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Topic with many replies

Create your own festival stereo


Author Message
Written on: 12.03.2009 15:14
Mr. Monster
Posts: 940
Saturnus made this great description in the Pay Phones topic but I thought it deserved it's own topic

Saturnus skrev:

First you need to make sure your boombox doesn't use very much power in the first place.

That doesn't mean it can't be extremely loud because unlike what most people think it's not the amplifiers output power that makes a speaker play loud, it's the speakers sensitivity.

I use a 2x15W class D amp (the amp6basic) from http://www.41hz.com because a class D amp is vastly more efficient than a regular class A/B amp. Mine has an efficiency of about 90%, that means that for every 10 watts the amp consumes only 1 watt is wasted as heat. A typical car stereo or home audio class A/B amp will have an effeciency of 40% or lower, meaning more than half of the power it uses is turned directly into heat in the amp. My amp uses so little power when not playing music that if I had a power LED (you know a small red diode that tells you it's on) it would use 3 times as much power in idle.

This doesn't mean a class D amp sounds bad either. The amp6basic is in sound quality about semi hi-end. And it sounds much better than the 2000 euro Denon monoblocks I had before. That's quite amazing for an amp that cost about 30 euro (in kit form, you have to solder it together yourself) and uses about 4 watts (350mA) at maximum volume (compared to the 110 watts my previous monoblocks used in idle.

Now you need to have a battery of some sort because the sun doesn't sunshine 24 hours a day, so you must have a battery as a buffer. I recommend a SLA (sealed Lead Acid) type over a car battery because with SLAs you don't have to worry about potential acid leaks and explosion dangers. A standard 12V 7Ah SLA you can buy for about 20 euro is enough for 20 hours of continious playing time at maximum volume with the amp I use. I use two such batteries just to be on the safe side.

Then you need a suitable solar panel, these can unfortunately be pretty hard to get at a reasonable price in Denmark, if you can get them at all. Denmark is very slow to adopt such things at a consumer level compared to other countries in Europe. I recommend a thin film amorphous type solar panel since they aren't as fuzzy about having to angle them directly at the Sun, and they even produce some power even when overcast.

The power output of the solar panel should not be much higher than the Ah rating of the battery (with SLA batteries, a fifth with car batteries), so maximum 15W if you use 2 paralleled batteries like me. Most ready made solar comes complete with a tiny recharging circuit protecting the battery against overcharging and reverse current, so you just connect it directly to the battery and leave it connected at all times.

I recommend something like this http://www.conrad.nl/goto.php?artikel=855360 at 100 euro it's about the cheapest you can get in Europe for a 15 watt amorphous solar panel.

http://media.conrad.com/xl/8000_8999/8500/8550/8553/855360_LB_00_FB.EPS.jpg

Last year I used some smaller solar cells but still ended up with having used no power at all. The batteries actually had slightly higher voltage when I came home from the festival than when I went. Even after having played at lot, and loud, and recharged cell phones and iPod on it.
Written on: 12.03.2009 18:18
Saturnus
Posts: 3047
You might think I came up with the idea and developed it because I wanted to make a "green" boombox. Well, I'd be lying if I said so because like 99% of all invention and innovation this was driven by convinience (a fanzy word for lazyness) in that I didn't want the hassle of having to drag huge car batteries along and having the recharged at the lockers. It's just way easier to have a boombox that just never runs out of power instead. Being "green" is just an added bonus. icon_biggrin.gif
Written on: 13.03.2009 23:36
Saturnus
Posts: 3047
Let's get physical! (, or how you make a speaker that sounds good outdoors). Part 1.

The outdoor enviroment, also called free-field, is completely different different from indoors, also when you make a speaker system because indoors reflections between the walls called standing waves augments bass response lowering the demands for power use and cone movement of the speakers.

You can test this by taking a speaker that has good bass in one room outside, and you instantly notice that most of the really deep bass has almost completely gone. In speaker building we say that free-field impose an acoustic highpass filter of 6dB per octave starting at 200 Hz, meaning the response is down 3dB (halved) at 100 Hz, -9dB (8 times lower) at 50 Hz and -24dB (256 times lower) at 20 Hz. Actually it's the complete opposite in that it's the indoors enviroment that augments the bass but it's just easier the other way around because speaker building programs and calculations all build on indoor enviroment.

Now the human brain will compensate for some of this loss just like it compensates for different types of light indoors and outdoors but only to a certain degree, and only in a certain way. If we compensate for the acoustic filtering mentioned above by boost frequencies below 200 Hz so that they become linear the brain will think that the speaker produces sounds twice as deep as it really does. For example if you make a 3dB boost at 100 Hz the brain will think the speaker is actually able to produce sounds of 50 Hz even if it can't. This only applies outdoors and have some rather good sideeffects.

Firstly we don't need to go as deep in the bass as you would expect and secondly you need moderate compensation. Remember even with this effect, producing a linear frequency range to 40Hz which would be needed if you wanted to sound like your system goes down to 20Hz will require a 10dB boost ... or 10 times as much power as the same sound level indoors.

So get really deep bass response in free-field on a boombox out of your mind, once and for all. It's not possible, wanted or practical. Aim for a much more practical and realistic linear frequency response to about 100Hz, a little higher or lower doesn't make that much difference.

You can achieve the needed boost in 2 ways, either electrically with active filtering which I will not explain because it would be too large a field to cover satisfactory, and will make you consume more power than is absolutely nescessary, over twice as much in fact.

I will however explain how you can compensate it for free acoustically ... but you'll have to wait for part 2 for that. icon_biggrin.gif



[This article was edited 1 times, at last 13.03.2009 at 23:46.]
Written on: 17.03.2009 13:54
Cos
Posts: 39
Hey guys, you seem to have alot of *hands on experience* with these things and i was wondering... Last year me and my camp built our own boombox (the one I'm sitting on in my profile picture) and we ended up using car batteries and it was quite the recharge hassle to say the least. my question is, would we be able to use solar panels to recharge our car battery as the one linked to in the first post? and how?
Written on: 17.03.2009 21:32
Saturnus
Posts: 3047
My first post pretty much thoughroughly explains how you can run a boombox on solar power but to reiterate the main point. You must make sure your boombox uses as little power as possible to start with. A flat car battery will take about 36 hours of mid-day Sun light to recharge even with a massive solar panel like the one above.

Get rid of that car audio head unit ... it uses way too much power... and get a class D amplfier instead.
Written on: 23.03.2009 17:54
Cos
Posts: 39
okay, so I've been looking at some of the T-class amps at 41hz.com and it all looks good and well, but my main concern is how much pull the amp6-basic really has. me and my freind are thinking about getting some pretty big speaker units put in to our box such as a couple of 200w 12'midrange/bass units and we are a little concerned about how the amp6 will handle it. so now we are looking at the amp10-basic wich is looking a bit more realistic considering our needs. but I would really like to hear your opinion on this matter because neither of us has any experience with DIY amplifiers. or if you yourself have an idea? We want built a real crowd pleaser for the festivalicon_smile.gif
Written on: 23.03.2009 20:37
Saturnus
Posts: 3047
Michael Orup Lundberg skrev:

okay, so I've been looking at some of the T-class amps at 41hz.com and it all looks good and well, but my main concern is how much pull the amp6-basic really has. me and my freind are thinking about getting some pretty big speaker units put in to our box such as a couple of 200w 12'midrange/bass units and we are a little concerned about how the amp6 will handle it. so now we are looking at the amp10-basic wich is looking a bit more realistic considering our needs. but I would really like to hear your opinion on this matter because neither of us has any experience with DIY amplifiers. or if you yourself have an idea? We want built a real crowd pleaser for the festivalicon_smile.gif


As long as the speakers sensitivety is high, the power needed is relatively low. Actually it's a good rule of thumb that the bigger the speakers are the less power is needed. I use 4 10" pro drivers in my boombox and the amp6basic has plenty of power for that. In fact I use one channel of an amp-basic to drive a 2x15" sub at home and I have never felt I needed more power.

Remember, more power = less battery time. So if you're a lazy fucker like me, keeping it low enough that you don't have to worry about rechanging during the festival is crucial.
Written on: 23.03.2009 22:16
Cos
Posts: 39
Thanks for all the advice, I might have a few more questions once we embark on the building faseicon_smile.gif here's a list of the things we're thinking about throwing together

http://lydshop.dk/sph_300tc-p-7808.html

http://lydshop.dk/spw_226_8-p-11173.html

http://lydshop.dk/dt_28n-p-10188.html

http://lydshop.dk/dn_10bc-p-8542.html

we're gonna rock your socks off icon_smile.gif
Written on: 23.03.2009 22:22
Freddyboy
Posts: 56
This looks really interesting, but I don't have any parts.
What is the price for the whole thing? icon_lol.gif
Written on: 23.03.2009 22:25
Saturnus
Posts: 3047
Michael Orup Lundberg skrev:

Thanks for all the advice, I might have a few more questions once we embark on the building faseicon_smile.gif here's a list of the things we're thinking about throwing together

http://lydshop.dk/sph_300tc-p-7808.html

http://lydshop.dk/spw_226_8-p-11173.html

http://lydshop.dk/dt_28n-p-10188.html

http://lydshop.dk/dn_10bc-p-8542.html

we're gonna rock your socks off icon_smile.gif


If you want my opinion, I think you should look at some pro drivers instead as they have much higher sensitivity. A standard 12" pro driver has about 96 dB/w/m sensitivity, that means it can play 4 times!!! as loud as the 12" you have listed on the same amplifier (remember each 3 dB is a dubling of sound pressure level).
Written on: 23.03.2009 22:33
Cos
Posts: 39
do you have a link to some?
Written on: 23.03.2009 22:39
Saturnus
Posts: 3047
Michael Orup Lundberg skrev:

do you have a link to some?


Sure. These are the ones I use

http://www.intertechnik.de/index.html/JTI2bmF2aWQlM0QxNzY4JTI2bGFuZyUzRGRlJTI2c2lkJTNEbjQ5YzgwMDlmYjQ4MTklMjZzaWQlM0RuNDljODAwOWZiNDgxOSUyNmIlM0Q=.html?basis=4354&detail=6366&suchwort=

I use 4 of these because when you parallel 2 of them you get 4 ohms to get the maximum power out of the amplifier. 2 of these parallel means you have 100 dB/w/m sensitivy, which means they'll play 8 times as loud as the ones you looked at. The price even be around the same (when you include the transport costs from Germany) .

[This article was edited 1 times, at last 23.03.2009 at 22:40.]
Written on: 23.03.2009 22:44
Cos
Posts: 39
Saturnus skrev:

Michael Orup Lundberg skrev:

do you have a link to some?


Sure. These are the ones I use

http://www.intertechnik.de/index.html/JTI2bmF2aWQlM0QxNzY4JTI2bGFuZyUzRGRlJTI2c2lkJTNEbjQ5YzgwMDlmYjQ4MTklMjZzaWQlM0RuNDljODAwOWZiNDgxOSUyNmIlM0Q=.html?basis=4354&detail=6366&suchwort=

I use 4 of these because when you parallel 2 of them you get 4 ohms to get the maximum power out of the amplifier. 2 of these parallel means you have 100 dB/w/m sensitivy, which means they'll play 8 times as loud as the ones you looked at. The price even be around the same (when you include the transport costs from Germany) .


What about midrange and tweeter?
Written on: 23.03.2009 22:51
Saturnus
Posts: 3047
Michael Orup Lundberg skrev:

Saturnus skrev:

Michael Orup Lundberg skrev:

do you have a link to some?


Sure. These are the ones I use

http://www.intertechnik.de/index.html/JTI2bmF2aWQlM0QxNzY4JTI2bGFuZyUzRGRlJTI2c2lkJTNEbjQ5YzgwMDlmYjQ4MTklMjZzaWQlM0RuNDljODAwOWZiNDgxOSUyNmIlM0Q=.html?basis=4354&detail=6366&suchwort=

I use 4 of these because when you parallel 2 of them you get 4 ohms to get the maximum power out of the amplifier. 2 of these parallel means you have 100 dB/w/m sensitivy, which means they'll play 8 times as loud as the ones you looked at. The price even be around the same (when you include the transport costs from Germany) .


What about midrange and tweeter?


A pro driver is a midrange in itself you don't need one but you do need a tweeter. There's several options but I'd recommend a piezo driver for this use since they are incredibly tolerant to moisture and abuse. Just go for one that has a sensitivty of about the same 100 dB/w/m, or combine several (again everytime you double the number add 3 dB sensitivity). A piezo tweeter don't really need a crossover either so that makes it even cheaper still, just add a 33-50 Ohms power resistor in series with the piezo and parallel over the woofers.
Written on: 23.03.2009 23:02
Cos
Posts: 39
Saturnus skrev:

Michael Orup Lundberg skrev:

Saturnus skrev:

Michael Orup Lundberg skrev:

do you have a link to some?


Sure. These are the ones I use

http://www.intertechnik.de/index.html/JTI2bmF2aWQlM0QxNzY4JTI2bGFuZyUzRGRlJTI2c2lkJTNEbjQ5YzgwMDlmYjQ4MTklMjZzaWQlM0RuNDljODAwOWZiNDgxOSUyNmIlM0Q=.html?basis=4354&detail=6366&suchwort=

I use 4 of these because when you parallel 2 of them you get 4 ohms to get the maximum power out of the amplifier. 2 of these parallel means you have 100 dB/w/m sensitivy, which means they'll play 8 times as loud as the ones you looked at. The price even be around the same (when you include the transport costs from Germany) .


What about midrange and tweeter?


A pro driver is a midrange in itself you don't need one but you do need a tweeter. There's several options but I'd recommend a piezo driver for this use since they are incredibly tolerant to moisture and abuse. Just go for one that has a sensitivty of about the same 100 dB/w/m, or combine several (again everytime you double the number add 3 dB sensitivity). A piezo tweeter don't really need a crossover either so that makes it even cheaper still, just add a 33-50 Ohms power resistor in series with the piezo and parallel over the woofers.


you mean something like this

http://lydshop.dk/lsr_470_20-p-8898.html

http://www.elektronik-lavpris.dk/product_info.php?products_id=30851
?icon_smile.gif
Written on: 23.03.2009 23:04
Saturnus
Posts: 3047
Precisely. Buy 4 of each of those and parallel over each woofer separately. That'll give you more options should you later want to upgrade.
Written on: 23.03.2009 23:14
Cos
Posts: 39
Saturnus skrev:

Precisely. Buy 4 of each of those and parallel over each woofer separately. That'll give you more options should you later want to upgrade.


wow! this can be done way cheaper than i thougticon_smile.gif
You say parallel over each woofer sperately how do i do that?
i have some experience but not alot.

and just to get everything clear, when it's time to hook it all up to the amp, each channel is supposed to drive 2 woofers and 2 tweeters each?

Written on: 23.03.2009 23:24
Saturnus
Posts: 3047
Michael Orup Lundberg skrev:

Saturnus skrev:

Precisely. Buy 4 of each of those and parallel over each woofer separately. That'll give you more options should you later want to upgrade.


wow! this can be done way cheaper than i thougticon_smile.gif
You say parallel over each woofer sperately how do i do that?
i have some experience but not alot.

and just to get everything clear, when it's time to hook it all up to the amp, each channel is supposed to drive 2 woofers and 2 tweeters each?


Yeah. It's not too expensive when you build it yourself. My solarpowered Boominator costs about DKK4000 in materials total, and DKK1000 of that is the solar panel alone, so just DKK3000 for a boombox that plays about 10 times as loud as the JVC tube ones and have a battery life that last an entire festival on a single car battery (with an average playing time of 12 hours per day at high volume and 8 days at the festival).

Put the resistor between plus on the woofer and plus on the piezo, and connect a piece of wire from minus to minus. Now connect plus on two woofers to one of the amps plus outputs and the same with minus. Repeat it for the two remaining woofers. It's that simple.

Written on: 23.03.2009 23:30
Cos
Posts: 39
Saturnus skrev:

Michael Orup Lundberg skrev:

Saturnus skrev:

Precisely. Buy 4 of each of those and parallel over each woofer separately. That'll give you more options should you later want to upgrade.


wow! this can be done way cheaper than i thougticon_smile.gif
You say parallel over each woofer sperately how do i do that?
i have some experience but not alot.

and just to get everything clear, when it's time to hook it all up to the amp, each channel is supposed to drive 2 woofers and 2 tweeters each?


Yeah. It's not too expensive when you build it yourself. My solarpowered Boominator costs about DKK4000 in materials total, and DKK1000 of that is the solar panel alone, so just DKK3000 for a boombox that plays about 10 times as loud as the JVC tube ones and have a battery life that last an entire festival on a single car battery (with an average playing time of 12 hours per day at high volume and 8 days at the festival).

Put the resistor between plus on the woofer and plus on the piezo, and connect a piece of wire from minus to minus. Now connect plus on two woofers to one of the amps plus outputs and the same with minus. Repeat it for the two remaining woofers. It's that simple.




Thanks alot for all the help it was very useful informationicon_smile.gif I hope it's okay to ask for your help again should I run into any snags during assembly. but for now, thanks a bunchicon_smile.gif
Written on: 23.03.2009 23:32
Saturnus
Posts: 3047
Michael Orup Lundberg skrev:

Saturnus skrev:

Michael Orup Lundberg skrev:

Saturnus skrev:

Precisely. Buy 4 of each of those and parallel over each woofer separately. That'll give you more options should you later want to upgrade.


wow! this can be done way cheaper than i thougticon_smile.gif
You say parallel over each woofer sperately how do i do that?
i have some experience but not alot.

and just to get everything clear, when it's time to hook it all up to the amp, each channel is supposed to drive 2 woofers and 2 tweeters each?


Yeah. It's not too expensive when you build it yourself. My solarpowered Boominator costs about DKK4000 in materials total, and DKK1000 of that is the solar panel alone, so just DKK3000 for a boombox that plays about 10 times as loud as the JVC tube ones and have a battery life that last an entire festival on a single car battery (with an average playing time of 12 hours per day at high volume and 8 days at the festival).

Put the resistor between plus on the woofer and plus on the piezo, and connect a piece of wire from minus to minus. Now connect plus on two woofers to one of the amps plus outputs and the same with minus. Repeat it for the two remaining woofers. It's that simple.




Thanks alot for all the help it was very useful informationicon_smile.gif I hope it's okay to ask for your help again should I run into any snags during assembly. but for now, thanks a bunchicon_smile.gif


No worries. Happy building. icon_biggrin.gif
Written on: 24.03.2009 20:45
Freddyboy
Posts: 56
Freddyboy skrev:

This looks really interesting, but I don't have any parts.
What is the price for the whole thing? icon_lol.gif
I don't intend to be an ass, but i'll just bump my own post
icon_razz.gif
Written on: 24.03.2009 21:07
Saturnus
Posts: 3047
Freddyboy skrev:

Freddyboy skrev:

This looks really interesting, but I don't have any parts.
What is the price for the whole thing? icon_lol.gif
I don't intend to be an ass, but i'll just bump my own post
icon_razz.gif


Whatever you want to spend!

If you wanna go really cheap you can probably find some wood and a set of old speakers in a dumpster or on a scrapyard. And find an old car cassette player (these use much less power than modern ones) at a car scrapyard.

Total cost could be anything zero to 1000s of DKK.

What's your aim?
Written on: 24.03.2009 21:32
Freddyboy
Posts: 56
Saturnus skrev:

Freddyboy skrev:

Freddyboy skrev:

This looks really interesting, but I don't have any parts.
What is the price for the whole thing? icon_lol.gif
I don't intend to be an ass, but i'll just bump my own post
icon_razz.gif


Whatever you want to spend!

If you wanna go really cheap you can probably find some wood and a set of old speakers in a dumpster or on a scrapyard. And find an old car cassette player (these use much less power than modern ones) at a car scrapyard.

Total cost could be anything zero to 1000s of DKK.

What's your aim?
Well a solar system looks awesome. And I'd like in on a nice trolley, so it doesn't get stuck in the mud. I prioritize sound quality aswell as playing loud, even though I've no intention in creating huuge festival parites. Just small ones for my own camp icon_cool.gif
Written on: 03.04.2009 11:45
Cos
Posts: 39
Hey Saturnus, so i finally ordered all the parts for the box except the solar panel. I've been looking at the one that are linked to in the first post but it seems just a little too exspensive for me. you wouldn't by any chance know off something a litlle cheaper?
Written on: 03.04.2009 11:49
Saturnus
Posts: 3047
Cos skrev:

Hey Saturnus, so i finally ordered all the parts for the box except the solar panel. I've been looking at the one that are linked to in the first post but it seems just a little too exspensive for me. you wouldn't by any chance know off something a litlle cheaper?


I think the same dealer has smaller versions but I'm not sure.


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