems. In the foreground are rolls of Tufflex acoustic material. The lab and wood cutting area are at the far end of the building.

1974

Speaker final assembly began at plant 5 but in the spring was moved to the new building, plant 7, in Conklin, a few miles south of the main plant. I had decided that I did not want to be in charge of both research as well as production. I was dedicated to research and designing more accurate speaker systems. I recognized one of the facets of the Peter Principle is where one gradually rises to their level of incompetence. That was not one of my goals. After discussing this with management, Bob Mayhood (left), who had been manager of the silk screening operation at Plant 2 on Bevier Street until it was moved to the main plant, was assigned to manage speaker production. Bob is shown checking the finish on an XL-1 cabinet. Patrick Sladdish, who worked for Bob, is making a final assembly of an XL-10 system. The extra space at plant 5 was then used for warehousing storage items.

About this time we purchased a coil winding machine recommended by George Krenz, a well known voice coil supplier. We also purchase a curing oven and a magnetizer. The magnetizer is a capacitor storage impulse type made by RFL labs in New Jersey.

Being a bike-riding enthusiast, I started riding my bike to work. It was 7-1/2 miles from my house in Binghamton to plant 5 in Hillcrest. I was able to find a safe route away from the main highways. It took anywhere from 35 to 45 minutes to get there depending on whether the wind was with me or against me. I rode 2 or 3 times a week. Weather was, of course, a factor. I had rain pants and jacket and rode several times in the rain. I found this very comfortable but took it easy because the wet caliper brakes don't hold very well. I always changed my clothes to dress pants, shirt and tie after I got to work. If the temperature was below 45 degrees at home, I wouldn't ride. At 7:30am the temperature in Hillcrest could be 40 or lower and was just too cold for me. I rode spring, summer and fall and found the freedom and scenery very worthwhile. I often took a camera with me.

I bought a Raleigh Sprite 10 speed bike to replace the 3-speed Raleigh I had used at college. I assembled a new gear cluster with higher gear ratios for hill climbing and strong wind. I also used Zeus non-pneumatic hollow urethane tires that just don't get flats. They were said to last for over 3500 miles. The Sprite was a touring bike and not a super light weight racing bike. I continued to ride even after we moved next to the main plant in 1979. In the background is the Washington Street Bridge, It was closed to cars and trucks but was open for walking and bikes. This is how I crossed the Susquehanna River on the way to Plant 5.

Instead of staying in the building during lunch time, I decided to get outside. There was a large field behind the building. I could walk across this to a wooded area and through there to the Chenango River. I found many interesting plants including troutlilies, bloodroots and ferns. I always had a camera with me and took many pictures. In the winter, the river ice made unusual patterns.

1975
About this time the Stereo Technology (Stereotech) line was introduced. To complement the first Stereotech receiver, we designed four speaker systems, ST 1, 2, 3, and 4. McIntosh assembled the systems and the crossovers. CTS, Rola-Jensen and Peerless supplied the drivers. The cabinets were to be lower cost and were purchased with a walnut vinyl laminate. Unfortunately the increase in material costs forced the Stereotech program to end in 1976.

The ML-1D and ML-10D

We were scheduled to come out with revised versions of the ML systems, the ML-1D, ML-2D, ML-2N, ML-4D, ML-4N and ML-10D. The systems were to have the same cabinets. Printed circuit crossover boards would be used in place of the hand-wired boards. Fuses were added to protect the crossovers and drivers from being overdriven by clipping amplifiers. Indicator lights were also added. Each system had a main fuse that was connected to the crossover network input. If the system was driven near the maximum power handling, a yellow warning light would be seen. If the main fuse blew, and the system continued to be driven, the yellow light would still be seen, but there would be no sound. A smaller high frequency fuse was used to protect the upper mid-range and tweeters. If the tweeter fuse blew, and the system continued to be driven, a red light would be seen but no highs would be heard.

The lights and fuses were mounted on two small plates on the front board of the ML-1D. The yellow light and main fuse were on the left plate and the tweeter fuse and red light were on the right plate. The lights could be seen between the slats in the grille and through the grille cloth. In the ML-2's and 4's, the fuses were on the front board behind the grilles. The lights were mounted under the base of the cabinet and clear plastic rods were used to bring the light to the front of the base.

Gordon Gow decided it was time to revise the style of the cabinets, however, and the D's and N's were never produced. As the decision was made close to the scheduled production date, some ML-1 and ML-10 cabinets already had cutouts for the fuse plates. These were covered with solid plates and sold as ML-10C systems. Some ML-10C systems had printed circuit boards with space ready for parts to be made as ML-10D’s. The lettering on some cartons said ML-1D and ML-10D. See my ML-10D page for a detailed description and pictures of this system.

The Polygon Systems were developed about this time. Although they were very unusual in design they never went into production.