| Electronics > Projects, Designs, and Technical Stuff |
| Want to do something with Audio without background in electronics |
| (1/3) > >> |
| soFPG:
Hi lovely EEVblog community, my mind comes up with new project ideas all the time. Usually they stick around for a while but eventually are replaced with other ideas. This idea though comes up every now and then and doesn't want to go away. What it's all about: * design a PCB which is able to measure the impedance of a loudspeaker chassis (usually 4 - 8 Ohm resistance) from 20Hz to 20kHz For me who doesn't have a background in electronic engineering and circuit design, this is not as easy as it might be for others who already have the necessary knowledge (I am more a software guy). Nevertheless, I want to describe possible solutions for this project which I came up with: * I am probably going to need a DAC which creates a sine wave from 20Hz to 20kHz * this sine wave probably needs to be fed into an operational amplifier (or any amplifier) whose output is connected to a speaker * then there must be a resistor with precisely known value in series to the second connector of the speaker * somewhere inbetween the resistor and the loudspeaker I have to measure the voltage with an ADC I have some questions: * How much output power does the sine wave has to have and at which voltage to be able to drive a 4/8 Ohm speaker properly? * How do I measure negative voltage (half period of the sine wave which is below 0)? Do I have to measure it at all or is there some workaround? * Are there any specific things I have to pay attention to while designing the PCB? * Do I need 24-bits of resolution or are 16-bits more than enough (again, I am only talking about Impedance not about sound quality)? I want to use an ESP8266 for that because it has a built in I2S interface which can be used to interface with the ADC/DAC. Also, It would be pretty neat to have a webinterface where the user (most likely I am going to be the only user) can see the curve (Impedance over Frequency) and save it to his computer. Any help / ideas / solutions are very much appreciated! Thank you so much |
| Messtechniker:
For this I went the sound card route. All you need: - A stereo sound card. Even a cheap one will do because any frequency response anomalies can be compensated for - A small power amp (10 W will easily do) - A 50 Ohm 5 W or so resistor - A measurement program like "Arta" or "Audio Tester", for example. Will do nicely. No need to bother making a pcb. |
| soFPG:
Thanks for your reply. I really appreciate your idea but (unfortunately) I am more interested in the way of how to solve such a problem than in the real impedance values at the end. |
| bob91343:
Read up on impedance bridges. That is perhaps the best solution. There are many types and some more suited than others. You indeed will need a source of signal, either from a signal generator or home brew. The latter is like reinventing the wheel but it's entirely feasible. For this you need to investigate oscillator circuits. You will need a standard of impedance, one you know accurately, such as a resistor and a capacitor. If you don't need great precision, an oscilloscope may be a way to measure phase angle and, thus, impedance. You can build what's called an Octopus, which will put a graph of impedance on the screen of a scope, which you then calibrate. |
| soFPG:
--- Quote from: bob91343 on January 12, 2020, 06:17:48 pm ---You indeed will need a source of signal, either from a signal generator or home brew. --- End quote --- Do you think a microcontroller could do that? I mean sending the digital values of a sine wave to the DAC? |
| Navigation |
| Message Index |
| Next page |