Designing a 2-way bookshelf speaker

[keith_correa]

Polyfill is available in siliconized & non-siliconized types. I've heard that non-siliconized is better for lining/stuffing speaker boxes. The siliconized stuff will be slick and slippery [and more expensive] as compared to the non-siliconized variety which is rough.

 

[jmascreen]

I have used the below Foam i is 1.5 inch thick, I got it here from a shop where they make Sofas & other type of furniture. This foam is very light weight & has a medium density. I have observed that this foam is more efficient in absorbing the mids & high frequencies. By putting ear on the vents I didn't heard any mid's or highs coming out from vent.

Sadik

I use the same for lining the walls not for stuffing

 

[sadik]

I use the same for lining the walls not for stuffing

Give it a try and i am sure you will be surprised by the results.

 

[Hari Iyer]

There is a Gadiwalas atThane who sells Recron brand polyester fiber. I searched after romaing for 3 weeks

I have seen Aquastuff available at amazon.in. They are not very expensive and are the best to use.

@ jmascreen.
The density of stuffing required for your box is decided by the simulation software.
You will need to convert that to grams reqd by multiplying the volume of your cabinet with the density. Care needs to be taken for unit of measure conversion as you are dealing with multiple units of measure to arrive at the grams reqd.

 

[keith_correa]

Give it a try and i am sure you will be surprised by the results.

Did you stuff the speaker with the foam?

 

[jmascreen]

Give it a try and i am sure you will be surprised by the results.

Isn't that change the volume of the box?

 

[sadik]

Did you stuff the speaker with the foam?

Yes I had stuffed... This is very cheap Foam and if you need u can try it out too in your future projects.

Sadik

 

[sadik]

Isn't that change the volume of the box?

The Purpose of Foam is to absorb the mid's and highs generated inside the enclosure & prevent them to escape through the Vents. This Foam has very low density & is very good at doing its Job.

Yes there will be change the total volume of Enclosure, but is is not that high which will effect the performance of the Enclosure.

You have to use it practically to hear the results.

Sadik

 

[Kannan]

The Purpose of Foam is to absorb the mid's and highs generated inside the enclosure & prevent them to escape through the Vents. This Foam has very low density & is very good at doing its Job.

Yes there will be change the total volume of Enclosure, but is is not that high which will effect the performance of the Enclosure.

You have to use it practically to hear the results.

Sadik

Infact by using the right material and quantity and in the right place, the apparent volume of the enclosure will increase due to absorption of back waves.

 

[captrajesh]

The Purpose of Foam is to absorb the mid's and highs generated inside the enclosure & prevent them to escape through the Vents. This Foam has very low density & is very good at doing its Job.

I'm intrigued at your statement. I thought that the purpose of stuffing is to absorb the standing waves inside the cabinet which are predominantly a result of LF sound. Secondly, I thought that there would not be any HF sound since the tweeter is sealed at the rear and whatever little HF coming out of the backwave of the midwoofer/ midrange driver would be cutoff drastically by the Xover. I'm truly intrigued. Could you substantiate!

 

[tcpip]

I'm intrigued at your statement. I thought that the purpose of stuffing is to absorb the standing waves inside the cabinet which are predominantly a result of LF sound. Secondly, I thought that there would not be any HF sound since the tweeter is sealed at the rear and whatever little HF coming out of the backwave of the midwoofer/ midrange driver would be cutoff drastically by the Xover. I'm truly intrigued. Could you substantiate!

Assuming that the speed of sound is 345 m/sec, a standing wave which, well, stands in a 12-inch space (a reasonable dimension in many enclosures) will have a wavelength of 24 inches, or multiples of this. A sound wave of wavelength 24 inches is 575 Hz. This is clearly midrange territory. Multiples of this means upper midrange or HF territory. In a 2-way speaker, the tweeter often takes over at 2.5KHz or so, which means that the midbass is pumping the enclosure space full of all sorts of frequencies upto this point. So, the standing waves will have a lot of midrange and HF waves. These need to be attenuated or else they'll break through the cone and distort the sound in strange ways.

 

[Hari Iyer]

I have successfully used felt behind the midwoofer to prevent the mids and high mids escaping from the cone and adding destructively with the midrange sound. The trick is to allow escape of low frequency and trap only the mids and mid-highs. A Banian type cotton cloth also does well in doing this.

Again my 2 paise.

 

[Hiten]

I'm intrigued at your statement. I thought that the purpose of stuffing is to absorb the standing waves inside the cabinet which are predominantly a result of LF sound. Secondly, I thought that there would not be any HF sound since the tweeter is sealed at the rear and whatever little HF coming out of the backwave of the midwoofer/ midrange driver would be cutoff drastically by the Xover. I'm truly intrigued. Could you substantiate!

A little limerick

Captain Saab what sadik meant is this,
stuffing gives reflections a goodbye kiss.

Some reflections are converted to heat,
wave energy is surely made to deplete.

internal standing waves can be nullifed,
with shapes and ratio by a proper guide.

Right you were about tweeter being sealed,
Important is if diffraction outside can be killed.

I am no speaker guru so can not be sure.
let others experienced chime in for more.

:lol:

Regards

 

[sadik]

I'm intrigued at your statement. I thought that the purpose of stuffing is to absorb the standing waves inside the cabinet which are predominantly a result of LF sound. Secondly, I thought that there would not be any HF sound since the tweeter is sealed at the rear and whatever little HF coming out of the backwave of the midwoofer/ midrange driver would be cutoff drastically by the Xover. I'm truly intrigued. Could you substantiate!

The primary purpose of stuffing in a Vented Enclosure is attenuation of internal reflections. I Can't Prove this just by doing some sort of calculation. Simple way is .. Make a Vented Enclosure don't do any kind of stuffing, Put your ear on the vent and you can hear the Mid's & Highs coming out through the vents, Now add the stuffing on the walls of Enclosure & you will find a lot of difference. This i am saying because i have experienced it practically. I don't have proof to prove it by doing some calculation. However i cant say if the same thing is applicable for Sealed Enclosures. May be what you wrote is applicable for Sealed Enclosure.

Secondly as per my thinking, most of us place the Speakers right in front of walls, so when the mid's & highs escapes through the vents they also get reflected by the walls which makes the sound distorted. (This is just my logic based on my experience)

 

[Hari Iyer]

The primary purpose of stuffing in a Vented Enclosure is attenuation of internal reflections. I Can't Prove this just by doing some sort of calculation. Simple way is .. Make a Vented Enclosure don't do any kind of stuffing, Put your ear on the vent and you can hear the Mid's & Highs coming out through the vents, Now add the stuffing on the walls of Enclosure & you will find a lot of difference. This i am saying because i have experienced it practically. I don't have proof to prove it by doing some calculation. However i cant say if the same thing is applicable for Sealed Enclosures. May be what you wrote is applicable for Sealed Enclosure.

Secondly as per my thinking, most of us place the Speakers right in front of walls, so when the mid's & highs escapes through the vents they also get reflected by the walls which makes the sound distorted. (This is just my logic based on my experience)

I shall post some simulated mages from LA for my Metronome TL FS speaker to prove your point.

 

[keith_correa]

The trick is to allow escape of low frequency and trap only the mids and mid-highs.

Isn't the sound at the back of the driver 180 deg. out of phase with the sound at the front of the driver? If you let the low frequencies escape from the back they would cancel, no?

 

[Hari Iyer]

Isn't the sound at the back of the driver 180 deg. out of phase with the sound at the front of the driver? If you let the low frequencies escape from the back they would cancel, no?

What I meant was escape from the back of the midwoofer and not blocking it. The low freq will be tuned to the box and will escape from the port/ terminus. Some part of it will be reflected back and be absorbed by the stuffing and some will escape from the midwoofer cone. I usually don't prevent the low freq escaping the cone, but will certainly block the mids and high mids from escaping from the back of the cone.

 

[jls001]

I have used the below Foam

Sadik

Isn't this "Hitlon" foam? Usually used for safely packing heavy items?

 

[sadik]

Isn't this "Hitlon" foam? Usually used for safely packing heavy items?

No. Its Not a Hitlon Foam, Usually this type of Foam is used in making Seat Covers of Cars, Arm Rests of Chairs or light furniture.

 

[jls001]

Okay:thumbsup:

Yes, it looks like the same foam used by car upholstery and sofa makers.

It's certainly a new learning for me

I have a couple of 2 inch thick sheets of about 4'x6' each I bought to ship heavy items.