Kev, yes I only showed with ONE TC2+. The only decent sub drivers that I'm aware of locally available are Adire and Peerless.
Vented subs are not necessarily more difficult to eq. In fact, where a sealed sub needs eq to get down low, vented does not and in that way it is most likely easier. The exception is rooms more typical in the US where room gain is such that a sealed box needs no eq, and a vented box needs eq to reduce the effect of room gain. Both vented and sealed subs need eq to deal with room modes, neither is easier in that regard.
Sloppy bass does not necessarily come from a vented box. I've heard sloppy sealed and tight vented. For home theatre, vented subs are more appropriate in Australia than they are in the US. Here, a sub should be designed to reach the target F3 in anechoic conditions, since room gain will not extend in room response much if at all.
I'm inclined to think that with your current amp, a single vented Tempest 15" is the most sensible choice.
The thing to keep in mind with GD is that it's related to response. If you eq a sealed box to exactly the same response, then you get the same GD. How much GD is audible is debatable, and has not been established for subwoofers. Low GD goes with a higher F3.
I modelled a pair of Shiva 15s in a 200L sealed box, and the output with your amp was still less than the single Tempest when I managed to eq the response the same. The GD was pretty much the same as well. You could squeeze out maybe 2 db more SPL from the dual sealed for music but not for HT since xmax is the limitation. To actually get the same response you would need to modify your parametric eq since you need the gain at 20 Hz, not at 30 Hz which is the minimum on that Jaycar unit.
I doubt you will find a driver that will match the advantages of the Tempest 15 with your amp, although if you do insist on a sealed sub and accept the disadvantages there may be some you might want to consider. They will be more like the TC2+ than the Tempest.
My suggestion is make this a value for money sub. Go with a venteed Tempest 15D4, be a little creative about the shape of the box and how it fits in the room, and if later you want something more sexy, more impressive then choose both the driver and amp together and count on spending a fair bit more. If you do then insist on buying the amp before choosing the driver, then get a pro amp like Behringer EP2500 which is very flexible since it can drive two 2 ohm loads, or be bridged to put 2.4kw into 4 ohms - in other words it will power any driver you are likely to choose, and its not much more expensive than a plate amp, but then you will have fan noise to deal with!
Vented subs are not necessarily more difficult to eq. In fact, where a sealed sub needs eq to get down low, vented does not and in that way it is most likely easier. The exception is rooms more typical in the US where room gain is such that a sealed box needs no eq, and a vented box needs eq to reduce the effect of room gain. Both vented and sealed subs need eq to deal with room modes, neither is easier in that regard.
Sloppy bass does not necessarily come from a vented box. I've heard sloppy sealed and tight vented. For home theatre, vented subs are more appropriate in Australia than they are in the US. Here, a sub should be designed to reach the target F3 in anechoic conditions, since room gain will not extend in room response much if at all.
I'm inclined to think that with your current amp, a single vented Tempest 15" is the most sensible choice.
The thing to keep in mind with GD is that it's related to response. If you eq a sealed box to exactly the same response, then you get the same GD. How much GD is audible is debatable, and has not been established for subwoofers. Low GD goes with a higher F3.
I modelled a pair of Shiva 15s in a 200L sealed box, and the output with your amp was still less than the single Tempest when I managed to eq the response the same. The GD was pretty much the same as well. You could squeeze out maybe 2 db more SPL from the dual sealed for music but not for HT since xmax is the limitation. To actually get the same response you would need to modify your parametric eq since you need the gain at 20 Hz, not at 30 Hz which is the minimum on that Jaycar unit.
I doubt you will find a driver that will match the advantages of the Tempest 15 with your amp, although if you do insist on a sealed sub and accept the disadvantages there may be some you might want to consider. They will be more like the TC2+ than the Tempest.
My suggestion is make this a value for money sub. Go with a venteed Tempest 15D4, be a little creative about the shape of the box and how it fits in the room, and if later you want something more sexy, more impressive then choose both the driver and amp together and count on spending a fair bit more. If you do then insist on buying the amp before choosing the driver, then get a pro amp like Behringer EP2500 which is very flexible since it can drive two 2 ohm loads, or be bridged to put 2.4kw into 4 ohms - in other words it will power any driver you are likely to choose, and its not much more expensive than a plate amp, but then you will have fan noise to deal with!
Here's an alternative thrown in for interest. Two of the Peerless SLS 15" in a large 400L vented box. The excursion isn't that high at 8mm but in a vented box tuned to 20 Hz you can exceed the output of all other options considered, probably with lower distortion than all of them. These drivers would also have more top end, so you could cross them higher than typical sub drivers, and if you wish use them in stereo configuration.
In the midbass you get 116db but below about 23 Hz the max SPL is the same as the single vented Tempest with the rumble filter on.
How much does it cost? I'm not sure but knowing Peerless it would be very reasonable.
Not as sexy, very large and not as much fun to watch the cones moving at high excursion, but it does show that there are many ways to reach a target.
In the midbass you get 116db but below about 23 Hz the max SPL is the same as the single vented Tempest with the rumble filter on.
How much does it cost? I'm not sure but knowing Peerless it would be very reasonable.
Not as sexy, very large and not as much fun to watch the cones moving at high excursion, but it does show that there are many ways to reach a target.
Thanks Paul,
I think I will go with the Tempest after all of that. I'll go with vented but preferably I would like to make it as small as is practical. My only other issue (with vented subs) is the vent chuffing issue. A few years ago I had an 8" small vented sub that hardly went below 60Hz and had rediculous chuffing from the vent, I think it put me off vented boxes a bit
For the ports should I get some ports from Jaycar, make a slot port or something else?
I am also curious why rooms in the US have so much room gain? I didn't realise they were built differently to our houses.
Hmmm part of me still wants to go with the two TC2+'s but it seems like a fair bit of money just to have something that looks cool. Going by your previous graph does that mean that 2 TC's vented would be very similar to one Tempest vented but better sounding, or does the push pull configuration only apply to sealed boxes?
Yeah it was the no fan that drew me towards the A500 as opposed to the higher model Behringers and it was a cheaper price for me than the Jaycar plate amp I was previously going to buy. When I finally build the sub it will (should) be louder than anything I've had/heard (in home) before so once I've heard it it will be easier to decide when and if I need to upgrade. I'm talking about upgrading already
I think I will go with the Tempest after all of that. I'll go with vented but preferably I would like to make it as small as is practical. My only other issue (with vented subs) is the vent chuffing issue. A few years ago I had an 8" small vented sub that hardly went below 60Hz and had rediculous chuffing from the vent, I think it put me off vented boxes a bit
For the ports should I get some ports from Jaycar, make a slot port or something else?I am also curious why rooms in the US have so much room gain? I didn't realise they were built differently to our houses.
Hmmm part of me still wants to go with the two TC2+'s but it seems like a fair bit of money just to have something that looks cool. Going by your previous graph does that mean that 2 TC's vented would be very similar to one Tempest vented but better sounding, or does the push pull configuration only apply to sealed boxes?
Yeah it was the no fan that drew me towards the A500 as opposed to the higher model Behringers and it was a cheaper price for me than the Jaycar plate amp I was previously going to buy. When I finally build the sub it will (should) be louder than anything I've had/heard (in home) before so once I've heard it it will be easier to decide when and if I need to upgrade.
I'm talking about upgrading already 
Only the Shiva's in dual 4 Ohms.
Forget Jaycar ports!
What you want is one of two options:
1. PVC vents - either 90, 100 or 150mm with flares on each end. Flares can be made in a number of ways and for high excursion drivers you will need a fairly large radius. Collo on this forum has actually done some experiments to determine the flare radius you need to avoid chuffing.
2. Rectangular vents (shelf vents) are useful in that they allow you to make vents which are very good aerodynamically since you can taper the ends out to get the kind of flare radius not possible on a circular vent.
As a general rule, aim to keep vent velocity 17m/s - 34m/s. The higher speed is the absolute limit and is a compromise, requiring special attention to aerodynamics, the lower end of the range will require smaller flares which will be easier to construct.
It is some extra effort to get this right, however, at 20 Hz a single vented sub matches two sealed subs. Some would say just spend more money on drivers, but if you have the money, then why not buy a better driver?
Kev, how much extra are those drivers now?
The SLS driver idea is probably not the best considering the size, but I showed it for interest.
As I understand, US houses more commonly have construction that is more solid than a single 10mm plasterboard layer on studs with particleboard flooring on joists. Such construction moves a lot with bass, and the whole room acts as a bass absorber. The result is that room modes are less severe, and room gain helps us out a lot less, if at all. My listening room is 4m wide x 5m deep x 3m ceiling, with double glass internal doors and three fairly normal sized windows. My measurments seem to indicate no room gain at all, and two room modes, the most significant one adding boost @ 35 Hz which is easily tamed with eq. Subjectively, this room mode adds some artificial midbass punch, and makes any speaker that can get down to 40 Hz seem like it has a lower F3 - my TLs or my sealed subs get down to about 23 Hz with the only eq being that which is used to cut out the room mode. Below the effect of this mode, response drops off to the extent that not even 15db of boost @ 20 Hz can get my system flat down that low. I accept this and allow my speakers to go to about 23 Hz without any boost and the room mode actually gives me a little free extension and SPL.
If I were to listen to the comments of many from the US about how room gain would affect in room response, then I'd think the extra extension were due to room gain, and would be confused about why the response drops off just before 20 Hz.
As a general rule, in Australia your anechoic F3 should be considered the same as in room F3, unless you have measurements showing otherwise.
Now if you consider that in many US residences a sealed sub will use room gain to get down to 20 Hz due to room gain, you will understand why vented subs are considered boomy - room gain gives you too much bottom end. In this situation a sealed sub or an EBS is more appropriate.
Might be worth asking John when the dual 4s come in.
What you want is one of two options:
1. PVC vents - either 90, 100 or 150mm with flares on each end. Flares can be made in a number of ways and for high excursion drivers you will need a fairly large radius. Collo on this forum has actually done some experiments to determine the flare radius you need to avoid chuffing.
2. Rectangular vents (shelf vents) are useful in that they allow you to make vents which are very good aerodynamically since you can taper the ends out to get the kind of flare radius not possible on a circular vent.
As a general rule, aim to keep vent velocity 17m/s - 34m/s. The higher speed is the absolute limit and is a compromise, requiring special attention to aerodynamics, the lower end of the range will require smaller flares which will be easier to construct.
It is some extra effort to get this right, however, at 20 Hz a single vented sub matches two sealed subs. Some would say just spend more money on drivers, but if you have the money, then why not buy a better driver?
Kev, how much extra are those drivers now?
The SLS driver idea is probably not the best considering the size, but I showed it for interest.
As I understand, US houses more commonly have construction that is more solid than a single 10mm plasterboard layer on studs with particleboard flooring on joists. Such construction moves a lot with bass, and the whole room acts as a bass absorber. The result is that room modes are less severe, and room gain helps us out a lot less, if at all. My listening room is 4m wide x 5m deep x 3m ceiling, with double glass internal doors and three fairly normal sized windows. My measurments seem to indicate no room gain at all, and two room modes, the most significant one adding boost @ 35 Hz which is easily tamed with eq. Subjectively, this room mode adds some artificial midbass punch, and makes any speaker that can get down to 40 Hz seem like it has a lower F3 - my TLs or my sealed subs get down to about 23 Hz with the only eq being that which is used to cut out the room mode. Below the effect of this mode, response drops off to the extent that not even 15db of boost @ 20 Hz can get my system flat down that low. I accept this and allow my speakers to go to about 23 Hz without any boost and the room mode actually gives me a little free extension and SPL.
If I were to listen to the comments of many from the US about how room gain would affect in room response, then I'd think the extra extension were due to room gain, and would be confused about why the response drops off just before 20 Hz.
As a general rule, in Australia your anechoic F3 should be considered the same as in room F3, unless you have measurements showing otherwise.
Now if you consider that in many US residences a sealed sub will use room gain to get down to 20 Hz due to room gain, you will understand why vented subs are considered boomy - room gain gives you too much bottom end. In this situation a sealed sub or an EBS is more appropriate.
Might be worth asking John when the dual 4s come in.
sriver suggestion
Here's some food for thought-I'm running two Altronics 15s(C3033) in parallel in a 360 litre common chamber box tuned to 35hz using two 6"I.D. x 3.5"L. ports, powered by a Jaycar 350W sub amp.Very adequete in a12 x 6m room.I know this sounds a bit over the top,but it rattles walls and scares the dog quite easily at the quarter volume setting.
If this sounds a bit too insane for you,they can be compound isobaric loaded into a 200 litre reflex box tuned to 30 hz with an f3 of 28hz.Or two Jaycar Venom 10s compound isobaric in 115 litres tuned to 30 hz for an f3 of 27hz.
Both subs are reasonabely priced and are usually on special every few months
Here's some food for thought-I'm running two Altronics 15s(C3033) in parallel in a 360 litre common chamber box tuned to 35hz using two 6"I.D. x 3.5"L. ports, powered by a Jaycar 350W sub amp.Very adequete in a12 x 6m room.I know this sounds a bit over the top,but it rattles walls and scares the dog quite easily at the quarter volume setting.
If this sounds a bit too insane for you,they can be compound isobaric loaded into a 200 litre reflex box tuned to 30 hz with an f3 of 28hz.Or two Jaycar Venom 10s compound isobaric in 115 litres tuned to 30 hz for an f3 of 27hz.
Both subs are reasonabely priced and are usually on special every few months
I don't want to shoot down your post, but I find those Venom drivers to sound terrible. I have used a cheap Jaycar driver for a sub for my dad, got it on special for $50, a 10" driver with 9mm xmax which is quite reasonable considering it is a cheapie used to add some bass to TV speakers. For serious use I would not consider any Jaycar subs. Even if they qualified as hifi, I have yet to find one that offers a good displacement/$ ratio. Those that are cheap are not so cheap when you consider the low xmax.
I didn't want to argue with Paul, but I do want to provide a second opinion.
But now Paul's gone off and done it-
What the..?
As a general rule?
and in Australia??
Room size, listening position, and speaker placement is consideration that must be made. I can not predict room interaction, and it is a decision that Big Kev ! will have to make.
I've built 3 sets of mains and 2 different subwoofers and at one stage or another, I've dragged my speakers into different room or different homes to do comparative listening. (6 rooms, in 4 homes but who's counting? ).
All speakers sounded different in the bass in the different rooms.
Aiming for anechoic 20Hz, using with dual 12" or 15" subwoofers in huge 200L cabinets?
Big Kev's room is 4x4m!
Do you want subwoofers to augment bottom octaves in music, or do just want bragging rights, or to shake off the plaster?
I think you should consider 18" horn loaded subwoofers...
Build this and be done with it, start listening.
But now Paul's gone off and done it-
What the..?
As a general rule?
and in Australia??
Room size, listening position, and speaker placement is consideration that must be made. I can not predict room interaction, and it is a decision that Big Kev ! will have to make.
I've built 3 sets of mains and 2 different subwoofers and at one stage or another, I've dragged my speakers into different room or different homes to do comparative listening. (6 rooms, in 4 homes but who's counting?
). All speakers sounded different in the bass in the different rooms.
Aiming for anechoic 20Hz, using with dual 12" or 15" subwoofers in huge 200L cabinets?
Big Kev's room is 4x4m!
Do you want subwoofers to augment bottom octaves in music, or do just want bragging rights, or to shake off the plaster?
I think you should consider 18" horn loaded subwoofers...
Build this and be done with it, start listening.
I think everything I have said is reasonable and logical given certain parameters.
Yes, what I am saying is that you should not count on room gain being there to lower in room F3 in a typical Australian listening room. In a more solid room there will be more room gain, however, in the absense of measurements, you shouldn't rely on it.
To some that would be over the top, to others that would be inadequate.
tkt, perhaps you are right - an XLS is a good place to start, and from there to get a good idea of just how much SPL he does want.
tktran, In all honesty I am probably never going to need the sort of SPL's I'm aiming for but its more for the fact that they are there if I even decide I do feel like using it. Being able to get the thump in your chest would be nice even if I only ever turn it up that much once in a while. I would rather have something thats a bit of an overkill. That said theres no point being loud if it sounds bad.
I have found though like you said that the room can make a bit of a difference or rather the placement of the sub in the room. My room is mostly square except for a little entrance at the doorway and this is where I find (if I put the sub there) where I get the most room gain, either that or the cupboard. Apart from that there is seemingly very little difference.
At this stage the Peerless drivers seem the way to go ( seems like I've done a full circle here). I've always found it weird modelling the drivers though (the 830500 inparticular), it seems that everyone that builds one has a different way of doing it with very different response graphs. I'm not quite sure what I'm looking for. I wouldn't mind going with a PR approach to save trying to make complicated ports and to keep volume down a bit. Would it be worth going 2 of the drivers and running them in series? At worst senario the amp would see 9.4 Ohm which should be well within its limits. But would the sound suffer from the lack of power? If 2 drivers worked well it may be worth sorting out the vent and instead of a PR just vent two XLS's.
The only other idea I was thinking of was a Peerless 830845 in a large vented box. I know Peerless recommend them for small sealed boxes but in a big 160L box tuned at 20Hz it seems to extend very deep and doesn't require huge ports.
I have found though like you said that the room can make a bit of a difference or rather the placement of the sub in the room. My room is mostly square except for a little entrance at the doorway and this is where I find (if I put the sub there) where I get the most room gain, either that or the cupboard. Apart from that there is seemingly very little difference.
At this stage the Peerless drivers seem the way to go (
seems like I've done a full circle here). I've always found it weird modelling the drivers though (the 830500 inparticular), it seems that everyone that builds one has a different way of doing it with very different response graphs. I'm not quite sure what I'm looking for. I wouldn't mind going with a PR approach to save trying to make complicated ports and to keep volume down a bit. Would it be worth going 2 of the drivers and running them in series? At worst senario the amp would see 9.4 Ohm which should be well within its limits. But would the sound suffer from the lack of power? If 2 drivers worked well it may be worth sorting out the vent and instead of a PR just vent two XLS's. The only other idea I was thinking of was a Peerless 830845 in a large vented box. I know Peerless recommend them for small sealed boxes but in a big 160L box tuned at 20Hz it seems to extend very deep and doesn't require huge ports.
With the XLS you need a PR for a small box, like say 40L, since the required vent would be huge, and would not fit inside the box. You would trade some extension, since for low frequencies, the box size relates to efficiency.
Try this. In WinISD make a vented box. Keep the tuning the same and double the box size. Notice how you get a peak at tuning when the box is too big? This means the box is "too efficient" at the point of tuning. You then make it smaller until the response is relatively flat. If there is a dip between the tuning point and the response higher up then you effectively have an EBS where the box is too big or the tuning is too high. Going back to the previous example, where you have the peak at tuning, keep the box size the same and lower tuning until you get it flat. You can enter the numbers or you can click and drag with the mouse on the box diagram under the Box tab.
A quick sim in WinISD finds that a single XLS with two PRs can get an F3 of 29 Hz in a 40L box. Make it a 60L box and I can get it down to 21 Hz. What is interesting is that the PR boxes have more midbass, however at 20 Hz they are not able to exceed the output of the vented box. The small 40L box hits 110db in the midbass, but is lacking in depth. Keep in mind this is with TWO PRs, which will in themselves cost more than the driver itself, although you could probably get away with just one PR.
160L for one XLS is DEFINATELY too big. You would have to tune it at 10 Hz to avoid the tuning peak, and this reduces max SPL to about 98db in the midbass. Sure you get an F3 around 10 Hz, but the output there is only about 95 db which isn't enough to make any real impact. There isn't much reason to make the box bigger than 70L per driver, except to reduce the size of the vent.
Try this. In WinISD make a vented box. Keep the tuning the same and double the box size. Notice how you get a peak at tuning when the box is too big? This means the box is "too efficient" at the point of tuning. You then make it smaller until the response is relatively flat. If there is a dip between the tuning point and the response higher up then you effectively have an EBS where the box is too big or the tuning is too high. Going back to the previous example, where you have the peak at tuning, keep the box size the same and lower tuning until you get it flat. You can enter the numbers or you can click and drag with the mouse on the box diagram under the Box tab.
A quick sim in WinISD finds that a single XLS with two PRs can get an F3 of 29 Hz in a 40L box. Make it a 60L box and I can get it down to 21 Hz. What is interesting is that the PR boxes have more midbass, however at 20 Hz they are not able to exceed the output of the vented box. The small 40L box hits 110db in the midbass, but is lacking in depth. Keep in mind this is with TWO PRs, which will in themselves cost more than the driver itself, although you could probably get away with just one PR.
160L for one XLS is DEFINATELY too big. You would have to tune it at 10 Hz to avoid the tuning peak, and this reduces max SPL to about 98db in the midbass. Sure you get an F3 around 10 Hz, but the output there is only about 95 db which isn't enough to make any real impact. There isn't much reason to make the box bigger than 70L per driver, except to reduce the size of the vent.
Back again
I've finally narrowed down my choices and I'm pretty sure I will go with the Peerless 830500 in a vented box. I looked at a few PR designs with WinISD but it seems that unless you use 2 there are no real advantages aside from ease of construction and slight volume reduction than going ported. So its a bit extra to spend.
A vented box of 68L tuned to 19Hz seems to be about what I'm seeking which gives (theoretically) 103dB @ 20Hz peaking to about 108 @ 50Hz. One of my concerns is the dip in impedance - its above 8Ohms from 25-55Hz but outside of that range can dip to 4Ohms. I think if I'm careful everything should be fine but I really don't want it cutting out all the time.
Another other idea was to use 2 of the drivers in a 150L box tuned to 20Hz which seems to give very similar results to above but with an extra 6dB across the board. Also I could run them in series and wouldn't have any impedance issues and it should hopefully satisfy my SPL needs (if not I need to start saving!).
Is there any advantage to going straight for 2 drivers in the one box? If I made another one later (twin 70L subs), I would only get an extra 3dB right? Is there something to do with having both drivers together which gives the extra SPL? At the price the 830500's are I'm thinking it may be the way to go, but if one will be enough then I could always upgrade I suppose - but I would prefer not to build a whole new box.
With the port I'm thinking of using 90mm stormwater pipe (because I have easy access to it), is it just a simple case of putting in a length of it that fits anywhere and flaring the ends? Or should I be mounting it in a specific spot?
Cheers
Btw, thanks Paul for all your help via email
I've finally narrowed down my choices and I'm pretty sure I will go with the Peerless 830500 in a vented box. I looked at a few PR designs with WinISD but it seems that unless you use 2 there are no real advantages aside from ease of construction and slight volume reduction than going ported. So its a bit extra to spend.
A vented box of 68L tuned to 19Hz seems to be about what I'm seeking which gives (theoretically) 103dB @ 20Hz peaking to about 108 @ 50Hz. One of my concerns is the dip in impedance - its above 8Ohms from 25-55Hz but outside of that range can dip to 4Ohms. I think if I'm careful everything should be fine but I really don't want it cutting out all the time.
Another other idea was to use 2 of the drivers in a 150L box tuned to 20Hz which seems to give very similar results to above but with an extra 6dB across the board. Also I could run them in series and wouldn't have any impedance issues and it should hopefully satisfy my SPL needs (if not I need to start saving!).
Is there any advantage to going straight for 2 drivers in the one box? If I made another one later (twin 70L subs), I would only get an extra 3dB right? Is there something to do with having both drivers together which gives the extra SPL? At the price the 830500's are I'm thinking it may be the way to go, but if one will be enough then I could always upgrade I suppose - but I would prefer not to build a whole new box.
With the port I'm thinking of using 90mm stormwater pipe (because I have easy access to it), is it just a simple case of putting in a length of it that fits anywhere and flaring the ends? Or should I be mounting it in a specific spot?
Cheers
Btw, thanks Paul for all your help via email
Regarding impedance, it will not be a problem with one channel to each driver. It is only if you bridge the amp to power one driver that the amp will effectively see the impedance drop down to 2 ohms. Either drive each sub with a channel, or bridge and wire the drivers in series - hence you are then connecting a 16 ohm load which will drop down to 8 ohms which is safe. Note that when you bridge and connect an 8 ohm load, the amp effectively sees a 4 ohm load.
If you use one driver then just use one channel of the amp, or if you bridge into one XLS be careful.
Two drivers in one box means better coupling. Two subs can in theory get 6db more output than one, but this is less likely to occur the further apart they are. 3db comes from twice the input power and 3db comes from twice the SD.
Two drivers in one box also allows push pull for lower distortion. According to Linkwitz, for push pull, one should have both drivers on the same baffle.
100mm is better and easy to get - just go to Bunnings, it is cheap. 90mm is a compromise and should only be used where you can't possibly fit in a 100mm vent due to the required length.
To choose a vent that will work without chuffing, you must juggle the following:
- vent diameter
- vent tuning
- vent flare radius
- box size
The vent velocity that won't chuff depends on the vent diameter and flare radius. Lower tuning means longer vent. Larger diameter means longer vent. Smaller diameter means larger vent flare and higher vent velocity. It's not complicated, its just a juggling match.
If you use one driver then just use one channel of the amp, or if you bridge into one XLS be careful.
Two drivers in one box means better coupling. Two subs can in theory get 6db more output than one, but this is less likely to occur the further apart they are. 3db comes from twice the input power and 3db comes from twice the SD.
Two drivers in one box also allows push pull for lower distortion. According to Linkwitz, for push pull, one should have both drivers on the same baffle.
100mm is better and easy to get - just go to Bunnings, it is cheap. 90mm is a compromise and should only be used where you can't possibly fit in a 100mm vent due to the required length.
To choose a vent that will work without chuffing, you must juggle the following:
- vent diameter
- vent tuning
- vent flare radius
- box size
The vent velocity that won't chuff depends on the vent diameter and flare radius. Lower tuning means longer vent. Larger diameter means longer vent. Smaller diameter means larger vent flare and higher vent velocity. It's not complicated, its just a juggling match.
Big Kev ! said:Back again
I've finally narrowed down my choices and I'm pretty sure I will go with the Peerless 830500 in a vented box. I looked at a few PR designs with WinISD but it seems that unless you use 2 there are no real advantages aside from ease of construction and slight volume reduction than going ported. So its a bit extra to spend.
Passive radiators don't unload beneath tuning. BIG advantage. Nobody likes an acoustic short circuit, except those dipole types
Interesting. If this is true, then it is not shown in simulations in WinISD. Assuming it shows what actually happens, I have not found any advantage here over a vented box. I note that in the old Adire Shiva PR applications paper, it is said that some driver protection is provided below tuning and that the PR does not fully unload.
I'd be interested to see more information on this if anyone knows of any. WinISD shows the same excursion below tuning as a vented box, given the same tuning point and box size.
Logic would suggest that the PR box will give a level of protection somewhere in between a sealed and vented box. Below tuning the difference to a sealed box is that the PR allows less pressure build up to restrict driver excursion. If the PR reaches its Xmech, the box will then behave more like a sealed box. However, I'd expect the driver will reach xmax before this occurs.
Does WinISD fail to model what actually occurs with excrusion in PR boxes?
As a result, the sub will still need a highpass filter (rumble filter).
I'd be interested to see more information on this if anyone knows of any. WinISD shows the same excursion below tuning as a vented box, given the same tuning point and box size.
Logic would suggest that the PR box will give a level of protection somewhere in between a sealed and vented box. Below tuning the difference to a sealed box is that the PR allows less pressure build up to restrict driver excursion. If the PR reaches its Xmech, the box will then behave more like a sealed box. However, I'd expect the driver will reach xmax before this occurs.
Does WinISD fail to model what actually occurs with excrusion in PR boxes?
As a result, the sub will still need a highpass filter (rumble filter).
Going the PR approach is still an option, and the smaller box size in the long run would be very useful. I just figured that if I'm buying 2 passive radiators I may as well just buy another driver (for the price) and build something big but ultimatly a lot better. If I could get away with one PR it may actually be not so bad an idea - no dealing with ports, still not super expensive, and later I can build another sub with a PR if I feel the need for more, or just get another driver and go ported... see how it goes. When you say it doesnt unload below the tuning you mean it doesnt over-exurt it self?? The reason I thought 2 PR would be a lot better than one was because 1 (from memory) reaches xmax more quickly. What do you think?
This will be of interest:
http://www.bamberglab.com/xls.shtml
You will find an answer there.
In general, a 12" driver is used with dual 15" PRs. The driver in front, PRs on the sides. If you use just one XLS 12" PR then you should use it probably with the 10" XLS driver. The conventional 12 plus 2x15PR makes sense due to the forces involved, and due to using less of the excursion of the PRs, which will mean they are more linear. Suspension linearity of the PR will become worse with higher excursion, and will affect distortion performance.
The XLS has a fairly low xmax, but a high Xmech so there will be less problems here.
But still, it only costs $10 for a length of PVC! Two PRs will cost more than a second driver.
http://www.bamberglab.com/xls.shtml
You will find an answer there.
In general, a 12" driver is used with dual 15" PRs. The driver in front, PRs on the sides. If you use just one XLS 12" PR then you should use it probably with the 10" XLS driver. The conventional 12 plus 2x15PR makes sense due to the forces involved, and due to using less of the excursion of the PRs, which will mean they are more linear. Suspension linearity of the PR will become worse with higher excursion, and will affect distortion performance.
The XLS has a fairly low xmax, but a high Xmech so there will be less problems here.
But still, it only costs $10 for a length of PVC! Two PRs will cost more than a second driver.
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