Originally Posted by maricm
I will explain.
These are the two heads of sm58 mic and they should be connected to one output and it does not lose dB and kHz.
XLR cable will go into the remote transmitter, which will be bonded to the accordion.
Thanks for all your effort to help me in solving problems.
There may be a slight language problem with my ability to understand what you would like to do, but as best as I can tell you want to mic your accordion into a single wireless transmitter to send to your sound system and/or a recorder.
Why you're using 2 Beta 58 capsules physically parallel apparently spaced about 100 mm from each other is your business, but presumably you believe it will somehow give you better sound. I can imagine that on the "chord" side of an accordion, since the various notes sound radiate from different areas of the instrument, using (2) mics, spaced will give you somewhat more uniform pick -up of all the chords even with the mics almost in contact with the accordion.
I'm no expert as far as mic placement for optimal accordion recording, but everything I've read and everyone I've ever heard speak about how to do it usually recommends using at least two mics, one a meter or so in front of the chord end and one in front or at a 45 deg. angle to the bass end.
Obviously that won't work if you have to move around very much so we can understand what you're trying to achieve.
Anyway, form your last post, I get the impression that you would like to combine the (2) Beta 58A capsules without loosing any signal level and without any loss of signal bandwidth (kHz). Connecting directly to the wireless transmitter eliminates the possible high-frequency loss due to cable capacitance, so that's not a problem. Combining the mics without using the isolation resistor network can be done by just wiring them directly in parallel. HOWEVER, that will not give you correct "combining" of the two mic signals. If the mics could somehow be in the exact same physical location in space, combining the outputs by wiring them in parallel would actually work. The electrical signal coming for each mic would be exactly the same voltage, the signals would be in phase and would combine like (2) batteries wired in parallel.
The problem with doing that with mics that are physically separate, but are also close enough to pick up the same signal, but with a phase difference because of their locations will not only "load" each others signal resulting in reduced output level, but they will have frequency response "anomalies" such as severe comb-filtering when you play a note that results in a 180 deg. phase shift between the two closely spaced, parallel capsules (which WILL certainly happen with your proposed set up). The other concern about your configuration is the considerable proximity effect of the Beta 58A. At 25 mm from the accordion you will have a bass boost of at least 9 dB at 200 Hz. This can always be toned-down with a HP filter or EQ on your mixer or PA amp, but may create a problem in the wireless transmitter unless the input gain is kept quite low.
Sorry, but there is no passive way (non-amplified) to combine the (2) mic capsule outputs without some signal loss at some (probably many) frequencies. As much as you might like it to happen, the laws of physics still apply here.
There is no harm in trying it, so you certainly can try simply wiring the (2) capsules in parallel and driving your transmitter from the result. It won't damage the capsules. You will get response from both capsules and the signal (even with the comb filtering), might be acceptable for your application. Some frequencies will add and some will cancel out each other resulting in "notches" in your frequency response. Alternately, it would be possible to construct a small portable dual channel pre-amp circuit that was battery powered that could be installed ahead of your transmitter and would be small and light. It's not a simple matter however to do it right. It would work somewhat better in that the signal loss would be eliminated, but the non-uniform frequency response would still be there.
Sorry for the long post and hope you can understand the content. I'm trying to keep it as simple as possible, but it is not a simple subject, and combining two slightly seperated mics very near the sound source is generally not a good idea.
If your budget allows it, using (2) transmitters (one on each capsule) and then mixing the two channels with one panned partly left and one partly right, and possibly adding 20 or 30 msec. of delay on one channel might actually enhance the sound you're trying to achieve. The spatial panning will eliminate most of the comb-filtering (as long as you don't re-mix to mono) and the effect might give your performance extra dimension. Something to think about.