Why are ports louder?

"its gotta be hitting a strong 150db."

Do you realize how loud that is? No one in the right mind would listen to 150db daily. Not only that, but I highly doubt you could get 150db out of those two subs..if he was hitting in the mid 130's that would be a lot from those.

Simple physicists of the speaker. The throw on it can be surpressed it the incloser does not allow for full motion. It it gets low pressure inside and there is no allowance it will burn up. This is why boxs that are sealed need so many cubic feet. If its ported it can be smaller but has a way for high pressure to seak the low pressure area. You also get a certian amount of pessure "Sound" leaving the port on the back stroke when the speaker returns. I tried this with a reverse phase sub and the sound was totally differant. I turned it around also.

Thats why the area inside a Auto is so important. There is just to many things that can affect sound quality. One reason one system sounds good but if you was to put it in a differant car it would sound totally differant.

Excellent as always, and sure to generate more discussion.

One factor why ported or vented or bass-reflex enclosures produce more SPL at the tuning frequency than do sealed enclosures with the same driver and amplifier is the vented enclosure itself basically becomes a large tuned resonance chamber.  So at the port frequency it is the enclosure producing the majority of the SPL.  Thus, the ported system produces more SPL at and around the port tuning frequency than the speaker is capable of producing by itself.

There is another major down-side of porting that I'm not certain was illustrated above is the driver becomes unloaded (no damping on its movement) below the tuning frequency.  This means it can be easily over-driven or "bottomed out" and can be damaged either mechanically or thermally (no cone movement = no cooling.)  A rumble filter (or what's commonly called a "subsonic" filter) must be used to high-pass the woofer at or less than one octave below the port tuning frequency.  This can severely limit the actual low-bass output of the system.

Also, just to piggyback a point on haemphyst's excellent summary... He said, "The maximum output of a driver is figured by multiplying Reference Efficiency (1 watt at 1 meter) by the maximum input power handling capability. 1, 2, 4, 8, 16 watts, etc, with a 3dB gain per input doubling."    Just a tip for all you out there shopping for speakers and shooting for max SPL using that formula.  Be careful before you put too much stock in the efficiency numbers, or max power handling for that matter, quoted by many of the popular retail brands.  Some do everything they can to fudge these numbers without outright misrepresenting themselves.  Others just flatly misrepresent themselves.  Measurements within a single brand are probably reliable.  Measurements between respectable brands are also probably reliable to a certain degree.  Just be weary of the fact that all efficiency and power handling ratings are not measured the same.

To again piggyback on haemphyst regarding the fact that a long throw driver may not actually be louder... Sometimes the large surround on a long throw driver harms the output by decreasing usable driver surface area, harming driver displacement.  This can decrease output in addition to the lost efficiency haemphyst was talking about.

Excellent posts by haemphyst, DYohn and kfr01...thorough, comprehensible, and original.  This thread is going into my bookmarks for future reference.

And oh, poorman, please credit sources when quoting.

Man those are some insane responses, sorta what I had hoped for, I will now always be able to use this as a reference which is awesome.  I think it will take me about a week to read through these 50 more times and completely figure them out.

audiobass - I based my guess of 150 off of my own system, the previous owner is a friend of mine who manages a local shop, he competed at one of their shows last year and had it metered at 156.7db.  These type r's arent as deep as mine and now quite as loud, but they are pretty close, so I just assumed it, even if hes hitting 10db less than me (which I doubt), then its still a VERY impressive number.  I could be hearing bad, or the previous owner of my system could have lied to me (which I really doubt, other people saw him compete), there are a few things that could have impaired my guess, which are all very possible.

I did not know about how important a subsonic filter was on a ported system (just thought it was somewhat recommended), maybe I should set one up for him, dont want to blow those subs.  Haemphyst - incredible post, honestly, just amazing how helpful that one is to understanding it all, sorta confusing how your engineer friend lost you in that stuff cause you really seem to know it; I did know about the high excursion subs not necessarily being louder, I just typed it as something to compare to so I wouldnt get flamed saying it was the loudest setup humanly possible in that car.

dyohn and kfr01, thanks for the input, you guys just further helped with the insane amount of information given by haemphyst, you guys always have great advice.  Im somewhat surprised to not have heard from Steven, hopefully he'll come by and elaborate even more on this one.  Thanks a lot guys please keep any information coming, this has been a great thread so far.

He is some stuff on the whys and hows from Audio Box Design.

Now, as to the pros and cons of the closed box system. They are relatively easy to build. They will tolerate some inaccuracy, with little degrading of sound quality. They achieve excellent transient response (damping ) with the addition of absorbent material. The one big minus for the closed box is the need for consid-
erable power to get much volume in return. We measure efficiency by the ratio of watts in, ( electrical ), to watts out, ( acoustical ). This is where the closed box falls flat on its face. We only consider the radiation from the front of the driver as being beneficial and try to retard that which is being radiated from the rear. The cone moves in two directions. Why throw half of the sound away. This leads us to our next, and possibly most popular, enclosure, the vented, bass reflex, type. Instead of throwing away the rear driver radiation it combines it with the front. These two components of driver movement produce a considerably more efficient system. We can thank, in part, a gentleman by the name of " Helmholtz " for dis-
covering that a certain volume of air, when excited, resonates at a specific frequency. This principal is what a bass reflex system takes advantage of. Smaller, fixed, volumes of air can have the frequency varied with the use of a duct, tube, added to the vent opening. In the, not to distant, past it was believed that the volume of the enclosure had to be increased so the vent was equal in area to the piston area of the low frequency driver(s). The one factor, either not considered or mis-understood at the time, was the velocity of air in the port or vent. As the size of the vent decreases or the length of the duct increases the velocity of the air within them increases. Most design criteria measures this velocity as a percentage of the speed of sound. If this is kept below 5% it is not considered detrimental. That is to say, for the most part, it is in-audible. If the velocity is allowed to increase much beyond this threshold it starts to produce harmonic components of its own. A loudspeaker system is supposed to be a transparent device. As soon as it adds its own sound to the mix, it no longer is.
 

      In the past 25 years or so loudspeaker enclosure design has, technologically, caught up with the times. An Australian by the name of AN. Thiele has brought order out of chaos. His formula, for the design of vented enclosures, has made the design of vented systems an achievable goal for almost anyone. Those of us a bit daunted with the mathematics involved can, with an affordable computer, both design and construct very respectable speaker systems. The programs available are numerous and priced reasonably enough to allow you to pick and choose. The program considered the best, unfortunately, has failed to take advantage of the newest and most accepted operating systems. Some of the other programs, including the least expensive, have. There are very few programs that include a C.A.D. component. The one, we have found, that does is called " Term-Pro " and is marketed by " Wayne Harris Enterprises " in Mesa, Arizona. We have about four basic enclosure design programs which we use. We always use at least two on a design as a double check for errors.

Hey haemphyst, I'm going to have my boss post as I think you are leaving some things out of your comments like enclosure effects on the efficiency as well as extention.  But he's much better at explaining things than I, and should provide a better description. 

Steven Kephart

Adire Audio

I guess I like to come at it from an actual application point of view.  In this case, efficiency is pretty much meaningless to the end user due to all those things you mention.  After all, if efficiency was so important, then every car audio company would be building highly efficient subs.  I actually commented about this a while ago in this thread: https://www.the12volt.com/installbay/forum_posts.asp?tid=41809&KW=efficiency+adire&PN=0&tpn=1 

Steven Kephart

Adire Audio

... and one reason why subs with too high efficiency are NOT too popular in car audio is the successful marketing efforts that have created a false demand for "high power."  I don't need to tell most regulars on this forum about the millions of idiodic consumers who say things like "Man, that thing is a 2000 watt sub!  Dude, that's GOTTA be loud!"  People have been sold the idea that higher power listings = "better."  That's why almost every consumer-level company advertises "max" or "peak" power ratings, and why the most unscrupulous outright lie.  There is no law or industry regulation currently in place to prohibit slapping "1000 watts!" in big letters across a piece of garbage that will smoke and fry with 1/5th that, and if an amplifier can sustain 1000 watts for 1ms, then by golly it's gotta be a 1000 watt amplifier! And then there is the demand to keep things small...

Electrical efficiency, mechanical compliance, overall system efficiency and accuracy are scrapped for the sake of big power numbers.  It's sad.  I've metered my ESS AMT1b towers at 124db between 45Hz and 18KHz with 100 watts input.  And it was flat within 1db (IEC C weighting) from standard.  That kind of efficiency and accuracy is my goal in my car applications....

I look forward to the impending discussion of high excursion VS efficiency and woofer area.  Should be fun.  I never considered them seperately, actually, and look for that fine balance!