The LM-1 Bookshelf Version

The LM-1 speakers are part of the Leach Memorial speaker project, started here. 

Introduction

The LM-1 is a small, two-way speaker kit using a 1" ring radiator and 5 1/4" woven fiberglass mid-woofer specifically designed to be placed on a bookshelf or desk. Because of these choices, on a bookshelf, the frequency response is smooth and extended with real output between 40Hz and 30kHz and is unusually efficient. It is suitable for high quality music production, desktop or home theater use as either main or surround speakers.

The LM-1 is also quite friendly to flea-powered digital amplifiers. 

The final cost to build is estimated at between $240 to $470 a pair depending on whether you build or buy the cabinets and the crossover parts you choose. Each speaker is approximately 12" H x 7.5" W x 10" D.

Background

One famous speaker design to come out of Dr. Leach's laboratory was a small 2 way design by a graduate student named Kirk Wrzesien which was published in 1990.  As stated, the goal was:

..to design a premium 2-way loudspeaker system for a small dorm stereo system and for use as rear loudspeakers in a home surround sound system

While the design was pretty popular, especially along engineering students, the parts are no longer available, so 26 years after the original design the time for a refresh has arrived.

In addition to the ageing of the original design we're now living in an era where advanced measurement, design and simulation tools are within the reach of many hobbyists, allowing us to access much of the same resources Kirk and Dave would have had at GA Tech in 1990. This let's us re-imagine the original design with modern drivers, as well as share the tools and techniques to any who wish to learn.

With similar goals in mind, but with no obligation to replicate the original design's frequency response identically I will add a few requirements to my poor ode and attempt to show how this can be done by most DIY'ers with a few tools.

• Sounds best on a bookshelf or desktop. I have to assume dorms don't have room for speaker stands!
• Is inexpensive enough for a graduate student to afford (under $500/pair including cabinets)
• Has a very simple crossover design
• Can be used for the front and rear surround speakers
• Try to stay true to the brands used by previous designs that have come out of the GA Tech audio laboratory.  
• Has a neutral, versatile, musical sound free of deliberate sweetening gimmicks. 

Output will be limited, as you would expect from a small, high quality monitor. Mate them with a subwoofer crossed over at 60 to 80 Hz and you'll have an outstanding full-range system.  It's not an exaggeration to say the parts chosen for the LM-1 would justify a store price of around $1,500 / pair or more depending on the brand name used. See my blog entry here about high-end speaker pricing.

The Design Documents

The part list

Mechanical drawings for the cabinet and port

Electrical Schematic

Electro-acoustic measurements

Tools used for the electro-acoustic measurements

Crossover simulation files and discussion

XSim Crossover Simulation Software

 

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