ADC SLM-100 Audio Dynamics Sound Level Meter ()
It won't tell you the year it was born, but plug in a 9-volt and this little meter starts listening. That's how it worked back when tuning your room meant breaking out actual test gear.
Overview
The ADC SLM-100 Audio Dynamics Sound Level Meter isn't glamorous. It was built to help you measure sound, not just hear it. It's a tool, though plenty of tinkerers and analog obsessives have treated it like a toy too. Marketed as a Sound Decibel Level Meter, the SLM-100 shows up in listings with a clear mission statement pulled from HiFi Engine: it's meant to be used with your frequency equalizer to adjust the frequency responses of your hi-fi system, right down to the speakers and the room itself. That was a fairly radical idea for its time. The listening environment becomes part of the signal chain, something to be measured and corrected, not just endured.
There are no glossy brochures or engineering schematics, but the use is easy to picture. A serious hobbyist crouches in front of a floor-standing speaker, holding this meter in one hand and nudging a graphic EQ with the other. No apps, no digital displays, just a needle responding to pink noise. The unit was tested in at least one listing where it powered up with a fresh 9-volt battery and responded to sound, though no further calibration or accuracy checks were performed. Another eBay listing claims all functions were working at the time of testing, which is about as good as it gets for vintage test gear showing up in the wild.
ADC, or Audio Dynamics, is better known among collectors for its high-end moving magnet cartridges, especially the XLM series, and the early metal-faced Sound Shapers, which remain sought after. The SLM-100 doesn't carry the same prestige, but it fits into the same family of analog tools for system tuning. Whether it was sold standalone or as part of a kit with ADC's equalizers isn't clear from the record, but its design intent ties it directly to system tuning and room correction.
Specifications
| Manufacturer | ADC (Audio Dynamics) |
| Product type | Sound Level Meter / Sound Decibel Level Meter |
| Power source | Operates on 9 Volt Battery |
Collectibility & Value
The ADC SLM-100 trades quietly on the secondary market, mostly surfacing in used condition with minimal documentation. Prices pulled from eBay listings vary widely: units have appeared at $9.33, $31.90, $60.00, and $66.90. That suggests demand is spotty and pricing depends heavily on seller, condition, and whether the unit is tested. One listing at Recycled Goods notes a past price of $100.00, though it's unclear if that was an original retail tag or a later asking price. Either way, it hasn't held.
It isn't a high-value collectible like ADC's golden-era cartridges or early Sound Shapers. It's a niche piece for restorers, vintage audio tinkerers, or anyone trying to recreate a period-correct tuning setup. York Scientific is a dedicated service provider, offering full diagnostic evaluation, troubleshooting, component and board-level repair, and even complete rebuilding for the SLM-100. Their repairs come with a 1-year warranty on parts and labor, which is a rare level of support for such obscure gear.
Confirmed production years, technical specs like measurement range or accuracy, and even basic dimensions are all missing from the record. It works, sometimes, and it has a job to do.
eBay Listings
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