Please 'Boom' Responsibly As most of you have noticed, the noise ordinances have become much tougher lately. Most of this is due to idiots, yes IDIOTS, who drive through residential areas with their windows down while their system is playing at full power. To make things worse, the music they listen to has all sorts of foul language that's not suitable for small children, (who may be playing outside). There are even a few people, who are even beyond idiot status, that play their systems at full power through residential areas after 10:00 PM (when many people go to bed). I don't believe that this type of behavior is good for the industry. If the fines get too stiff, people will stop buying large systems. If this happens, more people will get out of car audio (who wants a mediocre system). People get interested in things because they're exciting. A deck and four 6.5" speakers are not going to interest many of the younger car audio enthusiasts. If car audio enthusiasts keep annoying more and more people, the fines will keep getting tougher. All of this will only reduce interest in the equipment that fuels the industry. If you want to listen to your system at full volume, get out on the highway where there's little chance of bothering anyone. When you get to a red light, turn it down. If the only thing attractive about you is your 'system', you have some work to do. Bottom line... Think about what you're doing. Think about other people. It's not the end of the world if you have to turn the volume down for a little while.


Amp Rack:
An amp rack can be of almost any design, shape or size. The image below is a simple functional amp rack. You can do better (or worse). For the best cooling, the internal dimensions of the amp rack should be only slightly larger than the amp. This will significantly increase the air velocity along the sides and top of the amp and promote the best possible cooling. The red arrows indicate the direction of airflow. Amp Rack
If you want to use a single fan, simply leave one end of the rack off (the end opposite the fan) like the diagram below. Single Fan Amp Rack
 
Push-Pull vs Push OR Pull:
There has been a lot of discussion on different forums about the use of fans in push-pull configuration. Some people have said that it is not an efficient use of fans when they are used in a push-pull configuration. They've said that it's better to use both for pushing or both for pulling (either of which, they believe, is better than push-pull). I believe that push-pull is more efficient (although not significantly more). When using one or more fans to push air into a chamber (one end of the amp rack), they will only be able to build a certain amount of pressure. Multiple fans will not be able to generate more pressure (it's like adding batteries in parallel). The air pressure at the output end of the amp rack in this (push only) configuration is atmospheric pressure. The flow across the fins will be a function of the difference in pressure between the pressure in chamber 'A' and the pressure in chamber 'B'. Most fans can not develop more than about 0.25" of water of static pressure (~0.01PSI). To increase the flow without changing the shape of the amp or amp rack, you must increase the the static pressure or change the difference in air pressure from one side of the amp to the other. Since the static pressure that the fan can produce is fixed, to increase air flow, you need to decrease the pressure on the output side of the amp (in chamber 'B'). This can be done by using a fan to pull air out of chamber 'B'. The second fan pulls a partial vacuum on chamber 'B'. This means that the differential pressure across the amplifier will be increased and the flow will increase. If someone has any real proof that this is not true, please email me. I don't want to insult or offend anyone but I'd like to straighten this out one way or the other.


Quieting Fan Noise:
The following diagram shows a squirrel cage fan in an amp rack. The baffles will block the high frequency noise produced by the fan. Baffles on both ends are not necessary. If baffles are only put on one end of the rack, you should put the baffles closest to the fan's mounting location. The divider/seal acts as a baffle to separate the front of the the fan's intake from it's exhaust. This will greatly improve the fan's performance. For the best performance from the baffles, they should be covered with carpet or other material that will absorb high frequencies.

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