OK, so this may be a crazy genius idea, or it may just be a stupid question.
I've searched far and wide to find an answer and have not run across any articles or posts that would suggest this is either a good or bad idea, and/or if it is even possible. I have a couple old 4ohm car subwoofers in a sealed enclosure that I've been using as a home subwoofer. They actually sound great compared to several expensive "purpose built" alternatives I've heard. The problem is the enclosure is huge. So I thought it might be a good idea to redesign the enclosure to be much smaller. If I switch to a single woofer configuration the box is still too large for the WAF, so I thought if I go Isobaric I can reduce the box size further. In researching ways of reducing box size, I came across Aperiodic enclosures as an alternative for reducing box size. So the questions is:
Is it possible to build an enclosure that is both Aperiodic and Isobaric? (By aperiodic I mean using a resistive vent in the cabinet side, not a resistive membrane in front of the woofer).
If so, then there are some other questions. Since typically, with Isobaric, you can half the VAS of the single woofer (essentially halving the sealed box size), and in aperiodic enclosures you can half the VAS of the single woofer, when combining the two configurations can one essentially quarter the VAS and have a box 1/4 the size of the typical sealed enclosure? I know there are some major draw backs to doing this, specifically the efficiency of the overall system. I'm not to worried about that since I have a large enough amp to handle the loss and the subs have a fairly high SPL to begin with.
Any feedback would be appreciated, and thanks in advance to anyone who replies to my first post.
Thanks,
Damian
I've searched far and wide to find an answer and have not run across any articles or posts that would suggest this is either a good or bad idea, and/or if it is even possible. I have a couple old 4ohm car subwoofers in a sealed enclosure that I've been using as a home subwoofer. They actually sound great compared to several expensive "purpose built" alternatives I've heard. The problem is the enclosure is huge. So I thought it might be a good idea to redesign the enclosure to be much smaller. If I switch to a single woofer configuration the box is still too large for the WAF, so I thought if I go Isobaric I can reduce the box size further. In researching ways of reducing box size, I came across Aperiodic enclosures as an alternative for reducing box size. So the questions is:
Is it possible to build an enclosure that is both Aperiodic and Isobaric? (By aperiodic I mean using a resistive vent in the cabinet side, not a resistive membrane in front of the woofer).
If so, then there are some other questions. Since typically, with Isobaric, you can half the VAS of the single woofer (essentially halving the sealed box size), and in aperiodic enclosures you can half the VAS of the single woofer, when combining the two configurations can one essentially quarter the VAS and have a box 1/4 the size of the typical sealed enclosure? I know there are some major draw backs to doing this, specifically the efficiency of the overall system. I'm not to worried about that since I have a large enough amp to handle the loss and the subs have a fairly high SPL to begin with.
Any feedback would be appreciated, and thanks in advance to anyone who replies to my first post.
Thanks,
Damian
There's no reason it can't (or shouldn't) be done, but I'm doubtful you can safely halve the volume by going aperiodic, unless the original enclosure was ridiculously oversized to begin with.
IMHO, for a small cabinet with decent low-end, a Linkwitz Transform is hard to beat.
ESP - The Linkwitz Transform Circuit
Chris
IMHO, for a small cabinet with decent low-end, a Linkwitz Transform is hard to beat.
ESP - The Linkwitz Transform Circuit
Chris
It might work... but I suspect you will not get down to 1/4 size enclosure. Not with the same F3 or Fb point.
The Isobaric configuration generally takes up extra volume IF it is inside the box. One way to go is to put the woofers face to face, with a suitable spacer to keep the surrounds from touching... but that puts one magnet sticking out of the face of the box. Some folks don't like that. You can make a frame for some grille cloth to fit over the magnet bump for higher WAF.
Probably with aperiodic you will not get the same output as you would with a port at the port's tuned freq, so you may need EQ to pull the output back up...
I am unaware of any modeling software for aperiodic enclosures, so I guess some experimentation will be required...
_-_-bear
The Isobaric configuration generally takes up extra volume IF it is inside the box. One way to go is to put the woofers face to face, with a suitable spacer to keep the surrounds from touching... but that puts one magnet sticking out of the face of the box. Some folks don't like that. You can make a frame for some grille cloth to fit over the magnet bump for higher WAF.
Probably with aperiodic you will not get the same output as you would with a port at the port's tuned freq, so you may need EQ to pull the output back up...
I am unaware of any modeling software for aperiodic enclosures, so I guess some experimentation will be required...
_-_-bear
With aperiodic or transmission line, you need a certain line length to absorb frequencies up to a low enough point. I would think this would be the same for speakers mounted isobaric or single, so I don't expect much reduction in size can be achieved. Also not because most transmission line designs have also a quarter wave tube element to them.
For sealed, Chris gave the right recipe and this can be done isobaric, but beware. You will need a lot of xmax, perhaps more than some old car speakers can deliver.
vac
For sealed, Chris gave the right recipe and this can be done isobaric, but beware. You will need a lot of xmax, perhaps more than some old car speakers can deliver.
vac
Thanks everyone for your reply's. I honestly didn't expect this much interest in a "first time poster's" thread.
Chris, the Linkwitz Transform is intriguing but I doubt my 10 year old subs can handle the xmax that will be required of them. Specs say 5mm, so I don't think it's going to work. Thanks for the suggestions though. It gives me some ideas for future projects. I'll definitely have to look into it some more. I wonder if the Linkwitz could be used to boost the output that Bear suggests I might loose.
Bear, I'm still considering both configurations for the Isobaric. Each has it's pos and neg. Regardless of which way I go, the total box ends up almost the same size because of the grill needed for WAF. Good call on that though.
Ported unfortunately is out of the questions because it exceeds my max size requirement for the project. From what I understand, aperiodic helps to extend the low end and give the driver a more gradual roll off. Supposedly any modeling software that can account for the quality of the box (how leaky it is) can approximate aperiodic venting. That's just what a read somewhere though. I haven't modeled anything yet.
Vacuphile, from what I understand, an aperiodic vent should simply be placed as far from the driver as possible and should have an open path to the driver. I haven't read anything about a need for specific line lengths. Technically aperiodic is just a sealed but leaky box. A transmission line is essentially a ported labyrinth with some extra math. Though they supposedly produce very similar results (low end frequency response and impedance) they are completely different styles of enclosures. At least that is what I've read. by all means, correct me if I'm wrong.
I think the consensus is that I can do it, but I shouldn't expect to be able to halve the box size again by going aperiodic. Maybe a modest reduction, say 20%, beyond what I've calculated for the Isobaric enclosure is in order. What do you think?
Thanks again everyone!
Chris, the Linkwitz Transform is intriguing but I doubt my 10 year old subs can handle the xmax that will be required of them. Specs say 5mm, so I don't think it's going to work. Thanks for the suggestions though. It gives me some ideas for future projects. I'll definitely have to look into it some more. I wonder if the Linkwitz could be used to boost the output that Bear suggests I might loose.
Bear, I'm still considering both configurations for the Isobaric. Each has it's pos and neg. Regardless of which way I go, the total box ends up almost the same size because of the grill needed for WAF. Good call on that though.
Ported unfortunately is out of the questions because it exceeds my max size requirement for the project. From what I understand, aperiodic helps to extend the low end and give the driver a more gradual roll off. Supposedly any modeling software that can account for the quality of the box (how leaky it is) can approximate aperiodic venting. That's just what a read somewhere though. I haven't modeled anything yet.
Vacuphile, from what I understand, an aperiodic vent should simply be placed as far from the driver as possible and should have an open path to the driver. I haven't read anything about a need for specific line lengths. Technically aperiodic is just a sealed but leaky box. A transmission line is essentially a ported labyrinth with some extra math. Though they supposedly produce very similar results (low end frequency response and impedance) they are completely different styles of enclosures. At least that is what I've read. by all means, correct me if I'm wrong.
I think the consensus is that I can do it, but I shouldn't expect to be able to halve the box size again by going aperiodic. Maybe a modest reduction, say 20%, beyond what I've calculated for the Isobaric enclosure is in order. What do you think?
Thanks again everyone!
also, you loose max SPL with the isobaric because you have halved your radiating surface. but I built some speakers with a set of 8" SEAS drivers in a two way, and they were isobaric, and kicked butte... so it might sound great... dunno.
Depends a bit on how low you want to go...
also the EQ will reduce ur max SPL and increase ur amp requirements...
_-_-bear
Depends a bit on how low you want to go...
also the EQ will reduce ur max SPL and increase ur amp requirements...
_-_-bear
Excursion only really becomes a problem when you try to go below ~35Hz.
It really does depend on how low/loud you want to go. 5mm one-way travel on a decent-sized (10" or larger) pair of drivers will be plenty loud, even in a sealed cabinet.
It really does depend on how low/loud you want to go. 5mm one-way travel on a decent-sized (10" or larger) pair of drivers will be plenty loud, even in a sealed cabinet.
isit not true that woofers designd for in car use are of the spec range to suit a small enclosure ???????
Yeah, though the resultant cabinet often needs the cabin gain provided by the small environment within the car to provide boost to give a usable frequency response.
In half space, they're often found lacking. YMMV, but as always, the T/S specs tell a lot about the performance under various situations.
Well maybe the Linkwitz Transform is back on the table then. I'm really only shooting for 30 to 35hz, though they will perform below that down to about 22 hz @ -8db or so. I've worked out a slightly larger box design (that isn't too large for WAF) that may just barely allow me to sneak in a ported design. F3 is 19.42hz, which is plenty low. I'm not sure if the ported box is big enough to accommodate the port volume though. I'll have a better idea tonight.
You are correct. And my 12" subs do fit in a relatively small box for what they are. What's weird is the manufacturers spec sheet recommends using a 1cu.ft sealed box, but when calculated, the specifications indicate a 2.71 cu.ft box. I figured out that they were using a Qtc of 1.00, where I'm using .707 for a more balanced response. But that's not really the point. The point here is to figure out how small I can go. Since I have two subs, I want to see what I can do with them. Might as well try something cool. Otherwise I end up with a 12" sub sitting in a closet somewhere taking up space. Plus, this is practice for me as I have some other projects I'm beginning to think about, one of which is shoehorning a sub into a compartment nowhere near big enough for one in my Toyota Tacoma. And no, the 12" sub is not what I'm thinking of using for that. I'll have to go down to 5" or 6" for the Tacoma. But that's another project for another day.
On WinISD (pro), key in the driver's T/S parameters, add a Linkwitz Transform, then look at the Amplifier apparent load Power (VA). This'll give you an idea of how much power is being pumped into the drivers to do what's needed.
A Linkwitz Transform forces excursion by increasing power input. The smaller the sealed cabinet, the more amplifier power needed to move the cone around.
The maximum SPL of the system is the same for infinite baffle (mounted in-wall) as a tiny sealed cabinet, so long as the driver's power ratings are not exceeded.
You have a pair of 12" drivers, so I'd expect 30Hz to be a reasonable target. You could go for lower, but the maximum overall SPL available drops further.
You could use a tiny cabinet, and throw loads of power in (this is what most commercial subwoofers do) - this is why I mentioned the Amplifier Apparent Load on WinISD - you can find out how much power is going in, and then pick a compromise between extension, SPL, and driver safety.
Chris
A Linkwitz Transform forces excursion by increasing power input. The smaller the sealed cabinet, the more amplifier power needed to move the cone around.
The maximum SPL of the system is the same for infinite baffle (mounted in-wall) as a tiny sealed cabinet, so long as the driver's power ratings are not exceeded.
You have a pair of 12" drivers, so I'd expect 30Hz to be a reasonable target. You could go for lower, but the maximum overall SPL available drops further.
You could use a tiny cabinet, and throw loads of power in (this is what most commercial subwoofers do) - this is why I mentioned the Amplifier Apparent Load on WinISD - you can find out how much power is going in, and then pick a compromise between extension, SPL, and driver safety.
Chris
After doing a little more research into the Linkwitz Transform, I'm starting to think that this may be the way to go. I can keep the enclosure sealed and consiquently small, which was the main goal of the project. I'm not clear on something though, is the circuit essentially a pre-amp eq or is it a line level filter/booster? Also, what do they typically cost to build? I didn't state my design goals in the beginning, but the secondary consideration was minimum cost. Since I have the drivers and the amp on hand, all I need is some MDF, (which I can get for free from my cabinet maker),a port will be required if I go ported, some ancillary materials for finishing and such, and some grill cloth. So I'm looking at maybe $50 in the end. Probably more like $30 for total project. I'm willing to spend more to get a better product in the end, but I'm diverging from my original goals by doing so.
Thanks again!
Download the spreadsheet and have a play around.
Linkwitz Transform Subwoofer Equaliser
It's likely better to use WinISD to figure out the right Qp and Fp WRT excursion, power handling etc, but the spreadsheet will tell you the values.
I could make the circuit (completely from scratch) for ~ £10.
It's a TL072, a couple of resistors and capacitors, and some stripboard (see below - you guys in the USA might call it something different)
You'll need a split power supply. For a test, you could use say 8x AA batteries, giving a +/- 6v supply. The current draws for the chip will be tiny, so they'll last for a long time.
For more long-term use, you could use a 12v wall-wart, but you'll need to split the supply using some resistors, and add caps to block the DC on the input and output (the whole thing would sit at +6v to stay half-way up the supply).
Chris
Linkwitz Transform Subwoofer Equaliser
It's likely better to use WinISD to figure out the right Qp and Fp WRT excursion, power handling etc, but the spreadsheet will tell you the values.
I could make the circuit (completely from scratch) for ~ £10.
It's a TL072, a couple of resistors and capacitors, and some stripboard (see below - you guys in the USA might call it something different)
An externally hosted image should be here but it was not working when we last tested it.
You'll need a split power supply. For a test, you could use say 8x AA batteries, giving a +/- 6v supply. The current draws for the chip will be tiny, so they'll last for a long time.
For more long-term use, you could use a 12v wall-wart, but you'll need to split the supply using some resistors, and add caps to block the DC on the input and output (the whole thing would sit at +6v to stay half-way up the supply).
Chris
Sorry to drag up an old thread but my question is very relevant to the question originally asked.
If converting a sealed isobaric sub woofer to aperiodic does the vent / leak need to be in the front chamber or the back chamber or both ?
Many thanks.
If converting a sealed isobaric sub woofer to aperiodic does the vent / leak need to be in the front chamber or the back chamber or both ?
Many thanks.
I think i have worked this out. Vent in the rear chamber only. If i put a vent in the front chamber then it is no longer isobaric.