Effective Response of ER•4 Earphones

The ER-4S earphone has an equalized high frequency response. Most stereo recordings have been equalized, electronically or by choice of microphone type and placement, to sound good with mainstream "good" loudspeakers in typical living rooms. Several studies have been conducted dealing with the subject of loudspeaker response as affected by the listening room. The figure to the right shows the frequency response of loudspeakers considered to be "flat" in five studies. Even a loudspeaker with a perfectly flat power output exhibited a room response 4-10 dB down at 10 kHz, relative to the midband. The ER-4S has been designed with a gradual roll off in the high frequencies similar to that of the curve labeled MCK, which represents a compromise choice. The ER-4S is well suited for all types of stereo recording reproduction.

Loudspeaker Room-Equalized Response

ER•4 MicroPro Earphones are designed to match the acoustic response of the open ear. Music is naturally bright, but not harsh. The lack of coloration results in smooth treble, full bass, clear and natural piano, percussion and orchestral music.

How Etymotic Measure Response Accuracy
Earphone response was measured on a KEMAR® manikin that has the same acoustic properties as the average head and ear. 25-band accuracy scores are calculated by summing the difference between the earphone response and the target response in each 1/3-octave band from 50 Hz to 12.5 kHz.

ER•4 MicroPro Earphones provide the highest isolation of any earphone: 35-41 dB (two to three times that of active noise-canceling earphones). ER•4 MicroPro earphones reduce sound naturally, without the added weight, bulk, or external power supply required for active noise-canceling.

• 3-flange eartips: 35 dB external noise isolation (NRR = 22dB)
  
• Black foam eartips: 41 dB external noise isolation (NRR = 32dB)

How Etymotic Measure Noise Reduction

Real-Ear-Attenuation-at-Threshold (REAT) Measurement Method
The ANSI standard method of measuring the noise attenuation of hearing protectors and earphones is to compare the quietest sound that can be heard with the earphone in place with the quietest sound that can be heard with the ears open. This Real-Ear-Attenuation-at-Threshold (REAT) method is the basis for all OSHA Noise Reduction Ratings called the NRR. ER-4 and ER-6 earphones were measured with the REAT method at E-A-R CAL Laboratories.

Probe Microphone Measurement Method
Active noise-canceling earphones cannot be measured with the REAT Method because their circuit noise interferes with the measurement. ER-4 and ER-6 earphones were compared to active noise-canceling earphones using a probe microphone method: A calibrated 84 dB SPL broad-band pink noise was generated in a reverberation room using four uncorrelated noise sources. The sound pressure developed in the ear was measured with a 2.5 mm microphone located deep in the ear canal. The noise reduction of each earphone was calculated as the difference between the noise level in the open ear and the noise level with the earphone in place.

Why You Don't Need Active Noise-Canceling
Active noise-canceling circuits add noise of their own when you are listening in quiet surroundings. ER•4 MicroPro Earphones reduce noise naturally by sealing your ear canals. The result:

• Clean, clear, undistorted music
• Rich detail that you miss with over-the-ear headphones
• Awesome, in-your-head sound
• Lightweight, comfortable fit
• More external noise isolation than any other earphone in the world, including active noise-canceling