# Using a simple RC or RL filter as both high pass and low pass at the same time

If I had a simple RC or RL filter, and I connected both the high pass output and low pass output to the same output, would the overall output be roughly the same, assuming high efficiency components?

Further more, if I was to connect them to seperation outputs, let's say to two identical speakers with infinite and flat frequency responses,, would there be much difference between the input and output signal?

And if not, what effects from both ideal and realistic components would lead to inconsistencies?

EDIT

After some helpful discussion in the comments, I have been informed that my idea on the Vin and Vout of the circuit is backwards. This is the circuit diagram I had: • Is this a thought experiment or is there a specific problem you are trying to solve? Jul 25 '17 at 8:56
• A thought experiment, leading to better understanding of filters and electronics in general for filter designs I am embarking on Jul 25 '17 at 15:23

If I had a simple RC or RL filter, and I connected both the high pass output and low pass output to the same output, would the overall output be roughly the same, assuming high efficiency components?

No, because you would end up with a band-pass filter if the capacitor output and the inductor output were joined: - The above becomes this: - R in the above diagram would be the parallel combination of the individual resistors from the RL and RC stages. The inductor and capacitor would be joined electrically and this means that the potential for energy transfer between L and C is 100% i.e. you get a resonant tuned band-pass filter.

if I was to connect them to seperation outputs, let's say to two identical speakers with infinite and flat frequency responses,, would there be much difference between the input and output signal?

On the face of it I would say that at a distance from both speakers you would hear a flat sound i.e. spectrally flat. You could place a mono microphone equidistant from both speakers and, assuming the 3 dB points of each filter was the same you would reconstitute a flat signal.

It would be the same if you took RL and RC filters and fed each to a mixing desk - the signals could be added passively i.e. there would be no L and C interaction.

• Appologies, I might not have explained myself very well, although that is still some excellent information. What I meant was, if I for example had a simple RC filter, that can be used as either a lowpass or highpass depending on whether you connectthe resistor or capacotor to you signal out... So is there any good reason why you can't use both the low pass and high pass connections simultaneously, and use just that one circuit as a basic crossover? Jul 25 '17 at 11:38
• I mentioned RL as well because this question can be applied to both types of circuit. I will try and make my question clearer... Jul 25 '17 at 11:44
• @IronAttorney If you have an RC low pass filter (as an example) where would the high pass output be? Three nodes; one is input, one is ground and one is the output and this means you either short out the capacitor or you short out the resistor. Please draw what you mean because this makes no sense at the moment. Jul 25 '17 at 12:00
• I will draw it when I get back if I still need to, but the ground terminal of a lowpass RC filter is the output terminal on a highpass RC filter... The filters are the same, you just switch which terminal us output and which is ground... So my question is whether you can utilise both the low pass and high pass at the same time on a simple 1st order RC filter, and if so, what impact would this have on each output signal Jul 25 '17 at 15:27
• @IronAttorney Current doesn't take the path of least resistance - it shares itself amongst all the paths it can feasibly take and in a proportion to the impedances of those paths. For instance 1 volt across a 1 ohm resistor means 1 amp flows but, 1 volt across a 1 ohm and 10 ohm in parallel does not mean 1 amp continues to flow in the 1 ohm. If you have a schematic of what you talk about, please post a link to it. Jul 26 '17 at 8:17