vent length not given in WINISD means?

[cT equals piD]

I did have the impression that for a given driver and type of alignment that the box size and tuning frequency were pretty much etched in stone. Of the three books that I have referred to for designing a vented system, none of them suggest that you can stray from how the alignment is supposed to be. However working with a freq. response simulator, as Tim showed, can show to what extent you can fiddle with those two parameters without substantially degrading the response. That is good to know.

Thanks to all for your replies,
Pete

 

[LightBit]

Alignments were made in days when simulation was not easy. You would just select alignment and check in table and you knew what you will get.
Today alignments are still useful as starting point.

 

[kimmosto]

Alignments were made in days when simulation was not easy...

and crossovers were passive and drivers had high(er) Qe. Now we have very low Qe drivers and half of diy-systems are active so table alignments have lost 90% of their significance. Tuning has whole new targets different than just certain shape of frequency response to half space.

 

[cT equals piD]

and crossovers were passive and drivers had high(er) Qe. Now we have very low Qe drivers and half of diy-systems are active so table alignments have lost 90% of their significance. Tuning has whole new targets different than just certain shape of frequency response to half space.

Isn't it the case that what has happened is that the physics and math (developed by Thiele and Small) behind the table alignments has now been applied to computer simulation? So this means that the computer simulation has supplanted the tables because the simulation is simpler and easier to use than the tables, and allows for greater flexibility in developing an alignment according to what one wants. However, even in computer simulation, what Thiele and Small discovered and developed is still being applied (I would think).

To my understanding, low Qe and an active vs passive crossover (assuming a well-designed passive one), does not affect the operation of a vented system at all. One of the parameters of an alignment table is Qt, which can be quite low corresponding to low Qe.

 

[kimmosto]

To my understanding, low Qe and an active vs passive crossover (assuming a well-designed passive one), does not affect the operation of a vented system at all. One of the parameters of an alignment table is Qt, which can be quite low corresponding to low Qe.

Yes, but very low Qe probably leads to very small box volume and high f3 with alignment tables because alignment target was (decades ago) just certain response shape due to restrictions of passive XO which was de facto standard.
Today we can maintain large volume and low tuning also with very low Qe drivers and make certain response shape with active filter. Modern target of alignment could be low tuning to reduce GD or smaller excursion at low bass or whatever except certain response shape.

 

[Sven R]

WINIsd - port size and location question (?)

Greetings,

When I calculate 1x12¨ vented speaker enclosure (to contain also one H.F. unit in a two-way speaker) with WINIsd new version (7 or something like that...),

1. I have a choice of round and rectangular vents. I choose rectangular, one vent.

2. I have a choice of a smaller or larger rectangular vent:

2.A - in this case a vent 0.102 x 0.047 meters, which is area of 0.0048 sqare meters, or 48 sq. centimeters - length of vent is 0.12 meters, 1st port resonance of 1,434 kHz - and

2.B a smaller vent 0.082 x 0.047 m, which is area of 0.0039 sq. meters or 39 sq. centimeters, with length of 0.091 meters, 1st port resonance 1.88 kHz

My questions are:

Q1: Is it OK to use smaller vent (my preferrence, makes a better-easier box design). Do I loose something? I also like higher port resonance since it is above the X-over point to H.F. unit, which is around 1.2 kHz.

Q2: Is it OK to place the rectangular vent at the BACK of the enclosure instead of the usual front placement. Is it OK to use the bottom of the speaker enclosure as one side of rectangular vent wood ¨box¨ that would be placed (carpentry work, of course)?

Any experienced, knowledgeable help is much appreciated. Thanks, Sven

 

[LightBit]

Q1: Smaller (narrower) ports can/will create more noise (higher air speed).
Q2: Back is fine (if you have space behind). You can use bottom as part of vent, but it will change tuning a bit.


Round ports (preferably flared) are better than rectangular regarding noise.

 

[Sven R]

Thank you!