I have this old pair of Technics SB-3130, they are three way speakers. Both of the super tweeters are dead (infinite resistance) and I’m not sure if this impact the range of frequency feeded to the tweeter. Given the schematic diagram, if I remove the super tweeter, should I modify something to have all the high frequencied on the tweeter?
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if I remove the super tweeter, should I modify something to have all the high frequencied on the tweeter?
You will basically have to replace the 3-way crossover with a 2-way one, or you will be missing the complete upper range currently “assigned” to the super tweeter. You’d also have to make sure the current mid-tweeter is able to reproduce the upper frequencies. It will most likely be easier to simply replace the defective tweeters.
That’s my question, how do I get rid of the crossover. In my limited understanding of electronics, the c3 capacitor will do nothing if terminals 11 and 12 are open. I’m not sure though.
Yes C3 will do nothing if terminals 11 & 12 are open. You won’t get the high frequency super tweeter range just mid tweeter and low woofer
Will I get the high frequencies back if I remove L2?
I believe the C2, R2, and L2 are forming a band pass filter for the mid frequencies to the tweeter. Inductors (L) act as low pass filter and capacitors © act as high pass filter. The problem with changing anything is that the tweeter (mid) is likely not capable of moving at the super tweeter (high) frequencies nor the low (woofer) frequencies due to its mass (inertia) and stiffness of its diaphragm, etc. Best bet is to replace the broken super tweeters with others as they are actually designed for those high frequencies. It’s possible you tear the diaphragm of the tweeter unless you kept the volume low
If you follow the circuit, for the super tweeter, you have a RC passive high freq filter, while the tweeter has a passive RCL band filter.
Simply removing the super tweeter will remove the high frequency.
Otherwise you need to calculate a new band pass frequency with the new upper freq limit and change the 3.9uF cap accordingly
Edit: by simply removing L2, you will create a high pass filter with the high frequency being the value of the current C2 L2 Filter.
And if you remove L2, you will get all the subwoofer frequency as well.
So simply removing L2 won’t work.
You either replace the super tweeter or calculate a new value for C2 and replace it.
If the STs are open, don’t do anything. All the high frequencies are still going to the tweeter, it’s just that they won’t be reproduced as well as the ST could. You can probably compensate with the EQ at the signal source.
After further reading about filters I ended as the same conclusion as you. I first thought the L2 was removing high frequencies, but it is in fact an LC filter to remove bass more efficiently.
The thing about speaker boxes like this (if they’re built well) is that all the speakers are paired together based on the frequencies they handle best, and the crossovers are matched to those, so that each speaker is only being given the frequencies ot’s best at reproducing. The obvious fix to to replace the tweeters with new ones with an equivalent frequency response. If that’s not an affordable option at the moment, I can appreciate that, but any other fix is going to change the frequency characteristics of the box.
The simplest option is to just swap the dead tweeters with resistors equivalent to the tweeters. That’ll ensure that the other two speakers continue operating the same, but the box as a whole will no longer replay those high frequencies at all.
The other option is to replace the whole crossover, like you suggested, to be a two-way instead of a three-way. You can look up a calculator for picking out R and C values, based on where you want the frequency cutoff to be. Your best bet is probably to use the same cutoff as the lower end of the existing crossover, sobthat the middle tweeter just now gets the same frequencies it was getting already, plus the additional upper frequencies. The risk is that it wasn’t designed to reproduce those frequencies, so it may not play very well, and it might actually make the middle frequencies sound worse.
Just check the live circuit with an oscilloscope. It should be quite easy to see which part croaked.
