Icon HDP Noise Floor Technical Note
The Icon HDP has been designed to drive high-performance headphones (with impedances up to 600 ohms) with high-output capability (up to 9Vrms). If you're using the HDP with very sensitive in-ear monitors (IEMs), you may detect background noise when no music is playing. What you are hearing is the HDP's noise floor.
EMs have sensitivities in excess of 100dB/mW at 16 ohms. A typical over-ear headphone such as the AKG701 and Sennheiser HD600 has a sensitivity of 100dB/V. To illustrate the difference, let's compare the typical input voltage required to produce 100db of loudness:An IEM requires 0.1V to output 100dB, while big headphones need 1V to perform similarly.
The Icon HDP is designed to maximize performance for headphones with higher impedances than those of IEMs. However, owing to its exceptional sound quality, many customers prefer using their IEMs with the Icon HDP. Therefore, this caveat: using an IEM with the Icon HDP effectively adds 40dB of gain to the volume level, thus allowing people with especially sensitive hearing to detect the HDP's noise floor. Certain listeners are able to detect noise in the range of 0.1mV. With a 100dB/0.1V sensitivity IEM, this level of the noise output is 40dB; in other words, 1000 times below 0.1V.
To adapt the Icon HDP to an IEM's optimal requirements, we would have to adjust the gain, and that, unfortunately, would defeat our design goal. We prefer to disclose and discuss these noise issues in order to avoid confusion and disappointment. Again, most of our customers will not hear this extremely low level of noise.
- Based on our measurements, with a 16-ohm load, the background noise occurs at 0.01mVrms.
- The Icon HDP can easily output 4.5Vrms (before clipping) into a 16-ohm load to produce power of 1.2Wrms.
- The noise level of 0.01mV at 16 ohms has power = 0.00000625mW, i.e., 160,000 times below 1mW. (160,000 times equates to 52db.)
Here's a technical way of looking at the Icon HDP's nose level:
For an IEM such as the Shure 530 (119dB/mW), the background noise is 119-52 = 67dB. People with very sensitive ears using the Shure 530 or devices with similar characteristics may very well hear this level of background noise.
In terms of performance, our HDP produces a S/N ratio > 112dB. That's 4.5V/0.01mV=450000 converted to 113dB. In practical, real-world terms, one really cannot do much better than that.
