Need help with port length / size based on my enclosure - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

Old 02-17-15, 11:31 AM Thread Starter
Shackster

Join Date: Feb 2015
Location: DFW, TX
Posts: 70
Sorry, .311 cu ft for port
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Old 02-17-15, 09:38 PM Thread Starter
Shackster

Join Date: Feb 2015
Location: DFW, TX
Posts: 70
I will also account for bracing volume, such that "useable" volume remains 7.9 cu ft
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Old 02-18-15, 03:52 AM
Shackster

Join Date: Feb 2015
Location: Germany
Posts: 13
My System
Re: Need help with port length / size based on my enclosure

Quote:
TX1978 wrote: View Post
To verify, if I want a 7.9 cu ft enclosure, i need to make it with an internal volume of 8.46 cu ft to accomodate for the .22cu ft the driver displaces, and the .3[11] cu ft of the port, correct?
Quote:
TX1978 wrote: View Post
I will also account for bracing volume, such that "useable" volume remains 7.9 cu ft
Yes you have to sum up all the things leading to volume decreases and add these to your effective volume target. However like mentioned before I already considered the port volume in my calculations (which as a consequence resulted in more port depth) so no need here to add this to the enclosure volume furthermore. If you really demand 7.9 cu ft effective volume I would need to look up the calculations again for the unaltered port depth (if I remember correctly this was about 48cm instead the 50cm).

Quote:
TX1978 wrote: View Post
Will the dayton spa500 take up noticeable internal volume?
Just in case I would also measure the volume taken up by the amplifier's encapsulation or at least roughly calculate it from the outer dimensions (see the SPA500 User Manual).

EDIT: One additional point has to kept in mind. If you plan on rounding the port endings (what I really recommend you to do in order to reduce the audible port air velocity noises) you will have to add half rounding radius to the port depth (for each side of course).

Last edited by TheInfinitSound; 02-18-15 at 04:18 AM.
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Old 02-18-15, 06:27 AM Thread Starter
Shackster

Join Date: Feb 2015
Location: DFW, TX
Posts: 70
Would I gain anything by having the bigger enclosure (7.9 cu ft) plus port volume? If not, i will keep it at 7.9, including the port and add to it for driver and amp displacement.

What do you mean about port radius? I will of course round off the edges of the exit and entrance, but the long edges will be flush with the enclosure sides so I cannot round them. Do you mean to take into account the material removed for the radius in the port volume calculation?

As I build the box, which will be on the floor via cork feet, would I see any benefit of having the driver firing at the floor instead of into the room? Also, I can have the port firing into the room, or towards a corner. Is one better than the other?

Thanks as always
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Old 02-18-15, 11:01 AM
Shackster

Join Date: Feb 2015
Location: Germany
Posts: 13
My System
Re: Need help with port length / size based on my enclosure

Quote:
TX1978 wrote: View Post
Would I gain anything by having the bigger enclosure (7.9 cu ft) plus port volume? If not, i will keep it at 7.9, including the port and add to it for driver and amp displacement.
Now that there are no more dimension restrictions due to the inwall plan I made some new enclosure calculations for you:

• white: 214 liters (excluding port volume); port 38,9 x 5 x 56,4 cm (width x height x length)
• green: 222,5 liters (excluding port volume); port 38,9 x 5 x 53,9 cm (width x height x length)
• blue: 250 liters (excluding port volume); port 38,9 x 5 x 49,7 cm (width x height x length)
I thought increasing the port and thus enclosure width would make its look a bit more balanced cause the previous 35,36 cm (1,16 ft) is surely rather small for the Dayton 15" chassis (which is 38,84 cm). Besides that also the port's surface area increased hence further lowering its audible air velocity.

You can choose between these suggestions or ask me for another calculation if you would prefer still other enclosure dimensions (more specifically width). Sure you also could simply adjust the port dimensions by yourself considering the port's surface area and volume.

Quote:
TX1978 wrote: View Post
What do you mean about port radius? I will of course round off the edges of the exit and entrance, but the long edges will be flush with the enclosure sides so I cannot round them. Do you mean to take into account the material removed for the radius in the port volume calculation?
Since a picture says more than thousand words please look up the following thread where chrapladm posted a very good picture lately explaining right this topic: Click Me

Quote:
TX1978 wrote: View Post
As I build the box, which will be on the floor via cork feet, would I see any benefit of having the driver firing at the floor instead of into the room? Also, I can have the port firing into the room, or towards a corner. Is one better than the other?
This depends on your preference. Mounting your chassis facing the floor will give you more room shaking but in most cases poorer sound quality (in addition having a floor other than quite a solid one would suck off some of the hearable bass).

Referring the port positioning question: Personally I would place the port as near as possible to the backwall in order to have less interferences (and more room gain of course plus stronger room modes wherefore some would lapidate me now - To those: A few post above there is a short clarification) and additionally like explained before as far away as possible from the chassis. Not facing directly the port could also be an advantage if there should be some air velocity noises.
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Old 02-18-15, 11:00 PM Thread Starter
Shackster

Join Date: Feb 2015
Location: DFW, TX
Posts: 70
Regarding the blue model, does it much matter if the overall port volume remains tbe same but width and length swap? So the width is 49.7cm and the length is 38.9? This will be easier to build, as it relates to my internal volume dimensions.

Also, I follow about the port length. Food visual, and I will comply
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Old 02-19-15, 09:53 AM
Shackster

Join Date: Feb 2015
Location: Germany
Posts: 13
My System
Re: Need help with port length / size based on my enclosure

Quote:
TX1978 wrote: View Post
Regarding the blue model, does it much matter if the overall port volume remains tbe same but width and length swap? So the width is 49.7cm and the length is 38.9? This will be easier to build, as it relates to my internal volume dimensions.
This will not work as the port's volume isn't the only factor. Surface area and volume together in relation determine your tuning frequency. Please name me your preferred width and I will calculate the corresponding port dimensions for the chosen enclosure (the blue one right?).
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Old 02-19-15, 10:36 AM Thread Starter
Shackster

Join Date: Feb 2015
Location: DFW, TX
Posts: 70
I will use the blue option; 8.8 cu ft

I am debating between two options. These are enclosure internal dimensions.

1)
55.87cm x 41.9 x 106.67

2)
55.87cm x 55.87 x 78.739

Both options will have a port width of 55.87cm

To these dimensions I will add volume for port, driver, amp, and baffles.
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Old 02-19-15, 01:11 PM
Shackster

Join Date: Feb 2015
Location: Boston
Posts: 38
My System
Re: Need help with port length / size based on my enclosure

Quote:
TX1978 wrote: View Post
To verify, if I want a 7.9 cu ft enclosure, i need to make it with an internal volume of 8.46 cu ft to accomodate for the .22cu ft the driver displaces, and the .343 cu ft of the port, correct?
Will the dayton spa500 take up noticeable internal volume?
That's correct, if you design for 7.9 cu ft that is net volume. Your gross volume then needs to be 7.9+0.22+0.343=8.463 cu ft. Make sure you take into account the thickness of the material, if you only take exterior measurements you'll fall a bit short. Are you planning on any sort of bracing? For a box that large on 500+ watts you are probably going to want some internal bracing to minimize box flex. You also need to take into account the volume of any bracing you are using into your calculations.
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Old 02-19-15, 01:13 PM Thread Starter
Shackster

Join Date: Feb 2015
Location: DFW, TX
Posts: 70
By baffles I meant bracing.
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