Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Low Pass band stop?

Status
Not open for further replies.

mikesndbs

New Member
Hi

I need a simple RC filter to block audio at 2500hz.
Range would be 2300 - 2700 all other frequencies need to pass.
This is for use in a application where a 8ohm speaker is used for voice announcements and a 2500hz tone burst.
Its the tone I need to reduce.

Can anyone suggest RC values please?

Cheers

Mike
 
If the 2500Hz tone doesn't change its frequency and doesn't have any harmonics then a notch filter would get rid of it. Look in Google for Notch Filter Circuit.
 
A passive notch filter is a combination of a lpf and hpf. Simply tune them to the frequency of interest. You may find the passive's gradual 1st order roll off not sufficient - I really don't know since you didn't specify how much attenuation you wanted.
 
use an active bandpass filter with the high pass filter part cutting off everything below 2700Hz and the low pass fitler part cutting of everything above 2300Hz. That should give you want you want. Google active filters . passive ones wont attenuate the frequencies aswell.

if you only want frequencies below 2500 HZ to pass then just use a low pass filter
 
Last edited:
Hi and thanks for the suggestions

Looking for 50 - 80% attenuation of 2500hz.
Can't be an active circuit.
Must be simple and robust.

Thanks

Mike
 
mikesndbs said:
Hi and thanks for the suggestions

Looking for 50 - 80% attenuation of 2500hz.
Can't be an active circuit.
Must be simple and robust.

I think you're perhaps adding too many restrictions now?, bear in mind with passive filters you need to allow for the source and load impedances (which need to be constant). I would suspect you're also going to require an LC filter rather than an RC one?.
 
50% to 80% attenuation of the voltage doesn't sound much different from full level.
70.7% drop is barely audible. 50% drop is noticeable. 68% drop sounds half as loud, still pretty loud.

You could use a high-Q LC parallel circuit to block 2500Hz in the signal path, or a series-circuit to shunt 2500Hz to ground.
 
audioguru said:
50% to 80% attenuation of the voltage doesn't sound much different from full level.
70.7% drop is barely audible. 50% drop is noticeable. 68% drop sounds half as loud, still pretty loud.

You could use a high-Q LC parallel circuit to block 2500Hz in the signal path, or a series-circuit to shunt 2500Hz to ground.


How please?

Can solder and recognise but thats about it :-(

Mike
 
mikesndbs said:
How please?

Can solder and recognise but thats about it :-(

Mike
A filter is part of the entire circuit and will work best if it is part of the whole design. If you know nothing about electronics then ask your teacher to design it for you.
 
audioguru said:
A filter is part of the entire circuit and will work best if it is part of the whole design. If you know nothing about electronics then ask your teacher to design it for you.

:p I do know a bit just not a lot.

The system is 8ohm speaker, voice and tone indicator go through same speaker.
I want to reduce the tone burst but not the voice.
50% or more would be good but not totally as is needs to be heard.

I want to use just passive components and as few as possible.
I have seen RC networks and this looks the sort of thing.

What I don't know is how to select the values required?
 
Nigel Goodwin said:
Do you mean you want the filter in the wires to the speaker?, if so you're now asking a completely different question!.

Hi, kind of, on the back of the speaker would be the best location.
That was it would be easy to fit as I have a number to do.

:)
 
Some speaker systems have a notch filter to reduce a peak in their response. This system can have the same.
I wonder if all the voice frequencies a filter will reduce will be noticable?
 
audioguru said:
Some speaker systems have a notch filter to reduce a peak in their response. This system can have the same.
I wonder if all the voice frequencies a filter will reduce will be noticable?

Great, now all I need to know is how :)

Mike
 
Fit a parallel tuned circuit in series with the speaker, it needs to be a parallel one because a series one would damage the amplifier. Bear in mind you're probably looking at a fairly large (and expensive) inductor as it has to pass the power to the speaker.

You can go to **broken link removed** to do the calculations for you.

10mH and 0.4uF look fairly good?.
 
mikesndbs said:
Great, now all I need to know is how :)

Mike
Speaker's Notch Filter:
Connect a coil and a capacitor in parallel and select their values so that they resonate and make a high impedance at 2500Hz.
Then connect the their parrallel combination in series with one of the speaker's wires.
If they reduce too many voice frequencies then add a resistor in parallel with the coil and capacitor.
 
u can do it easly....

hi...

u can design any kind of active filter by using "multisim 8",by entring ur filter parameter , and the program will built ur filter of interest. i will do that also , and i will post u agian...

have a good time :)
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top