Hey guys, sorry if this post is in the wrong section.
So I'm building a bass reflex 2 way book shelf monitor and trying to figure out the minimum port diameter by using the equation provided in The Loudspeaker Cookbook. But for some reason, same with some of the online calculators, I'm getting strange results. I'm thinking its either the values I've input or I'm just being a silly sausage, I was never great at maths. The woofer I'm using is here:
Dayton Audio - RS150-8 6" Reference Woofer 8 Ohm
I know I could probably just pick a minimum diameter of around 3" but as this is for a university project I'd like to show some workings out.
A little bit about the values I have.
- Driver : Dayton Audio RS150-8 6" Reference Woofer 8 Ohm
- QTS : 0.34 FS : 47.8HZ VAS : 16.6 litres
- Chosen QB3 alignment
- Fb (tuning frequency) = H 1.1702 X FS 47.8 = 53.3926
- F3 = (f3 / fs) x fs = 1.3258 x FS 47.8hz = 63.37324
- VD = 34.03cm3
So the equations I'm trying to do are here:
Minimum port diameter - Album on Imgur
Equation 1 results:
Imgur: The magic of the Internet
172.2215769
Equation 2 results:
Imgur: The magic of the Internet
167.7433871
I'm assuming both results are supposed to be in inches? I've converted it from mm to inches just in case but nope, not a clue. 167 is a very high result.
Apologies in advance, I have checked other similar posts before but simply cannot get my head round it. Any help is appreciated massively.
So I'm building a bass reflex 2 way book shelf monitor and trying to figure out the minimum port diameter by using the equation provided in The Loudspeaker Cookbook. But for some reason, same with some of the online calculators, I'm getting strange results. I'm thinking its either the values I've input or I'm just being a silly sausage, I was never great at maths. The woofer I'm using is here:
Dayton Audio - RS150-8 6" Reference Woofer 8 Ohm
I know I could probably just pick a minimum diameter of around 3" but as this is for a university project I'd like to show some workings out.
A little bit about the values I have.
- Driver : Dayton Audio RS150-8 6" Reference Woofer 8 Ohm
- QTS : 0.34 FS : 47.8HZ VAS : 16.6 litres
- Chosen QB3 alignment
- Fb (tuning frequency) = H 1.1702 X FS 47.8 = 53.3926
- F3 = (f3 / fs) x fs = 1.3258 x FS 47.8hz = 63.37324
- VD = 34.03cm3
So the equations I'm trying to do are here:
Minimum port diameter - Album on Imgur
Equation 1 results:
Imgur: The magic of the Internet
172.2215769
Equation 2 results:
Imgur: The magic of the Internet
167.7433871
I'm assuming both results are supposed to be in inches? I've converted it from mm to inches just in case but nope, not a clue. 167 is a very high result.
Apologies in advance, I have checked other similar posts before but simply cannot get my head round it. Any help is appreciated massively.
Note that Vd should be entered in cubic meters, as stated below the equation. 34 cm^3 = 34e-6 m^3. Then Vd >= 1.7 inches according to the first equation.
Here is another tool to calculate the minimum port diameter: Flare-it - Free Speaker Design Software
Here is another tool to calculate the minimum port diameter: Flare-it - Free Speaker Design Software
Last edited:
Oops.. silly me. I was entering 0.34 instead of 0.000034 xD? Wow.
Hows this looking? new results - Album on Imgur . So now this equation shows that the minimum diameter is 1.7 inches? 🙂
I don't really understand ' 34e-6 m^3', as soon as I see the e-6 it scares me off haha. Always been really bad at mathematics.
Thankyou for the software recommendation, I shall check it out!
Hows this looking? new results - Album on Imgur . So now this equation shows that the minimum diameter is 1.7 inches? 🙂
I don't really understand ' 34e-6 m^3', as soon as I see the e-6 it scares me off haha. Always been really bad at mathematics.
Thankyou for the software recommendation, I shall check it out!
Also just a quick one.
The data I got from the box alignment are:
- QTS = 0.3400
- H = 1.1702
- A = 1.9699
- F3/FS = 1.3258
- Peak-dB = 0
This has resulted in me getting the following values:
Calculating the volume of the box -
VB (box volume) = VAS 16.6 L / A 1.9699 = 8.426823696634347 Litres
Calculating box tuning frequency –
Fb (tuning frequency) = H 1.1702 X FS 47.8 = 55.93556
Calculating f3 (minus three decibel half-power frequency, designates the beginning of low end roll off”)
I was just checking these are correct, the VB seems really low and the FB seems pretty high in comparison to similiar sized speaker plans?
Thankyou in advance
The data I got from the box alignment are:
- QTS = 0.3400
- H = 1.1702
- A = 1.9699
- F3/FS = 1.3258
- Peak-dB = 0
This has resulted in me getting the following values:
Calculating the volume of the box -
VB (box volume) = VAS 16.6 L / A 1.9699 = 8.426823696634347 Litres
Calculating box tuning frequency –
Fb (tuning frequency) = H 1.1702 X FS 47.8 = 55.93556
Calculating f3 (minus three decibel half-power frequency, designates the beginning of low end roll off”)
I was just checking these are correct, the VB seems really low and the FB seems pretty high in comparison to similiar sized speaker plans?
Thankyou in advance
The reason this baffles me is using said values above. When calculating the vent length using this equation:
vent length - Album on Imgur
I get these results:
port length results - Album on Imgur
33.3 inches seems like an extreme length for the port haha?
Would it be a case of over voluming the box (I know you have to do this anyway because of other features) to shorten the port length or?
Thankyou in advance whoevers reading.
vent length - Album on Imgur
I get these results:
port length results - Album on Imgur
33.3 inches seems like an extreme length for the port haha?
Would it be a case of over voluming the box (I know you have to do this anyway because of other features) to shorten the port length or?
Thankyou in advance whoevers reading.
Very strange as using this port calculator on this site Subwoofer Enclosure Calculators, Parallel, Series, Port Length and Volume which used cubic feet as the VB it recommends a port length of 7.63803 which sounds more realistic.
Last one for me I've truelly spammed the thread with questions, can tell i've been staring at a screen for way too many hours. Signing out for the night, peace!
Last one for me I've truelly spammed the thread with questions, can tell i've been staring at a screen for way too many hours. Signing out for the night, peace!
This entire discussion represents doom for the human race and questions the need for universal advanced education.
In the history of history, since the big bang, has any manufacturer made a bookshelf speaker with a 3ft port?
Maximum port diameter is largely governed by maximum internal dimension. You are not going to find many 'bookshelf' speakers with a port 3 inches in diameter. The length required would exceed the internal dimensions of the cabinet. Using bends and turns in the port is largely pointless as increased port volume reduces overall effective volume.
Generally speaking the maximum port diameter for a bookshelf sized speaker is around 40mm.
In the history of history, since the big bang, has any manufacturer made a bookshelf speaker with a 3ft port?
Maximum port diameter is largely governed by maximum internal dimension. You are not going to find many 'bookshelf' speakers with a port 3 inches in diameter. The length required would exceed the internal dimensions of the cabinet. Using bends and turns in the port is largely pointless as increased port volume reduces overall effective volume.
Generally speaking the maximum port diameter for a bookshelf sized speaker is around 40mm.
Entire discussion represents doom for the human race? Bit over the top.. just exploring a topic that I've never explored before... and new to all of this.
Thanks for the other information though 🙂
Thanks for the other information though 🙂
Sure, but can you share an example calculation of the diameter and length of the port from the doom equation? Or isn't your education advanced enough? 🙂
@ Cheznizz:
Using some equations or a box-modeling program is a good way to start a design. You have also learned the lesson to check your units!
Regarding the port diameter, larger is better in the sense that the speed of the air moving in the pipe will stay low enough that the flow does not become turbulent. At that point the resistance to flow increases a lot, and the port cannot "keep up" with the driver volume displacement. That causes the relative port output to fall off, meaning that the bass will "droop" at higher SPLs.
As you increase the port diameter, for the same resonance tuning frequency the port gets longer too. Also as the box volume gets smaller, for the same tuning frequency and port diameter the port length gets longer. This is why low tuning in small boxes results in very long ports if the diameter is large enough to keep the air speed low. Thus, successful ported boxes tend to be either small but with high tuning (Fb) and limited to small diameter drivers, or large with low tuning and somewhat larger drivers.
The typical check on port diameter is only large enough to keep the air velocity at max power below about 5% the speed of sound, which translates to about 17m/s. This is a pretty restrictive rule of thumb, so you can push it to 20-25m/s but only for max SPL playback.
When you try to use ports in boxes that are "too small" the result is a "long and skinny" port. Any tube that has a high aspect ratio (e.g. length >> width) start to resonate. This results in a "note" that is not part of the music, and it can be loud enough to hear in some cases. The resonance does not need to be excited by the music itself - the air movement causes it. This means you cannot filter it out. This has ruined many subwoofer projects! There is a free program on my web site called Unibox (it's an Excel program) that is a full-featured box-modeler and designer for speakers. It's very useful for checking your design for port resonances. Some other box modeling programs have the feature, too, but it helps to know about the things I mentioned above when trying to tweak your design.
Finally, keep in mind that many "alignments" are just points on a curve and were created/obtained with some goal in mind (flattest response, most bass extension for X dB response deviation from flat, etc.). Once you are familiar with using a box modeling program you only use these as a starting point, and then change things like box volume, tuning frequency, and port diameter from there to "tweak" the design to best suit your driver and your needs.
Using some equations or a box-modeling program is a good way to start a design. You have also learned the lesson to check your units!
Regarding the port diameter, larger is better in the sense that the speed of the air moving in the pipe will stay low enough that the flow does not become turbulent. At that point the resistance to flow increases a lot, and the port cannot "keep up" with the driver volume displacement. That causes the relative port output to fall off, meaning that the bass will "droop" at higher SPLs.
As you increase the port diameter, for the same resonance tuning frequency the port gets longer too. Also as the box volume gets smaller, for the same tuning frequency and port diameter the port length gets longer. This is why low tuning in small boxes results in very long ports if the diameter is large enough to keep the air speed low. Thus, successful ported boxes tend to be either small but with high tuning (Fb) and limited to small diameter drivers, or large with low tuning and somewhat larger drivers.
The typical check on port diameter is only large enough to keep the air velocity at max power below about 5% the speed of sound, which translates to about 17m/s. This is a pretty restrictive rule of thumb, so you can push it to 20-25m/s but only for max SPL playback.
When you try to use ports in boxes that are "too small" the result is a "long and skinny" port. Any tube that has a high aspect ratio (e.g. length >> width) start to resonate. This results in a "note" that is not part of the music, and it can be loud enough to hear in some cases. The resonance does not need to be excited by the music itself - the air movement causes it. This means you cannot filter it out. This has ruined many subwoofer projects! There is a free program on my web site called Unibox (it's an Excel program) that is a full-featured box-modeler and designer for speakers. It's very useful for checking your design for port resonances. Some other box modeling programs have the feature, too, but it helps to know about the things I mentioned above when trying to tweak your design.
Finally, keep in mind that many "alignments" are just points on a curve and were created/obtained with some goal in mind (flattest response, most bass extension for X dB response deviation from flat, etc.). Once you are familiar with using a box modeling program you only use these as a starting point, and then change things like box volume, tuning frequency, and port diameter from there to "tweak" the design to best suit your driver and your needs.
I like Basta! for volume/bass reflex simulation.
Use the serial number D4E5-EEA9-A5CE-8BD0 to get it started.
Here's a sim for your RS150 in a 12 liter box, Basta params from loudspeakerdatabase
Use the serial number D4E5-EEA9-A5CE-8BD0 to get it started.
Here's a sim for your RS150 in a 12 liter box, Basta params from loudspeakerdatabase
Attachments
Good vent area [Av] rule-of-thumb [ROT] for all but really low [Vas] and/or high [Xmax] driver alignments is [Sd]/3 and the others [Sd]/2 up to [Sd] where better to morph the box, vent volume [Vb] into a [folded] inverse tapered TL [TQWT].
FWIW, this is for the 4 ohm version, which has a bit different specs than the 8 ohm linked in the OP's post, though turns out it only changes its efficiency a minor amount.
Last edited:
Also, I've found enough [major] errors there to not use it after the last one had a [Sd] = 1.0 cm^2!, so instead search for whatever factory and/or measured specs I can find.
Thankyou so much for the help, again know it was a nooby question but I'm new in this area and had been staring at a screen all day so my brain felt fried, had a weekend off and now back at it! All the best.
A very talented British speaker designer I used to work with told me this in 1979: start with a port of optimum area (ie. equal to Sd), then compromise and work backwards until it fits in the box! Nothing whatsoever in the intervening forty two years has persuaded me otherwise...
Last edited:
That would be true for subwoofer duty.
If designing for a 2-way though, you don't want to make the vent too large, as that would require a longer vent for the same Fb, which in turn may make "organ-pipe" resonances a bit louder, lower in frequency and more difficult to address.
If designing for a 2-way though, you don't want to make the vent too large, as that would require a longer vent for the same Fb, which in turn may make "organ-pipe" resonances a bit louder, lower in frequency and more difficult to address.