What are the measurement units of sound intensity?

dB HL（hearing level）

Hearing level: it refers to “straightening” the hearing threshold curve of normal people aged 18-25 as the reference value of pure tone audiometry. The difference between the hearing threshold of patients and normal people at various frequencies is expressed as the hearing level of pure tone audiogram. It can be used to express signal strength and directly describe the degree of hearing loss.

Two

dB SPL（sound pressure）

Sound pressure level: it is based on the basic concept of physics. The reference sound pressure value is 20 μ PA, which is applicable to all acoustic measurements. The RMS value of relative sound pressure is measured by the minimum sound intensity (about 20 μ PA) heard by the most sensitive human ear. It is defined as taking the ratio of the effective value of the sound pressure to be measured to the reference sound pressure as the common logarithm and multiplying it by 20. Its unit is decibel (DB). Therefore, when the sound intensity is expressed by sound pressure level, it shall be calculated according to the following formula:

Sound pressure level (DB) = 20 LG [P (E) / P (Ref)]

In acoustic measurement, the reference sound pressure of sound pressure level is specified as 2 × 10-5 PA (20 μ PA). In this way, 20 μ PA is 0 dB SPL, pain threshold (20 PA) is 120 dB SPL, ordinary speech sound (0.02 PA) is 60 dB SPL, and gun sound (2000 PA) is 160 dB SPL. So, the intensity of sound can have a negative value.

Three

dB nHL（normal hearing level）

Normal hearing level: there is no international unified hearing zero level standard for other stimuli except pure tone. Therefore, with the biological calibration method, the hearing threshold (expressed by sound pressure level) of a group of young people with normal hearing for a certain stimulus sound is measured first, and it is regarded as the “zero level” of the normal hearing level of the stimulus sound, i.e. 0dB NHL. This is a method commonly used in clinic.

Four

dB SL（sensation level）

Sensory level: refers to the number of dB higher than the hearing threshold. The reference quantity is the signal hearing threshold of this frequency. It is often used to determine the signal intensity of auditory evoked potential stimulation.

For example, if an individual’s single ear (left ear) is stimulated with a subjective threshold of 30 dB SPL, the sound intensity of the left ear is 60 dB SL when the stimulus sound is 90 dB SPL. That is to say, the sound stimulation intensity can be converted into (90-30) dB SPL = 60 dB SL.

Five

dB A

A-weighted sound pressure level: if the noise level measured by A-weighted is 45 dB, then the “a” sound level is 45 dB or 45 dB (a) is written. In clinical audiology, A-weighted measurement is often used to evaluate the environmental noise.

Six

DB speech HL

Speech listening level: used for speech test.

Seven

dB eHL

Estimated hearing level: used to solve the problem of expression of pure tone hearing threshold estimated by objective test response threshold. The results expressed by DB EHL indicate that the threshold is estimated by objective audiometry, and its value can be equivalent to dB HL in auditory intervention                                                        

Eight

dB peSPL 

Peak equivalent sound pressure level: it is a calibration unit specially used for short-term sound intensity. It is the pure sound pressure level with the same amplitude of pure sound peak to peak at the peak of pressure change (i.e. the maximum pressure point) of short-term sound. It is obtained by comparing the amplitude relationship between the peak amplitude of short-term electrical pulse and pure sound signal on an oscilloscope.

Peak equivalent sound pressure level dB pespl for different types, different frequencies and different time intervals, the difference between the unit dB SPL and its equivalent DB pespl is not exactly the same. This unit is mainly used in auditory evoked potential test, such as auditory brainstem evoked potential, and has been gradually replaced by DB NHL unit in recent years.