M4
| Brand | Harbeck |
| Manufacturer | Electrocoustic Corporation |
| Function | Speaker |
| Produced | 1958 |
| Country | United States |
| Form Factor | Bookshelf / Stand Mounted |
| Signal Path | Analog Hardware |
| Dimensions | 58.4 × 30.5 × 17.8 cm (W × H × D) |
| Frequency Response | 375Hz-??kHz |
| Driver | Push-Pull Electrostatic |
| Impedance (Nominal) | 4Ω, 8Ω, 16Ω (User Selectable) |
| Crossover Frequency | 375Hz |
| Dispersion | 360° |
| Enclosure Type | Dipole |
| Finish | Walnut, Mahogany, Korina |
| MSRP (1958) | $125 |