DIY "Low Frequency Capture Device"?

[Marc Girard]

Hello there,

I recently tracked drums and I recorded the bass drum with a cheap Beta52 Clone and a small Peavey combo amp. I wanted to see if the "low-end" would translate good using a 10 inches speaker as a huge dynamic mic... It was really easy to do: I unconnected the speaker from the amp section and tied a 1/4" jack to the speaker connectors. Plugged the jack end in a DI box and send it thru my board...

I must say, it worked way better than I expected! The drummer was crying with joy when he heard his kick sound. I must admit, I wasn't crying but I was indeed excited.

Now, I found a place, they have a few NS-10M Woofers in stock... You can probably guess the rest of the story: I'm thinking about building my own "SubKick" device. Fairly easy-> a 10 inch drum tom/snare with a mesh head, mount the woofer inside et voila...

Now, shall I rip the guts of an old SM-57 for the electronics? How does a dynamic microphone works inside? Any suggestions for improvements? Any ideas you might have to improve this "low end capture device"? The idea is to build a big dynamic microphone and use the NS-10M woofer as the diaphram.

Let me know what you guys think... And if you are interested in building one for yourself, the store I know have around 10 woofers in store, brand new, in their boxes.

Take care all,

 

[Sammas]

I dynamic mic works in exactly the opposite way a speaker does.

you pass a voltage through the voice coil of the speaker and it moves the cone to create sound.

A dynamic mic's Diaphram (ie the speaker cone) moves as it picks up sound which pushes the voice coil in and out of the magnetic housing to generate a voltage.


I don't see why you just can't use the speaker as the microphone, without the need to chop up an SM57. It works on the same principles (mechanically speaking anyway)... but maybe someone more knowledgable will fill us in...

 

[Marc Girard]

Yes, I know that it works, I did it! I just want to know how can I make the output of the speaker balanced so that I don't need to use a DI no more... I might not even need anything between the speaker and the XLR connector... I don't know, that's what I'm looking for...

 

[bcarso]

The speaker is as balanced as the mic---just change the connector.

You might want to get inside and run out a wire to pin 1 of the XLR and tie it to the speaker frame for a bit of shielding as well.

 

[Samuel Groner]

http://www.groupdiy.com/FORUM/viewtopic.php?t=5818

Samuel

 

[Mark Burnley]

Yea,

This is a cool trick. I use a very humdrum 8R 8" speaker ripped out of some old hi-fi speakers. I use a (wait for it...) 120:12V mains transformer (not much use for anything else in the UK :wink: ) which has a 1:10 stepup ratio when connected in reverse (i.e. speaker terminals to 12V winding, 120V winding to XLR pins 2+3)

This solves the level problems, I get a nice hot output, and the impedance is stepped up to look like ~800R. The bottom end is phenomenal, and the natural EQ rolloff of the speaker means little EQ is needed. Different types of speaker have different attack and tonal responses.

As bcarso mentioned above, connect pin 1 to speaker chassis and transformer chassis.

Fun to play around with!

Mark

 

[rodabod]

That's a cool idea. This has been covered a bit over at

http://www.electrical.com/phpBB2/

I would maybe try using a cheaper speaker for the job, as I would imagine that the NS10 woofers are quite expensive. Also, I don't know the specs for the NS10 speaker, but I bet the bass extension is not amazing since it is not great on the actual monitor speaker.

Have a look around for different speakers by Celestion, Audax, etc.

I think Maplin do the Audax range and they are fairly cheap.

A transformer would be handy to step-up 4Ohms or 8Ohms to ~200Ohms.

A dynamic mic transformer would get you in the range. I recall the Shure dynamic capsules being around 2.5Ohms, so their transformers would work.

I'd watch out though - I've heard reports that the cheap shure transformers are crap, so you could miss out on a bit of bass. Maybe either get another better transformer off Ebay or just forget about the transformer and use a bit more gain on the preamp. I use a Shure dynamic with no transformer and it works fine.