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theil small parameters

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Gaston

Member
all of this speaker talk recently has really wetted my curiosity. i bought the radio shack speaker book years ago and it has the formula for enclosures based on the t s parameters. my question is, how do you know what frequency to shoot for with the formula? look for where the bass drops off or gets weak in the woofers output?
 

audioguru

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You can install a speaker in an enclosure and it might make a single frequency boom.
Or it might have no bass.
Or if you select a speaker with certain spec's then calculate an enclosure for it using its TS parameters then it will have a flat response down to a very low frequency.

If the enclosure is too small then there will be a upper-bass boom and no deep bass. If the speaker has poor spec's and the enclosure is too big then there will be no bass.
 

Gaston

Member
but when you calculate the port diameter and length of the tube you have to calculate for a certain frequency. how do you determine that frequency?
 

chemelec

Well-Known Member
Gaston said:
but when you calculate the port diameter and length of the tube you have to calculate for a certain frequency. how do you determine that frequency?

Haven't really designed many speaker cabinets, But I would probably first test the speaker to see what the "Free Air Resonance Frequency" is on them.

Probably if you tune the port to that you should get good bass. But maybe too Boomy.

Personally I like my 1950's Karlson Enclosures.
 

audioguru

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The size of the enclosure is also a very important calculation for a vented enclosure. Too big and there is no bass. Too small and there is a boom in the upper-bass frequencies. The speaker enclosure design software should calculate these things.
 

Gaston

Member
my design software = pencil,paper,and calculator:rolleyes: . i have been looking for speaker enclosure simulation software for years and have yet to find any
 

audioguru

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Most Helpful Member
There are lots of good speaker enclosure design softwares. Most have the TS parameters of many popular speakers.
I used Boxplot and there is another that I haven't tried yet I think is called ISD or something.

I obtained many good-looking enclosures that had garbage 8" speakers in them. I used Boxplot to design which woofer, the port dimensions and the bass-boost for them. The boxes were way too small but the port was tuned to a low frequency and the end result was good.
 

Gaston

Member
so basically all the port does is make up for an enclosure that is too small for the speaker which atenuates the lower frequncies? so what does the tube do? all of the sound reinforcement stuff never have tubes just ports
 

audioguru

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A ported enclosure is supposed to have a pretty big volume. If the volume is too small then the bass will be reduced, and a peak will occur at an upper bass frequency. I used an enclosure that was too small, tuned the port to a frequency too low for the size of the enclosure then added plenty of bass boost for good bass response. I used woofers with a low Qt so the peak wasn't audible.

At the frequency where the enclosure and port are tuned, the woofer's cone hardly moves, so it doesn't over-extend its movement at high levels.
 

Gaston

Member
At the frequency where the enclosure and port are tuned, the woofer's cone hardly moves

so how do you determine said frequency? i would assume that you would start your calculations with this number and work from there.
 

Speakerguy

Active Member
Gaston,

Go to linearteam.org and download WinISD (don't get the Pro alpha version, it's a PITA to use, get the other one). It's free, has a large driver database, and you can play around with what box sizes and tunings do to a driver. It's educational.

There is much better software out there, but this will give you the basics. I myself use LspCAD, which is commercial product, but lets you do a whole lot more.
 

audioguru

Well-Known Member
Most Helpful Member
For certain TS parameters of a woofer and for a certain enclosure volume, the software gives the dimensions of a port. You can see the frequency response curve and you can alter the enclosure volume and port dimensions to see how the response is affected.
 
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