1. Home
  2. Electronics Design
  3. Caps in a differential speaker output

Caps in a differential speaker output

What would be the impact of caps on the output lines to a speaker if it's being driven in differential mode? Say 10uf in series on each line, with a 16ohm speaker? I can calculate a normal single-ended RC circuit, but I'm not sure about this case. Would the low-frequency phase shifts match or go in opposite directions (which would cause cancellation by the two drivers at low frequencies)?

Thanks!

##-----------------------------------------------## Delivered via

formatting link
Electronics Enthusiasts' Community of the Net Web and RSS access to your favorite newsgroup - sci.electronics.design - 448567 messages and counting! ##-----------------------------------------------##

Reply to
jesup
Loading thread data ...

"jesup"

** What a dopey question.

Far as the speaker is concerned, there is only one drive signal - ie that appearing between the power stages outputs.

Normal RC calcs apply.

The two 10uF caps are in series so equal to 5 uF in series with 16 ohms

.... Phil

Reply to
Phil Allison

jesup had written this in response to

formatting link
: I know it's probably a silly question to an EE, but I'm a software guy, and all the examples show no caps for a differential bridged headphone amp

- but the HW engineer likes caps, and dropped them in, and I'm trying to debug a low-frequency (hard - 10+db/octave) rolloff.

##-----------------------------------------------## Delivered via

formatting link
Electronics Enthusiasts' Community of the Net Web and RSS access to your favorite newsgroup - sci.electronics.design - 448671 messages and counting! ##-----------------------------------------------##

Reply to
jesup

Attempts to reply normally to this thread seem to bounce.

You should probably be measuring SPL, rather than voltage; but the voltage will show low frequency reduction from ZRL/xc. A simple LTSpice circuit is attached for a passive example of varying inductance. A Dynamic driver is more complex.

Dynamic driver impedance may be complex at the low end; there's usually a peak as the frequency reduces, before it begins to look uncoupled. Low power dynamic transducers may be better controlled, as the air volume moved is small, and efficiency is low.

Your hardware guy's insistence on caps in series with the output may be misplaced, as these parts will not do much to protect the drivers from a short circuit, or reduce audibility of start/stop thumps, in a full bridge.

I assume you're expected to overcome the added loss, in software equalization of the processed signal. In that case, you should point out to the hardware guy that you can only do this over a fairly narrow range of known load LF characteristics - and you that need to know what they are. That's a hardware measurement issue. If he's been using

16R resistors for loads and measuring the voltage, it's time to get real.

RL

............................ Version 4 SHEET 1 880 680 WIRE 208 64 192 64 WIRE 96 96 0 96 WIRE 192 96 192 64 WIRE 192 96 160 96 WIRE 256 96 192 96 WIRE 0 160 0 96 WIRE 256 208 256 176 WIRE 0 336 0 240 WIRE 192 336 0 336 WIRE 256 336 256 288 WIRE 256 336 192 336 WIRE 192 352 192 336 FLAG 192 352 0 FLAG 208 64 Vout SYMBOL cap 160 80 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C1 SYMATTR Value 4E-6 SYMBOL ind 240 80 R0 SYMATTR InstName L1 SYMATTR Value {LS} SYMBOL res 240 192 R0 SYMATTR InstName R1 SYMATTR Value 16 SYMBOL voltage 0 144 R0 WINDOW 123 24 132 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value "" SYMATTR Value2 AC 1 TEXT 358 280 Left 0 !.ac oct 4 1 1000 TEXT 336 320 Left 0 !.step param LS 1 10 2 ............................................

Reply to
legg

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.