stock tweets good enough to handle xo point lowering? - diyAudio
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Old 17th May 2006, 06:23 AM   #1
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Lightbulb stock tweets good enough to handle xo point lowering?

I have an 02 accord which came with 6 speakers. I removed the rear 6x9s already. The front setup consists of 6.5s in the doors and tweeters below the windshield. Originally, the 6.5s and the tweets were powered off the same signal. The caps on the tweets are .84 uF, which yields an XO frequency of 48.5 kHz. I'm assuming the 6.5s roll off on the high end, and the XO rolloff on the tweets matches that of the 6.5s. I'm also assuming that the high XO frequency was chosen to match the mid/tweet levels.

My headunit is an Alpine cda-9855 set up for 3-way. I have the tweeters and mids powered by separate channels. When setting up an active XO, I noticed that most of the highs were coming from the 6.5s. After playing with the levels of the mids/tweets, I found that having the mids 5 dB quiter than the tweets provides good balance.

With the mids turned down, I have to turn up the volume to get the same loudness. At that level, I'm also starting to get distortion (h-u clipping?) I was thinking of changing the caps on the tweeters to lower the XO point. This would allow the tweets to play louder with less power coming from the head unit (less clipping). What would be a good XO frequency to aim for? (This is temporary until I get some good speakers.) The tweets are receiving a signal which rolls off as frequency decreases. If the XO point was changed to the audiable band, then they would be receiving a constant level signal above the XO point. Would the tweeters be able to handle this?

Edit: another thought is to set the XO at 20 kHz and adjust levels from there. I'm open to suggestions.
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Old 17th May 2006, 01:41 PM   #2
lndm is offline lndm  Australia
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If you have an active crossover now that wasn't there before and the tweeter's response is cut at some point, this may be giving the perception that the tweeters are much quieter when the highest frequencies are still there.

With just a cap on the tweeter, the rolloff will be shallow (first order) and would reach gently down to meet the mid. If I assume(?) the crossover might be second order, there will now be a third order tweeter rolloff below that point.

If you are up for an experiment, remove the tweeters cap (or preferrably replace it with a large value for safety), then using your crossover, set the crossover point and level to match the mids.

If you can get a quick rolloff with your crossover, the tweeter should be OK with the power. It may not want to go down beyond some frequency, you'll probably hear that if you try to go too low.

As long as you are careful to listen for tweeter distortion before you crank the volume, it should work.
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Old 17th May 2006, 02:06 PM   #3
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Are you sure the tweets are 4 ohms? I highly doubt they're using a xover freq that high, it should be closer to 6-7k or thereabouts. Whether they can take a lower xover freq depends on the tweets themselves, it would be nice if you could measure the Fs to get a general idea how they were designed, but without knowing that you might want to measure the DC resistance of them and see where they're actually being crossed, my guess is they're closer to 16 ohms which would give a 1st order xover freq around 11-12k.

My tweets are being crossed at 2.5k btw, though they're not stock.
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Old 17th May 2006, 03:31 PM   #4
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Quote:
If you have an active crossover now that wasn't there before and the tweeter's response is cut at some point, this may be giving the perception that the tweeters are much quieter when the highest frequencies are still there.
I had the mids running full range, and the tweet was cut off at 4 kHz (the XO point did't make a difference; I even had it at 10k and it sounded the same), and it sounded just like the factory setup. Once I lowpassed the mids at 4k, all the highs disappeared (most of them actually). So I know for sure that the tweet was much quieter than the mid.

Quote:
As long as you are careful to listen for tweeter distortion before you crank the volume, it should work.
I always do that, so no worries there.

Quote:
Originally posted by sr20dem0n
Are you sure the tweets are 4 ohms? I highly doubt they're using a xover freq that high, it should be closer to 6-7k or thereabouts.
Yes, I'm sure. I just measured the DCR and it's 3.6 ohms.

What I'm trying to figure out is if I should have the tweet roll off at 6 dB/oct below 20 kHz and then cut it at, let's say, 4-5 kHz, or should I keep it flat down to the active XO point?

Since the (stock) 6 dB/oct rolloff integrates nicely with the mid, I'm thinking a 20 kHz (passive) XO should give me that slope and will have the tweet playing louder than with the current XO. Then, I would go active to XO the mid to the tweet. How low should I go on the active XO?
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Old 17th May 2006, 04:03 PM   #5
lndm is offline lndm  Australia
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I think your theory about the high xo point being there to match levels, sound plausible. If you like the treble that way, then OK. Otherwise I would look at making it flat.

The tweeter concerns me. I think the high xo suggests the tweeter may not have been designed to go too low. The thing is, using many 6.5" cone drivers becomes tricky above about 3k (give or take an octave or so). I would probably desire a xo point somewhere there. Maybe with some xo tweaking you could go to 6k? (just an assumption).

Maybe your tweeter could go to 6k. I might consider trying active at 6k with flat above.
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Old 19th May 2006, 10:09 PM   #6
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if you have the active crossover capability with your deck and seperate channels for your tweeters and mids try 3-4k lp with a 6-12 db slope , then 4-6k hp for your tweeters at a higher 18-24 db slope for protection for the cheap factory tweeter- get rid of the capacitor in-line with the tweeter first, then tune accordingly,
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