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Old 25th July 2009, 03:01 PM   #1
mr ed is offline mr ed  United States
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Default Ported box volume question

I will apologize up front for fishing a little here, but...

With a ported box of smaller than optimal size for the driver, what is the typical result?

Thanks
Ed
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Old 25th July 2009, 03:04 PM   #2
AndrewT is online now AndrewT  Scotland
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one note bass boom.
Listen to spoken male voice and hear just how unrealistic it can be.

Very non High Fidelity.
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Old 25th July 2009, 03:56 PM   #3
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It all depends on degree. one could write a few pages about this, actually.
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Old 25th July 2009, 04:27 PM   #4
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As said above, it varies by degree.

If your box is way too small, you will get a big bump in the response, the smaller the box, the higher the bump. If the box is only slightly too small, the bump will be one or two decibels, which isn't too bad.

An example of manufacturers using this to create "better" sound is this:

A bump around 40Hz will improve the "kick" of a bass drum, 60-100Hz will create the more disco style "thud thud thud" which occurs in the dance/club music.

Personally, I prefer sealed boxes, as they are so much easier to make and use, and the driver's excursion is very predictable.

Chris
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Old 26th July 2009, 08:30 PM   #5
mr ed is offline mr ed  United States
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Thanks for the input guys I did my math wrong and the box in only slightly under size, but it is a large box, with a 18" driver.
Now from there, what about driver to floor distance, and also port location?

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Ed
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Old 27th July 2009, 08:37 AM   #6
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Front ported is easiest to position (no worries about blocking it).

Subs are generally quite close to the floor, and there's a really good reason for that which I can't remember.

What kind of set up are you going for? PA or home-use?
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Old 27th July 2009, 10:04 AM   #7
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the closer to a boundary the lower the delay of the reflection. It sounds like two in-phase waves.
It approximates to a 2Pi loading when tight against one boundary.
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Old 27th July 2009, 06:35 PM   #8
mr ed is offline mr ed  United States
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Quote:
Originally posted by chris661

What kind of set up are you going for? PA or home-use? [/B]
Chris
Home system, using two dayton 18s I got used for a super cheep price, so I thought I would work work them as eventual bass bins for a front horn full range from maybe 200 hz or 250hz up for the horns.

Thanks for help so far to all reply's!

Ed
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Old 27th July 2009, 07:59 PM   #9
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Of more importance is the horn/woofer vertical spacing than woofer/floor spacing, so working backwards from the desired 'FR' driver height makes sense to me.

Conventional theory dictates the vent(s) be as close as practical to the driver(s) due to its relatively high mid-bass/mids BW output, but this assumes a ~uniform particle density within the cab (golden or acoustic ratio dims) in its pass-band, so for high aspect ratio cabs it's better to take advantage of any pipe loading to increase vent damping, ergo near/at the floor placement is desirable.

GM
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Old 28th July 2009, 06:03 PM   #10
mr ed is offline mr ed  United States
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GM

As I understand your reply, I should keep the bass bin short enough to mount the mid/wide range horn above and keep the driver close to listening height.

I should place the bass driver up off the floor, maybe mid way or above and the ports close to the floor.

The cabinets they came with were made fairly close to the right volume but i plan to build new cabs to optimize things.

Thanks
Ed
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