posted
Here's the deal. I've noticed that a new trend on the high spl cars/vans seems to build boxes and enclosures with vastly oversized ports; i.e. the port itself is larger than the driver itself. (say a 150 sq. inches woofer and 220+ sq. inches port aera.)
When put in a simulation software (i use Bassbox Pro) a typical 4 cu. ft vented box using a oversized port, no matter what driver i use, tend to be tuned to unsualy high frequency (300/500+ Hz) wich in my book is way too high for any practical purpose.
The only logical anwser i found was to emmulate some kind of horn box.
So i address those question:
1:How do you calculate the port aera related to the frequency/efficiency you wish to obtain in your design or it's a randomly designed hole (wich i doubt) carved on the enclosure with no prior calculations.
2: Does the port is itself smaller at the box and the oversized port tend to be used as a horn. ( Here i want to be as clear and forthcomming as i can be, Imagine a vented box with a modestly sized port (the usuals ones tuned to low frequencies, like 45/55 hertz) and with a second box over this port with the oversized port, just to emmulate this horn-type box)
3: At last, does anyone can suggest any website or reference material on those particular design, or have any particular toughts on those design (experience, random insights, anything else that cross your mind)
Please correct me if anything i said up here is wrong or misinterpreted. Do not hesitate to ask for clarifications if it's not clear.
posted
well not too complicated.... but.. well i will let some of the other more knowledgable people answer this... i dont explain things very good
but in a nutshell... for extreme SPL its mostly trial and error... you cant really use a program to model what will happen at high DBs... not sure how or if horns come into play, but id say not.. um what else.. really big boxes and lots of port area and short ports... i dont see how that equals tunning frequency of 300hz..???
Posts: 1854 | From: freezing in FAIRBANKS ALASKA | Registered: Aug 2000
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posted
If you let a program determine the length of the port for you and the change the port area or box size, you're tuning will change. Bigger ports have lower velocities for the air rushing in-out of them. But you can only take it so far. When you make the port area larger, you have no choice but to make it longer. Usually, much longer. This takes up more space, making the need for a slightly longer port. Whichever program you use, trust it's tuning frequency. It it says 500 Hz, that port will resonate at 500 Hz.
Posts: 768 | From: Ottawa, On, Canada | Registered: May 2000
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