Box rise

[Aaron Tuck TBA]

Hey can anyone link my to some post to better understand rise and how I could possibly make it work for me instead of against?

[Triticum Agricolam]

Here is a widely misunderstood topic. I don't know of any one single source that explains it all well. I can try to explain my understanding of the issue though I don't always explain things well so bare with me and ask questions if you are unsure.

First off here are a couple things to remember:

1. Amplifiers put out volts, not watts

2. More volts = louder

3. More watts does not always = louder

4. How many watts you get out of your amp is a function of volts and impedance

5. Impedance (what box rise really is) actually works for you and it is closely tied to how much work the sub is doing.

Now for some examples, let's say you have a sub and amp and you have two boxes to pick from to put the sub in. For this discussion let's say you have a FI SSD 15 D2 with the coils wired in series for a 4 ohm nominal load and you have a 1200 watt amp. Your amp puts out rated power a 4 ohms. 1200 watts a 4 ohms is 69.3 volts.

Both your boxes are tuned to 30 hz, one is 3 cu ft net and the other is 4 cu ft. Larger boxes are more efficient around tuning, the more efficient a box is the less work the sub has to do to produce sound and thus the higher the impedance is. Here is what the impedance looks like for both boxes:

The green line is the 3 cu ft box, the red line is the 4 cu ft box.

Through most of the usable bandwidth the larger box (red line) has higher impedance.

Since both boxes get the same voltage from the amp, here is how much power is going into them:

At tuning there is 1248 watts going into the larger box and 1329 going into the smaller one. The reason both these numbers are above 1200 watts is because the DC resistance of the sub is less than 4 ohms.

So the larger box is getting 80 less watts of power than the smaller box is, but what about output? Here is that graph:

The larger box has more output even though it is taking in less power than the smaller box is. Right at tuning the larger box is almost 2 dB louder.

So what does this all mean?

1. If you change your box so it has lower impedance you will get more watts out of your amp, but produce less dBs.

2. Higher impedance is good because it means your box is producing more output on less power, it also is easier on your amp and if your box raises your impedance high enough you might be able to wire to a lower ohm load and further increase the sensitivity of your system.

3. The one time higher impedance is bad is when its cause by compression. Either port compression or power compression will raise the impedance of your system. Unlike when a more efficient box lets your sub do less work and thus raises impedance, compression limits the amount of work your sub can do, this raises impedance but you get less output.

[98crewcab]

geeze....smart fucker......

thanks for breaking it down......may have to read it again to take it all in, lol

[Aaron Tuck TBA]

Wow! Thank you so much! I'm trying to wrap my head around the rise issue. Your write up was very helpful! I won't be able to build a larger enclosure right now. But I figured it's what would need to be done. I currently have a 6 cubes enclosure with 90.75 inches of port at 36hz. On the meter I'm doing a 150.3 repeatable outlaw on a clamped 1500 watts.

[Aaron Tuck TBA]

Oops double post.

[Triticum Agricolam]

No prob, glad I could help!

Keep in mind that making an enclosure larger or smaller affects more than just max output and impedance. Frequency response, group delay, cone excursion all get affected too. Just how important those things are depends on what you are trying to do with your system. With audio there is no free lunch, everything is a trade off in some way.