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Discussion Starter · #1 ·
Hey all, quick question that I couldn't seem to find the answer to anywhere else

Referring to this image https://imgur.com/fJsO1hW

How does the tuning work in a double baffle configuration where the port width effectively changes along its length?

Do you use the wider or the narrower width to calculate the tuning of the enclosure?

In this example you would enter in the port length as 100cm I would imagine. Would the width be 10cm or 20cm here?

Also would the volume be just volume A or B? Or both combined?

Rob
 

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Visualise it as 100cm dumping before the rear wall...
(20cm wide.)

I would think that keeping the back at 20cm rather than 10 may help mitigate any port noise, and that would make the length something like 90 cm.
Or at least chamfer the sharp corners, or use a round over bit on those.

Or just shove a couple of passive radiators in between the two subs and save some volume, but you need more area... so live with the port... which should be fine.

Launceston? Hobart?
 

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Discussion Starter · #3 ·
Hey, thanks for the reply

Let me clarify by saying that I don't actually want to build this, I'm trying to understand tuning theory for a related project

My question is purely related to the calculations of the tuning frequency in this type of situation

Which values should be fed into the calculator

Anyway you've said that 20cm would be the value to feed in?

Ok thanks I'll roll with that one

Rob, Hobart
 

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Discussion Starter · #4 ·
Although one thing I forgot to ask is if I'm treating the entire port as 20cm in width, what do I treat the volume as? The volume of just one or the sum of both?

Thanks
 

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Hobart is pretty easy to take...

Although one thing I forgot to ask is if I'm treating the entire port as 20cm in width, what do I treat the volume as? The volume of just one or the sum of both?

Thanks
Linear dimension is length.
Length X width is area.
Area x depth is volume.

Usually the area is what is used in formulas, and the frequency determines the length.
The smaller the area the higher the Q, and shorter for a given freq...
But also the port velocity is higher and can lead to port noise.

So how high is the port? (Height x 20-cm = area)


The other common approach (which is uncommon) is a passive radiator, which is behaves exactly like a port, but it is tuneable. (e.g. Earthquake sounds S.L.A.P.S)
A home theatre system may like really low frequencies (20-Hz pr lower)... and in a vehicle some times volume likes a passive radiator to lower the box+port volume.

A PVC port in maybe 8", with flared ends, is also a variable option...
It is not uncommon to build two boxes... a test box, and then the right one...
(Like two heads :) )
 

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I would calculate it with one volume (A) and 10 cm port...(I look at this eclosures as it is built from two enclosures A and B and they share part of the port without middle barrier....that is why I would calculate 20 cm wide section of port as 10 cm per enclosure)
 

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I would calculate it with one volume (A) and 10 cm port...(I look at this eclosures as it is built from two enclosures A and B and they share part of the port without middle barrier....that is why I would calculate 20 cm wide section of port as 10 cm per enclosure)
^This^
 

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I would calculate it with one volume (A) asnd 10 cm port...(I look at this eclosures as it is built from two enclosures A and B and they share part of the port without middle barrier....that is why I would calculate 20 cm wide section of port as 10 cm per enclosure)
^Good ône^

It should give the same numbers as calculating it as a double wide enclosure, but it does seem easier.
 

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Discussion Starter · #9 ·
Hey all, thanks for the replies

It doesn't seem like calculating the tuning frequency with a double width and a doubled volume gives the same answer as single width and a single volume

If the consensus is that treating the two halves separately (e.g port width of 10cm and volume of just A or B) for calculating the tuning frequency is the mathmatically correct way to go then I'll roll with that then?

Thanks
 

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Hey all, thanks for the replies

It doesn't seem like calculating the tuning frequency with a double width and a doubled volume gives the same answer as single width and a single volume

If the consensus is that treating the two halves separately (e.g port width of 10cm and volume of just A or B) for calculating the tuning frequency is the mathmatically correct way to go then I'll roll with that then?

Thanks
I'm certainly no expert, so....

Here's what I got in WinISD (by way of example):

2.0 ft^3 @ 30 Hz 4” x 4” vent = 20.55” L

4.0 ft^3 @ 30 Hz 4” x 8” vent = 19.18” L

Perhaps the shorter length is due to less boundary layer effect (i.e. greater volume per surface area)?

FWIW, in my limited experience I've always ended up with a slightly lower Fb (i.e. slightly longer vent than needed) than that which had been predicted by WinISD modeling and vent length calculators. I've heard similar comments from others. No idea what that is about, but I've learned not to sweat exact vent lengths too closely. YMMV. :)
 

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Hey all, thanks for the replies

It doesn't seem like calculating the tuning frequency with a double width and a doubled volume gives the same answer as single width and a single volume

If the consensus is that treating the two halves separately (e.g port width of 10cm and volume of just A or B) for calculating the tuning frequency is the mathmatically correct way to go then I'll roll with that then?

Thanks
It should be the same answer, If you use double the drivers...
(But seems easier to do it one by one, rather than Noah's ark style.)
 

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I'm certainly no expert, so....

Here's what I got in WinISD (by way of example):

2.0 ft^3 @ 30 Hz 4” x 4” vent = 20.55” L

4.0 ft^3 @ 30 Hz 4” x 8” vent = 19.18” L

Perhaps the shorter length is due to less boundary layer effect (i.e. greater volume per surface area)?

FWIW, in my limited experience I've always ended up with a slightly lower Fb (i.e. slightly longer vent than needed) than that which had been predicted by WinISD modeling and vent length calculators. I've heard similar comments from others. No idea what that is about, but I've learned not to sweat exact vent lengths too closely. YMMV. :)
I found this common with slot port enclosures,....in this example that 1Hz of difference is like a fart in fresh shorts
 
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