What would the problem be making this "bass eaters" work from say... 10Hz to 500Hz?
I have a room mode at about 30Hz and would like the "phantoms" to get rid of that heavy slow dirty stuff 🙂
/Peter
I have a room mode at about 30Hz and would like the "phantoms" to get rid of that heavy slow dirty stuff 🙂
/Peter
10 Hz would not be a problem if you have a woofer that actually can go that low and an amplifier to support it. Most of the time we are not looking to get rid of 10 Hz.
500 Hz is pretty undoable simply because of the acoustic delay from the speaker to the microphone, which causes feedback instability in the same way that delay would in an amplifier.
500 Hz is pretty undoable simply because of the acoustic delay from the speaker to the microphone, which causes feedback instability in the same way that delay would in an amplifier.
The end is near
"Words of guidance:
TDA2040. Electret Mic from Digikey. Ordinary Woofer."
Nelson Pass recommending a girly-man IC power amp?
Can the end of the world be far behind?
I have the heard the active aborbers in a very problematic room and they were amazingly effective. The room was to be a state of the art listening room in a local high end audio store. The lunatic owner filled the space behind the sheet rock walls with some kind of spay-in self-expanding insulation foam that made it one the worst sounding demo rooms ever. I think it must have moved the resonant frequency of the walls into the midbass region.
Don't try this at home kids!!!
"Words of guidance:
TDA2040. Electret Mic from Digikey. Ordinary Woofer."
Nelson Pass recommending a girly-man IC power amp?
Can the end of the world be far behind?
I have the heard the active aborbers in a very problematic room and they were amazingly effective. The room was to be a state of the art listening room in a local high end audio store. The lunatic owner filled the space behind the sheet rock walls with some kind of spay-in self-expanding insulation foam that made it one the worst sounding demo rooms ever. I think it must have moved the resonant frequency of the walls into the midbass region.
Don't try this at home kids!!!
What about the woofer's phase shift WRT the input signal? This seems like a job for an equalized ELF alignment--nonresonant and flat phase throughout the passband.
I really am curious--how was phase shift dealt with in the Shadow? Was it simply controlled by the acoustic feedback loop?
Bill
I really am curious--how was phase shift dealt with in the Shadow? Was it simply controlled by the acoustic feedback loop?
Bill
Ok, patent says driver phase angle is electronically compensated.
What about doing one of these as an ELF system?
Off-the-cuff idea: mount a small sealed midrange driver (the microphone ) coaxially with an ELF-aligned bass driver. Feed the voltage from the mid through 4 integrators in series (two for the mic rolloff and two for the woofer rolloff) and into an inverting amp feeding the woof. Passband could run as deep as woofer Vd and amp power allows.
(Note: I'm an eletronics newb, so shoot me down if the shootin's good.)
What about doing one of these as an ELF system?
Off-the-cuff idea: mount a small sealed midrange driver (the microphone ) coaxially with an ELF-aligned bass driver. Feed the voltage from the mid through 4 integrators in series (two for the mic rolloff and two for the woofer rolloff) and into an inverting amp feeding the woof. Passband could run as deep as woofer Vd and amp power allows.
(Note: I'm an eletronics newb, so shoot me down if the shootin's good.)
How low can you go?
The second order high pass response of the system can be moved to a lower frequency with the following circuit to make the system phase response flatter.
12 dB/oct highpass equalization ("Linkwitz Transform", Biquad)
http://www.linkwitzlab.com/filters.htm#9
A possibly useful microphone element modification and preamp is described at:
http://www.linkwitzlab.com/sys_test.htm#Mic
The second order high pass response of the system can be moved to a lower frequency with the following circuit to make the system phase response flatter.
12 dB/oct highpass equalization ("Linkwitz Transform", Biquad)
http://www.linkwitzlab.com/filters.htm#9
A possibly useful microphone element modification and preamp is described at:
http://www.linkwitzlab.com/sys_test.htm#Mic
My experience is that it's much easier to make the thing work
with single-pole filters.
The choice of the TDA2040 simply reflects the 15 year old design:
No doubt gain-clones would be perfectly adequate.
By the way, the design really requires only low power, as the
loudspeaker cone is already heading the right direction due to
the pressure. You just need to help it along....
with single-pole filters.
The choice of the TDA2040 simply reflects the 15 year old design:
No doubt gain-clones would be perfectly adequate.
By the way, the design really requires only low power, as the
loudspeaker cone is already heading the right direction due to
the pressure. You just need to help it along....
By way of moving this thread along,
It's interesting to note that this device is not an absorber in the sense that it removes acoustic energy like a foam panel.
If you put Shadows in the corners of a room, the effect is like truncating the corners with a chain saw. This is a particularly appropriate use, as the corners are where pressure builds up in the major room resonance.
Shadows reconfigure the shape of the room acoustically, and are more closely related to diffusors in that respect. Art Noxon of ASC suggested a design in which the active unit is placed inside at the end of his tube traps to enhance their operation. By lowering the low frequency pressure inside a tube trap, you create better energy loss in the fiberglass tube walls, extending the effectiveness of the tube trap to lower frequencies.
This has struck me as a good idea, although I have never followed up on it.
It's interesting to note that this device is not an absorber in the sense that it removes acoustic energy like a foam panel.
If you put Shadows in the corners of a room, the effect is like truncating the corners with a chain saw. This is a particularly appropriate use, as the corners are where pressure builds up in the major room resonance.
Shadows reconfigure the shape of the room acoustically, and are more closely related to diffusors in that respect. Art Noxon of ASC suggested a design in which the active unit is placed inside at the end of his tube traps to enhance their operation. By lowering the low frequency pressure inside a tube trap, you create better energy loss in the fiberglass tube walls, extending the effectiveness of the tube trap to lower frequencies.
This has struck me as a good idea, although I have never followed up on it.
Nelson,
The patent mentions using these for bipole cancelation. Would you necessarily need a tube for that? I started a thread on the maggie user group about these and the question came up about using a mic mounted to a sub and using an inverting preamp for the mic capsule. With the appropriate filters would that work?
Russ in Tucson
The patent mentions using these for bipole cancelation. Would you necessarily need a tube for that? I started a thread on the maggie user group about these and the question came up about using a mic mounted to a sub and using an inverting preamp for the mic capsule. With the appropriate filters would that work?
Russ in Tucson
By the way, one of the guys at the MUG found a used pair for $500 and should have them soon.
Russ in Tucson
Russ in Tucson
o.k. i have the subwoofer in the corner crossed over at 125hz, phase at 180. playing a test tone at the loudest resonant frequency i can get about 15 to 20 db of cancelation by turning the mic preamp up. how much cancellation should i be looking for and at what level.
never did get the subwoofer setup to sound very good. i was able to get a high degree of cancellation playing a test tone, but listening to music was not so good. i recieved my shadows today and immediately took them apart. i did this to shorten them up a bit. my ceiling is a little low so i took a little off the top.(had my wife sew a new pocket on the bottom of the sock for the drawstring - they still look stock...really) also wanted to see how they were made. pretty simple really, just a sonitube, some foam, a couple wood pieces and the custom woofers. without the fancy trim and bases these could be made in my garage. with the shadows in the 2 most problematic corners i was able to move the sub into the 42hz node position without getting a node. i have my speakers and subs positioned pretty well except for the 42hz node/antinode. one position was an antinode and 2 feet down the wall was the node. no medium setting in between. i know this from hours of testing with etf. i prefered the antinode position because it was fairly narrow and the node position had very bad decay. i moved the sub into node position and took a measurement - nice and flat with fast decay -looking good so far but i still need to try a few more combinations. nice product mr. pass. in 5 minutes i was able to fix a problem i spent hours trying to fix with no results. this is just the tool i needed when i was moving speakers around for hours.
one more node and i think i've got it. the chainsaw reference got me thinking. i have a 105hz node in the listening position. it is also loud at the base of the rear wall. behind the rear wall is the unfinished utility room. when i cancel the 105hz tone (about 6db) at the base of the wall with the spare sub running backward i get a 4db drop at the listening position. i can hear the difference listening to music, but as soon as it starts sounding good the sub starts to ring. my idea was to remove the portion of the drywall on the back wall where the 105hz node is loudest and put some acoustic foam on the studs (about a 2' tall x 4' wide area). this would leave an opening in the wall where the buildup is into a pretty large storage room. what do you think before i start cutting?
question for Nelson Pass
Do you think active absorbers attached to the backs of pews in a church would be of any help?
I was thinking along the lines of a 5-1/4" speaker with a 10W amp distributed in some sort of grid.
They could be turned off for the organ music, and enabled for speaking.
Is this a totally crazy idea?
Do you think active absorbers attached to the backs of pews in a church would be of any help?
I was thinking along the lines of a 5-1/4" speaker with a 10W amp distributed in some sort of grid.
They could be turned off for the organ music, and enabled for speaking.
Is this a totally crazy idea?