by Neil Bauman, Ph.D.
© November, 2011.
A student asked,
What is the relationship between the SPL dB scale and HL dB scale?
Good question. I’ll bet there are lots of hard of hearing people that are unclear about the differences between those two scales, and often treat these two terms as though they are interchangeable and mean the same thing—if they even wonder about those acronyms on their audiograms.
When audiologists measure your hearing, they measure your hearing in units called decibels (dB). The catch is that there are several decibel scales. Thus, in order to be meaningful, your audiologist indicates which decibel scale she used. The two most commonly used scales are the SPL (Sound Pressure Level) and the HL (Hearing Level) scales.
Sound meters are calibrated in dB SPL. This makes total sense because the condenser microphones used in sound meters are sensitive to changes in sound pressure in the air, just as our ears are. In contrast, audiometers are calibrated in dB HL, not in dB SPL like you would think would be done. This begs the question, “Why not calibrate audiometers using the SPL scale and forget about the HL scale?”
Here’s the reason why. Our ears do not hear equally well at all frequencies. If our ears heard all frequencies of sound equally well, then we wouldn’t need the HL scale.
Our ears do not perceive low- and high-frequency sounds as well as they do sounds between 500 and 4,000 Hz. For example, the faintest sound a young person with normal hearing can hear at 2,500 Hz is 0 dB SPL. In contrast, at 20 Hz (a very low frequency sound), the sound needs to be much louder at 72 dB SPL in order to just faintly hear it. At the other end of the frequency spectrum, a very high-pitched sound at 15,000 Hz needs to be increased to 20 dB SPL in order for you to just detect it.
Thus, normal hearing, if plotted on an audiogram using the SPL scale, would be a curved, wavy line (like the lines on the graph at the bottom of the page). Since this line is both curved and somewhat wavy, it would be difficult to readily tell on an audiogram how much hearing loss a person has by frequency.
It would be ever so much easier to visualize the degree of hearing loss if normal hearing showed as a flat, straight line set at 0 dB on the audiogram. Then, any deviation from this line would indicate the degree of hearing loss.
This is the reason why they developed the HL scale. The curved SPL scale is normalized so that it becomes a flat, straight line at 0 dB. (We call this normalized SPL scale the HL scale.)
Using the HL scale, normal (“perfect”) hearing is a straight line across the top of an audiogram. When your audiologist tests you, any deviation from the 0 dB HL line indicates a hearing loss if it falls below the 0 dB line. (By the same token, if your hearing deviates above the 0 dB line, you have better than normal hearing at that frequency.)
To convert SPL readings to HL readings, audiometers are calibrated to add a specific amount to each frequency tested. This amount varies by frequency. For example, at 125 Hz, it adds 45 dB, while at 1,000 Hz it only adds 7 dB. Likewise, at 4,000 Hz it adds in 9.5 dB, while at 8,000 Hz it adds in 13 dB.
Here is the ANSI S3.6-1996 standard to convert dB SPL to dB HL.
| Frequency | ||
| Hz | dB SPL | dB HL |
| 125 | 45.0 | 0 |
| 250 | 27.0 | 0 |
| 500 | 13.5 | 0 |
| 750 | 9.0 | 0 |
| 1000 | 7.5 | 0 |
| 1500 | 7.5 | 0 |
| 2000 | 9.0 | 0 |
| 3000 | 11.5 | 0 |
| 4000 | 12.0 | 0 |
| 6000 | 16.0 | 0 |
| 8000 | 15.5 | 0 |
The result is that now your audiogram readily shows your hearing loss graphically in dB HL, rather than you trying to mentally visualize the degree of hearing loss if it were plotted in dB using the SPL scale.
As an introduction to audiology student I found this extremely helpful in distinguishing the differences between the two sets of scales, thank you!
Very helpful in my into to Audiology class!!!
I like the definition of the measurements, but I would like some more concrepts.
Such as in math in HL to SPL transform.
as serious that calculation??.
Another thing when measuring the auditory evoked potentials, these should be measured in SPL because its Insertion transducers.
Use the chart. To convert from HL to SPL at 125 Hz, add 45. To convert from SPL to HL at 1000 Hz, subtract 7.5 For other frequencies, interpolate.
Hi Solo Pilot,
Thanks for sharing. I am still a bit confused about how to use this chart though. Should we not deduct 45 from SPL at 125hz to get 0 dB HL as shown in the chart? I am taking an audiology course so I would really appreciate any help I could get. Thanks!
Hi Megan:
I just looked at Solo Pilot’s reply and it was exactly backwards, so I have changed it around. It is correct now. And you were right. You do deduct 45 from the SPL figure to get the HL figure at 125 Hz. Thanks for pointing out the mistake.
Cordially,
Neil
No, is not like that, important thing here to Note is that, there is a different level of detecting the sound in SPL and HL in normal hearingng. Therefore as the reference of of normal hearing threshold is 0 dB HL at 125Hz, it means in order to detect the presence of sound at 125Hz in SPL, there must be addition of 45dB as the softer sound.
Thank you Dr. Neil for your useful website.
I am a speech therapist. I know that our ear has tendency to enhance high frequency from 1k to 5k Hz (speech frequencies); so we hear these sounds louder. But, generally low frequencies have more intensity than the high ones. Why?
Do you have a conversion formula? Or at least can you post a trusted source from where I can get the frequency weighting table?
Thanks!
You might be interested in this: http://en.wikipedia.org/wiki/Equal-loudness_contour
One of the reason why is that the ear canal resonates around that frequency and furthermore the middle ear also adds some gain.
Hi Daniel:
You can get the frequency weighting table at http://comd.byu.edu/rh/dBcalculator.xls and then click on the 3rd tab in the spreadsheet.
Regards
Neil
Hello Dr. Neil, This link is dead, is there an updated version of this? Thanks.
Hi Swapan:
I can’t remember what the graph looked like, but I found another one and updated the article so you should be able to see it now.
Cordially,
Neil
Can you please tell me what this means PB Level (dBHL)Right 60 Left 55 and Threshold (SRT)30 Right 25 Left thanks.
Hi Fred:
PB (phonetically balanced) level is the level (basically your most comfortable listening level [MCL]) at which the list of phonetically balanced words (single-syllable words covering all the English speech sounds) is presented. They were presented at 60 dB HL (hearing level) in your right ear and at 55 db HL in your left ear. This does not say what the results were, just what the settings were.
The SRT (Speech Reception Threshold) is the level at which you are able to hear and identify correctly 50% of the spondee words (two syllable words with equal stress on both syllables such as cowboy, railroad, hotdog, etc).
According to these settings, your left ear hears 5 dB better than your right ear.
Regards
Neil
I was confused in my intro to Aud class until I read this .
Thank you for the help
So, i´ve measured the output levels of an device for audiometry. Now I got the values in dB SPL.
Do I just have to subtract the correction values from the measured values and i will get the values in dB HL?
Thank you SO MUCH!! I needed to explain this in an assignment I have, and I found this super helpful!
Brilliant. Thank you.
This post was really helpful for me as I am just starting to learn about audiology.
Thanks,
Paula
So much clearer and succinct than my audiology text book. Thank you!
Thank You so much for making this information available online. A friend asked me if I could help developing a mobile app for administering these kinds of tests. Looks like I’ll have my work cut out for me.
Where do I find conversion table from HL to SPL and vice-versa frequencies above 8000 Hz?
Hi Avi:
Good question–but I haven’t been able to find the answer to it. If you ever find out, please post the information here so we’ll all know.
Cordially,
Neil
I need to know this and I also can’t find it till now. Is there any formula to convert dBSPL to dBHL above 8000 Hz????
Hi Alaa:
I’m sure there is a conversion chart somewhere, but I’ve never found one for the high frequencies so can’t help you there.
Cordially,
Neil
HUUUUUGE THANK YOU!
This was an extremely helpful resource. Thank you!
I’ve been practicing for 20 years and this explanation was one of the simplest and easiest to understand. Thanks for posting this! I wish we had the Internet and sites like yours when I was learning. Thanks for helping these students and us older guys!
What about for speech levels? Also is a dB A for speech equivalent to either scale?
why don’t we usually write the type of hearing loss for clients with minimal hearing loss?
what is the cause for objective tinnitus?
Hi Aishwarya:
A good expample of objective tinnitus would be pulsatile tinnitus, or tinnitus that arises from the middle ear.
Cordially,
Neil
is epley maneuver for treating bppv is done by an audiologist or an ent specialist?
Hi Aishwarya:
Typically, the Epley maneuver is done by an ENT.
Cordially,
Neil
is there any complete cure for tinnitus?
Hi Aishwarya:
It all depends on the kind of tinnitus you have. Often the various kinds of somatosensory tinnitus can be cured/fixed, but typically the common kind of tinnitus can be managed, but it doesn’t always go away–but may fade into the background and not bother you anymore. Tinnitus from taking ototoxic drugs may go away when you stop taking the drug, or it may not.
There is no simple answer.
Cordially,
Neil
Sir what does 0 dbspl indicates
Hi Chethan:
You have to define what frequency you are talking about to know what 0 dB SPL indicates. 0 dB SPL was defined as the reference sound pressure that corresponds to the quietest sound at 1,000 Hz that the human hear can detect.
Cordially,
Neil
I have one more doubt why is occlusion effect more in lower frequencies
Hi Chethan:
I don’t have the answer. I think it has to do with the fact that there is more power in the lower frequencies, and that the wave length of the lower frequencies is longer.
Perhaps someone can answer this for both of us.
Cordially,
Neil
Sir ..what exactly speech banana is …where the frequency is upto 4 khz.but we know that human fundamental frequency goes maximum upto 400 hz ..what is the relation bwtween fundamental frequency and the representation of that speech sound in speech banana
Dr. Bauman,
Is the conversion between SPL and HL dependent on the transducer used? Or is this a transducer independent conversion?
Thank you!
Hi Katherine:
As I understand it, it is based on mathematics–sound curves and hearing averages for each frequency. It is not something you measure yourself. Your audiometer has these conversions built in so they are transparent to you when you test a person’s hearing.
Cordially,
Neil
Audiologist wanted me to buy $ 5000.00 a pair of hearing aids, neighbors advised Costco 1/3 [kf the price, my ENT said wait, wish my hearing loss is as mild.
So i will wait and recommend second opinions.
Dr. Bauman,
What would be the conversion from HL to SPL to the audiometer white noise? I am, the white noise covers a large bandwidth , so, how to convert HL to SPL in this situation?
Hi Thaly:
I don’t have a clue. Can it even be done since the whole point of SPL to HL is to correct for each frequency tested?
Cordially,
Neil
This is off-topic but you sound so intelligent and helpful. I am in my fourth week of cortisone treatment for sudden sensory-neural hearing loss which is scary. A little hearing and speech recognition has returned. It is likely to be auto-immune. Do you have any advice?
Hi Lynne:
Since the steroid treatment doesn’t seem to have worked very well at all, I sort of doubt that you have autoimmune inner ear disease. If you had autoimmune inner ear disease, I would expect you to also have some other autoimmune disease as well. Do you have any other immune system diseases?
More likely, in my opinion, your sudden hearing loss was caused by a virus rather than by autoimmune inner ear disease.
Cordially,
Neil
My daughter age 13 just had an audiogram done, and the result is between 0 and -10 dB from 250 Hz and up to 8000 Hz (except only 10 dB at 6000 Hz, right ear). Is this considered normal hearing? I have searched the net for a normal hearing curve, but only found out that normal hearing range is defined as being from +20 to -10. I ask since she suffers from an unusual and socially devastating sensitivity to certain sounds in her daily life, eg. paper on the table, socks on a wooden floor, chewing and many more (often to do with friction)
Thank you very much. Anita
Hi Anita:
You betcha. Your daughter has normal hearing–actually a bit above normal since she is consistently at -10 dB most of the way.
For children, normal hearing is anything down to 15 dB. Below that is slight hearing loss (15 to 25 dB).
I’m almost certain I know the condition your daughter has. Actually it is fairly common (it ranges in degree of severity), but it is seldom diagnosed properly and therefore considered quite rare.
In order to help me be certain, explain more about your daughter’s reactions to the sounds that trigger her. Exactly what sounds is she sensitive to? How does she react to these sounds? Does she react right away to a triggering sound, or does it take a while before the sound bothers her? What have you/she been doing about it? If you’d rather take this conversation private, my email is at the bottom of any page on the Center’s website.
I’m sure I can help you.
Cordially,
Neil
Thank you for this information.
Is there a way to calculate the dBSpl at a given frequency(1000hz) at various dB HL? Given the information on this page, I’ve learned that if the frequency is 1000hz and the db HL is 0, then dbSpl is approximately 7.5. What if the dbHL is 10..or 20…30 etc at the same frequency? Is there a formula or does it needed to be measured individually?
I don’t think it’s as easy as simply adding the db HL to the corresponding dbSpl value….right?
Hi VK:
I don’t know the answer to your questions–but I’d like to. I’d suggest asking an audiology professor and when you get the answer, post it here so we all know. You may have to ask several professors before you find one that knows the answer.
Cordially,
Neil
Hi VK, a late reply:
The dB SPL scale and the dB HL scale has equal dB-steps. This means that if you increase any sound measured in dB SPL by 10 dB the dB HL-value of that sound will increase by 10 dB as well. In your example a 1000 Hz tone at 10 dB HL will measure approximately 17.5 dB SPL etc.
Best regards,
Martin Eklöf
Hi Martin:
Thanks for the answer. Now that I see it, it’s so simple and makes perfect sense (so why didn’t I realize that? 😉
Cordially,
Neil
Does the HL conversion take into consideration the average canal resonance at 2700Hz?
Hi Douglas:
I don’t have a clue. Sorry.
Cordially,
Neil
As an audiologist I am doing some research on Occupational Hearing Loss, dB SPL, HL and dB A. I came across this conversion scale on a physics of sound sight. It is quite different than yours. I tried to copy the scale but it didn’t work so I’ll write in what it states:
Frequency dbSPL dBHL
250 Hz +15 0
500 +9 0
1000 +3 0
2000 -3 0
4000 -4 0
8000 +13 0
Please comment.
Hi Jeanne:
Where did you get these figures from? I need to see the source to figure out why the two sets of figures are different when they supposedly should be the same. After all, I took my figures from the ANSI standard–which by definition is correct because it IS the standard.
Cordially,
Neil
Hi Neil,
I’m just revisiting this topic again. The figures were from the very end of this link:http://www.sengpielaudio.com/calculator-soundlevel.htm
Another question I have is how does dBA scale relate to the dBHL scale?
Hi Jeanne:
Thanks for the link. Unfortunately, they don’t give any reference to where they got those conversion figures from SPL to HL. I don’t know why they differ from the official ANSI figures. Perhaps, since it’s a sound engineer’s website, that sound engineers use these terms in a different way than hearing professionals do. I’d like to think that the table is correct–once you understand how it was derived and how it is meant to be used. But obviously it is not to be used in the way audiologists understand the conversion from SPL to HL for the purposes of measuring hearing loss.
Cordially,
Neil
I’m finding this discussion helpful, thank you. One question on this topic (I’m an aging audio engineer).
I have hearing aids which are incredibly helpful in my work and living day to day in general.
I have the chart of my hearing loss (dB HL) and I’d like to translate those readings onto a graphic equalizer so I can mimic the hearing aid’s correction if I wear headphones. How would I go about doing that?
For example, I’m down 60dB HL at 4kHz, but even my most powerful multi-band equalizers don’t boost beyond 30dB or so.
Thank you!
Hi Timm:
First, you have to know what units your graphic equalizer is calibrated in. Is it in dB SPL or what?
Cordially,
Neil
What is RSTSPL and its importance
Hi Jijo:
What does RST stand for?
Cordially,
Neil
Hi Neil Bauman,
I have a question about the ANSI S3.6-1996 standard to convert dB SPL to dB HL table.
Is this for air or bone conduction?
I need the table for bone conduction for my report and I want to refer you.
Hope to hear from you soon, because my deadline for the report is monday.
Cordialy,
Meike Janssen
Hi Meike:
As far as I know, the ANSI S3.6-1996 standard is for air conduction only.
I’m no expert on this, but I think that the ANSI S3.43-1992 standard is the standard used for bone conduction.
You can see it in Table G-1 in Appendix G that you can get in pdf format from http://www.frye.com/wp/wp-content/uploads/2013/08/fa10calibration.pdf
Cordially,
Neil
This was very helpful in making sense of the difference between SPL and HL. When was this article written, I would like to reference it nicely?
Hi Hossana:
This article was published November 8, 2011.
Cordially,
Neil
Hi Neil,
I wondered what conversion figure SPL to HL and vice versa you would use for a click stimulus. I realize the click has a wide range of frequencies, but in humans through filtering function y the stimulus centres between 2000 to 4000Hz. Would you use a conversion figure in between these values?
kind regards
Susan
Hi Susan:
That’s a good question, but I’m sure I don’t know the answer. Sorry. Perhaps a professor of audiology can help you with this.
Cordially,
Neil
Hi. Dr Bauman, thanks for your helpful website. I have been practicing for a while, so long i have forgotten, is SRT/WRS measured in HL or SPL and if so what is the conversion for speech stimuli to HL?
Hi Kara:
As far as I know, they are measured in HL, but you better confirm it with someone who is certain of the answer. I could be all wet.
Cordially,
Neil
Is 0 dB HL the same as 0 Phons on the Equal-Loudness Contour graph?
Referring to the above question…trying to get to the bottom of the difference between HL and SPL, it seems as if there are websites that explain dB HL and refer to the minimum audibility curve – which looks very similar but not quite identical to the 0 Phons line on the Equal loudness contour graph – and then there are websites that explain Phons and the contour graph, but never the twain shall meet in terms of ever referring to all of these things in the same article!…so I’m a bit confused, Nev
Hi Nev:
This is outside my arean of expertise, so can’t help you there. Hopefully, someone who knows the answer will respond.
Cordially,
Neil
If I wanted to use dB A and adjust a noise source (recorded classroom noise, four talker babble, etc.) to present at a level equal to 45 dB HL and 30 dB HL (5 dB HL below presentations of speech test stimuli at 50 and 35 dB HL), what levels or conversion numbers should I use? Thank You
Hi Jim:
I don’t think you can do that–if I understand your question correctly–because the conversion between SPL and HL varies with frequency–so the conversion only relates to specific frequencies of pure tones, not to broadband noise which covers many/all frequencies of audible sound.
Cordially,
Neil
I tried to download the ANSI S3.6-1996 standard but I could not find it. Could you help me please to show where I can find it?
Or could you just send me the standard or just the page with the dB SPL to dB HL conversion.
I would really appreciate your assistance on this!
Hi Bengt:
ANSI standards are typically not available on-line. You have to purchase them from the ANSI store, unless you know someone that has a copy of the standard you want and will let you look up the information you want.
The table I have in this article gives the conversions, so what more do you want? I don’t have the original documents anymore so can’t help you there.
Cordially,
Neil
For suppose my sound level is 50 db for 1khz how to convert it into DBSPL and DBHL
Hi Lokesh:
Sound meters measure sound in SPL so if it reads 50 dB (SPL) that is what it is.
To convert that to dB (HL), the difference between the SPL and HL scales is 7.5 dB. no matter how loud the sound is at 1,000 Hz. So the dB HL is always going to be 7.5 dB lower than the SPL reading as shown in the table in the above article.
Thus, 50 dB SPL would be the same as 42.5 dB HL
Cordially,
Neil