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Old 30th October 2009, 06:21 PM   #1
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Default how accurate are the box simulations?

i want to learn about box building simulators like winISD. can anyone verify how accurate these can be or not be?

which is an easy one to learn on for first time users?

i am trying to build a a box for a kicker L7 12" and i keep getting different specs from different people and all i can get across the board from everyone is that they need big boxes. the vehicle i am working on doesnt really have any space limitations and i want the biggest bang for my buck.

so far i have the most faith in these specs from diy member "GM" 6.2 ft^3 tuned around 27-28 Hz with an 8" diameter vent 23-24"
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Old 30th October 2009, 06:48 PM   #2
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Just keep in mind that modeling an accurate in-car response is going to be next to impossible.
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Old 30th October 2009, 07:40 PM   #3
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The accuracy of simuators isn't the reason for variations. The user must define a target response, and the best target is a combination of opinion, physics, reasonable enclosure volume, power handling, etc.

Add to that Glowbug's point, and you'll see why I don't bother with box simulators.

Disclaimer: Not that there's anything wrong with that!
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Old 31st October 2009, 03:27 AM   #4
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so is there anything to be learned or gained from building a virtual box first? building 2x 6.2 cubic foot boxes is a pretty big commitment considering i havent been able to find anyone else use a box this big for a speaker this size.

i asked kicker for their recomendations and his dimensions were completely out to lunch.

im not to sure who to listen to
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Old 31st October 2009, 03:34 AM   #5
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I measure my drivers and use the basic equations published in Speaker Builder many years ago. The boxes have always performed very closely to the predictions, but as said above, radiating into the small volume of a vehicle may throw things off by quite a bit. The newer modeling programs may take a few more things into account, but the fundamental numbers are nothing you can't generate with an Excel spreadsheet or simple basic program. I wouldn't consider building a box for drivers I hadn't measured unless the company had a long history of publishing confirmed accurate specs on their drivers.
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Last edited by Conrad Hoffman; 31st October 2009 at 03:36 AM.
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Old 31st October 2009, 05:09 AM   #6
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Conrad's point is about measuring drivers is well taken. Specs can vary quite a bit from advertised, even 20% variation probably wouldn't be unusual.

Software can be helpful if you aren't accustomed to visualizing a response graph or comfortable with a bit of math or thinking in terms of numbers. But in the end, it's only a fancy calculator. You have to filter the information and decide what's the best compromise for yourself.

I've read many of GM's posts, and he knows what he's doing. The question is: does he know what you're looking for out of these woofers?
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Old 31st October 2009, 02:55 PM   #7
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The question is: does he know what you're looking for out of these woofers?

actually i am so new to this that i dont know which questions to ask yet. its why i was hoping that i could experiment with these box sims first. i have built 2 other boxes that failed miserably and it is time consuming and expensive just building boxes to see if they work.

my point is that to me it would make sense that if you tune a box to handle the power i plan on using and also if i use it to make sure i have the box acting as a brake at a certain frequency range. then i build the box and put it in a car then atleast i should be close

with the specs that kicker gave me, i built that box and GM ran the dimensions and told me that the box is designed to handle aprox 25 watts and believe me the box sounds that way exactly, any volume at all and the speaker starts clipping and the VC former is just smashing into the other parts of the speaker. i dont know what the guy at kicker was smoking but i lost all faith in there tech department, because i built the box exactly as he described

i understand that cabin gain cant be taken into consideration and probably other factors are too much of a variable to model. but there must be some information that can be taken from modeling first then building.
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Old 31st October 2009, 03:45 PM   #8
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It might be worth a look around on car audio sites, to see if anyone has measured the cabin gain of lots of different cars, then pick the car closest to yours and you'll know (roughly) how the sub will react in the environment you'd put it in.

A lot of car audio people swear by the Kicker, but it takes up too much space in a (properly) designed box. It might be better to look around for speakers that go similar bass in a smaller box, then you'd be able to fit more speakers!

What exactly do you want from this sub? High SPL or deep bass? How much power do you plan to put in?

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Old 31st October 2009, 04:48 PM   #9
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Quote:
Originally Posted by scampo77 View Post
i have built 2 other boxes that failed miserably and it is time consuming and expensive just building boxes to see if they work.
That's how we all learned! It encourages you to do exactly what you are doing now. Dig.

Though they didn't do what you wanted, did they do anything well?


Quote:
my point is that to me it would make sense that if you tune a box to handle the power i plan on using and also if i use it to make sure i have the box acting as a brake at a certain frequency range. then i build the box and put it in a car then atleast i should be close
Don't expect the box or port to be a "brake". Speaker cone motion will be at a minimum around port frequency...

But if that is chosen too low for the woofer/box combination -the woofer's output will already be falling off so the port's useful output will be reduced, and the assitance in power handling will not be effective in the woofer's critical lower range before the port begins to help.

If chosen too high for the woofer/box combination -there will be a bump in response accompanied by poor transient behavior, and the woofer will be completely unloaded below the port frequency. If you tune the port to 40Hz, the woofer will have NO power handling at 20Hz.

It's a balancing act, and what sounds great to some sounds like garbage to others.


Quote:
but there must be some information that can be taken from modeling first then building.
Absolutely. If you could measure or estimate what the previous box did and compare that to a simulation, the difference would be the effect of the truck's interior. That effect can be assumed to be in place with any other similar design (woofer placement, port location, large changes to box size in relation to the cabin, etc can make changes).



If you like the sound of GM's large box with the L7's but don't want to give up that much space, you can use 4 of them in isobarik configuration. This will cut the box size in half, but you will have to power 4 of them while only getting output equivalent to a 2 woofer system. Very inefficient and expensive, but performance is good. It may even make more sense to choose different woofers, but it's an option that works well.
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Old 31st October 2009, 08:19 PM   #10
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Quote:
Originally Posted by tsmith1315 View Post
If you like the sound of GM's large box with the L7's but don't want to give up that much space, you can use 4 of them in isobarik configuration.
L7's have isobarik properties built into them. I don't think they are designed to be iso'd.
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