Felt for lining speakers

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oceanobsession1
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#1 Felt for lining speakers

Post by oceanobsession1 »

Hi all has anyone used swaldale felt underlay for lining the inside of speaker cabinets and can comment on its quality. cheers all phil
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Toppsy
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#2

Post by Toppsy »

If it's the pure wool underfelt then yes I use a similar make for lining all my speakers. Excellent stuff. I prefer to use 15mm thick, but 12mm thick is OK for smaller speakers.
oceanobsession1
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#3 Re felt for lining speakers

Post by oceanobsession1 »

Hi there topsy what are you using then please cheers phil.
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Toppsy
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#4

Post by Toppsy »

Phil,
In the past I starting using Swaledale 54oz Pure New Wool Carpet Underlay as recommended by the pundits on some other forums who say pure wool is best, but I now use this http://www.carpet-underlay-shop.co.uk/o ... -213-p.asp,

OK it's not 100% pure wool but recycled wool and other fibres, but it is thicker and cheaper and having built 2-pair of identical speakers one lined with Swaledale 54oz pure wool and the other in the Own Label 54oz I could hear no sonic difference or performance difference in the damping qualities of either. So as I go through a couple of full rolls a year I now use the cheaper own brand. Some others may have a different opinion based on their experiences.
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#5 Re felt for lining speakers

Post by oceanobsession1 »

Hi again, ive ordered a sample of the swaldale, felt to have a look at, its ok
I used some felt that a friend got me it was a bit thicker and stronger I think
but yes I think what you have suggested is probably best or the slightly
dearer enviorolay 54oz,
Reffc
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#6

Post by Reffc »

I use the recycled pressed wool (12mm) and it's fine. It depends what you want it for. I use it under 40mm acoustic foam as an additional panel damping membrane, but if you don't intend to use acoustic foam or lambswool, then it isn't that effective on its own. you need a specific grade of stand alone felt, SAE F10, F11 or even F7 would do. Its very soft, density shouldn't exceed 0.25g/cm3 for stand alone acoustic damping and preferably 0.18 to 0.2g/m3 is best. When you get to that grade, it is also horribly expensive. Denser wool-mix felts are nowhere near as effective at absorbing mid/HF to prevent internal reflections.
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Toppsy
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#7

Post by Toppsy »

Reffc wrote
....but if you don't intend to use acoustic foam or lambswool, then it isn't that effective on its own.
Sorry to disagree with this statement as I find it most effective, mind I use thicker than 12mm. As I say I use it in all my speakers and they are designed for minimal damped cabinets that are only lined. I only add additional layers of Monacor MDM-3 to the bottom of the cabinets below the port tube to damped the standing waves in floorstander speakers.

I do so hate stuffing speakers with lambs wool as internal damping, sucks the life out the speakers in my opinion. But that's just my take. And for foam damping particularly the egg box stuff :shock: Forget it.

Perhaps you use a different cabinet alignment that requires a lot of internal damping?
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#8

Post by Reffc »

My take in this is that wool felt has to obey the laws of physics too :D

Dense wool felt (compressed recycled being an example) reflects as much as it absorbs. You have to use SAE10 or perhaps 7 where the density is such that it absorbs far more than it reflects. Simple physics.

Minimally damped cabs are fine providing that there is sufficient fully absorbant material directly behind the driver, adjacent to the drivers, top and bottom, all to prevent unwanted reflections passing back through the mid range causing phase distortion. Another one of those annoying physics things.

Finally, you can't attenuate standing waves by placing material top and bottom since these are nodal points of minimal (read zero) amplitude. To attenuate standing waves, there has to be material placed roughly half way down the speaker cabinet. Yet another one of those pesky physics facts :wink: Cabinet dimensions, if properly selected, can keep internal standing wave issues to a minimum irrelevance.All my cabinets are designed this way.
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Scottmoose
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#9

Post by Scottmoose »

Thank you for the lecture, but most of the speakers Colin currently builds are either designed by me, or have had some input, and the damping employed does what it is supposed to. Which does not involve extraneous resonances, reflections off internal walls coming back through the cones or any other related matters. Believe it or not, I know a little bit about speaker design. Damping is when necessary adjusted to reflect measured behavior (not often needed).

Addressing a couple of other aspects, the claim that a longitudinal standing wave is unaffected by material at the ends of the pipe is overly simplistic. In terms of perfect theory this would be true, but we do not live in a world of Platonic perfection. We live in the real world. Thus. Damping is indeed at its most effective when placed at the velocity maxima of a standing wave, and of significantly reduced effectiveness at the velocity minima. Two points there. First, the term 'at its most effective.' It is not the single point where it has any effect. Second, damping is three dimensional. It has depth, width and length. The latter can be quite substantial, moving it steadily away from velocity minima and further into the box. Thus it can and does affect the aforementioned longitudinal standing wave. How much depends on the frequency of said, the length & type of material involved & a host of other factors of which you are presumably aware. Now, if it is not practical for whatever reason to place damping at the point of maximum velocity, or if you have other reasons for not wishing to do so, an appropriately thick layer of an appropriately chosen type of damping on the base can be a perfectly valid alternative providing you have accounted for these matters in the design. You will simply need to use more of it to achieve the desired result. All speaker design is about balancing compromises, unless you have invented the first speaker in history without any.

As for golden ratio, or the various other acoustic ratios, they certainly don't hurt matters from the perspective of acoustics, but they rarely have a major impact upon standing waves in an enclosure. Golden ratio was largely employed by architects for visual appeal hearkening back to nature, but when it comes to speakers, the degree of improvement (if any) is rarely worth becoming too beholden to them, especially if it forces compromises elsewhere. You might (might) be able to get away with a little less damping depending on the box, but this is not in the realms of night and day or anything like, so while it's nice if you can do it, grown men will not swoon, maidens will not tear their hair and urchins will not weep if you can't. Its real advantage lies is in giving people something else to say in their adverts.
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#10

Post by Reffc »

It was not a lecture, it was simply my own take on things, and I have no doubt as to your views, abilities or your way of putting things. However, that does not mean that everyone will always agree on these subjects. I know a little myself when it comes to these things as you would gather if you ever met me and had a proper face to face discussion. I have no wish to enter into arguments or debate things where there is obviously strong feeling. Life's too short. Each to their own, and thank you for your lecture. I will be resigning my membership as tbh, when one states a viewpoint and receives unfriendly responses such as this, contributing further seems a rather futile waste of effort. However, there is very obviously a vast pool of talent and skill on show here and I doff my cap to a vast majority of members and wish you all well.
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#11

Post by Toppsy »

Paul,
I hope you receive and read my reply to your PM.
There obviously has been a misinterpretation of responses on this thread each with there own take on things. Just proves to me that when it comes to speakers there is no one answer and no one approach to get to the same end result. Each speaker design requires perhaps a different approach to internal damping not least the type of cabinet design, materials used in the construction, cabinet alignments etc. etc. There is no doubt you know this and your knowledge would seem to be far greater than mine. I only responded as to what I find with the designs I build and to some extents it down to what works for you.

Again don't make any rash decision about leaving the forum. We have all been here before, until we get to know each a little better and respect their knowledge and input to the greater good.

Colin
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#12

Post by Scottmoose »

Ah, the joys of the written word. I'm sorry you took such offense at my post Paul since that was not what was intended. One of the minor downsides of forums -misinterpretations happen. Since you obviously think I have some kind of problem with you, you may be interested to know that, over Christmas when I was contemplating giving up audio entirely (for reasons completely unrelated to anything or anyone on this forum) I strongly advised Colin to get in touch with you, since it seemed to me that there might be a possibility of your working together in some way to the benefit of all concerned. Colin can confirm that if you wish to check.

Either way, I'd second the comment about not making any rash decisions about leaving the forum. To coin the same phrase, life is too short, especially since we would almost certainly get on perfectly well if we met. If you're able to come to the next Owston, hopefully we can have a gibber about speakers together over a pint, or the equivalent thereof (sad man that I am, I always enjoy a gibber about speakers ;) ).
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#13

Post by Reffc »

Hi Guys

my apologies...I think we were probably having one of those "off days" when responses crossed, and there was certainly no offence intended so my apologies if it came across differently.

It was good to meet a few AT members last week in Bristol at Greg's bake-off and we're all pretty similar minded people when it comes down to it. If I can get to Owston this year I will. I may even risk a hernia and drag the Rhapsody speakers along.
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#14

Post by Scottmoose »

Go for it! (well, providing the risk of hernias is sufficiently low). More the merrier. :)
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