Making a PA system using cheap computer speakers

[webmiester]

Hi everyone,

When I was a kid, I rode on Disneyland's Haunted Mansion ride and I was inspired by the fact that each of their seats had small speakers behind the headrests of the passengers which gave out very weak but very clear sound.

Lately, our market is flooded is with cheap but weak computer speakers. These speakers can be plugged in to computers and come out with around 5w of sounds. They cost $1.25 a pair here. I wanted to setup a classroom for around 30 students with around 10 pairs of these speakers placed on the ceiling and scattered around the room (ceiling would be more practical than behind the headrests of their seats). The sound system will only be used primarily for microphone (voice input) only (used for lectures). In this case, my goal is to come out with a lot of weak speaker sounds which is positioned all over the classroom so that it can be heard well anywhere a person stays. In this case, 20 speakers all over the classroom coming out around 3-5watts each. The speakers for this setup setup for this will only cost $12.50 total.

I would like to ask your ideas on what specs of the amplifier would be good for this and how should I wire the speakers? I don't know what the ohms of these types of speakers are, and would appreciate any ideas regarding this.

Thanks.

 

[freddi]

assuming one channel (?), and each speaker ~4 ohms (?), then 4 sets each of 5 speakers wired in series with one another - then parallel the 4 sets for nominal 5 ohm load. If two channels, then each channel will have 10 speakers and could be wired with two sets of five speakers in series with one another then place those two sets in parallel for a nominal 10 ohm load (assuming 4 ohm speakers)

 

[webmiester]

Thanks! Thanks is sounds very good. Do you have an idea on how I should compute for the wattage of he amplifier I will put?

 

[JMFahey]

Those PC speakers put out less than a watt, usually between 300 and 600 *milli*watts; 3 to 5 W RMS is pure seller BS.

Buy real but inexpensve ceiling mount speakers, mount and wire them, and drive them with some inexpensve 15/30 W PA amplifier.

Cheap PC speakers can reach your ears from half a meter way ; ceiling is way too high for them.

Those Disney speakers were 20 cm or less from your ears, almost worked as headphones-

 

[webmiester]

Yeah, I agree that the Disney speakers were very close to the ears. Your suggestion is noted.

 

[brig001]

At Disney, the speakers are a few inches from your ears and the next nearest might be a couple a feet away and shielded by the seats. As you double the distance from the source, you lose 6dB, this along with the fact that there was probably no direct path from the next speakers to your ears mean that they are virtually inaudible. This would not apply in the scenario that you are suggesting and all the different path lengths might make speech unintelligible.

I'm not saying don't do it, but I would do a test before committing and making lots of holes in the ceiling.

Brian

 

[webmiester]

Thanks Brian. The unintelligible speech is also my concern. I think these speakers will be stronger than the Disney speakers though. Yeah, I want to do some experimenting before proceeding. Instead of putting hole in the ceiling, I am thinking of just hanging 10 speakers in a single rod which I can suspend on the ceiling. The next 10 speakers will be on another rod.
In this way, The speakers will be closer to the audience this way, and it will be easier to install than putting holes on the ceiling

 

[Enzo]

And the fact that the Disney thing worked was not due to the smallness and cheapness. They have serious engineering going into every detail of those parks.

I agree with Fahey, just buy some plain old ceiling speakers, that is what they are made for, restaurants are full. of them.

Also, instead of trying to come up with some crazy series/parallel arrangement to make a pile of speakers come out to 8 ohms, use a "constant voltage" arrangement. In that, each speaker gets a small transformer to match, and the PA amplifier should have a 70.7v output already. If not, then a larger transformer at the amplifier end will do. Then we can simply run two conductor zip cord speaker to speaker.

Here is an example:
https://www.parts-express.com/8-cei...source=google&utm_medium=cpc&utm_campaign=pla

 

[Gnobuddy]

They have serious engineering going into every detail of those parks.

Very true. I used to know a mechanical engineer who worked for Disney.

The powers that be at Disney want their parks to create a polished illusion, with no obvious flaws to break the spell for their customers. It's much easier to loot your customer's wallets if they're happy and under a spell. Steve Jobs used to apply the same principle with Apple products.

In that, each speaker gets a small transformer to match, and the PA amplifier should have a 70.7v output already.

Agree, and let's not forget to point out the biggest advantage of this approach: much less power is wasted in long runs of wires going to the speakers, because the power is being fed in high voltage/low current form, and it is current that dominates ohmic losses in long wires.

Here is an example:
https://www.parts-express.com/8-cei...source=google&utm_medium=cpc&utm_campaign=pla

I have one of those, which I tried out as a guitar speaker in a small, low-wattage DIY amp. I can tell you that the "45 Hz" part of the specification is complete fantasy - I measured the fundamental speaker resonance at about 135 Hz, and you won't get any significant bass output below that.

I can also tell you that I bought two of them, and one was dead on arrival. Quality control may be a little iffy. For me, it wasn't a practical option to return it, because of shipping costs to Canada. If you're in the USA, that particular issue may not arise.

But the speaker is efficient, very affordable, and will probably do an adequate job of reproducing speech. And it comes with the 70V audio line transformer already included, and even mounted and wired up, which is perfect for your application.

-Gnobuddy