subwoofer level problem

A few months ago I replaced the factory HU (Shaker 500 on a 2007 Mustang) with an Alpine CDE-125BT. I hooked it all up using the Metra 70-5521 adapter for ford's with amp. I added the 1K resistor to the amp turn on wire to eliminate the pop due to Ford using 5 volts instead of the normal 12 volts. The Alpine sounded great and the subwoofers bumped nice and loud. I could actually feel it on my leg everytime the bass would hit (the factory subs are in the lower front door panel). Then I added an EQ/amp and now I don't get the subwoofer levels I did before. The amp is just a cheap Boss AVA-1404. I am out of work right now and don't have much cash (not to mention a wife and a 10 year old son to take care of). My friend replaced his EQ/amp and said I could have his old one (the Boss) for free so I figured what the heck, why not!

The Boss has inputs for subwoofer and will control them when plugged in. I tried using those inputs (RCA) and the subwoofers get good level and bumped real nice but the drawback is that I get a very loud thump/pop when the unit turns on. I also get the thump/pop with several functions on the Alpine including changing source input, advancing tracks, adjusting HPF...etc. I'm guessing that this caused by the Alpine cutting the signal momentarily and then restoring it. So I have moved the subs back to the Alpine which the thump/pop is eliminated but again the subwoofer level is minimum. I get some but not what I use to get. I use to be able to use the Alpine's subwoofer level control to turn them up or down and you could hear a noticeable difference but now there is only a minimal difference going from 1 to 15 (15 is max) and vise versa. The subwoofers are connected solely through the Alpine just like they were before adding the Boss.

Any idea's on why it has changed? Is the Boss somehow pulling too much power from the Alpine for the speakers and not leaving enough for the Alpine to drive the subs? Does the Boss even draw any power from the Alpine? The Boss is connected to it's own separate power source and ground. The only connection they share is the source ground from the Boss (The Boss has 2 gounds...main ground to chassis and source ground which goes to the source input unit). It just makes no sense to me since the subwoofers are connected exactly the same way they were before the Boss was added and are being driven purely by the Alpine.

The front and rear speakers are connected with the high level inputs and the subwoofers are connected to the Alpine's RCA's (RCA's on Metra plugged into Alpine).

Oh and I just thought I'd mention that I've been installing car audio since the late '70s and was an electrician before my current occupation of computer repair/networking. So needless to say I do have experience working with electronics.

So, you are still using the factory amps?  When you connected the Boss amp, did you bypass the factory amp or still leave it in the circuit?  If you left it in, chances are you blew the input by sending it a high-level signal.

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what did you connect the boss amp to, the highs or the factory sub? there could be a lot of reasons for not having as much bass after adding an amp, one being that you might have the high pass filter turned on so that the bass is being filtered out and depending on which outputs you used from the alpine, the radio might also have a filter. you could have the speaker wire polarity out of phase.

so, which RCA outputs did you use to feed signal to the amp?

where did you connect the speaker wires to the amp?(behind the radio or at the factory amp?)

make sure to check all of the filter settings on the amp, EQ, and radio.


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Yes I am using the factory amps and subs. NO I did not connect the subs to the high level input. If you look at the Metra harness I am using https://www.amazon.com/Metra-70-5521-Radio-Wiring-Harness/dp/B000K50GTA you will see it has a pair of RCA's for the subs. Those are plugged into the RCA's on the Alpine. I also added a 1K resistor between the Alpines remote wire and the factory's amp turn on wires to drop the voltage from 12 volts to 5 volts which is how Ford designed them. If the resistor is not added then you get the classic turn on/off thump. Also if you look at the link above you will see that the harness is actually 2 separate harnesses, 1 24 pin which is the high level inputs for the front and rear speakers and the other non speaker related wires such as +12 constant, ground and so on. The other harness is a smaller 8 pin harness which is solely for the subs and has only a pair of RCA's and the amp turn on wires. To connect the subs to the Boss all I did was unplug the RCA's from the back of the Alpine and plugged in a Monster RCA cable going to the low level inputs of the Boss. I then took another Monster RCA cable and connected it from the Boss low level output to the RCA's on the Metra harness using a pair of barrel connects (because both are male). That is all that was done nothing else as far as the sub's wiring is concerned. The only speakers connected to high level inputs are the front and rears (6 speaker system...2 fronts, 2 rears and two subs). which they should be cause that is the way Ford wired them.

In the meantime I have removed the RCA cables and have plugged the Metra's RCA's back into the Alpine which is the way I had it when I originally installed the Boss. I wanted to try having the Boss control the subs to see how the subs sounded. They sounded quite good but the had the thump/pop problems as I described above and just contributed it to the fact that it was happening solely because the Boss is a cheap POS plain and simple. I figured I would just have the Alpine control them until I get a better EQ in the future. The main concern I have now is that when I installed the Alpine by itself the subs sounded great and bumped nice and hard. Since adding the Boss the subs have lost about 50% of their level (plugged into the Alpine) and hardly bump at all using the same configuration before the Boss was added. Therefore I would think that they should perfom the same as they did when the Alpine was the only unit installed prior to the Boss being added.

you can not have two different amps powering the same set of speakers. if you didnt disconnect the subs from the factory amp and simply added the aftermarket amp to the subwoofer wires then this is the problem. if you want to have the subs on an aftermarket amp then you need to disconnect them from the factory amp first then run them to the new amp.

its not good enough to just disconnect the signal to the factory amp, the subs need to be taken off of the factory amp too.



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I do not have 2 amps powering the same set of speakers. The factory amps power the subwoofers and the Boss is powering the front and rear speakers. Even when I had the subs plugged into the Boss it did not power the subs. The low level inputs on the Boss are NOT amplified and Boss themselves tell you that if you use the low level inputs you must supply another amp. The Ford amps only power the subwoofers which is the way it is setup up when the cars come off the assembly line. The amps are strictly for the subwoofers (2 total..1 amp per subwoofer) which is the way Ford designed the system. As I said in my OP I have been installing car audio equipment since the late 1970's and am well aware of what you can and cannot do and how to install and wire a simple HU/EQ plus speakers and subs setup!

However this is a moot issue because the subs are plugged into the ALPINE NOT THE BOSS. My problem is that the ALPINE IS NOT supplying the subwoofer output level that it did before the Boss was added even though nothing has changed in the way they (the subwoofers) are connected. In other words my configuration has NOT changed for the subwoofers after adding the Boss. The subwoofers are connected EXACTLY the same way they were before the Boss was installed. The only part of the configuration that has changed is for the front and rear speakers which are connected to the Boss and are working just fine and doing what they should be. Here is my configuration once again:

1) Subwoofers connected to preamp outputs (Low level RCA's) on the ALPINE . Preamp outputs on ALPINE are set for subwoofer.

2) Front and rear speakers connected through high level inputs and outputs on Boss.

3) System is all factory components except for the HU and EQ.

Also I forgot to mention that the Boss does not have a HPF or LPF. It has a xover but only for the subwoofers which are not connected.

The Alpine does have a HPF but it is turned off. I have always turned it off on all my Alpine HU's cause I like to get the full range of sound which as good a HU as Alpine makes their HPF always seems to filter too much no matter what you set it to except off of course!

ok now i understand it a little bit more. the only thing i can think of is maybe its still a phase issue because you have the normal speakers set on fullpass, therefore they are playing the same notes as the subwoofers are and can possibly be working against the subs due to the difference in location. its very easy to get subwoofers out of phase when they are in different spots throughout the car.

you might not notice this when having the fronts running off of the radio directly because the alpine wont have the power to really bring out those low notes enough to compete with the factory subs. but, since adding the amp they are now able to compete, it makes the bass seem to come more from the front and less from the subs in the back.

that is my theory right now. i doubt its possible that the boss amp is taking any power away from the factory amp, it probably only has a single 20 or 30 amp fuse in it.

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Thanks for the reply and sorry if I wasn't clear on my setup. Great theroy to except for one problem. My subs are in the lower front of the doors. Would this theory hold true for subs that are up in front like mine? Also I can turn the bass up to max and I still don't get a lot of bass. It's definitely there but normally it would almost overpower the other frequencies. Since my subs are in the lower front of the doors I use to be able to feel it on my leg when the bass would hit. I don't get that anymore which I would think I would if it was the speakers playing the same notes causing the system to play tricks on my ears. Or do you mean that if the speakers are "competing" for the same notes that the speakers would basicly steal or take away the bass from the subs? I was thinking that maybe the EQ/Amps was pulling more power from the Alpine's high level outputs then would normally be used by the Alpine itself therefore not enough power left for the Alpine's preamp outputs. In other words the normal preamp voltage of 2v would drop to 1v or 1.5v causing a weaker signal being sent down the RCA's. Is this possible or is the output power for the Alpine regulated and can not be changed by an amp trying to draw more then what is being offered? Again just a theory.

i thought the subs were in the back deck in the shaker system. so what else is located in the front door because it cant just be a subwoofer and a tweeter, there must be a mid of some sort. im sorry i havent done too many audio systems in newer mustangs so im not extremely familiar with the layout.

still, even if they are all up front they could still potentially cancel each other acoustically. this can always happen when you have two different type of speakers playing the same notes. they might not cancel each other out but they can interfere with each other and make the sound less clear or less powerful. you do have rear speakers in the deck right?

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There are 2 shaker systems. Mine which is the shaker 500...500 watt, 6 speaker system and then there is the shaker 1000...1000 watt, 10 speaker (I think) system. The shaker 1000 has the same subs in the door as mine but also has a subwoofer enclosure in the trunk. I have the shaker 500 which has the subs in the door but does not have the subs in the trunk.

In the front doors you have the subwoofer which is a DVC 8" and you have a combo tweeter and mid range just above it which is 4 ohm 130w. you can see it here:

https://www./itm/05-06-07-09-FORD-MUSTANG-SHAKER-500-LEFT-DRIVER-LOWER-DOOR-SPEAKER-130W-QQ093-/150917978411?pt=Car_Audio_Video&hash=item232369992b&vxp=mtr

and in the rear deck there are 2 6x9 speakers (don't know the specs).

Is there anyway to correct this cancelling out problem other then removing the EQ or changing the location of the door speakers?

a highpass filter on your highs should help a lot. if you dont like the set points on the alpine then you need an amp or better eq that allows you to have a variable crossover setting. this way the speakers wont be trying to play the same notes as the subs. i would suggest setting it around 70Hz so you will still get a little bit of bass from the speakers but not enough to compete with the subs. if my theory is correct then this should help out a lot.

also, panel flex might be something else that i thought could be a problem because of having the sub and the mid in the door. with the added bass of having the speaker and sub playing the same notes it might be causing the door panel to vibrate. anything that vibrates in the car could be another source of wave cancellation. i know the door is supposed to be designed to handle it but over time things could have loosened a little allowing the panel to flex.

try to feel the door while its playing loud and make sure it doesnt vibrate that much. if it does vibrate a lot then maybe buy some "dynamat-like" sound deadener and roll it onto the metal door skin and the back of the door panel to stop the vibration.

that was just a thought but it could be part of the problem.

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As far as the door vibrating I can tell you with out checking that the door not only vibrates but when I turn it up the door shakes enough that I can see my side mirror shake. And not just a little...it is very noticeable and clearly seen. I thought that was normal due to the subwoofer being in the door. Well it just goes to show ya that you learn something new everyday!! I will go through the doors and check for anything that has loosened up and see if I can get it all nice and snug like it should be. Or that may just be the way the doors were designed, I love my Mustang but after all it is built by Ford which I think says it all. Ford has definitely improved quite a bit through the last few years but there are still a few little things that were badly designed in the typical Ford way. It's too bad the Boss has that pop/thump issue cause it does have a built in variable (or semi variable...has 3 settings) crossover which is I guess why it did sound better for the couple hours I had the subwoofers connected to it.

just making sure you know i was talking about the interior door panel not the outside door skin. although in my opinion you can never have enough sound dampening, especially on doors. truthfully, im no expert on acoustics, i just figure that the panel flexing could be an issue although it might not have much effect on your overall problem. i just threw that out there as something to check on. maybe as a cheap experiment you can go buy some foam padding and install it between the door panel and the door to serve as a barrier between the two and also put some pressure on the door panel to keep it from vibrating so much.

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Ok I understand. I certainly can try some form padding just to see. It certainly couldn't hurt. Thanks for your help.