Good question. I’ll bet there room lots of hard of hearing people that space unclear about the differences between those two scales, and often treat these two terms together though they are interchangeable and also mean the exact same thing—if they also wonder around those abbreviation on their audiograms.

You are watching: Db spl to db hl conversion chart

When audiologists measure her hearing, lock measure your hearing in units dubbed decibels (dB). The catch is the there are numerous decibel scales. Thus, in order to be meaningful, her audiologist indicates which decibel range she used. The 2 most typically used scales space the SPL (Sound press Level) and the HL (Hearing Level) scales.

Sound meters space calibrated in dB SPL. This makes total sense because the condenser microphones provided in sound meters room sensitive to transforms in sound press in the air, just as our ear are. In contrast, audiometers are calibrated in dB HL, not in dB SPL choose you would certainly think would certainly be done. This begs the question, “Why no calibrate audiometers utilizing the SPL scale and also forget about the HL scale?”

Here’s the reason why. Ours ears execute not hear equally fine at every frequencies. If our ears heard all frequencies of sound equally well, then we wouldn’t need the HL scale.

Our ears execute not awareness low- and also high-frequency sounds and also they do sounds in between 500 and 4,000 Hz. Because that example, the faintest sound a young human being with regular hearing deserve to hear at 2,500 Hz is 0 dB SPL. In contrast, in ~ 20 Hz (a an extremely low frequency sound), the sound needs to be much louder in ~ 72 dB SPL in order to simply faintly hear it. At the other end of the frequency spectrum, a very high-pitched sound in ~ 15,000 Hz requirements to be raised to 20 dB SPL in order because that you to simply detect it.

Thus, typical hearing, if plotted on one audiogram making use of the SPL scale, would certainly be a curved, wavy line (like the currently on the graph in ~ the bottom the the page). Since this heat is both curved and also somewhat wavy, it would be daunting to easily tell on one audiogram how much hearing loss a person has actually by frequency.

It would certainly be ever so much easier to visualize the degree of hearing lose if regular hearing verified as a flat, right line set at 0 dB top top the audiogram. Then, any kind of deviation native this heat would indicate the degree of hear loss.

This is the reason why they developed the HL scale. The curved SPL range is normalized so that it i do not care a flat, directly line in ~ 0 dB. (We call this normalized SPL scale the HL scale.)

Using the HL scale, typical (“perfect”) hearing is a right line throughout the peak of one audiogram. As soon as your audiologist exam you, any deviation indigenous the 0 dB HL line shows a hearing loss if it falls listed below the 0 dB line. (By the very same token, if her hearing deviates above the 0 dB line, you have much better than typical hearing at that frequency.)

To transform SPL readings come HL readings, audiometers space calibrated to include a certain amount to each frequency tested. This amount varies by frequency. For example, in ~ 125 Hz, it adds 45 dB, while at 1,000 Hz it only adds 7 dB. Likewise, in ~ 4,000 Hz it adds in 9.5 dB, while at 8,000 Hz the adds in 13 dB.

Here is the ANSI S3.6-1996 standard to convert dB SPL to dB HL.

Frequency  
HzdB SPLdB HL
12545.00
25027.00
50013.50
7509.00
10007.50
15007.50
20009.00
300011.50
400012.00
600016.00
800015.50

The an outcome is that currently your audiogram conveniently shows your hearing loss graphically in dB HL, rather than you trying come mentally visualize the degree of hearing lose if it were plotted in dB using the SPL scale.


Comments

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Daniel Iancu says

May 31, 2013 in ~ 3:07 PM


Do you have a counter formula? Or at least can you write-up a trusted resource from wherein I can obtain the frequency weighting table?Thanks!

You could be interested in this: http://en.wikipedia.org/wiki/Equal-loudness_contourOne that the reason why is the the ear canal resonates about that frequency and furthermore the middle ear also adds some gain.


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Dr. Neil says

June 1, 2013 at 7:32 AM


Hi Daniel:

You can acquire the frequency weighting table in ~ http://comd.byu.edu/rh/dBcalculator.xls and also then click on the third tab in the spreadsheet.

Regards

Neil


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Swapan says

August 29, 2018 in ~ 2:17 PM


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Fred says

September 18, 2013 at 5:15 PM


Can you please tell me what this means PB Level (dBHL)Right 60 Left 55 and also Threshold (SRT)30 best 25 Left thanks.

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Avi Shupak says

May 8, 2016 at 8:27 AM


Hi Avi:

Good question–but ns haven’t to be able to discover the answer to it. If friend ever uncover out, please article the information below so we’ll all know.

Cordially,

Neil


I require to understand this and also I additionally can’t uncover it till now. Is there any formula to convert dBSPL come dBHL above 8000 Hz????