Topic: Combining the sound of 2 different mics by connecting them in parallel

[noam]

Omnis give a rich, lush sound and are generally preferable for classical concerts, except when remote from the sound source, like in an opera in a big house, where the orchestra pit separates you from the singers. The singers may not be heard clearly enough with omnis, even though the overall sound may be superb. I have been trying to find a way to combine the forward presence of the singers’ voices in cardioids with the rich sound the omnis give.

Today, after my daily workout of 80 laps, I stood in the shower in automatic pilot/ complete nirvana mode, when suddenly I heard the voice of a demon telling me “Dual Headphone Adapter”. I went to a Radio Shack, bought a dual headphone adapter with two 1/8” stereo female plugs and one 1/8” stereo male jack. I hooked up my omnis to one female plug, the cardioids to the other (they have almost similar sensitivity) – two pairs of mics in parallel – and connected the male jack to a battery box, to a HiMD. I checked to make sure I got signal from each pair separately as well as together and made some test recordings at home. All I can say is that the sound of the two together was different from each by itself, but I need to test them in a large auditorium, where the omnis will have more reflected sound to pick, in addition to the direct sound the cards will pick up. Any thoughts? Obviously that drains up the battery twice as fast, and I wonder if the double load may cause problems for the battery box over an extended performance. But it should perform with mics with half the resistance, which comes up to the same result. I don’t assume the recording device is having a double load due to the decreased resistance (I assume the battery box takes all the load) – but I’m not sure. Each mic pair is still getting 9v, of course. I placed the Lt. card next to the Lt. omni, and did the same with the right pair, so as to minimize any lag time (and there wasn’t any). It’s important not to mix the Lt. and Rt. Mics.

Noam

[BC]

cool idea! I take it you are stealthing so toting a mixer is not an option? Seems like a mixer would give more flexibility to dial in the exact ratio of each to get the sound you want.
+t for sharing those great in-the-shower ideas. 

[noam]

I posted this shower revelation on the Oade Brothers site, and Doug had some comments. The technical stuff is above me.

Doug wrote: tying the output of two dynamic mics together with a Y adapter
 is common with dynamic mics and will not damage them but is not a great idea with mics powered by the signal line. I suggest you build 2 separate battery supplies. What you are doing is tying the output of each output transistor together and they are working against each other, this not only increases current draw but distortion and may damage the mics over time. Low value resistor isolation is a good idea as a minimum but active buffers and a summing amp would be ideal and would get you the cleanest signal possible.

I asked: If I understand you correctly, you suggest connecting each mic pair to a battery box, and connecting the 2 battery boxes to the dual headphone adapter>HiMD line in? That will not overload the line in? What is the line in getting in this configuaration - 9V or 18V?

Doug replied: No it will not overload it as the output of the battery box has
capacitors in line to block the DC voltage from reaching the input of
the recorder. The line in should not see any DC voltage from the
battery box

By using a low value resistor in line with the output signal lead you
are building a passive summing circuit that will improve the signal
quality of the two combined mics. This can be no larger than a single
battery box with 2 sets of inputs for the mics all powered by one
battery and one output cable or stereo minijack.
Something like this as a minimum ...



         + dc
           |
      power resistor
           |
           |    DC blocking cap film type
           |---|(--summing resistor--tied to 2nd mic out ---->
Mic plus   +
           O                                           output
           _
Mic ground   ------ output ground --------------------------->

--------------------------------------------------------------------------------------------------------------------

Would appreciate any comments - Noam

[redbook]

Bump

I've been wandering the same, wanted to do a quick dual comparison for mics.

I thought in doing

OKMIIR > A3        |
                          |---- Y dual adapter > JB3
AT853 > SP-SPSB |

Would this work?
Can I isolate each channel (left right) so I can compare the sounds?

[noam]

Bump

I've been wandering the same, wanted to do a quick dual comparison for mics.

I thought in doing

OKMIIR > A3        |
                          |---- Y dual adapter > JB3
AT853 > SP-SPSB |

Would this work?

Can I isolate each channel (left right) so I can compare the sounds?

No, a Dual Headphone Adapter will combine channels from each mic, it will not give you a different mic in each channel.

BTW, my experiment was not a success because the sound I got was completely dominated by the slightly more sensitive mic, instead of getting a blended sound.
Noam

[wbrisette]

I have been using a combination of omnis and cardiods for a long time. However, to do it right you need a mixer. The reason for this as you have found, is the balance between the two. You usually don't want the omni mics to overpower the cardiods, yet that's what tends to happen because most omni mic manufacturers make the omnis more sensitive.

You might look into an inexpenisve mixer to play with and see if you enjoy your mixing more.

To hear some more experimenting like this, check out ftp.tapers.org.... There is a folder called gear comparisons, which contains a set of recordings I did where I did some samples of these. (by the way see http://www.tapers.org/public/  for the instructions on how to access the ftp site).

Omnis by themselves (Earthworks QTC-1)
Cards by themselves (Earthworks SR-77)
Soundboard only
Omnis & Cards mixed
all three sources combined.

Because I can keep each channel separate when I record, I am able to use the exact same selection for each of these combinations, so you really get a sense of what types of cool stuff you can do with the a mix of mics like this.

Good luck with your testing and recording and feel free to let me know if you have more questions about this.

Wayne

[redbook]

What I want to do is a comparison of some low - mid profile mics (CSB, OKMIIR, AT853...), in different situations (venues, kind of music), and then post a miniguide, so a newbie can understand the difference between mics under the same circumstances.

I should have realized about the mixer in order to mix properly all channels lol, that's the only way to do it right

Thanks for replies

[zowie]

My thoughts: russian roullette game that you won't get shitty tapes due to phasing problems, not to mention what could happen to the stereo image.

(Mixing 2 different mics in post like Wayne does, where you have control over levels and panning and retain the option to go with a single pair is something totally different, and totally good, if you have the gear and time for it.)

[redbook]

I know the recording will be a shit, what I want to get is two separate channels with indepentent sounds of each mics, so I can compare under exactly the same circumstances

[wbrisette]

(Mixing 2 different mics in post like Wayne does, where you have control over levels and panning and retain the option to go with a single pair is something totally different, and totally good, if you have the gear and time for it.)

For several years I straight mixer (Wendt X4) to mix 2 omnis and 2 cards. And dispite everbody's warnings about phasing, it was only something I experienced 3 or 4 times. Most of these were due to wind conditions.

The Deva has a built-in delay option, so you mix the signals with the delay if you have phase issues (this usually fixes most phase problems) and send that mix to the output for a downstream signal.

But again, a mixer of some type really is needed for this type of work. If for no other reason, you have the option to turn up and down signals independently of each other and not have to worry about the strength of a mic determining your mix.

Wayne

[Chuck]

I would often connect two dynamic mics together when I was doing live sound. In clubs with 16 channel boards I used to connect (2) SM 57's together (in series) to mic stuff like Leslie cabinets when there weren't enough mixer inputs. I made a couple special cables that I carried around with me for just that purpose.