[navin]

Originally Posted by mondymk3

2. regarding tyres noise i think it's better to have some weather proof materialpasted under the body as well area around tyres. that will help.

Rest one more thing which really helps in reducing noise level in general conditions (not in cars) is providing a air gap between the body and the dampening material. I'm not sure if this can be achieved in cars.but if done it'll reduce noise drastically.

Wurth sells a spray on damping that can be used under body

Air is a good thermal insulator but not a good sound insulator. However if you could make a vaccum in that space...hmm...

[mondymk3]

Hi
Air do works good as a sound insulator. i have recently got done acoustic treatment in power house. and air gap is very neccessary to dampen the noise level.
As i have told earlier that the material now being used under the bonnet only in few cars like Swift can be pasted around the engine and it'll work in reducing noise level i'm jus posting a pic of my mondeo where they have done the same thing. Also other under body pics but i cant really make out what material it is. check out if it helps in anyways.

[navin]

Originally Posted by mondymk3

Hi
Air do works good as a sound insulator.

think about it. If it did the sound of your speakers would be severly attenuated before they reached you.

[mondymk3]

im talking about air gap naveen which is not there in case of speakers. Also if u go deep into the acoustics you will see all the theaters and all power houses uses the same funda.

[nishantgandhi]

I had a question regarding sealed sub enclosure w.r.t Bhagwan's sealed enclosure in this pic

Now I know B is an exception when it comes to damping. Maybe 99% of people do not damp their enclosures at all, leave alone using Noise Kill for it.

However, is it advisable to use some other alternative form of damping for the enclosure? What other materials could be 'stuffed' or 'lined' inside the enclosure's wall to make it more effective?

Would damping/stuffing a sealed enclosure also increase the power requirement from the amp?

[greenhorn]

glass wool/polyfill from pillows, sand even

[BHAGWAN]

I used to use Reliance Polyfill. But do not use it now.

[navin]

Originally Posted by nishantgandhi

Now I know B is an exception when it comes to damping.

Originally Posted by BHAGWAN

I used to use Reliance Polyfill. But do not use it now.

B and I have slightly different philosophies when it comes to cabinet construction. I prefer cabinets that are stiff and damped but light so that less energy is stored in the cabinet.

B uses MDF, I use FRP.
B damps using noise kill, I damp using wool, foam and thermacol balls.

Ideally one would resort to "constrained layer damping" where a layer of damping maertial is constrained between 2 layers of MDF or FRP but finding a suitable material for this damping layer has proven diffcult.

In a sealed box the back wave of the speaker needs to be absorbed. I believe the best way to do this is to convert the kinetic energy into heat. wool, polyfil, etc.. are capable of this, each in a limited way. filling a tube with thermacol balls and jamming the tube between the speaker's magnet and the opposing wall is better.

Another option is to use Aperidoc loading of the box. Illustrated in link below. There is no free lunch. Aperiodic boxes are more power hungry and box losses increases (QL goes up). After QL goes beyond 15 the gains are limted so again this is only a partial solution.
Aperiodic Speaker Enclosure Design

Mass Loaded Transmission Lines also go an excellent job of damping but these are not suitable for most car installs.

If you want to follow the mass damping method one cheap option is to get 1.5mm lead sheet (available in Mumbai at places like HMT Metal Corp, Kolsa Mohilla, Pydhonie, Mumbai 3 - opposite the Pydhonie police station).

I think in the long run one needs to use each of these partial solution to damp the box as much as possible.

[DerAlte]

Originally Posted by navin

B and I have slightly different philosophies when it comes to cabinet construction. I prefer cabinets that are stiff and damped but light so that less energy is stored in the cabinet.
B uses MDF, I use FRP.
B damps using noise kill, I damp using wool, foam and thermacol balls.
...
In a sealed box the back wave of the speaker needs to be absorbed. I believe the best way to do this is to convert the kinetic energy into heat. ...

IMHO there is no comparison in what B is doing and you are doing, Navin.
* B's implementation, both the original one (with concrete) as well as with Noise Kill, is about preventing wall flex and the resultant out-of-phase release back into the box. These measures cannot dissipate the excess energy pumped by the rear-ward excursion of the speaker - for which B used horse hair et al in the concrete-box implementation (B: why horse hair???)
* You are systematical creating (pneumatic) resistance for converting KE to heat

Lead sheet, Noise Kill etc. wouldn't dissipate the (pneumatic) energy, but only the energy stored in the wall. In fact, Noise kill is likely be totally ineffective in B's case (wall mass is significant) as compared to your FRW box.

B's (concrete) philosophy is simple & effective for this: increase mass so that all that energy is never absorbed in the wall (infinite mass cannot be moved, and mass of air v/s concrete reaches that proportion!) - but it does not absorb any energy from the rear wave.

In fact, I have always had doubts about the practice of covering all parts in a door, whether narrow or wide, whether small area or large, with damping material. The doubt is w.r.t. "law of diminishing returns" in damping: smaller the flex area, lesser the travel due to flexing, hence lesser the energy stored and reflected back (what damping material is trying to absorb). So why cover each sq.mm. with damping sheet, when judicious application will provide max gains at min cost?

[BHAGWAN]

Dear DA,

You have explained things rather well; Good !

If you could be so kind so as to shed some light on how you would implement a 'sealed enclosure' I could take some tips on my next one - I am serious.

Thanks,

[DerAlte]

Originally Posted by BHAGWAN

... If you could be so kind so as to shed some light on how you would implement a 'sealed enclosure' I could take some tips on my next one - I am serious. ...

And show a light to the sun? No thank you, I prefer to be sane! I am better off at observing aberrations.

PS: Why horse hair?

[BHAGWAN]

Originally Posted by DerAlte

PS: Why horse hair?

Horse Hair when mixed with long sheep wool is a material that is used by 'speaker makers' to damp the inside of their speaker cabinates - there are different combinations with different ratio [proportions] that work on different frequencies.
We need to absorb 100 hertz and above [in a sub woofer i.e.].

Butamine too works - hence the damping 'noise kill'
High Density Foam etc. etc. there are lots of materials that can work - we just have to play around with them.

[navin]

Originally Posted by DerAlte

PS: Why horse hair?

DA you seem to having visions of Bhagwan running around the Mahalaxmi Race Course and Amateur Rider's Club chasing horses and plucking out their tails. LOL :-)

Originally Posted by DerAlte

preventing wall flex and the resultant out-of-phase release back into the box.

you are systematical creating (pneumatic) resistance for converting KE to heat

B's (concrete) philosophy is simple & effective for this: increase mass so that all that energy is never absorbed in the wall

DA, B, Gurus, correct me if I am wrong. When building a box I see 2 problems
(1) Stifness and (2) Damping. A box must be stiff so that the walls do not flex and a box must be well damped (wall as well as the volume contained within them) so that the wall do not Resonate. Stiff Walls if not damped will resonate.

Stifness is easier to achieve . Make a wall think enough and it will get stiff. But thick walls get heavy even if they are MDF. And heavy walls will store energy which will be released after some delay and decay.

My attempts have been to reduce wall flex and ensure that as little energy is stored in the walls as possible. I believe the best way to do this is by absorbing the energy before it hits the walls and by make the walls stiff but light. The same methods used to absorb the energy before it hits the walls will also aid in absorbing the energy released by the wall (however little that may be).

For home audio using 2 midwoofers in push push (this is very disimilar to isobarik) serves 2 functions. (a) since the drivers are in opposing ends their mechanical vibrations will cancel (b) using the second woofer on the rear of the cabinet allows you to address baffle step compensation without the use of high value inductors (that will again store energy).

I may be wrong; more companies are using the high mass philosophy than low mass but I belive this is more due to the ease of production than anything else.

Dont get me wrong. MDF is an easy material to work with, is quite dense and naturally well damped. Many DIYers who have experimented with other materials have realised that MDF offers 80% of the advantages for 20% of the effort and have gone back to MDF. FRP and the associated technologis mentioned above make sense only when one has the access to the infrastrcuture and when (for reasons that cannot be logically explained) one wants to march to the beat of a different drum.

[nishantgandhi]

Just to bring the discussion to saner and layman's levels - are the enclosures normally available with installers damped? If yes, with what material?

What about those readymade boxes like JBL, Blaupunt and Bassworx?

Finally, is foam a well enough damping material for sub enclosure?

OT - B, the sub box that you had given me - what was it damped with?

[navin]

Originally Posted by BHAGWAN

We need to absorb 100 hertz and above [in a sub woofer i.e.].

For most subs we need to absorb 100 Hz and below. However there are few materials that can do this. Tar, Noise Kill, etc.. wont absorb this it will only help make the cabinet stiffer and mass load the cabinet walls. If one only want to mass load the cabinet walls (not a bad idea in itself) I would recommend those lead sheets I talked about earlier.

I once built a MDF-lead-MDF-FRP subwoofer 130 liter cabient that was 70mm thick (2x 30mm MDF, 1.5mm lead, 6mm FRP and some glue) that used 20 kgs of lead sheet (40 kgs was used over 2 cabients) and weighed in 80kgs each including the 2 12" woofers. to move this cabinet easily I imported this
Appliance & Refrigerator Movers, Appliances Moving Equipment & Systems – Air Sled.

B, I still have the air sled, if you want to borrow it.

Getting back to absorbing 100Hz and below, this is where converting the kinetic energy into heat is a fair option (the other one being using 2 drivers in push-push).