Having been looking for said transducers, I've come across both receive and transmit versions of seemingly similar products. I would've thought that due to reciprocity, a so called transmitter could receive just as efficiently.

Could somebody enlighten me on the difference please? All I can gather really is slightly wider receiver bandwidths.

Examples Receiver: http://uk.farnell.com/prowave/400sr100/receiver-ultrasonic-40khz-10mm/dp/1007342

Transmitter: http://uk.farnell.com/prowave/400st100/transmitter-ultrasonic-40khz/dp/1007341

  • \$\begingroup\$ Example of such a product pair? I might assume ultrasound, but can't really tell. Please expand your question. \$\endgroup\$ – user2943160 Aug 28 '16 at 1:48
  • \$\begingroup\$ Edited to include examples, cheers! \$\endgroup\$ – Pyrohaz Aug 28 '16 at 1:55
  • \$\begingroup\$ Well, the example pair is all in one datasheet! Take a read of the differences all in the same document: farnell.com/datasheets/1719911.pdf \$\endgroup\$ – user2943160 Aug 28 '16 at 2:08
  • \$\begingroup\$ A speaker can be used as a microphone. But usually not well. I'd assume that these two devices are both transducers between electric signals and slight variations in air density over time. But that the transmitter is designed to be optimized for efficiency in converting electrical energy into air density changes, while the receiver is optimized for the reverse. It may mean only slight differences due to the effect of air as a response function, to optimize their use together, too. \$\endgroup\$ – jonk Aug 28 '16 at 2:08

A similar question piqued my own interest when I was building a Time Difference of Flight system.

There is a difference in the impedance of the components at the exact frequency for which it was designed. Low impedance on the transmitter allows it to be driven at high power, high impedance on the receiver turns the received signals into a high voltage.

I wish I had a better reference, but the answer by Tracy Allen explains it well at: Source

  • \$\begingroup\$ It seems to me you inverted high and low. The trasmitter has lower impedance; the receiver has higher impedance. As shown in the datasheet and in Tracy Allen answer. Lapsus digitae? :-) P.S. : "volatge" typo. \$\endgroup\$ – Sredni Vashtar Jun 5 '17 at 12:35
  • \$\begingroup\$ Edited answer, thanks! Blind leading the blind, eh? \$\endgroup\$ – 00iCon Jun 23 '17 at 15:33

This is the same as asking why we have both microphones and speakers instead of one device that works both ways. There are several reasons:

  1. Some means of detecting or producing sound are not reversible. For example, consider a laser interferometer microphone, or a air flow modulator for making a signal audible. You shouldn't assume all processes are reversible, especially when packed into a larger device. Coasting a car down a hill doesn't put gasoline back into the tank either.

  2. Some means are reversible, but the engineering tradeoffs are vastly different for receiving or transmitting efficiently.

    Dynamic microphones and speakers work on the same principle, and are reversible. However, the microphone is designed for very low mass to pick up tiny air movements. The speaker, on the other hand, has to be able to handle vastly more power. This means the mechanism will be bigger and heavier, and not work as well as a microphone designed for that purpose.

    Speakers can be designed to work well enough in reverse, especially with the right circuit receiving and processing the signals. Intercoms often worked on this principle.

  3. In general, the less efficient a conversion process is, the less likely that a device performing that process works well in reverse. Audio transducers are highly inefficient, so it should be no surprise that receivers and transmitters are designed specially for one direction at the expense of good operation in the other.

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    \$\begingroup\$ This comes off as patronizing and doesn't answer the specific question. \$\endgroup\$ – pericynthion Jun 23 '17 at 16:12
  • \$\begingroup\$ @peri: This explains why there is a difference between receivers and transmitters. Even if that doesn't answer the question outright, it provides useful information relevant to the question. As for patronizing, not really, but in any case grow up and get over it. \$\endgroup\$ – Olin Lathrop Jun 23 '17 at 16:20
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    \$\begingroup\$ The idea that reciprocity isn't universal would be a good comment on the question or short addendum to an answer, but it's not a useful answer by itself and certainly not worth 6 paragraphs. \$\endgroup\$ – pericynthion Jun 23 '17 at 18:47
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    \$\begingroup\$ @peri: I don't know why this bugs you so much, but it's useful information, and a lot more than just saying "processes aren't all reversible". Explaining why it's so, and giving some examples, is much more than simply stating a fact. \$\endgroup\$ – Olin Lathrop Jun 23 '17 at 19:56
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    \$\begingroup\$ It doesn't bug me "so much" - I'm just explaining my downvote. \$\endgroup\$ – pericynthion Jun 23 '17 at 22:00

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