Win ISD box program

[Guenter]

Hi all. A while back someone (wonderful!) posted info about this program - and I've been enjoying it tremendously. Recently I tried to put it to some real work after I acquired 4 Gauss 4583A woofers. When using the program I can't get the vent size to make any sense. Surely by 'vent' they mean 'port'. I notice that when I increase the diameter of the vent, then so does the suggested length increase. Shouldn't it obviously decrease! Anyone know what is going on??

- cheers, guenter

ps any comments about the Gauss by anyone per chance?

[Mr. Widget]

Originally posted by Guenter
I notice that when I increase the diameter of the vent, then so does the suggested length increase. Shouldn't it obviously decrease!

No, that is correct. With any ported system to keep the same tuned frequency, as the port (vent) diameter increases the port length will also increase.

I am not familiar with that Gauss driver, but they made many good models.

Widget

[GordonW]

No, that's right. Increasing the diameter of the port does neccessitate making the port longer, to maintain the same port frequency. To maintain the same inertial effects over a larger area, the length of the "air column" must be proportionally longer.

Those Gauss units are certainly built like tanks... but IME, they don't have the mechanical excursion capacity of similar JBL drivers. For horn apps, and midbass use, the Gauss stuff should work very well... it's just that in direct-radiator woofer and subwoofer applications, the Gauss may run out of available air movement capacity too soon, sometimes, compared to a similar JBL product.

Regards,
Gordon.

[Guenter]

[QUOTE]Originally posted by GordonW
[B] Increasing the diameter of the port does neccessitate making the port longer, to maintain the same port frequency. To maintain the same inertial effects over a larger area, the length of the "air column" must be proportionally longer.

Thanks GordonW and Mr. Widget. Now I'm really confused and I thought I understood a port If I may, above you refer to the 'inertial effects'. Well, that was my understanding, the air in the port has an inertial mass/compliance that needs to be matched the resonance of the driver/box to extend the speakers resonance response a bit. Now, I thought that this 'resonant air mass' would be fixed - to compliment the driver/box combination. Soooo, to keep this resonant air mass constant, if the port diameter increases then the port length should decreas. What am I missing here

- cheers and thanks, guenter

[johnaec]

Originally posted by Guenter
Now, I thought that this 'resonant air mass' would be fixed - to compliment the driver/box combination. Soooo, to keep this resonant air mass constant, if the port diameter increases then the port length should decreas. What am I missing here

Look at it this way - if you have a large cross-sectional area it's much easier for the air to move in and out, (just like it's easier to push a given amount of water through a large pipe than a small pipe). Since it's so much easier for the speaker to push air in and out of a large port area than a small port area, the tube has to be made longer when using a large port area, to add more resistance. Since it's much harder for a speaker to move air in and out of a small port, the tube doesn't have to be near as long for the resistance to balance when using a small port.

You may ask why people don't just use small area/small length ports all the time instead of big long ones if the resistance is the same - it's because the speaker will be trying to move as much air by volume in and out of the port at any given frequency/level, and a small port actually starts to "whistle" and make other noises as so much air tries to force its way through such a small, tight opening. Having more area for the port, (and more length to balance the resistance), minimizes this undesired port noise.

Clear as mud, right?

John

[Guenter]

[QUOTE]Originally posted by johnaec
[B]Look at it this way - if you have a large cross-sectional area it's much easier for the air to move in and out, (just like it's easier to push a given amount of water through a large pipe than a small pipe). Since it's so much easier for the speaker to push air in and out of a large port area than a small port area, the tube has to be made longer when using a large port area, to add more resistance. Since it's much harder for a speaker to move air in and out of a small port, the tube doesn't have to be near as long for the resistance to balance when using a small port.


Thanks John, that does indeed make sense.

A pressure argument. Where I fall down is by considering a passive radiator, said to be equivalent to a port. There, to tune to a lower frequency, mass is added. All else remains constant. Clearly mass effects resonance. Now with the port, for a constant resonance frequency, we increase the port length if the diameter increases. Are we not also increasing the 'effective' mass of the air column in the port and thereby lowering the resonance frequency - or is this a negiligible second order effect?
Possible I don't have a good handle of what constitutes the 'effective' mass of a column of air in a port.

so, yes, still mud :-)

cheers, guenter

[4313B]

"Where I fall down is by considering a passive radiator, said to be equivalent to a port."

Nope, passive radiator systems are more complex than vented systems.

BTW - for those who care, a good place to start might be with these:

Small,R.H.,"Direct Radiator Loudspeaker Analysis", J.Audio.Eng.Soc., Vol.20, pp.383-395, (1972 June)

Small,R.H.,"Closed Box Loudspeaker Systems", J.Audio.Eng.Soc., Vol 20, pp.798-808, (1972 Dec.); Vol 21,pp. 11-18 ( 1973 , Jan./Feb.)

Small,R.H.,"Vented Box Loudspeaker Systems", J.Audio.Eng.Soc., Vol 21, pp.363-372 (1973 , June); pp. 438-444 (1973 July/Aug.); pp. 549-554 (1973 Sept.); pp. 635-639 (1973 Oct.)

Small,R.H.,"Passive Radiator Loudspeaker Systems", J.Audio.Eng.Soc., Vol. 22, pp.592-601 ( 1974 June); pp.683-689 (1974 Nov.)



The Anthologies from AES are pretty neato. One might notice that our good buddy Mark Gander has a hand in there.

LOUDSPEAKERS VOL.1 edited by Raymond E. Cooke. Sixty-one papers, covering the years 1953 to 1977, written by the world's greatest transducer experts and inventors on the design, construction, and operation of loudspeakers. 448 pages

LOUDSPEAKERS VOL.2 edited by Raymond E. Cooke. Forty-nine papers from 1978 to 1983 by experts in loudspeaker technology, extending the work initiated in Vol. 1. 464 pages

LOUDSPEAKERS VOL.3 - Systems and Crossover Networks edited by Mark R. Gander. Forty-two papers with comments and corrections published on this specific area of loudspeaker technology from 1984 through 1991. With a companion volume on transducers, measurement and evaluation, this publication extends the work of the first two volumes on the important topic of loudspeakers. An extensive list of related reading is included. 456 pages

LOUDSPEAKERS VOL.4 - Transducers, Measurement and Evaluation edited by Mark R. Gander. Thirty-eight papers with comments and corrections covering this specific subcategory from 1984 through 1991. A bibliography of related reading lists essential titles in this field. 496 pages

With winter coming on this stuff is great reading in front of the fireplace.

[Oldmics]

Winters Comin

[paragon]

Gauss 4583A in 150 L enclosure with 10x20cm area and 40cm lenght duct. Left down is cone movement, right on top is SPL
and down right is max. SPL

Eckhard

[Ian Mackenzie]

I prefer a Port in front of the fire place.

Ian

[4313B]

[Ian Mackenzie]

Has anyone over there heard of Parametric modelling by Whise? Their sub is called the Profounder.

Tom Holman and N. Thiele have given it the thumbs up as the next major advance in port loaded modelling.

Ian

http://www.whise.com.au/index3.htm

http://www.whise.com.au/popups/popup_tech_tom.pdf

http://www.whise.com.au/popups/popup_tech_time.pdf

[paragon]

Doen`t know ???

Eckhard

[paragon]

What`s the problem ??

Going down under 30 Hz !! It`s top !
Doen´t understand your answers.

Eckhard

[paragon]

Yes oldmics,
Yourè right.
Read !! (and understand).
Winter comes.

Eckhard

P.S. What will you do in Winter ??