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Portable Marching Amp - I Need More Oomph
Portable Marching Amp - I Need More Oomph
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Old 10th June 2018, 03:25 AM   #1
jhillbergen is offline jhillbergen
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Default Portable Marching Amp - I Need More Oomph

I've created a somewhat simple backpack marching amp that I use with a Yamaha midi wind controller. It works quite nicely, but still wanting to get a little more volume. Seeking suggestions on how to improve on what I've done so far.
Design requirements are:
As light as possible
Runs for ~4 hours on a 12v LiFePO4 battery

I've attached some pics of my first generation build:
Speakers are 4 ohm Kicker 6.5" marine coaxials 90db sensitivity
Amp is Lepai 2020TI 20 watt amp ( measures 14 watts at max volume)
New battery, (not pictured) is Bioenno LiFePO4 12v, 10ah
The other component is the tone module for the midi wind controller.

The backpack is made from Coroplast and zip ties, to keep it light weight. I realize this is not a great enclosure design.

Are there any suggestions out there that could beef up the volume?
Uber sensitive speakers? A better amp that runs off a 12v battery?
Looking for any and all suggestions.
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Old 10th June 2018, 04:05 AM   #2
thoglette is offline thoglette  Australia
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Quote:
Originally Posted by jhillbergen View Post
Uber sensitive speakers? ..
Looking for any and all suggestions.
90db is not very sensitive (and that's probably at 2.83V not 1w).

You should be able to get the best part of 10db by looking at instrument speakers.

You may also be able to make that volume more effective by removing all the bass. Bass uses a lot of power (Hoffman's iron law and all that) and is likely to NOT be important for your application.

Indeed, with the speakers you've got it's probably not producing any useful sound but will be chewing up your headroom.

Lots of stuff on DC amps in the Battery powered Princeton Reverb thread. Read through that!
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Old 10th June 2018, 04:22 AM   #3
PRR is offline PRR  United States
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Last time I was around a marching band, decades ago, they added an electronic keyboard to the band. I know there were several unsatisfactory rigs. What worked for some years was 300 feet of extension cord, a 400 Watt amplifier (biggest there was in those days), two 100-pound PA speakers, and a wheeled cart with pullers.

What strikes me about your act: "wind" is generally higher pitch, especially in a military-tradition band (I have heard large/deep winds but as saloon sounds). You may not need anything under 400Hz. Bass is big, no-bass can be much smaller. And allows other techniques.

Start by switching from wide-range cones to speech-range horns. Commonly used as announcement loudspeakers where clarity (and size and cost) is more important than baritone rumble.
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Old 13th June 2018, 03:17 AM   #4
dotneck335 is offline dotneck335  United States
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Better speakers. Speaker Detail | Eminence Speaker
94.6db SPL sensitivity; about the best you will find for a 6.5" speaker
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Old 13th June 2018, 09:01 PM   #5
voltwide is offline voltwide  Ireland
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18 sound type 6ND410 are specified by 102dB
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Old 14th June 2018, 01:29 AM   #6
dotneck335 is offline dotneck335  United States
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Quote:
Originally Posted by voltwide View Post
18 sound type 6ND410 are specified by 102dB
WOW!! That's efficient!! But, at a cost---~ 9db/octave rolloff below ~800 Hz, and $146!!! But, if you want a squawker, that's your huckleberry!!

Last edited by dotneck335; 14th June 2018 at 01:32 AM.
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Old 14th June 2018, 02:53 AM   #7
PRR is offline PRR  United States
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Quote:
Originally Posted by dotneck335 View Post
Better speakers. ...620H...Eminence
94.6db SPL sensitivity; about the best you will find for a 6.5" speaker
PyleHome Model : PHSP6K $21
6.3'' Indoor / Outdoor 25 Watt PA Horn Speaker
Frequency Range: 400 Hz - 6 KHz
SPL(@ 1W/1m): 100dB

PyleHome Model : PHSP8K $27
8.1'' Indoor / Outdoor 50 Watt PA Horn Speaker
Frequency Range: 400 Hz - 6 KHz
SPL(@ 1W/1m): 103dB

PyleHome Model : PHSP4
6'' Indoor / Outdoor 50 Watts PA Horn Speaker
Frequency Range: 500 Hz - 5 KHz
SPL(@ 1W/1m): 100dB

The difference 95dB-100dB is like 3 times in amplifier Watts. 95dB-103dB is like 6 times in amplifier Watts. On wall-power, maybe you could go from 16W to 100W. But on battery, that gets absurdly heavy.

Of course it depends on tolerating a 500Hz-400Hz cut-OFF. It works for speech: aint nice, but perfectly intelligible. I have used sharp bass-cuts many times when cleaning old/bad recordings, and sometimes you can cut huge chunks off.

In this case, especially if the tubas and bari-sax will phatten-up the bottom, let you work soprano.
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Old 15th June 2018, 03:32 AM   #8
wg_ski is offline wg_ski  United States
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Get a real class D amp, not some 10 watt Lepai or Sure cr@p. Something like the RE Audio SA 90.4 car amp from PE. 60 honest watts x 4, bridgeable with a built in D.C.-D.C. Converter to get those watts. One of those and two Eminence Alpha 6 4 ohm will play effing loud for a long time on a 10 amp hour battery. And you get down to 100 Hz. Don't cheap out with the 50.4, it's not in the same league. Same power, but a ton of distortion at low levels (shouldn't have crossover distortion, but that's what it sounds like).
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