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Stuffing in Speaker - Need guidance

sudhirbhosale

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#1
Hi all
Need guidance on below questions as I planned to add recorn stuffing in my speakers:
1 How to decide optimum level of stuffing?
2 Pros Cons of over/under stuffing
3. Does driver size, 2way/3way matters
4 Any thumb rule?
5. What to covers i.e. Rear speaker wall, side wall etc.
Thanks
 
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Hari Iyer

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#3
sudhirbhosale, the amount of stuffing required will depend on type of enclosure ( sealed, vented, TL). Depending on your enclosure type, you can measure the impedance of your speakers while adding/ removing recron ill you get critical damping result. You can check critical damping impedance curve for various types elsewhere. Hope this helps.
 

saikatbiswas82

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#4
Correct me if I'm wrong. But I think stuffing material density/quantity varies in case of different types of design like ported, sealed, TL, horns etc. (like FM Hari already mentioned)

I'm also newbie in diy speakers. Hoping to gain some knowledge from experienced FMs.

Another important question I thought to ask. Why do we go for stuffing? Is it for cancelling standing waves or to reduce the speed of sound to make the enclosure bigger than they physically are?
 

keith_correa

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#5
Please read this.

https://www.diyaudio.com/forums/multi-way/80522-stuffing-box.html

As far as I know, only Martin King's sheets will allow you to accurately quantify and check the amount of stuffing against effect visually via a plot. There's a lot of science and Math behind his sheets and they're not free. Leonard Audio's free TL program also does this, but the effect of stuffing that it shows is inaccurate. But it can be used as a starting point. Then, it depends on your taste.
 
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hifitoaster

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#6
I think you can do a trial and error in one box until it reaches the sound u like. I always thought this was pseudo science. ;) I was able to improve(subjective) the sound of branded speakers this way. When u have more stuffing, u will hear less the box. But be aware at some point it will screw up free movement of driver. But u will know it as it would distort at that point.

Sorry that wasnt science. I would look for evening the sound from the cabin, when knocked, with neoprene or opdm sheets on walls before stuffing. If you open a spendor or harbeth u may see them, on walls. This makes the cabin vibration controlled. If you knock on those boxes, u will hear the same sound everywhere.
 

Naveenbnc

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#8
sudhirbhosale, the amount of stuffing required will depend on type of enclosure ( sealed, vented, TL). Depending on your enclosure type, you can measure the impedance of your speakers while adding/ removing recron ill you get critical damping result. You can check critical damping impedance curve for various types elsewhere. Hope this helps.
Dear Hari,

What equipment do we need to measure impedance ??? A mic, and some software i guess....
Can you throw some light please....
Regards,
Naveen
 

Naveenbnc

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#12
So basically this is what the above link says on standing waves ....

"This means that the cabinet has to be filled almost completely with polyfill or other sound absorbing material, only the space around the speaker and the vent has to be left free. A common bad solution like sticking a very thin layer open cell foam on the rear wall has got minimal effect, so it is useless..."

and in the link shared in post #5 diy people says too much filling made the mid range sound dull.
 

Sumanta

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#13
Hi all
Need guidance on below questions as I planned to add recorn stuffing in my speakers:
1 How to decide optimum level of stuffing?
2 Pros Cons of over/under stuffing
3. Does driver size, 2way/3way matters
4 Any thumb rule?
5. What to covers i.e. Rear speaker wall, side wall etc.
Thanks
What about making an Open baffle speaker set? No need to worry about stuffing inside cabinet and in the listening room as well.
 

keith_correa

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#14
Please don't overthink the stuffing/lining angle. I've done this many times before and it IS true that it has to be stuffed to taste. For a vented box, I'd line internal walls with at least an inch thick open cell foam and then stuff very loosely with fluffed up polyfill to taste. Just keep the polyfill away from the driver basket vents and the port end inside the box.
In addition, If you can also hang a sheet of open cell foam from roughly the middle of the top of your box till the middle of the bottom of your box - that's effective too.
 

Sumanta

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#17
But bass is issue with 6inch driver
Have a TL bass cabinet to supplement, there you stuff first 2/3rd part and leave the port side 1/3 free. I prefer trial and preferential type of filling in the cabinet. Stuffing can be done in a completed cabinet too (depends on the contour of the line as well) with a slim hook, say a straightened aluminium hanger.
 

Naveenbnc

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#18
To make this thread little more informatie and useful to everyone..... (I am not sure if we have a dedicated thread for stuffing and bracing)

Can you all share any further experiences with stuffing??? Somethings like....

1. Different stuffing materials - pros and cons (discussed here and there in different posts)

2. Filling the complete box Vs filling partially
(Some of us have already answered this above)

3. We can include braving techniques also (is Sudhir accepts:)) and how much bracing is optimum and the effects...

4. Any easy tips and tricks to handle standing waves etc etc etc....
 

Naveenbnc

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#19
What about making an Open baffle speaker set? No need to worry about stuffing inside cabinet and in the listening room as well.
With my very little experience .... currently i feel the best thing (atleast in terms of ease) is to do the following:
Put the bass driver in a box ... and leave the mid+tweeter or FR on OB
(ofcourse...you did a lot of work in this route :):))
 

smedhavi

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#20
If you are designing the speakers with drivers and box of your choice with known specifications, then you have to plan the stuffing accordingly. If you are doing it for speakers designed by someone else, just go by what sounds better to you. My experience is that open cell foam is useful for absorbing the extra/booming bass, pollyfill helps in cleaning up the boxy lower mid-range and shouty mid-range (glasswool is even better). Stuffing has no impact on the treble as most tweeters have no acoustic connection with the speaker chamber. If you have the bass and mid-range drivers in the same acoustic chamber, then you could create a partition between the two using a couple of layers of thick open cell foam sheets. Too much foam would kill the bass.
Some vintage speakers had just a cotton pillow behind the driver, and they sounded wonderful.

regards,
Sharad Medhavi
 
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