Good Article on Ported Speakers...

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jackman

Good Article on Ported Speakers...
« on: 21 Dec 2005, 08:00 pm »
Here are a couple articles written by an audio engineer, I thought were a pretty interesting read.  Part 1 "Compromise and Approximation" is about ported speakers.  

http://www.soundonsound.com/sos/oct00/articles/monitor.htm


Actually, I liked part 2 much better, especially the section on thermal compression in passive speakers.  

Quote
crossover filter circuits in passive speakers are dependent for their response accuracy on the input impedance presented by the drive unit. As the voice-coil resistance increases with temperature, the effective filter response's shape can stray very far from that intended and can introduce all sorts of errors in the system response. These thermal compression effects are notoriously difficult to predict or tie down -- they are entirely signal and signal-history dependent, for a start.


I also liked the part about off-axis response, particularly that of large drivers that are crossed over high, using low slopes.  It made me think of fellow audiofools who spend countless hours worrying about break-in and countless dollars on cables trying to correct speakers that are performing exactly as they were designed.  Let me put it another way, if you have a two-way speaker with a large woofer crossed over to a super-tweeter or to a normal tweeter at a high frequency, the large driver will most likely not have good dispersion, no matter how long you give it to "break-in".  It also explains what can happen if you have a tweeter crossed at too low.

Quote
Find out a little about the off-axis response of your monitors. Don't necessarily mistrust a published specification but treat it as the marketing material it almost certainly is. You can work out much of what you need to know simply by looking. If you have monitors with a large bass/mid driver (say, 200mm or more) and a high crossover frequency (above 3kHz) you can be pretty certain that, however flat the axial frequency response, the off-axis response won't be. Conversely if your monitors have a smaller bass/mid unit and a lower crossover frequency they'll in all probability be better behaved off-axis...


Here is Part 2:

http://www.soundonsound.com/sos/nov00/articles/ustandingmons.htm[/quote]

Folsom

Good Article on Ported Speakers...
« Reply #1 on: 22 Dec 2005, 06:54 am »
Compromise is the key word in all of this....

Although a few of these delimas are solved by insane amount of work on timing adjustments with crossovers and the shape of the box.

ctviggen

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Good Article on Ported Speakers...
« Reply #2 on: 22 Dec 2005, 01:11 pm »
That is a good article (at least the second part -- I didn't read the first).  I wish the graphs were larger, though.  They're unreadable.

Brian Cheney

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cdwg
« Reply #3 on: 22 Dec 2005, 02:59 pm »
It would be nice if a speaker had constant directivity full range, and used a 3way design with woofers crossed over, say, below 300Hz.  The author could have saved himself the effort of writing the article in the first
place.

ctviggen

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Good Article on Ported Speakers...
« Reply #4 on: 22 Dec 2005, 03:07 pm »
That's true -- CD would help mitigate one of the author's biggest complaints, poor off-axis response of the speaker.  And crossing over to larger woofers would help another of the author's peeves, distortion caused by driving the "woofer" (midrange) too hard.

Folsom

Good Article on Ported Speakers...
« Reply #5 on: 22 Dec 2005, 08:57 pm »
He understands acoustics very well, but aparantly has no idea how good and expensive some speakers get.

You can click on the graphs to make them readable. (on part one)

jackman

Good Article on Ported Speakers...
« Reply #6 on: 23 Dec 2005, 08:44 pm »
Quote from: Destroyer of Smiles.
He understands acoustics very well, but aparantly has no idea how good and expensive some speakers get.

You can click on the graphs to make them readable. (on part one)


I think you guys are missing the point.  He's talking about speakers that are commonly used and some of the issues associated with designs.   I agree regarding the earlier comments on compromises.  Anyway, I thought the article was interesting.  

Although speaker design is a combination of science and art, IMO, there are so many people who view it as voodoo or at least dark science or mystery.  Unfortunately, the rules of physics apply to everyone...no matter how many marketing departments would have you believe otherwise.  

J

ctviggen

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Good Article on Ported Speakers...
« Reply #7 on: 23 Dec 2005, 09:02 pm »
If you want to read a book heavy on science and light on subjectivity, here's one for you:

http://www.amazon.com/gp/product/1882580338/ref=cm_lm_fullview_prodimg_2/002-5017405-6944854?%5Fencoding=UTF8&v=glance&n=283155

It has hundreds of graphs.

_scotty_

Good Article on Ported Speakers...
« Reply #8 on: 23 Dec 2005, 09:22 pm »
jackman, I agree with your points. Thanks for posting the link.
Scotty

Folsom

Good Article on Ported Speakers...
« Reply #9 on: 23 Dec 2005, 10:45 pm »
I have that book next to me  :lol: .

GHM

Good Article on Ported Speakers...
« Reply #10 on: 23 Dec 2005, 10:52 pm »
Here's another good one for you and it's free Phase, Time and Distortion in Loudspeakers :wink: