jzr -

You got your post in while I was pondering. Looks like we're asking some of the same questions. It's a shame you're on the other side of the world, I'd love to be in on your test.

While I've been "into" stereos and speakers for a long time, I've never been part of the "acoustic wrench" crowd. (so called because instead of using "liquid wrench" to loosen bolts, they use acoustic power to loosen all the fastensers in their cars). I also have trouble visualizing a subwoofer voice coil capable of dissipating 760 watts of heat. A really good speaker might be 5% efficient, so 95% of 800 watts gets turned into heat, and that just sounds like toasted voice coils to me.

Anyway, see if you can do a test with the scope on the DC power input to the amp. If you see an AC voltage there, that will be where an added cap will help. Le us know, I'm really curious to see the results. Can you get pictures of the scope traces? That would bee interesting.

 

If I remember correctly, 1 farad is 1 coulomb of charge, so a cap so rated can output 1 amp for 1 second, or 100 amps for .01 seconds. It's been about 5 years for me, but the math is already mostly gone...

The amp on the left should be capable of RMS 400Wx2 at 14.4 volts, to power the sub. If I believe the techinician-signed test sheet that came with it, it's 65% efficient with a total power rating around 1200 watts.

If this amp doesn't work out too well, I'll try to get my hands on a Class D amplifier which will have higher efficiency and greater RMS power output (1000W or more), at the expense of higher THD. To answer your question, many amps these days use fans and one I've seen is even liquid-cooled with a pump and radiator!

Just caught your last post; here's the speaker I'm using: - its rated RMS power handling is 750, though some folks using them in comptetition say it can handle 4 times that! It weighs about 40 pounds by itself. I know even less about good speaker design than I do electronics, but somehow they've figured a way to vent the voice coil with the speaker movement to keep things cool.

I'll have my digital camera on hand to take photographs, and maybe capture some mpegs of things shaking themselves apart. I'll try what you said too, testing with scope on DC input side.

Oh and hey, if it does turn out that 1 or 2f of capacitance would really help, anybody know where I could get a "generic" capacitor in that size? $100/f is such a rip off!

 

Hey modifry,

On a different subject: a while ago you posted something about three optional connectors slots in the under dash fuse box. Do you happend to know the part number of the male connector insert piece? I'm trying to hook up a radar box and the parts guy at my dealer can't find the connector in his parts listings. Any idea?

 

Once again this discussion has gotten way way over inflated! I couldn't even bear to read the whole thing I skimmed.

What I can say is that if your putting a fuse of 50 amps or more in your car then you need a cap.(if your running a sub in the system) If your running 75 or better you surely should look into replacing your batterie. I replaced my stock batterie with a RED top Optima and GOT MORE BASS! Honest! Eventually I will be dropping in a bigger and or more powerful batterie in my car. A better batterie is always a good thing even for a stock car.

Yes you can get very technical and putting meters across terminals etc...........though for the average person you can follow the above as a guide line and if your unsure put a batterie in. You can never have to many capacitors!

 

Sorry to have overwhelmed you there Pinky!

Look at it this way: think of how often people make some modification to their car (air filter, exhaust, etc.) and say, "I definitely got more power from xxx mod" - you know, the infamous seat-of-the-pants dyno.

This is a from of audio "bench racing", trying to find a way of measuring system performance so that when somebody says they GOT MORE BASS, or tighter bass, or whatever, that it actually happened. I'm not saying it didn't really happen. I only wish to quantify it, and understand exactly why, by analyzing how those little electrons move about at a level most people wouldn't care to.

I've yet to see a conclusive test done to convince me that a cap will make a system sound better. Stop lights from dimming perhaps, but sound better or get louder, no. Since none of the cap manufacturers provide such info (at least not that I can find, and believe me I've looked), I'm going to have to find out for myself exactly how or why they affect system performance, if at all. Oh, and, I'm not the average person, and neither are most of the folks involved in this mental exercise. While for the average person your advice is probably perfectly legitimate, to me it sounds like my first grade teacher telling me Columbus discovered America.

Guess I'm just a cynic.

Cheers,

Jason

 

Hey let's lighten this up:

Hey Pinky, are you going to the Fall Color's Meet? I hope so...

One thought though: if we get all these extremely bright experienced highly vocal people together in one town, are we going to require a bouncer?

I will ask Rick about that... He's going to need to sell more T-Shirts to cover the expense of the bouncer!

 

modifry,

Here's a bit of help with the equations....I've simplified terms already for the cap.

v(t) - v(0) = 100 * [Integral from 0 to t (dTau)]

Since v(t) = 90% of v(0), things simplify again to:

v(0) = -1000 [Integral from 0 to t (dTau)]

which simplifies again to:

t = -v(0)/1000

So, starting @ 14.4V, the time of discharge to 12.96V is 14.4 milliseconds (assuming I did my math right )

 

Naw I will be the one doing the bouncing! No seriously. I will do my thing and do my business. I will be having my car out for exibition(still waiting on an amp!). I have no problems with other people doing what they like. Though years of real world experience and not so much class work give me a different view on things.

Only time I have problems with people is when they spout about things that I know they are wrong about but absolutely need a 100% indepth scientific EE Degrees answer........just to show them the light.

Were all very bright and experienced yes though many in our own ways/areas. I will not profess to know everything though I don't need to know the exact efficency of an amplifier and its exact clipping point to build a good stereo system. Though building a box may take some math but calculating out the FS QES and so on to make the perfect box is not needed because its going into A CAR! Im not saying that we should all be stupid or not think though just realize that most people out there have a slight background in stereo. Guide them don't dround them in scientific garble. Sadly see above post.

Those that won't try to understand that.........such as me its fine! I don't need to understand it. I just need to know what is the basis and upgrades to a electrical system to a stereo system that is overtaxing the factory system.

 

Just because you don't care to understand the theory behind your rules of thumb, don't think others are getting bogged down and don't want it. Modifry specifically asked that question, and I prefer to provide a fact-filled reason for my answers, not just because the answer makes me feel all warm and fuzzy inside. If it wasn't for the theory behind things, those rules of thumb you hold so dear wouldn't have a basis to stand upon...remember your own words, "I don't need to understand it!" the next time you tell people CD-Rs don't work in the stock player, or that 1000W of power into a 50W speaker is OK. Sometimes it doesn't take an EE degree, just common sense.

Don't get me wrong, I would trust you without question to install a system for me, to pick a speaker that sounds good, and a head unit that looks clean. But sometimes you just have to go beyond the standard envelope...when that happens, standard practices just won't hold water, and that mathematical gobbledy gook is the ONLY thing (other than blind trial and error) that will create a good system. If modifry was building a system that was beyond anything you have worked on before and those standard practices failed, he would be forced to fall back to that ol' high school electronics course and do some real figuring. Sure, most anyone could pop in a head unit and speakers and wire it all together, but not everyone is happy with what comes off the shelf.

 

Glad to see I'm not the only one.

I've been busy the last 2 days (disaster recovery test for a client) so I missed the usual Pinky rant. (just kidding Pinky, though we were having a good time discussing theory when you jumped in with the "voice of experience" when it wasn't really necessary, I think we're all gear-heads here).

jzr - Them's purdy speakers, not that purdy sounds better, but why ugly-up your S2000? I can't wait for your test results. Hope you don't fry anything.

And you're right-on with the engine mod reference. Here in Atlanta we had 7 guys go to the local dyno a few weeks ago. Guess what? The highest HP was a stock car, the lowest was the car with the most mods (1000's of $ worth). Do you think any of them would have come to that conclusion if they just took turns driving each other's cars? Not likely.

More bass we can measure, tighter bass we cannot. That's why marketing guys use terms like "tighter bass", "sparkling highs", "open mid-range". There is no engineering definition of those terms, so no way to prove or disprove the sellers claims. Strictly a subjective measurement, which is another word for an opinion. Opinions are great, but when I'm trying to form my own, I want some facts to go by too.


[QUOTE]Originally posted by MacGyver
[B]Here's a bit of help with the equations....I've simplified terms already for the cap.