Understanding Microphone Sensitivity

What do you understand about microphone sensitivity? Of late I have seen a number of people miss-interpret the specifications of microphones, especially when it comes to microphone sensitivity. For instance when comparing two microphones, one says it has a sensitivity of -65dBV and the other says -43dBV, which one is more sensitive? The answer is the -43dBV one.

How is microphone sensitivity specified?

Let’s start by looking at a typical specification listing for a popular vocal microphone – the Shure SM58. Under the heading of Sensitivity it states:  -54.5 dBV/Pa (1.85mV)  1 Pa = 94 dB SPL.

I think it is easier to start at the end and work backwards. The last bit 1 Pa = 94 dB SPL is simply stating the test criteria. That is, they are using the standard of 94dB SPL is equal to one pascal. This is the normal standard used these days by most manufacturers (an older standard used one pascal as 74dB SPL). A pascal (Pa) is a unit of pressure, named after Blaise Pascal (who among other things developed the barometer). For sound levels, the standard says that a sound level of 94dB SPL (Sound Pressure Level) generates one pascal of pressure (on the microphone diaphragm).

Microphone Sensitivity in Volts

So that is our test setup, one pascal, or a sound pressure level of 94 dB, is “heard” by our microphone. When this happens, the Shure SM58 will generate 1.85mV. So to compare the sensitivity of microphones, we need only to compare these figures. The higher the voltage produced at the given sound pressure level (94dB) the more sensitive the microphone is. For example if a microphone produces 15mV at the same sound level, then it is obviously more sensitive than the Shure SM58 which only produces 1.85mV.

Microphone Sensitivity in Decibels

So if that is simple enough to follow, it seems we must complicate these simple figures by converting them to decibels. Remember that a decibel is a ratio, in this case, the ratio between the produced voltage (1.85mV) and a reference level of 1 volt. This decibel ratio calculation gives us the number of -54.5 dBV. That is, with the test level of 94dB SPL (1 pascal), the SM58 microphone produces a signal 54.5 decibels below one volt. These measurements are always negative. -54.5 dBV is saying the microphone is producing a signal 54.5 dB below the one volt reference.

To help with all this conversion from milli-Volts to decibels and back again, here is a simple calculator you can use.

Comparing Microphone Sensitivity

So there are two ways we can compare microphone sensitivity, with milli-volts or with decibels. Both ways give the same comparison. Both use a test sound pressure level of one pascal (that is, 94dB SPL).  Both comparisons are easy to do without complex formulas. Simply compare the output of each microphone in milli-volts, or in decibels below 1 volt.

So let’s compare two microphones, the SM58 and the Rode Videomic.

microphone sensitivity, rode videomic In the specs for the Videomic they state Sensitivity: -38 dB re 1 volt/pascal (12.6mV @ 94dB SPL) +/- 2dB @ 1kHz. There it is, everything you would want to know about the sensitivity. The simple method: it produces 12.6mV at 94 dB SPL (compared to 1.85mV for the SM58) therefore it is more sensitive than the SM58. 12.6mV also equates to -38dBV/Pa or -38dB below 1 volt with a pressure of 1 pascal. Compared with the SM58 we can see the Rode Videomic is 16.5 dB (54.5 – 38) more sensitive.

millivoltsVolts/pascal
Shure SM581.85mV (1 Pa = 94dB) -54dBV/Pa
Rode Vidoemic12.6mV @ 94dB SPL -38dB re 1 volt/pascal

Note that the higher the negative dBV, the lower the sensitivity. That is, a mic with a sensitivity of -54.5dBV is less sensitive than a mic with a sensitivity -38 dBV, but more sensitive than a mic with a sensitivity of -65dBV. A more logical way to look at it is to think about how much gain will be required to amplify the test signal up to a level of one volt. For the SM58, we would need a pre-amp with a gain of 54.5 dB. For the videomic the pre-amp needs a gain of only 38dB.

The other figures in the specifications are also worth noting. Firstly +/- 2dB, this is telling us that all Videomics are within that range of sensitivity (that is between -40dBV to -36dBV). The other interesting figure is the last bit @1kHz. This is saying these figures are true and correct at the test frequency of 1kHz, or 1000Hz. Each mic is likely to be more or less sensitive at other frequencies.

More than Microphone Sensitivity

This is also telling us there is more to a good mic than its sensitivity. We must also look at its frequency response, its tone, its maximum SPL without distortion, its directionality and its handling noise among other factors. It is also important to note that mic sensitivity is not necessarily telling us it is a good mic or not. It all depends on what the mic is being used for. We wouldn’t want to use a Videomic as the vocal mic for a rock band singer, any more than we would want to use a SM58 for distance recording. But using them for their intended use is normally ideal.

Shure has been a popular brand of microphone used by professionals for many years. If you are interested in buying one, here is a link to Amazon’s range of Shure microphones.

Rode is a personal favourite of mine. They make great microphones, especially for recording and video work. If you are interested in buying one, here is a link to Amazon’s range of Rode microphones.

This article is based on one I originally wrote for my friends at CamcorderUser.net, and has been refined by their helpful comments

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19 COMMENTS

  1. Hi Geoff,

    Thanks much for this info; its very helpful.

    Do you have any insight about how to visualize mic and line voltage? Is there a software app, or a meter I could feed I mic signal into, (or a line level signal) and have the signal ‘displayed?”

    Thx much,

    Mike

    • Hi Mike,

      A simple way would be use Audacity. This is a free program used for recording audio, but I believe was originally designed by a university student who needed to visualize an audio input.

      Other than that, you could look at any of the oscilloscope programs that are available online

      Hope this helps

      Geoff

  2. Geoff,
    First of all – many thanks for this excellent article. I’m on a steep ‘audio recording’ learning curve and it’s proved very useful indeed in narrowing down microphone selection.

    One question if I may:
    Comparing two mics on the Rode site at http://www.rode.com:
    The NT1-A has a sensitivity of -31.9 dB and an EIN of 5 dB-A.
    The NT1 (the recent ‘black’ version) has a sensitivity of -29.0 dB and an EIN of 4 dB-A.

    What is I don’t currently understand is the spec stating “Maximum Output Level”
    NT1A = 13.7mV
    NT1 = 8.0mV

    Does “Maximum Output Level” relate to sensitivity in some way?

    For context: I’m looking for mics to record low sound level sources so looking for high sensitivity / low noise.

    Once again, many thanks,

    • Hi Mike,

      I’m pleased you have found the article useful.

      Rode mics are very nice, and I own a couple myself including a NT1A.

      Your question about the maximum output level is a good one, and had me thinking hard about it too, as it doesn’t make sense the way it is presented on the Rode webpage. The clue to understanding it is to look at the products’ data sheet or instruction manual. Then we read that the NT1A has a maximum output level of +13.7dBu, not 13.7mv as stated on the webpage. Indeed, every product that has a maximum output level stated on the web page is wrong. They all say mV. This is not only wrong, but rather confusing as you found out, as it is saying the maximum level is lower than the input sensitivity.

      However when stated correctly as being +13.7dBu, that makes more sense as this shows that they can handle quite loud sounds as well as very low sounds. According to my quick calculation, +13.7dBu equates to a maximum output level of nearly 3.5 volts!

      Rode are a good company, and have previously corrected a webpage error I pointed out. I will alert them to this error also, as they do like to have the correct info – it is probably a marketing department error, rather than an engineering one.

      Are you wanting to use these mics in a studio setting or in the field. If in the field, I wonder if a shotgun mic would be better is they are more directional.

      Hope this helps some,

      Geoff

  3. hey i’m thinking of getting a microphone and the sensitivity is 45dB±1dB would this be good for streaming my voice over games thanks

    • Hi Ryan,
      A microphone with a sensitivity of -45dB is quite sensitive. Whether this is good for steaming over games is dependent on whether you want a mic with high sensitivity or not. If you have a loud voice, or you shout, then this might not be so good. If you are a quite speaker and there is not much background noise, then it could be good. If you are close to the mic, then maybe not so good. If you are some distance, then maybe good. Does your recorder/soundcard have low gain or a lot of gain, is it low noise or not?

      There are many factors to make a mic a good choice. Most mics well work, whether it is the right mic for an application depends on many things – the sensitivity is just one.

      Sorry I can’t be more specific,

      Geoff

  4. Hello sir, I have Sony ECM 88B lavaliere mic , I can’t connect it yet to PCM-M10, because I need Sony DC-78 unit, I read in Sony manual it says Sensitivity is -39.0 dB (11.2mV), and-
    -52 dB +/- 2 dB (when used with DC-78), what does this mean, from this article it’s mean it would be better If I make other box and don’t use Sony DC-78, because it will give less sensitivity and more noise, do I right sir? Thanks

    • Hi Harut,
      It appears that the DC-78 has a 14db conversion loss. I think this is happening as it converts the impedance to a low impedance which is what most mixers and recorder wants.

      I think you’ll find it still works fine with your recorder.

      Geoff

  5. Hi! Is this Mic sensitivity -55dB±2dB good enough for recording? I mean, when recording for a music or a vocals?

    • Hi Zen,

      That sensitivity is very similar to a SM58.

      It will be good for close up miking. The result sill also depend on the quality and gain of the pre-amps in the mixer.

      Geoff

  6. Hi Geoff

    Thanks your professional explanation. help a lot .
    I see other microphone sensitivity unit, it is v/g, what it is? how to convert to dBV/Pa.
    another unit is -201 dB, a hydrophone sensitivity, is it 10 exp (-10.) of 1 v 0.1pv at 1 Pa
    thanks

    Luke Cheng

    • Hi Luke,
      I’ve had very little experience with Hydrophones. However it seems they still use decibels to measure their sensitivity. Rather than use a reference of 1 Pascal, they use one micro-pascal, that is one millionth of a Pascal. A ratio of 1,000,000:1 is 120dB, so to convert from V/uP to V/P, add 120 dB.

      Not withstanding the maths, the relative sensitivity of one hydrophone to another is still the same as in the article above.

      When you think about, hydrophone technology is quite complex. A microphone measures slight differences in the air pressure created by us talking. A hydrophone has pressure on it at all times – water pressure, and this pressure would change depending one how deep you place the hydrophone – this is a specialized field which I’m not across – sorry.
      Geoff

  7. Thank You Geoff ! This article demystified microphone sensitivity for me in a big way and helped me understand the concept much better.

  8. hi
    i want a equatuion for convert sound wave to voltage that show this voltage equal with the sound pressure that accident with diaphragm of microphone
    please help me
    i want a relation between sound pressure and voltage for simulation a mems microphone in ADS
    i want use a AC source voltage equivalent with sound pressure that make a variable capacitor with voltage
    this voltage in ADS equal with sound pressure in real space

    • Hi Javad,
      The answer is hiding above. For a SPL (sound level) of 94dB, you get the stated voltage for the given microphone. For example, for the SM58 microphone you get a voltage of 1.85mV with a SPL of 94dB, if you increase the SPL by 6dB (to 100dB) then you would double the voltage from the SM58 to 3.7mV – as +6dB doubles the voltage. To understand decibels better look at the articles on Understanding decibels.

      The formula you need is based on the standard decibel formula for voltage dB=20 x log(v2/v1). Using our example, voltage 2(v2) = 3.7, voltage 1 (v1) = 1.85, therefore the dB difference will be 20 x log(3.7/1.85) = 20 x log(2) = 20 x 0.3 = 6dB. Of course you can transpose the formula to find whatever value you need based on what is changing in your simulation program.

      hope this helps,
      Geoff.

  9. Nice explanation. Seems like everyone jumps straight into the math without explaining key concepts. Well done sir!

    One comment that might make this a tad better would be to post the specs side by side for the mics so people can see where the numbers are coming from and how they might appear in a datasheet or product manual.

  10. Perfect! That’s really helpfully explained. With (cheaper) condenser mics for bedroom recording, how much attention do I need to pay to the mic’s frequency response graph, or can a cheaper mic be balanced out with a good EQ?
    Thanks Geoff, great site!

    • Hi Steve, glad you found the article useful. The question of EQ with mics is a big one which requires a longer answer then this. However, most mics can be made to sound better with some EQ – don’t fall into the beginner’s trap of adding too much though. It is probably more important to make sure the acoustics of your bedroom is reasonably neutral, as any echos will be hard to hide in post.

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