posted
WOW ! What a refresher course. From what I understand of this string which started out trying to explain the difference between reactive and resistive loads,(which seems to be a topic often discussed on the forum) I believe the idea is to explain to some that spec sheets and real world are two completely different issues. There is certainly a lot of good information, such as explaining that current (I) is a by-product of voltage and resistance. And great questions, some of which are well over my head. As for real world testing I would say, only your ear can tell. ELI rules I like that
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E.C. Wuz here
[This message has been edited by Eli47 (edited 08-03-2001).]
Posts: 1057 | From: Vancouver, British Columbia, Canada 'eh | Registered: May 1999
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posted
i talked to my circuits II instructor last friday about using caps to correct the power factor in my application. we got some brand new O-scopes on the lab and i think he's gonna let me use one to find my impedance angles and stuff in my car if he does i'll definitely look into trying to correct the power factor.
Mr. Dank...could you email me whatever info you have on this? i think you emailed me some stuff a long time back...mostly interesting in which setups would benefit the most (you mentioned one whose SPL peaks half way up the second impedance spike) and the like. phatcow2@hotmail.com
thanks!
-------------------- "Those who give up liberty for the sake of security deserve neither liberty nor security" - Benjamin Franklin
DiRtY SoUtH DEAF SqUaD
Elemental Designs
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posted
That would be cool if you can use those scopes. Im trying to get one too.
Basically from what I know, the inductance is highest half way up the second peak on the side next to tuning. so this is where a cap could correct it the most. As soon as I have time Im gonna look into building an impedance matching network with hopefullly just caps and inductors and see If it can be corrected further than just with a cap. hopefully I will have a scope soon.
Posts: 1259 | From: Fullerton. CA ,USA | Registered: Oct 1999
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-------------------- "Those who give up liberty for the sake of security deserve neither liberty nor security" - Benjamin Franklin
DiRtY SoUtH DEAF SqUaD
Elemental Designs
To cheat is to admit defeat
--------------------------------- Loud...it's when you can see the ground move, it's when you have to force yourself to breath, it's when the rest of the world ceases to exist. Posts: 4136 | From: Lafayette, LA | Registered: Sep 1999
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posted
damn...and here i thought i was gonna get into a spiritual discussion on impedance.. ...now i can see what i dropped Engineering...i lack the attention span for it...it's interesting...and that was all quite amazing, but...not sumpin' i can do all the time...good discussion though...
-------------------- Linux Airline Disgruntled employees of all the other OS airlines decide to start their own airline. They build the planes, ticket counters, and pave the runways themselves. They charge a small fee to cover the cost of printing the ticket, but you can also download and print the ticket yourself. When you board the plane, you are given a seat, four bolts, a wrench and a copy of the seat-HOWTO.html. Once settled, the fully adjustable seat is very comfortable, the plane leaves and arrives on time without a single problem, the in-flight meal is wonderful. You try to tell customers of the other airlines about the great trip, but all they can say is, "You had to do what with the seat?" Posts: 2956 | From: Tinley Park | Registered: May 2000
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posted
What you guys are talking about is exactly what a zobel network is for. It compensates for the inductance of the speaker by using a capacitor. As RC said, this specific approach is only vaild far above FS. and is used very often in midrange drivers to counteract the impedance rise at higher frequencies so the amp percieves a purely resistive load. That said, nearly anything in electronics is possible. So, leveling out your entire impedance curve is not impossible. There are three major "capacitances" that affect loudspeaker impedance, and 4 major "inductances." The capacitances come from the acoustic compliance of the air load impedance on the front of the woofer and the back of the woofer, in addition to the mechanical compliance of the suspension. The inductances come from the acoustic mass of the air load impedance on the front and back of the cone, the mechanical mass of the moving parts, and the voice coil inductance.
I think this means you are going to need a 3rd order(or would it be 6th?) filter. There has been so much research into filter theory that I dont think they are allowing PhD research on it anymore, so old IEEE journals might be a good source of info. The problem arises when you realize that ambient air temperature, pressure, and a whole bunch of other stuff is going to change the air load impedances, and then throw your precious filter out of wack, making matters worse. A variable filter and some sort of constant monitoring system could be designed. The major adverse affect being immediate destruction of your 1000 dollar amplifier if the temperature shifts and you end up with a partly capacitive load impedance. Output transistors, and resistors are easily overloaded and blown from the oscillations a capacitive load can impose on an amplifier that is not specifically designed to cope with such loads(Read: Car Audio where Electrostatic speakers are not considered in the design process).
In an application note I read about a texas instruments class D amplifier solution, they stated that class D amplifiers are much more immune to bad power factors than A, and AB amps. I don't know if this is true or not, but the guy who wrote the article probably knows more than I do. I am not sure how well class D amps are suited to driving capacitive loads, and I wouldn't want to find out with any amp I owned.
jt
Posts: 56 | From: atlanta | Registered: Nov 2000
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