just aquired these old RTi12's.
In their place have been many varieties of speakers.
the rti12's sounded like they had remarkably bad imaging. from reading user comments these speakers should have decent imaging.
So i've taken some measurements. note am new to this so forgive errors / misunderstandings.
firstly had measured resistance at various points; the left speaker / side seemed to sound better. all seemed normal, variance between speakers at terminals is 0.2ohm iirc; variance between 7" drivers is 0.1 ohm. and no variance with mid/tweeter section of crossover (didn't measure that sections speakers individually)
from there measured with oscilloscope at various points and inputs.
first just to show "baseline" measures; again am new to this.
Pre-Amp with 1000hz input - both channels (Why is positive swing so much lower?)
Amp with 1000hz input - both channels (positive / negative differential not as big, which seems odd to me, given this is the amplified part lol, went back to verify not a connectivity issue and was not whats more both signals show this difference)
and finally Amp with zero input and both channels; note I had "zeroed" the charting with the leads not attached to anything. so this is a measure from that basis. and it sits in the negative side. perhaps that is measuring a DC voltage; subsequent-sorry am new to this and this is a "new perspective" to reading DC voltage for me. seeing electricity in graph over time..i.e thought a bit and realized just now lol can that be adjusted out? I only know of transistor bias adjustment. is there DC adjustment?
That said, imaged below is zero input measured at connection to midrange speaker; which shows balanced leads / zero voltage.
Anyways with that context for the crossover measurements....
The mids I think is the primary issue, below are most remarkable frequencies measured
Mid - 500hz
Compared to 700hz imaged below. The db difference is consistent at this freq. Which component of the cross over would most likely cause this?
Next is Mids - 1000hz (Subsequent - I just noticed left channel positive peaks higher than right, and vice-versa for the negative side. THAT must be the issue am hearing; left side piston stroke is more power and is reversed on right side...that would really mess with the directionality of the sound i figure? any ideas?)
Tweeters
had to change the oscilloscope timing for these frequencies
Tweeters - 2500hz for fun. is the crossover only cutting one side of the circuit, is that what am seeing?
And the amplitude gets crazy from 7500hz and up
5000hz
7500hz
and than 12500; no change in volume setting...
So with just the above, I don't think there is a timing issue. But certainly a crossover issue; and presumably given the age of these speakers and that there is apparently an electrolytic cap within, they're well overdue for a refresh and that will likely get the speakers back inline with each other.
I'd attribute me thinking phase issue at first because of how I didn't really notice much volume difference with up close listing comparatives. but suppose adding in room acoustics, slightly different amplitude, listened to at a normal distance could perhaps impacts sound like that.
Does that all seem reasonable? the difference in measurements between channels is likely due to the crossover. I did measure the drivers and crossover section for ohms and all seemed fine to me. variance of 0.1ohm on the 7"drivers; presume is non-issue. both side had that variance. and at speaker terminals the speakers are within 0.2 ohm iirc. only mean to compare the two speakers here; does not tell me at 35watts, 120hz (lol) what kind of difference there is between them.
what a fun thing, measuring like this. some surprising results. in particular what audessey does to the signal / wave lol a VERY interesting comparative there would be measured at signal & from microphone; see if audessey corrects and to what degree.
In their place have been many varieties of speakers.
the rti12's sounded like they had remarkably bad imaging. from reading user comments these speakers should have decent imaging.
So i've taken some measurements. note am new to this so forgive errors / misunderstandings.
firstly had measured resistance at various points; the left speaker / side seemed to sound better. all seemed normal, variance between speakers at terminals is 0.2ohm iirc; variance between 7" drivers is 0.1 ohm. and no variance with mid/tweeter section of crossover (didn't measure that sections speakers individually)
from there measured with oscilloscope at various points and inputs.
first just to show "baseline" measures; again am new to this.
Pre-Amp with 1000hz input - both channels (Why is positive swing so much lower?)
Amp with 1000hz input - both channels (positive / negative differential not as big, which seems odd to me, given this is the amplified part lol, went back to verify not a connectivity issue and was not whats more both signals show this difference)
and finally Amp with zero input and both channels; note I had "zeroed" the charting with the leads not attached to anything. so this is a measure from that basis. and it sits in the negative side. perhaps that is measuring a DC voltage; subsequent-sorry am new to this and this is a "new perspective" to reading DC voltage for me. seeing electricity in graph over time..i.e thought a bit and realized just now lol can that be adjusted out? I only know of transistor bias adjustment. is there DC adjustment?
That said, imaged below is zero input measured at connection to midrange speaker; which shows balanced leads / zero voltage.
Anyways with that context for the crossover measurements....
The mids I think is the primary issue, below are most remarkable frequencies measured
Mid - 500hz
Compared to 700hz imaged below. The db difference is consistent at this freq. Which component of the cross over would most likely cause this?
Next is Mids - 1000hz (Subsequent - I just noticed left channel positive peaks higher than right, and vice-versa for the negative side. THAT must be the issue am hearing; left side piston stroke is more power and is reversed on right side...that would really mess with the directionality of the sound i figure? any ideas?)
Tweeters
had to change the oscilloscope timing for these frequencies
Tweeters - 2500hz for fun. is the crossover only cutting one side of the circuit, is that what am seeing?
And the amplitude gets crazy from 7500hz and up
5000hz
7500hz
and than 12500; no change in volume setting...
So with just the above, I don't think there is a timing issue. But certainly a crossover issue; and presumably given the age of these speakers and that there is apparently an electrolytic cap within, they're well overdue for a refresh and that will likely get the speakers back inline with each other.
I'd attribute me thinking phase issue at first because of how I didn't really notice much volume difference with up close listing comparatives. but suppose adding in room acoustics, slightly different amplitude, listened to at a normal distance could perhaps impacts sound like that.
Does that all seem reasonable? the difference in measurements between channels is likely due to the crossover. I did measure the drivers and crossover section for ohms and all seemed fine to me. variance of 0.1ohm on the 7"drivers; presume is non-issue. both side had that variance. and at speaker terminals the speakers are within 0.2 ohm iirc. only mean to compare the two speakers here; does not tell me at 35watts, 120hz (lol) what kind of difference there is between them.
what a fun thing, measuring like this. some surprising results. in particular what audessey does to the signal / wave lol a VERY interesting comparative there would be measured at signal & from microphone; see if audessey corrects and to what degree.
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It's not clear what you're measuring, the preamp output, the amp output, the driver input. Fixing the imbalances would be different in each case. Why don't you tell us what you're trying to do and we can advise on how to do it...
Yes, you can adjust the amplifier DC output, did you mean to ask that question in the speakers sub-forum?
I'd suggest swapping the speakers from left to right (the whole speaker). If you hear a change it may be the speakers that are damaged. If you hear no change it may be the room or the electronics.
Yes, you can adjust the amplifier DC output, did you mean to ask that question in the speakers sub-forum?
I'd suggest swapping the speakers from left to right (the whole speaker). If you hear a change it may be the speakers that are damaged. If you hear no change it may be the room or the electronics.
Thanks or the reply Allen!
the measurements imaged are all described in the post.
First three are of the pre-amp and amp. Seems needed for context of the primary issue, imaging (speakers do not perform exactly the same). In that need to see what the signal looks like at those points before assuming the issue is with the speaker. the preamp seems a bit strange that the positive swing (peak) is less than negative. however that does not seem present once amplified as that signal seems more equal positive / negative.
The subsequent measures are at the driver terminals of the mid-range and tweeter; also noted in the post.
I also mentioned the what looks to the the issue; for the mid-range driver, the positive swing on one channel is greater than the other, and reverse for the negative swing.
most clear in the 1000hz midrange driver measurement.
the measurements imaged are all described in the post.
First three are of the pre-amp and amp. Seems needed for context of the primary issue, imaging (speakers do not perform exactly the same). In that need to see what the signal looks like at those points before assuming the issue is with the speaker. the preamp seems a bit strange that the positive swing (peak) is less than negative. however that does not seem present once amplified as that signal seems more equal positive / negative.
The subsequent measures are at the driver terminals of the mid-range and tweeter; also noted in the post.
I also mentioned the what looks to the the issue; for the mid-range driver, the positive swing on one channel is greater than the other, and reverse for the negative swing.
most clear in the 1000hz midrange driver measurement.
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If your pre-amp has a DC offset you should be able to measure it directly. I would expect that to disappear as you pass it on. What I see in the plot above looks like an offset and a slight level imbalance, it might be distortion.. you'd have to adjust the scale.
ah kk, that explains the pre-amp / amp difference in positive peak / negative peak difference.
For the last comment; what do you mean adjust the scale? both channels are same scale. 100mv. (err, perhaps you're meaning if I want to measure distortion I need to adjust scale)
I don't understand how left channel negative peak is higher than right.
And Right channel positive peak is higher than left.
when measured at the driver.
envisioning a signal passing through both left / right, wouldn't this condition cause imaging issues?
What's more, there is no such signal issue when measured at the Amp. imaged below is that measurement and both channels; which as expected are perfectly symmetrical
For the last comment; what do you mean adjust the scale? both channels are same scale. 100mv. (err, perhaps you're meaning if I want to measure distortion I need to adjust scale)
I don't understand how left channel negative peak is higher than right.
And Right channel positive peak is higher than left.
when measured at the driver.
envisioning a signal passing through both left / right, wouldn't this condition cause imaging issues?
What's more, there is no such signal issue when measured at the Amp. imaged below is that measurement and both channels; which as expected are perfectly symmetrical
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Am going to measure using same method a pair of CF-30's I have. I find they have very good imaging; so expect to see that come through the measurements. if not then these measures are not useful for me.
If this were so then you'd have a level imbalance between sides at that frequency.
Here are measurements from a pair of CF-30s that I find to sound fine.
Actually, they show a good example of imbalance at 100hz. The peak to peak of green is greater than yellow so a level imbalance (and a slight phase issue as well)
imaged below
compared to the imbalance in peak positive to peak negative between channels for the RTi12's at 1000hz. I think the crossover is causing this.
So the measurements are inline with what am hearing; the CF-30s, at directional level frequency 1000hz is nearly spot on.
CF-30s 1000hz both channels
CF-30s 750hz both channels
and the phase between channels gets worse the lower the frequency
CF-30s 500hz both channels
CF-30s 250hz both channels; the level imbalance starts to appear (not at all noticeable when listening)
So with all that am confident the most likely issue is the crossover components of the rti12's causing the poor imaging. I'll start there and will post post rebuild measurements. I suppose will be measuring crossover components directly next. if particularly off from stated spec (if stated anywhere lol) will post as that's pretty solid confirmation of issue at that point.
Actually, they show a good example of imbalance at 100hz. The peak to peak of green is greater than yellow so a level imbalance (and a slight phase issue as well)
imaged below
compared to the imbalance in peak positive to peak negative between channels for the RTi12's at 1000hz. I think the crossover is causing this.
So the measurements are inline with what am hearing; the CF-30s, at directional level frequency 1000hz is nearly spot on.
CF-30s 1000hz both channels
CF-30s 750hz both channels
and the phase between channels gets worse the lower the frequency
CF-30s 500hz both channels
CF-30s 250hz both channels; the level imbalance starts to appear (not at all noticeable when listening)
So with all that am confident the most likely issue is the crossover components of the rti12's causing the poor imaging. I'll start there and will post post rebuild measurements. I suppose will be measuring crossover components directly next. if particularly off from stated spec (if stated anywhere lol) will post as that's pretty solid confirmation of issue at that point.
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What you have in the first plot looks like a normal crossover imbalance, but would you say the next plot looks more like an amplifier issue?
note i've measured the amp and it is fine; nice and symmetrical.
The first plot is to show normal level course imbalance; one channel greater positive AND negative amplitude.
The second plot is the rti12 mid-range driver, and THAT I believe is being cause by the crossover.
The first plot is to show normal level course imbalance; one channel greater positive AND negative amplitude.
The second plot is the rti12 mid-range driver, and THAT I believe is being cause by the crossover.