Looking for opinions on wiring 4ohm woofers in series used with passive crossovers.
Anything negative about doing this. I thought I read something a while ago about this but could not find anything while searching.
Reason I ask, is I want to build an MTM but maintain an 8 ohm load.
Thanks
Anything negative about doing this. I thought I read something a while ago about this but could not find anything while searching.
Reason I ask, is I want to build an MTM but maintain an 8 ohm load.
Thanks
I have not built an MTM.
However, I performed some tests awhile ago myself on a pair of woofers. There is no change in Q or Fs when woofers are wired in series or in parallel.
The Re doubled, of course. Double the Vas as well. I did not measure, but I would guess the Le would double too. So hook them up in series and call them an 8 ohm speaker.
There is someone who did the same thing in the following thread:
http://www.diyaudio.com/forums/showthread.php?threadid=8940
Andy Graddon is the writer of the spreadsheet.
However, I performed some tests awhile ago myself on a pair of woofers. There is no change in Q or Fs when woofers are wired in series or in parallel.
The Re doubled, of course. Double the Vas as well. I did not measure, but I would guess the Le would double too. So hook them up in series and call them an 8 ohm speaker.
There is someone who did the same thing in the following thread:
http://www.diyaudio.com/forums/showthread.php?threadid=8940
Andy Graddon is the writer of the spreadsheet.
I did assume that the inductance would double. Does this negatively effect anything, or just cause a little more careful selection of your lowpass coils?
If you look at the old Bose 901 direct reflecting speakers they had 9 drivers wired in a series/parallel arrangement. They were amazing for their time.
Milzie said:
Well, I never heard of it affecting anything.
Never built an MTM.
If you want to wait a day or two, I can do a quick test where I test my test speaker at 100 Hz, 200 Hz, then 3000 Hz and 6000 Hz. Then I can wire it in series and test the same frequencies. If there is some change betwen the high and the low frequencies, then something is different. Say the word, I'll do the test.
I would be very surprised if 3000 Hz and 6000 Hz did not have the same decibel relationship to the midrange when two woofers are hooked up in series as when they are tested singly, but I will give it a shot if you want. My test speakers are a pair of 4 inchers without tweeters in sealed boxes, by the way.
I would really appreciate it if you did that test. Also, some sound quality impressions would be great....soundstage, image quality, etc. See if anything differs between the two.
Thanks,
Jeff
Thanks,
Jeff
I'm not sure how audible this effect is, considering how common series/parallel arrays are, but......
http://www.geocities.com/kreskovs/DP_comments.html
"The conclusion must be that wiring drivers or systems in series should only be done with extreme care. Slight mismatches of Fs can lead to significant problems with the response of the system around the resonant frequency."
"when we look at the decay after the input is cut off we see a very different picture with extended ringing in an out of phase response."
"the out of phase nature of the drivers' motion results in an exact cancellation of the electrical damping leaving only the mechanical damping to control the drivers"
http://www.geocities.com/kreskovs/DP_comments.html
"The conclusion must be that wiring drivers or systems in series should only be done with extreme care. Slight mismatches of Fs can lead to significant problems with the response of the system around the resonant frequency."
"when we look at the decay after the input is cut off we see a very different picture with extended ringing in an out of phase response."
"the out of phase nature of the drivers' motion results in an exact cancellation of the electrical damping leaving only the mechanical damping to control the drivers"
Milzie:
Rechecking my test results, I discovered that I already tested the frequency response for single woofers and two identical woofers hooked up in series and parallel into the midrange and high ranges.
The frequency response was identical both in bass, mid, and high ranges-no change. Not even a decibel.
The test was conducted with a Radio Shack SPL meter and an online tone generator. The SPL meter was directly in front of one speaker, about 1/4" from it's cone. I ran test tones through the speaker, and measured the results on the meter, and recorded the results.
Then I hooked the speaker up in series and parallel to an identical speaker and measured the results-the same speaker, the same range.
The Raido Shack SPL meter has an irregular frequency response-but if you run two sets of identical tones through it, it will measure the decibel difference between different ranges. Frequency response had nothing to do with it.
For instance, if a speaker is 90 dB with the setup at 200 Hz, and 86 dB at 1000 Hz, then if the speaker is hooked up in parallel to an identical one, we know there is no difference if it measures 90 dB at 200 Hz and 86 dB at 1000 Hz. 200 Hz is the Fc of the box.
If Qtc changed as a result of being hooked up to another speaker, then the SPL at resonance would change in relation to the midpoint and high range-it did not. Not a decibel.
The relation ship of Qts or Qtc to output is as follows:
20 log Qts, (or Qtc).
As a test, I hooked up a resistor in series with the speaker for the same setup. Boy, did the SPL at resonance ever change compared to the midpoint then!!
From this test, we can safely conclude that there is no change in Qts or Fs when identical woofers are hooked up in series or parallel.
As for the rest of what catapult said, I cannot argue with. I only tested for changes in Qts or response shape. Conclusively, though the tests were comparatively simple, I can safely say that there were no changes whatsoever in those parameters.
So there is no difference in the low, mid, or high ranges between a single speaker, and two identical ones hooked up in either series or parallel.
Rechecking my test results, I discovered that I already tested the frequency response for single woofers and two identical woofers hooked up in series and parallel into the midrange and high ranges.
The frequency response was identical both in bass, mid, and high ranges-no change. Not even a decibel.
The test was conducted with a Radio Shack SPL meter and an online tone generator. The SPL meter was directly in front of one speaker, about 1/4" from it's cone. I ran test tones through the speaker, and measured the results on the meter, and recorded the results.
Then I hooked the speaker up in series and parallel to an identical speaker and measured the results-the same speaker, the same range.
The Raido Shack SPL meter has an irregular frequency response-but if you run two sets of identical tones through it, it will measure the decibel difference between different ranges. Frequency response had nothing to do with it.
For instance, if a speaker is 90 dB with the setup at 200 Hz, and 86 dB at 1000 Hz, then if the speaker is hooked up in parallel to an identical one, we know there is no difference if it measures 90 dB at 200 Hz and 86 dB at 1000 Hz. 200 Hz is the Fc of the box.
If Qtc changed as a result of being hooked up to another speaker, then the SPL at resonance would change in relation to the midpoint and high range-it did not. Not a decibel.
The relation ship of Qts or Qtc to output is as follows:
20 log Qts, (or Qtc).
As a test, I hooked up a resistor in series with the speaker for the same setup. Boy, did the SPL at resonance ever change compared to the midpoint then!!
From this test, we can safely conclude that there is no change in Qts or Fs when identical woofers are hooked up in series or parallel.
As for the rest of what catapult said, I cannot argue with. I only tested for changes in Qts or response shape. Conclusively, though the tests were comparatively simple, I can safely say that there were no changes whatsoever in those parameters.
So there is no difference in the low, mid, or high ranges between a single speaker, and two identical ones hooked up in either series or parallel.
Your measurements with steady tones won't detect the effect John K is talking about. He is talking about an impulse response and ringing in the time domain after the signal quits. You'd need more gear than an RS meter and test tones to measure it. A mic hooked to a scope and an impulse test tone would probably do it if you measured outdoors to eliminate room resonances.
Like I said, I don't know how audible it is. An example of where to listen for it might be a kick drum. It wouldn't sound as "tight" as it should in the decay after the kick.
I don't understand and it's been puzzling me for a long time, but I never really needed to know for a project, but anyway I'll guess I'll ask since it has to do with this.
How come when you have an iso-baric step-up with 2 woofers they're wired in series and I guess has to be 180 out-of-phase. From what I understand about x-overs a passive 12 db/octive x-over almost always makes a tweeter and woofer 180 degrees out-of-phase at the x-over point. So the tweeter's or woofer's pos. and neg. terminals need to be swapped.
So as I've come to understand it if you wire something in series it's 180 degrees out-of-phase, so the sound waves would tend to cancel each other, if they're facing the same way on the same baffle. But I guess this isn't the case since I'm sure you're (Viper) design and others like it sound fine.
How come when you have an iso-baric step-up with 2 woofers they're wired in series and I guess has to be 180 out-of-phase. From what I understand about x-overs a passive 12 db/octive x-over almost always makes a tweeter and woofer 180 degrees out-of-phase at the x-over point. So the tweeter's or woofer's pos. and neg. terminals need to be swapped.
So as I've come to understand it if you wire something in series it's 180 degrees out-of-phase, so the sound waves would tend to cancel each other, if they're facing the same way on the same baffle. But I guess this isn't the case since I'm sure you're (Viper) design and others like it sound fine.
If the drivers are wired in series with the terminals like this + - + - and they are both mounted on the same baffle, their outputs will be in-phase with each other and assuming that the frequency is fairly low and the drivers are mounted close together, coupling will be reasonably good also.
As far as specs go, radiating area, Mms and a bunch of other specs also change, but the net result is that Fs remains the same in twice the Vas.
As far as specs go, radiating area, Mms and a bunch of other specs also change, but the net result is that Fs remains the same in twice the Vas.
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