question:
what if you use a piezo as feebback for the current amplifier in combination with a pd regulator??
what if you use a piezo as feebback for the current amplifier in combination with a pd regulator??
*kick*
Recently I purchased an oscilloscope, now I can do some measurements.
I taped a small Monacor ecm-2005 condensor microphone to my bassreflex sub that is tuned to 36 hertz.
The frequency response of this mic is very flat at subwoofer frequencies, distiortion levels are also low from what I can see.
When I pump about 100 watts in the sub at 30 hertz I see a lot of second harmonics, this could be the microphone or the woofer, I don't know but the sound level is too high for anyone to use for normal listening.
The phase response is almost identical to what winisd predicted:
I am going to try to correct this by using an allpass filter, I hope it works.
At 33 hertz the group delay is 30 ms, this is enough for a 360 degree phase shift, should I be worried about creating a power oscillator?
Recently I purchased an oscilloscope, now I can do some measurements.
I taped a small Monacor ecm-2005 condensor microphone to my bassreflex sub that is tuned to 36 hertz.
The frequency response of this mic is very flat at subwoofer frequencies, distiortion levels are also low from what I can see.
When I pump about 100 watts in the sub at 30 hertz I see a lot of second harmonics, this could be the microphone or the woofer, I don't know but the sound level is too high for anyone to use for normal listening.
The phase response is almost identical to what winisd predicted:
I am going to try to correct this by using an allpass filter, I hope it works.
At 33 hertz the group delay is 30 ms, this is enough for a 360 degree phase shift, should I be worried about creating a power oscillator?
Louis Erath had an old patent(expired now I think) on using a woofer in a known volume and adjusting the feedback loop of the amp to compensate at different frequencies.
I bought the old "servo controller" system and it worked VERY well until I used > 16ft spkr cables from the amp to the woofers.
He is in the process of building me a "new" design that is going on a four (4) Ucd-180 amp module bi-amped speaker.
I will comment on the "new" controller design once I hear it.
I did hear his "Trout" active pwred 6.5" two way that is flat to 20Hz and in a small to medium room it is very nice. But for higher volume music or larger rooms the add on sub is required.
Again, just another variation on active woofer control..
I bought the old "servo controller" system and it worked VERY well until I used > 16ft spkr cables from the amp to the woofers.
He is in the process of building me a "new" design that is going on a four (4) Ucd-180 amp module bi-amped speaker.
I will comment on the "new" controller design once I hear it.
I did hear his "Trout" active pwred 6.5" two way that is flat to 20Hz and in a small to medium room it is very nice. But for higher volume music or larger rooms the add on sub is required.
Again, just another variation on active woofer control..
thats good news!
I already tried something like the philips system, i used a mic in stead of an piezo. the only problem is that when you open a nearby door your subwoofer is as good as dead. the correction will kill your sub!
so if you are gooing to build something with feedback, use a accelerometer or piezo, if you want to use a mic; at least use it on the inside of the sub...
I already tried something like the philips system, i used a mic in stead of an piezo. the only problem is that when you open a nearby door your subwoofer is as good as dead. the correction will kill your sub!
so if you are gooing to build something with feedback, use a accelerometer or piezo, if you want to use a mic; at least use it on the inside of the sub...
hilbren said:
The only way to avoid this is to place a couple of dozens of additional mics on each and any object that may influence the initial woofer-mic by producing disturbance, and mix these "safety-microphones" back into the correction circuit. Of course this mixing has to be done with appropiate filtering, delays and inverse phase.
SCNR, I simply love overcomplicated setups! 😀
regards
BTW: similar effects could possibly even occur with any piezo pickup when a truck is passing your house and the vibrations...
The thermal capacity of my sub's voicecoil is 400 watts, I'm going to use a 100 watt amp so there is no problem there.
Here is a picture of the back (clickable):
As you can see there should be no problem with the voicecoil smashing against the magnet.
The vas is 17,51 liter, this is a rather low value so the excursion shouldn't reach extreme value's
Oh btw, piezo's suck 😉 and accelerometers are too expensive.
This woofer was on sale for 60 euro, its original price was 419 euro, an accelerometer is about 50 euro, almost as much as the woofer itself!
Here is a picture of the back (clickable):
As you can see there should be no problem with the voicecoil smashing against the magnet.
The vas is 17,51 liter, this is a rather low value so the excursion shouldn't reach extreme value's
Oh btw, piezo's suck 😉 and accelerometers are too expensive.
This woofer was on sale for 60 euro, its original price was 419 euro, an accelerometer is about 50 euro, almost as much as the woofer itself!
I tried the allpass filter, it doesn't work at all, the phase only gets worse.
Does anyone hyave any idea's about correcting the phase to be able to use feedback? Pherhaps a fir filter in a microcontroller or something similar.
Does anyone hyave any idea's about correcting the phase to be able to use feedback? Pherhaps a fir filter in a microcontroller or something similar.
I don't think anyone else posted this yet...
There is a page about building your own servo sub on www.danmarx.com...
Check it out here.
Perhaps someone here can decipher it and build something useful from it... I have been longing for a servo sub and was going to attempt something like this, but it is so vague in terms of parts to use and how to hook them up that I am afraid to try it. I wish someone offered a kit... (or just a servo sub that was a decent price)
There is a page about building your own servo sub on www.danmarx.com...
Check it out here.
Perhaps someone here can decipher it and build something useful from it... I have been longing for a servo sub and was going to attempt something like this, but it is so vague in terms of parts to use and how to hook them up that I am afraid to try it. I wish someone offered a kit... (or just a servo sub that was a decent price)
Yes... I meant an accelerometer-based kit, and, even more than that, a kit that used something other than 12" only...
I just found out from simulating in winisd that to get a flat frequency response from a closed box woofer you need a current drive amp to cancel out the lowpass from the voicecoil and a linkwitz transform to cancel out the highpass from the woofers mass and suspension.
To get minimal phase shifts at the desired frequencies you need to set the linkwitz transform to a Q of about 1 and an fs of about 1 hertz.
Of course this will amplify the low frequencies to extreme amounts which can possibly destroy the woofer, to correct this you need a highpass without phase shifts, something that is inpossible with analog filters.
FIR filters however have very very low phase shifts, there is only a small delay that should be no problem when using a high enough sampling rate.
Microchip has a pdf about implementing FIR filters in their PIC18F mcu's, I will be receiving 6 in a couple of weeks so I can try it out.
The PIC18F mcu's analog ports are only 10 bit which is not that much but hopefully it's enough for a subwoofer, if not then it's good practice in implementing FIR filters.
If I get a complete working system with a microphone I'm buying a fancy smancy accelerometer to be able to use it with a transmissionline, it adds about 6 db extra efficiency over a closed box.
A microphone is unusable as a feedback sensor because it also picks up the delayed signal from the open end of the transmissionline which in turn would create all sorts of nasty effects.
To get minimal phase shifts at the desired frequencies you need to set the linkwitz transform to a Q of about 1 and an fs of about 1 hertz.
Of course this will amplify the low frequencies to extreme amounts which can possibly destroy the woofer, to correct this you need a highpass without phase shifts, something that is inpossible with analog filters.
FIR filters however have very very low phase shifts, there is only a small delay that should be no problem when using a high enough sampling rate.
Microchip has a pdf about implementing FIR filters in their PIC18F mcu's, I will be receiving 6 in a couple of weeks so I can try it out.
The PIC18F mcu's analog ports are only 10 bit which is not that much but hopefully it's enough for a subwoofer, if not then it's good practice in implementing FIR filters.
If I get a complete working system with a microphone I'm buying a fancy smancy accelerometer to be able to use it with a transmissionline, it adds about 6 db extra efficiency over a closed box.
A microphone is unusable as a feedback sensor because it also picks up the delayed signal from the open end of the transmissionline which in turn would create all sorts of nasty effects.
A shelving highpass will also work to correct the woofer's lowpass when using a voltage drive amp, this way the woofer still retains its damping factor so there is no huge peak to correct at resonance.
Check out this site: http://www.servospeaker.com/index.html
It works by using the voicecoil former as a cilindrical capacitor.
Since my subwoofer has a dual spider the voicecoil former can be easily reached from the back, I will try this out as soon as possible!
It works by using the voicecoil former as a cilindrical capacitor.
Since my subwoofer has a dual spider the voicecoil former can be easily reached from the back, I will try this out as soon as possible!
To continue my monologue, I simulated some digital FIR filters, this will never work, way too much delay.
However a IIR filter reversed in time can be used to correct the phase shift from a woofer, even bassreflex.
There is a small delay, measured in microseconds 😉
However a IIR filter reversed in time can be used to correct the phase shift from a woofer, even bassreflex.
There is a small delay, measured in microseconds 😉
proportional- integrating.
Adding the differential part (and create PID regulation) can also help with stability and settling time, same as "feedback phase lead" in op-amps.
Adding the differential part (and create PID regulation) can also help with stability and settling time, same as "feedback phase lead" in op-amps.
yeah exactly, but don't get me wrong I don't mean the feed forwarding!
the PI is used to get back the time you lost by using mechanical components.
the PI is used to get back the time you lost by using mechanical components.
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