NS1000 damping ?

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sq225917
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Re: NS1000 damping ?

Post by sq225917 » Thu Jul 11, 2019 5:12 pm

Dynamat and similar products are to damp vibrations in lightweight metal panels, speaking wadding is to slow down air movement, other treatments are used for cabinet damping.

I used to use dynaflex mat. A lenticular lens patterned thick sorbothane sheet, about 12mm thick on the inside of my speakers. Strangely I feel no need to mod the yams
One more Paradise left to complete.

YNWaN
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Re: NS1000 damping ?

Post by YNWaN » Thu Jul 11, 2019 5:39 pm

Similar materials to those you link to are used but the damping of a thin metal sheet (as in a car) and a thick MDF/chipboard panel are quite different. Therefore, bitumen style panels are more often used for speaker cabinets. These are also used for cars but they are heavy and have a tendency to fall off as the metal panel expands and contracts is the sun and cold. In the case of speakers the problem is that such panels tend to add mass and just lower the resonant frequency of the cabinet rather than actively subdue it. The role of the internal filling is quite different, it’s not to damp the cabinet directly but to damp the air mass contained within. There are two resonances to consider, one is direct reflections from the cabinet walls and the other is standing waves set up between parallel surfaces - this is why angled surfaces are often used.
Mark

MTPapaDan
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Re: NS1000 damping ?

Post by MTPapaDan » Mon Jul 22, 2019 10:26 pm

Let me see if I have this. One could use Dynamat to line a speaker. Doing so would lower the resonant frequency. One could replace the fiberglass with Fiberfill to reduce standing waves. Fiberfill is a trade name for the white stuffing used in furniture and pillows as padding. Sometimes it is in sheets and other times in cotton ball form. Why would lowering the resonant frequency be a bad thing? Couldn't changing the RF to a different point be a positive? For example, lowering the RF from 200 Hz to 40 Hz. Isn't there considerably less sonic energy at 40 Hz anyway? How would such a change affect the low frequency (lobe?) points in a room? If the room was sensitive at 200 Hz wouldn't changing the frequency to 40 Hz be better? I understand that the application of Dynamat is probably unpredictable. One would never be sure how it effected the RF and that is perhaps the biggest drawback? And trying to removing it would be a nightmare. Now as to Fiberfiil, would one try different amounts to achieve the best results or put an amount equal to the fiberglass removed? Wouldn't one want to stuff in as much as possible, without infringing on speaker cones? Or is the amount contingent on the Q of the speakers in relation to volume? How would I know if the amount I have is about the same as when manufactured? Mark when you moved to external x-overs, did you have to put in more fill?

YNWaN
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Re: NS1000 damping ?

Post by YNWaN » Wed Jul 24, 2019 9:25 am

Yep, absolutely regarding the Dynamat and Fiberfill. The shifting of resonance is less clear though. Largely this is because the size of shift you suggest can be achieved just by applying Dynamat, the whole cabinet construction and material would have to be changed. As you say, there is less energy (usually) at 40Hz but that is also a frequency at which many rooms promote standing waves and so that whole (40, 50, 60Hz) range is a sensitive one. As to the other questions you raise, well yes, all very good points and difficult to answer without significant experimentation - even then there is a very subjective aspect to it all.

In my case, although it may look otherwise, I didn’t want to make significant changes to the balance of my speakers when I refurbished them and that is why I reused the original fibreglass filling and didn’t build new cabinets (though I did consider doing both).

I didn’t add more filling to compensate for the crossover removal but I did add an internal brace that braced the back of the bass driver to the rear edges of the cabinet. The volume of the added bracing was similar to that of the removed crossover so I just considered it quits.
Mark

MTPapaDan
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Re: NS1000 damping ?

Post by MTPapaDan » Wed Jul 24, 2019 4:01 pm

AH.... I guess I knew. Have leftover Dynamat from car. Was looking for an excuse to use it. In fall and winter I am going to build external crossovers and Fiberglass just effects me too much even with long sleeves and gloves. So I guess I'll change over to fiberfill in cabinet and use a similar volume of fiberfill to account for removal of crossover. Not worried about originality if I'm going to external crossovers.

ChrisOH1
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Re: NS1000 damping ?

Post by ChrisOH1 » Wed Jul 24, 2019 8:26 pm

Any use? Should be able to find wool in these parts

https://www.qtasystems.co.uk/loudspeake ... erials.htm

YNWaN
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Re: NS1000 damping ?

Post by YNWaN » Fri Jul 26, 2019 7:48 pm

Yes indeed - all good stuff. In the past I’ve used the long hair sheep’s wool. I’m not convinced it’s any better than glass fibre though. In fact, the glass fibre is very good in a technical sense. It’s not very nice stuff to work with but when it’s sealed inside the speaker it doesn’t really matter does it? The other problem with the sheep’s wool is that it gradually settles over time and so tends to, effectively, alter filling density. The recommended way to avoid this is to suspend the wool in netting separated layers inside the cabinet (what a pain that must be to do).
Mark

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