Need your professional opinions on this....

[Fish Chris]

or better yet would be, your experience with this, and / or straight up scientific facts..... But if SMD wasn't exactly sure, I can't imagine their are very many people who do know about this. In fact, Steve suggested that I ask about this, here on the forum.

So here's the scoop;

You guys have seen my box, which I built with the idea, of being able to add port extensions, for different tuned port frequencies, at will.

Just in case you haven't, here it is again;

Okay now, somewhere way back, I had read something that must have been pretty convincing to me, which basically stated that if you had 2 or more round ports in a box, and these ports were of different lengths, the only effect would be that you would end up with the tuning of the "average length" of all said ports. I remember the example was given, of a vented enclosure, on a slanted face box. Even if the air travel at the top of the vent was 20", and the air travel at the bottom of the vent was 30", you would use 25" for your tuning calculations, and the sound from such a box, would be exactly the same, as a flat faced box, which had a vent length, of 25", at any point.

~~~~~~~~~~~~~~~~~~~~~~~~

Anyway, my calcs show that adding one 18" port extension, should drop my tuning from just under 35hz, to about 32hz. And in the real world, it seems like it does. But the different length ports don't sit well with Steve Steve suggested that I run three port extensions of 6" each, instead of one at 18"..... OR, 3 port extensions at 12", instead of two at 18".

Of course I'd do it, if I knew it would help either my SQ, or SPL's.... and I might have to go on and do it anyway, just for experimentation...

But I'm curious what you guys think.... Or know about this ?

Peace,

Fish

[OrionStang]

Get to testin, man. I want to know, too.

[Robert8252]

When you add more vent ports need to be long. So another words.

1 port 20 inches long will be lower tuning then

2 ports 20 inches long assuming both ports are the smae diameter. to acheive lower tuning would require longer ports. Slot port is the easiest. I actually prefer it over aeroports. Easier to get the port to fit in the box with enough port area.

[Robert8252]

Sorry for the spelling. On my pos Droid. Lol. Let me clear that up a little.

Get torres calculator. Enter box specs and then play with the port. Enter the length and diameter and then change the number of ports to see how that affects tuning. also the least amount of ports you use the better.

[DTS909]

If it sounds good to you go with it call it a day and go fishing

[Ray]

I say......

All the same length and put the flares on.

You are losing big from no flares.

You will have to trim the edge of the flare because of where they are in your box.

I say build another box that can use full size aeros with flares.

Its a low cost change. Wood is cheap

Hell, im sure steve would even help ya, we were just talking about this.

And i can draw up a design if you like.

If steve is gonna help you build it i will do the design for free.

Yes...

Free.

[SPL2K]

The distance the rear wave of the sub travels through the port determines the frequency thats being reinforced and will not change (or average) with multiple ports at different lengths. If you have 3 different lengths then you will be reinforcing 3 different frequencies. It would still work and be beneficial over a sealed box but I think there would be some cancellation issues with the different frequencies around the exits of the ports in close proximity. I say all 3 the same length would be better. Or better yet, 1 large port.

Thats just my guess.

[Fish Chris]

Robert, yes, I did use the Torres calculator to build and tune my box.

Ray and SPL2K, I just finished this box a couple weeks ago, and it's the best sounding box I've ever built, out of the dozen or so I have built in the last 30 years. So I don't see myself scrapping it for a new one any time soon.

However, you have said enough to make me want to go on and chop my two extensions off a little, then complete the third one, at the same length, just to see if it really does make a noticeable difference.

Ray, as far as flared ports go, I have actually made flared 6" ports myself, by heating the edge of 6" PVC, and forcing it down over the top of (of all things ) a bowling ball ! It would take some work, but I could actually flare the end of these port extensions, too. The only reason I didn't, is that all up until recently, the only advantage I ever heard mentioned with flared ports, was that it greatly reduced the chance of port noise.... And I don't have any port noise.

As for increased DB's > Now they tell me ! LOL

Peace,

Fish

[Purplehaze]

The distance the rear wave of the sub travels through the port determines the frequency thats being reinforced and will not change (or average) with multiple ports at different lengths. If you have 3 different lengths then you will be reinforcing 3 different frequencies. It would still work and be beneficial over a sealed box but I think there would be some cancellation issues with the different frequencies around the exits of the ports in close proximity. I say all 3 the same length would be better. Or better yet, 1 large port.

Thats just my guess.

That is exactly what I was thinking too. The different length ports would be allowing different frequencies of tuning? Of course I have no idea, but what he says make perfect sense to me!

[Fish Chris]

SPL2K, I'm certainly not arguing you here, but just out of curiosity, what do you think about the example I gave, of a slanted face enclosure, where the vent has a shorter air travel path at the top, and a longer travel at the bottom ???

Fish