Hello, fellows!
I have built a subwoofer box with a 12" unit, and it is fed 140w through 4ohm.
The unit has a double voice coil allowing for either 2, 4 or 8 ohm.
It plays very well. The box is quite effective, and the only downside is, the unit reaches maximum linear excursion at around 110w.
Now, I simply want to get the most of those 140w, and want to confirm my theory:
Adding an extra, identical box and unit (power supply remains exactly the same to make it more simple) and running both Subwoofers in 8ohm each, so I end up with the same (theoretical) total load as it currently is, should yield, not only more headroom, but also a slight increase in volume because of increased surface area.
Of course the power will now be divided by two, but that's also partly the goal, since that should result in less linear excursion...
Hope it makes sense so far...
This in turn should allow me to play safely at higher levels, without risking the units shaking themselves to death.
Or am I way off in fantasy land here?
Thanks in advance and good day to all
I have built a subwoofer box with a 12" unit, and it is fed 140w through 4ohm.
The unit has a double voice coil allowing for either 2, 4 or 8 ohm.
It plays very well. The box is quite effective, and the only downside is, the unit reaches maximum linear excursion at around 110w.
Now, I simply want to get the most of those 140w, and want to confirm my theory:
Adding an extra, identical box and unit (power supply remains exactly the same to make it more simple) and running both Subwoofers in 8ohm each, so I end up with the same (theoretical) total load as it currently is, should yield, not only more headroom, but also a slight increase in volume because of increased surface area.
Of course the power will now be divided by two, but that's also partly the goal, since that should result in less linear excursion...
Hope it makes sense so far...
This in turn should allow me to play safely at higher levels, without risking the units shaking themselves to death.
Or am I way off in fantasy land here?
Thanks in advance and good day to all
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For the most part you're right. Two cabinets is a theoretical +3, double the power handling is another +3. 6db more output ability total if you ignore the fact you'll be limited by your amplifier.
With 2 of these drivers, your impedance options become 1ohm, 4ohm, and 16ohm from wiring the 4 coils in parallel, series-parallel, and series.
So there is no way to keep the same impedance if you add another driver to the mix.
This is the only part that does not make sense. If you have a dual voice coil driver, and if each coil is 4ohm (for example), your impedance options for a single driver are 2 and 8ohm from parallel or series wiring respectively.
With 2 of these drivers, your impedance options become 1ohm, 4ohm, and 16ohm from wiring the 4 coils in parallel, series-parallel, and series.
So there is no way to keep the same impedance if you add another driver to the mix.
Another thing I am curious about:
Does it make a difference if you,
a) wire the 2 4ohm voice coils in series, making 8ohm. And then wire those 2 8ohm subs in parallel making 4ohm, or,
b) wire the 2 4ohm voice coils in parallel making 2ohm. And then wire those 2 2ohm subs in series, making 4ohm?
I bet not
Does it make a difference if you,
a) wire the 2 4ohm voice coils in series, making 8ohm. And then wire those 2 8ohm subs in parallel making 4ohm, or,
b) wire the 2 4ohm voice coils in parallel making 2ohm. And then wire those 2 2ohm subs in series, making 4ohm?
I bet not
Not that this is all that important, but with dual coil drivers, you can run just one coil and short the other with a resistor. It changes the parameters of the driver some and a design was proposed that was based on this and a potentiometer to change the box Q, a variable Q tuning approach.
If I had two dual coil drivers that each had 4 ohm coils, I'd wire each driver in series for an 8 ohm load and then wire the two cabinets in parallel for a 4 ohm load. Test the DC resistance with a multimeter however to be sure the DC re is not really really low. I've occasionally seen that and you can end up with a amp shutting down or even being damaged. Better yet is to measure the actual impedance, but that is often not possible for the average person with average available tools, so DC resistance at least helps you gain some insight.
Are you planning to run the two drivers on the same amp or separate amps? I may have misunderstood your question. I assumed same amp with my comment above. If its the two different amps, I'd need to know what you are doing now to better understand.
It's worth noting that while you theoretically gain 3db's for doubling the woofers and 3db's for doubling the power, lots of factors can come into play that won't allow that to be what you actually gain. The first issue is that they must be perfectly collocated. The second is that they must be identical drivers and identical amplifiers to meet that criteria. The third is they must load the room identically. I actually have two identical subwoofers run off a 2 channel amplifier (each channel is 1500 watts RMS into 4 ohms) and when setting up and tuning the system, I had an opportunity to test this. The subs are stacked on top of each other, so while they are co-located, their size means they aren't actually occupying the identical space. At higher frequencies they are more than 1/4 wavelength apart, but once below about 80hz they are within a quarter wavelength and should generally couple as one subwoofer. What I found was that the response was only on average 3-4 db's louder than with just one sub operating. At some nulls it was quieter, the null was made deeper, and at other frequencies the increase was far greater, as much as 8db's. This suggested to me that their height difference was enough to load the room differently. I would guess a single subwoofer with double the displacement and power of the individual subs would not have measured in that way, but there is no way for me to measure and prove that.
None the less, doubling the subwoofers carries lots of advantages. First is that having two subs reduces the burden for the one sub and so should lower distortion and clean up the bass somewhat. This is because all subwoofers, for the most part, produce lower distortion at quieter levels, so if the sub is working less hard, so to speak, then there will be less distortion. The other is that if you don't co-locate the subs, but actually optimally place them, you can reduce the room mode abnormalities that plague bass in a normal sized room. Again, while I have two collocated subs, I actually have 4 total subs in my system placed at different locations, and this not only reduced seat to seat variation, but at the optimal seating location, it allowed me to use minimal EQ and reduce some nulls quite a bit.
My own experience with multiple subs is that in a large enough space and spaced apart far enough, you gain nothing in output, but you still gain quite a bit in smoother bass. That then becomes a choice you have to make, do you want to have one optimal seat and maximum bass output, or many good seats, but less output.
If I had two dual coil drivers that each had 4 ohm coils, I'd wire each driver in series for an 8 ohm load and then wire the two cabinets in parallel for a 4 ohm load. Test the DC resistance with a multimeter however to be sure the DC re is not really really low. I've occasionally seen that and you can end up with a amp shutting down or even being damaged. Better yet is to measure the actual impedance, but that is often not possible for the average person with average available tools, so DC resistance at least helps you gain some insight.
Are you planning to run the two drivers on the same amp or separate amps? I may have misunderstood your question. I assumed same amp with my comment above. If its the two different amps, I'd need to know what you are doing now to better understand.
It's worth noting that while you theoretically gain 3db's for doubling the woofers and 3db's for doubling the power, lots of factors can come into play that won't allow that to be what you actually gain. The first issue is that they must be perfectly collocated. The second is that they must be identical drivers and identical amplifiers to meet that criteria. The third is they must load the room identically. I actually have two identical subwoofers run off a 2 channel amplifier (each channel is 1500 watts RMS into 4 ohms) and when setting up and tuning the system, I had an opportunity to test this. The subs are stacked on top of each other, so while they are co-located, their size means they aren't actually occupying the identical space. At higher frequencies they are more than 1/4 wavelength apart, but once below about 80hz they are within a quarter wavelength and should generally couple as one subwoofer. What I found was that the response was only on average 3-4 db's louder than with just one sub operating. At some nulls it was quieter, the null was made deeper, and at other frequencies the increase was far greater, as much as 8db's. This suggested to me that their height difference was enough to load the room differently. I would guess a single subwoofer with double the displacement and power of the individual subs would not have measured in that way, but there is no way for me to measure and prove that.
None the less, doubling the subwoofers carries lots of advantages. First is that having two subs reduces the burden for the one sub and so should lower distortion and clean up the bass somewhat. This is because all subwoofers, for the most part, produce lower distortion at quieter levels, so if the sub is working less hard, so to speak, then there will be less distortion. The other is that if you don't co-locate the subs, but actually optimally place them, you can reduce the room mode abnormalities that plague bass in a normal sized room. Again, while I have two collocated subs, I actually have 4 total subs in my system placed at different locations, and this not only reduced seat to seat variation, but at the optimal seating location, it allowed me to use minimal EQ and reduce some nulls quite a bit.
My own experience with multiple subs is that in a large enough space and spaced apart far enough, you gain nothing in output, but you still gain quite a bit in smoother bass. That then becomes a choice you have to make, do you want to have one optimal seat and maximum bass output, or many good seats, but less output.
Alright, thank you, that cleared up a lot for me :-D
I am not planning on doubling the amp power for now, I want to see how much one can do.
At some point, the natural desire for bigger and better will of course arise, and now I am better prepared for that
I am lucky enough to have a perfectly tiny listening room as my little music cave (about 9 square meters) and I find that quite forgiving when rying to optimise my sound setup.
The second sub will be stacked on top of the current one with some kind of soft pads between them.
And you mentioned shorting the unused voice coil with a resistor? On the current subwoofer I actually just wired it to one of the two terminals and left the other one as is, expecting that was adequate.
Perhaps I should get back to the drawing board on that one.
Cheers
I am not planning on doubling the amp power for now, I want to see how much one can do.
At some point, the natural desire for bigger and better will of course arise, and now I am better prepared for that
I am lucky enough to have a perfectly tiny listening room as my little music cave (about 9 square meters) and I find that quite forgiving when rying to optimise my sound setup.
The second sub will be stacked on top of the current one with some kind of soft pads between them.
And you mentioned shorting the unused voice coil with a resistor? On the current subwoofer I actually just wired it to one of the two terminals and left the other one as is, expecting that was adequate.
Perhaps I should get back to the drawing board on that one.
Cheers
This works well only with very low Qts drivers, which I presume is not the case here.
I wouldn't know, he didn't specify. Certainly this makes sense since a high Qts driver would only get higher with a shorted coil.
Sounds like the OP needs to be careful. Driving two enclosures from one amplifier may not be ideal. If each coil is 4 ohm, then wiring them in series and then the two in parallel should give a 4 ohm nominal load. You could also wire them in parallel and then each woofer together in series, also would give a 4 ohm nominal load. None the less, I think it increases the risk that the low power amplifier could be damaged if the speakers impedance dips well below 4 ohms. A lot of these amps are chip based and don't like really low loads, some just go into protection, some let out the smoke, so to speak. I'm sure like many on this forum, I've blown a good number of cheap sub amps in my day.
Great point, pjpoes
To be honest, my current sub amp is the cheapest bit of my setup (and oldest).
If it gives in, I will have an excuse to finally upgrade it
Although it was always clean and cool even at 2ohm in a previous configuration, so it should survive on 4ohm.
Never blew a sub amp actually.
Killed a system, I have, though, when I was four years old, by sitting on the pickup, it didn't respond well to that, and it was so bad, Boney M decided to stop playing :-D
To be honest, my current sub amp is the cheapest bit of my setup (and oldest).
If it gives in, I will have an excuse to finally upgrade it
Although it was always clean and cool even at 2ohm in a previous configuration, so it should survive on 4ohm.
Never blew a sub amp actually.
Killed a system, I have, though, when I was four years old, by sitting on the pickup, it didn't respond well to that, and it was so bad, Boney M decided to stop playing :-D
I've gone through more amplifiers in my life than I care to even remember. I have a blown amplifier I made sitting next to me. Lightning hit the house and took it out.
I've gone through a few of those Dayton 500 watt and 1000 watt amps, they weren't particularly reliable. I started with 4, I now have one left, the rest died, some more than once.
I once had the bright idea of taking a fan cooled amp, unhooking the fan ,and continuing to use it, not so smart.
I'm surprised the amp handled 2 ohms ok, that is a low load for the typical plate amps, but who knows. There certainly are some chips that can do that, and if its older, many plate amps were of discrete design and would handle it, but be somewhat current limited.
Any plate amp should handle 4 ohms best, they typically were optimized around a 4 ohm load. They give the most power at that load. Most of them put out less power at 2 ohms due to power supply limitations and less at 8 ohms due to voltage limitations.
Experimentalist, if I knew exactly what you had, which plate amp, which driver, I could help you out much more. I mean, it is possible that a new 12" driver, new amplifier, and better box would give you more output than two of these 15's in two boxes. It just all depends. Most of the cheap 15" drivers that I see at MCM or Parts Express are really bad for subwoofers, too little excursion and too high Q. They aren't good subwoofers.
KRK V12S 250W Subwoofer Amp
This is a heck of an amplifier for the money. That 12" driver is pretty good for 50bucks too. You could build a series sub with that matchup and it might be a better use of $200 than what you are trying to do. Not sure your budget or what you are trying to accomplish, but I hate to see you go down a road that just doesn't benefit you.
I've gone through a few of those Dayton 500 watt and 1000 watt amps, they weren't particularly reliable. I started with 4, I now have one left, the rest died, some more than once.
I once had the bright idea of taking a fan cooled amp, unhooking the fan ,and continuing to use it, not so smart.
I'm surprised the amp handled 2 ohms ok, that is a low load for the typical plate amps, but who knows. There certainly are some chips that can do that, and if its older, many plate amps were of discrete design and would handle it, but be somewhat current limited.
Any plate amp should handle 4 ohms best, they typically were optimized around a 4 ohm load. They give the most power at that load. Most of them put out less power at 2 ohms due to power supply limitations and less at 8 ohms due to voltage limitations.
Experimentalist, if I knew exactly what you had, which plate amp, which driver, I could help you out much more. I mean, it is possible that a new 12" driver, new amplifier, and better box would give you more output than two of these 15's in two boxes. It just all depends. Most of the cheap 15" drivers that I see at MCM or Parts Express are really bad for subwoofers, too little excursion and too high Q. They aren't good subwoofers.
KRK V12S 250W Subwoofer Amp
This is a heck of an amplifier for the money. That 12" driver is pretty good for 50bucks too. You could build a series sub with that matchup and it might be a better use of $200 than what you are trying to do. Not sure your budget or what you are trying to accomplish, but I hate to see you go down a road that just doesn't benefit you.
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