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Kef 105.4 crossover refurbish & new bascabinets (p-6)
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willem-57
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PostPosted: Mon May 11, 2015 9:31 am    Post subject: Reply with quote

Yes, video's and the article are clear about this. I understand now why my newly build cabinets have a tight bass.
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willem-57
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PostPosted: Thu May 14, 2015 9:03 am    Post subject: Reply with quote

SaSi wrote:
The latex "skeleton" looks like closed cell material. If so, it will seriously lower the effective enclosure volume and you will notice a significant bump in the bass with a lower cutoff frequency. May create a "hole" in the upper bass.


Without the latex skeleton in the lower chamber i find the bass too weak, but with it too strong, what to do? Well, i made the latex more open, removed about 30 - 40% of it and filled the holes with acoustical foam. Also put a smaller piece off foam extra in the lower chambers. The total picture is now that in the upper smaller chamber there are 2 pieces of acoustical foam and the rest is lightly stuffed with baf.
The lower chamber has now a smaller piece of latex and 2 pieces of acoustical foam (less foam as in the upper one) and the rest with a smaller amount of baf. I think i've now a better balance because i have made the lower chamber a little smaller deu to the latex. It's difficult to decide what's the best result, i should measure it, but i have no means to do that. I will listen again and also ask friends what they think of the sound. At this moment, with michael franks in the DP70V, it sounds very beautiful, but i must listen longer for a honest meaning. Very Happy
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willem-57
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PostPosted: Wed May 20, 2015 11:27 am    Post subject: Reply with quote

I think i almost have the optimal sound, maybe a littlebit too strong in the lowest region, thatswy i made a new damping piece. With it it's possible to adjust the sound by means of using different materials. The latex piece have a number of hollow chambers with you can stuff with latex (more bass) or foam - baf (less bass). This way i can alter the internal volume of the lower baschamber.





Last edited by willem-57 on Thu May 21, 2015 8:52 am; edited 1 time in total
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SaSi
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PostPosted: Wed May 20, 2015 7:59 pm    Post subject: Reply with quote

I think you are having good fun.

In this mode, I would suggest you can also experiment with activated carbon. It's a KEF idea, to use activated carbon, which increases the effective enclosure volume, giving a better extension in the lower frequencies.

You can get activated carbon cheaply from contractors that deal with HVAC systems and air filters. Locally, got myself a quotation for 130 euros for a 25kg (50lb) bag. You would - realistically - need less than 1kg in small pouches made of air breathing cloth - the one used in covering sound absorbers.
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willem-57
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PostPosted: Wed May 20, 2015 8:55 pm    Post subject: Reply with quote

You mean this stuff, that they use in filters? https://www.google.nl/search?q=activated+carbon&hl=nl&biw=1920&bih=888&source=lnms&tbm=isch&sa=X&ei=ueVcVZvqGIHCUtL-geAN&ved=0CAcQ_AUoAQ

And also in aquarium's and ponts for filtering (dutch= actieve kool): https://www.google.nl/?gws_rd=ssl#q=actieve+kool+kopen&tbm=shop

another excamble http://www.a2koi.nl/actief-kool-10l.html?gclid=CJTbu_mv0sUCFarpwgodxRcATQ

And then make a breathing bag that is filled with the carbon and fits in the space that i've made in the foam?
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SaSi
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PostPosted: Thu May 21, 2015 5:22 pm    Post subject: Reply with quote

Exactly
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willem-57
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PostPosted: Fri May 22, 2015 8:50 am    Post subject: Reply with quote

Sasi, maybe it is better to make a filling with activated carbon for the upper baschamber witch is 4 liter smaller, that way the upper one becomes larger for the b200G woofer.
And the sound become more the same from both woofers. Questions are now, 1, witch type of carbon should i use and 2, how mutch should i use for a 20 liter bas chamber Question

Found this about active carbon, Kef invention as you mentioned. I think i don't need mutch of it because with that stuff you can make a speakerchamber 3 times smaller with the same output: http://www.hometoys.com/content.php?post_type=1725

Maybe this type, it's ment for fishtanks, if i tell to people that i use it for loudspeaker filling they will think i'm nuts Very Happy

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proffski
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PostPosted: Fri May 22, 2015 11:37 am    Post subject: Reply with quote

A clever idea, I believe that the KEF Blade uses this.
However, how long does the charcoal stay activated in the average room? Surely depending on what is in the air (smokers?) this will vary. And what happens gradually to the speaker performance as the carbon ages with captured pollutants?
Colin reckoned five years... there was a thread in this forum regarding the issue.

A quote from a manufacturer!
5.Does it expire?
If left exposed to the environment, in time, activated charcoal will adsorb various pollutants and eventually “fill up.”
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speakerguru
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PostPosted: Fri May 22, 2015 12:19 pm    Post subject: Reply with quote

I'm surprised that you can buy it for aquaria. One of the main problems with its use for loudspeakers was that the increase in apparent cabinet volume greatly decreased if the carbon adsorbed water vapour. Perhaps wrt carbon granules, water does not behave in the same way as vapour??
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willem-57
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PostPosted: Fri May 22, 2015 12:30 pm    Post subject: Reply with quote

proffski wrote:
A clever idea, I believe that the KEF Blade uses this.
However, how long does the charcoal stay activated in the average room? Surely depending on what is in the air (smokers?) this will vary. And what happens gradually to the speaker performance as the carbon ages with captured pollutants?
Colin reckoned five years... there was a thread in this forum regarding the issue.

A quote from a manufacturer!
5.Does it expire?
If left exposed to the environment, in time, activated charcoal will adsorb various pollutants and eventually “fill up.”


An advantage is that the RR105.4 is a closed box, so not mutch pollutants can infiltrate. And we don't smoke (anymore) Wink


Blade 1 next to version 2, i see no activated carbon!:



Last edited by willem-57 on Fri May 22, 2015 6:23 pm; edited 5 times in total
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willem-57
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PostPosted: Fri May 22, 2015 12:35 pm    Post subject: Reply with quote

speakerguru wrote:
I'm surprised that you can buy it for aquaria. One of the main problems with its use for loudspeakers was that the increase in apparent cabinet volume greatly decreased if the carbon adsorbed water vapour. Perhaps wrt carbon granules, water does not behave in the same way as vapour??


You must often change the filter in aquaria, but in a closed speakersystem it can work for a mutch longer time. But yes, one day you have to renew the carbon.
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SaSi
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PostPosted: Fri May 22, 2015 6:10 pm    Post subject: Reply with quote

In acuaria and HVAC systems it's used for filtration. And, of course, it's a consumable.
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willem-57
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PostPosted: Fri May 22, 2015 6:44 pm    Post subject: Reply with quote

Found a site here that sells a chinese version of it, cheap and it can be ordered in small portions of 250 grams packet in a nylon netting, easey and direct usable. What do you think, i can also buy the other dutch (norit) version. Witch is better, or is it all the same?

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willem-57
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PostPosted: Sat May 23, 2015 11:30 am    Post subject: Reply with quote

From the Kef site; http://www.kef.com/html/gb/innovation/ace/index.html
It is used in small speakers, to get a nice bass output. I think it will be too much in my 105.4 speakers.

Obtaining good bass performance from small speaker boxes has always been the ‘holy grail’ of loudspeaker design. Typically a small box will have less bass performance than a larger one. However, after years of research KEF has overcome this problem with the development of Acoustic Compliance Enhancement (ACE), where activated charcoal, just like in a water filter, is placed inside the loudspeaker cabinet.
Tiny holes in the porous ACE material act like the small air sacks in a lung by absorbing and giving out air molecules as the drive unit moves in and out. This helps the bass driver ‘breathe’ more easily allowing improved bass performance. In fact, a speaker using ACE technology can have the same bass performance as a conventional speaker of twice the size.
The bass response from a loudspeaker is critically dependent on the internal cabinet volume. If you want good bass extension, to hear all those powerful low notes from organ fundamentals to life-like movie explosions, you need a physically large enclosure. It all comes from the basic physical laws that determine how a conventional bass drive unit interacts with the air inside the cabinet.
ACE technology allows us to circumvent these basic restrictions and gain the freedom to adjust the ‘effective’ internal volume by filling the enclosure with activated carbon.
ACE works by a process called adsorption – the highly porous carbon granules take in or give out air molecules in response to the change in air pressure caused by the inward and outward movement of the speaker cone. This flow of air molecules is always acting to reduce the internal pressure variations – making the enclosure appear to be much larger than it actually is. The more activated carbon we put into an enclosure the bigger the effective internal volume becomes – up to a point where losses start to dominate. Typically, we can double the internal volume whilst still maintaining a high quality bass roll-off characteristic
The volume increase can be utilised in two main ways: (1) reducing the size of a particular speaker while keeping the performance the same or (2) increasing the bass extension from a given speaker whilst keeping the size the same. In general, it’s a bit of both as we will custom design the bass driver for each application and look for the best overall compromise.
In sound quality terms ACE has some major advantages – principally that it allows us to design a speaker with the bass extension of a reflex system but with the superior transient response of a closed box. In addition to the measurable parameters, the sound quality of ACE enclosures is consistently well liked by audiophiles, with a precise and detailed bass reproduction.
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SaSi
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PostPosted: Sun May 24, 2015 11:12 am    Post subject: Reply with quote

I read that and also the AES paper by J. Wright.

What activated carbon does is what stuffing with open cell foam does in a sealed cabinet, perhaps up to 10x more effective.

I just thought, that as you are experimenting with various stuffing material and methods, it wouldn't hurt to try this as well.

Avoid the pellet type carbon and aim for "granules". They appear to be more effective. You won't need more than 200-400gr for your tests.
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