Austin DIY HT Projects - Page 9

Hank Frankenberg · 03-31-2003, 09:26 PM

Scott: careful some things are way too cool to be handled by the inexperienced, and could be VERY dangerous

Jeff Meininger · 03-31-2003, 10:26 PM

So far it has been very fun and rewarding. It will be REALLY rewarding to have some nice speakers, but I place a good amount of value on the HUGE amount of knowledge I've gained so far. I've learned so much not only about speakers and how audio works, but also lots about woodworking and the fundamentals of how electronics/electricity. After all, the learning experience is really why I'm doing this in the first place. I'm looking forward to starting my XO design. I imagine that will be my favorite part of the whole project.

My wife is awesome. The Shiva sonosub really sold her on the whole HT idea, and DIY in particular. Now we're both just plain hooked. The first time we fired that sucker up, we knew we'd be taking the plunge with the rest of the audio setup. She even helped me build the flexi rack!

Ultra-Cool. It's a fake pack of cigarettes that I roll up in my sleeve so I can look, well, cool. No wait, it's that deep-heating muscle rub stuff. No, it's actually a grooming product for that perfect coiffure.

No, not really.

It's a quiet PC case cooling fan. I did some research, and it should be among the least noisy 80mm fans you can buy. And it was only $5! COOL!!! I'm going to build a hood contraption to sit on top of the receiver and suck the hot air out. The built-in fan in the receiver is LOUD and quite distracting when it kicks on. Not sure if the idea will even work.

See here...
http://www.hometheaterforum.com/htfo...hreadid=131944
...and here...
http://www.hometheaterforum.com/htfo...hreadid=132607

Wood dye? I was planning on thinning some oil based enamel to a wiping stain consistency or something. Is that the same thing? Anyway, I'm not going to finish the rack until I finish the speakers. That probably won't be for quite a while because I'm going to want a weekend or two _without_ a garage project. So bare+bondo will be the motif for the short term. Bondo, baby! Yeah! Fender-bender chic! Mark can have his velvet, you can have your leopard print, we'll stick with our BONDO.

By the way... thanks for the quick disconnects. I'll need to order more, so I'll be stuck with way too many in the long run. I'll give you plenty of my leftovers to restock your supply.

Hank Frankenberg · 04-01-2003, 08:02 AM

Methinks this boy is hooked. Jeff, we can talk stain, dye, etc next time we meet. Speaking of MEET - I wonder what month we should target for a meet...hmmmm.

Jonathan DA · 04-01-2003, 10:41 AM

04-03-2003, 10:46 PM

Hank -

Where did you get that "spray lacquer" you've used for some DIY experiments? I have some unfinished wood bar stools that could use that kind of a finish.

By the way, I think I still owe you money for food you bought on my behalf after the "Lawrence of Arabia" showing at the Paramount. I meant to mention this to you at the last HTF meet but got caught up in the thrill of four rooms jam-packed with HT equipment. Next time I make it to a meet or movie night that you're attending, please remind me...

Hank Frankenberg · 04-04-2003, 08:10 AM

Colin: I don't use spray lacquer. My finish of choice is the one I demoed at the big DIY meet at Johathan's: hand-rubbed Danish oil finish - you know, the labor intensive one. I would definitely NOT recommend that finish for any furniture that would be exposed to liquid spills. Oil finishes, while giving a very deep, rich, warm look that really brings out the grain, offer almost no moisture protection. For your bar stools, I strongly recommend polyerethane finish. Spray would be quick and easy, but subject to *runs* if you spray a bit too thick per coat. I'd use brush-on poly. You have your choice of gloss, semi-gloss or satin. Poly gives excellent moisture protection and is tough. For ultimate tough, you might consider Behlen's Rock Hard varnish. I built a baby highchair and finished it with that stuff and it has survived the world's most brutal abuse: 2 babies.

You owe me nothing. I enjoy your HT and lust after your Maggies. Okay, a high-end beer will do.

Jonathan DA · 04-07-2003, 12:27 PM

Jeff, don't keep us in suspense, how did the crossover modelling go for your speakers? Based on those tweeter measurements we took I'm anxious to find out if they sound as good as they measured.

Jeff Meininger · 04-07-2003, 01:42 PM

It's coming along slowly. I seem to be able to either creat a flat frequency response or a nice phase null, but not both at the same time. I also find it odd that when I add my 4th order LR network to the tweeter, the impedance drops. When I optimize it, it drops even more.

This being my first project, I'm not exactly sure what to shoot for.

One question... here is an overlay of the MT and MTM woofer response measurements (blue line is MTM). Shouldn't I expect to see the MTM putting out 6 dB (or at least 3 dB) more than the MT across the board rather than just below 400 Hz?

Thanks!

Mark Hayenga · 04-07-2003, 02:01 PM

When the impedance of the tweeter drops, what's the value of the first parallel inductor (usually put into net 2 I think)?

Mark

Jeff Meininger · 04-07-2003, 02:24 PM

EDIT: I whacked the component values and graphics because my LspCAD skills are evolving and things are getting flatter and less expensive. I'll post more graphics when I _really_ think I have it right.

Jeff Meininger · 04-07-2003, 02:47 PM

EDIT: I whacked the component values and graphics because my LspCAD skills are evolving and things are getting flatter and less expensive. I'll post more graphics when I _really_ think I have it right.

BUT...

I'm worried about the level of tweeter padding because I'm unsure of the level of the woofers (see MTM vs MT image). I remember you guys hitting the volume knob at some point due to the sound card beeping. If that was done after some other measurements were already saved, could it explain the different SPL calibrations I'm seeing in the FRD files? Or do I just not know how to import these suckers properly?

Mark Hayenga · 04-07-2003, 04:44 PM

The level is the same because we didn't do an actual SPL calibration (that's why everything is referenced to 0dB instead of its 2.83V sensitivity). Don't worry about comparing the two woofer files. It only matters that a) the volume wasn't touched between the woofer and tweeter measurements on each speaker, and b) that you use the MT tweeter measurement with the MT woofer measurement and likewise for the MTM. If the volume control was fiddled with in between then there may be some problems (I can't remember if I touched it or not, I may have - sorry. This is why I have Scott do my measurements

)

Tips:

I usually put the tweeter attenuation resistor last in the network. Try it in either place and see what works best for you.

The low tweeter impedance is caused by the parallel L that's only .1 to .2mH. Kick it up to at least .3mH.