Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Headphone Model | Headphone Class | Sensitivity (dB) | Impedance (Ohms) | Driver-matched dB | Construction | Earpads | Termination | Succeeded by |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| SR40 | Unknown | 100 | 32.0 | Unknown | Plastic | Foam | 1/8" (3.5 mm) plug with 1/4" adaptor | iGrado |
| SR325 | Prestige | 98 | 32.0 | 0.05 | Aluminum Alloy | Bowls | 1/4" (6.5 mm) plug | SR325i |
| HP1000 | Joseph Grado Signature | Unknown | 40.0 | Unknown | Aluminum Alloy | Flats | 1/4" (6.5 mm) plug | No Successor |
| SR100 | Prestige | Unknown | 32.0 | Unknown | Plastic | Flats | 1/4" (6.5 mm) plug | SR125 |
| SR200 | Prestige | Unknown | 32.0 | Unknown | Plastic | Flats | 1/4" (6.5 mm) plug | SR225 |
Question:
Name the driver matched db for joseph grado signature
Answer:
Unknown