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Old 18th April 2006, 04:11 PM   #1
LEESTER is offline LEESTER  United States
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Default multiduct subwoofer enclosure

Would there be any benefit from designing a multiple woofer / chamber box, tuning each chamber to a different vented frequncy? for a car enviroment ?
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Old 18th April 2006, 04:40 PM   #2
Eva is offline Eva  Spain
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As a vent introduces a 180 degree phase step in the phase versus frequency response, having several systems together tuned to different frequencies produces partial SPL cancellation. Same happens when mixing vented and sealed.
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Old 18th April 2006, 04:47 PM   #3
LEESTER is offline LEESTER  United States
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Quote:
Originally posted by Eva
As a vent introduces a 180 degree phase step in the phase versus frequency response, having several systems together tuned to different frequencies produces partial SPL cancellation. Same happens when mixing vented and sealed.
I can understand the phase shift, but the cancelling each is over my head. if all the drivers and ports were pointing in the same direction, would there be any way of compensating. I'm currently running an infinite baffle type set-up, with 4 x 8" drivers. would it require more power or less ?
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Old 18th April 2006, 05:12 PM   #4
Eva is offline Eva  Spain
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The phase step is introduced at different frequencies depending on the tuning of the vents. Also, cancellation or poor summing happens when you put together several systems that don't have the same phase response (you can imagine it as several horses pulling a stone block through ropes in different angles, the more dissimilar the angles the more energy wasted).

Which is the Qts of your drivers? You can probably gain some LF efficiency just by going into sealed boxes of the right volume.
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Old 18th April 2006, 05:19 PM   #5
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Staggered tuning as you propose can work if implemented properly, but often the result is just a watered down effect of doing it correctly in the first place.

In a car environment and assuming you are meaning a sub-woofer I would say just use a normal vented, or sealed box.
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Old 18th April 2006, 05:46 PM   #6
LEESTER is offline LEESTER  United States
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originally i planned for a sealed box, some installation issues lead me to an infinite baffle type box, poor planning ! Now i'm considering rebuilding a box to maximize sound quality results versus the rush job i did before.

See car and sub box @
car pics
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Old 18th April 2006, 06:10 PM   #7
Eva is offline Eva  Spain
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You did a very clever work by leading the radiation of the speakers directly to the cabin. The remaining work is just to prevent them to radiate into the hatchback, and that will make a *great* improvement.

You already have the front chambers of a 4-th order bandpass system, and you can tune it by changing the size and the shape of the openings to the cabin (note that all should be the exact same size and shape, also, you have left these openings free, haven't you???). An ideal tuning should be around 105Hz (you can use a signal generator and feel the cone with a finger to check this, minimum feeling of "vibration" is achieved at the tuning frequency, it may be hard to detect if you are not used to it, disable any lowpass or eq to do that test). The only remaning bit are sealed or reflex back chambers of suitable volume (tune them in the 35Hz range if you ever go for reflex).

Also, if you decide to rebuild the box, try to avoid parallel walls as that will produce cleaner midbass output and will allow to cross the "rear bass system" higher and get more "punch" without actually perceiving anything coming from behind. Note that such a bandpass system is already self filtering, so it may ask for a low-pass as high as 250Hz when properly tuned.
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Old 18th April 2006, 06:24 PM   #8
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ok, you lost me again, but if i'm understanding this right, i should minimize the amount of air flowing through the grill between the speaker chamber and the cabin. right now the opening is very close to the and designed to be the same as the displacement of the driver cone. so air flow is not restricted, but not helped either. You can see how the original box was a sealed wedge type, and then the top ripped off. the trunk portion is also sealed off from the cabin. and this car is a convertible with the top folding on top smothering the opening. ( i turn down the sub when the top is down). given the limited parameters what would the best type of enclosure be, to maximize sound quality ?
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Old 18th April 2006, 07:00 PM   #9
Eva is offline Eva  Spain
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I think that you misunderstood me. The drivers should radiate into the cabin through that opening in the ceiling of the enclosure and in the back of the cabin that some of your pictures show, nothing should restrict air flow between the drivers and the cabin (you should seal the borders of that opening to prevent any sound from escaping to the hatchback, though).

It's in the hatchback space where additional either sealed or reflex-to-the-cabin enclosures should be added.
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Old 18th April 2006, 08:45 PM   #10
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is your car a hatchback or does it have a normal trunk?

If it's a trunk, the best way to do sub bass in a car is free air period...you may loose a Db or two, but the low end ext. you get along with the seamless ability to be able to blend it with your front stage is why if aplicable, will always be the best way to go... also..there will never be any reason why you should ever cross a sub any higher than 100Hz...in fact..if your doing a 2way look to have an xover point in the 60-50Hz range and even lower if doing a 3way..the whole point of car audio is to have as close to a live performance as possible......which means having as much of the freq range infront of you...which n turns means having the sub play as small as a freq range as possible..
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