What is the calculation people use to determine the dimension of a port?
A simple question but I can't find consistent advice and the online calculators are all over the place
what do you guys use ?
Lx
A simple question but I can't find consistent advice and the online calculators are all over the place
what do you guys use ?
Lx
You can have a look at a physics formulary and the amx area of the port is about 30% of the surface of the driver.
what is a physics formulary 😕 sorry this doesn't help much
1/3 of driver area is helpful but what about the depth and its relationship to box volume and driver specs ?
Lx
1/3 of driver area is helpful but what about the depth and its relationship to box volume and driver specs ?
Lx
I use a few online calculators. I use end correction factor of 0.73. Then I multiply the calculated port length by 0.85. It should be close enough. I did some reading on this, and sifted through pages and pages to come to this conclusion.
I'll try find the link. At the end of the day, the calculation is an estimate and you need to measure. The thing is (as quoted indirectly from the link I'll find) that if your measurement shows incorrect tuning, what do you do? Especially if the port is too short? In other words, design for a removable port...
great that is the sort of thing I was looking for, have you always had optimum results with this calc or have you experimented with other ideas?
Ill post the link I ended up on as it has advice for slot ports as well
The Subwoofer DIY Page - Port Calculations
Lx
Ill post the link I ended up on as it has advice for slot ports as well
The Subwoofer DIY Page - Port Calculations
Lx
I used many calculators, and they all gave the same result (the outliers that didn't were discarded). I haven't measured, and I'm not that precise. I've also read that link you posted, but not in depth, and quite a long time ago. The more you read, the more you know, but in the end, you have to build for yourself.
For Port design, I find that Winisd is easy to use and you can see many Plot Types - port velocity and more.
A Round port on the "front" can affect midrange clarity so a Bottom slotted port could be better to prevent this. I''m looking at this closer for a few designs. I have a round front ported speaker now, and can't say its a problem, but building the same speaker with slotted port and comparing the two will give me more insight.
A Round port on the "front" can affect midrange clarity so a Bottom slotted port could be better to prevent this. I''m looking at this closer for a few designs. I have a round front ported speaker now, and can't say its a problem, but building the same speaker with slotted port and comparing the two will give me more insight.
To tune a volume Vb (in liters) to a frequency Fb (from Small-Margolis again)
Lv = 2350*Dv^2/(Vb*Fb^2) - 0.73*Dv
Lv and Dv are vent length and diameter in millimeters, Lv is assumed to be larger than 50mm for this formula, so if it comes out shorter, pick a larger Dv.
If you measure Fb and find it to be different from the predicted value, you can figure out how much to add or subtract by calculating:
deltaLv = -deltaFb*Dv^2*2350/(Fb^2*Vb), where deltaFb = Fb_desired-Fb_measured.
Agreed.
I use simulation then divide length by 1.2, then listen, measure, then cut to length to get desired fr.
Also like already mentioned 1/3 Sd is minimum port area.
You even might want to use more port area for high excursion drivers (or in bandpass enclosures for sq) to keep port velocity in check.
Yeah, for woofers one ideally needs to take Xmax into consideration, which with low Xmax drivers allows smaller than 'normal' vents, so I follow this guideline for HIFI/HT apps [scroll down]: TA Speaker Topics: Vent FAQ's
GM
GM
I am looking at building a bass reflex system and aim to use a slotted port. So I have done a fair bit of reading and I have seen this formula however I am also aware that end correction factor 'k' varies depending on the port layout. The graphic attached has been posted on diyaudio in the past but worthwhile adding it here.
So my approach to port design is this - I would appreciate feedback on whether I am on track:
- use WinISD to calculate Vb and port dimensions
- as WinISD uses k=0.73, then Lv needs to be corrected. The REDUCTION in length equals (new k * Dv) - (0.73*Dv). If k = 2.2 for a slotted vent, then the reduction is (2.2-0.73)*Dv = 1.47*Dv.
- Equivalent Dv for a rectangular slot given by W*D = Pi*(D^2)/4
- then using Troels Graveson info, port may be shortened by another 20%
What do smarter people than me think about this?
Attachments
For slot port calculations, the best software i found is Boxsim. Under the Extras menu the most detailed and accurate calculator i've seen so far, it includes even port positions inside the enclosure.
Boxsim - Homepage
Boxsim - Homepage
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