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Will playing with Sub Sonic Filter kill my sub?

 

upsetsubguy
Unregistered guest
Amp's a kx400.1, will toggling it (subsonic filter) on or off when the system's powered up kill my subs? If so.. how does it kill? i mean will it fry the VCs,rip the spyder..etc. I need indepth explaination..please Jon, Isaac, Glass if u guys are reading this.. need help.
 

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 7848
Registered: Dec-03
if you're using a ported box, lack of that filter can cause the sub to lose damping below the tuned port frequency, and when the sub unloads all at once that way, it over extends and you blow the sub.

there is a possibility of some distortion when the switch is flipped as well, but that's arguable and not guaranteed.
 

Gold Member
Username: Subfanatic

Walton, Ky

Post Number: 3228
Registered: Dec-04
glass, could you please explain to me what a subsonic filter does, what it does when its on/off, and what everyone means by damnpning, or lthe like THD dampning of this amp is this much, if u know what im talking about. thank you
 

upsetsubguy
Unregistered guest
So toggling the filter on or off when the system's powered up WONT kill my subs? Amp's a kicker 400.1 and the subsonic is @25hz. It's the 2002 model. I dont have the manual, but Kicker states in their newer model's manual to NOT switch the filter when the system's powered up. Doesnt say why.. i need to know why cuz im trying to eliminate every possibility.
I got my JL W3D4(old one, not the V2) sub installed at a local shop and i dont know what went wrong.. but its just not producing any bass. It has 'output' low deep tones that follows the beat..but its DEFINATELY not makin any bass. And limited to barely visible cone movement. As far as i can tell the box is made according to JL specs. I need to get my facts straight before i confront them later. I greatly appreciate any help u can give me. I have more details on what went on if u want it.
 

Gold Member
Username: Fishy

Tamarac Ft.Laud, FL USA

Post Number: 1106
Registered: Sep-04
Its simply a high pass filter that cuts off some of the lower frequencies to prevent a driver in a ported enclosure from unloading. A good rule of thumb is to set it 1/3 of an octave below tuning.

A full octave below is simply half the frequency. If you want to estimate the frequency 1/3 an octave below tuning divide the tuning frequency by six then subtract that number + 1 or 2 Hz from the tuning frequency.

There's a more accurate way of figuring this, but I've totally forgotten the logarithmic stuff. I think it would be something like half the frequency plus that same frequency to the 2/3 power or:

ft/2 + ft^.67

where ft is the tuning frequency.

So 1/3 an octave below 40 Hz would be:

20 + 20^.67 = 20 + 11.8 or about 32 Hz.

How's that for a bunch of useless information Sub? hehe.

-Fishy
 

Gold Member
Username: Fishy

Tamarac Ft.Laud, FL USA

Post Number: 1107
Registered: Sep-04
Hey upset. If that w3 is in a sealed enclosure you don't need a subsonic filter. In fact it might sound better(play lower) w/o one.

Regardless there's not much music material recorded below 25 Hz so it shouldn't make that much of a difference.

Maybe the gains were set improperly.

-Fishy
 

Gold Member
Username: Fishy

Tamarac Ft.Laud, FL USA

Post Number: 1108
Registered: Sep-04
Oh and Sub, the term damping is usually used when describing something that "sinks" power like a shock absorber that converts the motion of a suspension into heat. Sound dampening works the same way to some extent by limiting panel vibration by converting some of the panels vibrating energy into heat as well.

When its said that the cone of a sub is damped by a port at tuning it simply means that much of its energy(motion) is converted to acoustic output at the port.

That make any sense?

I'm sure Glass can explain it better than I can.

-Fishy
 

Gold Member
Username: Fishy

Tamarac Ft.Laud, FL USA

Post Number: 1109
Registered: Sep-04
And by the same token the term damping factor refers to the relationship between the internal impedance of an amp to that of the speaker its driving. A lower internal resistance means that more of a drivers kinetic energy is converted into heat in the wiring when there's no signal. The more energy "sinked" the quicker the driver's motion is stopped. This is what is meant when someone says an amp with a lower dampening factor has more "control" over a driver.

Now I know that didn't make any sense, but here's a couple articles Glass wrote that deal with the subject:

http://www.wickedcases.com/caraudio/amplifiers.html

http://www.wickedcases.com/caraudio/ampspecs.html

Hopefully those will help.

:-)

-Fishy
 

upsetsubguy
Unregistered guest
Fishy, it was ported. The subsonic is set @25hz and is non variable. I can only toggle it on/off. First time playing all gains/boost/XO were set to flat. I set the gain to match the HU CDA 9831 (4v). Then we got sound, "low deep tones that follows the beat..but its DEFINATELY not makin any bass. And limited to barely visible cone movement". At this point i went in my car to adjust the HU controls, i wasnt gone for more than 5 mins..when i came back and checked on the amp and some %$#!%had set the Gains to FULL! Could that have killed the sub? Though even then there were no improvement on the bass, a lil bit more volume. I wasnt gone that long.. considering the amp is 400Watts RMS @2ohms (470 in the birth sheet) and the JL's 250Watts RMS.. could it have been fried in that amount of time i was gone?
 

Gold Member
Username: Fishy

Tamarac Ft.Laud, FL USA

Post Number: 1110
Registered: Sep-04
[edit] lol, that should read damping factor not "dampening".

Sry, my brain hurts now.

:P

-Fishy
 

upsetsubguy
Unregistered guest
im gonna go back to the shop now, but i'll be back later to see what u guys think.. and an update.
 

Gold Member
Username: Fishy

Tamarac Ft.Laud, FL USA

Post Number: 1112
Registered: Sep-04
Where do you have the lowpass filter set? If the gains are set correctly either it may be set too low or somethin else is wrong.

How do you have that sub's voice coils wired? If you have them in series then the amp's seeing an 8 ohm load and is producing 1/4th the power. That sub should still kickorz with 100 watts however.

Make sure you post back when you determine what the problem is.

Sounds interesting and is probably something really simple.

-Fishy
 

upsetsubguy
Unregistered guest
I've got HU's LPF set to 80hz. Something strange, if i set it to OFF(fullrange) there's no output from the sub. Also, the crossover on the amp itself i've set to 100hz. But messing with the amp's crossover had little effect on the sub's output though..
I believe the gains are set properly.. its set at 4V which matches the HU.
Now here's something wierd..in the subs manual, it draws a diagram of how u shuld wire the VCs. Here's a pic:
<img>
if u dont see it:
http://tinypic.com/4ta4hi

The first figure shows how the shop wired the VCs. The second is what the JL's manual had. I'm no expert, but so far i havent seen a DVC connected in that manner. I could be wrong. The shop refused to wire it according to the manual cuz they said wiring it like dat would cause a short and fry the sub.
 

Gold Member
Username: Fishy

Tamarac Ft.Laud, FL USA

Post Number: 1114
Registered: Sep-04
The shop wired it correctly and I think you copied JL's recommendation wrong. It shows the vc's wired in parallel with a jumper that is effectively shorting the amplifier's outputs. Not good. This is what JL's recommendation should look like(2nd diagram from the top):

http://www.jlaudio.com/tutorials/wiring/index.html#1dvcp

The diagrams you provided have one voice coil's pos and neg terminal reversed from what they actually are in real life. If the shop has wired your sub physically as you have shown then that IS your problem. In other words if each jumper goes from one voice coil terminal to the other's on THE SAME SIDE, unlike what is shown in the link I provided, then the polarity on one voice coil is backwards and they're actually providing force in opposite directions(pushing on each other) and effectively cancelling each other out. This could result in exactly the type behavior you're describing.

I'd check that sub again and MAKE SURE the positive of one voice coil is connected to the positive of the other and the same with negatives.

-Fishy
 

Bronze Member
Username: Car_bangs

Post Number: 20
Registered: May-05
U SHOULD NEVER EVER ADJUST SUB SONIC FILTER WHILE YOUR AMP IS ON ANOTHER GOOD WAY TO BLOW A SUB
 

Gold Member
Username: Fishy

Tamarac Ft.Laud, FL USA

Post Number: 1117
Registered: Sep-04
and how exactly would it blow a sub?
 

Gold Member
Username: Invain

Michigan United States

Post Number: 2160
Registered: Aug-04
Freedom, changing the subsonic filter will have no effect on the current running to the sub. All it will do is cut off/let on certain frequencies. It's not as if you get a surge of power, or a drop in the voltage rails.
 

Gold Member
Username: James1115

Wilton, Ct

Post Number: 2739
Registered: Dec-04
I concur with Fishy and Joe here it will not do anything and like Glass said some people will argue that it will but there is no evidence of this at all!
 

Gold Member
Username: Invain

Michigan United States

Post Number: 2168
Registered: Aug-04
Thank you do-jo.
 

upsetsubguy
Unregistered guest
Fishy, i did that diagram out of memory. So the arrangement of the [-] and [+] terminals may not reflect real life. Sorry. But, the fact remains that the piece of paper that came with the sub had the second diagram's connection method. What gives?! Factory misprint? I'll try and get a scan of it, might take me awhile cuz scanner's acting up.
If the shop had followed the second diagram, would that have damaged either the sub or amp?

Update:
Went back to the shop yesterday and they took out the sub and enclosure and hooked it up to another amp in another car. Works perfect. So that eliminates DVC wiring issues or enclosure error. Is my amp damaged?
It's a kx400.1 and i checked the green and red LEDS when its running, but it hasnt gone into protection mode or anything cuz the green led stays on. Adjusting the crossover knob on the amp gave little result on the 'tone' of output. The gains are set correctly at 4v matching the HU. The subsonicfilter's ON. Gets a little warm but not hot.
Is it possible the sub's phase is being affected by the car's trunk space? The car's a '92 Honda Civic 4doors. The way they made the enclosure made it approx. 3-4 inches from touching the trunk's ceiling. Oh and sub's pointed upward. Whether the trunk's closed or opened, the bass or lack of it remains the same.
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