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Old 9th April 2009, 02:05 AM   #1
TheMG is offline TheMG  Canada
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Default Crossover electrical characteristics and questions.

I'm by far not an expert on loudspeaker passive crossovers and what the typical crossover frequencies should be, so this is why I'm asking.

Attached is a graph showing the electrical characteristics of the tweeter crossover in one of my Technics SB-S25 speakers.

I'm wondering, is it looking like the crossover frequency is a little bit too high or is that typical?

Crossover here is just a simple series capacitor which I can't read the value of (its almost impossible to reach even getting a scope probe in there was quite tricky), thus the 20dB/dec roll-off rate.

Something just doesn't sound right in the high end of the spectrum, almost like there's a lack in the high end of the spectrum, and maybe distortion, either way, the highs sound kind of washed out.

Anyways, I'm investigating into whether or not the capacitor is ok.


While typing this, I've just thought of something else. The main full-range driver (4" diameter, 6 ohms) is not crossed over, in other words just connected directly across the input. Is it possible that this lack of a low-pass filter on the main driver is the problem? Perhaps the phase-shift introduced by the tweeter's capacitor is causing destructive interference between the full-range driver and the tweeter at certain frequencies?

Tweeter is a 6 ohm driver of some type (can't tell, front grille is not removable, all I can tell you is that it's 6 ohms, the number is EAS-5PH03G-T, and it's 1" diameter.


So I guess the main questions are:

1) is the tweeter HPF performing as it should?

2) would adding a LPF to the full-range driver improve overall sound quality/response in the high end of frequencies? If so, what characteristics should the LPF be designed for?


Thanks.
Attached Images
File Type: png crossover.png (16.9 KB, 131 views)
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Old 9th April 2009, 04:54 AM   #2
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Join Date: Aug 2008
Default it appears that you have a ribbon tweeter

for that is typical but may not as steep for if you want to get an idea of the raw response of tweeter you can go to different websites
if you go below 1khz it may have more of a steeper slope
and if you are not getting any buzzing sound from it is working properly, yet it may sound too bright
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Old 9th April 2009, 12:15 PM   #3
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK
Hi,

The SB-S25 are surround speakers and the "crossover" seems to be
the bare minimum possible, difficult to comment on without the raw
responses of the drivers, ideally measured in the box.

It is almost certainly possible to improve the crossover, but for
this measurements are needed, the electrical feed sometimes
does not tell you much at all, other than your capacitor value
is ~ 2uF.

http://www.acoustic-reality.com/ar-sxo2.htm
(see last link in list below for John Ks current website)

Is as good a way of doing it by ear as any other, though i'd
suggest starting with ~ 0.07mH for L1 and ~ 1mH for L2.

/sreten.

http://www.rjbaudio.com/Audiofiles/FRDtools.html
http://www.geocities.com/woove99/Spk...esigningXO.htm
http://undefinition.googlepages.com/diy

http://www.zaphaudio.com/
http://www.rjbaudio.com/projects.html
http://www.geocities.com/woove99/Spkrbldg/
http://www.troelsgravesen.dk/Diy_Lou...r_Projects.htm
http://htguide.com/forum/forumdisplay.php4?f=39
http://www.humblehomemadehifi.com/

http://www.linkwitzlab.com/
http://www.musicanddesign.com/
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Old 9th April 2009, 12:21 PM   #4
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

Quote:
....
... my old old Technics SB-S25 bookshelf speaker,
which use those crappy piezo disc tweeters ...
Hi,

Ignore my post above if this is the case, if it is no way should
the tweeter measure 6ohms without a resistor being involved.

/sreten.
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Old 9th April 2009, 02:00 PM   #5
TheMG is offline TheMG  Canada
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Join Date: Jan 2008
Yeah after taking a good look at it and doing some measurements I realized they aren't piezo discs.

I updated my post with that information but forgot to edit out my previous statement saying that they are piezo discs.

Too bad I don't have the proper equipment to measure the actual acoustical response of the loudspeakers, that would make things a whole lot easier.
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