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Old 01-06-2017, 02:37 PM   #1
mossman

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Adjusting Crossover Points with O-Scope

The xover scales on my Sundown SAX 100.4 v2 amp do not have enough resolution to set accurately, so I plan on using my o-scope to set them to the exact frequencies I want. For example, the subsonic scale is 10 Hz to 500 Hz (wtf?) and both the LPF and HPF range from 50Hz to 5 kHz. Way too broad to set accurately. My plan is to use a test tone disc and play tones at my desired xover points and adjust the pots until I reach the -3dB points, or 70.7% of signals in the passband. For example, to set my LPF, I would set the LPF pot to something above my target, like 100 Hz, play an 80 Hz test tone, then adjust the pot CCW until the peak voltage on my o-scope drops to 70.7% of the original signal. Is this the best way to do it? Should I aim for a -6dB knee voltage since my amp is 12dB/octave?

Last edited by mossman; 01-06-2017 at 03:09 PM.
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Old 01-06-2017, 03:01 PM   #2
basicxj

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I am betting you won't need a 'scope- just some test tones and a pair of ears.
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Old 01-06-2017, 03:19 PM   #3
mossman

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Quote:
Originally Posted by basicxj View Post
I am betting you won't need a 'scope- just some test tones and a pair of ears.
True, but I'd like to at least get things close to where they should theoretically be. Right now, I don't know if my subsonic is set to 15 Hz or 100 Hz or my LPF is at 100 Hz or 60 Hz because the scale is so large.
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Old 01-06-2017, 04:31 PM   #4
SPL_Krayzie112

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I think you might be better off buying a used RTA.
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Old 01-06-2017, 10:22 PM   #5
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Quote:
Originally Posted by SPL_Krayzie112 View Post
I think you might be better off buying a used RTA.
Having owned an RTA, I'd say he's better off with test tones and learning to train his ear.
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Old 01-07-2017, 01:50 AM   #6
basicxj

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Quote:
Originally Posted by SPL_Krayzie112 View Post
I think you might be better off buying a used RTA.
...and for that purpose, RTA apps for smart phones are more than adequate .
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Old 01-07-2017, 12:03 PM   #7
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Quote:
Originally Posted by basicxj View Post
...and for that purpose, RTA apps for smart phones are more than adequate .
I had an RTA app on my tablet, but it has disappeared. I tuned everything flat when I first installed the system and it sounded like crap, so I ended up tuning by ear. So I agree, the ear is the way to go with the RTA as a supplemental evaluation tool.
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Old 01-07-2017, 04:26 PM   #8
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Quote:
Originally Posted by mossman View Post
I had an RTA app on my tablet, but it has disappeared. I tuned everything flat when I first installed the system and it sounded like crap, so I ended up tuning by ear. So I agree, the ear is the way to go with the RTA as a supplemental evaluation tool.
You'll hear a lot of talk about people tuning their audio systems "flat," but understand that flat response doesn't always sound good to the human ear. A better way to use a tool like that is to identify any odd peaks and valleys in response that do not sound good, and read where they are to easily target them with equalization.

For music, the human ear usually prefers something more like a banana or smiley face curve, with a little boost in response near the top and bottom end (a little equalization the far left and far right of the frequency range) with the ear being most sensitive to a narrower range of frequencies in the same neighbourhood as human speech. I usually prefer an EQ curve that sounds accurate- how the same track sounds on a good reference system or in a live setting rather than shooting specifically for a flat response. Other people I know prefer something that sounds all jacked up to my ear- sizzling highs and overboosted bass from more EQ in those same areas, but to each his own.

http://www.independentrecording.net/...in_display.htm

Most of the time, I can tune a system pretty well using a handful of well-recorded, uncompressed reference tracks on a CD or other device and will only break out the RTA app when that fails and a particular range needs some fine tuning with a parametric EQ in bands not as easily identified.
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Old 01-17-2017, 03:44 PM   #9
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I just realized my Audio Control processor has a Linkwitz-Riley filter, so I'll experiment with it as well. I currently have the sub out of my car (preparing to install the new enclosure), so I've been tweaking the filters and EQ for my HSK 165s. I essentially had no midbass and didn't even realize it because of the sub. I also had the tweeter passive crossovers set to +2dB, so they were getting too loud before the mids could get enough power to play to their full potential. I knocked the tweeters down to 0dB and boosted the lower freqs a tad and now they sound awesome. Can't wait to get the sub back in.

Last edited by mossman; 01-17-2017 at 03:48 PM.
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Old 01-18-2017, 01:28 AM   #10
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How do the Hertz compare to the Kicker speakers you started out with?
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Old 01-19-2017, 02:18 AM   #11
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Quote:
Originally Posted by basicxj View Post
How do the Hertz compare to the Kicker speakers you started out with?
Much better in terms of SQ and clarity. I can hear sounds in tracks I've been listening to for years that I didn't know existed. The mid bass is nice and tight as well, whereas the kickers were loud but sloppy sounding when I cranked the volume up.

BTW, I threw the IDQ8 back in temporarily and it sounds really good. Nice and balanced and not overwhelming. Evidently I need to turn down the gain to the IDQ10 to my liking so it isn't blasting my ear drums. I'm getting too old for that, but it's nice to be able to crank it up if I get the urge. I believe my DM608 should be arriving in a couple weeks, so I can finally get everything dialed in the way it should be.

Last edited by mossman; 01-19-2017 at 02:21 AM.
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Old 01-20-2017, 12:32 PM   #12
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I just realized that the Hertz crossovers supplied with my HSK 165 components have a rolloff of 12dB/octave. Doesn't this create a +3dB peak at the crossover point? Would it be better if I ditched the passive crossovers and powered the midrange and tweeters individually using all four channels of my SAX 100.4 amp and use the built-in 24dB/octave Linkwitz-Riley crossovers? I already have a second pair of wires run up front so it would be very easy.

Last edited by mossman; 01-20-2017 at 12:35 PM.
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Old 01-20-2017, 07:36 PM   #13
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Most crossovers are spaced to avoid a 3db peak at the crossover.
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