What I discovered about the factory amplifier

[landcrshr]

It uses high-pass filtering on the rear channels! (cuts off the bass). Those outputs are what feeds the subwoofer amp!

So I finally finished installing my (4) Polk db651's last night and was immediately impressed with the bass response of the front door speakers (dash speakers are removed).
The rears however seemed kinda thin. Did I get them out of phase? Nope. Did the PO install capacitors on the 4"ers he had in there? Nope. Did some investigating and found it was in the amp.

I know it's pretty common for small powered "sub" woofers to use subsonic filters because those frequencies would rob them of their meager power...but putting the filter in the main amp? And with such a high crossover point? That kind of limits aftermarket options.

I guess that's why that little sub-thingy in back never did any good. I hope nobody ever tries to use those outputs to feed a real subwoofer amp.

Just thought I'd pass this along.
Next project: New 4 channel amp.

 

[DARKNESS]

Interesting. I know the OEM roof speakers do have capacitors on them and they're 25 ohm. That may add to the thin sound in the rear as well.

 

[landcrshr]

Yeah, I discovered that too about the roof speakers when I was trouble-shooting.
Disconnected those as well, they just add an unnecessary load since they'll never be heard.

 

[nigelsiam]

Did you use the Polk db651 's' (slim mount) variant? How was the installation for you? Any clearance issues?

 

[landcrshr]

I used the standard version, not the slim, with the spacers in between the door and door panel (front and back).

The fronts were a litte PITA to get the spacer ring seated into the speaker recess, needed some customizing (sorry, no pics) but no clearance issues once in.

The rears went easier after opening up the hole with a jig saw. I opened them up to the diameter of the hole in the panel.
Since the original speakers were already removed, I didn't have to remove the panel. I then just popped a couple clips loose at the bottom and slid the spacer up behind. Plenty of clearance and no visible spacers.

Glad I went with the standard version after I checked the spec's:

Frequency response: 35 ~ 22kHz vs. 50 ~ 22k for the slims.

35 Hz, that's subwoofer territory! Pretty amazing for a 6.5"

I'll do some testing to see what I'm actually getting after I get rid of that factory amp.

 

[Kajun]

I'm interested in what you find. I replaced all of my speakers (all Pioneer) with the exception of the dash speakers. I even put a shallow mount kicker sub in the rear.
I didn't expect tremendous improvement but I'm still not pleased. I started hunting around the forum for technical reasons and cost effective solutions.
I saw where you posted in another thread that the better improvement will come from the speakers rather than an amp, but it appears that with a speaker upgrade the factory amp is actually impeding the performance of newer speakers. Correct?
I'm not interested in replacing the factory head unit just yet because of budget reasons. However if bypassing the factory amp improves the performance of the upgraded speakers I can manage a wiring job.
Again this isn't on the top of my to do list, but am interested in short term options.

 

[JCruse]

Any idea what the cutoff frequency of those filters was?

I recently read somewhere that these amps have crossovers/filters in them but this filtering sounds pretty stupid.

My VW does just the opposite, the front doors are 6" full range coaxials and the rear doors are "subwoofers" - a plain 6" cone with low pass filtering from the amp. I'd like to do something like this in the 80. I'm planning on using the same polks you have in front (or components) and then some kind of woofer in the rear doors since I don't really need mids and highs back there. If I don't find anything suitable then I'll go with the Polks all around.

I'm glad you like them, I've had my eye on those for a long time now, instead of the Pioneers so many use. I've been impressed with Polk speakers for about 30+ years now.


These also look rather interesting

http://www.amazon.com/Polk-Audio-AA2651-A-6-5-Inch-Speaker/dp/B001C3P6FI/ref=sr_sp-atf_title_1_3?ie=UTF8&qid=1373251208&sr=8-3&keywords=polk+651




.

 

[landcrshr]

....but it appears that with a speaker upgrade the factory amp is actually impeding the performance of newer speakers. Correct?
....However if bypassing the factory amp improves the performance of the upgraded speakers I can manage a wiring job.

I just returned from my first long trip with the new Polks and I'm happy to report that I'm pretty impressed, even without the rears runing full-range. Certainly a noticable improvement over the Pioneers I had before. You can definetly hear more of the fundamental bass notes, instead of just the harmonics. I think that restoring the bass to the rear speakers will really reinforce that even more.

Bypassing the factory amp however is no simple wiring job. Toyota has it set up as more of an extension of the head unit.
The amp supplies 12v the the HU and the HU puts out a low-level signal, but there are no RCA jacks. Signal muting is also handled in the amp.

I think the route I'll go is to take the amp's front outputs and go into a low-level adaptor, then into an EQ with a fader, and finally into a 4 x 30w amp I have.

 

[landcrshr]

Any idea what the cutoff frequency of those filters was?

...I'm planning on using the same polks you have in front (or components) and then some kind of woofer in the rear doors since I don't really need mids and highs back there. If I don't find anything suitable then I'll go with the Polks all around.

These also look rather interesting

http://www.amazon.com/Polk-Audio-AA...=UTF8&qid=1373251208&sr=8-3&keywords=polk+651




.

I didn't get a chance to do any real testing, but I'm guessing the x-over is around 60Hz or so!

I had the idea of just woofers in the rear doors too, but you might have to go with 8"ers if you want to extend the bass much beyond the capability of the Polks. That would then mean building custom pods and so on....

I only glanced at the link, they do look interesting. I'll look into those some more.

 

[shockeere]

It uses high-pass filtering on the rear channels! (cuts off the bass). Those outputs are what feeds the subwoofer amp!

So I finally finished installing my (4) Polk db651's last night and was immediately impressed with the bass response of the front door speakers (dash speakers are removed).
The rears however seemed kinda thin. Did I get them out of phase? Nope. Did the PO install capacitors on the 4"ers he had in there? Nope. Did some investigating and found it was in the amp.

I know it's pretty common for small powered "sub" woofers to use subsonic filters because those frequencies would rob them of their meager power...but putting the filter in the main amp? And with such a high crossover point? That kind of limits aftermarket options.

I guess that's why that little sub-thingy in back never did any good. I hope nobody ever tries to use those outputs to feed a real subwoofer amp.

Just thought I'd pass this along.
Next project: New 4 channel amp.

Very cool! Thanks for sharing.

1997 lx450: 135k miles, unlocked, packasport

 

[shockeere]

Any idea what the cutoff frequency of those filters was?

Do you guys know the size of the capacitors? That can directly tell you what frequencies are attenuated / filtered out.

1997 lx450: 135k miles, unlocked, packasport

 

[landcrshr]

The amplifier uses active (electronic) filtering.

 

[shockeere]

The amplifier uses active (electronic) filtering.

So then both resistors and cap values need to be known to determine the cutoff frequency.

1997 lx450: 135k miles, unlocked, packasport

 

[landcrshr]

Well, that's true (for an analog filter), if I really wanted to know, but you would also need the schematic to see the full circuit. I would be happy to bypass the filter circuit, but it looks like it is all integrated into one do-everything pre-amp IC.

 

[npg170]

Does anybody know how many watts the stock subwoofer amp put out?

 

[landcrshr]

Not sure, maybe like 20 Watts/30 Watts max.

 

[Timpanogos Slim]

I have one disassembled and that sounds about right to me from what I recall - I looked up specs for the chips. Something like 40w into 2 ohms max.