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Old 26th March 2011, 10:21 PM   #1
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Default Advantages and disadvantages in the location of the port - bottom speaker

what are the advantages or disadvantages in this case ?
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Old 26th March 2011, 11:44 PM   #2
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room reflection can make it sound booomy.
Some manufacturers make boxes that have woofer facing the dottom, sometimes it can be helpful, many times can sound horrid.

It vastly depends on the room it self to be honest.
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Old 27th March 2011, 01:06 AM   #3
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Quote:
Originally Posted by kappa_ii View Post
what are the advantages or disadvantages in this case ?
Try and remember that a port is a Helmholtz resonator. There should be little or no difference regardless of where you install a port, as long as its flow isn't impeded or changed by nearby boundaries. Also you don't want port placement to allow backwave (midrange frequencies) from the woofer to leak out of the enclosure through the port.

If you have a down firing port, you need to take into consideration the nearest boundary, which is the floor. Floor loading is actually pretty good as long as it is done right.
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Old 27th March 2011, 01:52 AM   #4
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There is a seamless transition between 'BR', and a mass
loaded quarterwave speaker.

In a tall speaker, where e.g. the driver is mounted on the
top and the port is at the lower end, you will get
noticeably different behaviour than calculated for a 'pure'
helmholtz resonator, where it is assumed to have the
(inner) port near the driver and the cabinet's air acting
like an ideal spring.

For common dimensions there is of course some freedom
in port placement, as the driver-port distance is usually
small compared to a quarter wavelength at the tuning
frequency.

Having the (inner) port at pressure maxima of standing
waves in the cabinet, may lead to upper bass/lower
midrange resonances being more audible when radiated
through the port, especially as a typical BR is not
stuffed heavily ...

It is important to know, whether the box will be used
as a subwoofer or as a 2-Way e.g.

To have a modal analysis of the box resonances and
not place the inner port near the pressure maxima of
the lowest modes may be advantageous in case of
a larger band to be reproduced. This is for the inner port.

To have the outer port near the floor e.g. may yield a
little boost in the port's radiation and dependent from
the port's orientation the mass component may increase,
allowing to make the duct a little shorter for the same
tuning.
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Last edited by LineArray; 27th March 2011 at 02:11 AM.
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Old 27th March 2011, 02:13 AM   #5
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Well, I guess it all depends upon whether he is building a bass reflex or a mass loaded quarter wavelength.
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Old 27th March 2011, 08:54 AM   #6
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is for this project
witch 8948A usher driver .
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File Type: jpg port jos1.jpg (142.8 KB, 154 views)
File Type: jpg 1.jpg (89.2 KB, 149 views)
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Old 27th March 2011, 09:01 AM   #7
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Quote:
Originally Posted by kappa_ii View Post
is for this project
witch 8948A usher driver .
That is going to be an ML-TL

dave
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Old 27th March 2011, 09:15 AM   #8
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fb is at 40hz
inside useful volume is 23 L

for now project looks like this
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Old 3rd April 2011, 09:58 PM   #9
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Other opinions, suggestions
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