posted
Yeah that was sort of good reading, lot's of good information and theory. Sort of reminds me of a cartoon on my page. I tried to copy it here but was unsuccessful, sorry.
[This message has been edited by Eli47 (edited 07-15-2001).]
Posts: 1057 | From: Vancouver, British Columbia, Canada 'eh | Registered: May 1999
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quote:Originally posted by Eli47: Yeah that was sort of good reading, lot's of good information and theory. Sort of reminds me of a cartoon on my page. I tried to copy it here but was unsuccessful, sorry.
[This message has been edited by Dante (edited 07-15-2001).]
Posts: 1408 | From: Stacyville, IA, USA | Registered: Jan 2000
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posted
I noticed a couple of mistakes in people's posts... so I'll try to stop the spread of some false information...
the tuning frequency of a ported enclosure is not going to be the loudest frequency in a ported SPL enclosure. The loudest frequency(not taking in account vehicle resonances... in other words, free air) will be where the port and subwoofer are closest to being in phase.
And... don't think of a port working because the back wave of the sub reflects off the inside of the box, and then goes out the port... If this "reflection" is what makes the sound from the port, then wouldn't the depth of the enclosure be an important factor when tuning enclosures? Nope. Also, the subwoofer's and port's phase relationship will vary depending on frequency. The closer they are to being in phase, the more output you will get out of the enclosure. If you try to picture how the bass is produced from the port you'll probably just give yourself a headaque. Physics is complicated. I like Bob Carver's anology..... get a slinky. Hold the slinky in air, dangling. Think of your hand as the woofer cone. Move your hand down. This represents, let's say, the subwoofer moving "inwards", into the box. BUT, when you move your hand(and slinky) down, you would think the bottom of the slinky would go down too... but it goes up. Now picture the subwoofer moving inside the box. You would think that when the woofer moves inwards, it pushes the air in the port outside of the box. This is not the case. This doesn't mean that the port and woofer are "in phase", because they're not... they're just closer to being in phase(0 degrees diff) than out of phase(180 degrees different), and how close they are to being in phase will depend on the frequency.... and I think this is because of the actual time it takes the woofer to move. Actually the woofer and port might be 180 degrees out of phase at a certain frequency... check out Richard Clarks forum at Carsound.com. Maybe the port is delayed by exactly how long it takes the woofer to complete it's inwards movement. I don't know..... (I never took physics or anything)
Build an enclosure that will have the port and subwoofer the most "in phase" at a vehicle's resonance, and watch the SPL meter get excited
Hammer One.... I'm not sure a parabolic design will yield higher SPL than a similar flat wall... radio frequencies are omni-directional, so they'll reflect right off a surface(which is a problem for engineers when designing a cellular network in a metropolitan area), bass frequencies aren't really. I'm not sure just how omnidirectional a 60 hertz signal would be... but if you have success in getting subsonic sound waves to reflect like you want them... let us know!... and goodluck
posted
Dante, thanks buddy , you'll have to tell me how you managed to load the gif on there, I seem to be having a major problem in that regard on this and other forums.
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E.C. Wuz here
Posts: 1057 | From: Vancouver, British Columbia, Canada 'eh | Registered: May 1999
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posted
The port is in phase at and above the tuning frequency (for our purposes) and out of phase below the tuned frequency, right?
I wouldn't think the phase of the port could supercede the phase of the speaker...it could, I guess, but it would look like at that point out of phase but one whole period plus the fraction out of phase.
Putting ports on different planes would be like putting speakers on different planes, sometimes it works, sometimes it doesn't- but a general rule to have them on the same (or as close to the same plain) to avoid cancelations and to maximize acoustic coupling...correct?
It is late, my brain hurts...
------------------ ID Sound Performance Team Sick Bastard SQ? Huh? IASCA Novice 1-600
Posts: 7866 | From: Charlotte,NC USA | Registered: May 1999
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posted
well in an ideal world the port and sub would be in perfect phase. BUT, if the port is pushing out, what's going to happen? the box is going to suck in, countering some of the affect the sub makes. I am wondering, how far off is the phase? Is there a way to find out?
posted
You shouldn't think of the negative pressure as negating the effects of the port. More so the negative pressure acts as a control device. That is why we make the enclosures bigger/smaller. This allows for the maximum pressure to be exerted while still maintaining control. All speakers that I know of have sort of spring type action associated with the cone to bring it back to a neutral position.
Posts: 736 | From: Albertville MN USA | Registered: Mar 2000
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posted
You have to think of the air inside the port as being a solid mass, and that isn't concerned with what is happening inside the box- when the speaker moves out, the air in the port moves out in the same direction at the same time. This is at tuning. This is another reason to figure out port displacement.
I think what you are looking for is an explaination of group delay.
------------------ ID Sound Performance Team Sick Bastard SQ? Huh? IASCA Novice 1-600
Posts: 7866 | From: Charlotte,NC USA | Registered: May 1999
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posted
wow, when i started this topic i didn't think it would still be going on this long!
But what I was questioning when I started this, is whether or not ports are more effecient than another speaker? Ports MOVE air, and given proper phasing, could possibly help pressurize it, but creating another sound wave?
But all subs would be all pressure. with phase shifters, they can all create a wave together. Can ports be more efficient at doing that? I just don't get how that is possible.
I am not doubting 4 subs ported, is louder than 4 subs sealed. But wouldn't 6 subs be more powerful than 4 subs with 50% port area?
------------------ 2001 BMW 330i Harmon Kardon Sound (too broke to buy more)
[This message has been edited by solosier (edited 07-26-2001).]
Posts: 438 | From: The Beach | Registered: Feb 2000
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posted
Solo- A truly optimized port will have vent losses, heat losses, etc. It can NOT approach a 100% efficient energy transfer, which means that a port will not be as effective as another speaker, right?
ShadowStar
------------------ Still looking for that CHEAP Thunderdome :D
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Posts: 2578 | From: Somewhere In the Northeast | Registered: May 1999
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