Quite a few singers, including celebrities Plant such as Bono and Robert, have all Albums with the good old Shure SM58 or its close relative, the SM57 is sung. What ultimately counts is precisely the Performance. And if a singer is only his beloved stage micro feels comfortable, then you should do the devil and it take away!
On the other hand, it obviously has his reasons, why in the studio condenser microphones preferably attacks: They sound fine, and above all, its signal can be mixed better. Dynamic stage mics usually have a pronounced presence boost, for good speech intelligibility provides and helps the singer, against the Band enforce. In a carefully blended Studio recording sounds very signal-present an SM57 or SM58 sometimes But something harsh and quäkig. so what to do
When trying to increase the presence of Offset by microphones EQ, it depends only too easily to new damage. Many EQs Whether hardware or plug-in, let the Sound "bent" and work artificially. The subjectively genuine sound most offer passive EQ - but they are very expensive and often not flexible enough for surgery.
Passive EQ-priced
This is where our DIY proposal to: a fixed passive filters for a few euros, The increase in the presence of the Shure SM57 SM58 or straightened. The idea is not entirely re: Some of the better dynamic Mics work with electronic filters, including the Beyerdynamic M201, the Sennheiser MD441 and Shure SM7. And here too, so the developers, a dynamic system to studiotaug - Lichem sound behavior to help.
Our EQ is a passive LCR filter, consisting of a coil (L), a capacitor (C) and a resistor (R). In simple terms It looks as follows: A coil passes low frequencies, but disabled high. A capacitor allows high frequencies through, but prevents the deep. If both switches in series, resulting in a Peak filter which freely only in the midrange through. The dimensions of the Components determines the frequency range and the width (ie quality) of the filter. Using a additional resistance may be the Strength of the filter effect vary.
Our LCR filter sits between the two Signal wires of the balanced microphone cable, it interrupts the flow signal so not. It provides the output signal of the Microphone virtually an alternative way. to drain If you both signal wires connect with each other, would the microphone silent, the voice coil would be short-circuited. If you were both cores with a microphone Connect resistance, there would be loss of level, and indeed all the greater, depending smaller the resistance.
Exactly what happened before, when we, the micro connect to a preamp. The input - impedance of the preamplifier is a (AC) Resistance, a part of the signal can drain away. On a pre-amp input with Produced 2.000 ohms to 250 ohms output - impedance of the SM57/58 a level of loss about 1 dB. At a very low input with only 250 ohms would have half the signal voltage drop, ie, the impedance loss would be 6 dB.
Our LCR filter is yes, only certain Mid frequencies, ie, it generates a frequency-dependent impedance loss exactly where these Microphones its presence superelevation have. This is why, our filter the desired effect even with the Shure SM57 or SM58: It is accurate to the output impedance and adjusted other parameters of these models.
In this respect was the exact size of these simple Circuit not so trivial. There were the electrical Parameters of all components identified - SM57 and SM58 consist of a low-impedance voice coil and a molded handle in the up transformer - and for circuit simulation using approximate the components determined. The final vote was on hearing tests and frequency response measurements. Figure 1 and 2 show the frequency responses of SM57 and SM58 with and without filters.
By the way, I was surprised that the series variance against all internet rumors was very low. My two SM57, which I at a distance of about one year bought have almost coincident frequency responses!
Theory and practice
Described how our filter consists of a coil, a Capacitor and a resistor. Capacitors and resistance, you get into any electronics store. Coils (inductors) are somewhat more difficult to obtain. But we're lucky, we need an inductance of only 20 mH (milli Henry). Such small values get known as predefined components that are in the jargon "Inductor" calls. We need the coil is not so wrap itself.
There would be another problem: If a Coil as in our filter between the signal-veins of the microphone on, you can hear buzzing sounds. Coils are just sensitive to electromagnetic Interference - that we know of so of Single-coil pickups for electric guitars. The solution the problem is also found in Electric Guitars: The Humbucker pickups are two coils in opposite phase wired so that the hum of the two coils extinguish each other. Similarly, we do it well: instead of a 20 mH 10 mH inductor, we take two Inductors, which we connected in series, said second reversed relative to the first is. In the illustrated Arrangement must usually the caption into the same direction. Unfortunately, the caps are probably not always the same set up - hum should be heard be, simply unsolder one of the inductors and flipped reinsert. Even silence is in a box!
The optimal capacitor value for the SM57 is 47 nF (UF = 0.047). This value also works well with the SM58. Whoever the last remnant of this minimally would like to tackle the problem remove deeper presence boost, takes 68 nF. The whole thing can also be switched make (see below).
A little note about it is the third component the filter, the 220-ohm resistor. Who the increased presence is not completely straighten out, but only wants to reduce, may be somewhat greater resistance to 400 Ohm try.
The electrical structure is simple (Fig. 4): the two fixed inductors, the Capacitor and resistor are in Connected in series - that's it. For such a simple Circuit, we need not etched circuit board, but come with a great Piece of breadboard clear. Just the components plug in and the legs, the to be joined together turn and soldered together. Done is the LCR filter. But how do we get the now between the two signal wires? As is so often is the mechanical side a bit difficult.
The Pulmoll punk Method
Is probably the cheapest in the metal case's Drugstore for € 1.15: a can of Pulmoll. The second advantage of Pulmoll method is that they only minimal tooling requires. There have only two cables namely - penetrations of approximately 6 mm diameter be drilled. A pair of cable couplings gives red tape by one short-patch XLR cable (from about 4 €) in the center cuts. Subsequently isolated is about 4 cm at each end and the signal wires soldered to the two ends the filter circuit.
If the two signal wires as in the photo red and blue, then there are the two red Wires to the one and the two blue wires to the other end of the filter circuit. The Copper shielding of both cables is another twisted and with a short cable soldered at the other end to the bottom Pulmoll the can is soldered. Only when the Housing is connected to the ground, unfolds There shielding effect.
So that the circuit no contact with the Case back gets, it needs to isolated and fixed. Both can be combined with the Hot glue gun within easy reach. As the train-relief for the two cable recommended the cable tie (70 pieces for 1 € at Woolworth). Finish.
Chic and flexible
A more professional solution offers a small Aluminum housing, as is the case for Conrad some € is available. Disadvantage: For bring the XLR jacks, large Holes with diameters of approximately 20 mm be drilled. For this one needs a cone drills and a drill with stand.
Since the filter circuit itself takes up little space, leaves room for various switches. Very useful is an on / off switch for the Filter (Fig. 9, right). Thus, for "on the fly check "whether the filter circuit in the the application improves the sound. Because there are certainly sources for which the Presence rise is just right. furthermore useful is the ability to switch the Frequency filter for SM57 and SM58. As mentioned, is the ideal capacitor value the SM58 is a little higher. About a switch with an additional 22-nF capacitor the total capacitance of 47 nF can to 69 nF (Fig. 10).
A third switch is for switching impedance (Fig. 9, left). Nearly all microphones sound better when they Preamps with relatively high input impedance over 2 ohms runs. Among the very few Exceptions to this rule include the Shure's classic SM57 and SM58. It may related to it that the old Shure Broadcast Mixer unusually low input impedances had. My American Colleague Paul Stamler has certainly With hearing students performed a unambiguous language to speak: On impedances sound of about 500 ohms, the Shure Oldies round. Although the effect on the frequency response is minimal, also seems the subjective listening impression me much more comfortable at low impedances. disadvantage: The result is a loss in level of approximately 3 dB. The third switch does nothing as a 680-ohm resistor between the signal wires to switch. together with the input impedance of the preamp shown Then about 500 ohms. The low impedance position lends itself to be especially if you get the increased presence would like (ie, the filter is disabled), but something is a rounder Sound wishes.
Finish
Of course, accounts for a small passive filter The Shure SM57 and SM58 are classics not a $ 10,000 microphone. but the "Gently ironed" signal can be significantly smoother shape - and this makes Microphones used flexibly: Who electric guitars, Percussion and other instruments with the SM57 had decreased, yet live with the that all of these signals in the range between 5 6 kHz and extend their elbows. our small filter, leaving the decision as to whether, where and how much of the frequency range con - should be featuret, the person who for The overall sound is responsible, the mix-Engineer. Only remains for me to have fun! wish
Text, photos and measurements: Dr. Andreas Hau
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