Subwoofer as Microphone--A Question - diyAudio
Go Back   Home > Forums > Live Sound > PA Systems

PA Systems A forum for discussion of all parts of a sound reinforcement or DJ system: loudspeakers, mixers (desks) etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 7th June 2013, 09:39 AM   #1
didge is offline didge  United States
diyAudio Member
 
Join Date: Apr 2010
Location: Utah
Question Subwoofer as Microphone--A Question

Hi, I'm using a subwoofer as a microphone for low frequencies on a didgeridoo and find that it seems to pitch shift everything slightly downward. I've read about adding a pad switch, and that it is important that impedances match, and the possibility of using a DI box. But all this is in the context of how it is a hot, unbalanced signal, prone to distortion and feedback, etc. Nothing I have read tells me why this pitch shift might be happening. I am hoping someone here might have a good explanation.

I do understand that every mic (or speaker used as a mic) is going to have a different frequency response curve. I also understand that the subjective perception of pitch is colored by the relative loudnesses of the various harmonics that make for timbre. So, perhaps my perception of pitch shift is just an illusion based on the different cones and their respective frequency response curves, but it really seems too pronounced to be just this. I've compared the sub-mic (a 4 or 5 inch Genesis subwoofer) to a Sennheiser e906 mic, and the sub-mic seems about a 1/4 tone lower in pitch.

So I'm asking, would the fact that the impedance of the sub-as-mic likely does not match the input impedance on my pre-amp be responsible for pitch shifting the signal? Is there another potential explanation? Any way to correct it (other than finding a different speaker)?
  Reply With Quote
Old 7th June 2013, 10:07 AM   #2
diyAudio Member
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Send a message via Skype™ to JonSnell Electronic
Complicated electronics is required to "Pitch Shift". The sub will give more lower register than upper but cannot shift the pitch on its own, whatever the impedance mismatch or whatever.
Yamaha Music use a 4" bass speaker as a kick drum mic and it works very well!
  Reply With Quote
Old 7th June 2013, 11:14 AM   #3
didge is offline didge  United States
diyAudio Member
 
Join Date: Apr 2010
Location: Utah
"Complicated electronics is required to "Pitch Shift". The sub will give more lower register than upper but cannot shift the pitch on its own, whatever the impedance mismatch or whatever."

That's what I am inclined to think.

"Yamaha Music use a 4" bass speaker as a kick drum mic and it works very well!"

Now why would I waste my money on that?! I'm sure it works great, but it would be a $400 waste when less than $50 and some time will get the same results--or better from some of the reviews I read.
  Reply With Quote
Old 7th June 2013, 12:07 PM   #4
diyAudio Member
 
Join Date: May 2002
Location: Switzerland
I don't think it is necessary to use a subwoofer for that purpose in the first place ! A smaller driver like they use with the aforementioned Yamaha mic would take up your didgeridoo as well IMO.

Regarding phase shift: Did you ever try to connect a resistor with very few ohms accross the subs terminals ? You may probably excite the subs fs and perceive the ringing on fs as pitch-shift. If you load it then you will dampen the resonance. But this comes at the cost of lower output voltage.

Regards

Charles
  Reply With Quote
Old 7th June 2013, 12:25 PM   #5
didge is offline didge  United States
diyAudio Member
 
Join Date: Apr 2010
Location: Utah
The aforementioned Yamaha mic IS a subwoofer. See SKRM-100SFV - Subkick - Acoustic Drum Accessories - Drums - Musical Instruments - Products - Yamaha United States
And it is 6.5", not 4". (Unless there is another Yamaha subwoofer mic I haven't heard about)
I have experimented with a variety of mics vs. subwoofers, and no small diaphragm mic can capture the low end like a subwoofer. Not even with the added bass effect of placing the mic right up in the bell end of the instrument. And not with fancy EQ either. But I'm not here to defend my experiment-backed point that, no, you can't get as impressive results with a small diaphragm. I am here to ask for advice regarding the pitch shift issue...

No, I have not connected a resistor or anything like that. I'm not sure I understand: "You may probably excite the subs fs and perceive the ringing on fs as pitch-shift."
  Reply With Quote
Old 7th June 2013, 12:34 PM   #6
diyAudio Member
 
Mark.Clappers's Avatar
 
Join Date: Jan 2010
Location: The Netherlands, near the German border
Do you have access to a spectrum analyzer or osciloscoop with FFT math? if it really is a pitch shift it should show up in the frequency domain, if you use a sine wave as input signal and compare it to the signal from the woofer they should overlap if there is no pitch shift. If there is a pitch shift probably some sidebands are generated (AM modulation)
__________________
Music is art - Audio is psychoacoustics & engineering
  Reply With Quote
Old 7th June 2013, 06:51 PM   #7
diyAudio Member
 
indianajo's Avatar
 
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
Intermodulation distortion can cause sum and difference frequencies to appear in a signal. Perhaps you are hearing the IM difference signal instead of the fundamental as your "frequency shift".
I worked on a thunder recording project in 1972, where we used commercial microphones that were specified to be flat 100 to 1/3 hz. They had about a 2" diaphragm.
__________________
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300
  Reply With Quote
Old 7th June 2013, 07:39 PM   #8
didge is offline didge  United States
diyAudio Member
 
Join Date: Apr 2010
Location: Utah
I haven't yet, but I can open it in Ableton Live, which has a decent spectrum analyzer. Can you elaborate on what you mean when you say "If there is a pitch shift, probably some sidebands are generated (AM modulation)"?
  Reply With Quote
Old 7th June 2013, 08:00 PM   #9
didge is offline didge  United States
diyAudio Member
 
Join Date: Apr 2010
Location: Utah
Indianajo, can you elaborate on what you mean by intermodulation distortion? Sum and difference frequencies make sense to me, but sum and difference of what two starting frequencies? Is this related to what Mark.Clappers said?
  Reply With Quote
Old 7th June 2013, 10:36 PM   #10
diyAudio Member
 
indianajo's Avatar
 
Join Date: Jan 2010
Location: Jeffersonville, Indiana USA
Yes, sidebands and sum and difference frequencies are two different names for the same phenomenon. See Intermodulation - Wikipedia, the free encyclopedia
If your speaker as microphone is non-linear (and there is no reason to think it is not, linearity costs money and a lot of testing to achieve) then a sine wave going in comes out as the fundamental frequency plus other frequencies. There may be more than one frequency generated, in fact a whole range of them.
__________________
Dynakit ST70, ST120, PAS2,Hammond H182(2 ea),H112,A100,10-82TC,Peavey CS800S,1.3K, SP2-XT's, T-300 HF Proj's, Steinway console, Herald RA88a mixer, Wurlitzer 4500, 4300
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Electret microphone question zobsky Parts 23 14th May 2011 09:22 PM
condenser microphone question jonslaten Analog Line Level 9 13th November 2010 07:24 AM
Subwoofer as Microphone - A Question didge Instruments and Amps 7 17th April 2010 07:46 PM
Question about microphone clicktheleftbut Everything Else 2 29th April 2007 03:34 PM
Microphone In Guitar amp Question Trout Tubes / Valves 10 30th June 2006 02:02 AM


New To Site? Need Help?

All times are GMT. The time now is 05:45 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2