# Why a Large Diaphragm Microphone is limited to lesser frequency range

Here Above are the frequency responses of different size microphone(condenser)

what actually is the relation between the microphone capsule size and frequency response ?

The conclusion is that a large diaphragm microphone will have a more limited frequency range than a small diaphragm. This is illustrated in the graphs

i found some sites explaining the reason but i did not get the reason well, can any one illustrate for me plz

There are typically two reasons: First, a larger diaphragm is also heavier and hence it's inertia is bigger, which slows it down at higher frequencies (but also provides for significantly higher max SPL handling).

The main reason, however, is the relationship between wavelength and diaphragm size. The microphone basically "integrates" the sound pressure over the spatial area of the diaphragm. For a plane wave, the sound pressure is the same everywhere, but in a diffuse field that's not the case anymore. The wave length at 10 kHz is about 34 mm. So there are points on the diaphragm that are half a wavelength apart and it's entirely possible that one point sees positive pressure and the other negative pressure. These can cancel each other out (to some extent).

• your first reason says heavier diaphragm makes it to move slowly or in other terms makes it difficult to move during high freq but in contrary a large area is easy to be moved with a little pressure,but when continous(very frequently) pressure is applied its not able to move the diaphragm doesn't it seem conflicting Dec 24, 2013 at 17:01
• The 1st reason is correct and so seems the 2nd by @Hilmar . It is the very same reason you see tweeters are smaller than woofers. I think, the damping in a large diaphgram (which are also thick) will be very high and oscillations cannot be sustained at high frequencies. Dec 25, 2013 at 14:00
• @Electro: Good thinking, so let's do the math: if we double the area the force double as well (F = p*A). If retain the thickness of the membrane, the mass doubles as well and so the overall acceleration stays the same. However, typically you will have to make the membrane a little thicker to maintain stability and the same mechanical properties, so the mass goes up faster than the Force and the acceleration goes down Dec 25, 2013 at 14:29
• sorry @Hilmar still i am confused,my confusion increased more with your broadened explanation :),ok keep it simple and answer straight to question ,heavier diaphragm =large mic,small diaphragm =lighter in weight,so when equal amount of pressure is applied on both ,smaller responds good thats according to one parameter weight,but when it comes to other theory taking area in to consideration the opposite happens ,will the microphone makers try to maintain same weight while going for large diaphragm ? gone mad :) Dec 26, 2013 at 5:59
• Large or long thin items (a train bridge for example) can get very fragile, and much more likely to fail under any vibration or pressure. Dec 26, 2013 at 17:39