Hi Ian,
That's interesting, thanks. What connector and cable technology do your products end up getting used with? RCA/phono or XLR? All the best James From: McBurney, Ian <[email protected]> Sent: 05 September 2018 08:51 To: James Pawson (U3C) <[email protected]>; [email protected] Subject: RE: [PSES] RF immunity - audio noise in headsets Hello James. We produce digital products with multiple analogue audio inputs and outputs and have to include common mode filtering on every port to reduce the susceptibility to radiated rf but also to attenuate the digital rf emissions from within the product. Ian McBurney Lead Compliance Engineer. Allen & Heath Ltd. From: James Pawson (U3C) <[email protected] <mailto:[email protected]> > Sent: 05 September 2018 08:17 To: [email protected] <mailto:[email protected]> Subject: Re: [PSES] RF immunity - audio noise in headsets Hi Amund, hope you are well. Some general thinking aloud follows, some of which you may have already considered. I would have expected that some kind of non-linear function (e.g. diode) would be required to demodulate the AM RF carrier. This is unlikely to be present in a "dumb" speaker set but there's usually a JFET amplifier inside electret microphone cartridges. Therefore most of the demodulation from RF carrier to 1kHz tone is going to take place inside the equipment. Assuming that the equipment is not outputting audio (active but silent) to enable detection of any AM demodulation then it would be the effect of the RF carrier on the audio amplifier circuitry in the equipment that causes this 1kHz tone to appear. The unshielded wire from the headset is the antenna or means of coupling of the noise into the circuit. It's unlikely (but still possible) that it would be noise on the ground / screen wire of the headset that causes the issue. More likely that the signal conductor is the most susceptible part of the system. This means that shielding of the cabling and speakers would be a main method of preventing this issue. The shielding could be examined by disassembling a product. In my experience of taking audio equipment apart for this purpose the cabling is almost always some kind of enamelled copper wire in a twisted pair. The connections at the end points of the cable is where the symmetry breaks. It also raises the question of immunity as a product quality issue rather than a regulatory one. Earphones / headphones are a very personal choice for many people. Its fine to state in the product literature that a well shielded pair of headphones must be used for compliance but if someone wants to wear their potentially less immune Beats or Sennheiser headphones and has problems as a result then it reflects on the product rather than the accessories. Maybe this is why Apple have started using AirPods - no cable to worry about! Hope some of this was useful All the best James From: Amund Westin <[email protected] <mailto:[email protected]> > Sent: 05 September 2018 07:01 To: [email protected] <mailto:[email protected]> Subject: [PSES] RF immunity - audio noise in headsets Wired headsets and microphones connected to a product, often acts as receiver for induced RF fields. That means you quite often hear the 1kHz modulation tone under the RF immunity tests. This is quite annoying for the user and above a certain level, not acceptable. To avoid such phenomena is quite a big task to conduct. But have anyone of you any experience how to determine if the headsets / microphones or the connected final product is the source to this problem? 3rd. party headsets / microphones have of course different RF immunity performance, and after a lot of testing, you might be able to find headsets / microphones that are does not pick up fields and the hearing audio noise level is acceptable. I assume that the final product may have great level of immunity, but as long the headsets / microphones has poor immunity level, you will have this audio problem anyway. Has anyone been into this problem before? BR Amund - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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To post a message to the list, send your e-mail to <[email protected] <mailto:[email protected]> > All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) <http://www.ieee-pses.org/list.html> List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected] <mailto:[email protected]> > Mike Cantwell <[email protected] <mailto:[email protected]> > For policy questions, send mail to: Jim Bacher <[email protected] <mailto:[email protected]> > David Heald <[email protected] <mailto:[email protected]> > Allen & Heath Ltd is a registered business in England and Wales, Company number: 4163451. Any views expressed in this email are those of the individual and not necessarily those of the company. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
