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Old 9th October 2005, 08:41 PM   #1
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Default Simple high school project - advice requested

I am running the Tech club at a local high school and the idea of building a stereo has come up. I am a fairly resourcefull person but my experience with soldering and circuitry is limited. I want to help point the students to a simple straightforward project that they can complete at home with help at school. I have never built a speaker before.

I purchased a Sonic T-Amp and have been fairly impressed by it (Though I din't have any really efficient speakers to try it on). It has a great price point and seems fairly easy to mod (atleast putting it in a different box with different connectors...) This seems like a good starting point. I don't mind the head phone jack connector since most students will have a mp3 player, cd walkman or computer to hook it to.

For a speaker I am looking for something that can be done simply for under $100 of parts...

The Fostex full-range drivers seem an easy way to go. It means we wouldn't have to mess with a crossover atleast. I would like the finished project to be bookshelf sized and the port to be on the front so it can be placed against a wall.

How do I work out how much volume the fostex drivers need? Is putting a single 4.5" driver like the FE126E in a bookshelf sized box going to produce enough bass? I could step up the 6.5" but it seems like the box would need to get bigger, and the 6.5" is pushing the price range.

Would a 2 way system be cheaper and more compact... could it still be as sensitive even build cheap. Is there an extremely simple way to build or buy a crossover... I also have access to a computer and microphone but not much more equipment than that for analysis.

I am thinking of using plywood or wood for the 1st iterations... They seem cheaper and easier to work with (especially to finish) though probably not as good as mdf.

Any advice is greatly appreciated. My most important question is how do I work out the volume needed for a given driver.

- Mountaingoat
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Old 10th October 2005, 04:29 AM   #2
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I'm not the most experienced member here so take what I say with a bit of salt.

How do I work out how much volume the fostex drivers need?
Depends on the specific driver and how much you can give it. Download WinISD and play with it a bit to get a feeling for how each driver will respond in different sized enclosures.

According to the optimal plot for the FE126's you mention, the ideal bass reflex is around .5 cubic feet

s putting a single 4.5" driver like the FE126E in a bookshelf sized box going to produce enough bass?
Depends on what you mean by enough bass. Some people are happy with the bass a fullrange driver can output in a small box but quite a few aren't. That's why the build horns and transmission lines or use subwoofers. Again, play around with the specs in WinISD to see if you can get a specific combination that has enough bass for you. (My guess is you will probably be okay with it... so long as you don't want to rock the floor!)

According to WinISD's optimal plot the 126 is -3dB at 87 Hz... Which is a little high IMHO. In a little bigger box (around .7 cu ft) with a higher tuning frequency (65 Hz) you can get the -3dB point down to 66 Hz which seems a little more reasonable but doing this makes the speaker less linear. (Use WinISD to plot the two graphs and you'll see what I mean)

Is there an extremely simple way to build or buy a crossover can hook you up with pre-built crossovers... though if you have any soldering skills they aren't hard to do.

I am thinking of using plywood or wood for the 1st iterations... They seem cheaper and easier to work with (especially to finish) though probably not as good as mdf
You'll see a hundred different arguments for or against different materials. It seems like most people prefer good quality plywood to MDF... but I could be wrong.

Edit: Almost forgot here's some links to plans that are pretty similar to what you are looking for:
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Old 10th October 2005, 04:46 AM   #3
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Have a look here
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Old 10th October 2005, 05:47 AM   #4
Tweeker is offline Tweeker  United States
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Making your own first and second order crossovers.

You can make your own crossovers and even go so far as to buy magnet wire off Ebay and wind your own inductors. There can be savings here at the thicker gauges for low DCR if you can measure inductance. Designing good crossovers is involved and can end up costing quite a bit more too if your not carefull.

Making the speakers smaller will entail a loss of efficiency and/or low end extension.

The FE126 has a low q and really needs a horn to make bass. Id suggest a folded TL using the FE 127 for a compact affordable reasonably efficient speaker with some bass.

This thread has some suitable suggestions.
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Old 10th October 2005, 07:22 AM   #5
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You could do a lot worse than using fostex's recommended enclosure and an FE127E driver for simplicity and performance.

The FE126E is less suitable for your application as tweeker mentioned, unless you wanted to build a horn enclosure.
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File Type: pdf 127e_enclrev.pdf (92.2 KB, 56 views)
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Old 10th October 2005, 12:02 PM   #6
MPM is offline MPM  United States
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Many of these projects use a 4" speaker called the NSB. Cost $.49(thats 49 cents) each and is a great speaker for group projects.
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Old 10th October 2005, 03:31 PM   #7
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Another driver to conder might be the new 4" Tang Band. Could be quite easy to work with...
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Old 11th October 2005, 05:07 PM   #8
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Default Thanks for the help!

Wow! I am amazed at all of the fast and helpful responses!

You have given me many great ideas and pointers...

A few thoughts:

The recommendation of:
was great, fun to check out yourself...

I am going to buy a few of the NSB drivers... for 49c you can't go wrong... can even cut one open to show the students how it ticks... I plan to by a few cheap tweeters(around $1) as well just to play with... This will give us something cheap to mess with and then tear apart and rebuild without feeling bad.
Had a lot of great and cheap speaker designs... A couple of good options... 3 or 4 for under $100 of parts

The crossovers don't seem so hard if I keep them simple and am not that picky. I don't expect the first Generation to sound that good... We'll get more technical and precise for the second gen...

I am thinking of building for myself around the fostex FE167E their standard bass reflex box... and maybe adding a FT17H tweeter with just a simple capacitor:

This seems a relatively good first project for myself though the drivers aren't quite so cheap and should yield a very sensitive bookself style speaker to pair with a sonic impact t-amp... Not much bass to speak of but I think everything else is fine... should approximate an Omega Grande 6 (though I've never heard one and they don't seem to be making them anymore):

I've heard good things about the FT17H tweeter and the FE167E... though the box is probably not the best for bass, I want it to be small and portable (I may set this up at outdoor festivals)... Any thoughts on how this might work?

Now I just got to convince the shop teacher to let me have access to the wood shop.
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Old 12th October 2005, 04:19 AM   #9
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I wish I had a club like that at my school.
I'm 17

There are tons of things that would be great inexpensive projects for your students.

I think using a cheap driver to cut open and show how it works is a great idea. Also to add to that you may go toHow stuff

Are the student's paying for the drivers?

Some variety would be nice instead of everyone creating the same enclosure design.

If using the Sonic T amp you may want to consider using 4 ohm drivers. TB w4-1052sa. Those 4" Tang Bands have good low end extension for $22.

Here is my project using the Fostex FE127 This also includes GM's transmission line design. If some of your students are up to the challenge there are many other enclosures online too including different horns. This is also true for the smaller fostex drivers too, which again are less expensive.

If you want efficient drivers with some bass you can try Audio Nirvana their 6.5" is $98/pair.

Good luck,

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Old 12th October 2005, 05:00 AM   #10
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Since I notice your affinity for Omega... here's a theoretical plan I drew up as a copy of their Minuet speaker which uses the rather intrigueing TB w4-1052sa that edjosh23 mentions. Basically it is the same as the Minuet but a bit bigger (for a touch lower bass) and (of course) without any magic dampening or supports that they use in theirs.

I've never built this design but it simulates well and could be a fun one to build.

I don't know if you're interested, but there are a several somewhat simple Class-D DIY amp kits floating around... If your students are interested in a follow-up project, I'd say one of these would be ideal. The easiest one would probably be the 41Hz Amp 6: .

Its great to offer something like this at a high-school.... Heck, I would have loved it if my college or my grad school had offered something like this too!
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