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Old 13th December 2001, 03:29 AM   #1
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hey everybody,
im brand new here im 20 yrs old a go to UTexas in austin
my car was recently robbed and i have a 12" sub in a q-logic box was wondering how i can convert my car audio into home audio for my TV mostly....i am an educated person and i learn well after i am taught but i am not sure exactly what i need to know to do this
all i do know is that i need an ohm converter bc my sub runs at 4 and homeaudio is at 8, but am i converting TV to 4 or sub to 8
help me oh wise ones or tell me where to get help
thanks!
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Old 13th December 2001, 03:46 AM   #2
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I can simplify your 'wall of worry' by a notch.
You won't need an 'ohm converter.' A 4 ohm load is no problem for most home stereo gear. There's no standard, per se, regarding 4 or 8 ohms. There are plenty of examples of 4 ohm speakers in home stuff.
Also, there's no real difference in requirements between stereo and AV/TV/HT (whatever you like to call it), although some people will try to tell you that there are. A good speaker is a good speaker, regardless of what gets played through it.
Car audio, however, is a horse of a different color.
Hooking a car sub to a TV will give you sound, but not necessarily flat response. They're frequently designed for volume rather than finesse. The ones that are of better quality are generally set to deliver optimum response in a tiny space, i.e. your car--not in a room.
Possible options:
--Bring the sub in, hook it up, and live with it as is
--Take the driver out, get the Thiele-Small parameters, design a new box, and see if you like the results
--Buy a new sub, and continue to use your car sub in your car

Grey
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Old 13th December 2001, 04:59 AM   #3
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thanks grey !! but i have a prob still...did u happen to read my profile??! lol
you said
"Take the driver out, get the Thiele-Small parameters, design a new box"
what part is the driver? and what is the thiele-small parameter? sorr y for stupid ?s

thanks!
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Old 13th December 2001, 05:10 AM   #4
JoeBob is offline JoeBob  Canada
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The driver is what most people would just call "speaker", you know the voice coil, cone, etc etc etc. The Thiele-Small parameters are the Qts, Qms, Vas, Fs, SPL and many more. If you bought your sub seperate from your car more then likely it came with a data-sheet which will most likely contain the Thiele-Small parameters, if not try going to the web page of the driver makers. Worst comes to worst, post the name/brand/model of your sub driver here and someone might be able to help you if it's a well known one. Or try asking where your purchased it. You can derive the Thiele-Small parameters yourself, but it requires alot of messing around and isn't worth it if you do as I said (I learned this the hard way).

You use the Thiele-Small parameters to help design an enclosure for your driver, some drivers are best suited for different enclosures (vented, ported, etc). You may also want to sacrifice the lower sounds in favour of a smaller box, maybe for space reasons or size. Try getting WinISD and the Thiele-Small parameters of your driver, from there you can get an idea of what would would be involved in creating the enclosure. Hope that clarifies a couple things at least.
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Old 13th December 2001, 05:15 AM   #5
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yes yes very good info i assumed most of that but wasnt sure
also what do i need between the sub and tv do i need an amp? crossover etc...i have nothing but the sub and tv at the moment
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Old 13th December 2001, 05:26 AM   #6
JoeBob is offline JoeBob  Canada
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Yes, you will need an amp to power that sub. And a crossover would be a good idea as well. Am I correct to assume that when you say you'll use it with you're TV you don't have a stereo or Home-Theater system hooked up to your television? If so volume control might be akward (everytime you change the TV volume, you also go and change the sub volume to the apropriate setting). A sub definately works best when coupled with a set of stereo speakers (or HT), on it's own, it's less usefull.

If you're hellbent on using your sub with your TV's speakers then the easiest way to sincronise the volume adjustments would be to set up an IR controled volume on your sub amp and have it be able to recieve from your TV remote, up tv volume and up sub volume simultaneously. This would require some fine tuning, but would be easier then directly siring it up to the cuirtry in your TV (as well as not voiding any warrantees). Although there are probably others with better ideas then mine (best would be not to use a sub without a stereo system).

If I was wrong to understand that you don't have a stereo system set up, I apologise for waisting your time...
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Old 13th December 2001, 05:58 AM   #7
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Okay, it goes like this...
A speaker is a finished box that makes noise, complete with all the pieces-parts.
The driver is the actual dingus that moves back and forth, and makes the music, usually round.
Somewhere in this whole process, there's also a crossover, which is the traffic cop who sends low frequencies to the woofer and high freqencies to the tweeter, etc. Since this will quickly spin off into a discussion of active and passive crossovers, we'll leave that until later.
If...and I say if...you choose to take the driver and build a new cabinet for it (thus making a new speaker), you'll need to find out some basic things about the driver (the Thiele-Small parameters).
Take a ruler. Hold it to the top of a table with the majority of the ruler out in the air. Thump the end. Booooing! It has a natural resonant frequency. Move the ruler so that only half is sticking out into space. Thump it again. A higher frequency.
Every mechanical system has a natural resonant frequency. (We could also throw in that they are internally damped to greater or lesser degrees, but we'll leave that for later, too.)
Your driver has a resonant frequency. It you were to thump the cone, it would resonate. For various reasons, this is a pretty clumsy way to determine the resonant frequency of the driver, but in principle it would work.
There are a number of nice, useful little numbers that describe the behavior of your driver (amongst them, the resonant frequency). Yes, you can determine them yourself, but it's a pain. Much easier to look them up.
Back 25 years or so ago, two fellas named Thiele & Small figured out that there are optimal combinations of these numbers with the cabinet size, depending on what you're trying to do.
So...if you choose the new box option, you'll need to pull the driver out of the existing cabinet (I'm using 'box' and 'cabinet' interchangably, here--don't panic) and look it over. See who made the critter. What model it is. Then, armed with this information, you go cruising for the Thiele-Small parameters (the nifty little numbers) on the web, or call the company, or whatever floats your boat. One way or another, you're going to need those numbers.
Yes, there are other ways to approach speaker design. You can do extensive computer modelling. You can cut and try. You can pay someone else to do it. You can...huh? Not interested. Right. Those avenues are for those who have time and/or money. You want something a little more here-and-now.
So we're back to the Thiele-Small stuff. Everything that's practical from your viewpoint will depend on getting those numbers.
Once you've got them, you plug them into a computer program (there are websites that have it available as a downloadable program and others that solve the math right on your screen). You will have, realistically, one choice to make: Ported or Sealed.
A ported cabinet is one with a hole in it; a sealed one has no holes. People get just as hung up over this as they do talking about Fords vs. Chevys. Fooey! The Thiele-Small numbers contain, hidden within them, stong hints as to which kind of cabinet you should build. You can ignore these hints and build the other kind of cabinet, but you won't necessarily be pleased with the results.
You mission: Pull out the driver. Find the T-S numbers. If you want to build a new cabinet, that is.

Grey

P.S.: There are numerous books on this kind of thing. There are threads here with lotsa recommendations from various people for this book or that. I'll stay out of it. It's too much like religion. But if you want to read books, they're out there.
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