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My DIY 4 way speaker system


Bokke
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1 hour ago, MF 1000 said:

1 x6” port would need a length of 1 metre to get down to 16 Hz or 670mm fir 20 Hz 

A 100 mm port of 470 mm length would give you 16 Hz ….so bigger isn’t always easier too 

but my cabinet length is only 600mm minus the mdf thickness of 25mm

so would 2 x 6 inche ports  at 300mm be any good?

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48 minutes ago, MartinC said:

What frequency range are you looking to cover with your lowest frequency cabinet @Bokke? There are loads of DIY subwoofer designs if it's only below ~100 Hz, and clear advantages to having boxes that only cover this range since you can then place them at different locations in the room than the rest of the speakers.

I mean id need to experiment with the perfect cross over but I've got around 150 hz as a starting point. then it will go over to be smaller bass driver until the midrange takes over.

as regards placement of the cab - they will have to be all together as if one speaker even though its going to be a 3 box plan.

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Super Wammer
8 minutes ago, Bokke said:

but my cabinet length is only 600mm minus the mdf thickness of 25mm

so would 2 x 6 inche ports  at 300mm be any good?

My port is 100 mm and 650mm with a 90 deg bend to fit inside the cabinet 

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30 minutes ago, MF 1000 said:

My port is 100 mm and 650mm with a 90 deg bend to fit inside the cabinet 

ok that's interesting 

can you tell me what you think I should do? as the original drawing was 100mm holes and I'm stuck as to solution for the chuffing you described .

if i could use the original 100mm diameter flange and just make it longer inside with 90 degree turns to extend then that would be much easier.

Please let me know your thoughts

Edited by Bokke
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Super Wammer

I don’t get chuffing with 1 x 100 mm dia port 

1B540BD8-974B-4C0D-8D60-DFFD18F77BFD.jpeg.296e0f9cc56bcf85536785c12444658f.jpeg
 

before I trimmed it to length ….it’s std underground waste piping 

Edited by MF 1000
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9 minutes ago, MF 1000 said:

I don’t get chuffing with 1 x 100 mm dia port 

1B540BD8-974B-4C0D-8D60-DFFD18F77BFD.jpeg.296e0f9cc56bcf85536785c12444658f.jpeg
 

before I trimmed it to length ….it’s std underground waste piping 

thanks 

but i have a question - if i also use just one port off 100 mm diameter is that ok if i make it longer like you have done?

what length should I make it?

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Super Wammer

500 mm long 100 mm port would give a cabinet tuned to 16Hz 

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1 hour ago, MF 1000 said:

500 mm long 100 mm port would give a cabinet tuned to 16Hz 

ok im getting there 🤣

so my next question is: 

is it multiple ports that cause the chuffing noise or just the diameter size?

the reason I ask is they were originally already 100mm diameter but just 3 of them 

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This isn't something I've ever really looked into, but I thought that the shape of the flaring at the end of the port was significant in terms or reducing port noise?

One way to completely avoid any risk of port noise is to go with a sealed design of course. Not that I ever noted any issue on the ported sub that I used to use.

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Super Wammer

The chuffing noise is from fast moving air in smaller diameter ports and also compression of the air in the port can affect the response - calcs for this are beyond my pay grade.  

Hence  why multiple ports are sometimes used for  a cabinet tuned to low Hz.  There are equations available to calculate this but I’ve avoided it all by using one large port….large port low air speed low compression etc 

eg a 200 litre cabinet with 3 x 40mm ports tuned to 16Hz would need a port length of approx 225mm per port 

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I just Googled out of curiosity re. port flaring and noise and it looks like I was remembering correctly:

https://www.researchgate.net/publication/339726207_Loudspeaker_Port_Design_for_Optimal_Performance_and_Listening_Experience

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1 hour ago, MF 1000 said:

The chuffing noise is from fast moving air in smaller diameter ports and also compression of the air in the port can affect the response - calcs for this are beyond my pay grade.  

Hence  why multiple ports are sometimes used for  a cabinet tuned to low Hz.  There are equations available to calculate this but I’ve avoided it all by using one large port….large port low air speed low compression etc 

eg a 200 litre cabinet with 3 x 40mm ports tuned to 16Hz would need a port length of approx 225mm per port 

I see now where the confusion is

in the cabinet drawing the ports are not scaled to be 100mm

but they are meant to be 100mm diameter so in reality would look a lot larger than that.

just so I'm 100% sure I'm correct  on your thought process.

so if the ports are 100mm its ok even if there are more than one port as volt say the more ports the lower it will go 

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Super Wammer

According to my calcs 3x10 cm ports 34 cm long in a 200 litre cab would give a tuning frequency of 32 Hz.  If you wanted to get down below 25 Hz that’s 56 cm per port and 16 Hz is 138 cm ! 
 

But …..you could squeeze 2 ports in either side of the driver at 92 cm using my 90 deg bend setup in your cabs 😁

Edited by MF 1000
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Using this calculator; http://www.calculatoredge.com/new/ventlength.htm

Something interesting here;

A 196L box with 3 x100 dia 32 cm long ports is tuned to 30 hz.(end correction factor(k) of 0.73).

Block one port leaving 2x 100 @32cm and the box is tuned to 25hz.

Block 2 ports leaving 1x 100@32cm long and the box is tuned to 17.5hz.

All "or there abouts".

The 3 port arrangement would be flexible given driver parameters and room position/gain.

Edited by cooky1257
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Super Wammer

How do you get to 32 cm long Frank ……it gives 117 cm when I’ve run it to get 17 Hz ?

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