Porting a fullrange enclosure?

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I've done a lot with subs, and know that sub-bass is non-directional, but this is my first fullrange speaker project, and coincidently my first home audio project. I had a little help the other day with my measurements (thanks guys) and am now just having a little trouble with the porting. I was thinking of using a 2.5" port, which WinISD says only needs to be 5.85" long to achieve my desired 35hz tuning.

My only real question is, how can I face the port, does it really matter if it's not facing directly at the user? With a tuning this low, I believe I could get away with downfiring it, or even upfiring the port, but I really just don't want it facing out... something about ports on cabinets just doesn't look right to me. Also with the option of up or downfiring the port is that I can use a larger port, with more length. For example a 4" port, 16.75" long. (from what I've heard, larger ports sound better... but again, my fullrange experience is limited)

Any help would again be greatly appreciated.

(if it matters, the exterior dimensions of the cabinet are 10"w - 30"h - 13" deep with a full double baffle)
 
The placement of your port shouldn't make any difference, although I think I would avoid a downward firing port because the floor might impeed airflow. I think a more accurate description of larger ports is that they are "safer". The larger the port the less likely it is to produce "port noise" (basically a whistling sound caused by a large volume of air moving through the port, usually occuring around the resonance frequency of the enclosure). WinISD actually reports the calculate "port velocity", green numbers being "safe", red numbers meaning there will probably be port noise. Generally speaking I would only recommend using a 2.5" port with speakers 6.5" in diameter and below, but it really depends on the specific driver.
 
Am I perhaps tuning this enclosure too low? I'm working with a Peerless CSX 176 and a Morel MDT39. I also plan on having seperate subs... should I aim for a higher tuning like 40Hz?

My only real concern with the 4" port would be pipe resonance, which I believe wouldn't be a real issue at only 16-18" of length with proper bracing

Also, is there some huge magical difference between premade port tubes and ABS or PVC pipe? I understand flaring the ends to reduce whistle, but is it really necessary to spend $10+ on something vs. using I've already got kicking around the house? (and can get more of for pennies, or less)
 
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I always liked forward facing ports only because there are fewer issues to contend with, but that's me. The port will work fine in any direction as long as the port opennings are unobstructed. That if it's facing downward, it is at least a few inches off the floor, or if it's rearward facing, you place the speaker far enough from the back wall. Common sense prevails here.

BTW, use the length the program gives you or your tuning will be off. However, you can experiment with radiused or flared edges which will change the required port length.
 
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HiggityHank said:
Am I perhaps tuning this enclosure too low? I'm working with a Peerless CSX 176 and a Morel MDT39. I also plan on having seperate subs... should I aim for a higher tuning like 40Hz?

My only real concern with the 4" port would be pipe resonance, which I believe wouldn't be a real issue at only 16-18" of length with proper bracing
I would try to keep the length-to-diameter ratio les than 3 to 1. You might want to try a 3" port.
 
Is the ratio that important ? I mean what if I want to double port my cabinet...I would need 20'' long ports with 2'' opening. Pretty ridiculous for a 5.5 woofer project but I can't get rid of port noise and now I don't want to have any so :smash: Should I brace the port ? It sounds contradictory to me but who knows!

I noticed that smaller diametter port, at higher volumes, just pass the air, as if there was no more sound coming out of the port. I'm not talking of unloaded situation but when air travels too fast in the tube. Is having longest largest or mutiple port will avoid that?
 
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The ratio is important. In general, I try for the largest dimeter that will give me a L-to-D ratio of between 1 and 2 (this is not to say that higher ratios won't work). This will usually keep the air velocity in the port down to an exceptable value. Higher ratios and you run the risk of turning the port into a Helmholtz resonator. Mutiple ports work like a single port of the same area and length with some resistive loading added.
 
m0tion said:
Another quick note, the length of your tube should be measured WITHOUT including the portion of the tube located in the baffle. (ie. you've calculated 5" as your tube length, and you have a 1" thick baffle, your tube needs to be 6" long).


Never heard this one before... Something tells me that would throw off my tuning, unless the entire baffle thickness was used as a flare, which in this case, it won't be. I can't see that 1.5" of extra port would be needed to clear my 1.5" baffle... but I guess I could be wrong.

Experts?
 
I have built a test ML TL for a Fostex FE206E with a downfiring port, I extended the cab below the port and used a slanted panel to deflect the port's output toward the back. Works great. Even better is a tractrix contour cone centered underneath the port to diffuse the output, but a lathe is with a large capacity is almost essential, stacking sections and then using a rasp to file the contour is also plausible but some "artistic" skill is necessary to keep the contour accurate.
Using the Baffle thickness as a flare is a good practice I use in all my front firing port cabinets. I use a ring with the inside rounded glued to the port end inside of the cab as a flare. The driver cutout is great stock for making these, cuts down on waste.
Regards,
Bart G.
 
You guys just scared me...and you still! And BTW, sorry for hijacking the thread turning it on my own for a while :cannotbe:

Using a single 2x9 port I had a match of 13 :(
Using two 2x20 port gave me a match of 03 which is satisfying. The ratio would then be 1:10 right ? Which is not desirable. In your experience, is it worth destroying a nice responce to fit a port ratio?

65Hz to 200Hz at -1dB (MIGHT be compensated by a significant raise a these freq from the woofer)
 
Guss said:
You guys just scared me...and you still! And BTW, sorry for hijacking the thread turning it on my own for a while :cannotbe:

Using a single 2x9 port I had a match of 13 :(
Using two 2x20 port gave me a match of 03 which is satisfying. The ratio would then be 1:10 right ? Which is not desirable. In your experience, is it worth destroying a nice responce to fit a port ratio?

65Hz to 200Hz at -1dB (MIGHT be compensated by a significant raise a these freq from the woofer)

First off, that's Mach, not Match for your ports. The Mach number that WinISD is giving you is, the speed of the air traveling through the port. Generally, a good rule of thumb is to keep the Mach speed under Much .1, although WinISD will still stay green a little higher. As far as your 2x20 port with a Mach speed of 0.03, that will actually be very good. throw that ratio thing out. You don't need it now that your modeling software can tell you the Mach speed of the air in the ports. A Mach speed of 0.03 will ensure that your ports never resonate, as the air speed through the ports will be quite low. In fact, you will barely be able to feel the air coming out of them at that speed.

My current speakers use 2 3"x9" ports, and the Mach number I got was 0.03. I can only feel the air moving through them during VERY loud LF passages. I hope this helps.

Cheers,
Zach
 
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usekgb said:
...throw that ratio thing out. You don't need it now that your modeling software can tell you the Mach speed of the air in the ports. A Mach speed of 0.03 will ensure that your ports never resonate, as the air speed through the ports will be quite low. In fact, you will barely be able to feel the air coming out of them at that speed.

Cheers,
Zach
You can through it out the "ratio thing" if you wish, it's my preference and Small's recommendation. The air speed in the port has nearly zero to do with the Helmholtz resonate frequency of the port. The Helmholtz resonance of the port is a factor of the length of the port and to a lessor degree, the diameter.
 
Sorry Rod.....I don't mean to offend. But, with some of the newer sofware models, it isn't really a strict rule anymore. It is a good idea to keep the ratio smaller, but I think Guss's 2 2x20" ports should work just fine. Personally, I would try to use a 3" port as you suggested earlier. 2" ports just make me nervous.

Cheers,
Zach
 
mOtion if there was a Nobel prize for missinformation you should have it. Y.ou must include the baffle thickness in the length of the tube. If you have a 5" thick baffle you just make a hole. A 4" and you make the tube 1". What counts is the air volume in the tube. Don´t post if you don´t know.
 
roddyama said:

You can through it out the "ratio thing" if you wish, it's my preference and Small's recommendation. The air speed in the port has nearly zero to do with the Helmholtz resonate frequency of the port. The Helmholtz resonance of the port is a factor of the length of the port and to a lessor degree, the diameter.


Yeah actually I know about the winsid match the speed of air and resonance blablabla. When you mentionned Helmholtz I was affraid reproducing it with very long tubes, anyway I'll see... I'll flare both ends :smash:

Thanks

3" port as you suggested earlier. 2" ports just make me nervous.

Well I'd need a 23''long tube for a single one to get a match ( winsid ) of 6. I had the pipe bought long time ago and I didn't want to waste much money, just another way saving for the drivers.
 
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