A compression driver is the engine of almost every professional horn loudspeaker — the device that turns electrical signal into the intense, controlled sound pressure a horn then projects. If you buy PA equipment, you already own their output; this article explains what they are, how they work, and how a large driver catalogue is organised.
The basic idea
A conventional loudspeaker cone pushes air directly. A compression driver works differently: its diaphragm — small, stiff, and driven by a voice coil in a powerful magnet — faces a phase plug with narrow passages that compress the air into a small throat. That high-pressure, small-area output then enters a horn, which expands it gradually to the full size of the horn mouth. Compressing first and expanding second is what gives horn systems their efficiency and reach: sensitivities in this catalogue's specified driver reach 106 dB at 1 watt (the GD022), far beyond direct-radiating tweeters of similar size.
The anatomy that matters
- Voice-coil diameter — the primary size classification: 25.4 mm and 34.4 mm at the small end, 44.4 mm and 51.6 mm in the middle, 72 mm and above for high-power work.
- Diaphragm material — titanium for output and durability, phenolic for a mellower response and lower cost; both are stocked as replacement parts in the standard sizes.
- Magnet — ferrite for most duty; neodymium where weight or size is constrained, as in the HDN series.
- Mounting format — screw-on (a threaded throat screws into the horn) or bolt-on (a flange bolts to it). The driver and horn must match in both throat diameter and format.
- Phase plug and back cover — the plug shapes the compression passages; some models use aluminium back covers, as in the GD017 series, for heat and rigidity.
How the GRANVOZ driver catalogue is organised
The driver family lists 70 published models. Twenty-two carry titanium diaphragms in their titles; twenty-five are titled as horn driver units. The GD017 and GD018 series cover the 44.4 mm and 51.6 mm titanium classes in screw-on and bolt-on variants, GD099-3 is a 4 inch tweeter-format titanium model, and the DR-012 pair covers 25.5 mm phenolic-diaphragm duty. One model — the GD022, a 25.4 mm screw-on unit — carries a complete published specification table: 40 W RMS, 106 dB sensitivity, 1 kHz–15 kHz response, titanium diaphragm. One further model, the HND31-99 bolt-on driver with a 99 mm voice coil and neodymium magnet, is documented with the manufacturer's full product description.
Why the parts catalogue matters to driver buyers
A compression driver's diaphragm is its wear part, and this catalogue treats that seriously: the parts family stocks replacement diaphragms in the same 34.4 / 44.4 / 51.6 / 72 mm sizes, in titanium and phenolic, plus the TYF aluminium horn range the drivers couple to. A driver programme bought with its matched spare diaphragms confirmed on the same order is a programme that can be serviced for years — ask the sales team to confirm the matching diaphragm when you specify the driver.
Compression drivers vs large tweeters
Buyers crossing over from car audio often ask why a PA system does not simply use a big tweeter. The answer is output density and control. A compression driver concentrates its diaphragm's work into a small throat and lets the horn do the spreading, so the system can be both loud and directional — it throws sound to the back of a venue instead of spraying the ceiling. A large dome or bullet tweeter radiates from its full face at once: simple and wide, but it cannot match the horn system's level at distance or keep its pattern as the frequency climbs. The two devices are not rivals; they are answers to different room sizes. The catalogue's own structure reflects that — the tweeter family's top end (the HDN-30-44 driver-style unit) and the driver family are stocked side by side, and many pro buyers source from both.
A short history the buyer can skip — but shouldn't
Horn loading predates electronic amplification: the acoustic gramophone horn was a compression device with no electricity at all. When cinema sound arrived in the 1920s and 1930s, engineers needed one driver to fill a theatre, and the compression driver plus horn was the answer that worked. The physics has not changed since — only the materials have. Modern titanium diaphragms, neodymium magnets and precision phase plugs are refinements of a century-old idea, which is why the format's size standards (the 34.4 / 44.4 / 51.6 / 72 mm ladder) are so stable across manufacturers, and why a replacement diaphragm bought today fits a driver housing designed around the same geometry.
Choosing a compression driver
Start from the horn: its throat diameter and mounting format bound the choice. Then set the voice-coil size from the power and band the system needs — larger coils handle more power and reach lower, smaller coils reach higher and cost less. Then choose the diaphragm material for the duty, and confirm every figure for the exact model in the written quotation, because most models in this family are documented by title and description rather than by full tables. The GD022 shows what complete documentation looks like; hold the rest of the family to the same standard in your enquiry.