Pleiades 8 ohm speaker to 200 ohm mic out converter for recording bass drum

It would be nice making a step up transformer for using any speaker as microphone or bass drum mic.


Any speaker is already a moving coil microphone and vice versa, (reciprocity principle).


All needed to be done is connecting a Pleiades transformer made from Magnetec Nanocrystalinne core or equivalent. A step up ratio of 5, ie secondary number of turns 5 times greater than primary will give a 5x5=25 impedance increase balanced out. So any speaker of 8 ohms will be converted to a mic capsule of 200 ohms.


The number of primary turns can be adjusted to compensate for proximity effect. The less the number of turns the higher the cutoff frequency, the brighter the sound.


The whole lot can be fitted inside the excellent Neutrik XLR modules. Therefore in the direction of signal flow, from speaker as mic to its balanced 200 ohm output we can have:


1 Speaker connecting clips, each with shielded cable.


2 Both twisted and the pair inserted in Neutrik module cable outlet (inlet in this case) CM.


3 The Neutrik NN3MXI  XLR male out threaded to CM and inside it the Magnetec 073 tape wound core. We wind some turns as primary and 5x as much as secondary, solder primary to twisted pair and secondary to XLR pins 2 and 3 and we should be ready.


A step up transformer may not even be needed as the signal may be already large. In that case the 8 ohms speaker out is connected directly to a mic input or XLR out of the Neutrik module.


If bass cut is needed to brighten the sound then a Pleiades filter (just an inductor in parallel) can be connected to cut bass. This is the same principle used on speaker crossover networks, but reciprocity wise.


A suitable Pleiades cutoff frequency filter can be selected to make an interesting vocal mic, or making an excellent mic such as an AKG D112 or D12 proximity compensated for excellent close vocal recording or live application.