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Old 21st March 2002, 03:19 PM   #21
Wizard of Kelts
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Join Date: Sep 2001
Location: Connecticut, The Nutmeg State
A couple of more things. Parts Express website has a Titanic 10 Mk II White Paper. In that White Paper, they recommend a port size of 3". This is for an unflared port size. Flared ports give better performance, that is why people bother with them. If the manufacturer says the unflared is acceptable, I would think that a flared 3" port gives you an extra margin of safety.

I personally have never used flared ports, so I could not tell you absolutely how to fit them over 3" PVC pipe. Madisound sells them, and they have a tech line. So you might want to give them a holler just to make sure. From the picture, it looks like a straightforward fit. You might want to put a brace on the interior of the box to anchor the port inside. You might find a muffler clamp handy for this.

The White Paper also says that the Titanic 10 can be used in a downward firing sub. It says the suspension can handle it. Myself, I don't like the idea, since you are putting an extra weight on the suspension for every minute of every day. Seems to me, sooner or later that is bound to take it's toll. But I am not an engineer, and the people at Parts Express are, and they say, "Go ahead".

Also on the White Paper, Parts Express provides a chart of the Titanic 10 Mk II's free air, (unenclosed), response. Subwoofer crossovers routinely go up to perhaps 200 Hz. Not this one. It has a natural 6 dB/octave rolloff after 80 Hz. An interesting point is that if you wanted to hook this up on a passive crossover, (which I am sure you are not), all you would have to do would be to add a choke in series to get a 12 dB/octave filter. Anyway, I enclose the response graph. Boy, they really DID intend this thing only for subwoofer use!

Let us know what you decide size-wise and otherwise. Good luck!!
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File Type: jpg titan 10 pdf 2.jpg (73.9 KB, 258 views)
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Old 21st March 2002, 03:54 PM   #22
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Join Date: Nov 2001
Location: Virginia USA
Kelticwizard

2 foot size looks like just the ticket. I am going to post a question to Parts Express about the 3 inch ports. Unibox predicts the air speed going way over their .08 threshold starting at about 29 Hz and going straight up from there. I would hate to have this puppy start whistling at every crescendo - but if I could use a 3 incher, then by coincidence the Madisound flare is almost exactly the correct length. I'll let you know what they say.

adios
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Old 23rd March 2002, 01:07 PM   #23
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Join Date: Nov 2001
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Contacted PE about the 3'' VS 4'' ports and they replied more or less: "Gee I guess 4 would be better but then it gets too long...."

However I did find an interesting article by Dick Pierce from Speaker Builder posted on the Adire site. It was mostly about when ports are too BIG but near the end he addresses the too small question:

"At the other end of the limit-consideration of the minimum diameter-I suggest that things are not as neat and tidy as some of the literature might suggest. Usually, as mentioned, the criteria used is to limit the particle velocity to some small fraction of the speed of sound to limit potential nonlinear motion. However, I don't recall either a rigid theoretical study nor careful measurements confirming the existence and magnitude of these suggested effects.
Further, the maximum particle velocity will occur for a given SPL only at the Helmholtz resonance Fb, and is reduced on either side of that. It is at Fb, remember, where the port is producing most of the system's acoustical output, and the output from the driver is at a minimum. Outside of the range of Fb, more and more of the system's output is from the woofer, and less from the port. Rest assured that the nonlinear behavior of even the best woofers is far worse than all but the tiniest of ports at the kinds of sound pressure levels where the port velocity might be an issue."

If I read this correctly he's saying don't sweat it about small ports unless they are really small and besides no one has done a real study of port air mach speeds anyway.

Also their is a thread here about port sizing and someone makes the point that when ports are too long the acoustic mass of the air in the port takes on a life of its own causing (phase?) problems.

So when is the port size too small and what is a 'chuff' anyhow???

regards
peter
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Old 23rd March 2002, 04:32 PM   #24
Wizard of Kelts
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Javaman:

"Chuffing" is the sound of air coming out of a port that is too small, but not so small as to manufacture whistling. If the woofer is big enough, and the port small enough, I have read that the port acoustically closes down completely. It has to be pretty small to do that, though.

Much of what was written in your quote makes sense. Since I am not engineer, I did not want to contradict a simulation program, but I WAS wondering how, if high air velocity is caused by trying to squeeze a large amount of air through a port, the velocity of air could rise as the output of air coming through the port is falling-which it certainly does in a properly tuned box as you move away from the tuning frequency.

For this reason, I like to go by "rules of thumb" and general judgment. For most 10 inchers, a 3 inch port works fine, for 15 inchers, go to a 4 inch port. The Titanic 10s move as much air as many a "long throw" 15 incher, however, so the larger port would be indicated. I figured the flared 3 inch port would approximate a 4 inch port, but I have no evidence this is so. Various audio reviews have stated that systems that use flared ports exhibit less port noise than you would expect from a port of a given size, I know that much. Thomas W, in his 6 cu ft enclosure for a Blueprint 1503-a driver with a 2 inch front-to-back excursion-said to use a flared 6 inch ports or unflared 8 inch port, which would tend to indicate an equivalence of sorts. So the flares must actually work.

One possibility is, since the port can be anywhere on the box, put the port pointing toward the wall and down to the floor. Since the unwanted noise is higher in frequency than the wanted port output, by the time it gets done bouncing around the walls, absorbed by any caprpeting and comes to the listener, it will be reduced in volume. The higher the frequency, the more it gets reduced by bending and stuffing material, such as rugs.

After all this, would you still feel more comfortable with a 4" port? Okay, the volume of the 3" port of 17.5" length, (what is required to tune a 2 cu ft box to 22 Hz), is 1/13th of a cubic foot-virtually negligible. The volume of a 4" port of 32" length is .23 cu ft. Not entirely negligible.

At 22 or 23 Hz, instead of being 3 dB down, the output will be 4.5 dB down. It is up to you to decide if that is acceptable. Personally, I don't think that is so bad. However, if you don't like it, you can:

A) Retune to 24 or 25 Hz-you will be 3dB down there)

B) Compensate for the difference in the design. It won't take much. If your box was going to have internal-not outside- measurements of 12" square by 24" high, then the new box will have internal measurements of 13" square by 24" high. Is this acceptable?

One more thing. We have been playing with numbers on this thread as if they written in stone. Take 1.5 dB here, add 2 dB there, etc. These are really just general guides. Even good quality manufactuers sometimes exagerrate the specs a little. It has been my experience that if you use good quality manufacturers and build a good strong box, the yield should be somewhere in the ballpark. I can't gurantee anything. To which I would add that the space occupied by the speaker itself is usually negligible, but might not be in this case-the Titanic looks big. But I still think you are going to be happy at the bass you get coming out of this box.
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