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  #25  
Old 04-05-2010, 07:38 PM
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Re: Making Your own Passive Crossover.

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Originally Posted by TimmyB View Post
I do have two extra JL XR crossovers and the tweeters I bought in a set where I only needed the woofer. I can use those, but then I would have to pick out raw drivers that would work with them. Any ideas? Keep in mind I want to do this sytem cheap, thats why I want to buy raw drivers and do everything myself. Partsexpress has Dayton SDS 6.5's for 10 bucks each on sale that has good reviews. Thats what im looking to do, nothing fancy or expensive and using all the spare wires and amps I have. Im about to just rip out my TR's from the rear doors and give them to her. I want to do something nice for her, but I have limited money to do it.
Hmm, I'd email JL and get the specs for the crossover.

Try to get;

Tweeter x-over point, slope and if there's any attenuation)
Woofer x-over point, slope

Then go from there.

The Peerless SLS (on buyout) aren't a good match for a door. They have a pretty high inductance (Le), very low QTS and not a whole lot of Xmax - definitely stay away from those unless you're going to use an enclosure for them.
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  #26  
Old 04-05-2010, 08:16 PM
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Re: Making Your own Passive Crossover.

Good info, and good starting point. What is a good Xmax for a 6.5 woofer? I am seeing about 5mm on average. The other references you mentioned I have no idea about or what they even mean, the Le and QTS, so im going to research some more.

I just tested my extra XR crossovers and tweeters and they work great. So now I just need to get a set of 6.5's that will work with them. Im emailing JL right now to see if I can get some detailed specs on the XR's.
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  #27  
Old 04-05-2010, 09:10 PM
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Re: Making Your own Passive Crossover.

Now im completely confused. The JL XR tweeters are 8 ohm but the 6.5 mids are 4 ohms. So the only thing I can think of is the resistors in the crossover make the amp see a 4 ohm load for the tweets? My amp is not stable at an 8 ohm load, so I would be getting an overload light on if the tweets were trying to run off 8 ohms.
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  #28  
Old 04-05-2010, 09:29 PM
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Re: Making Your own Passive Crossover.

Quote:
Originally Posted by TimmyB View Post
Good info, and good starting point. What is a good Xmax for a 6.5 woofer? I am seeing about 5mm on average. The other references you mentioned I have no idea about or what they even mean, the Le and QTS, so im going to research some more.
5mm is about the minimum I would go. It may not seem like much but going from a woofer that has 4mm xmax to 5mm xmax is a 25% increase.

Le (inductance) is tough to explain, especially since I don't fully understand it. The lower it is, generally the better a driver will perform in a door (properites like: faster response, snappier punchier, etc). Definitely shoot for something under 1mH.

Qts is also tough to explain, especially since I don't fully understand it. But the higher the Qts, the better it is for a door application. Shoot for something over .5 Qts.

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Originally Posted by TimmyB View Post
Now im completely confused. The JL XR tweeters are 8 ohm but the 6.5 mids are 4 ohms. So the only thing I can think of is the resistors in the crossover make the amp see a 4 ohm load for the tweets? My amp is not stable at an 8 ohm load, so I would be getting an overload light on if the tweets were trying to run off 8 ohms.
Amp stability is only a floor (not a ceiling), so if your amp is stable down to 2 ohm, or 4ohm, then it will be fine for anything above that ohm load (i.e. 16ohm). Power output will be reduced though.
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  #29  
Old 04-06-2010, 12:35 AM
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Re: Making Your own Passive Crossover.

Ok, thats what I was under the impression of. That if per say I have an amp rated for 100 watts per channel at 4 ohms, if I were to hook up an 8 ohm speaker it would still "work" but the output of the amp would be cut in half? And it only works when using a higher ohm speaker, as in if an amp is rated at 100 watts per channel at 4 ohms I would not be able to use a speaker rated below 3.9 ohms because it would overdraw that amp? I am still really unclear to all this, but trying to at least grasp the concepts.

So if what I am thinking is correct, I can buy a 12 ohm 6.5 woofer rated at 30 watts RMS and safely run it off my JL amp fronts that are spec'd out at producing 150 watts per channel at 1.5-4 ohms. Because the higher ohms would drop the watts to a "safe" level?
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  #30  
Old 04-06-2010, 06:06 AM
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Re: Making Your own Passive Crossover.

Quote:
Originally Posted by TimmyB View Post
Ok, thats what I was under the impression of. That if per say I have an amp rated for 100 watts per channel at 4 ohms, if I were to hook up an 8 ohm speaker it would still "work" but the output of the amp would be cut in half?
Pretty much yep!

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Originally Posted by TimmyB View Post
And it only works when using a higher ohm speaker, as in if an amp is rated at 100 watts per channel at 4 ohms I would not be able to use a speaker rated below 3.9 ohms because it would overdraw that amp? I am still really unclear to all this, but trying to at least grasp the concepts.
Correct. Some amps that are 4ohm stable (and that's their lowest rated ohm load) can still dip below that, but it's always best to stick within the manufacturers limits.


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Originally Posted by TimmyB View Post
So if what I am thinking is correct, I can buy a 12 ohm 6.5 woofer rated at 30 watts RMS and safely run it off my JL amp fronts that are spec'd out at producing 150 watts per channel at 1.5-4 ohms. Because the higher ohms would drop the watts to a "safe" level?
You could also buy a woofer that's rated for 4ohm and be just as safe, well actually safer; It's all about gain control. Headroom is a good thing... the lower you can keep your gain, the less chance you'll have at clipping, the lower you can keep your noise floor.

If I could I would have 500w amp channels driving my dash drivers (rated at 15 watts) and my mid woofers (rated at like 80 watts). Remember, your speakers don't ever see those rated numbers - those are the absolute peak! So it's not like your speakers will see 150 watts ever from your amp... even at 1.5ohm. Music is dynamic.
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  #31  
Old 04-06-2010, 06:59 PM
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Re: Making Your own Passive Crossover.

I swear, the more I try to research speakers and crossovers the more confused I am. I am now wondering why the need for going "active" and having crossovers. I know both will filter out frequiencies that the dedicated speaker is not rated for. But here is why I am confused, or why my mind is now thinking.

I have been researching two way speakers and it appears that the woofer receives a full signal from the amp or headunit and there is only a capacitor on the positive going to the tweeter. I was just looking at my stock speakers, and they appear to have nothing to filter out any highs or lows. I keep going back referring to my JL TR components, because there is only the 6.5 woofer and a capacitor soldered onto the poistive wire going to the tweeter. So going with this, I can safely make a component set by getting a woofer and soldering a cap onto the tweeter for it? That is what is basically in a 2 way car audio speaker.
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  #32  
Old 04-06-2010, 07:04 PM
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Re: Making Your own Passive Crossover.

Here is a simple two way speaker, it only has a capacitor on the tweeter positive wire.




I was also looking up 2 way speaker pattens.

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  #33  
Old 04-06-2010, 08:33 PM
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Re: Making Your own Passive Crossover.

Quote:
Originally Posted by TimmyB View Post
I swear, the more I try to research speakers and crossovers the more confused I am. I am now wondering why the need for going "active" and having crossovers. I know both will filter out frequiencies that the dedicated speaker is not rated for.
It also, more importantly, gives you the flexibility to try out as many different drivers as you'd like. With a passive, you're stuck with those settings. Also, pretty much all active decks give you the ability to level set, time align, and very good equalizers. All that you don't get with a passive crossover.


Quote:
Originally Posted by TimmyB View Post
But here is why I am confused, or why my mind is now thinking.

I have been researching two way speakers and it appears that the woofer receives a full signal from the amp or headunit and there is only a capacitor on the positive going to the tweeter. I was just looking at my stock speakers, and they appear to have nothing to filter out any highs or lows.
Your stock speakers are being sent a filtered signal from the amp. The factory Boston Acoustic amp has built-in filters.

Quote:
Originally Posted by TimmyB View Post
I keep going back referring to my JL TR components, because there is only the 6.5 woofer and a capacitor soldered onto the poistive wire going to the tweeter. So going with this, I can safely make a component set by getting a woofer and soldering a cap onto the tweeter for it? That is what is basically in a 2 way car audio speaker.
Yes you could. Here's the difference between a separate, external passive crossover and an inline capacitor wired between the mid woofer and tweeter.

The separate passive crossover will designate/filter frequencies for BOTH mid-woofer and tweeter. This ensures a smooth transition between drivers when playback occurs. (assuming the passive crossover is in fact meant/built for the the mid-woofer and tweeter).

The full-range signal sent to the woofer, inline capacitor system relies on the natural roll-off of the mid-woofer instead of an actual filtered (crossover) signal. So, with this method, you are leaving a lot of overlapping frequencies - being covered by both the tweeter and mid woofer. This causes confusion for the listener/ear.

It's much cheaper for manufacturers to build a simple inline cap for a mid/tweeter 2-way speaker, and most people don't know the difference anyways, so why would they even bother with an external crossover.
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