DC Offset / rules / damage to speaker? - Page 1
Forum section: electronics / beginners

author: BadPenny
author_rank: Contributor
timestamp: October 08, 2018, 06:31:35 am
content: I bought an inexpensive function generator for some simple testing, I noticed it had an unwanted DC offset potentiometer. So measured the output to set the DC offset to zero. My assumption is that should I alter that above zero- then the DC is sent to the speaker and without a fuse might/will damage it. But not sure if that is true or not. DC obviously for any length of time other than a click like a metronome I believe can damage the voice coil (I assume that is what fries, hence why the decent ones they are fused).So any input appreciated about "rules" or URL's with tutorials of DC on speakers would be appreciated. This is low wattage right now, but should I use say a 50 watt amplifier between the function generator and the speaker, not sure how the DC offset is dealt with on the amplifiers input.Thanks.

author: Mr. Scram
author_rank: Super Contributor
timestamp: October 08, 2018, 06:38:18 am
content: Quote from: BadPenny on October 08, 2018, 06:31:35 amCan you maybe use a capacitor to protect your speaker while allowing AC to pass?

author: Zero999
author_rank: Super Contributor
timestamp: October 08, 2018, 08:02:27 am
content: If the power dissipation rating of the speaker is not exceeded, then I wouldn't expect anything bad to happen to the speaker. Of course the power being dissipated by the speaker will be equal to the DC power and AC power added together, so it will depend on the signal strength too.What's the output impedance of the signal generator? I suspect it will be around 50Ohm, which will be enough to limit the current to a safe level.Your audio amplifier has AC coupled inputs, which will block the DC bias from the amplifier, so I doubt it's a problem.

author: arno
author_rank: Contributor
timestamp: October 08, 2018, 07:34:38 pm
content: Hi,as another option you could use a transformer between the function generator and the speaker.BRArno

author: Zero999
author_rank: Super Contributor
timestamp: October 08, 2018, 08:53:29 pm
content: Quote from: arno on October 08, 2018, 07:34:38 pmUnfortunately transformers don't like DC either. In the case of a signal generator, the 50 Ohm output impedance won't cause any harm. It can result in a lot of distortion though.

author: arno
author_rank: Contributor
timestamp: October 08, 2018, 09:33:23 pm
content: Hi,Quote from: Hero999 on October 08, 2018, 08:53:29 pmDepends on the type of transformer - just think about single-ended tube amps. But in most cases you are right.BRArno

author: David Hess
author_rank: Super Contributor
timestamp: October 09, 2018, 04:27:03 pm
content: Audio power amplifiers almost always include AC coupling somewhere to either block DC completely or reduce gain at DC to a very low level.Unlike most audio transformers (1), speakers can handle considerable DC bias because they are designed for high power dissipation and have a built in air gap.I have never had a problem with the residual DC offset from my function generators in audio applications.(1) Except audio transformers intended for single ended applications which is designed to operate correctly with considerable DC bias.