How to build a rudimentary Speaker with a decent level of sound?

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TheBlackSword

Joined Dec 13, 2018
1
Hopefully this is the right place to post this. I'm trying to build a rudimentary speaker using a 32 awg wire coil and four small magnets stacked on top of each other, with a paper cone attached to the coil. I built a prototype using a 44 awg wire coil on the same magnets with the same cone and it worked, however it was very quiet. The 44 awg coil had fairly high pure resistance (about 60 ohms) so I figured using a larger gauge wire would result in louder sound due to higher current. However, the new coil produces hardly any noise at all, despite having a pure resistance of 7 ohms. I'm not an audio engineer, I'm a student, so I'm really in the dark as to what the correct construction would be that would result in a decent level of sound. My main questions are as follows:
1) How much current do you need to produce a decent level of sound? Would this relate to how heavy the coil was, e.g., would you need higher current to move a bigger coil? Would making a voice coil with less turns be valuable at a certain point due to having lower inductive reactance, and thus higher current?
2) I'd assume that a coil could become too heavy to work properly, but how heavy is too heavy? Is there a function or ratio that I could use to determine this? Mine is probably only a few grams.
3) In general, what is the optimum number of turns in a voice coil?

Mainly I'm just wondering if there are formulas/ratios or just common knowledge on speaker construction that I'm unaware of.
 

djsfantasi

Joined Apr 11, 2010
8,565
The four factors affecting an electromagnets strength are as follows.

Core material affects strength, as the magnetic field is dependent on the core. Neodynamium cores are the strongest.

Wire size and current are two more factors. A smaller gauge wire will conduct more current, that is true. However, the larger current will drain a battery faster. Or in your case, will affect the audio signal. Current drawn is dependent on the resistance of the wire. 12 gauge may look like a direct short and your audio source may not be able to provide the resulting current. Thus, you may have to trade off current versus the resistance the wire presents.

Which leads us to the last factor. The number of turns... More turns create a greater field. Thus, another trade off must be considered. Using 12 gauge may require more space than is practical in your application. But a high gauge wire can provide many more turns in the same space.

The trade off is for a given wire gauge, how many turns can you make and what is the effective resistance of that many turns? Remember, more terms = more magnetism.

While you went for maximum current, you may have exceeded the maximum current available from your audio source.

Start with the current available. Calculate how many turns can be made for different wire gauges. That will give you a total length of wire. Using that length of wire’s resistance, calculate the current drawn. If it’s greater than current available, start over.
 

crutschow

Joined Mar 14, 2008
30,774
Note that most commercial speakers have large and strong magnets around the voice coil to increase their sensitivity and efficiency.
 

cmartinez

Joined Jan 17, 2007
7,826
Hopefully this is the right place to post this. I'm trying to build a rudimentary speaker using a 32 awg wire coil and four small magnets stacked on top of each other, with a paper cone attached to the coil. I built a prototype using a 44 awg wire coil on the same magnets with the same cone and it worked, however it was very quiet. The 44 awg coil had fairly high pure resistance (about 60 ohms) so I figured using a larger gauge wire would result in louder sound due to higher current. However, the new coil produces hardly any noise at all, despite having a pure resistance of 7 ohms. I'm not an audio engineer, I'm a student, so I'm really in the dark as to what the correct construction would be that would result in a decent level of sound. My main questions are as follows:
1) How much current do you need to produce a decent level of sound? Would this relate to how heavy the coil was, e.g., would you need higher current to move a bigger coil? Would making a voice coil with less turns be valuable at a certain point due to having lower inductive reactance, and thus higher current?
2) I'd assume that a coil could become too heavy to work properly, but how heavy is too heavy? Is there a function or ratio that I could use to determine this? Mine is probably only a few grams.
3) In general, what is the optimum number of turns in a voice coil?

Mainly I'm just wondering if there are formulas/ratios or just common knowledge on speaker construction that I'm unaware of.
Take note: the gap between the coil and the magnet is critical...
 

crutschow

Joined Mar 14, 2008
30,774
How are the magnets configured?
They need to be arranged so there is a small gap between two of them where the coil moves.

The magnets from an old hard-drive read-head actuator are very strong and are designed with a small gap, so may work for your purpose.
 

Alec_t

Joined Sep 17, 2013
13,149
Magnet polarisation is important too. For example, disc-shaped magnets with one face N pole and the other face S pole are no use if arranged co-axially inside a cylindrical coil, since the magnetic flux would be mainly parallel to the coil axis. The flux needs to cut the coil.
 
Last edited:

MisterBill2

Joined Jan 23, 2018
13,115
In addition to the above comments, the power require can be quite a bit. Even the very good speakers are not very efficient at converting electrical watts to acoustical watts. There is a whole lot of information available but not much of the good stuff has been published in the past 40 years.
 
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