[TX1978]

I will soon be embarking on my first sub build, and plan to put the enclosure inside a current wall void. The internal box dimensions that I came up with are as follows; 1.16' wide x 3.256' tall x 2.08' deep. This nets 7.9 cu ft for a Dayton rs5390hf. Don't worry about room between studs. I will handle that.

Since this will be "in wall" the driver and port will need to be on the front face. What size and length port do I need to hit 18 Hz?

Thanks!

 

[TheInfinitSound]

Why do you want to hit 18Hz? You know that you rather feel those low frequencies than you actually can hear them? What you're hearing with most subwoofers at these frequencies are the way too much raised distortions.

Another point to consider is the listening room. With single subwoofer configurations this is often the limiting factor. In most cases you will not get a reasonably reproduction of frequencies under your first room mode. I say this from my personal experience. I myself had different subwoofers able to play down to 20 Hz and lower. But in nearly every room I tested them I wasn't able to hear these frequencies only in rooms with one dimension taller than 8 meters it was possible. A way around this would be a dipol subwoofer, double bass array or a single bass array with huge back wall absorption. Just mentioning...

Referring to your question: With your given enclosure dimensions you can reach good 19Hz (at the -3db point). If you're planning to run the Dayton with its rated 500 watts the port should be big enough in order to avoid audible port air velocity. I would choose at least the following internal port dimensions so you can keep the air velocity under 20m/s at 24Hz and up (with a peak of 27,5m/s at 17,5Hz): 35,36cm (wide) x 5cm (tall) x 50cm (deep). And no need to worry I already considered the port volume (liters) in my calculations and subtracted it from the box volume of 222,5 liters. Here is the max possible spl within the xmax of 14mm and power rating of 500 watts (sorry for the spaces in the link that's because my account is still limited):

pic-upload . de / view-26142476 / Dayton_RSS390HF_BR_01 . jpg . html

 

[TX1978]

I want it able to produce such low frequencies for effect during movies. Whether I can hear or feel them, I would like to have the "true" theater experience.

My current sub is an older big-box store unit; 15" downfiring with twin 4" ports on the back. It does well enough, but when low frequencies are played during movie playback, all I hear is the driver unloading and it flapping around.

My theater room is greater than 8 meters, length wise.

Thanks for the help.

 

[chrapladm]

Why inwall?

If I was only given one spot to put a subwoofr and HAD to use an inwall location I would somehow make it dual opposed. That would cancel out most mechanical vibrations. And a room your size with 8m is going to need a lot more than a single ported 15. Why not just buy as many SI 18HT's as you can afford?

 

[TX1978]

I was hoping to install it in-wall to free up floor space, and figured it would look a whole lot cooler. But if its going to net less/worse acoustic performance, thats not going to work.

I know that my current sub isn't cutting the mustard, but the more I read on here the more confused I get. Build a ported 15", build a sealed 18, build as many XXs as I can accomodate. I'm kinda lost
I just want quality lows for movies.

Would the sealed dayton 18" kit (4 cu ft box) play low enough with the spa1000?

 

[TheInfinitSound]

A sealed 18" instead of the vented 15" doesn't make sense with regard to the aim of as much (quality) spl on the low end as possible. A fitting sealed enclosure for the Dayton RSS460HO for example would give you 8db less output at 20Hz than my suggested vented enclosure for the 15" Dayton. Here is a comparison of the two (red the RSS390HF BR and blue the RSS460HO CB):



In my opinion the vented Dayton RSS390HF is a fairly good starting point and if you actually need more output you could just build another identical one which would also give you a much more regular bass spreading in your room. And if you really want to impress with your setup you could upgrade to a single or even better a double bass array later on too...:thumb:

Referring to the inwall question: I don't see any huge drawbacks here. If you prefer the look a lot more I would definitely build it like this. One not to deny benefit of inwall speaker mounting is in fact that you will get less troubles with interferences caused by the speaker to wall gap. Of course you also have more pronounced room modes but it's a lot easier to correct those sonic rises than obliterations (sorry I don't know the correct expressions here). The by chrapladm suggested dual opposed construction (you mean impulse compensation right?) is ideal with freestanding speakers because this cancels out most of the enclosure vibrations. With a reasonable implemented inwall construction I think this could be obsolete if you make sure there is a really solid connection to the surrounding walls.

Just my thoughts on this...

 

[TX1978]

thanks for the help!

I climbed into the wall cavity yesterday night, and the in-wall won't work. I could build the box, but wouldnt be able to fit it through the opening into the cavity. I considered assembling it inside the cavity, but i would have no room for clamps or a screw gun. So on the floor in the main room it will go. With that said, i have a few more questions:

As I am no longer constrained by the wall cavity, can I mod the enclosure dimensions as long as I stay at net 7.9 cu ft?

Regarding ports, does round vs slotted make a difference as long as they are equal volume? Also, does it make much difference where they are on the enclosure? Same face as driver, 90 degrees to driver, etc.?

If the enclosure will reside on the floor, does it need feet?

Thanks again!

 

[TheInfinitSound]

As I am no longer constrained by the wall cavity, can I mod the enclosure dimensions as long as I stay at net 7.9 cu ft?

The shape doesn't make that much of a difference as long as the volume stays the same. Only immoderate length in one dimension you should avoid because you then could get troubles with internal enclosure resonances within the subwoofer's frequency range.

Regarding ports, does round vs slotted make a difference as long as they are equal volume? Also, does it make much difference where they are on the enclosure? Same face as driver, 90 degrees to driver, etc.?

Theoretically the port shape also doesn't matter if there is equal port volume. But I would build a slotted one anyway because in most cases it's more solid and you can already use three of the enclosure walls as spatial limitations so you have to add only one additional panel which at the same time is a enclosure stiffening too.

On the contrary the port positioning does make a minor difference. It's not like one position would mess up the entire performance but what it does is in fact influencing the port efficiency above your tuning frequency. As you probably know the sound radiation is 180 degrees in phase on the other side and thus would normally cause an almost complete sound cancellation in front of the chassis. Therefore one enclosure's purpose is either turning phase optimally to 360 or 0 degrees in order to use the back sound or destroying it (sealed box concept). Having said this one can conclude that with rising distance between chassis and port also the sound addition rises above the tuning frequency as their radiated sound waves are more in phase whereas the output around the tuning frequency stays the same because here the port resonance (delayed) already achieve this phase turn. According to measurements this turns out true but in nearly all cases compared with the tuning frequency's wavelength the enclosure's dimensions are so small that the impact here is relatively neglectable. With large floorstanding speakers the max possible port distance will give you a few extra db but not much.

Long story short - Choose it to your (visual) liking...

If the enclosure will reside on the floor, does it need feet?

Which kind of feet are best sound quality wise depends on the underground. If your floor is made of solid material like concrete spikes could be the way to go because they achieve coupling of the enclosure to the ground which suppresses then most of the vibrations. But if your floor isn't solid enough and resonates by itself then it could be more intelligent to use decoupling from the ground while simultaneously destroying the vibrations within the feet. Viscoelastic materials like a rubber cork sandwich for example would reach this. Alternatively as already mentioned before you could just impulse compensate your subwoofer which would make all these actions obsolete. However you then will need a second identical chassis in your enclosure (of course this results in more output level too).

 

[TX1978]

I cant thank you enough!
I will start the build next weekend. Stay tuned!

 

[TX1978]

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?

 

[TX1978]

Sorry, .311 cu ft for port

 

[TX1978]

I will also account for bracing volume, such that "useable" volume remains 7.9 cu ft

 

[TheInfinitSound]

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?

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).

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).

 

[TX1978]

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

 

[TheInfinitSound]

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.

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

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.

 

[TX1978]

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

 

[TheInfinitSound]

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?).

 

[TX1978]

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.

 

[bigsausagepizza]

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.

 

[TX1978]

By baffles I meant bracing.