Box Rise?

[Gearstix]

Can somebody explain to me box rise? I'm trying to find an amp for my two Mach 5 SPL-12s, which are dual twos.

How would box rise affect me? Would I be able to buy an amp that does say 3200W @ 1 ohm, and wire to 1/2ohm, and box rise would put it close to 1 ohm?

[n-stereo]

Can somebody explain to me box rise? I'm trying to find an amp for my two Mach 5 SPL-12s, which are dual twos.

How would box rise affect me? Would I be able to buy an amp that does say 3200W @ 1 ohm, and wire to 1/2ohm, and box rise would put it close to 1 ohm?

unfortunately you can't assume impedance rise . you'll have to wire an amp ( most any amp) to your sub and box setup . measure the amperage with a ac amp meter and measure the ac voltage at the same time to determine your impedance rise . then and only then will you know your impedance rise which will then help you purchase an amp designed for that load and the power you want .

Edited September 28, 2008 by n-stereo

[Nightshade]

unfortunately you can't assume impedance rise . you'll have to wire an amp ( most any amp) to your sub and box setup . measure the amperage with a ac amp meter and measure the ac voltage at the same time to determine your impedance rise . then and only then will you know your impedance rise which will then help you purchase an amp designed for that load and the power you want .

Like he said after finding ac current of the amp and then finding ac voltage of the amp both on the output side you will divide the ac voltage by the ac current and that will tell you what your box rise is. For example, my setup sets at 1.2 ohms nominal and when rise is calculated it is 3.9 ohms reactive. The reactive load is the actual load the amplifier sees and also determines what kind of power it will make. So if you have an amp that makes 3K at 1 ohms and your box rise is in the neighborhood of mine your amp isn't going to make nearly that kind of power, but in my situation I have a 3K amp and with my rise I'm still making 1900 watts at almost 4 ohms. That is some serious power to be made at that impedence. That's why in my situation I plan on doing an amp per woofer in the future to help some with the rise. If I split the rise between two amps then each amp will see less rise then if the subs were wired to one large amp. In my case I will have each amp wired to .5 ohms and if they carry the same trend as when wired to 1 ohms on the large amp each amp should see around 2 ohms after box rise. The amps I plan on getting run about 1800 watts at 1 ohm, so in the area of 2200 or more at .5 ohms. They will more than likely be putting out 1600 watts or possibly more at 2 ohms. This will effectivly give me an increase of 1300 watts, which is adding more than half the power I had before. This should also result in a gain in spl. It might not be too great, but I would expect around a db or a little more. Other variables also may affect it such as the efficiency of the woofer. In my case I do believe that my woofers take more power to move than most, so I may see a slightly larger gain then some because the woofer is in the range of power that it opperates best in. Another way to help out with the box rise is to put the woofer in a smalle enclosure. By cutting down the box size it will also help the rise at the amp. You could also try stepping up port area to get the rise down some, but this can also result in a smaller box with a frequency that the woofer isn't comfortable playing in. Most people never even take the time to find out what their amps are actually putting out. I've heard a lot of guys that have a Sundown 3000D say well I'm putting 3K to each woofer and they're more than likely wrong unless they've clamped the amp and measured the outputs and figured for rise. Don't assume that if you buy a 2K amp that is rated to do 2K at 1 ohm that it will do that in your setup. It will more than likely do that 2K, but only if your reactive load is at that 1 ohm that it is designed to put out the rated power at. A friend of mine has 16 Sound Stream PCA2000D's on 8 solo X 18's. He is amp shopping for next year because the most he gets out of a pair of these amps strapped is 1600 watts. They have the potential to do 4000 watts but in his setup they are very inefficient. To make a long story short they only way you will know what your box rise is, is to test for it. It's also good to do this to know how much power you are actually putting out so you know where you are able to get gains at by adding more power if necessary. Sorry about my short novel here, but hopefully it helps you understand a little better.

[littleitaly1990]

Is there anyways to counter the effects of box rise? Without getting a different amp?

[Nightshade]

Is there anyways to counter the effects of box rise? Without getting a different amp?

I burried one solution in there and it is to decrease the internal airspace of the box. In a smaller box the rise isn't as much as a larger one, but you will also lose efficiency of the sub in a smaller enclosure so you better have the power to compensate for the loss. I've also been told that tuning the box to a higher frequency will also help bring the rise down some, but that may go hand in hand with shrinking the airspace down I'm not really sure.

[littleitaly1990]

I burried one solution in there and it is to decrease the internal airspace of the box. In a smaller box the rise isn't as much as a larger one, but you will also lose efficiency of the sub in a smaller enclosure so you better have the power to compensate for the loss. I've also been told that tuning the box to a higher frequency will also help bring the rise down some, but that may go hand in hand with shrinking the airspace down I'm not really sure.

hmmm I guess I really need to start planning this box out...thanks!

[Nightshade]

hmmm I guess I really need to start planning this box out...thanks!

No problem. Do yourself a favor, if you're planning on building a new box take a look at maybe doing some aeroports. In several situations I've seen them be .8-1+ db's louder than a standard slot port. I can tell you in my case what I found out. Without changing internal volume at all I went from a 4cuft after displacement box with woofers and subs up doing a 145.7. To a 4cuft box after displacement with aeroports and subs up and woofers back to a 148.1. I don't know what made the biggest impact, if it was firing the port back instead of up. Or if it was by adding aeroports to the setup. Anyway the gain in spl was 2.4 dbs with only making those two changes. Aeroports are the shit. And by using the least ammount to get the desired port area is the best way to go. In the box I have now I have 4 4" aero's which equal out to 50.24sqin of port area. If I were to use 2 6" aero's which would be 56.52sqin of port I would see a slight rise in tuning freq that could be compensated by adding length to the port, but I would also see a gain in spl due to the two ports making the enclosure more efficient that running 4 ports. I have yet to try this, but when I do I'm not changing anything but making a pannel that will screw onto my box that will have the 2 6's and 4 4's and then metering it to see which is actually louder. I'll post the results when I get around to doing this. First I gotta add some new amps before I start doing surgery to my box. Good luck with the build!!!

[littleitaly1990]

No problem. Do yourself a favor, if you're planning on building a new box take a look at maybe doing some aeroports. In several situations I've seen them be .8-1+ db's louder than a standard slot port. I can tell you in my case what I found out. Without changing internal volume at all I went from a 4cuft after displacement box with woofers and subs up doing a 145.7. To a 4cuft box after displacement with aeroports and subs up and woofers back to a 148.1. I don't know what made the biggest impact, if it was firing the port back instead of up. Or if it was by adding aeroports to the setup. Anyway the gain in spl was 2.4 dbs with only making those two changes. Aeroports are the shit. And by using the least ammount to get the desired port area is the best way to go. In the box I have now I have 4 4" aero's which equal out to 50.24sqin of port area. If I were to use 2 6" aero's which would be 56.52sqin of port I would see a slight rise in tuning freq that could be compensated by adding length to the port, but I would also see a gain in spl due to the two ports making the enclosure more efficient that running 4 ports. I have yet to try this, but when I do I'm not changing anything but making a pannel that will screw onto my box that will have the 2 6's and 4 4's and then metering it to see which is actually louder. I'll post the results when I get around to doing this. First I gotta add some new amps before I start doing surgery to my box. Good luck with the build!!!

hey thanks a lot man, I will consider them for sure now, I just posted my new request for box help, so this is good info.

[Eric B]

No problem. Do yourself a favor, if you're planning on building a new box take a look at maybe doing some aeroports. In several situations I've seen them be .8-1+ db's louder than a standard slot port. I can tell you in my case what I found out. Without changing internal volume at all I went from a 4cuft after displacement box with woofers and subs up doing a 145.7. To a 4cuft box after displacement with aeroports and subs up and woofers back to a 148.1. I don't know what made the biggest impact, if it was firing the port back instead of up. Or if it was by adding aeroports to the setup. Anyway the gain in spl was 2.4 dbs with only making those two changes. Aeroports are the shit. And by using the least ammount to get the desired port area is the best way to go. In the box I have now I have 4 4" aero's which equal out to 50.24sqin of port area. If I were to use 2 6" aero's which would be 56.52sqin of port I would see a slight rise in tuning freq that could be compensated by adding length to the port, but I would also see a gain in spl due to the two ports making the enclosure more efficient that running 4 ports. I have yet to try this, but when I do I'm not changing anything but making a pannel that will screw onto my box that will have the 2 6's and 4 4's and then metering it to see which is actually louder. I'll post the results when I get around to doing this. First I gotta add some new amps before I start doing surgery to my box. Good luck with the build!!!

Aeroports are the shit! I can attest to that. My single 15 with 1800rms in 4 cu ft box with 2 4in aeroports tuned to 30Hz is almost as loud as my 2 12s off 3000watts tuned 36Hz in a 5cu ft box with a regular rectangular port, not slot..

[audiofanaticz]

Is there anyways to counter the effects of box rise? Without getting a different amp?

I burried one solution in there and it is to decrease the internal airspace of the box. In a smaller box the rise isn't as much as a larger one, but you will also lose efficiency of the sub in a smaller enclosure so you better have the power to compensate for the loss. I've also been told that tuning the box to a higher frequency will also help bring the rise down some, but that may go hand in hand with shrinking the airspace down I'm not really sure.

meh, I just order crazy coil configurations on my subs so when I parallel them together Im well below 1 ohm and have room for impedance rise without losing tons of power.

But its not always the safe way of doing it, esp if your amp is only 1 ohm stable and your nominal load is much lower then that. So if your running amps like RF this is not too good of an idea, but if your running amps that you can somewhat street beat at .5 ohms your golden