Thanks, good to know someone else did, and like me prefer. I came from a booming bass reflex. Something wrong with my original design or my living room. So I enlarged the reflex hole to insert a new driver. Than I tested in series, parallel, disconnected with many resistors. And at the end shorted (0.1 ohm resistor) was the best, more dynamic and clean. And no more booming.
Dynaudio made the Variovent in the 90s, an this sound remember them in effect.
Dynaudio made the Variovent in the 90s, an this sound remember them in effect.
Aperiodic means 'without period' i.e. no oscillation.
Your shorted driver must oscillate to have any effect.
A Variovent does not exhibit such behaviour, it simply resists the flow of air in and out of the enclosure.
Your shorted driver must oscillate to have any effect.
A Variovent does not exhibit such behaviour, it simply resists the flow of air in and out of the enclosure.
I did the second passive shorted woofer thing using an l pad to adjust dampening. It worked very well to compensate for placement of speakers in proximity to a boundary, so LF can be dialed in. There is a patent on this somewhere, which I looked into applying for about 20 yrs ago and it was obviously already taken.
The more you load the passive woofer coil, the lower the second amplitude prak drops and it slightly raises the tuning frequency.
The second passive driver can also be used for motion feedback to augment LF response.
The main issue I ran into with all this is the non-linearity you run into once xmax of the second passive driver is reached, which happens rather quickly running it as a passive radiator. There is a sharp rise in odd order HD as xmax is exceeded. The other non-linearity is the woofer Le variance. It's all just like the same issues you run into with a common types of long throw, high Le drivers.
The more you load the passive woofer coil, the lower the second amplitude prak drops and it slightly raises the tuning frequency.
The second passive driver can also be used for motion feedback to augment LF response.
The main issue I ran into with all this is the non-linearity you run into once xmax of the second passive driver is reached, which happens rather quickly running it as a passive radiator. There is a sharp rise in odd order HD as xmax is exceeded. The other non-linearity is the woofer Le variance. It's all just like the same issues you run into with a common types of long throw, high Le drivers.
Technically correct of course, but when nearly so, close enough for most folks on the various audio forums I've frequented over the decades, though technically, should have posted '~aperiodic' 😉. Ditto the Variovent is ~aperiodic.
Well it would be nice if adding a resistance to the passive driver lowered the tuning.
So you would not have to add mass.
seems like behavior might be the opposite
Would be very interesting, to be able to model the behavior
Otherwise at low listening levels you might not find to much audible distortion.
But just like a passive radiator. you would likely want double the cone
area for the passive element or basically more xmax/cone travel.
Assuming its high tuned, the passive driver likely reaches distortion quickly.
It is also possibly the previous setup as a reflex was little high tuned
or the driver itself has a boomy response.
You might have been happy as well plugging the port and running as sealed
and adding more dampening material.
Either way as long as your happy, just a fun experiment.
And could be possible influence, to model / build
a passive radiator system in the future.
With more predictable results.
So you would not have to add mass.
seems like behavior might be the opposite
Would be very interesting, to be able to model the behavior
Otherwise at low listening levels you might not find to much audible distortion.
But just like a passive radiator. you would likely want double the cone
area for the passive element or basically more xmax/cone travel.
Assuming its high tuned, the passive driver likely reaches distortion quickly.
It is also possibly the previous setup as a reflex was little high tuned
or the driver itself has a boomy response.
You might have been happy as well plugging the port and running as sealed
and adding more dampening material.
Either way as long as your happy, just a fun experiment.
And could be possible influence, to model / build
a passive radiator system in the future.
With more predictable results.
I came across a post long time ago about adding in a capacitor to it. Maybe a capacitor at high frequencies short out the coil and dampens it. At low frequencies it would be determined by resistor.
Oon
Oon
I’ve played with a dual vc woofer in an oversized box by resistively damping the second undriven vc which acted like a brake to stop the driver from being over driven. It worked better than nothing but it was not ideal. I used an lpad as a variable resistor to dial it in. It controlled the boominess.
I read in this DIY forum about the following article, but unable to find on the web. Does anybody have the link?
"There's a good article in an old TAA titled, "The Not Quite Passive Radiator". The author experimented with several passive elements between the terminals."
"There's a good article in an old TAA titled, "The Not Quite Passive Radiator". The author experimented with several passive elements between the terminals."
You're welcome!
FYI/FWIW, all I did was highlight your "The Not Quite Passive Radiator" and clicked 'Search Google' and it took me to some links that included it, etc..
Fast forward to just now and surprisingly [to me anyway] it only takes me to this thread! 😱 😡 🙁
A pity as once upon a time we could find anything in however many ways, places it was and even till recently, a page full, but now all of my mega bookmarks I've tried so far are 'dead'. 😡 🤐
FYI/FWIW, all I did was highlight your "The Not Quite Passive Radiator" and clicked 'Search Google' and it took me to some links that included it, etc..
Fast forward to just now and surprisingly [to me anyway] it only takes me to this thread! 😱 😡 🙁
A pity as once upon a time we could find anything in however many ways, places it was and even till recently, a page full, but now all of my mega bookmarks I've tried so far are 'dead'. 😡 🤐
True in general and forgot to mention it in my apparently never ending haste nowadays, but many early ones, not to mention the archive's also, are MIA.
ygg-it,
If it sounds better to your ears, it is. From experience, I can recommend both shorting and full removal of the motor, it all depends on your goal and what you are starting with.
First things first though. Always make sure your drone is at least one size up from your driver as in a 15" drone for a 12" woofer or doubled ie: one 12" woofer and two 12" drones. This helps control the drones as much as weighting and shorting does. Try shorting first and if it doesn't measure well, remove the motor, paint the backside of the cone and the inside of the dustcap with PVA glue to stiffen it. If you are trepid, use putty to add weight at the base of the coil temporarily. Permanent weight can be anything from pennies, to nuts bolts and washers, to bits of almost anything and combined with PVA glue. I usually add any necessary weight inside the coil up against the dustcap. Weigh how much putty you added. Replace the putty with your permanent weight.
If it sounds better to your ears, it is. From experience, I can recommend both shorting and full removal of the motor, it all depends on your goal and what you are starting with.
First things first though. Always make sure your drone is at least one size up from your driver as in a 15" drone for a 12" woofer or doubled ie: one 12" woofer and two 12" drones. This helps control the drones as much as weighting and shorting does. Try shorting first and if it doesn't measure well, remove the motor, paint the backside of the cone and the inside of the dustcap with PVA glue to stiffen it. If you are trepid, use putty to add weight at the base of the coil temporarily. Permanent weight can be anything from pennies, to nuts bolts and washers, to bits of almost anything and combined with PVA glue. I usually add any necessary weight inside the coil up against the dustcap. Weigh how much putty you added. Replace the putty with your permanent weight.
Shorting an inductor (motor) will stop it moving or at least heavily dampen its movement.
They do a similar trick on car wipers to stop the wipers moving back up the screen when turned off. They short out the motor when off.
They do a similar trick on car wipers to stop the wipers moving back up the screen when turned off. They short out the motor when off.