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built the 142.5 EBS shiva sub, .. some questions
built the 142.5 EBS shiva sub, .. some questions
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Old 31st December 2004, 08:29 PM   #1
zobsky is offline zobsky  India
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Default built the 142.5 EBS shiva sub, .. some questions

built this design yesterday (already had the shiva lying around) as per adire specs (http://www.adireaudio.com/Files/Vent...plications.PDF) with a 4" x 17" PVC port (12" + 5", as spec'd by the doc, .. vent tuning is theoretically about 17Hz


intended purpose: extreme low freq (< 25Hz) for movies (something that my "bill fitzmaurice" autotuba can't do). i eventually want to run a 3 sub setup (2 autotubas and 1 shiva). currently, the driver fires downward and the port upwards.


subjective impressions: good balenced bass for a ported box, ..not the bumpy bass so often associated with ported designs. not as fast and articulate as the horn loaded autotubas with the 8" MCM driver but goes a tad deeper (which is what i expected)

i haven't had a chance to test it with movies yet but ran a set of since wave test tones 20Hz upwards. Turning the volume up at 20 - 25Hz, .. i notice serious air movement through the port and hear a "whoosh whoosh" noise , i also notice the driver excursions. plugging the port with a towel, the driver excursion is still noticed but the port noise vanishes. ...

is this port noise typical of ported enclosures and it it an issue in normal operation?

is the driver unloading?

thanks
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Old 1st January 2005, 04:42 PM   #2
herm is offline herm  United States
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I ran this setup using UniBox, and it suggested a much larger
vent diameter.

Now, Unibox may be a little conservative, but it appears
that your vent is too narrow.

-herm

P.S. Go with Adire's 5" by 12". If they say it's enough, it is.
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Old 1st January 2005, 04:44 PM   #3
zobsky is offline zobsky  India
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thanks for the reply, .. what i built used the recommended adire port dimensions, ...

you may be right concerning the port being too restrictive
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Old 1st January 2005, 05:04 PM   #4
Ron E is offline Ron E  United States
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One 4" port is pretty marginal for high power use with a shiva. Your location of the port is exacerbating the problem. You could try flaring both ends of the port, that should help quite a bit. Most times, test tones are an order of magnitude more severe than what you will experience in real operation.
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Old 1st January 2005, 10:01 PM   #5
xstephanx is offline xstephanx  Canada
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Test tones ALWAYS give alot more port noise cause its just reproducing a pure wave with i believe -0db reference input(?) Also try putting a reflecting surface 4" above the port, it should minimize noise.
Hope the new sub brings hours of infrabass.
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Old 1st January 2005, 10:24 PM   #6
zobsky is offline zobsky  India
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Hi All,

Quote:
Originally posted by herm
I ran this setup using UniBox, and it suggested a much larger
vent diameter.

Now, Unibox may be a little conservative, but it appears
that your vent is too narrow.

-herm

P.S. Go with Adire's 5" by 12". If they say it's enough, it is.
adire suggests 12" x 4" for their EBS alignment if using their FP-4 flare kit, .otherwise (17 x 4")


Quote:
Originally posted by Ron E
One 4" port is pretty marginal for high power use with a shiva. Your location of the port is exacerbating the problem. You could try flaring both ends of the port, that should help quite a bit. Most times, test tones are an order of magnitude more severe than what you will experience in real operation.
many of the sonotube designs on the web (including the sonotube kit by CSS) use the same port location, .. maybe i'm just being more stressful in my testing, .. regardless, .. i can see why one would prefer a port not facing the driver, .. wonder if i put a short right angle or U elbow just to see if that changes things


Quote:
Originally posted by xstephanx
Test tones ALWAYS give alot more port noise cause its just reproducing a pure wave with i believe -0db reference input(?) Also try putting a reflecting surface 4" above the port, it should minimize noise.
Hope the new sub brings hours of infrabass.
i agree, .. i haven't noticed the port noise that much with music or HT yet, .. except on some electronica (may have been sine waves on that mix, .. or maybe its just that most program material doesn't go that low)


also, . i still have a question whether the driver is unloading at very low frequencies. .. can anyone suggest a simple impedance jig?

thanks
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Old 2nd January 2005, 12:20 AM   #7
DanWiggins is offline DanWiggins  United States
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All our designs assume the use of a flared port. Replace your straight pipe with a flared port and you'll eliminate all your port noise.

Dan Wiggins
Adire Audio
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Old 6th January 2005, 01:08 AM   #8
crippledchicken is offline crippledchicken  United States
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Default Adire DPL 12 port length in shiva 142.5 L box? DanWiggins

Quote:
Originally posted by DanWiggins
All our designs assume the use of a flared port. Replace your straight pipe with a flared port and you'll eliminate all your port noise.

Dan Wiggins
Adire Audio
hi Dan, i built the shiva 142.5 ebs box in advance but then couldn't find a shiva just my luck he he. so i ordered the DPL 12" instead. using schedule 40 pvc pipe with elbow,how long should the total port length be to get closer to 16hz tunning instead of the normal 18hz required for the shiva?
i'm not for sure how to calculate it and if you know how to figure it i would be verry greatful! thanks, crippledchicken

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Old 6th January 2005, 06:41 AM   #9
zobsky is offline zobsky  India
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Quote:
Originally posted by DanWiggins
All our designs assume the use of a flared port. Replace your straight pipe with a flared port and you'll eliminate all your port noise.

Dan Wiggins
Adire Audio
thanks for the response,

.... to clarify, .. do you imply that using a flared port will eliminate port noise even with my current port location (port facing the back of the driver)?

thanks in advance
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Old 6th January 2005, 07:26 AM   #10
aaroncgi is offline aaroncgi  United States
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Default Absolutely.

zobsky,

Flared ports greatly reduce port noise compared to a straight port, regardless of where they are located. Assuming you are using a suitable low pass crossover (4th order, 80 Hz or below), there's no reason to expect problems by having the port directly opposite the driver. Even on full range speakers, the port may be opposite the driver and it doesn't necessarily cause trouble.


Aaron Gilbert
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