WinISD Pro & Other Design Questions (1 Viewer)

[Robert_CA]

I need some help!
I was trying use WinISD Pro to model port length for a Stryke AV-15 for my 214L cabinet tuned to 18.5Hz with dual 4" vents to replace my Tempest which is tuned at 15.5Hz using the dual 3" vents. Does WinISD Pro calculate the length of a straight port or a flared port? The reason why I'm asking this is besause I plugged in the port parameters for my original Adire Alignment box using the Tempest driver and 15.4Hz tune on another project folder and got a different port length from Dan Wiggin's recommended lengths. The other thing I noticed is that the port length WinISD Pro calculates actually increases if you increase the number of ports. Is the calulated legnth the TOTAL length of all the ports? How do you calculate for the effect that the polyfil has on the volume of the cabinet? What could I be doing wrong here?
P.S.
I'm trying to use the 4" ports besause I dont know if I could fit dual 6" ports into my baffle. My internal cabinet height is 26.5 inches so I'll need to find out if they will have enough clearance.

 

[ThomasW]

>>>Does WinISD Pro calculate the length of a straight port or a flared port?

Straight

>>>The reason why I'm asking this is besause I plugged in the port parameters for my original Adire Alignment box using the Tempest driver and 15.4Hz tune on another project folder and got a different port length from Dan Wiggin's recommended lengths.

Yeap Dan's an expert, he's using LspCAD Pro and optimizes his designs to include the damping and all the specific characteristics of each driver. Also the Adire designs are tested and proven designs not computer models.

>>>The other thing I noticed is that the port length WinISD Pro calculates actually increases if you increase the number of ports.

All programs do that.

>>>Is the calulated legnth the TOTAL length of all the ports?

Nope it's the length for each port.

>>>How do you calculate for the effect that the polyfil has on the volume of the cabinet?

Don't try. Optimize the design for the driver, then fine tune the in-room performance with the damping.

>>>What could I be doing wrong here?

Trying to design without understanding design theory?

>>>>P.S.
I'm trying to use the 4" ports besause I dont know if I could fit dual 6" ports into my baffle. My internal cabinet height is 26.5 inches so I'll need to find out if they will have enough clearance.

You certainly don't need dual 6" ports for a single 15"

 

[Rob Formica]

Thomas is right on all the points.

The other thing I noticed is that the port length WinISD Pro calculates actually increases if you increase the number of ports. Is the calulated legnth the TOTAL length of all the ports?

Nope it's the length for each port.

If you look at the actual math, the larger the vent's x-sectional area is, the longer it needs to be to keep the same tuning. So a 4" port will be longer than a 3" port for the same tuning.

A single 6" port with a AV15 should be no problem. I believe WinISD recommends keeping the velocity in a non-flared port below 17m/s... but I think you can push that without having any noticeable port noise. Maybe some others with more experience could better say how high a velocity is still reasonable in practice. Also note that you would need four 3" (7.07in2) ports and over two 4"(12.56in2) ports to equal one single 6" (28.26in2) port.

Good luck...
Rob

 

[Robert_CA]

Thank you for the responses. I am really new at this and was just trying to get an understanding on the software and the theory. I played around with it some more last night and discovered that I may be able to use that tuning in my cabinet but not without some tweaking the design parameters during testing as you have suggested(There will be a trade off when it comes to port velocity). These are some of the things I noticed using WinISD last night:

1) The group delay of the stryke EBS AV-15 design @ 250L with one 6' port models higher than the Adire Alignment design @ 214L with two 3" ports.

2) The Stryke design 6" port velocity is still fairly high and there is a double impedance peak present in the Stryke design vs. the Adire design.

3) In the modeling of both the Stryke AV-15 and Tempest in the same 214L enclosure and input power of 350 watts that I have, the AV-15 will begin to roll off a bit little lower than the Tempest but its average overall SPL is 1.5 to 2db lower. When I bumped the AV-15 up to 500 watts, it did close the avg. SPL gap somewhat.

4) The AV-15 is not as excursion limited as the Tempest and the AV-15's cone velocity is less than the Tempest's over their respective operating ranges and using the input of 350 watts. The Tempest is happier with about 250 max whereas the AV-15 is just coasting at that level.

I'll keep plugging away at the modeling today. I hope that I will be able to make a decision on whether to go with the AV-15 before the pre order ends period ends on Monday. Again, I appreciate you suggestions and instruction. If you have any other suggestions, I would certainly appreciate your sharing them with me. Thanks again.

 

[ThomasW]

If this is a 'do I buy one?' senario, then the answer is yes only IF you need greater output, and no if you think that the AV-15 is going to offer any better sound quality at most SPL's.

Tempests are VERY good drivers, but not audio jewelry with a fancy alu cone and cast basket. The only benefit to using a AV-15 is in a situation where you needed quite a bit more output than you're are getting with you existing sub.

'Bench racing' with computer sims only gets you a rough idea of what's going on with any speaker design. So ruminating over things like differences in GD, etc, are an 'abstraction'. Some people claim to here these differences, other don't.

BTW WinISD isn't a good learning tool. If you have MS Excel, download a copy of Unibox. It's one of the best woofer/subwoofer modeling programs available, and is freeware.

 

[Robert_CA]

Thanks Thomas. I'll give Unibox a try.