amp questions.

[mobomelter]

It sends such low current that it shouldn't be a problem. You can always run a separate wire if it is. In many cases, amps have auto-sensing turn on so the remote wire isn't even necessary.

i beileve the mtx thunder 342 that i bought has that feature. so i won't need to run a remote wire at all?

 

[tsunami]

how does a capacitor reduce noice??? 10 micro farads is some small stuff but where would you put that with rca to reduce noise...??

 

[BrianG]

how does a capacitor reduce noice??? 10 micro farads is some small stuff but where would you put that with rca to reduce noise...??

A capacitor by nature passes AC and blocks DC. It also stores a charge - which is the feature we take advantage of when using a large one on an amps' power wire.

If you attach the + of the cap to the remote wire and the - of the cap to ground, it will shunt the very small induced AC (noise) to ground. The uF value of the cap to use depends on the load and the frequency. Since the induced noise has very little sourcing current and the frequency is fairly high, a small cap is all that is needed. This cap is a decent example: http://www.radioshack.com/product.asp?catalog_name=CTLG&product_id=272-1013 An even smaller cap may be necessary (1uF or even lower). Again it depends on the amount of sourcing current of the noise and the "load".

You wouldn't want to do this on an RCA signal wire since you'd end up blocking or shunting (depending on the configuration of the cap) the signal! If you have noise on the RCA itself, they must be running alongside a fairly heavy current wire somewhere. You can either move the wire or shield it at the problem area.

Another way to supress noise is to use an inductor (choke) in series with the power. An inductor is basically just a coil of wire wrapped around a core (usually air or ferrite). An inducator passes DC, but blocks AC by using back EMF. The mH value to use depends on the load and the frequency. SInce the load is in series with the inductor, the size of the wire in an inductor depends on the current the load needs. Sometimes simply getting a ferrite choke core (http://www.radioshack.com/product.asp?catalog_name=CTLG&product_id=273-105) and wrapping the remote wire through it a few times is enough to eliminate the noise.

Those noise supressors on the market are basically just a capacitor and inductor network wrapped in a small box. Actually, this is basically a low pass crossover meant to pass very low AC (to the point of being DC).

Speaking of crossovers, the principles explained above is what makes them work. A high-pass xover uses an inductor in series and then a cap in parallel to the load. The inductor blocks some AC and the cap shunts the rest. Since the frequency determines the impedance of the xover network, the output is a slope - 6db for a single component (inductor or cap), 12 db when using both of them, and so on. Reverse the order of components for a low pass xover.

Sorry about the long explanation and the slight deviation from the topic on hand... I do tend to get carried away.

 

[tsunami]

ah so it takes the ac to ground and b/c its such a small cap doesn't interfer with the dc... did i read that right??? no worries bout the explanation on my end, i always try to learn bout stuff i don't understand... thats why i ask a lot of questions... i just can't help it!!!

 

[BrianG]

ah so it takes the ac to ground and b/c its such a small cap doesn't interfer with the dc... did i read that right??? no worries bout the explanation on my end, i always try to learn bout stuff i don't understand... thats why i ask a lot of questions... i just can't help it!!!

Sort of. Think of a cap as a variable resistor whose resistance is dependant on frequency. The higher the frequency, the lower the resistance. Formula:

Xc = 1 / ( 2*Pi*F*C)

Xc=impedance
Pi=3.1415926538...
F=Frequency
C=Capacitance.

So, if the noise is 1kHz and the capacitor is a 10uF, the impedance is 15.9ohms. So, to the noise (at 1kHz), it looks like there is a 15.9 ohm resistor going to ground - but to DC, there is nothing there (infinite resistance). This is because we can consider DC to be 0Hz and I said that the impedance will go up as frequency goes down. Plugging in 0 to the equation as frequency will result in an error because most calculators can't handle a division by 0 - but actually the answer is infinity. While the cap effectively blocks the DC, it will also store a DC charge, so the remote wire will remain on a little bit longer than normal when the radio is shut off (maybe 1/2 second - not much).

I can see we are getting really far off track here: from what amp to buy, to AC component theory. For the sake of the thread, PM me if you have any more questions.

 

[tsunami]

I can see we are getting really far off track here: from what amp to buy, to AC component theory. For the sake of the thread, PM me if you have any more questions.

haha....will do... though thanks for explianing that, really started to make some sense there (kinda scary)

 

[mobomelter]

haha....will do... though thanks for explianing that, really started to make some sense there (kinda scary)

i just installed the amp tonight and it works great. i got the amp for 50 bucks on ebay and the sub for 120 from cardomain. i finally got around to testing my audiobahns and it turns out they are actually alum10q's which have dual 2 ohm voice coils. i'm running a single audiobahn set up for a 4 ohm load until my image dynamic shows up in the mail.

 

[tsunami]

congrats man... i assume the install went smooth enough and you didn't have any magor snags?

 

[mobomelter]

nope none at all. the sub is a tad bit loud though.

 

[tsunami]

yeah you are seriously overpowering your stock speakers with the sub... my problem is my sub isn't loud enough....yet...

 

[mobomelter]

whats going to make me angry is if my image dynamic isn't as loud or nice as the audiobahn. oh and having hatchbacks is great the whole trunk area acts like a box so it sounds so sweet inside the car.

 

[chuyler1]

The two subs are close in price range but I'm pretty sure the ID10v3 is going to sound much better. It should have a smoother frequency response and will probably play a little deeper with the same amplifier power.

Please give us an honest review when you do the swap. Listen to a few songs just before you pull out the audiobahn, then listen to them again with the ID. Pay carefull attention to dynamics, tone, frequency response, and accuracy.

 

[mobomelter]

its scheduled to be here wednesday so i'll try and get it in the car when it gets here.

 

[mobomelter]

i've actually decided i'm going to be selling my new sub because i can't find anyone that wants to buy my audiobahns. so i have no reason to replace the one i am using. if anyone wants the image dynamic sub let me know asap because i'm going to be returning it if not.

 

[chuyler1]

You're not even going to listen to it? Sell the Audiobahns on ebay. Someone will bite.

 

[mobomelter]

thats true. now what do you think would be a good price for those audiobahns 160 shipped?

 

[chuyler1]

Just do a search on ebay for the model number and add watches to the auctions. When they finish, base your starting price around the starting and ending prices of the other auctions.

 

[mobomelter]

i installed the image dynamic sub today and its just not as loud as the audiobahn. right now i'm going to chalk it up to it being brand new and the audiobahn being way past worn in.

 

[tsunami]

deffinatly could be true... as i have read a sub does need a "slight" wear in period for full throw??? but then again, i read it on the internet so....???

 

[mobomelter]

i hope thats the case.