Home Built Passive Subwoofer, HELP?

Question

Hello /diy/ I need some helpful advice, I want a subwoofer for my room that pwns all ***... But even after hours and hours of research something still stumps me about the crossovers. Do I need a cross over for the subwoofer drivers or will they have one built in? The crossovers I have planned to get for each driver are limited to 600watts MAX (not RMS value) so I'd only be able to unlock half the potential of the two drivers (one crossover for each driver). So if the crossover is built into the driver or the driver only responds from 26Hz - 200Hz (Frequency Response, not sure if this means its recommended for that driver or thats ALL it will filter out).

Google: MTX T615-44 RoadThunder

^ Those are the drivers I'm using for the subwoofer

Power Amplifier I'm using (If the driver has an in built crossover then I can bump up the wattage (RMS) of the amp I use).

Google: Ekho RX-1500 2 x 750 Watts Power Amplifier

This is the Crossover I'm using

Google: Internal Subwoofer Speaker Filter 600W 4 Ohms 12dB 120Hz

Got my old Philips Pre-Amp so gonna link an RCA cable from that to the Power amp for the Subwoofer

Got power wires from the Power amp to the Subwoofer

Got wires for inside the actual subwoofer linking the Terminal cup to the crossovers, then to the drivers themselves.

I have uploaded the plan so you can have a look (It isn't fully finished as I still need to work out the dimensions of the enclosure)

Link for plan: http://www.mediafire.com/?8v7nl1p5yl6dxih

Its a .PNG Image not a Virus BTW.

Answer 1

You're putting the crossover in the wrong place. The crossover belongs before the amplifier. You could use these... http://www.parts-express.com/pe/showdetl.cfm?Partnumber=266-254 Or better yet you could just get an amplifier designed for use with subwoofers because it will have the crossover built in. http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-809



You're next mistake is using car audio woofers. I would also stay away from ported designs especially with a large woofer with high X-max and a small diameter port. Ever heard that "Cuffing" sound coming from a ported speaker? This comes from excessive air velocity in the port, to reduce this the port must have a larger cross sectional area and consequently more length to maintain the same tune frequency.



Look at some better woofers on the PE web site. http://www.parts-express.com/speakers.cfm Don't pay much attention to power ratings, these have nothing to do with performance. The amount of bass a woofer can provide is strictly determined by how much air it moves, it has nothing to do with the power rating. Ideally it will provide the most air movement with the least amount of power. The thermal capability of the coil needs to handle enough power to fully utilize the mechanical excursion capability, anything beyond that is irrelevant. The less power required to bottom out the woofer, the better... that just means it's more efficient. You can't go beyond bottoming out anyway, just short of that is the most output the woofer can produce... why would you want it to require thousands of watts to reach that output???? You need to think about woofer power ratings a bit like gas milage ratings but in terms of gallons/mile... big numbers are bad. Surface area and X-max determine how much air the woofer can move and thus how much output it's capable of.



I didn't look that closely at your drawing, just make sure it's been modeled correctly using Bass Box Pro or similar software or just avoid this design and go with a sealed system.



mk

Answer 2

What you want to look for is a x over whether it be passive or electronic that will cover you from about 80 htz and down to about 18 htz, get rid of anything else before or after it,come down from the speaker terminals to the x over,then on the other side of the x over connect your speaker wires.if you are going to use an electronic then it goes in before your amp and only the desired freq are amplified,not wasting power on the unwanted. then from the amplifier you hook up the wires to you sub box,no further x over is required at the sub box, hope this helps.

Answer 3

A passive XO between a sub and it's amp is just a bad idea. (buffer factor, choke saturation etc.) If your sub amp doesn't already have it built in, you can build a line level low pass filter and channel mixer with some resistors and capacitors, but maybe best you just buy one. I recommend 18dB/octave @ 150Hz.