"Green" OB speakers project

[TMHutson]

Rather than admit I have no job and am broke (wait... ooops!) I will use the excuse of using old, stained, nasty plywood that I found for this project as a way to "go green". I "recycled" wood from an old restaurant booth.
Took forever to take out all the staples and remove the ugly veneer.

I had to buy 6 screws (picture shows I need to color them black), and a pair of RCA splitters.
No screws in wood, only glue and clamps.
No table saw, used handmade guide for circular hand saw. Better than stupid hand held jigsaw, that's for sure! Still not perfect.
Gaps or wood issues were dealt with by mixing wood glue with wood powder left over from cutting.
I then sealed inside woofer box with caulk. It is airtight. Woofer/wood does not move, or make any huffing noises.
Fostex FS-21RP and ribbon tweeter were sourced at swap meet for 30 bucks (I think they are actually new old stock).
8" woofers are first generation Infinity Beta car 4 Ohm woofers with Injection Molded Graphite cones that I got at 75% off retail with my employee discount back in 1998. I think I paid around 120 for both? I don't recall exactly. I noticed some of the Dayton reference woofers use the same basket! (Different motor and cone).

I bi amped the speakers by cutting up the 1st order 3 way crossover. Coil is connected to woofers on main speaker channel with 70 watts. The mid band and high pass are running on rear channel with 70 watts.
I split the CD output, and connected one pair to EQ for volume control to the rear discrete input, and then the other pair connected to the main channel input. By using the discrete inputs, I now have no sub output so I had to use the speaker level inputs on sub. Works great.

I have no measuring equipment yet, so am not worried about tweaking the crossover or eq right now. I do know that the crossover seems to not be designed very well...

Only the tweeter is not ready to be permanently mounted. I just taped it into place to test sound. I need to decide how I am going to make a mounting plate for it. And what kind.

These are by far the best speakers I have ever built or owned. I have never bi-amped before. I have also never owned open box speakers.
I really love the sound quality, low distortion, clarity and sound stage. Highs are a bit off due to funky crossover setting. The mid and tweet are working in some frequencies bands, making them harsh. I can't fix it right now
These speakers were originally going to be built as fully enclosed speakers. But money and wood issues made me decide to try something new...
I am impressed. I would have to build a whole new enclosure to see which I like, side by side. Too bad these ribbons are no longer available anywhere


I have the matching infinity Beta 5.25" woofer, and Beta one tweeter with passive 24db crossover if I want to go with cone speakers. But can't do OB with that set up... Oh well.

Wood is going to be painted and cleaned up in the future.. maybe. Wood is a little warped, so may have to build something for the back, or just buy new wood when I am able to. What this setup needs first, is some crossover work, and some EQ'ing... Won't be able to do that until I get measuring stuff sorted. I can't believe how good these sound for how little money I have invested I wish all audio was this cheap.

Thanks to all the people on this forum that have posted thier projects and information... Even as ghetto as this set-up is, it's still way better than anything I have owned or done

[Pano]

Originally Posted by TMHutson

...wood powder left over from cutting.

Sometimes known as "Sawdust".

Hey, those don't look so bad. Nice to use old stuff. And welcome to the fun and wonderful world of the Open Baffle. Now time to get that crossover in shape.

OB=fun.

[TMHutson]

hahahaha. Yeah, I ate too much sugar and have been speaking spanish all day. I lose an english word every time I learn a new spanish word

Trust me, nothing is more frustrating that not being able to sort the crossover right now. I did buy some cheap caps to add to the coil to change the woofer xo point from 365 Hz or so at 6db to a Linkwitz 12db at around 710. The coil is 1.88 Uh. Which, I think is a more suitable point for the mid and woofer based on the fs-21fp requency response. It starts to drop at around 650 or so. I just don't have the funds to rebuild the Mid and tweet crossover and I don't know how to make inductor coils. Can't find them locally, and not really wanting to spend money via the internet at the moment. I can find cheap caps locally to play with.

Plans are to go fully active with a little minidsp/amp combo. Using the little 20 watt amp on the tweeters. They will be crossed over at 3150 or so. Only if I can find an inexpensive way to control volume. If I go three way, I can't use my receiver volume control anymore. Only bi-amp with mid and tweet together with passive xo.
The mids seem to be about 3 db louder starting at around 3200 all the way up to 10k. The tweets should be reasonably flat starting at around 3100 all the way above 20k.
I was considering making a really nice crossover for tweet and mid so I can do a simple bi amp set up. But I think for the price of crossover stuff, I might as well get the miniamp with the minidsp... If I build a passive xo for the tweet and mids, I only need one minidsp. If I go completely active 3 way with sub, I have to buy an additional minidsp AND buy an amp... hmmmm

Currently, it seems the 1st order crossover looks like this...
Woofer, up to 367 hz or so.
Mid from 367 to about 7k
Tweet above 1900. I have no clue why so low. It's a small supertweeter.
Looks like mid and tweet are playing together between 1900 and 7k. And you can really hear it...

I would prefer the crossover points be
80, 700 and 3150. With active I can get 24db or higher slope, too. 6db just does not work with this set up...

I don't recall reading anywhere if minidsp can do summed mono output for subs. I need a mono input for my discrete surround inputs... Then I can have volume control for highs, midbass and sub... I may even try to experiment with using the center channel amp 70 watts on a sub to see if it fills in some empty spots in room...

[dave_gerecke]

Here's a few links that explain the making of an air core inductor. Always remember, the internet and search engines are your friend!


Air Core Inductor Coil Inductance Calculator

How to make an Air-Core Inductor Electronic Circuits-Circuit Diagram-Electronics Projects-Design

An introduction to the air cored coil


Peace,

Dave

[TMHutson]

Thanks for the links. When I searched "inductors" and "coils", I seemed to be only able to find ways to measure inductance, and I don't have any equipment like that
This will help greatly, as a local electronics store sells wires for making electromagnets.
I will have to give it a try.

[dave_gerecke]

Cool. Good luck and glad I could help. I can understand what you are saying about searches, picking the right word(s) can make all the difference.
The thing to remember with winding the coils is that the formula given is for an air core coil, i.e. no ferrous material in the middle. Best thing for that is either a wooden dowel, or perhaps a plastic or carboard tube. You could also use the plastic former for a transformer as the base to wind around. Just remember to keep the windings tight to each other, as this affects the inductance. Also, keep in mind the resistance of the wire per foot, and how many feet of wire goes into the coil. That way you keep the resistance down, and the coil can handle higher power.

Peace,

Dave