1) How do I calculate the capacitance value for a capacitor to filter out any sound below 80Hz to solder into my speaker wires?

2) As the current going into the speakers is AC, to do two 6x9's will I need 4 caps?

3) Sound deadening.. Hmm... What effect does this stuff actually have? I notice with a few frequencies, probably somewhere around 80-100Hz which are too high for the sub, and just in the range for the 6.5" ers, that with the bass hits they sound really tinny... sorta. lol
It's hard to describe, but it sounds like they've got no guts. But it's only those frequencies. :confused:

If I sound deaden the front doors should this fix the problem and give them some oomph?! :P

Cheers guys!

C(Farads) = 1/(2*pi*R*F)

3) Sound deadening.. Hmm... What effect does this stuff actually have? I notice with a few frequencies, probably somewhere around 80-100Hz which are too high for the sub, and just in the range for the 6.5" ers, that with the bass hits they sound really tinny... sorta. lol
It's hard to describe, but it sounds like they've got no guts. But it's only those frequencies. :confused:

If I sound deaden the front doors should this fix the problem and give them some oomph?! :P



Depends where the rattling and tinnyness is coming from really. I personally would recommend sound-deadening the front doors, simply because it will increase the quality of the sound coming from the speakers a lot. I also suggest doing your boot-lid, your boot floor/sides including the spare-tyre well. I sound-deadened my boot floor/sides today with SoundOff paint today, and I've noticed a big improvement. I also did the backseat and that too has helped a lot. I've got plenty more to do (including cabin floor and cabin roof) and after that I should be done.

Sound-Deadening keeps the sound inside the cabin, therefore, a higher volume from your system can be achieved, but it also increases the quality too. Such an important aspect of any sound-system (I hope I don't sound like s_tim_ulate taking words pretty much out of his mouth) :-)

Ok, Im going to expand on my previous post... :D

6dB per octave High Pass X-over

Need: One capacitor in series On the +ve wire or each speaker.

C = 1,000,000 / (2*pi*f*R)

Where:
C = Capcitance (Farads)
pi = 3.141592654
f = frequency (Hz)
R = Speaker impedance (ohms)

So for a HP filter @ 80Hz you need:
2 ohm speaker: 1000uF
4 ohm speaker: 500uF
8 ohm speaker: 250uF

12dB per octave High Pass X-over
Need: One capacitor in series and one inductor in parallel.
The wiring order is amp, then capacitor, then inductor then speaker.

I = 1000*R / (2*pi*f)

Where:
I = inductance (mH)

So for a HP filter @ 80Hz you need
2 ohm speaker: C = 700uF, I = 8.2mH
4 ohm speaker: C = 330uF, I = 11mH
8 ohm speaker: C = 180uF, I = 22mH

The capacitor values differ slightly for the 12dB circuit as you have to take into account the reactance of the parallel inductor etc, so to make it easier I just gave you the values! :D

Enjoy!
Pete

Ok.. What's the difference between 6dB and 12dB/octave? :confused:

I think the first equation was right too... C = 1,000,000 / (2*pi*f*R) give the answer in uF :P



Depends where the rattling and tinnyness is coming from really. I personally would recommend sound-deadening the front doors, simply because it will increase the quality of the sound coming from the speakers a lot. I also suggest doing your boot-lid, your boot floor/sides including the spare-tyre well. I sound-deadened my boot floor/sides today with SoundOff paint today, and I've noticed a big improvement. I also did the backseat and that too has helped a lot. I've got plenty more to do (including cabin floor and cabin roof) and after that I should be done.

Sound-Deadening keeps the sound inside the cabin, therefore, a higher volume from your system can be achieved, but it also increases the quality too. Such an important aspect of any sound-system (I hope I don't sound like s_tim_ulate taking words pretty much out of his mouth) :-)

It seems I'm gonna have to go shopping then... What is the difference between the paint on ones and the sheets? Does one have benefits over another, or just a different design?

12dB is a sharper cutoff. I like them better and it is the most commonly used, but personal prefernce I guess.

These might help:

6dB 1st order (http://www.lalena.com/audio/tables/xover/1stOrder.shtml)
12dB 2nd Order (http://www.lalena.com/audio/tables/xover/2ndOrder.shtml)
18dB 3rd Order (http://www.lalena.com/audio/tables/xover/3rdOrder.shtml)

I understand those pics... and you just copied the values straight from there cheater :P

But not sure on the sharper cutoff thing.. wtf does that mean? Is it something that's gotta be heard, or just trial an error and see what you like?

Ok.. What's the difference between 6dB and 12dB/octave? :confused:

I think the first equation was right too... C = 1,000,000 / (2*pi*f*R) give the answer in uF :P




It seems I'm gonna have to go shopping then... What is the difference between the paint on ones and the sheets? Does one have benefits over another, or just a different design?

Ok, the sheet ones are a lot more expensive but I recommend using them for bootlid and front-doors because they are more effective, use Stinger Roadkill or Dynamat. After you've done that, I would then go and get some "SoundOff" paint (I made a thread about that today, located in the Car Audio section) and do the rest of the boot (sides/floor) and then used some for the rear seat. This is a lot cheaper, 1L does about 1 sq meter (that's two doors) for about $65.

The paint isn't as great as the sheets but it does a wonderful job nonetheless, and you really don't want to be paying over $1000 just for sound deadening material do you? :-)

I would go with 12db / octave if you can dude, I have my 6x9's HP with a cap @ 150Hz @ 6db / octave and it was no where near the result I wanted. I still have the HP filter on the Head unit set at 50 because 6db / octave is not steep enough to cut out most the bottom end effectively.

It wasn't until I used my LP filter on my Audison which is 12db or 24db / octave selectable that you realise what a difference it makes. :D

Don't forget if your playing around with caps for crossovers you should use either bipolar electrolytics or the better and more expensive mylar capacitors. Jaycar is your best friend here.

with a slower rolloff (6dB) your midrange will be playing more of the same frequencies as your tweeter so less distinction. With a sharper rolloff (12dB), they will be playing less of the same frequencies. So better sound in the end.
12dB is the most common and sounds much nicer.

Of course I copied the values!!! Whats the point of working them out yourself if all the work is already done!!!!

If you just go to Jaycar and ask for caps suitable for a inline crossover for a car stereo they will show you the right ones. You cant use normal electrolytics etc.

Cheers
Peter

Cheers guys! i'll head into Jaycar over the weekend :D

Generally higher is better in terms of db cut. I use 24 db for most of my system. But when blending mids and subs it helps to try a shallower cut. 18 or 12 db works well to disguise the location of the sub.