car speakers

Well, maybe...
In car audio, the largest factor to contend with is called "cabin gain" This means that somewhere in the 30-40Hz range the driver's response will typically roll off. The small size of the encloser and proximity to other walls of the car's interior significantly contributes to "boosting" the lower frequencies. This means that the free air response of the driver may not be flat, and may indeed roll off too soon for home use. The same "rolling off" in home audio is sometimes made up with "room gain", but room gain is significantly smaller in magnitude than cabin gain from a car.

However... The way to tell this for sure is to look at the T/S specs provided by the manufacturer. For home audio, it is often best to desing for "flat" response, so look for a driver with Fs somewhere in the low 20's.

Another point to be aware of is to make sure that your amp can handle driving the 4ohm load found in most auto woofers as opposed to the 8ohm load of the typical home audio speaker.

The driver that I used in my home subwoofer is the Mass2012 S24 from <a href="http://www.audiomobileinc.com/masssubs.htm">audiomobileinc.com</a> a well known and highly regarded manufacturer of car audio speakers. With this driver, its possible to get nearly flat response down to about 17-18Hz!
 
Eric...

Flat to 17 Hz ?? That's pretty impressive !!
Are you applying any EQ to get that low down or did you get that 'straight out of the box' ??
I've read that a major issue at VLF is cone excursion (to shift the air required to create usable SPL), and that the bigger the cone area the less excursion required. How does your 12" sub manage to do this (without disappearing up its own voice coil)??

Simon.


[Edited by Simon on 07-17-2001 at 02:33 PM]
 
Huey,

It is often easy to spot the differences in design/build quality of home theater and car audio subwoofers. As mentioned earlier, the majority of car audio subwoofers are 4 ohms vs the typical 8 ohm HT subwoofer. But also, especially in lesser quality car audio subwoofers, the materials of construction vary greatly. Lesser car audio subwoofers are generally paper cone, and are often treated with chemicals for extra resistance against moisture and humidity. But in general, car audio woofers are designed to just move mass amounts of air, with little regards for accuracy and response without cabin gain. Although there are several exceptions, you are likely to notice a significant price increase between typical car subwoofers, and those that are suitable for home theater use. And depending on how old your equipment is, you might be safer in using an 8 ohm driver, designed for HT use.
 
Subwoofer Drivers

Simon: Check out the following link for some ideas/tips/tools for building a home subwoofer:

<a href="http://members.tripod.com/~terryctheater/shivaphotoalbum/page12.html">Sonotube Subwoofer Resources</a>

The Mass driver is a very high quality driver and costs about $300. There are others available for about $125-150, but they are not quite up to the standard of the Mass. The mass has 20mm *CLEAN ONE WAY* excursion. It is an underhung design meaning that at high excursion (capable of 2 inches peak-to-peak!) the voice coil always remains within the magent/pole structure. It is a titanium/aluminum cone with a heavy duty rubber surround. No cheap paper and foam on this one! The magnet structure weighs in near 20 lbs, and the entire driver weighs 30lbs!

I have mine mounted in a 135L vented enclosure that is tuned to about 18Hz. I've measured flat response down to 15Hz (room gain helps a little here) from the driver & port combined. I am *not* using any kind of equalization, just a properly designed enclosure. Be sure to download a copy of WinISD (use Internet Search). It is a simulation program for designing subwoofer enclosures. Its free, pretty easy to use, and fairly accurate.

Many other "so called" subwoofers only have an xmax of about 6-10mm one way, this is not sufficient for high SPLs. You might also want to check out the Shiva from AdireAudio.com - its a very economical alternative to the Mass although it does not have the same extreme capabilities...