I suspect almost every small vented SUBwoofer design exceeds that rule of thumb
And if they don't, I'd suggest that the vent is likely too small for subwoofer duty.
Some more PR notes:
Hi nicasiox2,
Just more stuff : PE has a buyout sale on Titan loudspeakers, you could use 2ea. of the 8" woofers as passive radiators (PRs); $8.88 ea. With two PRs you can mount them on the sides of the box, and the forces should cancel. As with any PR you will probably have to add weight to the cone to adjust the system resonance; depending on how much weight you need you could glue an MDF disc to the cone. You could remove the magnet assembly, or leave the speakers as are, and connect a potentiometer across the voice coils to alter the response.
Brian Steele has a nice write-up on how to calculate PRs: The Subwoofer DIY Page - Passive Radiator Systems , and
AESpeakers has a good FAQ on the subject:
AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.
Jeff Bagby's spreadsheet is great for simulating PR subwoofers, and you can verify your results in WinISD or Hornresp:
Loudspeaker Design Software
Regards,
Hi nicasiox2,
Just more stuff
: PE has a buyout sale on Titan loudspeakers, you could use 2ea. of the 8" woofers as passive radiators (PRs); $8.88 ea. With two PRs you can mount them on the sides of the box, and the forces should cancel. As with any PR you will probably have to add weight to the cone to adjust the system resonance; depending on how much weight you need you could glue an MDF disc to the cone. You could remove the magnet assembly, or leave the speakers as are, and connect a potentiometer across the voice coils to alter the response.Brian Steele has a nice write-up on how to calculate PRs: The Subwoofer DIY Page - Passive Radiator Systems , and
AESpeakers has a good FAQ on the subject:
AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.
Jeff Bagby's spreadsheet is great for simulating PR subwoofers, and you can verify your results in WinISD or Hornresp:
Loudspeaker Design Software
Regards,
It is 13 square inches, do you think it's small and not enough? that's a little bigger than manual recommend.
Hi nicasiox2,
Just more stuff
Brian Steele has a nice write-up on how to calculate PRs: The Subwoofer DIY Page - Passive Radiator Systems , and
AESpeakers has a good FAQ on the subject:
AE Speakers --- Superb Quality, Unforgettable Performance, Definitely.
Jeff Bagby's spreadsheet is great for simulating PR subwoofers, and you can verify your results in WinISD or Hornresp:
Loudspeaker Design Software
Regards,
So that's possible!? I thought about this this morning, but didn't know if it certainly would work. I observed how some PR costed much more than a couple of cheap price speaker (pyle, boss, lanzar, etc). As somebody said, maybe the port I was working with, its too small, I followed that number given on the sub website, but that was the enclosure that sorter port as much as possible, which was in length around the half size of my port. Because that I am not more interested on the passive radiators, if I fix my port design, and I ended with a very huge enclosure, then I have lost my purpose of the compact as possible, but powerful. I was expecting no more than 2 cubic foot, with maybe with the proper port it will finishing with 3 cubic foot or something like that.
Talking about the passive radiators, I think that I like the idea of putting two passive radiators of 8" size, which is the same than sub, and leaving a space around 1.75 or 2 max cubic foot, surely it will sound wonderful, with two radiators it will mean that you really took care about good performance. Can they go on any position? parallel and perpendicular.
My comment was in reference to the suggestion that the length of the port should be no more than twice the port's diameter.
If you want to determine whether or not your vent is large enough, use a sim program that can sim the velocity of the air flow through the vent when the subwoofer is driven to Xmax.
Probably not. PR resonance and also Xmax (i.e. how far the PR's cone can move linearly) are both important qualities of a good PR. Cheap drivers are likely to have a resonance that's too high and an Xmax that's too low to serve as good PRs. Adding mass to them to reduce the resonance will work, but there's still the Xmax issue to consider.
Hi nicasiox2,
Post #24: "... Can they go on any position? parallel and perpendicular."
The PRs interact with the air in the enclosure, so as long as they can do that freely the position does not matter. The preferred position is to have an even number of PRs, mounted so that the motion forces oppose. As has been noted before, a single 12' PR would also do the job; see MCM Electronics for really cheap 12" woofers.
Regards,
Post #24: "... Can they go on any position? parallel and perpendicular."
The PRs interact with the air in the enclosure, so as long as they can do that freely the position does not matter. The preferred position is to have an even number of PRs, mounted so that the motion forces oppose. As has been noted before, a single 12' PR would also do the job; see MCM Electronics for really cheap 12" woofers.
Regards,
Will try to simulate it.
I have another question, related to using real speakers as passive drivers. Only thing is that you should glue something to the cone in order to low down the fs? a mdf disc, as mentioned before, what dimensions should it has for a 8" subwoofer? should it cover all the cone? I think... but with 1/4 or 1/2 mdf, 3/4 seems me like it would be too heavy, but I really don't know.
You need to work out how much mass you have to add first. Then, use that to determine what size that MDF disc needs to be to achieve that.
Hi
Good discussion here.
Are you saying use a 12"cheap woofer from MCM for a PR?
How would tune it weights or add resistor across the speaker tabs/leads?
Good discussion here.
Are you saying use a 12"cheap woofer from MCM for a PR?
How would tune it weights or add resistor across the speaker tabs/leads?
That´s funny. At least you understand it well.
Best way is to remove the magnet of those speakers to be used as PR, and only keep the cone, and spider (with or without coil). Then you load it with weights somewhere in the coil place (center). And then measure impedance curves of the speaker (the main one left with the magnet).
Best way is to remove the magnet of those speakers to be used as PR, and only keep the cone, and spider (with or without coil). Then you load it with weights somewhere in the coil place (center). And then measure impedance curves of the speaker (the main one left with the magnet).
Hi ODougbo,
Post #31: "...Are you saying use a 12"cheap woofer from MCM for a PR?
How would tune it weights or add resistor across the speaker tabs/leads?"
Post #32: "...Best way is to remove the magnet of those speakers to be used as PR, and only keep the cone, and spider (with or without coil)..."
Yes, and I second Crashpc's answer. This is just one way to experiment w/ PRs.
You need a frame, a diaphragm w/ tuning weight(s) and a suspension. You could glue a surround to the exterior wall of the box, a spider to a properly aligned internal brace, glue a MDF disk as diaphragm/weight to the surround, and a cardboard tube to connect the disk to the spider...then you can use the inside of the cardboard tube to add more weight... If you simulate a PR enclosure you'll find that it takes quite a bit of weight to get to the correct moving mass, and the initial fsp (resonance of the passive radiator before adding tuning weight) is usually a lot higher than the resonance of the PR w/ tuning weights which is always well below the system resonance. It is best to simulate, but you can get there by trial and error, and using Brian's method (Post #22) of calculating the PR...
Regards,
Post #31: "...Are you saying use a 12"cheap woofer from MCM for a PR?
How would tune it weights or add resistor across the speaker tabs/leads?"
Post #32: "...Best way is to remove the magnet of those speakers to be used as PR, and only keep the cone, and spider (with or without coil)..."
Yes, and I second Crashpc's answer. This is just one way to experiment w/ PRs.
You need a frame, a diaphragm w/ tuning weight(s) and a suspension. You could glue a surround to the exterior wall of the box, a spider to a properly aligned internal brace, glue a MDF disk as diaphragm/weight to the surround, and a cardboard tube to connect the disk to the spider...then you can use the inside of the cardboard tube to add more weight...
If you simulate a PR enclosure you'll find that it takes quite a bit of weight to get to the correct moving mass, and the initial fsp (resonance of the passive radiator before adding tuning weight) is usually a lot higher than the resonance of the PR w/ tuning weights which is always well below the system resonance. It is best to simulate, but you can get there by trial and error, and using Brian's method (Post #22) of calculating the PR...Regards,
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Long slot .... does it work?
About a long bending slot. For a sub with low tuning point in a small box, there is more or less only two practical options; long slot port or passive radiator.
I have built a sub with a long slot port recently and it works quite well. Peerless 12" XLS in 33 l tuned to som 33 Hz.
A commercial product using a long slotport is e.g. Martin Logan.
Is it ideal? probably not at all but for a sub I think it is good way to go.
Just my 2 cent
About a long bending slot. For a sub with low tuning point in a small box, there is more or less only two practical options; long slot port or passive radiator.
I have built a sub with a long slot port recently and it works quite well. Peerless 12" XLS in 33 l tuned to som 33 Hz.
A commercial product using a long slotport is e.g. Martin Logan.
Is it ideal? probably not at all but for a sub I think it is good way to go.
Just my 2 cent
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