What in the blazers am I doing wrong.

[Nusnud]

So tonight I have just been plugging random drivers into the Speaker box designer spreadsheet thingy I found, and well how can this be asking for a 2.5 meter port on recommended?

For this Driver

Surly I have cocked this up somewhere and have had too much wine to see it?

 

[5th element]

You haven't done anything wrong. Large diameter port, small box volume, low tuning? Expect a very long port. This is why PRs are popular for some designs!

 

[Nusnud]

Ok so forgive a stupid follow up question, why is it also recommending a min port dia.

Basically this is telling me that ported design is going to be prohibitive?

 

[Lojzek]

Unibox spreadsheet (Excel) suggests 3,5" as min diameter. Woofer box and circuit designer as well.
Depending on the power draw, you can use a smaller port diameter than suggested. Unibox is a better software to deal with.

 

[TBTL]

Ok so forgive a stupid follow up question, why is it also recommending a min port dia.

A quick search would answer your question. Stupid questions don't exist, but some questions have been answered many times before.
Flare-it - Free Speaker Design Software
The Subwoofer DIY Page - Port Calculations

 

[Ron E]

While it won't change your results much, you have entered 6.5 instead of 5.9 as Re, and you have a 0.3 ohm series resistor.

The minimum port diameter is a suggested minimum to keep the port from making unmusical noises - rushing air / chuffing noises. A 4" port gives the usual 17m/s figure at 105dB output. Even a 3" diameter port needs to be nearly a meter long. This small box volume needs a Passive Radiator.

To tune a small box to a low frequency needs a very long vent. Just to play with numbers, change your box volume to 60 (or 600) liters and see what happens to port length...

 

[hollowboy]

FYI: "in the blazes" (a minced oath, meaning "in hell") vs. "in the blazers"

https://en.wikipedia.org/wiki/Minced_oath

 

[Nusnud]

FYI: "in the blazes" (a minced oath, meaning "in hell") vs. "in the blazers"

https://en.wikipedia.org/wiki/Minced_oath

I blame the wine.

 

[Nusnud]

Could you get away with folding a slotted port to get that distance?

 

[chris661]

Not really. Chances are, with a port approaching metres long, that you're going to introduce pipe resonances in or just outside of the intended bandwidth. That's gonna put some ugly peaks/dips and general weirdness at the top end of the useful range of the device. Makes it much harder to integrate with whatever's covering the rest of the range.

PRs are good here, or you could fire up Hornresp and morph it into a a transmission line. At the very least, the resonances will show up.

Chris

 

[gedlee]

A 19 liter box with a resonance of 29 Hz is never going to be practical. The port will be bigger than the box.

I have made band pass designs with very low tuning and ports big enough to not restrict the output and they were some 2 meters long made from three 4" PVC tubes. And even this was not tuned as low as 29 Hz.

 

[David McBean]

Chances are, with a port approaching metres long, that you're going to introduce pipe resonances in or just outside of the intended bandwidth. That's gonna put some ugly peaks/dips and general weirdness at the top end of the useful range of the device. Makes it much harder to integrate with whatever's covering the rest of the range.