As i said in part 1 of this project i wanted to build a 2.1 system with good sound using most of the components i already owned and keeping the costs as low as possible.  Since the satellite speakers are not going to be used below 100Hz you can fit almost any 6.5″ woofer in there and since the box is closed. You can also use speaker filling to match the Qtc of the satellites with the subwoofer’s low pass filter. However you need to focus on voicing. Crossover between woofer and tweeter is very important and many times i found it’s making a big difference in sound. If you open most mainstream commercial speakers you will see a only a capacitor and/or resistors or something like that.

Now the subwoofer, since i don’t have much information on the drivers i have, i had to do some measurements. I found a Qts of about 0.76, Fs – 46Hz and Vas – 36l. Yes, i guess it’s made in China. No matter, it will fit a 60l (internal) box very well. The box will be sealed because the woofers are not that good and i will place it in a corner this way i will gain up to 6db in output. The thing about rooms is that their dimensions equals the wavelength for low frequency and this leads to room modes and room gain. If you have a subwoofer you might have experienced that in the room there are certain places where the bass seems to disappear. Take one step away and the bass appears again. This is due to room modes. Going lower in frequency there will be no more waves in the room and the room starts to pressurise and you have a gain going 12db per octave.

This is a generic box. You can fit in there a couple of 10 inchers too. What you must look at is strong motors in the woofers. Big magnets, thick top plates, big diameter voice coils all this will help the woofer perform in a sealed box.

Now to the build itself, first i cut the material i need using a circular saw.

circular saw wood sub box

After all the wood boards are cut, i use glue the boards together. Use of clamps makes things easier. Bracing the box and making the joints as solid as it possible will lead to best results. Heavy is good in subwoofers! After the glue is dried i applied the carpet on the box, corners protection, handles and connectors.

carpeting1 carpeting2 carpeting3 carpeting4 amp

Once subwoofer construction was completed i focused on it’s amplifier. I had a car amplifier with it’s smps busted and i thought it’s just what i needed because it already has adjustable low pass filter. The corner frequency can be selected from 40Hz to about 200Hz. So i removed the defective smps and i installed a mains transformer rated 150VA which gave me +/- 35V dc after rectifier bridge. Also used 10’000uF caps for filtering. In most car amplifiers the case is used as a radiator so i had to put new radiators for the power transistors. All this and the amp board i put in a deceased Pioneer Cd player case.

Here’s the 2.1 speaker system:

2.1 speakers

Time to power the system. The satellite speakers are amplified by a JVC integrated amp and the subwoofer by it’s own amplifier with each channel to its woofer. Set the subwoofer low pass filter to about 100 – 120Hz. Sound was good however some tweaks were still needed in satellite crossover, it sounded bright. Waveguides rule! Here are frequency response graphs. Between two horizontal hard lines there is a 3db difference divided into 5 other thinner lines. The roll off after 10Khz is caused by my old mic.

fr1smooth – satellite speaker                           frwholesys – whole system

I compared the sound of this 2.1 system with a pair of Cerwin Vega CLS-12. On the high mid-range and highs my system has more detail. I think that tweeter with the waveguide is too good to be used with this system haha. Ofcourse the CLS goes deeper and with a couple dbs louder and the big difference is seen when you turn the volume up. The 8″ woofers from my sub can’t keep up with the 12 inchers from the CLS but they do have a fair amount of excursion as you can see from this small video:

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Here are the dimensions of the speaker cabinets and the crossover schematic with one modification the 6.8uF cap from the tweeter high pass filter must be changed with a 4.7uF cap.

schita final xover

This is it for now, I’m sure there will be more changes to the crossover and probably i will test other drivers for subwoofer as time goes by but for now i’m pleased with the result. I wanted a 2.1 system to use with my PC because the two CLS-12 speakers are too big to be placed near my desk.

Anyways if you have some woofers, drivers, tweeters, horns my advice to you is to get your tools and try and build a speaker for them and you might be surprised with their sound and you will have lots of fun in the process specially when you will blow your friends’ commercial setups.

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It seems generating sync-ed sound and video on AVR its not that easy. AVR Atmega88 microcontroller is clocked at 20MHz and so it generates 45 full VGA display lines at almost 60Hz frame rate. Sound is generated during VGA horizontal blanking periods. That gives a sampling rate of 31496kHz which is enough for good chip-sound quality. Sound player is capable to play four sound channels. And all that beauty is programmed in pure assembly language for best performance.

Generate Sound and Video on the same AVR chip: [Link][Via]

April 24th, 2008

DIY Sound Card with PCM2702

 DIY Sound Card with PCM2702 _ the board

Make a sound card is no more a complex issue. If you use great IC PCM2702 from BURR BROWN / Texas Instruments you can create a fully functional USB sound card. This sound card can be powered from USB port and has one stereo output. You don’t need to install any driver for Windows XP and Vista, because they are already inside. This is really plug and play.

DIY Sound Card with PCM2702: [Link]

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