Noisy Router Investigation
Hmm, interesting, thanks, I've edited my post above for the benefit of future readers 
Hi All,
We’ve been pondering the problem of noisy routers for some time trying to get to the bottom of the issue.
We had our supplier place one of our routers in a sound proof chamber and recorded the sound of it running with a wide acoustic range microphone. They found a tone spike at 4kHz which you can see in this plot of frequency vs. amplitude.
Only a handful of people are able to hear this noise without putting the router up to their ear, the noise is only a few dB above background levels so is very hard to hear for the majority of us. For the people that can hear it however it is very annoying!
Further investigation showed that the noise source is a component known as Inductor L14, this component is part of the 1.2V DC circuit. The noise from L14 is due to magnetostriction: the mechanic interaction between the inductor ferrite material and its electrical winding.
The noise has a frequency of 4Khz, if you’d like to hear this noise then watch this https://www.youtube.com/watch?v=lO9uRNrP8Mo video (turn your speakers down!)
We’ve identified a solution which is to introduce a capacitor to remove the 4Khz harmonic without any negative effects (this component is normally present in TG582n devices with the USB port).
The routers with USB ports are not affected because they already contain this extra component which stops this noise, this component is part of the dying gasp circuitry which is not present in the non-USB version. We’ll be making a change in our next manufacturing run which is scheduled for the end of June, these take a while to come from China so will begin shipping to customers later in the year.
If you can hear the noise then let us know, we have some of the quieter routers in the office with this extra component that we can send out.
Thanks,
Matt
We’ve been pondering the problem of noisy routers for some time trying to get to the bottom of the issue.
We had our supplier place one of our routers in a sound proof chamber and recorded the sound of it running with a wide acoustic range microphone. They found a tone spike at 4kHz which you can see in this plot of frequency vs. amplitude.
Only a handful of people are able to hear this noise without putting the router up to their ear, the noise is only a few dB above background levels so is very hard to hear for the majority of us. For the people that can hear it however it is very annoying!
Further investigation showed that the noise source is a component known as Inductor L14, this component is part of the 1.2V DC circuit. The noise from L14 is due to magnetostriction: the mechanic interaction between the inductor ferrite material and its electrical winding.
The noise has a frequency of 4Khz, if you’d like to hear this noise then watch this https://www.youtube.com/watch?v=lO9uRNrP8Mo video (turn your speakers down!)
We’ve identified a solution which is to introduce a capacitor to remove the 4Khz harmonic without any negative effects (this component is normally present in TG582n devices with the USB port).
The routers with USB ports are not affected because they already contain this extra component which stops this noise, this component is part of the dying gasp circuitry which is not present in the non-USB version. We’ll be making a change in our next manufacturing run which is scheduled for the end of June, these take a while to come from China so will begin shipping to customers later in the year.
If you can hear the noise then let us know, we have some of the quieter routers in the office with this extra component that we can send out.
Thanks,
Matt
Thanks for the explanation Matt, well done. PS. Get an interesting little beat if you play razer's recording with the one above at the same time
Interesting stuff Matt!
I was most intrigued by the "dying gasp circuitry" bit of your explanation.
Now that I understand what it means, I think it begs the question, why would it be missing from newer(?) revisions of the router? Or are these a model for cutting costs, hence stripped down to the bare essentials, which is understandable in the current financial climate?
Anyway, top marks for a top investigation and explanation
[Moderator's note by Dick (Strat) Linkfixed broken.
Fixed again - Pedro
I was most intrigued by the "dying gasp circuitry" bit of your explanation.
Now that I understand what it means, I think it begs the question, why would it be missing from newer(?) revisions of the router? Or are these a model for cutting costs, hence stripped down to the bare essentials, which is understandable in the current financial climate?
Anyway, top marks for a top investigation and explanation
[Moderator's note by Dick (Strat) Link
Fixed again - Pedro
Well there was rumour that it used to, it would be nice to find out for definite, both 20CN and 21CN
Interesting read, Matt. Thanks. It's nice to have the 'proof' (although I'd recorded it myself) just to show others that it is a real sound and not imagined by some, or even that it is tinnitus. Wide acoustic range microphone? Can't remember what mine is, but obviously enough.
Anyway, I'm STILL waiting for another bag to return the other two routers I still have.
Anyway, I'm STILL waiting for another bag to return the other two routers I still have.