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Topic: Adafruit wave shield + other questions (Read 2386 times)previous topic - next topic

N_Tesla

Apr 12, 2013, 03:08 pmLast Edit: Apr 12, 2013, 03:51 pm by Mad physicist Reason: 1
Hi,

I'm considering buying the Adafruit wave shield for my Arduino alarm clock, but, as a newbie in audio electronics, I have some questions/concerns I'd like to resolve before acquiring one.

Will the shield deliver enough power to my speakers?
The shield is said to deliver enough power for headphone-type speaker. The fact is, I think my speakers are somewhate bigger than this, and should play the audio at a rather strong volume (it's an alarm clock !). My question then is : what happens if I connect my (perhaprs too "big") speakers directly on this shield ? Will they just produce a low-volume sound or/and the shield itself will be in a dangerous condition ?

Now, you will probably ask : "what is the impedance of your speakers?" I don't know! I guess this won't be of much help, but their dimensions are 5cm*11cm (they have been salvaged from an old television). Actually, they are now fully enclosed in the clock's case and will be very difficul to remove, which brings me to my second question.

How to cheaply measure speaker impedance?
Will a simple mesure of resistance and inductance do the trick ? I dont need a precise value, just an order of magnitude in order to make it work (actually, I don't have much equipment at home -but I can borrow some if necessary-).

What can I do if my volume is too low?
If the power delivered by the shield is actually too low, will a simple amplifier like this one solve my problem ? (i guess it depends again of my speaker's impedence)

Thanks for your time.

Magician

#1
Apr 12, 2013, 05:25 pm
# 1 Depends on "enough", physiological parameter
#2 You can measure speakers impedance with DMM, same as any regular resistor.
#3 3.7W is quite high power, it's about level in vast majority TV sets (2-3W).

N_Tesla

#2
Apr 12, 2013, 05:50 pm
Thank you for your answers.

I don't think I have a specific impedance-meter, but i can measure inductance and resistance. And assuming most of the speaker's impedance will be contained in its inductance, I can compute the impedance manually (2*pi*nu*L + R), right ?

Magician

#3
Apr 12, 2013, 05:53 pm
Quote
All you'll measure with the ohmmeter is the coil's resistance, it's a length of fine enameled wire.
Exactly. Speaker's inductive /  mechanical impedance is highly   non-linear over specified frequency range and doesn't have any sense for real world application. Moreover, it's affected by enclosure, so enameled wire resistance is only parameter that important for amplifier selection

N_Tesla

#4
Apr 12, 2013, 05:56 pm

Speaker's inductive /  mechanical impedance is highly non-linear over specified frequency range

Alright ! Ignore my previous post then

xl97

#5
Apr 17, 2013, 07:13 pm
to driver bigger speakers you may need an amp..

smaller (hobby, non-powered) speakers are fine...

by default the volume on the Waveshield is NOT loud IMHO...

but I read you can hack this by adding a new resistor (or using a different value one in the beginning/during assembly)

search over at adafruit forums to get more details on it.

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