What brand of speakers do you recommend and where can I get them? I don't want to spend an arm and a leg on them, just nice quality ones.

Are you building your own amp?

If it's that 100 watt monster you'll need expensive speakers.



There's plenty of hobby sites that sell speakers.
I have used these folks but you should check around. Might be someplace right in your hometown..

I would start with something similar to these and make my own box to put them in.
http://www.mcminone.com/product.asp?product_id=55-1240&catalog_name=MCMProducts



http://www.mcminone.com/product.asp?product_id=53-526&catalog_name=MCMProducts



Put this capacitor (7.5 uf) in series with each tweeter:
http://www.mcminone.com/product.asp?product_id=50-4581&catalog_name=MCMProducts

and this inductor (0.5 mh)with each woofer:
http://www.mcminone.com/product.asp?product_id=50-4581&catalog_name=MCMProducts

These will sound great and shouldn't cost you over a hundred bucks in materials for the pair...

If you get serious look up "Thiele parameters" and learn how to select the proper box volume for your particular speaker. There's lots of enthusiast sites.

I'd guess that about 1.6 cubic feet will work okay. You could get a couple of sink tailpieces from any hardware store and experiment with venting the enclosures. But with that high powered amp you wont need the extra decibels of a reflex.

I made my first speaker enclosure with a hand crosscut saw, even the rectangular vents. If your school shop has a table saw you can do a much better job.

Speaker boxes is one application where particle board is okay - it's denser and straighter than plywood. Use at least 5/8 inch and 3/4 is better.

These speakers in a decent enclosure will make a lot of sound of surprising quality. After you blow them up with a monster amp it's time to move on to a three way system with higher end 12 or 15 inch drivers and a proper sized enclosure. But don't sink that much money into your "Learner" project. Polish your carpentry skill on small ones.

a.

I would go for this Tang Band tweeter.

http://www.partsexpress.com/pe/pshowdetl...FTOKEN=28545238

They are on sale for $12 and that is a really good deal on this brand.

Hey Analog I fired up the old desktop and dug out the email and info on that amp I mentioned. Instead of cluttering up the board here I packaged it as an HTML page and uploaded it.

"Bob" Is Robert Berkovitz one time manager at MATTES Electronics and sometime later one of the original staff of the US division of Dolby Labs.

This little amp was sold for nearly $400 in 1965 !!!. I bought it in a thrift store about ten years ago for $15.

The output on one side was blown when I got it but it was easily restored to full operation. This thing is really solid and well built and actually pretty small in size, but very heavy for it's size. It's also an extremely rare find.

Well here's the link if you're interested. I'm sure Bob wouldn't mind me sharing this little slice of history.

http://consist.sitesled.com/MATTES/Mattes.htm

<edit>

Another bit.

Quote:

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If you own a Mattes amplifier, I'd say you are both lucky--because it is a very good product--and brave, because to the best of my knowledge, you won't find it easy to get any technical information about it. The amplifier was designed to a topology patented in the name of the company by Madan Sharma, a friend of mine, but someone I have not seen in many years. Sharma subsequently worked for TRW, but I cannot say more than that. At http://www.aes.org/e-lib/browse.cfm?elib=1201 you'll find a way to buy Sharma's 1965 AES paper describing his circuit.

Apart from answering any other specific questions, there is little more that I can say.

Regards,

Bob

---

The amps design does have a fault, a single latching diode failure can result in a cascade failure of the final two amplification stages in that side of the amp. That's what I discovered when troubleshooting the unit and was the original cause of its problem when I bought it.

But I can verify that when operating correctly the sound, even though this thing is 40+ years old is clear and crisp and it has no problem driving modern speakers.

Interesting article. I remember those days.

I looked for the patent you mentioned but could only find his 1961 patent on an amplification technique using PWM .

Does this thing work like Class D, that is modulate the duty cycle of a very high frequency carrier like the one-bit D/A converters everybody uses today? If so he was forty years ahead..........

If there's a patent number on your amp let me know and we'll see what is in the patent office's public records.

a.

Sorry, the link for inductor should have been
http://www.mcmelectronics.com/product.asp?product_id=50-3019&catalog_name=MCMProducts

Click on the "crossover components" link at top of page, you'll find lots of parts. You might want a terminal cup too.

Ask your friend if he can design proper volume using the Thiele parameters - they're on the speaker link. That'll add some class to your design and prepare you for an exotic 3 way system down the line....

Midrange is optional. The two speakers suggested have plenty of overlap in their response and those crossover components are around 2500 hz, a high whistle well within both speakers' range. That woofer extends far enough into midrange you don't need a separate midrange speaker. You could spend a lot more money for an exotic woofer with less response but I still advise you to wait until the next speaker project for that. The two speakers linked have same sensitivity, an exotic woofer may not match whatever mid and tweeter you pick and that would complicate your crossover design. Shelving is the term you'd have to add......

If you want to build a three way I'd suggest going for higher end drivers, 15 inch woofer in the $200 each range, 8" midrange and ribbon tweeters. Get a copy of Howard Sams' book "How to build Speaker Enclosures" and digest it, there's considerable science in doing it right. You should be sure you're ready to do justice to that kind of monetary investment. It is SOOO easy for a first time builder to poke a screwdriver hole in your $200 woofer's surround,,, (I know I've done it but fortunately only a $40 woofer).

That little woofer is rated 40 watts continuous so it is conceivable you could burn it out with that 50 watt amp. But it would take enough time that your neighbors would likely have called the police first. SO no, the 50 watt amp would not easily blow them out. You'd have to work at it.

My advice remains start modest. You will learn a lot building these and will be way better prepared to do a fine job on the bigger speakers. You might peruse some speakerbuilder forums...

Did you notice that amplifier kit does NOT include the heatsink pictured? Pay attention to that 1.4 deg/watt, don't buy sinks with a higher number, lower would be better, and be sure to use "heatsink compound" under the power transistors. Bolt them tightly to the heatsink. It is REAL important that the heat get out of your power transistors.. The kit directions should tell whether you need insulators under the power transistors, if so get ones with lowest deg/watt you can. The heat has to make it through the insulator to get to the heatsink.



Material for the amp?
If you want to show off your amp use Plexiglass and put in accent lights - blue LED's or something..
Myself I like wood - your local Home Depot should have birch veneer plywood that you can stain to resemble exotic wood.
There are door kickplates made of brass that'd make a beautiful front panel....... and leave vent holes over the heatsinks.

50 watts is a good choice for the speakers Analog suggested Dan.

One thing to be aware of tho is that if you turn the volume all the way up the output power can actually exceed the rated specs because the rated specs are predicated upon an unclipped signal. Even an amp rated less than the maximum speaker rating has a potential of burning out speakers if driven into clipping. When an amp goes into clipping it is basically outputting straight DC for a period each cycle and that DC component really generates a lot of heat in the voice coil.

So if you turn it up to the point where you begin to hear any distortion then throttle it back. Most amps are actually only good for the first two thirds or three quarters of their volume range. Beyond that not only starts to sound terrible but also causes enormous stress on the components.

That woofer makes more midrange than you will need Dan. The human ear is most sensitive in the midrange. Analog is correct they will overlap quite nicely in a two way system. If you need more bass later just add a dedicated sub.

The only advantage of a three way over a two way is when driven at extreme volume levels in a single driver system or two way system the big speaker has to produce all of the bass and the midrange at the same time. Since the cone is moving a great deal trying to produce the bass this has the effect of modulating the midrange to some extent.

It's only noticeable at very high volume though so two way systems can have a remarkably good sound for normal listening.