Subwoofer project using a 12" Peerless 835017 (or better) - Page 2 - diyAudio
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Old 15th May 2013, 10:38 PM   #11
shmb is offline shmb  Australia
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Ok, thanks, so it looks like a single 4.5" diameter or more is required.

Looking at the simulations, the ideal tuning frequency would probably be anywhere between 19-22Hz??

Parts Express sells 4" and 6" dia dual flared ports, but 6" port lengths will be impractical. I would need an elbow. (if I can fine one for that size)
Is this an issue with regards to port noise etc?

Any ideas of who else sell these sorts of things?

Thanks.

Last edited by shmb; 15th May 2013 at 10:51 PM.
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Old 16th May 2013, 03:51 AM   #12
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You can resource a PVC tube (construction, other) for loudspeaker ports locally. If using the 4" from PE you can use/test it's max. length of 17".
Precision Port 4" Flared Port Tube Kit 268-352
4" flared speaker ports - DIY Audio & Electronics - StereoNET Australia
Commercial Port Flares
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Old 16th May 2013, 04:01 AM   #13
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You can make also a rectangular flared port with the same wood you are using in one of the sides of the box.
If the port is not directed to you (to your face), you will have less noise problems, only at max SPL.
Only use bends if not enough space for straight ports.
RAM Designs: Step by Step Ported Subwoofer Box Design - YouTube
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Old 16th May 2013, 04:10 PM   #14
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Default long round flared ports

I bought an extra PE 4" port kit and used the couplers along with the tube cut in half to make a pair of 24" long ports
It sounded a little boomy, or maybe had allot of group delay.
And there are L/D limits that supposedly should be followed and the quoted audiophile (Length / Diameter) limit that I have heard is something like 2 or 2-1/2 meaning that a 4" ID port should only be 10" long.
I do not know how much there is to this rule of thumb, but I think my 24" port was too long.
I finally took it out, sealed the boxes, made them into the main woofers and replaced them with proper subs with flared shelf ports.

Dave
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Last edited by Shadydave; 16th May 2013 at 04:14 PM.
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Old 17th May 2013, 01:31 PM   #15
shmb is offline shmb  Australia
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Ok interesting, about the diameter vs length limit.
Maybe someone else could explain if that is or isn't the case???

I think I'd still prefer to stick with the round 'flared on both ends' ports.

Anyway I'm still investigating for now.

Thanks.
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Old 17th May 2013, 01:53 PM   #16
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Quote:
Originally Posted by shmb View Post
Ok interesting, about the diameter vs length limit.
Maybe someone else could explain if that is or isn't the case???

I think I'd still prefer to stick with the round 'flared on both ends' ports.

Anyway I'm still investigating for now.

Thanks.
The 2.5 rule is probably to do with port resonances: simulate a ported box in Hornresp and note the additional peaks and dips >100Hz.

If a port gets too long, you start to get resonances within the pass band of the subwoofer, which can prove interesting to integrate with other speakers

Chris
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Old 17th May 2013, 04:15 PM   #17
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Default Flare shape

One problem with commercial flared ports is they have a spherical radius on their ends.
While this looks good, at higher flows there will be flow separation causing the port to flow less than the nominal (4") diameter.
It would be better to have a flare shaped more like a funnel. with straight sides rather than sides that exponentially curve more and more.
The spherical radius port does work better at lower SPL's, it is when you crank it up and get higher velocities that the flow separation and hence turbulence in the port exit occurs.

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Old 18th May 2013, 01:17 PM   #18
bjorno is offline bjorno  Sweden
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Hi,FYI:
Here is another late suggestion for a Sub using the Peerless-835017 Driver:

b
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Old 21st May 2013, 01:58 AM   #19
shmb is offline shmb  Australia
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That may be a little big.

Anyway, the size/volume is now finalised, I'll end up with about 118-119L with everything fitted except port(s)
The volume of those still need to be subtracted so it depends on what size ports I use.

Looking at all the compromises, it seems I should go for the 4" dual flared port. Precision Port 4" Flared Port Tube Kit 268-352
It would be approx 40cm long. That will reduce the effective volume to about 114-115L.

Now on WinISD from my simulations, it seems that at 175 watts (the drivers RMS rating), port air velocity is about 30-31m/s at around 20Hz with the 4" port. (worst case at 175w)

Is this reasonable and acceptable?

This calculator from earlier in this thread: mh-audio.nl - Home tells me at least 11.5 cm diameter is required.

So will the 4" flared be enough in practice?

Thanks.

Last edited by shmb; 21st May 2013 at 02:07 AM.
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Old 21st May 2013, 04:45 AM   #20
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Originally Posted by shmb View Post
This calculator from earlier in this thread: mh-audio.nl - Home tells me at least 11.5 cm diameter is required.

So will the 4" flared be enough in practice?

Thanks.
You must be an engineer.
Read my post, you can't have max. power at Xmax. This was the suject of discussion in other threads (read SI 18"). You blow the woofer before you get max elongation...

Peerless 835017 XXLS 12"
Nominal Power RMS 120W
http://www.tymphany.com/files/XXLS-P...0Rev%201_0.pdf
2 examples for this project:
a) 115L/21Hz (38.84cm = 15 19⁄64in)
To go to max elongation you would need double the power more close to 300W@3Ohms.
b) For VB = 110.0 L, FB = 20.5 Hz, length (43.34cm = 17 1⁄16in).
You would need Pmin. 308.0 W@3.1 Ohms@20.5 Hz for max elongation (12.3mm/V=31.13 V) so don't worry (be happy) about max power output before you will blow the sub.
note. dB for max. SPL is unachievable by all standards so you will have a relative power off less than half or about that at a percentage of time you have max. volume in your system.
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