Axiom Home Page Forums General Discussion The Water Cooler Car Audio and "Bass Blockers"

OK, now that I've got a new (to me) car, and I don't want to upgrade the head unit (loved doing it last time, but it is a long story and I am not doing it now). Anyway, I've upgraded the rear 6x9 speakers and I still have my sub that I built earlier this year. The front speakers are being upgraded as well for free (a deal I worked up from the dealership to get new aftermarket speakers all around)... Like I said, factory head unit, so no RCA outputs for the sub. The Amp I have has a special plug with 4 wires, two for the left rear and two for the right rear to connect up to the 6x9 speakers.

OK, fine and dandy, but if I am using a powered sub, I'd like to reduce the low end frequencies sent to the 6x9 speakers, but since the sub gets the bass signal from the same wires that teh 6x9 speakers do, I would need the low end signal in order to get the sub to work.

So I found these things at Parts Express called "Bass Blockers" that I would plug in between the speaker and the "splice" that the sub signal would be at, thus full range signal is received by the sub amp (with crossover set as needed), and then the signal after that has the bass blocked so that the 6x9 speakers don't have to try to do the low end stuff.

Do these things really work?

What frequency should I get? They have the following options to block the following freqency ranges:
0-300 Hz (6 dB per octave roll-off. power handling is 75 watts)
0-600 Hz (6 dB per octave roll-off. power handling is 150 watts)
0-800 Hz (6 dB per octave roll-off. power handling is 150 watts)
0-1.2 kHz (6 dB per octave roll-off. power handling is 150 watts)
0-2.8 kHz (6 dB per octave roll-off. power handling is 150 watts)
0-5.6 kHz (6 dB per octave roll-off. power handling is 150 watts)

So which would work best for this situation? Is there something else that would work better but be just as cost effective as these things are just $2.65 each?

EDIT:
I see that Crutchfield sells PAC brand ones that filter 0-150 Hz as well at up to 50 watts RMS with the same 6 dB per octave roll-off....

Bringin' back the high school memories now....

Yes they work, but you've got to pay attention to your cross-over slopes.

The frequency you want depends on how low of a frequency you want your 6x9's to try to play. 6x9's can actually be pretty good with low frequencies and proper amplification. If you upgraded the 6x9's to aftermarket ones, the documentation (or the box) ought to list the low-end of the frequency range. I'd match the bass blocker up as best you can to that range.

For 6x9's, that 0-150 one from Crutchfield sounds good to me. The other ones are more meant for smaller speakers (4.5", 3", 1" tweeters) that can't handle low frequencies at all in a setup where larger speakers (5.25", 6", 6.5",6x9) to handle the midrange.

However! I'd not use them at all. Crossover points & slopes are critical in getting good sound in home and car audio. I'd not trust a $2 part to do that properly. I'd get an actual active crossover or a little amp with crossover controls to do the job. Something so that you can precisely split the frequencies going to the 6x9's and the sub. The 6x9s would sound much better with an amp anyway, rather than being run off the headunit.

Does the sub itself have a crossover? I know I had one once (back in the day...) that had rca & line-level inputs, and rca & line-level outputs controlled by the sub's variable crossover. It was handy, because I could just run the rear channel directly from the headunit to the sub, dial in the crossover I wanted, and then the rca-output from the sub to an amp running full-range (already crossed via the sub) to power the rear speakers (Polk 6x9's, actually - loved em). Made it very easy to dial in the crossover correctly.

I wouldn't think you'd want your sub to try to produce much over 100-150hz. Anything higher than that and you're going to start to get 'directional' sounds from the trunk. Not so good.

Installing that 0-300 on your rear 6x9's would leave you with a lovely 'Bose-esque' hole from 100-300 hz.

Good luck and have fun. I sort of miss the days of spending hours in the garage after school tinkering on my car's stereo. Fun times.

Something like this...

http://www.crutchfield.com/App/Product/Item/Main.aspx?g=82600&i=20603KX2&tp=117

paired with a smaller amp like this to power the 6x9's...

http://www.crutchfield.com/App/Product/Item/Main.aspx?g=120&i=023THA275&tp=115

Edit: You wouldn't even need the crossover. The amp has a built in high/low pass variable crossover, though you might need a line-output-converver (LOC) for the input side.

Headunit -> Sub @ 100hz
Headunit -> LOC -> Amp @ HP 100hz -> 6x9's.

And you can tinker with the points to get the sound the way you like it.

I'm used to the ol' 80 Hz home theater type cross over, so I was thinking that the "lower" the better too, but didn't see anything that did that.

The sub amp does have a crossover, so it can filter out the highs just fine.

The sub amp is just a Pioneer GM-7300M and the sub itself is a 10" Pioneer TS-W251R. I don't recall the 6x9's but they were again Pioneer brand but I bought them about 7 years ago and they sat in the box for most of those 7 years. The fronts are unknown right now as the dealer hasn't called me back yet today to let me know what they are, but that is besides the point.

I'll look up the 6x9 specs tonight to see, but I think that they claim a frequency response down to 28 Hz. I just don't like the sound coming out of them down that low, and it doesn't have enough "punch" like the sub will ad.

You're correct, even though they'll play down to 28hz, they won't put out the kind of bass you want down there. But that does say that they have the ability to go pretty low. I'd still say that 100hz is the magical point where you ought to cross this over. Especially with a 10" sub.

The higher you go, the less effective the sub will be and the bigger the hole you'll have.

As for all of this I would need to power by sub amp, the rear speaker amp, and the electronic crossover? I've got a big enough power cable for my one amp and it has a "splitter" to work with 2 amps, so I guess that wouldn't be too bad. Of course, it would be another $140 $80 to do it vs. potentially $15 for the passive. Increased control and better sound quality, sure, but heck this isn't a top end car audio system. Hmmmm.... I wonder how much real world difference I would see going that route with the mid-grade (if that even) gear I've got.

Some of the main reasons that I don't just upgrade the head unit like I did in my last car, which had full control over crossover to the front speakers and another setting for the rear speakers, and yet another setting for the sub, is because the car has a 1.5 DIN opening, meaning a piece of plastic molding that takes away from the clean look, plus I would need a head unit that was illuminated red to match the Pontiac red, then add the special PAC brand interface to get the factory steering wheel controls to work still ($65), plus the fact that I would lose all head unit information displayed on the heads up display, it just doesn't seem very attractive. I even found the following 1.5 DIN faceplate to try to clean it up (which I was thinking illuminated red would look nice for $95 )



$160 + HU Cost - Head Up Display =
$60 Amp + $20 Line Output Converter = $80 controllable option
$15 Bass Blockers = $15 mediocre option


So the speaker connections on the Blaupunkt THA275 are for output only, right? It gets the audio input via RCA and then also passes output back out the RCA connections (for the sub amp) as well as the speaker outputs? Right?

I don't think you'd have to upgrade the headunit. I totally understand wanting to keep the stock unit. I'd keep it stock too. These days (IMHO), OEM headunits aren't nearly as bad as they were 10-15-20 years ago. And with all the extra doo-dads like steering wheel controls, heads-up displays, etc, it can be exceedingly difficult to do so anyway.

So just so I'm clear, you're tapping into the rear channels, right?

The catch is how to get two sets of outputs from that. One for the sub amp, and the other for either the 6x9's directly with some kind of passive crossover, or with the rear 6x9's amped.

I'd go with your option 'B' ...

The LOC will take the two line-level outputs (L+R) and convert it to two RCA plugs (L+R), which is a lot easier to work with. Then I'd buy two RCA splitters, and split the outputs into two pairs (2L + 2R). I don't think you would have a problem splitting the signal like that. I seem to recall doing this a few times in various setups and never having any problems.

Connect one pair to the sub, and the other to an amp. Any little 2-channel amp would do so long as it has a variable high-pass crossover. I didn't pick the Blaupunkt one for any reason other than it was the first one that popped up on Crutchfield's site and it was pretty cheap. You could probably get one even cheaper at your local big-box store. Run the speaker-outputs from the amp to your rear 6x9's, no surprise there.

If you went with that Blaupunkt at $60, the total cost to you would probably be less than $100. A LOC and RCA cables are pretty cheap (RadioShack). You'd get fully independent crossovers to play with (sub & rear), and enjoy a nice power boost to your 6x9's. The only problem I can see here is that it might take a bit of work to balance out the sound volume between the front speakers (running off the HU), the sub, and the rear 6x9's. For that reason, if you use a rear-channel amp, make sure it has a level control on it (most do).

I would guess that you can probably power the little 2-channel from the existing power lines & remote turn-on that you have run for the sub amp. It depends on the gauge of wiring you used and how it's fused. But I can't think that a little 2-channel amp, especially one high-passed, would draw enough current to really make much of a difference.

I don't recall the exact power wiring sizes, but the kit was rated as being designed for "dual amps" with "1400 Watts"...


Yup, I am just looking to tap into the rear speakers.

So when you are saying line-level outputs, you really just mean the rear speaker wires, right? Sorry if this sounds so dumb, but I just want to make sure.

It sounds like power won't be an issue for you. So long as your total peak wattage is below 1400 watts, it ought to be ok. Provided you've properly fused it all (fuse right by the battery, right?) then you shouldn't have a problem. If you start blowing the fuse(s) when the volume is cranked up, then you need to explore other options. Again, we're not talking about adding another huge sub amp...

No questions are dumb! Yes, by line-level outputs I'm talking about the speaker wires coming from the head unit. The wires carrying the signal & current that connect directly to the speaker. The wires that you've disconnected or cut to get access to the rear channels.

Nick - this is the perfect solution:

http://www.crutchfield.com/App/Product/Item/Main.aspx?g=82600&i=20603KX2&search=crossovers&tp=117

Speaker lines that would normally go into the rear speakers would connect to this, and then you run the crossed over signal into each of your amps, and then to the speakers.