# Do I need a bandpass crossover on an amp?



## brandontw (Jan 21, 2012)

I've been lurking and searching and reading for quite a while on this forum. And i'm usually pretty good at picking up the gist of things, but i'm having a heck of a time wrapping my head around the options for going active.

I want to do really simple, fairly cheap install, it going to just be 6.5" or 7" Woofers in the front doors, tweeters nearby, up higher on the door. And a fairly small sub in the back.

This is all really conceptual as I don't even have the vehicle yet (im shopping around for an old beater truck, and i want to put too nice of a system in it)

I have a head unit already that i want to keep, its nothing special, just a jvc arsenal with 3 pre-outs. 

I get the impression it doesnt have the crossover adustments i need to go active... but i really dont know.

So I thought about getting a decent 4 channel amp and running the front door speakers off that. 2 channels to mids, 2 more to tweets 

But most amps don't have a bandpass crossover... 

I know i can do a high pass crossover on my headunit that will do 100 Hz, 120 Hz, 150 Hz, or Off.
and it has a low pass for the sub outputs that does 55 Hz, 85 Hz, 120 Hz, or off.

Is that good enough? Whats a good crossover point for a sub?

Could i set the HU highpass to 120, the lowpass to 120, then use the highpasses on the amp to adjust the mid/tweeter crossover point?

Or do i need to get an adjustable crossover that i can use to do all the crossover work?


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## schmiddr2 (Aug 10, 2009)

brandontw said:


> I've been lurking and searching and reading for quite a while on this forum. And i'm usually pretty good at picking up the gist of things, but i'm having a heck of a time wrapping my head around the options for going active.
> 
> I want to do really simple, fairly cheap install, it going to just be 6.5" or 7" Woofers in the front doors, tweeters nearby, up higher on the door. And a fairly small sub in the back.
> 
> ...



Tweeters need a HP in the 2KHZ-5KHz range depending on the speaker.
The woofer will need to be bandpassed. It will play down to the sub crossover frequency and up to the tweeter crossover frequency.


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## brandontw (Jan 21, 2012)

schmiddr2 said:


> Tweeters need a HP in the 2KHZ-5KHz range depending on the speaker.
> The woofer will need to be bandpassed. It will play down to the sub crossover frequency and up to the tweeter crossover frequency.


I guess i knew most of that.... But Im asking if i can just use the HPF on the head unit to get the bottom half of the band pass (around 120), then find an amp that will let me adjust the mid channels up to, say 3K with a lowpass, then the tweeter from 3K+

So i'd need an amp that lets me adjust all the way up into the 2-5k range on both LPF and HPF?

Looks like an MB Quart ONX4.125 would do it, but im not sure i want an MBquart amp, and I think i'd rather have one that does it like the JL 300/4 with the x1/x10 switch.

Am i even going about this the right way at all?

Im still not even sure im understanding.

Should i be planning on getting another piece of equipment if i want to go active? like a clarion mcd360? 

Or something else completely... am i missing a piece of the puzzle?


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## schmiddr2 (Aug 10, 2009)

I replied in your post, in red. You can use the HU HPF for the woofers and the LPF for the subs. I would go with 100Hz, not 120Hz.


The JL amp will work fine for setting the crossover point for the woofer and tweeter. The MB Quart will not work because the LPF only goes up to 250Hz. With that said, I would buy this over either of those, Precision Power P900.4 (p9004) 4-Channel Phantom Car Amplifier It should allow you to bandpass your mids and has HPF for your tweeters! And that lets you set the subwoofer filter lower, like 55Hz or 85Hz as I suggested before.

If you get an amp with good built in crossovers then you should not need an additional unit like the clarion.


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## brandontw (Jan 21, 2012)

schmiddr2 said:


> I replied in your post, in red. You can use the HU HPF for the woofers and the LPF for the subs. I would go with 100Hz, not 120Hz.
> 
> 
> The JL amp will work fine for setting the crossover point for the woofer and tweeter. The MB Quart will not work because the LPF only goes up to 250Hz. With that said, I would buy this over either of those, Precision Power P900.4 (p9004) 4-Channel Phantom Car Amplifier It should allow you to bandpass your mids and has HPF for your tweeters! And that lets you set the subwoofer filter lower, like 55Hz or 85Hz as I suggested before.
> ...


Sorry, i missed some of that for some reason.

Very helpful, thank you. I think i have a better picture of what i want now.

So i guess im looking at amps...

Ive been just basically looking at the pictures of the endplate to see if it has what i want, and the crossover range and slope. Is that the best way to do it?

I like the PPI amp a lot, and thats actually one ive had my eye on... i just want to know what else is out there. Any 5 channels around?


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## Candisa (Sep 15, 2007)

Personally, the internal crossovers of an amp would be the last thing I'd look at. More important is signal-to-noise ratio (you want this 95dB or higher, an amp with 90dB SNR or less is hissing very audible!), THD at 1W (as low as possible, preferably .01% or lower) and at full RMS power (.2% or less), power, stability...

With stability, I do not necessary mean the amp should be 1ohm/ch stable, that's nonsense if your running 4 or 8ohm comps, but I always check if an amp (almost) doubles power when running in 2ohms vs 4ohms...
If amp A does 120W/ch @4ohms, 160W/[email protected] and is 1ohm stable; and amp B does 80W/ch @4ohms, 140W/ch @2ohms and isn't 1ohm stable... I'd get amp B, even if I'd run it at 8ohms/ch.
Why? Amp A is already flirting with its limits at 4ohms/ch, amp B isn't!


So what about the crossover: Find an AudioControl 2XS (I thought I've seen one in the classifieds?), 24XS or 4XS. These models are easy to find for an acceptable price.
With the 2XS or 24XS, you can do the bandpass on the midwoofers and highpass on the tweeters, any frequency you want. The low-pass on the sub can be done in the headunit or sub-amp.
With the 4XS, you could do all filtering: bandpass on the sub (lowpass+subsonic), bandpass on the midwoofers and highpass on the tweeters. With some clever wiring, you can even use it as a 4ways crossover if you'd decide to expand later...

Isabelle


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## brandontw (Jan 21, 2012)

Isabelle:

Thanks a lot for the reply... very useful information. Thats the kind of stuff i need to know.

I guess my whole deal was that i didnt see a reason to spend 100-150 on an audiocontrol if i could get an amp that had the crossovers i needed built in. But it would give me a lot more flexibility in amp choice, and would be something i could use for a long time.

With that said, what are the choosing factors when looking at an electronic crossover?

Why would i want an audiocontrol over something like this?

And am i understanding correctly that you have to take them apart and put new resistors in to program the crossover frequencies? Not a complaint, just a question.

I suppose a minidsp would be another option to do this type of job huh? I like the looks and function of the 2x4 and i like that i can program it on the computer.

I guess i was trying to avoid the electronic crossover/processor purchase, and still go active, but its starting to sound like if i want to do it right ill just have to bite the bullet.


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## minbari (Mar 3, 2011)

one thing I dont think anyone touched on. you dont have to LP the upper end of the door woofer. you can let it roll of naturally with no harm at all to the speaker.


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## MarkZ (Dec 5, 2005)

brandontw said:


> Isabelle:
> 
> Thanks a lot for the reply... very useful information. Thats the kind of stuff i need to know.
> 
> ...


There's no reason to buy an external crossover if you select the right amp to do it. Your plan to let the HU do the lower crossover point, and the amp do the higher crossover point, is perfectly fine. It looks like your HU provides enough options for a typical install.


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## Candisa (Sep 15, 2007)

I recommend AudioControl crossovers because of their flexibility. You do have to take them apart and change resistor-modules to change the frequencies, but that's a good thing: you can put whatever frequency-module in there!

Most crossovers, including that Clarion have turning knobs to set the x-over frequency, so you have a limited range and less precise tuning.

If you look around well and with some patience, a nice AC crossover can be found on the used market for a nice price.
I wouldn't buy them (alsmost) new, because if you're spending more money, there are better options nowadays.

A miniDSP is one of those options and it's not only a x-over, but also an equalizer and it has time-alignment. There are a few downsides too: I heard about power-on pops on these things, and if you can't feed them with a digital signal, you have 2 totally useless sound-conversions in the path: the headunit converts the digital signal coming from the cd-player to an analog signal, and the first thing the miniDSP does is convert it back to digital... Doesn't make any sense and all that is 'good' for is reducing the signal-quality.

An AC x-over keeps the signal analog, so there are no useless conversions.
One day, I will build a system (not the current Saab-project) with both a headunit/dsp (Clarion HX-D2) ànd analog "processing": 
- The headunit's internal dsp (no useless conversions from digital to analog and back this way) can do a lot, but I'm limited to 8 channels and that project I'm talking about needs 12 channels, so...
- After the headunit has done its part of the processing and the signal is converted to analog, I'll use AC analog gear to do the rest of the "processing" so the signal doesn't have to be converted to digital again (to end up with an analog signal at the end).
By doing this combination, there will only be 1 conversion in the path of each channel, so analog devices do have their pro's, even with their limitations compared to dsp-solutions...

Isabelle


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