Hello. I'm building a portable speaker system, currently I use 3' woofer and two PRs, with total surface area about 3x of woofers. Both PRs are identical, and while system works nicely, I can hear sharp resonance at PR tune frequency and almost no bass below it. So what if I add weight to one of them, to shift resonance frequency lower?
The one that's tuned higher will still unload, cancelling LF output.
From mechanical losses in the higher-tuned PR, you might get a little bit more output below the higher tuning frequency, but I'd be surprised if it was more than a dB or two. Conversely, the higher-tuned PR will now be working much harder, and you risk distortion at higher levels.
Chris
From mechanical losses in the higher-tuned PR, you might get a little bit more output below the higher tuning frequency, but I'd be surprised if it was more than a dB or two. Conversely, the higher-tuned PR will now be working much harder, and you risk distortion at higher levels.
Chris
You may be interested in this blurb from the old TC Sounds website (found it using the wayback machine)
Passive Radiator Systems
Passive radiator or drone systems are very similar to ported systems. They both exhibit a steep roll off below tuning, gain lots of low end sensitivity from the resonator and require approximately the same internal air volume.
The difference is, ports are literally replaced with passive radiators to function as the Helmholtz resonator. Now there is not easy conversion, but there are several key differences that could make passive systems ideal.
Passive systems don’t suffer from port turbulence or port resonance because they don’t require an air mass to resonant, but rather a loaded mass and piston to displace the air. These two distortion mechanisms exhibited by ported systems can increase high order harmonic distortion in a ported. Additionally, drone systems can often fit in less space since the port area + length is not a requirement. On the down side, drone radiators have a slightly deeper roll off below tune, generally are less efficient to their ported counterparts and cost more.
Passive radiators should ideally be used in pairs with a single active driver but this criteria is not always necessary. Like ports, drone radiators need to displace a lot of air – much more than the active driver, so using two or more drones to each active is often necessary to minimize compression effects.
The TC Sounds VMP is a drone radiator, but is also has a distinct advantage: It can be returned without rebuilding the box my simply loading or unloading the mass washers. Adding mass to a passive radiator is analogous to increasing the length of a port. Adjusting tuning for maximum SPL or maximum low end extension is now possible.
This is the equivalent of using port plugs, but without having to reduce the port area – a valuable advantage. Passive radiators also have an advantage of being able to tune a system very low without requiring a large box. Because the mass of the drone is heavy, it dominates the resonate frequency of the system. Using a high performance driver that works in a small box can be paired with drone radiators to achieve a much lower tuning without compromising resonator displacement (port area) than an equivalent ported box.
In the follow example, the tuning is kept the same as the box volume is increased. Too small of a box and the system will ring and produce a hump in the response from the active driver, too large of a box and the system will a peak from the port’s high Q
Passive Radiator Systems
Passive radiator or drone systems are very similar to ported systems. They both exhibit a steep roll off below tuning, gain lots of low end sensitivity from the resonator and require approximately the same internal air volume.
The difference is, ports are literally replaced with passive radiators to function as the Helmholtz resonator. Now there is not easy conversion, but there are several key differences that could make passive systems ideal.
Passive systems don’t suffer from port turbulence or port resonance because they don’t require an air mass to resonant, but rather a loaded mass and piston to displace the air. These two distortion mechanisms exhibited by ported systems can increase high order harmonic distortion in a ported. Additionally, drone systems can often fit in less space since the port area + length is not a requirement. On the down side, drone radiators have a slightly deeper roll off below tune, generally are less efficient to their ported counterparts and cost more.
Passive radiators should ideally be used in pairs with a single active driver but this criteria is not always necessary. Like ports, drone radiators need to displace a lot of air – much more than the active driver, so using two or more drones to each active is often necessary to minimize compression effects.
The TC Sounds VMP is a drone radiator, but is also has a distinct advantage: It can be returned without rebuilding the box my simply loading or unloading the mass washers. Adding mass to a passive radiator is analogous to increasing the length of a port. Adjusting tuning for maximum SPL or maximum low end extension is now possible.
This is the equivalent of using port plugs, but without having to reduce the port area – a valuable advantage. Passive radiators also have an advantage of being able to tune a system very low without requiring a large box. Because the mass of the drone is heavy, it dominates the resonate frequency of the system. Using a high performance driver that works in a small box can be paired with drone radiators to achieve a much lower tuning without compromising resonator displacement (port area) than an equivalent ported box.
In the follow example, the tuning is kept the same as the box volume is increased. Too small of a box and the system will ring and produce a hump in the response from the active driver, too large of a box and the system will a peak from the port’s high Q
No but it say "They both exhibit a steep roll off below tuning" so there may be no easy way to get additional deeper bass.
It also mentions "Adding mass to a passive radiator is analogous to increasing the length of a port" so perhaps you can get a little more bass by adding some weight to the passive radiators.
The TC Sounds have a convenient threaded section on the back of the PR to add weight to it. You might need to fabricate something.
It also mentions "Adding mass to a passive radiator is analogous to increasing the length of a port" so perhaps you can get a little more bass by adding some weight to the passive radiators.
The TC Sounds have a convenient threaded section on the back of the PR to add weight to it. You might need to fabricate something.
My concern like the others would be the others that tuning the PR's to different frequencies could create imbalance in the box.
If one PR is lighter than the other it will move differently with equal pressure (the active driver) so as one might be moving back, the other might be still moving forward due to the additional mass.
You could wind up with some kind of PR whip effect happening in the box. Or one PR could cause the other PR to stall both PR movement.
If one PR is lighter than the other it will move differently with equal pressure (the active driver) so as one might be moving back, the other might be still moving forward due to the additional mass.
You could wind up with some kind of PR whip effect happening in the box. Or one PR could cause the other PR to stall both PR movement.
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Yes, ultimately you wind up with an averaged tuning between the two same as with different length tube vents, just with a lot more cab vibration, so the cab needs to be seriously mass loaded to damp it and if it's a suspended/floating floor like mine it could in theory wind up being a whole house bass shaker.
GM
GM
Fb with both PRs should actually be higher than what you'd get if you use either PR alone. If the Fb with one PR is 25 Hz and with the other it's 50 Hz, with both PRs in place Fb will be higher than 50 Hz, not between 25 Hz and 50 Hz.
Just like you'd end up with if you use vents sized to achieve two different resonance frequencies with the same enclosure.
I don't see it working exactly the same as fixed ports, since the ports are fixed dimensions, whereas the PR are dynamic and both subject to equal box pressure. I have no proof, but am inclined to think GM may be right.
A simple thought exercise for you. Take one PR, use it to tune an enclosure to Fb. Now, add another PR of exactly the same size and weight. Do you expect Fb to (1) go down, (2) go up, or (3) remain the same?
If your answer is (2), which of the PRs on its own would have a higher Fb than the new one that's achieved when both of them are used?
A simple thought exercise for you. Take one PR, use it to tune an enclosure to Fb. Now, add another PR of exactly the same size and weight. Do you expect Fb to (1) go down, (2) go up, or (3) remain the same?
If your answer is (2), which of the PRs on its own would have a higher Fb than the new one that's achieved when both of them are used?
(4) Let you know when I build my new sub. I can easily adjust both PR individually to find out.
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To Go Lower, Change Driver & Tweak System Parameters
If the enclosure volume is fixed, then to lower system resonance you must change driver free air resonance Fs and increase its volume displacement VD. Operating a PR system below system resonance is a bad idea. Changing the effective mass of one PR will further compromise system LF performance. Try adding weight equally to both. Also try stuffing the enclosure with a fibrous material, netting it off near the driver and PRs. Note: no matter what the collective PR Sd is, at system resonance, the PRs will be displacing approximately twice the VD of the driver. WHG
If the enclosure volume is fixed, then to lower system resonance you must change driver free air resonance Fs and increase its volume displacement VD. Operating a PR system below system resonance is a bad idea. Changing the effective mass of one PR will further compromise system LF performance. Try adding weight equally to both. Also try stuffing the enclosure with a fibrous material, netting it off near the driver and PRs. Note: no matter what the collective PR Sd is, at system resonance, the PRs will be displacing approximately twice the VD of the driver. WHG
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Interesting take on it, and one that is very logical. I am interested in your comment about netting and it is something very rarely discussed. I personally have issues with filling coming in contact with the driver, but some big names in speakers pack it in tight against the driver. I have often wondered if this is detrimental to the driver movement.
Not really touching the cone but too close for my liking...
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A loose fiber-fill, that increases effective enclosure volume, requires a net to hold it inplace.
Your best tack, is to optimize mid-bass performance and then add sub-woofers for the low end. Based on my experiance, you may expect to be pleasently suprised by the results acheived. WHG
Your best tack, is to optimize mid-bass performance and then add sub-woofers for the low end. Based on my experiance, you may expect to be pleasently suprised by the results acheived. WHG
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