Member
Joined 2004
Hi there
I need an basstrap that is transportable and can be tuned to different fundamental room frequencies. While i was calculating the port lenghts for several fundamental room frequencies and could not find an adjustable port tube to fit the range i wanted my corner bass trap to absorb, i thought of an passive radiator instead of an adjustable port tube.
Is this an crazy idea? Or might it work out ok. I like the idea of mass tuning, instead of tubes between 4 and 30 inches long.
Roland
I need an basstrap that is transportable and can be tuned to different fundamental room frequencies. While i was calculating the port lenghts for several fundamental room frequencies and could not find an adjustable port tube to fit the range i wanted my corner bass trap to absorb, i thought of an passive radiator instead of an adjustable port tube.
Is this an crazy idea? Or might it work out ok. I like the idea of mass tuning, instead of tubes between 4 and 30 inches long.
Roland
That sounds quite reasonable, in theory.
In practice, you may find that a bass trap based on a port will have a sharper resonance than the passive radiator, and will pick out a single frequency more accurately. That's just a guess- it would have to do with whether the passive radiator's surround is more or less lossy than the air moving in a port tube.
One phenomenon that you may observe is distortion in your bass trap. As the surround reaches the end of its excursion, I think the nonlinearity will cause some harmonics to be produced. Of course, if there's so much bass in the air that the passive radiator is running out of excursion.... you may not care if it starts to sound funny since it will be so loud.
In practice, you may find that a bass trap based on a port will have a sharper resonance than the passive radiator, and will pick out a single frequency more accurately. That's just a guess- it would have to do with whether the passive radiator's surround is more or less lossy than the air moving in a port tube.
One phenomenon that you may observe is distortion in your bass trap. As the surround reaches the end of its excursion, I think the nonlinearity will cause some harmonics to be produced. Of course, if there's so much bass in the air that the passive radiator is running out of excursion.... you may not care if it starts to sound funny since it will be so loud.
Member
Joined 2004
Hi Joe
Thanks for the reply. Your post remembered me to make the volume of the Helmholtz enclosure not smaller than 50 times driver vd to minimize distortion caused by the non linearity's of compresed air.
I am, going to build it and will tell if it works ok.
Roland
Thanks for the reply. Your post remembered me to make the volume of the Helmholtz enclosure not smaller than 50 times driver vd to minimize distortion caused by the non linearity's of compresed air.
I am, going to build it and will tell if it works ok.
Roland
Hi,
as far as I'm aware it would be impossible to drive a bass
trap with a PR to anywhere near the PR's excursion limits.
🙂/sreten.
as far as I'm aware it would be impossible to drive a bass
trap with a PR to anywhere near the PR's excursion limits.
🙂/sreten.
Ive have often thought of using an inexpensive 12 or 15 inch woofer for just that. instead of mass loading a PR you could and and electrical filter to the terminals of the woofer, a resistor just to damp and or an arrangement capcitor and inductor as an easy to ajust notch, high pass or low pass filter - adjustable!
Member
Joined 2004
Cool idea! with the adjustable Q and fs!
I just ordered some cheap dayton 10 inch Passive radiotors for the basstrap.
Thanks for the advice.
I just ordered some cheap dayton 10 inch Passive radiotors for the basstrap.
Thanks for the advice.
A more typical way to make tunable resonators is to use hardboard with different hole patterns in it. You could just use pegboard and put painters tape over some of the holes to tune it.
You could also just make a big membrane out of hardboard and put varying amounts of mass to it bay adding asphalt shingles or lead sheet or some such ....
You could also just make a big membrane out of hardboard and put varying amounts of mass to it bay adding asphalt shingles or lead sheet or some such ....
Member
Joined 2004
Hi Ron
I want to use them in this type of bastrap, not in an panel absorber.
http://www.mhsoft.nl/Helmholtzabsorber.asp#HelmholtzPanelAbsorber
The type called Helmholtz-Resonator.
Groet Roland
I want to use them in this type of bastrap, not in an panel absorber.
http://www.mhsoft.nl/Helmholtzabsorber.asp#HelmholtzPanelAbsorber
The type called Helmholtz-Resonator.
Groet Roland
roland bios said:
Ron E said:
As RonE states the above is a Helmholtz Resonator trap.
I built a whole series tuned 1/2 an octave apart ranging from 2"
depth all holes open to 8" depth with 1/4 of the holes open.
Area does not affect the tuning but they were 8ft x 2ft each.
🙂/sreten.
Member
Joined 2004
Hi
something like this:
Every Radiator tuned to an different fundamental freq. And 3 separated enclosures inside.
Would it be an good idea to put the radiators on the small side to give them some better "corner loading"?
Groeten Roland
something like this:
An externally hosted image should be here but it was not working when we last tested it.
Every Radiator tuned to an different fundamental freq. And 3 separated enclosures inside.
Would it be an good idea to put the radiators on the small side to give them some better "corner loading"?
Groeten Roland
Member
Joined 2004
Hi
Finally tuned the passive radiator bass trap!
Room Lenght 6.60 m. 26.06 hz fundamental.
Room Depth 5.50 m. 31.27 hz fundamental.
Room Height 4.00 m. 43.00 hz fundamental.
I used a 150 watt sub with a 10 inch woofer (closed). A sine wave generator and a piece of paper taped to the cone to make the tuning frequency visible. (lots of vibration is bingo...)
The bastrap is placed in the corner of the room. The 43 hz and 31 hz where easy. The 26 hz still needs some extra mass and is now tuned to 28 hz.
There is still room to make the enclosure smaller. Cone movement starts at +- 3 hz of the tuning frequency. The volume per passive radiator is 55 liters in this version.
Here is a drawing of the basstrap:
Next version will be a cube of +- 16*16*16 inch. I plan to use accelorators connect to a small led or light bulb to make the tuning freq. visible. There are car hifi woofers with led's that light on the beat of the music. Does someone have a tip or hint on what accelero meter to use? Or what is used in these car sub woofers? I want the tuning lights to function without batteries / external power source.
Best regards
Roland
Finally tuned the passive radiator bass trap!
Room Lenght 6.60 m. 26.06 hz fundamental.
Room Depth 5.50 m. 31.27 hz fundamental.
Room Height 4.00 m. 43.00 hz fundamental.
I used a 150 watt sub with a 10 inch woofer (closed). A sine wave generator and a piece of paper taped to the cone to make the tuning frequency visible. (lots of vibration is bingo...)
The bastrap is placed in the corner of the room. The 43 hz and 31 hz where easy. The 26 hz still needs some extra mass and is now tuned to 28 hz.
There is still room to make the enclosure smaller. Cone movement starts at +- 3 hz of the tuning frequency. The volume per passive radiator is 55 liters in this version.
Here is a drawing of the basstrap:
Next version will be a cube of +- 16*16*16 inch. I plan to use accelorators connect to a small led or light bulb to make the tuning freq. visible. There are car hifi woofers with led's that light on the beat of the music. Does someone have a tip or hint on what accelero meter to use? Or what is used in these car sub woofers? I want the tuning lights to function without batteries / external power source.
Best regards
Roland
roland bios said:Hi
Finally tuned the passive radiator bass trap!
Room Lenght 6.60 m. 26.06 hz fundamental.
Room Depth 5.50 m. 31.27 hz fundamental.
Room Height 4.00 m. 43.00 hz fundamental.
I used a 150 watt sub with a 10 inch woofer (closed). A sine wave generator and a piece of paper taped to the cone to make the tuning frequency visible. (lots of vibration is bingo...)
The bastrap is placed in the corner of the room. The 43 hz and 31 hz where easy. The 26 hz still needs some extra mass and is now tuned to 28 hz.
There is still room to make the enclosure smaller. Cone movement starts at +- 3 hz of the tuning frequency. The volume per passive radiator is 55 liters in this version.
Here is a drawing of the basstrap:
Next version will be a cube of +- 16*16*16 inch. I plan to use accelorators connect to a small led or light bulb to make the tuning freq. visible. There are car hifi woofers with led's that light on the beat of the music. Does someone have a tip or hint on what accelero meter to use? Or what is used in these car sub woofers? I want the tuning lights to function without batteries / external power source.
Best regards
Roland
Very cool idea! I'm thinking about doing this myself. Any comments on enclosure size, or how to choose a passive radiator? Do you calculate the mass needed for the cone, or tune by trial-and-error? How well of a job does it do in terms of absorbing bass?
One question on the trap
I've not read of this type of application. How does the trap have a significant enough impact? The energy of the resonance is widely distributed in the room. You've got eight corners in a typical room. The resonance would load opposing walls rougthly equally, but to counter it the trap has to either absorb the energy or it is has to do so by resonating in opposition and at the correct phase relationship.
It wouldn't have to be 100% effective of course, but it has to be significant. The cross sectional area of the port/PR is small in comparison to the area of interest (an entire wall). As a passive device it can only counter the energy that impinges on it, which will end up less than that due to losses in the port/PR.
It also is only going to act on one of the two loaded walls.
I just don't see how one of these can alter the room response in a significant way. They can only react to the energy that is applied directly to the opening/diaphragm. In relation to the room, it seems pretty insignicant to me.
dlr
I've not read of this type of application. How does the trap have a significant enough impact? The energy of the resonance is widely distributed in the room. You've got eight corners in a typical room. The resonance would load opposing walls rougthly equally, but to counter it the trap has to either absorb the energy or it is has to do so by resonating in opposition and at the correct phase relationship.
It wouldn't have to be 100% effective of course, but it has to be significant. The cross sectional area of the port/PR is small in comparison to the area of interest (an entire wall). As a passive device it can only counter the energy that impinges on it, which will end up less than that due to losses in the port/PR.
It also is only going to act on one of the two loaded walls.
I just don't see how one of these can alter the room response in a significant way. They can only react to the energy that is applied directly to the opening/diaphragm. In relation to the room, it seems pretty insignicant to me.
dlr
Member
Joined 2004
It is the same principle as a basstrap with a tube. Placement in the cormers is the most effective. If the passive version doesn't work why should the tube version work?
kind regards
Roland
This is my question. I don't see how either can work with much influence. I can see how a trap that has significant damping can work, but that's an absorption function. I'm just not familiar with resonating traps, neither tube nor PR.roland bios said:
Both require that the resonance be within it be energized by the surface area, port or PR. In speakers these are driven by the total energy output from the driver and is significant in relation to the energy output from the front of the driver. However, in a trap, the energy actually impacting the PR is nowhere near the total energy in the room that is creating the resonance in the first place.
All one need do is examine the massive amount of area required of a studio to tame the resonances in them to see that it takes a large area to have an impact. These are tuned, if I understand them correctly, but occupy a significant percentage of the wall area. A tube trap in a room is small in relation to the area of the wall.
I'm sure it has some effect, but I'm just skeptical of the absolute ability of a small surface area passive device to have much impact. I'm not saying that it is not the case, but I don't yet see support for it.
dlr
"instead of mass loading a PR you could and and electrical filter to the terminals of the woofer, a resistor just to damp and or an arrangement capcitor and inductor as an easy to ajust notch, high pass or low pass filter - adjustable!"
I don't electrical circuits will change the mechanical resonant freq.
So Roland, how effective is it?
About 15 yr ago Stereophile used to talk about a product that was an active bass trap (essentially a sub driven to cancel modes), which they said was quite effective.
I don't electrical circuits will change the mechanical resonant freq.
So Roland, how effective is it?
About 15 yr ago Stereophile used to talk about a product that was an active bass trap (essentially a sub driven to cancel modes), which they said was quite effective.
Hi Roland, I know this is a very old post but what was the outcome please?
I am thinking about doing a very similar project
About tuning: I was wondering if the box itself shall be tuned to the desired frequency (fb - the resonant frequency of the box where you put in the passive radiator) instead of tuning the PR itself - since I guess if you put a PR with a certain tuning frequency into a sealed box the final resonant frequency of the "system" will not equal to the fs of the PR
Thank you
I am thinking about doing a very similar project
About tuning: I was wondering if the box itself shall be tuned to the desired frequency (fb - the resonant frequency of the box where you put in the passive radiator) instead of tuning the PR itself - since I guess if you put a PR with a certain tuning frequency into a sealed box the final resonant frequency of the "system" will not equal to the fs of the PR
Thank you
Hoping that the thread starter will drop by, but Roland has not been seen here for around 10 years.
I know nothing about these things but wouldn't a passive radiator system be problematic due to the relatively slow speed of sound? i.e. a sound wave travelling across a distance to vibrate something else which due to distance travelled will be vibrating out of synch.
I don't know maths but I used to DJ. It becomes increasing difficult to mix tracks when your audio source is more than three or four metres away.
I don't know maths but I used to DJ. It becomes increasing difficult to mix tracks when your audio source is more than three or four metres away.