Recommended sealed box size for RSS390HF-4 15"

S

Sylar

Full Audioholic
I have obtained the Dayton RSS390HF-4 15", and require advice on the design.

After reading Ray Alden's speaker building book and having browsed through 100's of threads. The recommended ported box size is around 9 cu ft, which is not reasonable by any means. Going ported is completely ruled out. Same with other designs like isobaric. Which leaves me with a sealed design. For this driver with sealed, I understand I might have to compromise on the low end or something else to a certain degree. After much contemplation, the only design that I can do, is sealed. Hence this thread.

So, I have made three decisions to begin with.
  1. Driver is RSS390HF 15" (I already have it).
  2. Design is Sealed box.
  3. Amp is external - XLS 1500 or XLS 2002 (I have both). I also have a MiniDSP.
Next up is box size. Which is where I require advice.
Reading through numerous threads across different forums, I find the sealed box size for this driver vary widely from 2.5 to 6 cu ft.

So what is the best sealed box size for this driver and why?
 
Last edited:
TLS Guy

TLS Guy

Audioholic Slumlord
I have obtained the Dayton RSS390HF-4 15", and require advice on the design.

After reading Ray Alden's speaker building book and having browsed through 100's of threads. The recommended ported box size is around 9 cu ft, which is not reasonable by any means. Going ported is completely ruled out. Same with other designs like isobaric. Which leaves me with a sealed design. For this driver with sealed, I understand I might have to compromise on the low end or something else to a certain degree. After much contemplation, the only design that I can do, is sealed. Hence this thread.

So, I have made three decisions to begin with.
  1. Driver is RSS390HF 15" (I already have it).
  2. Design is Sealed box.
  3. Amp is external - XLS 1500 or XLS 2002 (I have both). I also have a MiniDSP.
Next up is box size. Which is where I require advice.
Reading through numerous threads across different forums, I find the sealed box size for this driver vary widely from 2.5 to 6 cu ft.

So what is the best sealed box size for this driver and why?
The optimal box size is 2.5Cu.ft. However you have to add driver displacement and bracing to that. So you final box volume will be something like 2.75 cu ft, when you add back the air volume displaced by those items. This box size will give you are very satisfactory Qts of 0.7, so the bass will be tight.

As will all sealed designs, you will have to add a boost of 12 db per octave starting at 40 Hz. The driver starts to get significantly power limited below 25Hz, so a 12 db per octave high pass filter should be placed at 25 Hz. All this is normal practice when designing a sealed sub. Sealed have simpler carpentry, but more complex electronics. However Mini DSP should get this job done for you.

This will be a good sounding sub, but output limited compared to a ported design. However, I think unless you space is huge you will be happy with it.
 
S

Sylar

Full Audioholic
The optimal box size is 2.5Cu.ft. However you have to add driver displacement and bracing to that. So you final box volume will be something like 2.75 cu ft, when you add back the air volume displaced by those items. This box size will give you are very satisfactory Qts of 0.7, so the bass will be tight.
Was stuck with work. Just got some time to get back to this.
Curious to know what happens when I increase box size (for example 2.5 to 3 Cu ft)? What do I gain and what do I lose?

Got 2 weeks off from work. Will try and build it during this period.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Was stuck with work. Just got some time to get back to this.
Curious to know what happens when I increase box size (for example 2.5 to 3 Cu ft)? What do I gain and what do I lose?

Got 2 weeks off from work. Will try and build it during this period.
The program I used calculates the optimal box. That means what it says. So what it does, is find the optimal balance between bass extension, Q and power handling.

So you only have downsides from making variations away from the optimal box. So if you increase box size, then you will move away from optimal Q, and above all loose power handling, as the restoring force on the driver cone will be reduced. So that will limit your ability to apply the required Eq.

I have to say that you are calling to mind a well documented incident that involved Peter Walker founder of Quad Electroacoustics at an Audio Fair at the Russel Hotel.
A visitor kept asking him the same question repeatedly. Finally he got hold of the guy by his lapels, and said: "If you are not going to believe the bloody answer, then don't ask the bloody question!"
 
S

Sylar

Full Audioholic
The program I used calculates the optimal box. That means what it says. So what it does, is find the optimal balance between bass extension, Q and power handling.

So you only have downsides from making variations away from the optimal box. So if you increase box size, then you will move away from optimal Q, and above all loose power handling, as the restoring force on the driver cone will be reduced. So that will limit your ability to apply the required Eq.

I have to say that you are calling to mind a well documented incident that involved Peter Walker founder of Quad Electroacoustics at an Audio Fair at the Russel Hotel.
A visitor kept asking him the same question repeatedly. Finally he got hold of the guy by his lapels, and said: "If you are not going to believe the bloody answer, then don't ask the bloody question!"
Sorry, My bad.I was reading stuff and trying to understand effects of different box sizes. Attempting to use a subwoofer design tool with not much success.

I am currently drawing the box plans for this.
Dimensions look like this with target internal volume of 2.5cu ft. Following are the dimensions that I came up with for this.

Internal: 16.5 x 16.5 x 17 inch
External: 18 x 18 x 18.5 inch
Woofer and Bracing volume: 0.173 cu ft
Final box volume: 2.505 cu ft

A few quick questions:
  1. Should I double up the driver side panel? I do not intend to flush mount. Will be using 18/19mm wooden panels.
  2. How much should I fill up the sub with fiberglass?
  3. Which nuts do i use to mount the driver. While building my previous sub i had some trouble with the nuts.
  4. Should MDF be good enough? Or should I use Birch Plywood?
 
ryanosaur

ryanosaur

Audioholic Spartan
Sorry, My bad.I was reading stuff and trying to understand effects of different box sizes. Attempting to use a subwoofer design tool with not much success.

I am currently drawing the box plans for this.
Dimensions look like this with target internal volume of 2.5cu ft. Following are the dimensions that I came up with for this.

Internal: 16.5 x 16.5 x 17 inch
External: 18 x 18 x 18.5 inch
Woofer and Bracing volume: 0.173 cu ft
Final box volume: 2.505 cu ft

A few quick questions:
  1. Should I double up the driver side panel? I do not intend to flush mount. Will be using 18/19mm wooden panels.
  2. How much should I fill up the sub with fiberglass?
  3. Which nuts do i use to mount the driver. While building my previous sub i had some trouble with the nuts.
  4. Should MDF be good enough? Or should I use Birch Plywood?
Baltic Birch will be lighter and work great for Subs. I would recommend seeking that out as your option.

Doubling up the Front Baffle is is common, and for a 15" driver, not a bad plan.

Which nuts?
Deez Nuts GIF by imoji for iOS & Android | GIPHY
Sorry, couldn't help myself.
...
Low hanging fruit! :D

But seriously... are you thinking of installing T-Nuts or threaded inserts? Bolting through the layers or just some heavy wood screws?
 
S

Sylar

Full Audioholic
Baltic Birch will be lighter and work great for Subs. I would recommend seeking that out as your option.

Doubling up the Front Baffle is is common, and for a 15" driver, not a bad plan.

Which nuts?
Deez Nuts GIF by imoji for iOS & Android | GIPHY
Sorry, couldn't help myself.
...
Low hanging fruit! :D

But seriously... are you thinking of installing T-Nuts or threaded inserts? Bolting through the layers or just some heavy wood screws?
Was thinking of using T-Nuts. Do I have a better option?
 
TLS Guy

TLS Guy

Audioholic Slumlord
Sorry, My bad.I was reading stuff and trying to understand effects of different box sizes. Attempting to use a subwoofer design tool with not much success.

I am currently drawing the box plans for this.
Dimensions look like this with target internal volume of 2.5cu ft. Following are the dimensions that I came up with for this.

Internal: 16.5 x 16.5 x 17 inch
External: 18 x 18 x 18.5 inch
Woofer and Bracing volume: 0.173 cu ft
Final box volume: 2.505 cu ft

A few quick questions:
  1. Should I double up the driver side panel? I do not intend to flush mount. Will be using 18/19mm wooden panels.
  2. How much should I fill up the sub with fiberglass?
  3. Which nuts do i use to mount the driver. While building my previous sub i had some trouble with the nuts.
  4. Should MDF be good enough? Or should I use Birch Plywood?
For a driver that large I always double the front panel.

The box needs to be filled. Fiber glass is not optimal. The best and cheapest option is Polyfill used in cushions. Fill the box but do not compress it.

T-nuts are fine and a good option for a heavy driver.

MDF or Baltic Birch are good options for a sub.
 
S

Sylar

Full Audioholic
I'm not getting any decent rubber feet other than for spikes. (I'm in India) Any suggestions for subwoofer feet?

My PSB towers came with these rubber feet, 20mm in length. The ply board is 18mm. Would this work?
 

Attachments

TLS Guy

TLS Guy

Audioholic Slumlord
I'm not getting any decent rubber feet other than for spikes. (I'm in India) Any suggestions for subwoofer feet?

My PSB towers came with these rubber feet, 20mm in length. The ply board is 18mm. Would this work?
You can use any furniture feet from a hardware store. I'm sure any hardware store will give you lots of options. They do not have to be for speaker use specifically.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Just done with 2 boxes. Much of it has come out well.
The front panel was glued together at the last and there is some airgap that I can see.

What is the best way to fix this?
They look to be nice boxes. Well Done! Any gaps can be filled with silicone sealant.
 
highfigh

highfigh

Audioholic Overlord
Was thinking of using T-Nuts. Do I have a better option?
T-nuts to hold the woofer in place? If you double the front panel and use the proper screws, you may not need to, but another way to hold the screws is with threaded inserts- they're installed using an Allen wrench and use machine screws- a very secure and strong way to hold something in place.

You don't need to use the parts from this seller- the link is only to show the parts-


As far as the effect of making the box larger, it will reduce power handling, make the sound looser and cause the response to fall off higher in the response curve. Pay attention to what TLS posts- the word 'optimum' means that it can't be better.

Think of the air in the box as a spring that controls the movement of the cone assembly. A larger box is a weaker spring and a smaller box is stronger. Tap the cone when the driver is outside of the box and you'll see it vibrate for a short time after the tap but in the correct box, you tap it and the vibration stops immediately. You want it to stop vibrating immediately.
 
S

Sylar

Full Audioholic
They look to be nice boxes. Well Done! Any gaps can be filled with silicone sealant.
Silicone didn't help much.
So removed it and used saw dust + glue mix on the inside.

Now the box seems to be air sealed to a large extent. The driver cannot be pushed in easily. Needs quite a bit of effort. I presume very minor air leaks would not be an issue as long as the driver is "tight".
 
ryanosaur

ryanosaur

Audioholic Spartan
Generally you want to close up everything. One reason why some drivers have a foam gasket already installed... for those that dont, there's products like this gasket tape:

Likewise, it is common to use sealant a;; around the internal joints to make certain there are no air leaks, and to seal up any places where wires or connectors are not tightly installed. Even in a ported enclosure, these leaks and losses will be deleterious to final performance.
 
S

Sylar

Full Audioholic
Here are couple of pics of the sub. Finishing is pending.
Not sure what to go with.

IMG_20210202_095519565_HDR~01~01.jpg


IMG_20210202_095502162_HDR~01.jpg
 

Latest posts


newsletter
  • RBHsound.com
  • BlueJeansCable.com
  • SVS Sound Subwoofers
  • Experience the Martin Logan Montis
Top