What factors determine tuning point (1 Viewer)

[Russell R]

Hello,
I am thinking about building another sub. Currently have a shiva in a 142.5 tuned to 21.5hz. What determines the tuning point? Considering an Fs of 21hz for the shiva, what are the pros and cons of higher and lower than Fs?

The above sub is awesome, especially since I only have $325 invested into it. There are times when port noise is heard from the 4" flare. I am bouncing around the idea of changing my port to ports, or larger port.

Thanks,
Russell

 

[GrahamT]

If you have Lspcad you can do some modeling with different tuning frequencies. To determine dimensions of the ports try these links.

http://www.quux.net/roo/diy/sonosub/sonocalc.html

http://www.loudspeakers101.com/VentCal1.htm

 

[Russell R]

What does loading and unloading of the driver mean? When does this happen?

Thanks,
Russell

 

[GrahamT]

Above the tuning frequecy of the system, the port air and the driver are moving in phase, although the driver is hardly moving near the tuning freq. Below the tuning freq the port air and driver are out of phase. THis is when the driver is unloaded and excursion increases. With enough power the driver will exceed xmax and bottom out.

 

[Frank Carter]

What determines the tuning point?

The tuning point is determined by the cross-secton/length fo the vent and the effective internal volume.

 

[Jack Gilvey]

http://www.hometheaterhifi.com/volum...ayporting.html

 

[Russell R]

Thanks for all the replies. I want to read what Jack had sent.

I have a question on the above:
"Above the tuning frequecy of the system, the port air and the driver are moving in phase, although the driver is hardly moving near the tuning freq. Below the tuning freq the port air and driver are out of phase. THis is when the driver is unloaded and excursion increases. With enough power the driver will exceed xmax and bottom out."

So, below the tuning frequency of the system means the port/enclosure tune and not the Fs of the driver, correct?

What does this mean with the Shiva EBS alignment? The drivers Fs is 21hz and the enclosure tune (Adire) is 18.1hz. What happens with this combo versus the 142.5L tuned to 21.5hz?

I want to understand this better for future projects. Has anyone built their port/flare that stuck out of the enclosure? Something that looks like a TL sub. I am pondering the idea for quick tuning/retuning possibilites.

Thanks again,

Still learning,

Russell

 

[Todd Shore]

Sure, the port can be outside the sub. I do it all the time on test boxes.

Remember that port volume must be deducted from the enclosure if mounted internally, but not if mounted externally.

 

[GrahamT]

There is much to know about designing ported subs. Get a copy of the Loudspeaker Design Cookbook by Vance Dickason. This will give you the info you need to properly deign a vented sub. You can find it at a local library.

 

[michael-e]

Has anyone built their port/flare that stuck out of the enclosure? Something that looks like a TL sub. I am pondering the idea for quick tuning/retuning possibilites

i calculated the volumes all correct so my tuning for my sub was exactly spot on no retuning needed.

+ my port was a MDF shelf port.

however it maybe interesting to compare different tunings.

but u can only do so much.

 

[Russell R]

What type/size/tune sub did you build?