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-   -   Portable Busking P.A. (http://www.diyaudio.com/forums/pa-systems/211073-portable-busking-p.html)

curtisthorpe 18th April 2012 10:10 PM

Portable Busking P.A.
 
Hi

I am a traveling busker looking to make a small, portable, light weight P.A. I've tried out many of the Roland battery powered amps and such but they all contain way to many features and are way overpriced, so I thought I'd look into coming up with my own system.

I discovered the Dayton DTA-1 amp and I think it might be the solution to my portability problems. I understand that all I need aside from this device is a passive speaker cabinet (which I plan on making myself) and that battery life of the DTA depends on how much power the speakers draw.

Here's where I need some help. What is the best way to get the most battery life and volume out of the DTA? I'd like to have a decent amount of bass so maybe a 2 8" speakers? or will this suck too much battery life out of the unit? I don't really understand how to calculate these sort of things. Also, is there anyway to add another input to the unit? Does anyone have any experience with this amp and how long the batteries tend to last?

I am also having a hard time understanding whether output is affected by only having 1 speaker hooked up to the amp. It has stereo output so do I need to have 2 speakers plugged in to get maximum volume?

Perhaps there is an easier way to do this not involving the Dayton at all?

Any advice is appreciated. Really!

Thanks.
Curtis.

chrispenycate 19th April 2012 07:17 PM

What you need is the maximum efficiency, both in amps (Class D) and in loudspeakers. Decide what frequency range you need – guitar and voice is not the same problem as running an mp3 player with full mixed backing track. (What are you intending to amplify?)

I assume weight is a critical consideration; even if you mount wheels on the speaker (a good idea, even if it does occasionally wander off) you're going to find you're lugging it quite a bit, and if you've a musical instrument as well…

Bigger speakers do not tend to higher power consumption; indeed, at low frequencies they do much better than small ones. But the trade off comes in efficiency against weight. Generally light cone speakers with big magnets in horn enclosures give the best efficiency. Unfortunately, horn enclosures use more wood, and tend to be bigger, than their ported/sealed equivalents, and the magnets only add to that weight. Professional PA builders use cabinets based on a sort of surf-board building technique, with a foam structure fiberglassed over, with carefully calculated ridges to maximise structural rigidity, with minimum weight. I Used to use plywood considerably too thin for the job, with widespread bracing and fiberboard damping out the panels. If it were me, I'd seriously consider a two way speaker system, with a tweeter, partly because this cleans up the high frequencies, but mainly because it reduces the 'beaming' of information, spreads clarity over a wider front.

Stereo amp hardly seems necessary, but if available you could bridge it (not spectacularly difficult, but not negligible either) to get all its power through one 8Ω speaker.

Now, what are you going to plug into it? It has no tone controls, no mixing, and sesitivity for an mp3 player, not a microphone or an instrument. You could quite easily find yourself having to buy a battery mini-mixer, even if you do consider guitar rigs too sophisticated – not ridiculously expensive, but another thing to carry around (sure, goes into a backpack with the amp a treat, but it's all that to plug up every time). If it has balanced outputs you only need a slightly special lead to do the bridge amp bit.

curtisthorpe 19th April 2012 09:22 PM

Quote:

Originally Posted by chrispenycate (Post 2992315)
What you need is the maximum efficiency, both in amps (Class D) and in loudspeakers. Decide what frequency range you need – guitar and voice is not the same problem as running an mp3 player with full mixed backing track. (What are you intending to amplify?)

I assume weight is a critical consideration; even if you mount wheels on the speaker (a good idea, even if it does occasionally wander off) you're going to find you're lugging it quite a bit, and if you've a musical instrument as well…

Bigger speakers do not tend to higher power consumption; indeed, at low frequencies they do much better than small ones. But the trade off comes in efficiency against weight. Generally light cone speakers with big magnets in horn enclosures give the best efficiency. Unfortunately, horn enclosures use more wood, and tend to be bigger, than their ported/sealed equivalents, and the magnets only add to that weight. Professional PA builders use cabinets based on a sort of surf-board building technique, with a foam structure fiberglassed over, with carefully calculated ridges to maximise structural rigidity, with minimum weight. I Used to use plywood considerably too thin for the job, with widespread bracing and fiberboard damping out the panels. If it were me, I'd seriously consider a two way speaker system, with a tweeter, partly because this cleans up the high frequencies, but mainly because it reduces the 'beaming' of information, spreads clarity over a wider front.

Stereo amp hardly seems necessary, but if available you could bridge it (not spectacularly difficult, but not negligible either) to get all its power through one 8Ω speaker.

Now, what are you going to plug into it? It has no tone controls, no mixing, and sesitivity for an mp3 player, not a microphone or an instrument. You could quite easily find yourself having to buy a battery mini-mixer, even if you do consider guitar rigs too sophisticated – not ridiculously expensive, but another thing to carry around (sure, goes into a backpack with the amp a treat, but it's all that to plug up every time). If it has balanced outputs you only need a slightly special lead to do the bridge amp bit.

Hi,

Planning of playing acoustic guitar and vocals/vocal percussion through the P.A. Weight is definitely a concern as I might need to travel via plane. I was planning on putting an eq pedal between my guitar and P.A. to provide me with some control over the sound.

Here is my plan...

So heres what I'm thinking.

Small 12V 8aH battery
http://www.atbatt.com/product/24211/...h/battery#tabs

Dayton DTA-2 T-amp
http://www.parts-express.com/pe/show...number=300-385

It says the recommended power supply is 12V 2000mah. The battery is 8000mah. Will this be problem?

Speakers
Not to sure what I'm going to use for speakers. I'd like a set of 6" speakers or an 8" and a tweeter of something like that. Does it need to a specific ohm rating to use with the poweramp I choosing? I don't really understand how that works. Any speaker recommendations would be excellent. I looked up 'pro sound' speakers but did not really get any result. Can anyone post a link? Any recommendations would be excellent.

Cab
I'll make my own.

chrispenycate 20th April 2012 11:21 PM

Matching amplifier output with loudspeaker impedance gives you the maximum loudness possible, though not necessarily the best battery life. Each half of your amp produces its maximum power into four ohms, or the two halves bridged a mono output into eight ohms. A higher impedance will strain the amp less, but take less power.

But getting 3 dB extra efficiency on the driver will be the equivalent of doubling the amplifier power, without reducing battery life. An 'ordinary' 8" driver tends to have an efficiency around 88 dB at 1 watt at 1 metre, so one with 92 (quite findable, if you can believe people's quoted specifications) would effectively double your amp power. Unfortunately, generally higher efficiencies come at higher powers, and when I Googled 8 inch speakers (no, I've been in a recording studio for the last twenty years, and no longer know what's on the market – it's at least ten since I ran a PA with less than a couple of thousand watts) I found prices ranging from below 20 dollars to over 300, and guess what? Most of the efficient ones were in the upper price range. However Monacor had a 7" unit that claimed 92 dBs, the SP-167E; I don't know if we can entirely believe them, since it was less than $20 - claimed HiFi, but they do make PA units so they're probably going to be tough enough to transport (hmm, car speakers? They've the same problem of low voltage…)

And no, as long as it's the right voltage more ampère hours can only be useful, although the amp's built in battery charger might get a bit surprised.

Yes, of course you're going to build your own cabinets, I assumed that, but to what design? Not all cabinets are equal, you know.

But the main thing we're likely to be short of is voltage gain. The amp didn't state it's sensitivity, but if it's designed to take an mp3 player, I expect it to need about another 30dbs of gain to handle mic level signals, and I don't expect an eq pedal to supply this. Of course, I would probably build one, and incorporate the mixing and the equalisation at the same time (and it wouldn't look very pretty; drilling neat holes in little boxes is not one of my strengths), since while there are a number of very cheap simple mains powered mixers, it seems there's nothing with tone controls under $100 battery powered (um why? It would seem easier). But you need gain, as much as you need power.

chris661 22nd April 2012 11:22 AM

Hi,

I'd consider attaching a small mixing desk (Behringer do a 5(?) channel one that's very compact), and feeding the amplifier from that.
For speakers, I'd get a single Speaker Detail | Eminence Speaker
with the tweeter that goes with it. Use a stock 3kHz crossover if you want an easy life (though you may need to reduce the level of the tweeter).

The reason behind this particular speaker is simple: its efficiency is high, so the amplifier doesn't need to put out much power in order to produce a lot of sound. This also aids battery life.

Chris

chrispenycate 23rd April 2012 08:59 PM

Do Behringer do that mixer in a battery version? Generally their products are very good value for money, (and it is a five, yes; I think it's one XLR mic, one mono/stereo instrument, and one stereo line in) but I could only find it in mains powered.

Plenty of battery mixers, but 'spensive; possibly I'm on too professional sites.

Um, are the microphones professional low impedance balanced, high impedance unbalanced, or electret unbalanced? It makes a difference to what is required as input circuitry.

chris661 24th April 2012 07:13 AM

I don't think they do a battery version, but it's powered by a laptop-style supply: a PSU part way along some cable - should be easy to read off the voltage(s) and go from there.

chrispenycate 24th April 2012 04:28 PM

Quote:

Originally Posted by chris661 (Post 2998529)
I don't think they do a battery version, but it's powered by a laptop-style supply: a PSU part way along some cable - should be easy to read off the voltage(s) and go from there.

Normally, with Behringer, that's just a transformer (with a fuse wound under the outer paper, or possibly a thermal cutout; I've had to replace a few); the rectifiers and stabilisers are in the machine itself. And with 48volt phantom (I know, this application doesn't need that; but would you choose to lose it if there's the slightest possibility you'd be using it for something else?) there's a risk it needs quite specific voltages (although the bigger ones use 17–0–17 volts AC).

Which is why I suggested, this being a DIY site, we could custom design a mixer, mono with polarity inverted output for bridge driving, with two or three inputs and running off a 9 volt battery, or 8 rechargeable AA cells, three band equaliser, simplistic compressor, low current for longest possible battery life, no metering or sophisticated stuff; the sort of thing you can design and build in an afternoon, once the hardware's drilled.

sreten 24th April 2012 04:34 PM

Hi, All 12V T-amps are already bridged output and you cannot bridge them, rgds, sreten.

mr. doom 24th April 2012 08:03 PM

Quote:

Originally Posted by chrispenycate (Post 2998111)
Do Behringer do that mixer in a battery version? Generally their products are very good value for money, (and it is a five, yes; I think it's one XLR mic, one mono/stereo instrument, and one stereo line in) but I could only find it in mains powered.

Plenty of battery mixers, but 'spensive; possibly I'm on too professional sites.

Um, are the microphones professional low impedance balanced, high impedance unbalanced, or electret unbalanced? It makes a difference to what is required as input circuitry.

http://www.google.com/imgres?hl=en&s...,r:10,s:0,i:97

This battery powered mixer (Behringer XENYX 1002B) runs around $120 USD. It has phantom power for condenser mics.


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