Embarking on a journey of audio rediscovery, I stumbled upon a pair of Infinity SM120 speakers tucked away in a dusty corner of a local junk shop. For a mere ten dollars, these vintage giants became the foundation for an exciting restoration project. Despite their imposing size, promising powerful sound, I wasn’t entirely sure where they would ultimately reside. However, the potential for sonic revitalization was too tempting to resist.
My primary goal was clear: to craft a set of speakers that delivered exceptional sound quality, tailored to my preferred music genre – classic 70s rock – while maintaining versatility across other musical styles. I appreciate the nuanced control offered by traditional amplifiers and digital processors like Audirvana for fine-tuning audio. My typical setup involves Volumio on a Hi-Fi-Pi, coupled with a Topping DAC, feeding into either a modern Pioneer D-class amp or a vintage Harman Kardon powerhouse boasting 300 watts. My aim isn’t sterile audio perfection, but rather a sound signature that resonates with my personal taste and listening preferences.
Upon closer inspection, the original drivers revealed a history of questionable repairs. The woofers suffered from poorly executed re-foaming, a common issue in older speakers. More alarmingly, the midrange drivers had been replaced with generic car speakers – a clear deviation from the original design. The tweeters were a mismatched pair: one original but damaged, the other crudely jammed into place using brute force and a drill. To rectify this, I sourced genuine PolyCell tweeters, opting for a full-range driver for the midrange and a robust Dayton Audio aluminum cone 12″ woofer. Driver selection prioritized physical fit within the existing enclosures and compatibility with the crossover frequencies, rather than strict adherence to original specifications. While a full-range driver might raise eyebrows as a dedicated midrange, its performance in this application proved surprisingly effective. While not strictly “Sm Car Parts”, the generic car speaker replacements highlighted the importance of using appropriate components even when considering budget or readily available options.
The speaker enclosures were the original Infinity SM-120 cabinets, devoid of internal bracing, baffles, or damping material – a common characteristic of speakers in their class. The cabinets were originally clad in vinyl veneer, which demanded considerable effort to remove using a heat gun and scraper. While opinions on these speakers vary, experienced speaker manufacturers generally possess a solid understanding of design principles. Whether the final product resonated with consumers is subjective, but these speakers were often favored for their party-ready sound.
Constructing entirely new enclosures might have simplified aspects of the project. However, as the restoration progressed, applying new veneer seemed impractical and aesthetically questionable. Instead, I meticulously sanded the cabinets, ensuring all residual adhesive was eliminated. A custom mounting solution was devised for one of the tweeters, proving successful. I decided against adding bracing, baffles, or midrange enclosures, guided by a blend of pragmatism and curiosity about the original design intent. A modest amount of polyester fiberfill was added for damping. The cabinet finish exceeded expectations: a shellac-based primer followed by multiple coats of high-quality trim paint, carefully applied with a roller to match my home decor. The result was a smooth, durable, and visually appealing finish achieved with readily available materials.
For the crossover, I initially replaced the capacitors on the original boards with premium components. However, testing revealed an issue: one crossover was triggering the amplifier’s overload protection, while the other performed flawlessly. Rather than troubleshooting further, I opted for new 3-way crossovers. It turned out the initial problem stemmed from a wiring error on my part – the original crossover was likely functional. The new crossovers included L-pads, offering additional sound-shaping flexibility.
DIY Audio Tips & Tricks:
It’s easy to get lost in audiophile debates and online forums chasing theoretical perfection. In audio, the pursuit of the last fraction of performance can be incredibly expensive and time-consuming. Often, this pursuit distracts from simply enjoying the music.
Invest in quality drivers and aim for a reasonable match with your enclosure volume and type. Remember, you are building a speaker, not crafting a piece of fine furniture. Focus on sonic performance over excessive cosmetic detailing if budget is a concern.
Thorough preparation is crucial for any finish, regardless of the material. Latex trim paint, often overlooked in audio circles, can deliver excellent results when properly applied. Shellac-based primer is essential for sealing MDF, creating a stable base for paint.
When restoring or modifying existing speakers, consider the original design. If you can make sensible improvements without overcomplicating the project, go for it. But don’t discard proven design principles without good reason.
Conclusion:
The revitalized Infinity speakers proved their sonic worth. A listening session with friends, featuring classic tracks from Styx, Kansas, James Taylor, and others, was met with enthusiastic approval. The bass response is deep and articulate – a testament to the importance of driver size. The midrange is clear and detailed, and overall, the speakers deliver a musically engaging performance precisely suited to their intended purpose. Their substantial dimensions – 34 inches tall and 16 inches wide – contribute to their impressive soundstage. Restoring vintage speakers underscores the enduring principles of speaker design. While materials have advanced, fundamental acoustic principles remain relevant. Despite initial doubts, the restoration yielded spectacularly satisfying results.
About the Designer:
My journey in audio began in 1974 with a speaker building guide from Radio Shack – a testament to accessible audio knowledge. Now at 63, my upper hearing range naturally tapers around 14kHz, a factor consciously considered in my driver selections. My background includes a decade in the Navy and later in the computer industry. Now semi-retired, my approach to audio is driven by practical experience and a focus on enjoyable sound, rather than rigid adherence to audiophile dogma.
Project Parts List:
| Part # | Description | Qty |
|---|---|---|
| 260-311 | Gold Banana 5-Way Binding Post Banana Jack Round Recessed Speaker Terminal Cup | 1 |
| 264-958 | Tang Band W5-2143 5″ Paper Cone Full Range Driver 8 Ohm | 1 |
| 295-534 | Dayton Audio DSA315-8 12″ Designer Series Aluminum Cone Woofer | 1 |
| 260-154 | Dayton Audio XO3W-625/5K 3-Way Speaker Crossover 625/5,000 Hz | 1 |
