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Using Arduino => General Electronics => Topic started by: xcxl on Oct 18, 2012, 10:56 pm

Title: 4 pins on a Speaker?
Post by: xcxl on Oct 18, 2012, 10:56 pm

Hi,

I have just bought a little piezo speaker like that : http://www.newark.com/pdfs/datasheets/spc/25R0936.pdf (http://www.newark.com/pdfs/datasheets/spc/25R0936.pdf)
The problem is there are 4 pins to connect at the back of the speaker, and I don't understand why they are here... is it not just Gnd and V+ usually?

Thank you.
Title: Re: 4 pins on a Speaker?
Post by: johnwasser on Oct 18, 2012, 11:10 pm
That looks more like a dynamic speaker than a piezo disk.

From the drawing it looks like the terminals are connected together in pairs.
Title: Re: 4 pins on a Speaker?
Post by: DVDdoug on Oct 18, 2012, 11:12 pm
The data sheet is not clear and I've never seen that before, except some woofers have dual voice coils...  Can you see any small wires soldered to the terminals?

I would guess that two termminals are connected together and connected to +, and the other two terminals are connected together and to - .

Do you have a multimeter to check if any of the terminals are connected together?

If you have a series resistor (a couple-hundred ohms or so) to limit the current, you can simply try it out.    If you connect a "short" with a current limiting resistor in-place, nothing bad will happen.

Quote
...is it not just Gnd and V+ usually?
If it's just a speaker/transducer and not a "buzzer" or "beeper", you don't connect V+.    You connect signal and ground.  It won't make any noise with V+ connected.     V+ won't hurt a piezo, but it's not good to put constant DC voltage into a speaker with a coil.   5VDC into an 8-Ohm speaker coil is 3 Watts of heat, with no sound. ;)

Title: Re: 4 pins on a Speaker?
Post by: MarkT on Oct 19, 2012, 01:24 am
Just one little curiosity, the tech drawing says "Speaker & Receiver", so perhaps there are two coils?  Bit unlikely but multimeter is going to tell. And its 8 ohm, so not piezo, but listed in Farnell as piezo... 
Title: Re: 4 pins on a Speaker?
Post by: Docedison on Oct 19, 2012, 01:52 am
If it is a "Transceiver" one set of terminals might well be 8 ohms... The Microphone, The piezo will measure as a capacitor and I won't even begin to try to guess the capacitance as I know nothing of the Er or dielectric constant or the piezo material (barium titanate, typically) or it's size. however a 4K7 resistor in series with a 5V supply (polarity unimportant) and note a small click with the pair that has no continuity with each other... Thee resistor will limit the current to 1 mA. not enough to produce much noise from the microphone (magnetic microphones make inefficient speakers) but since the piezo doesn't require much current to operate it should be a noticeably louder "click"...

Bob
Title: Re: 4 pins on a Speaker?
Post by: dhenry on Oct 19, 2012, 01:59 am
Quote
I don't understand why they are here


Read the "Polarity Test" section of the datasheet and  take a closer look at the drawing.

Quote
the tech drawing says "Speaker & Receiver", so perhaps there are two coils?


Speakers are necessarily receivers, particularly for piezo.
Title: Re: 4 pins on a Speaker?
Post by: retrolefty on Oct 19, 2012, 02:10 am


Hi,

I have just bought a little piezo speaker like that : http://www.newark.com/pdfs/datasheets/spc/25R0936.pdf (http://www.newark.com/pdfs/datasheets/spc/25R0936.pdf)
The problem is there are 4 pins to connect at the back of the speaker, and I don't understand why they are here... is it not just Gnd and V+ usually?

Thank you.


It is not a piezo speaker as with 8 ohms of impedance it can only be a dynamic speaker, that is simply a 8 ohm coil driven speaker. Piezo elements are high impedance devices. I can't make out the contact arrangement very well, but if there are four pins it's probably just for better mechanical stability for mounting to the PCB. Simply take your ohm meter and identify two terminals that read out a nominal 8 ohms and use them, and ignore the other two. Also there is no + and ground for a speaker as it's designed as a AC device so is polarity insensitive, there are just two signal terminals, and you are free to ground either one if required to be ground based.

Lefty
Title: Re: 4 pins on a Speaker?
Post by: xcxl on Oct 19, 2012, 07:33 am

it's probably just for better mechanical stability for mounting to the PCB


Yes you were right, I have just test the 4 pins with the multimeter and they are connected by pairs. So just Gnd and Signal! I thought it was more complicated....
Thank you very much!
Title: Re: 4 pins on a Speaker?
Post by: fungus on Oct 19, 2012, 10:17 am


Hi,

I have just bought a little piezo speaker like that : http://www.newark.com/pdfs/datasheets/spc/25R0936.pdf (http://www.newark.com/pdfs/datasheets/spc/25R0936.pdf)
The problem is there are 4 pins to connect at the back of the speaker, and I don't understand why they are here... is it not just Gnd and V+ usually?

Thank you.


Stereo?
Title: Re: 4 pins on a Speaker?
Post by: kf2qd on Oct 19, 2012, 07:07 pm
"+" and "-" on a speaker are there for phasing purposes. On a speaker this small it wouldn't really make much difference, but on large speakers where they are not phased properly makes for a big loss in bass.

A way to test the the result of phasing is to take and drive 2 speakers, side by side, from the same source and reverse the phasing on one and listen for the difference in the quality of the sound. One effect from 2 speakers that are closely spaced but different in phase is that the sound will be quieter at a distance as when on speaker is pushing air, the other is pulling and thus they will tend to cancel out.
Title: Re: 4 pins on a Speaker?
Post by: retrolefty on Oct 19, 2012, 07:31 pm

"+" and "-" on a speaker are there for phasing purposes. On a speaker this small it wouldn't really make much difference, but on large speakers where they are not phased properly makes for a big loss in bass.

A way to test the the result of phasing is to take and drive 2 speakers, side by side, from the same source and reverse the phasing on one and listen for the difference in the quality of the sound. One effect from 2 speakers that are closely spaced but different in phase is that the sound will be quieter at a distance as when on speaker is pushing air, the other is pulling and thus they will tend to cancel out.


Another means of testing for proper phasing on loudspeaker is to simply wire a 1.5vdc battery to the speaker terminals and note if the cone moves out or in. At my age I never trust my ears alone to make these kind of connections.

Spent a decade or so in the late 90s early 00s collecting quality vintage solid state hi-fi equipment made in the 70s (Marantz, Kenwood, Sansui, etc) from thrift stores as people were giving away their quality stuff for the cheap plastic 5 channel stuff. Sold lots of the stuff on E-bay for pretty big bucks and keep some of the better stuff for myself. Fun hobby until the whole world seemed to learn about the golden age of hi-fi equipment and the thrift store finds dried up.  ;)
Lefty  
Title: Re: 4 pins on a Speaker?
Post by: keeper63 on Oct 20, 2012, 06:40 am

Fun hobby until the whole world seemed to learn about the golden age of hi-fi equipment and the thrift store finds dried up.  ;)


Every now and then you can still find some of this stuff at Goodwill, at least here in the Phoenix area. I once picked up a really nice Sansui turntable for my system; still had a nice cartridge and the manual came with it. I think I paid $15.00 for it.