Indian equivalents of the following DIY items.

[tcpip]

I found this thread in the Full-Range forum on diyaudio, where one person wanted to know what drivers to use for building speakers which could handle full orchestral music. And a lot of responses seem to point to the JX92S. I knew the Jordans were highly regarded, but I am a bit surprised that people try to handle full orchestral music using them.

Stuart, I thought you might find that thread interesting, in case you haven't seen it already.

[Ronnie22]

Somebody in this thread had recommended using Racron (found in pillows) as an acoustic absorbent inside cabinets. I need to use this material inside the speakers i'm making but how does one use this stuff? i mean how do i get the thing into shape to fit against a wall and hold it in that shape? And how do i stick the thing against the walls?

Racron is very fluffy.

[tcpip]

Originally posted by Ronnie22
Somebody in this thread had recommended using Racron (found in pillows) as an acoustic absorbent inside cabinets. I need to use this material inside the speakers i'm making but how does one use this stuff? i mean how do i get the thing into shape to fit against a wall and hold it in that shape? And how do i stick the thing against the walls?

Recron is, AFAIK, Reliance Industries' take on what is internationally known as Dacron.

If you take that material in your hands, and lay it out in a flat layer on a horizontal surface about 1-1.5" thick, you can press it down with your hands and almost make it into a sheet. Since the fibres are long, this sheet will hold its shape. In this way, you can first apply a uniform layer of Fevicol on one inner surface of your box, then apply a layer of this Recron, and then pat it down such that it sticks in one fairly uniform layer. Upto about one inch to 1.5" thickness is not a problem at all. Wait for this surface's Fevicol to dry, then turn the box over, get some other surface horizontal, and apply the Fevicol+Recron on that one. And proceed this way, slowly, waiting for each surface to dry before trying the next one. The Recron will stay.

A more thorough way of doing this, for heavier fibres and thicker layers is to first create flat pouches using nylon netting (the stuff out of which mosquito curtains are made in India). Make the pouch of roughly the size of your inner walls. Then fill these pouches with the fibre, uniformly, taking care to spread it so that it becomes a flat sheet, like a cotton-filled quilt, not a round pillow. Then take the whole net-pouch and stick it using Stikfast or SuperGlue (not Fevicol, because Fevicol won't stick nylon) to the walls of the enclosure. Pad it down to ensure that it retains its flat shape.

For the one or two boxes I've made, I've stuck Recron directly to the walls.

I presume you already know this, but this wall-lining is used for vented enclosures. Sealed enclosures are generally filled completely.

[s_zimble]

Thanks for the lead on the FR thread TCP!! . I do visit there occationaly but have not participated yet (need to read more of the past threads first).

One comment/question for the damping materials: I often see pictures or diagrams of vented TQWTs or TL designs that are literally "stuffed" with damping material, usually in the top part of the tube. Can you help explain why a "wall damping" might be prefered over a total stuffing in tube-type enclosures? Thanks for your insight.

BTW, I went to the market and bought a bag of this Indian Dacron. It is supper fluffy and hard to determine how dense I should pack it. I think this was somewhat discussed earlier in this thread, but the question arises again. It seems like a very inaccurate science. I am imagining opening and closing my cabinets dozens of times with different densities of stuffing and having a listen with a very familiar piece of music. How off base am I??

Stuart

[tcpip]

Originally posted by s_zimble
One comment/question for the damping materials: I often see pictures or diagrams of vented TQWTs or TL designs that are literally "stuffed" with damping material, usually in the top part of the tube. Can you help explain why a "wall damping" might be prefered over a total stuffing in tube-type enclosures?

Please remember that I've not built many speakers. Take all my comments with an inch of salt (preferably iodized).

It seems the prevalent opinion is that stuffing is generally a substitute for box volume, therefore, a smaller box with lots of stuffing will be acoustically equivalent to a larger box with no stuffing. That's the reason to fill a box completely with fibres. For sealed boxes, more filling broadly means ==> more acoustic volume ==> lower frequency. However:

• Filling also seems to make the driver "slower" to react, i.e. it seems to lose some of its "sparkle" and "dynamics". This means that midranges may not sound as detailed. Therefore, fill the box, but don't fill too much. This "slowing down" of course is more of an issue with midranges than bass boxes, therefore subwoofers are sometimes filled quite heavily.
• For vented boxes, it seems that completely filling the box upsets the T/S calculations for box size.... the bass reflex effect doesn't behave properly any more. Therefore, only the walls of the box are lined, so that just standing waves and reflections can be attenuated, but the overall volume is largely retained air-filled, not fibre-filled.
• Filling directly behind the driver seems to affect its dynamics particularly sharply. Hence, many people seem to feel that a few inches of space behind the driver should be unfilled, even if the rest of the box is filled.
• Rules for controlling fibre-filling in TL are quite different from sealed boxes. I have even less clarity about those rules than about sealed and vented boxes.
• People who demand more accurate reproduction than deep, deep low frequency (i.e. the music lovers as against the HT school) seem to prefer light filling even in sealed woofers. They seem to dislike very heavy filling... it apparently makes the driver really sluggish.

Acoustically, adding stuffing to a box is sort of like adding mass to the cone of a driver, I think. Both will lower the Fs, but both will increase Mms and therefore make the driver less capable of responding lightly and quickly to subtle details. I could be totally wrong, but this is my understanding. However, some degree of fill (in sealed boxes) is always good because it reduces internal resonances, standing waves, and so on, which can otherwise cause lots of distortion and peaks in the freq response.

Vance Dickason's speaker-building bible has a detailed quantitative analysis of effects on speaker parameters with various degrees of different kinds of stuffing. Please check out that section for some good insight. However, after all that analysis, the subject still remains somewhat of an art rather than science... there seems to be no theoretical or empirical way to predict what will sound the best in your speaker design.

BTW, I went to the market and bought a bag of this Indian Dacron. It is supper fluffy and hard to determine how dense I should pack it.

For sealed boxes, I prefer to start by filling it lightly, i.e. I tease the fibres till they expand in volume, and then I drop flakes bit by bit into the box till the entire box fills up. This method may be too light for really low-freq woofers in 3-way designs... in that case, a heavier fill may be better. Some texts seem to measure degrees of fill in terms of pounds/cubic-foot of stuffing material.

Yes, it's an inexact science. But then, since you are fiddling with just one degree of freedom when you experiment with the filling, I think you can arrive at some sort of optimal point over a fairly small number of iterations. And for vented boxes, just line the walls and get on with it... no real experimentation needed AFAIK.

Tarun

[tcpip]

Originally posted by s_zimble
I often see pictures or diagrams of vented TQWTs or TL designs that are literally "stuffed" with damping material, usually in the top part of the tube. Can you help explain why a "wall damping" might be prefered over a total stuffing in tube-type enclosures?

A thought just occurred to me: have you read Lynn Olson's writeups about the Ariel? In particular, have you read the portions where he describes the addition of good bass to the Ariel, and issues of box design and stuffing and so on? If not, it's a must-read. Check out
this page and ideally, read everything before and after it.

[ajju]

Acoustically, adding stuffing to a box is sort of like adding mass to the cone of a driver...

If you get to dig out Acoustics by Leo Beraneck, there is a good explanation on the physics behind the effects of stuffing on the wave. The last I saw this book was in the reference section of ISRO technical library7-8 yrs ago, and sadly my dad is retired...

From the book, all I can remember now is that, there was a mention of, stuffing slowing down the effective speed of sound as the process becomes more adiabatic in nature. The reduction in the speed, is of the factor of .7, to that under free air conditions..
Whenever the speaker cone moves it compresses air in the box. In a closed box, or for that matter any column of air behind the cone, the limited compressible nature of air, results in an opposing force on the cone. This springiness adds to the existing compliance of the loudspeaker increasing its Fs. Or in other words it improves the stiffnesss of the loudspeaker. (this also explains y sealed boxes can handle more momentary peak power than any other form of enclosure, without launching the cone into a near earth polar orbit. )

Acoustical compliance of the air in an enclosure is given by
Cab =(Net_internal_volume) / (density*speed_of_sound)
Vab is the equivalant volume of air having the same compliance as Cab.
now if we take two volumes, one without stuffing and one with and try equating them for Cab we would get..
V_air = V_stuffed *(density_air/density_stuffed) * (speed_air/speed_stuffed)
Theoritically, for the loudspeaker to see a larger volume loading, we could either reduce the speed of sound, or reduce the density inside the enclosure.
Stuffing tries to achieve the first, however the amount of gains are limited, as an increase in effective density with more stuffing, tends to negate the gains. The law of dimnishing returns prevail.
SImilarly, thick stuffing in ported enclosures is not reccomended as it increases the flow resistance thus broadening the box resonance peak, or decreasing the Q of the box system. With high stuffing, a ported system approaches the behaviior of a closed one or worse..! Stuffing has an added advantage that it absorbs the frequencies higher up in the spectrum pretty efficiently. This prevents internal reflections and relaunch through the diaphragm.
When we talk of transmision lines, there is a slight difference in concept that we are mass loading the loudspeaker, (instead of adding a series box compliance to it.) This has the benefit of reducing the effective resonance frequency since the rear mass load adds upto the existing Mms. The reduction in speed of sound caused by stuffing, causes the line to apear longer than what it is physically. Hence by carefull designed we can achieve a comparitively shorter physical line tuned to a lower frequency by judiciously using stuffing. However design of any transmission line is rather diffcult and relies on more of trial and error. In transmission lines stuffing is inavetiable as it is very much required to absorb the higher harmonic resonances of the line. If left untreated certain sound would appear kind of robotic..

Until now, option two was kind of impossible. The quick thought that comes to our mind when trying to reduce density is; get rid of the air, or rarefy it....but this creates a partial-vacuum and causes a pressure bias across the speaker diaphragm, which means it is more or less useless..!!
However, KEF have pioneered a new method using carbon dust, and they claim to have achieved a density reduction by a factor of upto 3.
This means that they can do away with bulky enclosures and is quite apparent in their new product line up..! Refer KEF KHT series.

using Racron (found in pillows) as an acoustic absorbent

If I remember correctly, Vivek from bangalore, had once procured sheets of Racron for his MTM.
Vivek...your inputs please..!!

Many thanks
ajju

[s_zimble]

Again.... Thanks for all the feed back. Let me read and then experiment a bit.

Stuart

[sachi]

Guys can you giveme your views on this stuffing that i have done...



after reading your posts am feeling a bit nervous..
nervous cause i may have to donn all the protectve gear before i remove some of that glass wool.

Thanks,
Sachi

[tcpip]

Originally posted by ajju
Acoustical compliance of the air in an enclosure is given by
Cab =(Net_internal_volume) / (density*speed_of_sound)
Vab is the equivalant volume of air having the same compliance as Cab.

I've read so many things in so many places, but these three lines made my day. They cleared up some fundamental equations and their meaning so beautifully, that I'm thrilled. My basic understanding has gone up to a new level entirely. From the time I read about Vas, I've been struggling to get an intuitive understanding of what Vas stands for. Till just now, I had not succeeded. Thanks a ton.