Need serious help with frequency cutoffs

[Bigpete123 1]

This post is going to be a little bit technical, but since most of you are more "technical" than I am, I'm sure you can handle it. I need help setting up my amps, and more specifically setting my amps' crossover frequency cutoffs. I understand if nobody wants to take the time to reply, but I'll just throw all of it out there.

First, my setup. Some of you have probably seen my installation log (and my sig), but I'll lay it out more specifically here. I will be installing my amps very soon, and need to set all of the dials before I screw them into the amp rack.

Amps

JL Audio 500/5 (for front speakers and sub)

JL Audio e2150 (to drive my rear fill only)

Speakers

Fronts: Focal 165 V3E's (3 ways that include the 165 v3 6" mid, 100vslim 4" mid, and TN47 tweeter)

Rears: 100vslim and TN47 tweeter (same as the ones in the 3-way setup).

Sub: Infinity Kappa Perfect 10vq 10" single VC sub, to be run via infinite baffle

Now, installation details. You all may be wondering why I have a second amp if I have a 5 channel amp already. I have decided to "tri-amp" my setup... meaning, I will run my sub on one channel, my tweeters on another, and my 4" and 6" drivers on another.

The 500/5 splits the channels as follows (all stated in RMS):

Sub: 250 watts

Rears: 25 watts per channel

Fronts: 100 watts per channel

Here's a pic to make it easier:

So my tweeters will run off of the "rear" channel, my 4" and 6" drivers off of the "front" channel.

So let's take it channel-by-channel.

Front Channel (for 4" and 6" speakers)

I am having a difficult time understanding what the frequency ranges of these speakers are. Focal provided charts with the owners' manual, but I have no idea how to interpret them. They provide the frequency response for the whole 3-way system together, but since I'm gonna be running my tweeters separately, I need to know the low-pass cutoff for the mids... Here is the frequency range of the whole 3-way setup:

55hz - 25khz

So obviously, the absolute lowest I would want to set my high pass crossover is 55hz, although I will probably set it higher since that's down in the subwoofer's range. But somewhere in there is the lowpass cutoff for the mids. Unfortunately, I have been unsuccessful in finding the frequency range of the tweeter alone. Here is the chart I was talking about. Maybe you guys know who to interpret it:

So, to sum up, my question is:

What should I set the high pass and low pass filters at for my mids? Or in other words, where should the bandpass cutoffs be?

Luckily, my 500/5 is very smart, and automatically uses the highpass filter of the "rear" channel (i.e. the tweeter channel) and automatically uses it as the lowpass filter for my "front" channel (i.e. the mid channel). I thought that was pretty slick. That way I only need to set one dial for the cuttoff point between the tweeters and the mids.

Sub Channel

Sub's frequency range: 25hz to 400 hz

Since I'm running my sub via infinite baffle, I will use JL Audio's protection circuitry that cuts off frequencies below 30hz using a steep roll-off. My understanding is that sub-30hz frequencies aren't audible to the human ear anyway.

My question is this: how do I figure out where I should cut the frequencies off between the sub and the mids? My mids can go down to 55Hz, as I mentioned above, and my sub can go all the way up to 400hz. But I completely understand the concept that just because a speaker can handle a given frequency, it doesn't mean it will sound good doing it. So what's a reasonable range for my sub?

Obviously this question is related to my question about the mids, because this plays a role in determining the cut off for them, too.

If you've read this far, I really appreciate it. I have the frequency range for my rears, so I'm not going to ask any questions about that.

But please help!! It may seem like an obvious thing to some of you, but it doesn't to me!!

[Bigpete123 1]

anybody? :)

[///M5 2,833]

I'd run the mb as low as they can go. If the installation is such that you can run them all the way down it will be fine, if not go ahead and notch them up.

I haven't used those focals, but would imagine that I would try to start cutting off the mb in the 200-600 range. Play around with the mr alone and see with what power it starts to distort and cross them a bit higher. This will let you know how high to run the mb.

[Bigpete123 1]

cool, thanks for chiming in, man. So at the risk of sounding like a huge idiot, I'm assuming MB=midbass and MR=midrange? no?

I figured that this would be more of a "tuning to the ear" sort of thing. Unfortunately, I cannot mount my amps and adjust them while they're mounted. So I guess I'll just have to wait to install my amp setup until I have all of my speakers installed. I hate the feeling of my trunk being all messy, but such is life. ha ha

Thanks. I just don't want to damage my tweeters. I sure wish Focal would publish the frequency ranges of each driver within the 3-way system...

[///M5 2,833]

You are right on the mb/mr and I am too lazy to look for specs on your speakers but being active your ear in your installation is a better judge anyway.

[PaulD 0]

if you look at the "tweeter" chart - the bottom curve that has a huge spike just over 1000 is saying the resonant frequency of the tweeter is just under 2 KHz, the top curve shows it has pretty flat response above 2 KHz. These are telling you not to crossover the tweeter any lower than 2 KHz.

If I were you, I would hook the mid and tweet to the passive crossover (just like the rears speakers) and connect them to the front 2 channels. Then connect the midbasses to the 2 rear channels on the 500/5.

Typical crossover point ranges:

sub to midbass 50-75 Hz

midbass to midrange 250-400 Hz

midrange to tweeter 2-4 KHz

Edited July 20, 2006 by PaulD

[Bigpete123 1]

If I were you, I would hook the mid and tweet to the passive crossover (just like the rears speakers) and connect them to the front 2 channels.

Edited July 20, 2006 by Bigpete123

[PaulD 0]

I didn't realize the rear channels were so much uderpowered as the fronts. I was really thinking like a "normal" 75X4 amp, in which case my idea was to give the midbass the same power as the mid/tweets. Understand that if you use a passive xover 1) it saps a little of the power 2) each speaker receives the total power of the amp IN IT'S FREQ RANGE (minus what the passive saps off the system). The 100x2 is great for the mid/tweets, but 25x2 is gonna be a bit lacking for the midbass.

maybe you can use the 2150 in there somewhere and use the rear of the 500/5 for the rear speakers ? Lots of options to consider. Also, don't worry about matching power of speakers to power of amps that closely. If you are into SQ and clip the squat out of your system all day - you could use a 100w/ch amp to power the tweets and not blow them. Power is headroom, not volume (unless you have a megawatt SPL machine)

[Bigpete123 1]

Understand that if you use a passive xover 1) it saps a little of the power 2) each speaker receives the total power of the amp IN IT'S FREQ RANGE (minus what the passive saps off the system).

Wow, I didn't realize that. But first let me make sure I understand what you mean. For example. If I send 100 watts of pink noise to a crossover, assuming that the crossover doesn't sap any power (just for illustration purposes), and assuming that the two drivers connected to the crossovers have no frequency overlap, both speakers would receive 100 watts each? Is this what you are saying?

If so, that's fascinating. Intuitively to me, I would think that the two drivers would split the power 50/50. Am I completely misunderstanding you?

The 100x2 is great for the mid/tweets, but 25x2 is gonna be a bit lacking for the midbass.

Does this mean you agree with my plan? i.e. having the 4" and 6" drivers on the front 100 watt channels and the tweeters on the rear 25 watt channels?

Thanks for your help, Paul!!

[ANeonRider 3]

Nope, you understood him completely... each speaker would, in that example, be receiving 100W.

[PaulD 0]

that was one of the hardest things for me to get thru my hard head ..... if you have a 100 W/ch amp and the passive skims off say 20% of the power (just using round numbers), each speaker could see up to 80 watts if a frequency is in that speakers range. The downside is that during loud, complex music, the amp will most certainly be taxed mightily.

According to alpines site, the rear channels are also 25 w/ch from 1-4 ohms. Given your current amp channels and power for each, the way you have it connected wil probably best suit your needs.

[ANeonRider 3]

that was one of the hardest things for me to get thru my hard head ..... if you have a 100 W/ch amp and the passive skims off say 20% of the power (just using round numbers), each speaker could see up to 80 watts if a frequency is in that speakers range.  The downside is that during loud, complex music, the amp will most certainly be taxed mightily.

<{POST_SNAPBACK}>

And that is where having headroom becomes important

[Bigpete123 1]

Wow, that's crazy. I'll just take your word for it, because I can't sort that out in my mind. Electricity/physics are not my thing!!

According to my owners' manual for the 500/5, speakers over 4 ohms will cause watts to cut in half everytime you double ohms. Since my tweeters are 8 ohms, I'm correct that the wattage will be 12.5ish, right?

I'm pretty excited to get this installation done, obviously. Back to the topic of frequency ranges, I will have access to a spectrum analyzer when everything is installed, but I sure would prefer setting the amps active crossovers before I even install it. I was hoping just to use my 6-ch Audiocontrol EQS unit to tune the system... But it sounds like I'm just gonna have to suck it up and spend the time mounting and unmounting the amp to get it right! Oh well, such is life.

Thanks for your input guys, I definitely have learned something new!

[Bigpete123 1]

that was one of the hardest things for me to get thru my hard head ..... if you have a 100 W/ch amp and the passive skims off say 20% of the power (just using round numbers), each speaker could see up to 80 watts if a frequency is in that speakers range.

[Bigpete123 1]

Alright, at the risk of flogging a dead horse, here is what I'm thinking for my frequency cut off points:

Subwoofer: 30Hz - 100Hz

Midbass/Midrange: 65Hz to 3,000Hz

Tweeters: 3,000Hz and up

Here are the charts for all three speakers in the 3-way system:

Do my cut offs look right when you compare them to these charts and to the knowledge that the 3 way system is good for 55Hz - 20kHz?

Thanks!

[PaulD 0]

sounds good ... you will have to hook up and see - just be careful of so much overlap between sub and midbass.

why is the low end on the 6" midbass just a little better than the 4" midrange ? I guess that's why I am gonna use a 8" midbass for my next "project"

[Bigpete123 1]

sounds good ... you will have to hook up and see - just be careful of so much overlap between sub and midbass.

why is the low end on the 6" midbass just a little better than the 4" midrange  ?  I guess that's why I am gonna use a 8" midbass for my next "project" 

<{POST_SNAPBACK}>

Yeah, you know I was wondering the same thing. I'm particularly baffled by the fact that the overall specs for the 3-way system say that the overall frequency response is 55hz and up. The chart seems to indicate that it's really only 90Hz... It seems very strange to me. If worse comes to worse and I set my 6" woofers too low, I can just dial it up.

I will take your recommendation and reduce the overlap between the sub and midbass. Now that I think about it, that's pretty excessive.

[PaulD 0]

well, just see how it works ... you may need an overlap or underlap. One thing is for sure, there is NO magic formula - every car and set of components will have to be set up so it sounds best. Do you have access to an RTA ?

[Bigpete123 1]

Yeah, apparently a friend knows a friend... Since I will also have an Audiocontrol EQS 6 channel EQ, I will have a little more flexibility... I'm sure I'm gonna drive myself nuts with it though...

[PaulD 0]

that's just part of the fun ......