Tuning Sub Boxes

[GCT]

Hi

I'm used to tuning speaker boxes flat with win ISD. After building some flat subs with 2241s, I compared with some other subs that have the same 2241s loaded. They are also front facing, have the same volume but have a taper. The ones with the shorter than "correct" port tubes had more punch in the bass drum area.

What's a good tuning port arrangement for a front facing sub port for SR work. I could easily change the ports.

Any thoughts would be most appreciated.

Cheers

GCT

[Fort Knox]

Hi

I'm used to tuning speaker boxes flat with win ISD. After building some flat subs with 2241s, I compared with some other subs that have the same 2241s loaded. They are also front facing, have the same volume but have a taper. The ones with the shorter than "correct" port tubes had more punch in the bass drum area.

What's a good tuning port arrangement for a front facing sub port for SR work. I could easily change the ports.

Any thoughts would be most appreciated.

Cheers

GCT
You can push a speaker harder with more port .....
and get less boom

[Baron030]

Hi
I know from my own experience that there might be a very minor flaw in the WinISD port calculation algorithm. The WinISD program appears to not take into account the virtual volume that is added when damping materials are added to an enclosure. Damping materials like fiberglass will make an enclosure appear to be larger than it really is, hence the term “virtual volume”. The BassBox Pro version 6 software, does allow for filler materials to be included into its calculations. Now that is not to say that WinISD is not a very good product and considering its very low price. It’s still a very useful tool. But, I would recommend testing your enclosures to confirm that ports are indeed tuned correctly. In my own project, WinISD stated that I needed 3 – 4” diameter ports that were 9.5” long. BassBox Pro version 6, on the other hand, had calculated the same ports to be 8” long. And after some actual testing, I did find that I need to trim the ports down to 8” long on my own project. While computer simulations are good, actual testing is always better.

Barron030:)

[GCT]

So are you saying that I should still aim at the correct port for absolutely flat response?

Is there anything to be gained from tuning a sub box for live sound to peak at say 55Hz? Would this damage the speaker?

I will measure the port tuning and see what's happening.

Thanks

GCT

[GCT]

You can push a speaker harder with more port .....
and get less boom

The resonance "seems" to be favourable - at least at low volumes - to the punch. The best sounding sub was the one which had half length ports (Someone brought me 2 subs with different port lengths - according to winISA the long one was the "right" one.)

Did you mean more port diameter at same length? Or more port length at same diameter? Or same tuning just larger ports?

[Lee in Montreal]

Shorter port = higher tuning frequency = more punch = less lower extension

You can design the front panel to accept two different ports depending on what you want. And swap them.

[GCT]

So any tips on tuning frequency?

[Lee in Montreal]

So any tips on tuning frequency? Have you read my post? :D

[GCT]

Yes. Just wondered exactly what frequency I should tune my subs to.
If I retune I get the following from WinISA:
34Hz = flat
40Hz = +1dB @ 62Hz
45Hz = +2dB @ 62Hz
50Hz = +3.5dB @ 63HZ
55Hz = +5dB @ 67Hz

What's the best choice?

GCT

[allen mueller]

The best way would be to determine what the box you like is tuned to by testing it than match your new subs to that. An impedance sweep would be the best.

I've found that WinISD will get you close but i do final tuning with using WT3. The 1979 enclosure manual gives some alternate methods of determining your tuning frequency. If you have a voltage meter and a frequency generator (you can use the one in WinISD) you can use the steps outlined in the below document to find the frequency. I did it that way once and it takes some more time but I got good results.

http://www.lansingheritage.org/html/jbl/plans/1979-manual.htm

Al

[GCT]

Thanks. Will get round to it when I get time.

Cheers

GCT