Ported box volume question

mr ed · 25th July 2009, 02:01 PM

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

AndrewT · 25th July 2009, 02:04 PM

one note bass boom.
Listen to spoken male voice and hear just how unrealistic it can be.

Very non High Fidelity.

Ron E · 25th July 2009, 02:56 PM

It all depends on degree. one could write a few pages about this, actually.

chris661 · 25th July 2009, 03:27 PM

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

mr ed · 26th July 2009, 07:30 PM

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?

Cheers
Ed

chris661 · 27th July 2009, 07:37 AM

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?

AndrewT · 27th July 2009, 09:04 AM

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.

mr ed · 27th July 2009, 05:35 PM

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

GM · 27th July 2009, 06:59 PM

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

mr ed · 28th July 2009, 05:03 PM

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

25th July 2009, 02:01 PM	#1
mr ed diyAudio Member Join Date: Jan 2009 Location: austin tx	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 __________________ currently watching electrons party under glass

25th July 2009, 02:04 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	one note bass boom. Listen to spoken male voice and hear just how unrealistic it can be. Very non High Fidelity. __________________ regards Andrew T.

25th July 2009, 02:56 PM	#3
Ron E diyAudio Member Join Date: Jun 2002 Location: USA, MN	It all depends on degree. one could write a few pages about this, actually. __________________ Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan Science is a way of thinking much more than it is a body of knowledge. --Carl Sagan

25th July 2009, 03:27 PM	#4
chris661 diyAudio Member Join Date: Feb 2008 Location: Lancashire Blog Entries: 7	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 __________________ "Throwing parts at a failure is like throwing sponges at a rainstorm." - Enzo My setup: http://www.diyaudio.com/forums/multi...tang-band.html

26th July 2009, 07:30 PM	#5
mr ed diyAudio Member Join Date: Jan 2009 Location: austin tx	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? Cheers Ed __________________ currently watching electrons party under glass


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27th July 2009, 07:37 AM	#6
chris661 diyAudio Member Join Date: Feb 2008 Location: Lancashire Blog Entries: 7	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? __________________ "Throwing parts at a failure is like throwing sponges at a rainstorm." - Enzo My setup: http://www.diyaudio.com/forums/multi...tang-band.html

27th July 2009, 09:04 AM	#7
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	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. __________________ regards Andrew T.

27th July 2009, 06:59 PM	#9
GM diyAudio Member Join Date: Jun 2003 Location: Chamblee, Ga.	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 __________________ Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.

28th July 2009, 05:03 PM	#10
mr ed diyAudio Member Join Date: Jan 2009 Location: austin tx	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 __________________ currently watching electrons party under glass

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