built the 142.5 EBS shiva sub, .. some questions

[zobsky]

built this design yesterday (already had the shiva lying around) as per adire specs (http://www.adireaudio.com/Files/VentedShivaApplications.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

 

[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.

 

[zobsky]

thanks for the reply, .. what i built used the recommended adire port dimensions, ...

you may be right concerning the port being too restrictive

 

[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.

 

[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.

 

[zobsky]

Hi All,

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")

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

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

 

[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

 

[crippledchicken]

Adire DPL 12 port length in shiva 142.5 L box? 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

 

[zobsky]

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

 

[aaroncgi]

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

 

[simon5]

Re: Adire DPL 12 port length in shiva 142.5 L box? DanWiggins

how long should the total port length be to get closer to 16hz tunning instead of the normal 18hz required for the shiva?

If you use normal 4" diameter pipe, you would need a 23 inches long pipe, not feasible unless you do a folded slot port...

 

[crippledchicken]

hi simon, i went ahead and made the port 28" and will try going from there and trim if need be after close listening and break in. i'm glad the port is on the bottom should help conceale any port noises. later on down the road, i plan to get the pr15 to go with the DPL and build a different enclosure. i've heard of pretty good results with that approach. also, plan to get a spl meter later. best reguards, crippledchicken

 

[simon5]

You made the box rectangular to enter a 28" port? Or it will be a bit outside?

 

[crippledchicken]

You made the box rectangular to enter a 28" port? Or it will be a bit outside?

hello again, the box is 21" cubed internal volume the port is flush with bottom with driver next to it. it extends upward then elbows toward back wall with 6" clearence between end of port and back wall with, about 4.5 or 5" clearence between side of port and top of enclousure.

 

[simon5]

With your 28" port, you tuned it to 14,7 Hz, I hope it's a flared port hehe! Don't use more than 150W RMS or overexcursion will be a problem!

It's a very good idea to tune it that low with a DPL12, with your tuning of 14,7 Hz you match room gain well, you'll have a very flat curve. Same curve as if you used a Shiva with a 17 inches port tuned to 18,4 Hz.

Your subwoofer will go deeper, less SPL but deeper.

 

[crippledchicken]

yeah, i know what you mean about the 150 watts. in this small mobile home with a small 100 watt 10" jbl sub it did a good job running about half power so, the 150 should be more than i'll ever use although the amp will be rated at 240 watt, i'll just have plenty of reserve maybe for a cleaner sound. no, it's not flared but, the port velocity i measured in WINISD PRO, didn't show to be real high though. with actual music or HT instead of actual test tones, maybe i won't have any bad port noises. but, if i need i flare for some reason, i'll just glue a toilet collar on port inside he he. i've heard of it being done but, i've sure never tried it before.