What is box rise

[Impalalpine]

as stated above. I have heard about it all up and down these forums?

[Jd1102]

Read through damore engineering part of forum and watch his school vids

[CleanSierra]

Box rise is when your enclosure reaches a "zen-like" state and starts to levitate.

In all seriousness, it's not called box rise, it's impedance rise. As far as explaining, I'm hoping someone else jumps in, too much to type. It involves the change in ohm load at your amp due to the dynamic and ever changing nature of music.

[Jd1102]

Box rise is when your enclosure reaches a "zen-like" state and starts to levitate.

In all seriousness, it's not called box rise, it's impedance rise. As far as explaining, I'm hoping someone else jumps in, too much to type. It involves the change in ohm load at your amp due to the dynamic and ever changing nature of music.

exactly why I sent him there to much to type

[Wicks]

A raw audio driver will have a base impedance curve.

When placed inside an enclosure, the impedance curve can change, sometimes drastically.

There is much more to an audio driver then just its "nominal" rating.

Here's a combination of a few impedance sweeps done on a Hertz ES200 8" sub of mine:

Notice the blue line which is the raw driver in free air and its impedance peak of almost 30 ohms at about 30Hz.

The orange line is with it placed into a sealed enclosure. Notice the impedance peak changes to about 28 ohms at 40Hz.

The red line is with the driver in a ported box which is tuned to 38Hz. Notice the impedance sweep now has two peaks:

One at 22 ohms at about 21Hz and another of 21 ohms at about 54Hz. The impedance dip occurs at the box's tuning frequency of 38Hz.

Watch Tony D's videos. He mentions that you'll also see that these impedance curves change when your doors are open, windows up/down, trunk open/closed, different amount of people in the cabin....

So you can see that the true impedance that your amplifier sees is much more complicated then just the nominal value that you're wired to (0.5ohms,1ohm, 2ohms, etc).

[Dwn4BassAlan]

The mystical powers or impedance and inductance mixing into a nirvana-like state, in full harmony with the Ohm (see what I did there? lol) and totally screwing with your theoretical specifications.

But really:

A subwoofer is a magnetic coil with an inductance. When you input AC current, the resistance (actually called impedance) varies depending on the frequency of the AC signal, as well as temperature. A woofer has its own impedance rise at the Fs of the woofer. Since the coil acts like an induct or, the impedance changes with frequency. If you look at any T/S sheet, you will see the peaks at it's resonant frequency (Fs). Many people do not realize this and understand that the impedance they are calling "impedance rise" is actually there with the woofer out of the box. But that being said, putting the woofer in a box also creates additional impedance spikes due to the box resonance and the port tuning, and because in the box, the cone has a different reaction with pressure behind it, which can change the impedance plot. Impedance of a woofer is based on an average as long as it is a certain percentage over the minimum/nominal impedance, but it is not a flat "X ohms", and again, it rises well above the nominal rated impedance at Fs.

If you really want to know in your case specifically, and you feel apt enough to try it out;

You can map out your impedance rise by measuring it at each frequency and then plotting the numbers. Hopefully you have a digi-multi meter and a clamp, that way you can use V(voltage)= I(current) x R(resistance).

If you only have a DMM, you can add a series non-inductive resistor and look at voltage at the amp vs. the voltage across the known resistor. The difference is the voltage dropped across the sub. Current can be calculated by the voltage across the resistor / value of the resistor. Once you know the current and the voltage across the sub, you can calculate the impedance at that frequency.

[Dwn4BassAlan]

summarization credit to b-ri if he is still alive. My full explanation would take hours to write. But if you want any more detail, I'll be glad to get into it