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Something not right on Rockford sub/sub amp


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Hey stereo guys,

Hoping you can  help with a stereo upgrade I was in the middle of and ran into some issues with, mainly with the sub/sub amp:  Boat is '13 23 LSV new to me this year.  Head unit is Rockford RFX5000 w/Bluetooth, amps are Rockford P500x2 (2 tower), P300x2 (sub), P400x4 (8 in boats) and sub is RF 12".  Speakers seemed to work somewhat randomly this year and I planned to do something with system this winter.  Issues may  have been due to moisture somewhere, not sure as they all seem to work now.  So boats in the garage now and based on all I've read here (quite a bit) the best bang for the buck is to build a sealed, correctly sized sub box and see where it gets you.  So I've done that I've also bought a used WS420SQ + new WS Bluetooth as well.  I've ran the new RCA's and power/ground/remote only rough for now w/ WS420 installed and was only playing around with the amp gains prior to final placing of the new sub box and  doing any final tuning, but the sub/sub amp isn't putting out much at all, even with sub amp gain and 420 sub knob way up.  Towers and in boats seemed to have gotten a real boost from the 420, but the sub isn't doing much and I'm not sure why.  All connections seem good and amp is getting power (light on), just seems very lacking in output, like it's running at 20%-no real thump at all.  Sub amp is set to LP and punch eq is all the way down.  Main input for 420 is Rockford RCA outs, WS Bluetooth is Aux input.  Either input seems to have same underwhelming bass...Is there an easy way to test the sub/sub amp to see if one of them is bad? Or what else should I be looking at? 



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If the tower and in-boats zones seem to have plenty of output, youve likely eliminate an input issue. SO this leaves the Sub section of the zone controller, the RCA, or the subwoofer amp. 

Amp setting correct? 

Drop in another RCA between the amp and zone controller. If either the left or right chnls are missing, the woofer's output will be reduced. 

Swap the woofer's RCA from the sub zone to the in-boat or tower zone's output. The zone controller passes through a full-range signal on all 3 zones, so the woofer amp will not know the difference. 

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Have you setup the WS420SQ + new WS Bluetooth to replace the old head unit (RFX5000)?  That wasn't stated; however, that would be my expectation due to WS420SQ capabilities are mostly redundant features if the RFX5000 fed into the WS420SQ.

If you are leaving the RFX5000 in place and that is where your test media originates, then you should confirm the sub-out has been disabled in the RFX5000 because you no longer have anything connected to its sub out.  Guessing here, that you have the WS420SQ feeding the sub; hence, nothing on the RFX5000 sub RCA connectors.


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-Swapped out RCA connectors for another pair, no change

-Moved sub RCA to 420 tower connection, no change

-As far as amp settings,  nothing is tuned yet and was just playing around to see if the new sub box had noticeable improvement before installing.  I had PLC unplugged (sound seemed better) at amp, Xover was set to LP, Punch eq all the way down, gain all the way down, as a start.  But as said to get much at all from the sub, gain needed to be way up, and 420 sub knobs way up as well. 

So does that mean its the amp causing the issue? Or how would I know if the sub itself is the problem? 



-Rockford is still in place and the main input tot he 420, but the WS BT is the aux input for the 420SQ.  Both seemed to yield the same result.  When using RF as input I did disable the sub and sound changed, but still very lackluster.         


Thanks so far guys.  

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7 hours ago, mtagher said:

-Moved sub RCA to 420 tower connection, no change

But did you connect the tower RCA to the zone controller's woofer output and compare the tower output to previous? 


7 hours ago, mtagher said:

So does that mean its the amp causing the issue? Or how would I know if the sub itself is the problem?

You have not completely ruled out the zone control's woofer section. You can ohm the woofer's impedance, its a 4 ohm woofer. A bit of work, but you can move the woofer to the tower speaker amp and reset the setting and see if the woofer's output responds.

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Fully agree with @MLA here, time to do temporary rca connections to rule out what is and isn’t working. 
Just to confirm wiring, the rca cables should be on the left pair of inputs with right-most pair of rca empty on the sub amp and the speaker wires connected to the outer speaker connections to get the bridged output. 

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Ok finally got a chance to play around again.  Ran the tower amp/speakers from the sub zone on 420, sounded similar to using the tower zone.  Let me know if I misunderstood the connections MLA, but I think that checks the sub zone on the 420.   

Yes, RCA inputs are on the left side, right side are pass thrus and empty.  Speaker wires are on outer terminals, bridged.

I did pull the woofer and check resistance, fluctuated a little but around 4 for the most part.

I've read several posts about tuning the amps but  not much specifically about how to tune the sub, assuming it were ok.  Some direction there would be appreciated.         


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2 hours ago, mtagher said:

Ok finally got a chance to play around again.  Ran the tower amp/speakers from the sub zone on 420, sounded similar to using the tower zone.             

Wow, I'm surprised that the sub output is full range, but apparently it is.

on the sub amp, the crossover switch should be set to low pass and the frequency to 100 (starting point)

the gain setting will increase the volume relative to the signal from the rcas.  More gain = higher volume relative to signal from RCAs, less gain = lower volume relative to signal from RCAs.

You may want to try to incrementally increase the gain on the sub amp and see if it makes a difference.  To tune by ear, you'd basically want your system cranked as loud as it will go without distorting, then slowly bring up the sub gain till you hear the sub start to distort, then back the gain off a tick till the signal is clean again.  There are many other and different ways to set gains involving oscilloscopes and special tools, but that's the basic tried and true DIY method.

Once you have the gain set you may find that you still want to pull some gain for songs that don't need as much bass or songs that have an unrealistically strong bass track.  That's where a remote level controller for the sub (a knob that lets you turn the sub gain down) can really come in handy.


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All right thanks for the tips.  

Any recommendations for new amp? Sub is the Rockford 12” M212S4B 300 RMS 600 peak.  In a nice new sealed box. 

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Id suggest a mono that will deliver an RMS @ 4 ohm in the 400W to 600W range. or, a 2 channel that will deliver the same when bridged. 

Heres another option, that ive done before. Move the woofer to the existing 500x2 thats powering the tower speakers and install a new amp for the towers thats an upgrade. 

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So dumb question for @mtagher, when you are testing output, how do you have the WS420's volume knobs and sub volume knob set?  It occurred to me when considering @MLA's comment about potentially overpowering your sub with @Stevo's amp (which realistically should be the upgrade to the towers that @MLA was suggesting, not the sub amp) that you can effectively gain the sub to zero if the volume knob on the sub output from the ws420 is zero.  If the sub volume knob is set very low, you will get no output.  I can't remember for certain, and the ws420sq manual doesn't say, but I'm 99.99% sure that the volume of the sub is first tied to the summed output of the tower and cabin zones and then to the volume knob on the sub.  So if the volume of the tower and cabin zones is very low, so too will the volume of the ws420's sub output also be low, even with the sub volume knob cranked up.  Alternatively, if you have the boat and tower zones cranking but don't also turn up the sub volume, the sub would also be faint.

I'm sure you've tried all that, but just wanted to mention it so you don't end up throwing an amp at a non-problem (especially since you believe the amp worked fine before the ws420 was added).

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On the SQ version zone control, the tower, cabin and sub are 100% independent of each other and only attenuated by the master dial. So in theory, you can have only the sub woofer zone going and identify as a 78 Caprice Classic 0n 22's. Previous version did have the woofer zone tied to the cabin zone. 

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"Here's another option, that I've done before. Move the woofer to the existing 500x2 that's powering the tower speakers and install a new amp for the towers that's an upgrade"

-Was thinking exactly this over the weekend, or upgrade the in boat amp.  May try hooking up the 500x 2 to the sub to see how it sounds tonight.


When I did my very amateurish tuning I did each amp individually, removing RCA's from other amps.  This is what the WS420 instructions advised.  I had master volume and sub both up to ~75% of max and started amp gain at zero, then gradually increased gain.  I had gain up to at least 75-85% to get decent volume from the sub, then sounded somewhat muffled.  Honestly the amp may just be underwhelming.  It was never great even before the box rebuild, but system acted up a lot and I was always planning to do something to improve so didn't focus on it too much.  The original enclosure condition I found to be ok-ish, manly in tact with no major cracks like I've seen posted.  I just didn't get what I was hoping for I guess.  For reference my old boat had Fusion RA210 with a Kicker 700.5 and bass seemed to sound much more powerful to me.        

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Temporarily repurposing the 500/2 to the woofer is about the last step to 100% isolate the issue. Just note though, the amp setting will be drastically different going from tower speakers to a woofer, so make sure you adjust accordingly before making a judgment on the outcome.  

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Ok the 500/2 sounded much better.  So likely I’ll use that for sub and get something improved for towers or in boats.  

Any amp suggestions welcome. Also where new would be best.  

Stevo, I’ll consider yours for sale as well. 


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Here are a few amp options I was considering:

-Move the P500x2 from tower to the sub

-Move the P400x4 (and bridge) to the towers.  That would be 200Wx2 and speakers are 150W max - Can I gain down and still be ok?

-Buy option 1) Wetsounds Syn4 refurb 800W/4 channel (=125Wx4) for in boats for $300 Black Friday deal.   I suppose that would be 60W per speaker for 8 in boats?  Current is the P400x4 at 50x4 channels, so >2x current.

-Buy option 2) Exile X15x4 new at $480 (20% off) so 150 x 4, which I suppose is 75W/speaker.  

Goal is to get good power to sub, and improve the in boats if possible.  Don't really want to buy more than 1 amp right now, and I think this accomplishes that.  Budget <$500 if at all possible.

Comments welcome.



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Marc, if you are careful with the gains/volume knob, the P400x4 bridged would work great.

I think on the wattage from the four channel amp you are forgetting that you are getting greater output out of each channel because you are running two speakers off of each of the four channels.  That will present the amp with a 2ohm load, not 4ohm.

A syn4 will do 200w x 4 at 2 ohms, or 100w per speaker.   That would be a very good choice for a cabin speaker amp, and it would also allow for an upgrade to Rev 10s on the tower if you were ever motivated to do so (you'd put the P400x4 back on cabin duty and then bridge the syn 4 to two channels to power the tower speakers).  The exile amp would give you a negligible additional power bump to each cabin speaker (about 12.5w under ideal conditions -- it does 225w per channel at 2 ohms).

I ran a syn 4 in my last boat and it was fantastic on the cabin speakers.

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Thanks for the feedback that's exactly what I was looking for.  Wasn't sure how the 2 speaker/channel and ohm load work exactly.  I guess that means the P400x4 is currently delivering 100W/channel @ 2 ohms, so 50W/speaker then.  I'd essentially be doubling the power if I understand correctly with either new amp driving the 8 in boats, give or take.  I'll have to decide if the 90 day warranty on the refurb is worth the discount.  Probably is.  



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