Two questions - microphones and Speakers

[Light Dependant Resistor]

The first is should or what would happen to recorded sound if Microphones were the same size as speakers ? . Imagine the size of a quad ESL as a microphone

There is much equivalence of each being equally capable - - you can use headphones for instance as a microphone.

The second, what would a speaker the size of a microphone sound like ?. bass response obviously a problem but its sameness then in size
as the microphone that captured its sound being subsequently reproduced, has an air of correctness.

I am of the opinion microphones reduced in size to capture high frequencies and more so aid portability, and could be made much larger - the concept of a big microphone akin to a ESL would be interesting.

[guy]

Just guessing, but would a really large flat panel as a microphone miss high frequencies - not enough energy to move the diaphragm ?

Your mention of using headphones as a microphone reminds me of the old (70's?) Sennheiser HD414 headphones which could be used for "dummy head" recordings as it was easy to reverse the earpieces on the headband.

I understand that Russians used this on US embassy:

https://www.youtube.com/watch?v=1MrudVza6mo

[walpurgis]

I don't know much about microphones, but assume they must operate with a compensation curve much like the RIAA correction applied to phono pickups. Seems to me a ribbon mike must offer the least moving mass, so possibly the best performance? I know some can be pretty expensive.

Speakers are transducers in the same electromechanical way that microphones are, which makes me wonder if a plasma mike is possible? Probably not :).

[guy]

https://blog.digilentinc.com/plasma-arc-microphones/

[walpurgis]

https://blog.digilentinc.com/plasma-arc-microphones/

Well, what do you know? :)

[YNWaN]

The premise of this thread strikes me as bizarre because, surely, the answer to both questions is largely obvious. A pair of speakers the size of a microphone would sound like a pair of headphones - tiny speakers. A microphone the size of a speaker would just be hugely insensitive and have a mass of irrelevant and unnecessary cabinet and air volume attached to it.

[Barry]

I have used a small loudspeaker (3" diameter) as a microphone, and have heard a microphone used as a speaker. Just listen to any speaker using an STC (Coles) 4001 'tweeter', the 4001 was originally designed to be a microphone capsule, but was found it could be used as a tweeter when driven 'in reverse'.

To reproduce low bass frequencies to be audible, one has to move a lot of air. Since there is a limit to the excursion permitted by the voice coil (even on 'long throw' designs), the area of a drive unit used as a woofer has to be large, and hence large in diameter. However to detect low frequencies, the bass instruments are themselves already moving a sufficient amount of air when played, so all a microphone has to have is a diaphragm large enough to be able to sample the air motion.

Most microphones are so-called electrodynamic designs (either moving-coil, or ribbon; which is a 'half turn' moving coil design). These produce a voltage output according to Lenz's law, which states the voltage generated is proportional to the rate of cutting magnetic flux. Since bass frequencies are low, this rate is low, hence the output is low, The output increases with frequency (6dB/octave), so as Geoff points out, electrodynamic microphones need to have equalisation applied, whereby the low frequency output is boosted and that due to the higher frequencies attenuated.

With condenser (capacitor) microphones, the microphone diaphragm is one electrode of a capacitor, the gap or electrode separation being altered by the incident modulated air. Condenser microphones do not themselves generate a voltage output, but the varying capacitance is used in an amplifier circuit to generate a voltage. The capacitance is proportional to electrode area, and inversely proportional to the electrode spacing, The latter is modulated by the frequency of the sound wave, so there is no advantage in having large electrode area as that would reduce the relative change in capacitance and reduce the sensitivity of the microphone. Condenser microphones thus tend to have a small diameter diaphragm: in fact the largest one I am aware of was that used with Grundig reel-to-reel recorders of the '50s.

But probably the main reason why microphones "the size of a Quad speaker" are not used is that they would be far too directional as well as being insensitive. The beam-width in any plane is inversely proportional to the dimension of the moving element in that plane; so large area, narrow highly directional beam-width.

[walpurgis]

Good stuff there Barry.

Yes, I had heard that the 4001 tweeter had microphone origins. I seem to recall ITT having a version too.

[Barry]

Good stuff there Barry.

Yes, I had heard that the 4001 tweeter had microphone origins. I seem to recall ITT having a version too.

STC (Standard Telephone and Cables) was a UK company set up by Western Electric. Western Electric later sold off their foreign telecommunications companies to ITT (International Telephone and Telegraph). Manufacture of microphones was in turn passed on to Coles.

https://en.wikipedia.org/wiki/Standard_Telephones_and_Cables



STC manufactured many microphones for use by the BBC. Most of these were designed by the BBC themselves and some are still in use. The Model 4038 is a particularly iconic design.

https://www.canford.co.uk/Images/ItemImages/large/92-391_01.jpg