Building a Franken-system.

[Quartersawn]

Hi all! First time poster, probably bringing something a little different to the table. I have a background in music and live sound but don't deal with car audio at all. My goal is simple. To learn enough about car audio to build the loudest, most monsterous sound system for the lowest dollar amount to be used in a demolition derby car in Novemeber. These are the factors in order of importance.

LOUD (enough that a small race track can hear and make out well chosen songs)

CHEAP (this is gonna be a derby car. Chances are lieces of the system will break)

That's it.

My idea is to find a decent amplifier, and use my totally tubular garage sale and craigslist skills to piece together a sound system capable of blowing the doors off my opponents before we even make contact. I am thinking bass amp subs (cheaper than dirt if I find an old cab in a garage sale).

Can I power this kind of thing off a standard car battery? If not, how much extra juice do I need? In general? I only have a basic concept of car audio. Electricity, power, ???, profit!

Help me on my journey! I will continue to browse the forums for info in the mean time!!!

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[Talontsi90]

Peavey Black Widows would be my choice if i were to use 15's in a car.

 

[Quartersawn]

As promised, I did some due diligence! Corect me of I am wrong but the basics are as follows.

Amp output should closely match the RMS of all speakers on a channel. Example: an amp with a sub channel of 700w can have a 700w sub or two 350w subs (if there is the option for two). The ohms of the speakers need to match the output of the amp somehow. Wheather that is two 8 ohms wired in parallel or two 4 ohms wired in series. They still need to equal 8 if the amp is rated for 8. Ohms is more important than wattage, but wattage still needs to be close to avoid speaker breakup at higher volumes or starving at lower. It shouldn't matter if I am using a guitar bass speaker as long as I follow these rules. (Quality will be lower probably but I am going for loud not good) If I am right theb that is relatively basic.

I cannot find much info on how to power a system like this. Anyone wanna weigh in and tell me if I am on the right track?

 

[Quartersawn]

Peavey Black Widows would be my choice if i were to use 15's in a car.

I actually found an old 90s peavey bass guitar amp cab which gave me the idea in the first place!

 

[Talontsi90]

As promised, I did some due diligence! Corect me of I am wrong but the basics are as follows.

Amp output should closely match the RMS of all speakers on a channel. Example: an amp with a sub channel of 700w can have a 700w sub or two 350w subs (if there is the option for two). The ohms of the speakers need to match the output of the amp somehow. Wheather that is two 8 ohms wired in parallel or two 4 ohms wired in series. They still need to equal 8 if the amp is rated for 8. Ohms is more important than wattage, but wattage still needs to be close to avoid speaker breakup at higher volumes or starving at lower. It shouldn't matter if I am using a guitar bass speaker as long as I follow these rules. (Quality will be lower probably but I am going for loud not good) If I am right theb that is relatively basic.

I cannot find much info on how to power a system like this. Anyone wanna weigh in and tell me if I am on the right track?

Sort of... The amp can output 700w at X load, usually 4ohm mono, this means that the load of the subs must equal that 700w regardless of how many you have. What happens is the wattage gets split up based on each speakers resistance as seen by the amp.

If you have two 8 ohm subs, they must each be able to handle 350w as the 700w will be split in two. If you have two 4 ohm subs (and the amp cant do 2ohm mono) then you wire in series and each sub still gets 350w. But, if you have four 8 ohm subs and wire in series/parallel for a 4ohm load each sub gets 175w. This may not seem like an optimal outcome, but the rule of thumb is, in order to get a 3db gain in output you must either double your output or cone area. So even though, the 4 subs would only be getting 175w, the four would be 3db louder than the 2 sub setup. This was done in the past as subs were a LOT cheaper than a second amp was for most people.

 

[Talontsi90]

Forgot to say at the end of that: Using lower wattage subs in greater number would allow you to get the same output with less chance of blowing one.