Success! Low-Cost Subwoofer Experiment

[Edwards]

EDIT - I've renamed this to "Success" as I finally figured it out! Skip to here to read the solution or keep on to read all the gory details.
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I've got the 12" HK system and replaced the dash speakers with Infinity's years back. Easy, cheap upgrade well worth it.

Maybe I was bored but I recently replaced the door 6x9's with CDT's for $220 (all four) and it made a tremendous difference - once you unplug the factory sub. I was able to move the bass from -7 to +3 and it actually sounds like a more serious audio system. But it just kept nagging at me that I'm missing anything below 60Hz with no sub (even though it sounds better - my wife thinks I'm crazy). So I've been noodling on how to get a lower-cost sub. I'm sure a JL Stealthbox is amazing, but $1800 + another $1000 for the amp leaves me shaking my head. I don't need to win a thump contest with gangsters. I just wanted decent sub bass added.

So after reading some posts about how much better the factory sub sounded in a larger, ported box, I bought a cheap generic ported box, moved the factory sub into it and fired it up. Hmm. Got my son for a 2nd opinion and we both agreed the system sounded better without the sub. The sub still had that higher frequency boominess.

So I drove for a week like that and rocked hard.

Back of head, "But there is still a sub missing..."

I started researching more and wondered if the factory sub driver was to blame. It is a ~2" thick, more than shallow job with a plastic basket on it. So I ordered a Pioneer 10" 1200W sub to try out. Now the Pioneer is a 4 ohm sub and the factory HK is a 5.2 ohm single voice coil so I had Amazon ship me a 100W 1 ohm resister that I wired in series. Put it into the generic box and listened away.

It definitely sounds better than the factory sub - no surprise. But that overboosted, high-bass boominess is still there. It's obvious from this that Ram applied a weird EQ to just the sub. You don't hear it at all in the 6x9's. So I pulled it all out and I'm back to the CDT Audio 6x9's and no sub. It really does sound SO MUCH better than stock. Night and day. I'm now off to therapy to convince myself I don't need an expensive sub.

If anyone does figure a good, <$500 sub, I'd love to hear about it though!

 

[SpeedyV]

I've got the 12" HK system and replaced the dash speakers with Infinity's years back. Easy, cheap upgrade well worth it.

Maybe I was bored but I recently replaced the door 6x9's with CDT's for $220 (all four) and it made a tremendous difference - once you unplug the factory sub. I was able to move the bass from -7 to +3 and it actually sounds like a more serious audio system. But it just kept nagging at me that I'm missing anything below 60Hz with no sub (even though it sounds better - my wife thinks I'm crazy). So I've been noodling on how to get a lower-cost sub. I'm sure a JL Stealthbox is amazing, but $1800 + another $1000 for the amp leaves me shaking my head. I don't need to win a thump contest with gangsters. I just wanted decent sub bass added.

So after reading some posts about how much better the factory sub sounded in a larger, ported box, I bought a cheap generic ported box, moved the factory sub into it and fired it up. Hmm. Got my son for a 2nd opinion and we both agreed the system sounded better without the sub. The sub still had that higher frequency boominess.

So I drove for a week like that and rocked hard.

Back of head, "But there is still a sub missing..."

I started researching more and wondered if the factory sub driver was to blame. It is a ~2" thick, more than shallow job with a plastic basket on it. So I ordered a Pioneer 10" 1200W sub to try out. Now the Pioneer is a 4 ohm sub and the factory HK is a 5.2 ohm single voice coil so I had Amazon ship me a 100W 1 ohm resister that I wired in series. Put it into the generic box and listened away.

It definitely sounds better than the factory sub - no surprise. But that overboosted, high-bass boominess is still there. It's obvious from this that Ram applied a weird EQ to just the sub. You don't hear it at all in the 6x9's. So I pulled it all out and I'm back to the CDT Audio 6x9's and no sub. It really does sound SO MUCH better than stock. Night and day. I'm now off to therapy to convince myself I don't need an expensive sub.

If anyone does figure a good, <$500 sub, I'd love to hear about it though!

Why not just add an inline low-pass filter? I haven’t done any homework, but I think it’d be cheap.

 

[Edwards]

Thanks @SpeedyV - I was not familiar with speaker-side filters that could handle the wattage. Had to do a lot of searching but found one to try. I'll post the results and I'm hoping that if it works, it might work on the factory sub and solve our problem.

Not sure if 200W is sufficient since we don't know what the factory amp puts out per channel but this is what I've ordered: https://www.amazon.com/dp/B096FT2XBY?psc=1&smid=A3S807LE0L63AP&ref_=chk_typ_imgToDp

 

[SpeedyV]

Curious to know how it works out, as I don't see a cutoff frequency or curve listed.

I see this one from Dayton Audio that cuts off at 500Hz with a 12dB/octave curve at 4 ohms, for example. 500Hz may be what you're looking for, or maybe a higher cutoff if you want to blend with your CDTs a little better (depending on their frequency response). You might have to try a few (500, 700, 1kHz).

 

[HSKR R/T]

I have the CDT 3ohm speakers in my front doors and infinity reference 3.5's in dash. I always thought there should be more volume out of the CDTs than they were putting out. About smmonth ago, I decided to try some EQ settings. Found setting bass to -3, mids to 0, and highs to -1, I could turn up the volume more and actually get sound from the CDTs and it also had better bass sound. I have the Alpine system in my truck with factory sub.

 

[Edwards]

Curious to know how it works out, as I don't see a cutoff frequency or curve listed.

I see this one from Dayton Audio that cuts off at 500Hz with a 12dB/octave curve at 4 ohms, for example. 500Hz may be what you're looking for, or maybe a higher cutoff if you want to blend with your CDTs a little better (depending on their frequency response). You might have to try a few (500, 700, 1kHz).

I saw that but I can't believe RAM is putting anything as high as 500Hz to a sub. I know, I'm assuming a lot...

On the Amazon one I ordered, I found on Alibaba that it cuts off at 50/60Hz which is exactly what I'm looking for. Gets here Sat so we'll see.

 

[Edwards]

OK, I got the low pass filter in and hmm. I have mixed feelings.

I got this one: https://www.amazon.com/dp/B096FT2XBY?psc=1&ref=ppx_yo2ov_dt_b_product_details

The internet is mixed on what the 0Hz/8Hz switch actually does but looking this dude up on alibaba has "The switch of this product can be adjusted between bass and heavy bass." Anyway, having it on 0Hz seemed to be a bit more muddy.

Anyway, wired it in with my 1 Ohm resister and fired it up on the Pioneer sub. It definitely cut out the "boomy" upper bass coming from the sub and this definitively tells me that RAM is sending way too wide of a signal to the sub. But, for most sources/songs it still is over-boosted and puts out muddy bass. It's more pronounced on HD radio but some songs do just sound amazing.

I wondered if maybe my aftermarket sub/box was too efficient so I put the filter in the factory sub. If you are contemplating trading in your truck over the crappy sub RAM/Harmon Kardon put in, then this could be a $13 "make it better." I won't say fix because the bass is overall too boosted and muddy but this gets rid of that punch in the upper bass, like "did RAM make loudness a default?"

Before all this I had my bass set at -7 to tame the punchiness, but now I'm at -3 to 0 depending on the source and you can hear the door 6x9's now. I cannot call this a true fix, but it is noticeably better than stock and only sets you back $13 and an hour or so.

Remove your sub:

1. Can be done without removing the seat. Under passenger side rear seat, pull up the carpet covering the foot of the sub and unscrew the two 10mm bolts.
2. Pull seat forward, pop latch behind seat back to lean fwd.
3. Pop one round plastic thingy (rivet, upholstery push pin?) and pull backliner carpet away from door side. I was not gentle. It can take it.
4. Remove two 13mm bolts at top.
5. Unplug sub (bottom, driver's side) by pushing in tab facing front of truck and slide to drivers side.

To "upgrade" sub:

1. Remove six T20 screws holding in driver and unplug.
2. Pop electrical connector off holder (slide to driver's side) and push rubber plug surrounding wiring into the sub and then remove.
   
3. Now I installed the filter inside the sub box because there was plenty of wire inside and a distinct shortage outside. You could also wire it in at the amp but I already had the sub out and handy. I finger measured from the wiring hole to where I was going to sandwich the filter in a foam taco shell right below and to the right of the "kardon" in the image above. I just cut the factory wires, stripped off a schmekel, and tightened them down. (No idea bout polarity, BUT I did wire in the aftermarket sub with green as + and black as - and had no issues with ANC wonkiness or anything else so I kept that here.
   
4. Next I put the foam taco shell (1" soft closed cell foam to keep it in place and from rattling - also, after driving this thing hard for 30+ minutes it was even warm to the touch) in place.
5. Now you need to reinstall the rubber grommet which was harder than I thought. I couldn't get my hand far enough into the box to push hard and had to pull/massage with my other hand to get the flange to pop out enough to satisfy a RAM installer. Git'r'done.
6. Smush the filter into the taco. I put it with the switch side up so any sub-induced wiggling won't change it.
7. Replug the driver and reinstall. Reinstall box as a reverse of the above.

I was also concerned about this filter as it's rated for 200W and we have no idea how many watts RAM's amp puts out, but again, I drove it hard and it took it all in stride without even getting warm.

I may tinker further but this is cheap progress. I'd still like to have drinks with the RAM/HK "engineers" who signed off on this...

 

[SpeedyV]

Excellent info, as always. Better control could be achievable with an active crossover, but I’m guessing this might disqualify you from “low cost”.

 

[djevox]

OK, I got the low pass filter in and hmm. I have mixed feelings.

I got this one: https://www.amazon.com/dp/B096FT2XBY?psc=1&ref=ppx_yo2ov_dt_b_product_details

The internet is mixed on what the 0Hz/8Hz switch actually does but looking this dude up on alibaba has "The switch of this product can be adjusted between bass and heavy bass." Anyway, having it on 0Hz seemed to be a bit more muddy.

Anyway, wired it in with my 1 Ohm resister and fired it up on the Pioneer sub. It definitely cut out the "boomy" upper bass coming from the sub and this definitively tells me that RAM is sending way too wide of a signal to the sub. But, for most sources/songs it still is over-boosted and puts out muddy bass. It's more pronounced on HD radio but some songs do just sound amazing.

I wondered if maybe my aftermarket sub/box was too efficient so I put the filter in the factory sub. If you are contemplating trading in your truck over the crappy sub RAM/Harmon Kardon put in, then this could be a $13 "make it better." I won't say fix because the bass is overall too boosted and muddy but this gets rid of that punch in the upper bass, like "did RAM make loudness a default?"

Before all this I had my bass set at -7 to tame the punchiness, but now I'm at -3 to 0 depending on the source and you can hear the door 6x9's now. I cannot call this a true fix, but it is noticeably better than stock and only sets you back $13 and an hour or so.

Remove your sub:

1. Can be done without removing the seat. Under passenger side rear seat, pull up the carpet covering the foot of the sub and unscrew the two 10mm bolts.
2. Pull seat forward, pop latch behind seat back to lean fwd.
3. Pop one round plastic thingy (rivet, upholstery push pin?) and pull backliner carpet away from door side. I was not gentle. It can take it.
4. Remove two 13mm bolts at top.
5. Unplug sub (bottom, driver's side) by pushing in tab facing front of truck and slide to drivers side.

To "upgrade" sub:

1. Remove six T20 screws holding in driver and unplug.
2. Pop electrical connector off holder (slide to driver's side) and push rubber plug surrounding wiring into the sub and then remove.
   View attachment 155769
3. Now I installed the filter inside the sub box because there was plenty of wire inside and a distinct shortage outside. You could also wire it in at the amp but I already had the sub out and handy. I finger measured from the wiring hole to where I was going to sandwich the filter in a foam taco shell right below and to the right of the "kardon" in the image above. I just cut the factory wires, stripped off a schmekel, and tightened them down. (No idea bout polarity, BUT I did wire in the aftermarket sub with green as + and black as - and had no issues with ANC wonkiness or anything else so I kept that here.
   View attachment 155770
4. Next I put the foam taco shell (1" soft closed cell foam to keep it in place and from rattling - also, after driving this thing hard for 30+ minutes it was even warm to the touch) in place.
5. Now you need to reinstall the rubber grommet which was harder than I thought. I couldn't get my hand far enough into the box to push hard and had to pull/massage with my other hand to get the flange to pop out enough to satisfy a RAM installer. Git'r'done.
6. Smush the filter into the taco. I put it with the switch side up so any sub-induced wiggling won't change it.
7. Replug the driver and reinstall. Reinstall box as a reverse of the above.

I was also concerned about this filter as it's rated for 200W and we have no idea how many watts RAM's amp puts out, but again, I drove it hard and it took it all in stride without even getting warm.

I may tinker further but this is cheap progress. I'd still like to have drinks with the RAM/HK "engineers" who signed off on this...

The hz cut off very important to know, otherwise you don’t know if the filter you installed has any chance of fixing your issue. The only thing I found as an answer (and what I’m thinking also) is the filters are mid-level crossovers (technically called high pass crossover). I personally prefer my sub crossover to be 65hz and never higher than 88hz, but people have different preferences.

 

[Edwards]

Excellent info, as always. Better control could be achievable with an active crossover, but I’m guessing this might disqualify you from “low cost”.

Well if you know of an active crossover that can handle the power post-amplifier, I'd love to know about it!

 

[Edwards]

The hz cut off very important to know, otherwise you don’t know if the filter you installed has any chance of fixing your issue. The only thing I found as an answer (and what I’m thinking also) is the filters are mid-level crossovers (technically called high pass crossover). I personally prefer my sub crossover to be 65hz and never higher than 88hz, but people have different preferences.

View attachment 155809

Thanks. I saw this but it was one data point vs. the description that says 60Hz so I tried it. If you know of any 60Hz solutions I'd love to hear about them.

 

[Hackmunch]

the problem is the dsp in the factory amp. the stock sub with about 250w rms and no dsp actually doesnt sound bad at all.

 

[SpeedyV]

the problem is the dsp in the factory amp. the stock sub with about 250w rms and no dsp actually doesnt sound bad at all.

Have you analyzed that output signal to the sub? It would be interesting to see if they’ve over-boosted mid-bass output to the sub (e.g., to compensate for factory 6x9 frequency response limitations).

 

[djevox]

Thanks. I saw this but it was one data point vs. the description that says 60Hz so I tried it. If you know of any 60Hz solutions I'd love to hear about them.

I missed where it said 60hz, so I apologize. I’ve always used either an amp’s built-in LPF or a full dsp unit that I use a spectrum analyzer to tune. If you’re trying to avoid using an external amp for the sub, then I think you’ll be stuck with what you’ve got.

 

[Hackmunch]

Have you analyzed that output signal to the sub? It would be interesting to see if they’ve over-boosted mid-bass output to the sub (e.g., to compensate for factory 6x9 frequency response limitations).

not really i did mess around and wired it at 6 ohm (3 2ohm coils in a series) to my 3000w rms amp. obviously i couldnt turn it up but it took a beating and actually sounded good but that plastic sealed box was about to break into pieces lol. you can tell for sure the stock amp has a dsp circuit dedicated to the sub channel.

 

[Edwards]

The hz cut off very important to know, otherwise you don’t know if the filter you installed has any chance of fixing your issue. The only thing I found as an answer (and what I’m thinking also) is the filters are mid-level crossovers (technically called high pass crossover). I personally prefer my sub crossover to be 65hz and never higher than 88hz, but people have different preferences.

View attachment 155809

I've done more digging and based on an inductor calculator here, I've discovered what might be the problem. There is no resistance switch on this filter but it claims to work from 4-8 ohms. However, as the resistance increases, so does the cutoff. Now I don't know what inductors are on this unit, but if it really does cut off the bass above 60Hz at 4 ohms, then it also cuts off at 120Hz at 8 ohms.

Using this same calculator, it would have a cutoff of 78 Hz at 5.2 ohms, which is what the HK sub is.

I did find a fairly close inductor to what is needed, a 13.8mh, here for $43 and I'm toying with picking one up. The other issue is the general over-boosting of the sub and I'm going to experiment with putting another 1 ohm resister inline to bring it to 6.2 ohms. That should quiet it down a tad more but that will then change the inductor required to low pass 60 Hz to 16.45mh.

Man, I wish Radio Shack was still around.

 

[Edwards]

More fiddling. I measured the resistance of my 4 ohm Pioneer sub with two 1 ohm resistors in series and it comes to 5.7 ohms, but when I measured the resistance including the above low pass filter it clocks in at 8.3 ohms. I think that partially explains why the aftermarket sub is not nearly as obnoxious. Once this distraction called work gets out of the way, I'll try it again without the 1 ohm resistors. I only added them to try to match the RAM sub at 5.2 ohms but if the filter adds enough maybe something magic will happen.

 

[Edwards]

Thanks to all for the ideas here. I've finally got it nailed down and wow does it sound so much better than stock. I'm going to make another post with the low-cost solutions for fixing the HK sub boominess, but for now, here's where I am and what I learned.

1. The magic: The Amazon low pass filter works great, but only at lower ohm loads. In my effort to cut the overall factory amp output with additional resistors, I was also inadvertently raising the low bass cutoff. I moved the two 1 ohm resistors to before the filter and all of a sudden it sounded great!
2. The factory amp seems to put out ~200-250W to the sub and it drives it well when you want to pound. Now make no mistake - you will absolutely lose a bass battle to Sir Thumpsalot with a $3500 subwoofer setup but I'm not looking for that. I just want a fairly low cost setup that sounds really good. And there's no impact to the ANC system since any higher frequencies it wants to balance are handled by the door 6x9s.
3. The factory amp still has the sub channel over-boosted so I added in two 1 ohm resistors to balance it with the CDT Audio 6x9's. I played around using just one and on a lot of songs, especially on HD radio, that "too much bass" was back. All of this was done with the bass EQ at 0. That should so you how well this approach works!
4. Resistance. The HK sub (single coil) is 5.2 ohms so a 4 ohm sub would be bad, BUT if you use the low-pass filter it effectively makes it 6.2 ohms. I'm also using two 1 ohm resistors so it comes out to 8.2 ohms.
5. You will also need the factory wire (pictured above on the factory sub box. That way you can plug it into the factory sub connector, pop the pins out of the plastic connector on the other end, and wire them right into your box/filter. Use the green wire as positive for the filter and sub. Easy.
6. I'm moving forward with this setup:
   1. Ordered this box to hold my aftermarket sub. Yes, I'll lose a bit of storage, but don't care. I also removed the factory sub so I can stuff rarely used items behind the seat now. $168 delivered. I had been using a cheap, generic truck box that was ported. Quickly figured out the port added boominess so I stuffed it.
   2. I'm using this Pioneer sub ($104) as it was cheap and fit the box volume and mounting reqs.
   3. You'll need these resistors ($10) and this low-pass filter ($13) to complete everything. You need to ensure the resistors are between the amp and the filter. You can also leave one out for more power going to the sub, but that caused too much of the "ghost of the HK sub" for me so I used both. Also, the filter has a mysterious 0/8Hz switch on it. I can't tell any difference in how it sounds and using a multimeter on the back, don't even think it is wired in to actually do anything. The farthest legs on it are not even soldered in.
7. Now I will say that the CDT Audio 6x9s are worth every penny. I got them on sale for $220. But I was certain I could hear the low cutoff due to the factory amp. It's reported to be 60Hz. I can say than when I extensively played around with sub on / sub off I can hear the missing "fullness" it adds, especially on more modern recordings - and it sounds good now.

Overall, $295 and the factory boominess and over-boosted bass is gone. On top of that, since I can now use the bass EQ the way God intended (0 to +3 instead of leaving it at -7) the door 6x9s have come alive and the deep bass that a sub should provide is there soothing the soul.

 

[Scion]

Outstanding content here, Edwards. Thank you! I've been hoping to find good options for a good, deep, single 10" sub that doesn't take up all of my storage. This gets me on the right track. I may try this method before buying and installing a wiring kit for my PG amp. That amp with a single JL 10" pounded hard in my 05 with the Infinity premium system, so I'd like to do something similar to clean up and strengthen the HK system in this one.

 

[Edwards]

Outstanding content here, Edwards. Thank you! I've been hoping to find good options for a good, deep, single 10" sub that doesn't take up all of my storage. This gets me on the right track. I may try this method before buying and installing a wiring kit for my PG amp. That amp with a single JL 10" pounded hard in my 05 with the Infinity premium system, so I'd like to do something similar to clean up and strengthen the HK system in this one.

Thanks. I just got the new box in and the combination of it and firing up into the seat bottom seems to have tightened up and muted the sound even more. I'm just test driving now but am considering removing one or both resistors to add volume to the sub.

I'll snap a pic but the other bonus is that this box has the jack in just the right spot so you can simply use the factory wiring (from inside the factory box) to go right into the new box. I just popped off the factory connector and the crimped on pins fit into the new jacks.