I heard about The Mosquito, the teenager repellent noise, a few weeks ago, and thought it was an interesting idea. Then early last week, I read that teenagers had co-opted it and turned it into a ringtone. At the time, I shrugged it off as BS, because I was pretty sure that cell phones’ speakers did not have the range to reproduce such sounds. Then today, I saw a New York Times article (sell your soul required, etc.) and a similar Times (UK) article about teens using the sound to hide the ringing of their phones from adults. The NYT article states that the tone is right around 17KHz and the Times cites a version that’s 15KHz. Both are still well inside my audible range, but I can’t imagine why a cell phone speaker would be able to reproduce that sound.
So, Dopers: what are the upper and lower limits on the frequency that a cellphone speaker can reproduce? Is the Mosquito ringtone real, or just buzz?
Higher frequecies are easier to produce than low because the size of the speakers needed to produce them. Think of it like this, low frequency bass requires huge speakers with a fair amount of movement (you can see them thumping). High frequency sounds can be made by insects just by going fast (frequency) over a short distance. Small tweeters are the easy to make.
Frequency response of Mobile Phone Speaker (pdf).
Short form: They’re good out to 20 kHz.
The amplifier might not like 17kHz, or might contain a high frequency filter, or the MP3 compression might do some weird aliasing because of the sampling frequency, but the speakers can handle the signal.
Sounds like myth to me. Most cell phones use a piezoelectric speaker. The frequency range on cell phone piezo speakers is about 10MHz. That means, if you wanted to manufacture a cell phone speaker capable of outputting anything above 14MHz, you’d have to truncate everything below 4KHz. Frequencies outside that range gets recoded at some freq inside the reproducible range.
Although I suppose the newer high-end MP3 capable cell phones might have speakers with a larger frequency range.
Piezo speakers are excellent for reproducing high frequencies of 20 kHz and beyond- there are a lot of speaker systems that use piezo tweeters and even “super tweeters” not to mention those ultrasonic pest repellers.
The speaker element itself’s not going to be the trouble. I’d imagine the sound gets absorbed quite well by being in a pocket or backpack.
No argument. It’s the responsive range that I believe to be the limitation. If this noise is around 15KHz, then using a speaker with a 10KHz range, you can’t reproduce any frequency below about 5KHz. And that’s gonna be problematic for a human speech application.
I just tried playing one of the sounds from a previous thread on this topic on my phone, and bloody hell it was loud. Much louder than when I’d listened to it through my computer. And the frequency is around 18KHz.