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can a bridged 150 rms input do justice to a sub of 300 rms?

Discussion in 'In Car Entertainment' started by tushargn, Apr 7, 2013.

  1. tushargn

    tushargn Amatore

    Guys, I have follwoing setup which I am planning to take to next step by adding a sub.

    Front Speakers(Make/Model/Type/NA): Helix B62C comp- 50 rms, doors damped
    Rear Speakers(Make/Model/Type/NA): Helix 6X co-ax: 40rms
    HU : Kenwood KDC-U4549SD: 3 Preout (2.5V)
    Amp: JVC 3104

    • 4/3/2 Channel Amplifier
    • 800W Max Power
    • 60W RMS @ 4Channel @ 4ohm
    • 90w RMS @ 4Channel @ 2ohm
    • 150W RMS @ 2Channel Bridged @ 4ohm
    • Class-AB Circuit

    I am thinking of adding Infinity Ref1220se sub as I found the factory fitted enclosure makes justice to the performance. The sub is 300 rms @2 or 4 ohm (same sites say 2 and some reviews say its 4 ohm) however for now, I want to connect the front comps to front 2 channels of amp, rear co axials directly to the HU and rear 2 channels of amp to be bridged for sub which would offer 150W RMS @ 2Channel Bridged @ 4ohm.

    1. Is this feasible?
    2. would it be risking the amp?
    3. can a bridged 150 rms input do justice to a sub of 300 rms?
    4. Amp is directly powered through the battery, do I need to get a capacitor while introducing a sub?
    5. ohm part of the matching?
  2. Better buy a monoblock amp to power the sub.
    1 person likes this.
  3. tushargn

    tushargn Amatore

    Thanks for suggestion Praveen, would see how it performs on 150 rms bridged input and then may go for a monoblock if not satisfied.ordered Infinity Ref1220SE today..... too eager for the delivery! For anyone and everyone@pune, there is one demo piece at Reliance auto@Mukundnagar!
  4. khoj

    khoj Amatore

    It is quite allright to bridge 2 channels and use them to drive a subwoofer.

    As long as the amp is giving out clean power it is not allways necessary to feed the full amount of rms power to the sub to make it sing, unless it is a power hungry sub. Infinity subs are not and should be ok with the 100W odd that the amp will be able to put out after efficiency losses etc.

    There is no need for a capacitor at these power levels except for cosmetic purposes. You would do well however to introduce a fuse close to the battery. Check the current consumption of your amp and then get an ANL fuse holder with a fuse rated to 20% over the amp's current consumption.

    Ohm matching ! Well depends what version of the sub you have bought the one with 2Ohm voice coil or that with 4ohms. The connection between the amp and the sub will have to be wired accordingly. Refer to the sub's manual for details.

  5. jayadev

    jayadev Esperto

    Kannur, India
    Grande Punto 1.3 90 HP
    An amp does not see the power of what it drives. it see impedance .

    Power = i^2 x R

    i is current through loudspeakers and r is the impediance.

    a bridge power amplifier delivers 4 times power into same load.
    Power = 4 X i^2 x R

    When impedance is high current is low and power goes down and vice versa.

    Wrong loudspeakers can fry your amplifier or slip it into clipping or protection mode.
  6. tushargn

    tushargn Amatore

    Thanks Khoj, Thats the piece of assurance/info I was looking at! I am not looking at the early bird, but rather thinking of the 'second mouse' theory! (Its always the Second mouse who gets the cheese! ) I wanted to know whether it can play sub without burning anything.

    Thanks Jaydev for explanation, it confirmed that I have to go for 2 ohm mono amp, one day or other!

    By the way, the latest update is I have received the sub. Being over excited n impatient, I disconnected 1 rear door cable from rear channel and connected the sub cable to it by reducing amp gain all the way down and also by keeping all the settings flat on HU. After a few mix n match rounds,

    Now the sub is alive and so is my listening experience! ::O I cant crank the volume the way I used to with my earlier setup as now the music is clearly audible outside even at 60% vol.. at >20 feet. the fur toy hanging to my RVM shakes along with the RVM. Though the sub may be under-performing without 300rms 2ohm input but the heck, it already maxes my expectations. I drive for more than 2 hours everyday, I wanted a bare-able punch that I can listen for long... I got it with mere 75w input!

    The sub is still occupying half of the rear seat as i dont have time to go and get the pro fitment for boot. Planning to do it over weekend.

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