Any difference putting two of the same sub drivers into one, say 100 litre sealed box as apposed to each driver in its own 50 litre box? Woodwork/bracing issues aside.
Trying to compare what effect it might have on excursion limits, SPL ect in Winisd but you cant model the output of 2 'seperate' boxes.
Trying to compare what effect it might have on excursion limits, SPL ect in Winisd but you cant model the output of 2 'seperate' boxes.
/sreten.
Acoustic performance will be identical between the two, as will the load on the amplifier. The benefits will be it's easier to make a stiffer/deader small box, and placement options are more which is beneficial as sreten pointed out. Downsides none that I can think of, other than possible form-factor. Unless you put them so far apart that the acoustic coupling does not happen.
If you happened to be looking a ported boxes, going to a single box might give you an extra choice of ports
If your port velocity was excessive with the pair of boxes, you would normally have to go to a larger port, or a pair of ports. This might be more than you actually need, resulting in overly long ports.
With a single box, you have twice the volume, so the port is roughly half the length. You have two drivers, so you need roughly twice the area on the port, which makes it twice as long - getting you back to the original length, only larger diameter.
This might not seem any advantage, but you might end up with a single 6inch port instead of a 4incher in each of the separate boxes.
If your port velocity was excessive with the pair of boxes, you would normally have to go to a larger port, or a pair of ports. This might be more than you actually need, resulting in overly long ports.
With a single box, you have twice the volume, so the port is roughly half the length. You have two drivers, so you need roughly twice the area on the port, which makes it twice as long - getting you back to the original length, only larger diameter.
This might not seem any advantage, but you might end up with a single 6inch port instead of a 4incher in each of the separate boxes.
"Push push", now this is something Im seeing mentioned more and more. It isnt outlined in Vance Dickason's book. (is it isobarik?) Trying to find out more about it. Would this simply be the drivers at each end of a 100L sonotube, one facing in and one out, both wired in phase?
Are the any dissadvantages to it over one single sealed box? Does the basket frame become an issue of crossed at 80Hz?
Are the any dissadvantages to it over one single sealed box? Does the basket frame become an issue of crossed at 80Hz?
Yes there may be some confusion with push push mounting, but basically you are making a bipole(if woofers were directional).
The woofer on the front of the box moves out(with respect to the box) with a positive signal, and the woofer on the back of the box also moves out with a positive signal.... The advantage is in vibration cancelation... instead of the inertia of a single cone vibrating the box, the net inertia is zero(since the two cones inertial forces cancel). The sound pressure remains the same.
The woofer on the front of the box moves out(with respect to the box) with a positive signal, and the woofer on the back of the box also moves out with a positive signal.... The advantage is in vibration cancelation... instead of the inertia of a single cone vibrating the box, the net inertia is zero(since the two cones inertial forces cancel). The sound pressure remains the same.
Push-Push the SPL is the same as two drivers mounted
A. In a single box
B. in two seperate boxes of equvilant volume(when the volumes of the two seperate boxes are added together) to the single box(assuming they're placed close enough to benifit from mutual coupling)
C. In a single box, both on the same side of the box
Basically push push is just making a single box with 2 subs, mounting one on the front of the box, and mounting one on the rear of the box... you wire the subs up the exact same way, and voila the box doesnt shake.
A. In a single box
B. in two seperate boxes of equvilant volume(when the volumes of the two seperate boxes are added together) to the single box(assuming they're placed close enough to benifit from mutual coupling)
C. In a single box, both on the same side of the box
Basically push push is just making a single box with 2 subs, mounting one on the front of the box, and mounting one on the rear of the box... you wire the subs up the exact same way, and voila the box doesnt shake.
A second sub driven by the same amount of power gives +6db, not 3db as you are doubling the cone area and the power. If you make 2 subs separate and in different locations in the room, you may not get 6db more from the second sub - put them together and you can be sure they will couple.
There are quite a number of issues to balance. Two drivers in one box has some advantages:
* +6db from the second driver is more certain due to close coupling
* cancellation of forces with back to back mounting is possible
* push pull is also possible to reduce distortion
* can be more space efficient, using the same footprint
Separate subs also has advantages:
* may be less intrusive and visually smaller
* flexibility with placement to work with room modes better
* stereo subs are possible, useful if you cross very high > 80 Hz
Either way is equally viable, it just depends on your particular preferences and situation.
It can get confusing ... but let me see if I can make things clear.
With isobarik, one driver radiates to the outside of the box. There are a number of ways to do it, but they all have this in common. The other one merely works at compressing and decompressing the air inside the box, thus making the first driver stronger. The result is that the net box volume is halved.
Push push - or back to back mounting. Two drivers are on opposite sides of the box. They each move outward at the same time so they don't cancel each other. As their mechanical forces are in opposite directions, the net forces are all cancelled. The result is less box vibration. Take a box like this and turn off the power to one of the drivers. You will lose 6db of output and the box will vibrate quite a bit more. You may be surprised.
Push pull. You can do this still with the drivers on opposite sides of the box to get the vibration cancellation. But it has a twist. Face one of the drivers to the inside of the box, so its magnet sticks out. If you leave it like that, they will cancel each other out like a speaker with no box. So what you have to do is reverse the polarity of the wiring on that second driver so that both cones move out to the outside air space at the same time. What's the point of this? It cancels out some 2nd order harmonic distortion, making it sound slightly tighter. This is a mechanical means of doing a similar job to a shorting ring, except that inductance isn't affected (correct me if I'm wrong on that one.)
I had two of the AV12 each in a 70L sealed box. I decided to put them in one 70L box, back to back and push pull. I noticed vibration go down with push pull, and the bass a bit tighter with push pull. I have had them stereo mode either side of the room. I like it best this way.
There are quite a number of issues to balance. Two drivers in one box has some advantages:
* +6db from the second driver is more certain due to close coupling
* cancellation of forces with back to back mounting is possible
* push pull is also possible to reduce distortion
* can be more space efficient, using the same footprint
Separate subs also has advantages:
* may be less intrusive and visually smaller
* flexibility with placement to work with room modes better
* stereo subs are possible, useful if you cross very high > 80 Hz
Either way is equally viable, it just depends on your particular preferences and situation.
It can get confusing ... but let me see if I can make things clear.
With isobarik, one driver radiates to the outside of the box. There are a number of ways to do it, but they all have this in common. The other one merely works at compressing and decompressing the air inside the box, thus making the first driver stronger. The result is that the net box volume is halved.
Push push - or back to back mounting. Two drivers are on opposite sides of the box. They each move outward at the same time so they don't cancel each other. As their mechanical forces are in opposite directions, the net forces are all cancelled. The result is less box vibration. Take a box like this and turn off the power to one of the drivers. You will lose 6db of output and the box will vibrate quite a bit more. You may be surprised.
Push pull. You can do this still with the drivers on opposite sides of the box to get the vibration cancellation. But it has a twist. Face one of the drivers to the inside of the box, so its magnet sticks out. If you leave it like that, they will cancel each other out like a speaker with no box. So what you have to do is reverse the polarity of the wiring on that second driver so that both cones move out to the outside air space at the same time. What's the point of this? It cancels out some 2nd order harmonic distortion, making it sound slightly tighter. This is a mechanical means of doing a similar job to a shorting ring, except that inductance isn't affected (correct me if I'm wrong on that one.)
I had two of the AV12 each in a 70L sealed box. I decided to put them in one 70L box, back to back and push pull. I noticed vibration go down with push pull, and the bass a bit tighter with push pull. I have had them stereo mode either side of the room. I like it best this way.
Paul,
I'm pretty certian you only get +3db from using two drivers with the same power... The +6db from mutual coupling is in maximum output as you get +3db for doubling cone area and +3db from doubling power handling....
now if you wire up the subs in parrallel you get +6db with the same input voltage due to +3db efficiency and a double in the current drawn(also double in the power to the subs)
I'm pretty certian you only get +3db from using two drivers with the same power... The +6db from mutual coupling is in maximum output as you get +3db for doubling cone area and +3db from doubling power handling....
now if you wire up the subs in parrallel you get +6db with the same input voltage due to +3db efficiency and a double in the current drawn(also double in the power to the subs)
I need to clarify.
Doubling cone area gives you 3db gain in efficiency, assuming identical driver and response
Doubling power by providing the second driver with the same amount of power gives another 3db increased output.
As a result, you get 6db increase in max SPL by adding a second active sub where it receives the same power as the first sub.
Now if you use the same amplifier but add another driver, it is not so simple, because then you will have a different impedance, and will be at the mercy of how much power that amp can put into the impedance that results from your configuration.
This depends on the amplifier in question. I prefer to deal with db and watts here, as you can easily find in the specs how much power you will get into a certain impedance load.
Doubling cone area gives you 3db gain in efficiency, assuming identical driver and response
Doubling power by providing the second driver with the same amount of power gives another 3db increased output.
As a result, you get 6db increase in max SPL by adding a second active sub where it receives the same power as the first sub.
Now if you use the same amplifier but add another driver, it is not so simple, because then you will have a different impedance, and will be at the mercy of how much power that amp can put into the impedance that results from your configuration.
This depends on the amplifier in question. I prefer to deal with db and watts here, as you can easily find in the specs how much power you will get into a certain impedance load.
I registered an account on this forum so that I could necro this ancient thread and say THANK YOU for this simple explanation of mutual coupling with subwoofers.
I keep reading vague interpretations of how you "magically" get +3 dB instead of the commonly known +3 dB from doubling power. This makes sense (assuming it's accurate). There's a formula somewhere that is getting a doubling in power AND speaker volume, and that volume accounts for the extra 3. Bless you.
So from this, I would take it that even without the coupling part (placing subwoofers next to each other) you're getting the +6 dB no matter where you place two subwoofers, but placing them together guarantees that you're ONLY getting constructive interference without any destructive wave interference?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.