Analysis with recommendations for Fostex TH909 headphones based on the measured characteristics
| Analysis and recommendations for Fostex TH909 based on the measured characteristics | |||||
| Sources (to which the headphones will be connected) |
Areas of using headphones | Sensitivity | Impedance | The type of acoustic design | Total |
| 118.48 dB/V SPL | 25.04 ohm | Open | |||
| Low-power sources -18dBV/6dB(mA), S/N 105 dB:
a smartphone a player a tablet Examples |
Home or studio, where sound from the headphones does not bother anyone | 3 ★★★☆☆ | 4 ★★★★☆ | 5 ★★★★★ | 4.0 ★★★★☆ |
| Office and home, where people should not hear the sound from the headphones | 3 ★★★☆☆ | 4 ★★★★☆ | 1 ★☆☆☆☆ | 2.7 ★★☆☆☆ | |
| Street with active traffic | 2 ★★☆☆☆ | 3 ★★★☆☆ | 5 ★★★★★ | 3.3 ★★★☆☆ | |
| Metro (subway), public transport | 1 ★☆☆☆☆ | 2 ★★☆☆☆ | 1 ★☆☆☆☆ | 1.3 ★☆☆☆☆ | |
| Mid-power sources 6dBV/30dB(mA), S/N 120 dB:
a computer with sound card a Hi-Fi player a portable amplifier a mixer console Examples |
Home or studio, where sound from the headphones does not bother anyone | 5 ★★★★★ | 5 ★★★★★ | 5 ★★★★★ | 5.0 ★★★★★ |
| Metro (subway), public transport | 5 ★★★★★ | 5 ★★★★★ | 1 ★☆☆☆☆ | 3.7 ★★★☆☆ | |
| Recording a voice or instrument in the studio | 5 ★★★★★ | 5 ★★★★★ | 1 ★☆☆☆☆ | 3.7 ★★★☆☆ | |
| Hi-power sources 18dBV, S/N 120 dB: a home system with a headphone amplifier Examples |
Home or studio, where sound from the headphones does not bother anyone | 5 ★★★★★ | 5 ★★★★★ | 5 ★★★★★ | 5.0 ★★★★★ |
| Office and home, where people should not hear the sound from the headphones | 5 ★★★★★ | 5 ★★★★★ | 1 ★☆☆☆☆ | 3.7 ★★★☆☆ | |
Analysis of acoustic design Fostex TH909
The Fostex TH909 headphones are made with an acoustic design of an open type.
Due to the open type, the headphones do not have noise isolation - the people around can hear well the music from the headphones, while you can hear ambient sounds too.
Headphones without noise isolation are well suited for home and studio in a quiet environment, as well as on the street with active traffic, allowing you to notice the danger in time.
Headphones without noise isolation are unsuitable for use in noisy public transport, as due to external noise it is necessary to increase the volume level of reproduced music, which is harmful for hearing during long listening. Loud sound is unpleasant to passengers nearby. In a studio, while recording vocals or instruments by a microphone, the open headphones are likewise not suitable, because sound from the "minus" from the headphones will gets into the microphone.
Due to the open type, the headphones do not have noise isolation - the people around can hear well the music from the headphones, while you can hear ambient sounds too.
Headphones without noise isolation are well suited for home and studio in a quiet environment, as well as on the street with active traffic, allowing you to notice the danger in time.
Headphones without noise isolation are unsuitable for use in noisy public transport, as due to external noise it is necessary to increase the volume level of reproduced music, which is harmful for hearing during long listening. Loud sound is unpleasant to passengers nearby. In a studio, while recording vocals or instruments by a microphone, the open headphones are likewise not suitable, because sound from the "minus" from the headphones will gets into the microphone.
Analysis of the sensitivity of Fostex TH909 headphones
The sensitivity of the Fostex TH909 headphones is 118.48 dB/V SPL by the voltage and 102.46 dB/mW SPL by the power. The sensitivity by voltage reflects the relative "loudness" of the headphones among others - the higher is the value, the louder are the headphones. The sensitivity by power reflects the efficiency of the headphones. High sensitivity of the headphones means less energy need from the source (for portable devices - less power from the battery).
Depending on the sensitivity, headphones are best to use with sources of optimum power. If the source is too powerful, then there is a high probability of constantly hearing background noise. If source power is weak, there will be insufficient volume level.
In a quiet environment for the Fostex TH909, an amplifier with a voltage level of at least -8.48 dBV at 25 Ohms is recommended for listening to music with a level of 90 dB SPL (without noise isolation). An amplifier with a level above 29.52 dBV is not desirable if the volume control is digital, not analog.
For noisy environments, an amplifier with a voltage level of at least 3.52 dBV at a load of 25.04 ohms is desirable.
If you want to listen to music at a different volume level, you just need to add or subtract a change in dB to 90 dB SPL (for example, for a desired level of 105 dB SPL, add 15 dB and the minimum voltage level for the amplifier is -8.48 dBV + 15 dB = 6.52 dBV).
Analysis of the impedance of Fostex TH909 headphones
The average resistance at the headphones Fostex TH909 is 25.04 Ohm.
The resistance affects the amount of current that the amplifier should give to the headphones. If the current is not enough, the sound quality will deteriorate, beginning with harsh in the sound and ending with a crackling. In most cases, at low current values, the amplifiers operate in comparable quality to class A, and as the current level rises, the quality decreases toward AB, B, and the clipping zone.
Imagine that you have a water tank, which gradually fills with water. The voltage from the amplifier this is the pressure with which the pump draws water from the reservoir. If the inflow of water in the tank is lower than the volume that the pump pumps out, then at the pump outlet we collect water and "bubbles". Similarly will be with the sound from the headphones, which are lacked the current from the amplifier.
For a quiet environment, an amplifier with an output current level of at least 15.05 mA in a given class of quality is desirable (preferably orientated to comparable class A) and 59.91 mA for loud.
The resistance affects the amount of current that the amplifier should give to the headphones. If the current is not enough, the sound quality will deteriorate, beginning with harsh in the sound and ending with a crackling. In most cases, at low current values, the amplifiers operate in comparable quality to class A, and as the current level rises, the quality decreases toward AB, B, and the clipping zone.
Imagine that you have a water tank, which gradually fills with water. The voltage from the amplifier this is the pressure with which the pump draws water from the reservoir. If the inflow of water in the tank is lower than the volume that the pump pumps out, then at the pump outlet we collect water and "bubbles". Similarly will be with the sound from the headphones, which are lacked the current from the amplifier.
For a quiet environment, an amplifier with an output current level of at least 15.05 mA in a given class of quality is desirable (preferably orientated to comparable class A) and 59.91 mA for loud.
Frequency response
Sensitivity
The Fostex TH909 sensitivity is 118.5 dB/V SPL.
These headphones are 6.6 dB quieter than most Over-ear headphones.This difference is insignificant and not exceeding a threefold deviation from the mean. So, most devices designed to work with full-sized headphones should fit quite well with the Fostex TH909. A sufficient volume should be provided during playback and background noise from the source should not be noticeable.
In general, to listen to music with a level of 90 dB SPL in a quiet environment, the amplifier will require a voltage of -19.5 dBV.
It is desirable that the amplifier provides a margin of 12 dB in cases of rare noisy environments or for too quiet recordings. Thus, the amplifier should provide a maximum voltage level not lower than -7.5 dBV.
Excessive volume margin is undesirable, since for analog regulator, the adjustment range is about 40 dB and below that the channels imbalance begins. For a discrete regulator the pitch may be too large. For digital controllers are possible options for adjusting the sound level before a DAC or in a DAC. As a result of that will be decrease the signal-to-noise ratio and accordingly it is probable the appearance of audible noise.
The average sensitivity to power for Over-ear headphones is 99.1 dB/mW SPL (average by measured 508 headphone models). The Audeze LCD-2C sensitivity is 102.5 dB / mW SPL. FostexTH909 have just a little more sensitivity than other headphones of this type. This means that their power consumption is lower and being connected to mobile devices, the operation time of this bundle will be longer than of many others.
