Scratch Build – In Progress Megablaster 2010 work log (diy ghettoblaster)

Use a coordinate measuring machine. If you wait a few weeks they will show Haoki and me how to operate one. And if we get lucky that thing will fit inside the working space of the one in the student metrology lab at TTY.

 

True... Thought about that solution as well Btw... It's next week we'll have to get into grips with that one. Oh and the 0.5 mm accuracy shouldn't be any problem

 

Javerh: oh cool! Blaster measures roughly 70x35x14cm.

Sleepstreamer: Yes I wan't highly glossy black finish. I tried this technique already with my subwoofer. Sub had less strange shapes so laser cut parts fitted without any work. Here's two shots how it looks:

 

This is some seriously awesome work, as are your previous builds. I will be keeping a close eye on this one.

 

Why are you making it sealed out of interest? Wouldn't that just decrease the sound volume and require more power to be louder?
*with my rudimentary understanding of sound physics

 

^^ Speakers produce a front wave and a back wave. Usually when the back wave gets out of the speaker box it is out of phase with the front wave. The back wave then interferes with the front wave diminishing the sound pressure level. The back wave can get out through unsealed joints. This can also produce hissing sounds when air rushes through.

 

You sure about that, go look at all speaker boxes, and you'll find they are sealed.

 

Unless they are a woofer box, then they have an air duct.

 

Err... look at the pic above of his custom made subwoofer box.
It's mostly used on woofers because they move a lot more air than normal speakers and at lower frequencies (obviously), but the holes are actually designed to increase sound and are placed so that you get a correlating wave coming out so it doesn't create a point of no sound with the woofer in the room.
It's physics

 

^^ No. That's already acoustics. And physics ain't part of philosophy anymore.

 

Nice woodworking skills! I love it!

 

I'm making it sealed since the bass drivers in my build work best in sealed box. Some drivers work better in reflex box (the box with "duct" aka. reflex port) Properly designed reflex box will add couple of db's to the lowest bass. Main problem with reflex tuning with my drivers would be the size of the box. Blaster would be even bigger if I chose reflex box. I have two bassdrivers since it guides the bass frequencies more to the front of the box. Normally bass frequencies escape to all directions. When listening in a room this is not a big problem.

So I have this 20 liter sealed 2x8" box. 1x8" driver would work in same 20 liter reflex box but I will get more bass from sealed box since it looses less bass to wrong directions because it has more drivers. Reflex box has also steeper roll off curve so bass extension cut's just where the tuning frequency is.

To make it short is chose sealed design as I wanted the box as small as possible.

 

How many volts are you powering the amplifier with? I ordered one since I was curious and I found out that there is a big difference between 12 and 24 volts. Guess you get more watts with more volts.... but have you tried?

 

2x100W @ 36V. My battery is 18,5V which gives me about 2x40W

 

Finally attached the handle:



Placement of crossover and amplifier:



Grilles:



Scanner running:

 

First test of the led scanner, sorry for the cellphone quality:

 

Measuring the box with help of Javerh. Now I start drawing the plastic parts in CAD.

 

Too bad I'm not familiar enough with the interface. We couldn't get all the needed dimensions.

 

What the heck.. Ghettoblaster goes hi-tech..

 

I removed the fan from the amp and went to lan party to test if it runs without fan. Amp works great when taking 30-40w power from it. I gave the unfinished blaster a good abuse and since it survived the weekend I can now finish it. Here's some cover parts I've already drawn.



I hope this short clip gives some idea of the sound it generates, it's pretty loud since you can't hear the 20 drunken people talking and shouting in the room :]