i have a Sony mp80 HU and a PG Octane-R R5.0:4 amp. Both have a crossover built in. My question is should i use the crossover that is built into the headunit for the output signal or just have the amp crossover the work?

 

You are talking about the Crossover for the Sub. Outputs? If you list the Specs for the crossovers, it will make it easier. (slope, level control, etc..)

Both will work fine. JUST DON'T USE BOTH. I don't think I need to say it but I will anyways. I'm searching for info on the MP80, but it's hard going and Sony's site is shitty.

 

Never Mind. I found all the info I needed.

I'd say the Amp. It has Variable crossover Frequencies and is probably a better piece than what is built into the Radio.

The HU will still be able to control volume without the Crossover engaged, so you'll be fine.

Here are the Specs for you if you don't have them:

CDX-MP80: 125Hz/78Hz. +/- 6 on level. and +/- 10 for Sub.

PG Octane-R 5.0:4: variable high- and low-pass filters (40-400 Hz at 12 dB/octave)

 

that's silly advice. use both for further attentuation. if the amp provides a 12 db/oct slope and the HU provides a 12 db/oct slope, use both crossovers and get a 24 db/oct slope. i use both crossovers and i prefer them both being used simultaneously. i have no idea why YOU SHOULDN'T USE BOTH.

 

This is some bad advice, I'm sorry. Doubling up x-overs does so much bad things to sound and freq reesponse. If you are serious about sound, you only use one device to modify your sound.

With that said, use your amps. If you had an alpine headunit, I would have used it's internal x-over.

If you have the cash, get an AudioControl unit. I love my 3xs. Ebay has some good deals on those.

 

I agree with tuffluck. Two filters in series simply provide more a steeper filter slope as stated. There may be differences in the phase response of the filters when they are added together but why would that matter.

Can someone provide an actual reason why this is bad?

 

First off, whether it be Home Audio, Home Theater, or Car Audio... Doing what is mentioned will almost always result in muddied up midrange or bass.

When not dabbling into performance on my Suburban, my bike, or monitoring my network at the office.. I like to dabble in Audio. I've done a lot of things including but not limited to designing 2-way speakers, 3-way speakers, passive radiator systems, bandpass boxes, passive x-overs, etc. I've built my own home audio 2 ch amps. From tube amps to chip amps. I've plotted and anlyzed lots of different types of speakers and x-over networks.

What I've found is that, doubling up x-overs, does not double the slope. I've also found that x-overs vary by a great degree and can provide too much or too little of a cutoff for what you think it's set at.

I would like to go into more detail, but I'm going to leave it at this... From avid enthusiast to the Audio Pro, You have ONE x-over network per driver. Doing both or even having too steep of a slope on certain types of drivers really does a number on sound quality.

Besides, one less item in the audio chain is always good.

 

I leave my deck setup for pass through on all channels (no x-over). The crossovers on my three amps are much higher quality than the built in h/u ones. Not to mention this will filter AFTER any potential cross talk.

 

I'm glad someone already smaked this point into it's corner and gave it time out to think. Lol. Just messing with you tuff. But I'm suprised you even said that. Bad. Bad idea. Go in your corner!

http://www.sensorsmag.com/articles/0701/24/main.shtml

I was about to type out a bunch of letters, but this saves me a bunch of time.

("Cliff-Notes": *<EDIT>*Don't use 2 or more crossover circuits on the same band. it is OK to use a high pass and then a different frequency x-over.

Phase Lag and Band Coupling causes ripple effects and Timing issues that are impossible to clean up. The direct Summing (adding +) doesn't take effect.

 

a component set carries a crossover to wire both the tweeter and midwoofer into, so does that mean you turn your amp crossover off when you run components? no, becaues then you can't cut off the low frequencies that run to your component mids.

 

So what's the verdict?

 

i would say you can have worse phasing (which is bad) by using more than a single crossover. you are definitely complicating the signal further by using more equalizing equipment. however, i'd say it's perfectly safe to use as many crossovers as you want, and in addition, you can achieve that further attentuation by doing so. so basically, do that which you wish and what sounds the best to you; you definitely, definitely aren't going to damage any equipment regardless.

 

He's got a point there. Rebuttal?

 

In an ideal world, you have a bandpass filter for your mids, a highpass for your highs, and a low pass for your subs. That would cover your bases for the most part.

In a real world, we have a highpass for our highs, a low pass for our lows (with a subsonic filter hopefully) and for our mids... Most people just play it either full range (as low as it can play and as high as the x-over allows). In some cases, people may put on a "bass blocker," type item. Which essentially creates that bandpass xover from our ideal world.

So whats bad is this... Using x-overs that double up a cut-off freq. If your headunit has a highpass output of 80Hz, and a sub output at 80Hz. Then you also use your amps built in 2-way x-over to drive seperates and a sub. This is where you run into potential SQ issues. Additive math does not apply in this case. Your 12db/oct x-over in your head unit with your 18db/oct x-over in your amp does not make a 30db/oct slope.

So whats better passive or active? I prefer the simplicity of active, but the warmth of passive. When building passive x-overs, I can play with notch filters, change the slope for my highs, and also design some other impedance circuits into them. Slope plays an important role in mids and highs. But too steep a slope on your subs actually makes them sound bad IMO.

In the end, it's kind of hard to articulate the above, but if you truley are happy with what you have, leave it alone. We've given you whats ideal and tried and true in the real world. It's up to you to try it and see for yourself what you like.

 

sure, i'll take this one....

the reason you don't turn off the amp's (or head unit's, or even seperate) crossover off is because you are in essence creating a "bandpass". you are using the amp's active crossover (well, filter really in most cases....but that's another whole discussion) to limit the amount of bass going to the component set's woofer. this keeps the low bass from distorting the frequencies that the component woofer is meant to play, i.e., the midbass/midrange. then the high pass keeps the treble frequencies going to the tweeter, which is the most efficient driver for those frequencies. depending on the component set, the woofer may or may not be affected by the high pass filter, as some sets are designed to let it just roll off the high pass naturally.

this method of using two crossovers is totally different from (and infinitely more acceptable than), say, using the 12db/octave filter at 80Hz low-pass filter on your amp in conjunction with the 12db/octave filter at 80Hz low-pass filter built in to your head unit. for one, both pieces of equipment are most likely going to be using different branded & manufactured components for the filter, so there will be inescapable discrepancies at the exact frequency that each filter is actually set at, even when using the same rated value for the components....this is compounded by the fact that most amps use an "infinitely variable" type filter (within a frequency range) as opposed to using filters that are "notched" (ones that can only be set at a specific frequency, or frequencies), with the frequency depending on which "notch" it is set at. think of it as using a dimmer switch on one of those halogen lamps as opposed to one of those 3-way "clicker" type lamps that only has 3 brightness settings.

when you set one filter (such as in your head unit) at a setting that is specified, and not variable, and add it to a signal that is being filtered by a variable setting so that you don't know exactly what the frequency setting is, you can really screw up the sound. will you damage the speakers? not unless you send the wrong frequencies to them. will it hurt sound quality? most likely. you can possibly achieve good results by doing this, but it would be best to not do this unless you have access to some high-dollar audio analyzation equipment/software.

bottom line? experiment. find out whether or not you can benefit from this. but more often than not, you'll want to KISS (Keep It Simple, Stupid).

 

What is all this db/octave stuff about? What's a slope? My current 5 yr old Alpine HU has 4 settings I used to know nothing about. BC, TC, LPF, HPF. I know the LPF and HPF, but I still don't know what the BC and TC settings are about. I assume they're some sort of slope thing, since the little graphics on the head unit show a slope when I mess with those settings. I just have no idea what it's actually doing, and can barely tell the difference in sound.

 

slope is how rapidly tones are minimized once they reach a cutoff point. for instance: if you have a 12 db/octave slope and a 100Hz low pass filter on your subs (100Hz is the crossover point), once a 200Hz frequency is submitted to your sub (which is one octave above 100Hz), the crossover will decrease the volume of that 200Hz frequency by 12 decibels.

alpine units have a feature called digital time correction (TC). time correction basically enables the user to measure the distance from each speaker in their car to their head. you input the numbers of the distance from each speaker to your head, and then when sounds are submitted to each speaker within the car, they are time delayed so that every sound wave played by each speaker will reach your ear at approximately the same time.

BC, which i think you actually mean BF for "bass focus," is merely an extension of time correction. if you have an f-body, the exact time correction level for just the front speakers is 1.6, since the passenger door speaker is 1.6 meters away from the driver's ear. once TC is set, BF is pretty much set in accordance; so you only really need to mess with one.

 

and of course i can still give you a great example for why that's very wrong: a 24db/oct Linkwitz-Riley crossover is 2 cascaded 12db/oct Butterworth filters in series with each other. once again, two crossovers, doubling the slope, and i can bet you aren't going to be finding many people that criticize those crossovers!

 

A linkwitz-riley x-over is not what is being discussed here. This particular x-over is built for a specific purpose. It's characteristics make it ideal for particular drivers (mostly subs and sub outputs)

Having your amp and HU x-overs enabled and inline doesn't make it a linkwitz-Riley deign.

Try again.

 

the discussion is regarding whether to use more than one crossover or not. in that example, 2 crossovers are combined to get the effect of one crossover. i don't ever recall this thread saying, "can i use more than one crossover, as long as it isn't a linkwitz-riley?" and this makes your point beyond puerile and moot.