Help specifying a 12v amplifier / Full range speaker combo

[electricpedals]

Hi

I'm wondering if someone can help. I'm working on a bicycle powered cinema. The idea is that the energy from a single person, can be used to show films in remote parts of the world. I've already built a few of these, so have some experience with power generation and power management.

But where I've consistency failed is with the audio. It's never quite right. The last system I made used 2x 4" speakers and tweeters. It looked good, put was not loud enough.

So I need your help to help me specific a full range speaker and 12v amplifier combination. I've recently been testing a Beyma 10AG/N and BassFace DB4.2 4 amplifier which sounds pretty good. Problem is that the amplifier is 800g, so it's a bit of a lump. You can see the prototype here:

https://www.instagram.com/p/BNujdmvAcj5/

So what I'm looking for is a full range speaker and amplifier combination. Voltage wise the system runs from 10v to 15-16v DC. Price? £250 for the two?

Please go easy on me, I don't have much experience with audio.

Thanks
Colin

 

[ICG]

Interesting idea, I like it. 🙂

The amplifier isn't as powerful as you might think. 800W is pure fiction but even the 70W per channel are not realistic, that's for 10% THD, at (acceptable) 1% its most likely only 50W, on 4 Ohm that is. And at 15V. At 10V it will only be roughly half of that. At 8 Ohm that's only the half of that, which leaves you with meager 12,5W.
To choose a high efficient speaker is a very good idea, the Beyma is good, it's 8 Ohm though. Bridging the amp could help, but another amp which got a higher output at 8 Ohm would be better.

 

[electricpedals]

Interesting idea, I like it. 🙂

The amplifier isn't as powerful as you might think. 800W is pure fiction but even the 70W per channel are not realistic, that's for 10% THD, at (acceptable) 1% its most likely only 50W, on 4 Ohm that is. And at 15V. At 10V it will only be roughly half of that. At 8 Ohm that's only the half of that, which leaves you with meager 12,5W.
To choose a high efficient speaker is a very good idea, the Beyma is good, it's 8 Ohm though. Bridging the amp could help, but another amp which got a higher output at 8 Ohm would be better.

That's very interesting... yes i forget to mention that I'd bridged the amp. I was thinking that the amp was over-powered for the Beyma. In fact I'd started looking for a mono amp of around 300W.

Perhaps this is not such a good idea?

 

[ICG]

Well, at such a low voltage you have very huge currents if you want a that high power output. I don't know what your bike and the batteries can deliver but I somehow doubt 300W are realistic. I mean, at 15V that would be 20A, at 10V even 30A. Plus the losses of the amp, charger, cables, plugs (yes, at that high currents that's an issue!), that could add up to another 100W. I would expect an average Joe to have an output of 150-200W over some time, short term power might be higher (double? triple?) but that's not applicable to calculate with.

I would look for a BTL amp (not PBTL), which reaches a higher power at a higher impedance. Such an amp will most likely use a higher voltage, you can use a DC-DC converter for it. A TDA7498E board might be a suitable candidate but I haven't heard one of those. Maybe someone else can say more about these or suggest something else.

 

[electricpedals]

Well, at such a low voltage you have very huge currents if you want a that high power output. I don't know what your bike and the batteries can deliver but I somehow doubt 300W are realistic. I mean, at 15V that would be 20A, at 10V even 30A. Plus the losses of the amp, charger, cables, plugs (yes, at that high currents that's an issue!), that could add up to another 100W. I would expect an average Joe to have an output of 150-200W over some time, short term power might be higher (double? triple?) but that's not applicable to calculate with.

I would look for a BTL amp (not PBTL), which reaches a higher power at a higher impedance. Such an amp will most likely use a higher voltage, you can use a DC-DC converter for it. A TDA7498E board might be a suitable candidate but I haven't heard one of those. Maybe someone else can say more about these or suggest something else.

In that video Steve is averaging about 55W constant and there is no battery. The system is completely real-time with the exception of a small 58F capacitor that gives a minute's worth of energy if pedaling stops. So the audio (although very loud) is drawing an average of 10-15watts. Surprising but true.

 

[ICG]

In that video Steve is averaging about 55W constant and there is no battery. The system is completely real-time with the exception of a small 58F capacitor that gives a minute's worth of energy if pedaling stops. So the audio (although very loud) is drawing an average of 10-15watts. Surprising but true.

Ah, okay. I know the Beyma fullrange speakers have a very high spl but on a video it is extremely hard to tell how loud it really is. Okay, that narrows it down, the maximum power can be much lower. At this point I have to add, in these regions you won't get much more acoustical output, if you double the power, you gain 3dB but to make it twice as loud you need 10dB more, which equals to 10x the power! So without more power from the bike you won't gain significant more loudness. You can get 3dB more from doubling the membrane surface (a 2nd speaker), if you wire it parallel, it halves the impedance, which will a. result in drawing the double current (which adds another 3dB) and b. makes your amp more useful since it is optimized for 4 Ohm. But that means also you need double of the volume of the enclosure and ofcourse, if the biker can deliver more power.

Overall it seems under these circumstances to buy another amp doesn't make that much sense though. You will gain some more spl but it seems you've already reached the upper third or fourth of the maximum.