Home Theater Forum and Systems banner
1 - 5 of 5 Posts

·
Registered
Joined
·
2 Posts
Discussion Starter · #1 ·
OK, I know this is and unusual subject and possibly crazy idea but I was wondering what I could/would measure if I used an acoustic piano as a source to see time domain room quality such as RT60 and modal ringing as well as other aspects.

If an acoustic piano is the source of music in a given room, why not measure IT in that room? It might be easier to use a speaker in the piano's position and run REW in the usual way, but I'd like to see what I can do using the actual piano as a source.

Technically, I beleive REW compares the signal the internal oscillator produces with the signal picked up by the mic in the room. If I understand this correctly, I could use a contact mic on the soundboard of the piano as the reference and a standard calibrated measurement mic in the usual way, but to pick up the room sound from the piano instead of a loudspeaker. I accept there will be frequency response deviations between the contact mic and the room mic but I'm willing to overlook that for starters and possibly address that later if this even works at all.

The question is: How can I get the soundboard pickup mic signal into REW? I think that's it.

Thanks for any and all comments or suggestions!
 

·
Super Moderator
Joined
·
9,309 Posts

Welcome to the Forum, Pno!

Since RT-60 is a signal decay measurement, the frequency response of the signal is of little relevance.

I don’t see any problem using the piano to generate the signal; however, I don’t think it will get you anything that a signal generated by REW would. After all, signal decay time is signal decay time. It doesn’t matter what the source if the signal is.

I don’t see how the soundboard mic could do anything positive to the measurement. It’s essentially the same as taking a measurement with the mic inside the speaker that would normally be generating the signal: It’s only going to get you an RT-60 of whatever is going on inside the speaker. That will tell you absolutely nothing about the signal decay characteristics of the room the speaker (or piano) is in.

It should be easy enough to accomplish if you want to, though: Just make sure you USB sound card has connections for both mics.

Regards,
Wayne

 

·
Registered
Joined
·
2 Posts
Discussion Starter · #4 ·
Thanks for the replies.

The in "Getting Started" it says - "A process called "Fast Fourier Transform" (FFT) is used to calculate the individual frequencies (their amplitudes and phases) that made up the sweep we sent to the source (its spectrum). The same process calculates the amplitudes and phases of the frequencies in the signal the mic picked up. By comparing the amplitudes and phases of the signals the mic saw with those the sweep contained we can work out how each frequency has been affected by the room we are measuring. "

So what I'm thinking is that if the soundboard mic could be substituted for the internal sweep signal then REW will compare phase and amplitudes with the the room mic signal. I wonder if there is a way to have REW use my SB mic instead of the sweep. I could play an ascending chromatic scale manually or just one note. I realize each note on the piano has it's own spectrum produced virtually instantaneously so that may be a challenge for REW but I don't know. If the FFT is not real time, it should not be a problem, but once again, IDK.

I know this may not provide and useable data but I'd like to know if REW will allow this to be done, and if so how.

Thanks!
-p
 

·
Premium Member
Joined
·
1,562 Posts
I don't think so. That requires a dual channel FFT to compare the input signal to the output signal.

I think REW compares the input signal to the theoretical signal it creates. It uses a sweep signal that provide a full range, equal amplitude signal. The REW sweep signal is optimized to maximize the resolution of the freq response and S/N ratio and provides the ability to calculate an accurate impulse response of the system+room. The accurate IR provides the ability to extract much more information on the system as shown in the various graphs available. It is much more powerful that a random signal.

That said, there may be reason to use another signal for special purposes? I think Arta software may be dual channel and may be able to do what you want.

My understanding may not be entirely correct as I am not really a expert on this matter. It's just my best understanding.
 
1 - 5 of 5 Posts
Top