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Rudy H · 03-31-2002, 07:04 PM

DIY: Subwoofers: Understanding Powerhandling

Take a driver such as the Adire Shiva (or it's smaller-box cousin) the 12inch Dayton DVC. They have a RMS power rating of 650watts RMS and 600watts RMS, repectively. What exactly does that mean? That's the thermal power handling ability of the driver. It's the maximum amount of power they could reliably throw at the driver without the driver bottoming out (happens when the cone attempts to move beyond the limits of it's suspension... kind of like your car going over a speed bump too fast). With drivers like the Shiva and Dayton DVC, the limit of the suspension is almost always a bigger cause of concern than the actual power handling.

Take the 12inch Dayton DVC for example. In a 1.2cf sealed box (very popular choice for this driver), at 600watts power input, is free from bottoming until 20hz, however below 20hz it will bottom. This is due to the fact that the cone must move more to reproduce lower frequencies than higher ones. Crank your system loud and take a look at your tweeters, chances are you wont be able to see them moving at all... however when you look at the woofers, they're probably moving quite a bit. The volume is the same for both the bass and the highs, but because bass, which contains lower frequencies, require much more cone movement than high frequencies. The Adire Shiva however is quite different with it's recommended 2cf sealed box. It would start bottoming at roughly 33hz, at the same 600watts power input.

Now for vented boxes. 2 main factors affect power handling in a vented box: Box size and tuning frequency.
The larger the box, the greater the cone excursion. Where tuning frequency comes into play is in the fact that roughly a 1/3rd below the tuning frequency, the woofer's back pressure from the box/port is practically eliminated. This causes a sharp and continous rise in cone excursion below that point. Another point of excursion to worry about is just above the tuning frequency where cone excursion is also very high.

Take for example the 12inch Dayton DVC in a 2cf vented box tuned to 24hz, again at 600watts power input. A great box for a car audio system since it is flat to roughly 40hz. Excursion rises progressively to a peak at 35hz, drops down very low at 24hz (the tuning frequencY), and then skyrockets, causing bottoming below 20hz. Again, great for a car, but aweful for HT applications. Now lets take the same sub, but in a HT-oriented vented box... 4cf tuned to 20hz. This provides very deep bass response, perfect for HT.
This is the case where the excursion above the tuning frequency is also in focus, since the woofer will bottom above the tuning frequency, peaking at 27hz. Excursion then drops to the tuning frequency, and as expected, skyrockets until bottoming reoccurs at 18hz.

What's the solution to keep the woofer from bottoming?
Either use less power (recommended) or make the box smaller.

Usually if there's a problem with the driver bottoming, the tuning frequency can be lowered as a quick fix (if it will help, remember the excursion rise above the tuning frequency too), or for a sealed box, the box size can be reduced (by adding a phone book, brick or bracing into the enclosure).

03-31-2002, 07:04 PM
Rudy H Member Join Date: Mar 2002 Local Time: 10:39 PM Local Date: 10-10-2008 Posts: 105	DIY: Subwoofers: Understanding Powerhandling Take a driver such as the Adire Shiva (or it's smaller-box cousin) the 12inch Dayton DVC. They have a RMS power rating of 650watts RMS and 600watts RMS, repectively. What exactly does that mean? That's the thermal power handling ability of the driver. It's the maximum amount of power they could reliably throw at the driver without the driver bottoming out (happens when the cone attempts to move beyond the limits of it's suspension... kind of like your car going over a speed bump too fast). With drivers like the Shiva and Dayton DVC, the limit of the suspension is almost always a bigger cause of concern than the actual power handling. Take the 12inch Dayton DVC for example. In a 1.2cf sealed box (very popular choice for this driver), at 600watts power input, is free from bottoming until 20hz, however below 20hz it will bottom. This is due to the fact that the cone must move more to reproduce lower frequencies than higher ones. Crank your system loud and take a look at your tweeters, chances are you wont be able to see them moving at all... however when you look at the woofers, they're probably moving quite a bit. The volume is the same for both the bass and the highs, but because bass, which contains lower frequencies, require much more cone movement than high frequencies. The Adire Shiva however is quite different with it's recommended 2cf sealed box. It would start bottoming at roughly 33hz, at the same 600watts power input. Now for vented boxes. 2 main factors affect power handling in a vented box: Box size and tuning frequency. The larger the box, the greater the cone excursion. Where tuning frequency comes into play is in the fact that roughly a 1/3rd below the tuning frequency, the woofer's back pressure from the box/port is practically eliminated. This causes a sharp and continous rise in cone excursion below that point. Another point of excursion to worry about is just above the tuning frequency where cone excursion is also very high. Take for example the 12inch Dayton DVC in a 2cf vented box tuned to 24hz, again at 600watts power input. A great box for a car audio system since it is flat to roughly 40hz. Excursion rises progressively to a peak at 35hz, drops down very low at 24hz (the tuning frequencY), and then skyrockets, causing bottoming below 20hz. Again, great for a car, but aweful for HT applications. Now lets take the same sub, but in a HT-oriented vented box... 4cf tuned to 20hz. This provides very deep bass response, perfect for HT. This is the case where the excursion above the tuning frequency is also in focus, since the woofer will bottom above the tuning frequency, peaking at 27hz. Excursion then drops to the tuning frequency, and as expected, skyrockets until bottoming reoccurs at 18hz. What's the solution to keep the woofer from bottoming? Either use less power (recommended) or make the box smaller. Usually if there's a problem with the driver bottoming, the tuning frequency can be lowered as a quick fix (if it will help, remember the excursion rise above the tuning frequency too), or for a sealed box, the box size can be reduced (by adding a phone book, brick or bracing into the enclosure).