Hey everyone,
I'm currently working on a small 2.1 sound system for a friend, aiming for a flat response and clean overall sound in as small a package as possible.
For the satelites, I've settled on using a pair of FaitalPro 3FE25 Full Range drivers, as they have a relatively flat response and excellent off-axis sound. For the sub, I am using a Dayton Audio DC160-8 6.5" Classic Woofer and a matching 8" Passive Radiator, also from Dayton. This combination will allow me to cross over nice and low, hopefully somewhere around 90-100 Hz.
I've read elsewhere on the forum about the same woofer-PR combination being used in a sub known as the Bitty Boom V.2, which is a 14" length of Sonotube with one element in either end. The gross volume of this enclosure is about 11.5L, and apparently it can reach frequencies as low as 25Hz pretty comfortably with 25g of mass added to the PR.
So my question is, basically, how much of that LF extension is attributable to the shape of the enclosure? All the other designs I've seen have the PRs mounted to a panel adjecent to the woofer, rather than directly in line with the back wave. Is there a known trade-off for this design? Is there one preferable way of doing it? I have no prior experience with building PR-tuned cabinets, but I'd definitely prefer to build either a cube or rectangular design over a tube.
Another side-note question: Can I make up some of the losses in cabinet volume (from the baskets, motor, and onboard amp) by stuffing the box with wool? Or is it preferable to just add more mass to the PR to maintain the tuning?
Any help would be appreciated!
Thanks
I'm currently working on a small 2.1 sound system for a friend, aiming for a flat response and clean overall sound in as small a package as possible.
For the satelites, I've settled on using a pair of FaitalPro 3FE25 Full Range drivers, as they have a relatively flat response and excellent off-axis sound. For the sub, I am using a Dayton Audio DC160-8 6.5" Classic Woofer and a matching 8" Passive Radiator, also from Dayton. This combination will allow me to cross over nice and low, hopefully somewhere around 90-100 Hz.
I've read elsewhere on the forum about the same woofer-PR combination being used in a sub known as the Bitty Boom V.2, which is a 14" length of Sonotube with one element in either end. The gross volume of this enclosure is about 11.5L, and apparently it can reach frequencies as low as 25Hz pretty comfortably with 25g of mass added to the PR.
So my question is, basically, how much of that LF extension is attributable to the shape of the enclosure? All the other designs I've seen have the PRs mounted to a panel adjecent to the woofer, rather than directly in line with the back wave. Is there a known trade-off for this design? Is there one preferable way of doing it? I have no prior experience with building PR-tuned cabinets, but I'd definitely prefer to build either a cube or rectangular design over a tube.
Another side-note question: Can I make up some of the losses in cabinet volume (from the baskets, motor, and onboard amp) by stuffing the box with wool? Or is it preferable to just add more mass to the PR to maintain the tuning?
Any help would be appreciated!
Thanks
The enclosure can be 'virtually' enlarged by wool but I would do that only on sealed enclosures, on ported (PR is technically a kind of port) enclosures you're losing efficiency, to gain ~20% volume you're losing ~2dB, that's a horrible pay back. Don't do that.
The PR has always be tuned by adding or removing weight. Check the fb by impedance measurement or by watching the membrane excursion.
E: For the placement of the PR: Just like for drivers, don't put it on the top or bottom because it will sag over time and your voice coil becomes off center (equals DC offset) and the motor drive gets an side-to-side unlinear propulsion (driver) and the suspension is working asymmetrical too (driver & PR), that's increasing the nonlinear distortions vastly. If you absolutely have to mount it that way, turn it 180° (up/down) every half year.
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Ok, that's useful advice. Thanks guys!
One follow-up question though: I'd definitely heard about the dangers of mounting PRs flat (especially with added mass), but I was actually thinking of making the active driver down-firing. Would that be an option for this driver? It has a pretty lightweight paper cone...
One follow-up question though: I'd definitely heard about the dangers of mounting PRs flat (especially with added mass), but I was actually thinking of making the active driver down-firing. Would that be an option for this driver? It has a pretty lightweight paper cone...
Moving mass is 0.029 kg, so gravity exerts a force of 0.29 N. With a compliance of 0.68 mm/N this results in a offset of 0.2 mm, which is 6% of xmax. This is not a problem, though at the long term it can sag more. How much, I do not know. I would not worry about it, unless you plan on keeping the system for multiple years.
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Thanks TBTL, really appreciate you figuring that out! I think if that's the case then down-firing will be fine... I rarely keep a system together for more than a year.
I think all that's left to do now is actually build the sub. Will let you know if anything comes up. Thanks for all the help!
I think all that's left to do now is actually build the sub. Will let you know if anything comes up. Thanks for all the help!
FYI/FWIW, ~6.27%, 5 % considered long term limit: Resrc - How to Tell if a Woofer Can Be Mounted Up- or Down-Firing
Short term - no problem. The long term influence is unknown and 0,2mm don't sound like much but it will get more because that's the compilance of a new driver, it will rise. And the driver got only 3,15mm Xmax. What's worse is the asymmetrical suspension because of the DC offset, it produces nonlinear distortions far earlier than the Xmax is reached.
With a PR you typically need 3-4x the Mms, sometimes even more. If you use the same driver without the magnet as passive membrane and a bit higher compliance because of being broke in, you use up almost half of the Xmax because of the DC offset even on idle. So that's not an issue of 'multiple years'.