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Class D Switching Power Amplifiers and Power D/A conversion

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Old 25th May 2008, 05:24 PM   #81
NED 209 is offline NED 209  Ireland
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your battery is going to be 12v. theres only so much volume you can create with 12 volts. so the thing to do is get really sensitive speakers, that way you can maximise the volume output from 12 volts.

theres an article here on speaker sensitivity -

http://en.wikipedia.org/wiki/Loudspe...s._sensitivity

read the paragraph below the bullet points.

then re-read it
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Old 25th May 2008, 10:08 PM   #82
Pillah is offline Pillah  Denmark
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Saturnus> been trying to email you... Just checking you're not out of town or anything
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Old 26th May 2008, 05:38 PM   #83
y8s is offline y8s  United States
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Quote:
Originally posted by NED 209
your battery is going to be 12v. theres only so much volume you can create with 12 volts. so the thing to do is get really sensitive speakers, that way you can maximise the volume output from 12 volts.

theres an article here on speaker sensitivity -

http://en.wikipedia.org/wiki/Loudspe...s._sensitivity

read the paragraph below the bullet points.

then re-read it
what about two 12V batteries in series? A lot of these amps are VERY happy at 24VDC.
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Old 27th May 2008, 02:28 AM   #84
NED 209 is offline NED 209  Ireland
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if you were to ask me i would say one thing - weight.
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Old 27th May 2008, 08:37 AM   #85
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Weight is not really a huge concern; the thing is going to have wheels.

Anyway, thanks for the lowdown on speaker sensitivity. What's considered a high sensitivity? Wikipedia says around 95 to 102 dB for outdoor speakers, but would e.g. 90dB suffice [1]?

I'm pretty settled on buying a 41Hz amplifier. I just don't know whether to get an AMP6 or an AMP6-basic. Do you have any hints in that direction. And, again, what about the volume knob. Is there any or is the amplifier locked to a certain amplification, so to speak?

[1] http://thansen.dk/product.asp?c=1820...pn=-2035762707
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Old 27th May 2008, 05:52 PM   #86
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The difference as I am sure you know is the basic does not have the power supply circuitry built in, and the regular unit does. With the addition of a transformer, you can use the regular model by plugging it into an outlet. To use a battery, you will have to figure out how to separate the power supply part of the Amp 6 from the amplifier part, and put a switch in there that will allow you to go back and forth between the AC and the battery. Part of that circuit would ideally be a battery charger that also works off the AC, so when the switch is flipped to the "AC" position, the battery is also charging.

It comes down to how you plan to use the unit. I used the Amp 6 basic and built a small switching PS. the kind you can get cheap on eBay as an LCD monitor supply, and also a battery charger/conditioner from Batteries.cm:

http://www.batteries.com/productprof...p?appid=298436

The setup works well, although to save weight, it would be ideal if the battery charger and amp PS used the same transformer--although I haven't torn into the charger to see if this is feasible. Also, I don't know whether this would "kick back" any noise from the charger, as it does create some HF pulses that help keep the battery in good condition.

--Buckapound
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Old 27th May 2008, 07:07 PM   #87
v-bro is offline v-bro  Netherlands
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Hi guys,

car coaxial speakers have a down side, there is no 'real' filter, it's just a tweeter protection cap. So that shouldn't be a reason not to use a separate woofer and tweeter the same way. From there you can work out a better functioning filter. Making it better than just a cap isn't going to be hard

The sensitivity a manufacturer publishes in the specs sheet is nothing reliable, when it says 93db it is possible that this is just at a given frequency. It is therefore wise to have a look at a frequency spectrum diagram. Click the image to open in full size.

Here you can see exactly where the driver has good sensitivity.

Another misunderstanding is speakers don't draw power, they merely receive and convert it into motion and heat. The only thing drawing power here is the amp and auxiliary equipment.

If weight is no issue than that's a big bonus, you CAN use a car battery, although there are issues with the risk of acid pouring out (yes they all do, especially during the charging) and the gas that comes free when charging is more or less flamable. (can be explosive! ) So you can have holes burnt in your creation from the burning acid (or worse in your fingers or your favorite T-shirt)

I would certainly advise the use of SLA...

Than the amp, if you still contemplate on them than the AMP9-B is still an option, it does use more power than an AMP6, but with 24V and 2 ohm speakers it's really loud....

I do think that if money is an issue you shouldn't overdo it and go the same route as Saturnus did, get the AMP6 which is the easiest to build T-amp and go for really sensitive speakers.

Note: Placing two speakers really near eachother raises the sinsitivity by about 3 db! So that doubles the loudness! Just make sure that the AMP can handle the load...(two speakers in parallel halves the impedance)
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Old 27th May 2008, 10:37 PM   #88
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Actually I had bought the AMP6-BASIC before your answer. I plan on running it on a ~60Ah car battery. Some guy earlier in this post said that he got 6 hours of play time on a battery holding 4 Ah.

I'm still a bit in doubt about what kind of speakers I need. It's a jungle! Anyway, the amp specifications state 2x25W 4Ohm. Most of the car speakers I see are >200W, so how is that possible? What kind of speakers should I buy? NED 209 told me I wanted something with high sensitivity, so I guess that's right. Should I just go for one of those >200W speakers?
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Old 28th May 2008, 02:13 AM   #89
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jchillerup, you should be aware that car batteries are not designed to be drained down very far from their maximum charge. So, in a portable power situation, repeated deep use and charge cycles will result in shorter life.

Marine batteries, usually described as "deep cycle" and/or gel-cell type batteries are more expensive per hour but will work longer than a car battery, and don't have the potential to spray acid in anyone's face.

--Buckapound
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Old 28th May 2008, 10:37 AM   #90
NED 209 is offline NED 209  Ireland
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it doesnt really matter what wattage the speakers are, your only going to be putting 25 watts into each one. your supposed to leave a bit of leeway, so speakers that can handle 50 watts or above will be fine. theres a bit written here about it

http://reviews.ebay.co.uk/Buying-Spe...00000000063388
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