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ok, thanks, that help out alot. I dont know much about the hz and all that stuff for the boxes. I got my 2 kicker 12s in a sealed box in my explorer and they hit down to 25hz and they sound good as they are but will look into a better box later. What would the measurements be if i used both speakers? Also I will go for the optimized box bc I want what sounds the best. Thanks for the help.

EDIT: Also would the 3.2 x 3.2 be a round port or square?
 

Robert_J

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I'm going to disagree with Cees in that there is no such thing as an optimum box. Both Unibox and WinISD will give suggestions but they are not what I consider optimum. Optimum is what meets the designer's goals for the sub. I like extremely low bass. My ported design in post #12 will give you that at the expense of overall SPL. Yes, the response is not as flat but the graphs in both programs are just estimates. Neither take into account room acoustics, subwoofer placement and room gain.

Also, Cees extremely large enclosures will limit you on the amount of input power as well as require the modification of any plate amp that you choose. Both of my designs use the 50w Parts Express power amp as the source. They come standard with a subsonic filter set at around 20hz. Using this amp on his ported design will destroy your driver at mid to high volume the first time you watch an action movie. I don't have time to post graphs but trust me, those Legacy drivers can't take any abuse.
 

well until I have the money for a plate amp I was just going to use a car amp or just the reciver. I have tried just the reciver through the sub output and it pushes it fine. Right now in my room I have two floor standing speakers. They are Omni Audio SA 12.3 but they are not making the bass I want.
 

Robert_J

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A car amp is not a good idea. The AC to DC power supply to properly power it will cost as much as a small plate amp.

If your receiver has a powered sub output, then you don't need a plate amp. What receiver are you using.

What kind of bass do you want? You mentioned the Kickers in your vehicle earlier. Are you wanting car audio style bass? Will you be listening at car audio levels as well? Is this for movies, music or both? Both, what percentage of each?
 

Cees Alons

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Robert,

Well, then I have to disagree with you of course. [/url]

Optimum is what meets the designer's goals for the sub.
OK, but in my book the designer is part of the process. If the designer's goals are lousy, the box meeting those goals is lousy.
But I agree that "optimum" is subjective. My criteria are: pretty straight frequency curve, not too much phase shift and output power where it matters.

I use WinISD indeed. It's a good program, using my kind of criteria. It's well designed and you may want to take a close look at its "hall of fame" (under Help/About) to understand why I believe in it.

I like extremely low bass. My ported design in post #12 will give you that at the expense of overall SPL.

... and a 6dB per octave down almost from 100Hz on. "Your" box will not outperform WinISD's optimum design above 25Hz .And that's at a -10dB level anyway and it also needs the plate-amp to be cranked up between 50Hz and 30Hz, because that's where WinISD's optimum box's overall higher SPL is significant.


Yes, the response is not as flat but the graphs in both programs are just estimates.
which doesn't help to make the curve of the little enclosure any flatter.


Neither take into account room acoustics, subwoofer placement and room gain.
No, and it shouldn't.

Also, Cees extremely large enclosures will limit you on the amount of input power (....)
"Extremely large" is rather subjective. And yes, because the bigger box will have a more efficient system, you will get the desired SPL at a lower input power. Dampening the driver with a much smaller box will only force us to crank the amp up, to get the same sound pressure at our ears. But needing more input power is not the same as rendering a higher yield.


They come standard with a subsonic filter set at around 20hz.
That's nice indeed. However, we must realize that there's not much sound power below 25Hz on a DVD. Also, the filter will add more phase-effects.

Quote:
(...) trust me, those Legacy drivers can't take any abuse.
I admit I don't know these drivers. But 400W car speakers must be able to take some current. Yes, in a bigger box the cones will swing a bit more: but you won't have to turn the volume up so much to get the same sound pressure a more dampened design will produce. If these coils can only move in a so limited way, I can't believe they're rated at a whopping 400W max (200W typical).
But agreed: I have no personal experience with these boys.


David,

Bottom line: I stand by the design I gave above, but it remains your choice.

I'm not particularly in favour of using both speakers, but to help you anyway: a box for two speakers (having the same properties as the WinISD "optimum" for one), would have the following dimensions:

Box tuned at 31.81Hz for 2 speakers: volume = 6.37 cf
Outside dimensions: h x w x d = 38.0" x 24.5" x 15.5"
vent: 5.5" x 5.5" (yes, that's square; a round one would need to have a diameter of 6.4") and 8.4" deep.

You would either need two amplifiers (and make sure both speakers are driven in phase), or one more powerful amplifier. If the amplifier is rated at 2 Ohms, the speakers can be connected in parallel (both + and both - pins together as well as to the amplifier), if the amplifier is 8 Ohms, you'd connect them in series (+ pin of one speaker connected to - pin of the other one, and the two respective free + and - pins each to the amplifier).


Cees
 

Robert_J

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Cees,
The RMS and peak power rating are the most useless spec of a sub when building a sub. That is how much power the voice coil will handle without melting. Most of the time, this is determined with a 1,000 hz sine wave. That's a lot of current without much cone motion. In my designs, it only takes 50w of power at 20 hz to reach 8mm of excursion. Since xmax wasn't given as a parameter I chose 8mm based on experience with that basket/magnet style used on other drivers.

There is a LOT of information that is below 25 hz. In fact with recent movies it is like the sound engineers are trying to add more extreme bass. Go to a few other forums and read the posts about the latest Star Trek movie. Within 24 hours of the release threads with titles like "Star Trek killed my sub" started to pop up. I've seen some waterfall graphs of those scenes and there is a huge amount of energy in the 12 hz to 15 hz range. A lot of people don't realize this because their current sub filters that information out. I don't have a filter on my sub. I've played a 5 hz tone though my dual 15's and it is a very unusual feeling. You can't hear anything except rattles in the room but you can definitely feel the energy in your chest.
 

Cees Alons

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Yes, I know they add those low-frequency noises now. Gives you a rumble.

That's the reason I'm not advocating tuning boxes for relatively small speakers to an extremely low non-audio frequency. Indeed you may need a plate amp then, like you suggested, that has a 20Hz-down filter in place, and although I find that a useful addition, it makes the whole point moot in this thread, because with it you won't get those frequencies out anyway.

In fact, if you super-impose filter characteristics like that over the frequency curve of the 2 cf box, all "advantages" of the curve below 25 Hz, even at the -10 dB level, as compared to the 3.18 cf box, are gone, and all you have left is a lousy -6dB/oct curve, and a box without much bass between 30 and 50 Hz, lacking any musicality.


Cees
 

Robert_J

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But in your ported design tuned to 32hz, even a stock plate amp is not a good idea. The factory subsonic filter of 20hz will still allow a half octave of full power bass below the tuning frequency of the box. The filter will need to be modified to move it to around the 30hz area.

David,
Are you comfortable with de-soldering and replacing resistors on a circuit board? If you decide to choose Cees' ported design, you will need to do this. If you aren't, then I will gladly do this for you as long as you pay shipping. It's the least I can do since we hi-jacked your thread with sub discussion. I'm sure Cees would offer the same but shipping to him will be a little higher.

Speaker building is a great hobby. I started in 1985 and it has been one of my most satisfying. But then again, I love to build things and the math and geometry required keeps me sharp with those skills as well.
 

Well I would like to be able to produce the car like bass but in my room I want to go for quality instead. I already have the car am and a spare computer power suppy is the only reason I am using it for now. I the receiver is not like your thinking. It is a Bookshelf stereo and have a surround sound built in a sub out and it will push them fine. I hooked them up that way but the amp will give me the bass boost and other things.
 

Robert_J

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You will never ever, ever, ever be able to reproduce car audio like bass in your room unless your room is the size of a closet or a phone booth. Cabin gain gives you a huge boost on the bottom end of car audio. Room gain is nice boost but since rooms are much larger than cars, it doesn't help a lot.

I assumed you were using a PC power suppy. How many amps of power can it supply? How many amps of power does your car amp pull at full power?

You should never use bass boost in either home of car audio. Let's say you are pushing 10w of power to your sub. If you use bass boost, to increase the low end by 10db, you now need 100w of power for the extra 10db of output that you wanted.
 

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