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Discussion in 'Home Cinema Speakers' started by Brox, Aug 6, 2002.

  1. Brox

    Brox
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    I have a Kef 20b series 2 (100 watt amp) that I have had for about 2 months however I suspect that it is not giving me the output i have been led to expect,

    In order to get much output from it i need to set the o/p from the amp to +10 and have the sub turned up to the 2 0 clock position.

    If I have the sub's volume turned up any higher it clips in certain movies scenes, but my amps overall volume is at the -33 db position.

    I have spoken to Kef who have played it and said 'It's as much as you are going to get from a sub this size' however I've been led to believe i should be getting more out of it.

    Does anyone have this sub or have experience of it - what are it's limitations, I know it doesn't go really low but I expected more.
     
  2. Brox

    Brox
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    Well I hope someone can help as i'm at a bit of a loss now!!
     
  3. chas_jjj

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    I remember listening to a Kef 20b some time ago at a friend's house, but it didn't appear to be struggling to give a good room-filling sound.
    Don't recall what the settings were and he has sold it now.

    Not a lot of help I'm afraid - good luck
     
  4. Brad_Porter

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    Hi,

    The sub you talk about seems to be only registered at 70W on a few dealers site.

    I kind of had a similar problem with my REL Q150E. Although it has 150W of power it just didnt fill the room to a standard that I thought was acceptable. I expected a lot more for a 150W sub. Silly really, because on a box which is around 1ft x 1ft x 1ft, its not going to boom.

    I have recently upgraded to a M&K sub which is about is 456(H) x 384(W) 554 (D) ins size. Yours is 326(H) 302(W) 335(D) . Not a massive difference but big enough. Also, the power rating of the M&K is 125W compared to my RELQ150E what was a bigger 150W. However, the differnce in depth and slam that I get from the M&K is just unreal. Its completely engrossing and makes me grin everytime I watch The Mummy Returns. The REL cannot compete.

    What I am trying to say (in my very humble and short experience) is that the smaller subs tend to lose a bit of oumpgh unless you really get something quality; of which I dont know what make!

    I dont know how big your room is, but 70W in a small box wont really put out earth shattering deep bass and will start to distort if pushed. My god, my 150W REL used to die at -15 db on my Denon amp. My M&K sub will take it up +00 and still want more.

    I am just rambling now. But I think that you are a little like me. I wanted big big sounds out of a small box. I didnt get it. The only time I started to get that bigger sound is in a bigger box.

    Maybe KEF is right - it might be the best you can get from the box. Maybe its put up or upgrade time. Overall, it looks like you are not satisfied with the sound.
     
  5. Brox

    Brox
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    Thanks for the reply Brad,

    My sub is the series 2 of which only 500 were made and it used the amp from the 30b rated at 100 watts.

    You may be right but my room is not large at all and i've had to up the o/p from the amp to +10, and when I listen at the -30 level on the main amp with the sub volume at about the 10 past position in some scenes the cone just rattles/buzzes, have you ever experienced this type of sound?

    I wonder if the amp in the sub is performing as it's supposed to, I would feel better if Kef could measure it but they say they don't have the equipment as it was made in Canada.

    I feel like getting them to try a new amp in it but I would rather get some info of my own first before making a nuisance of myself.
     
  6. Brad_Porter

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    What does sound odd to me is that you have to have the volume knob at the 2 o'clock position. Once again (in my humble experience!) all the subs I have had neve really leave the 10 - 12 o'clock position. It sounds very high.

    This is probabley why you are getting distortion.

    What actually happens if you have the sub volume at 11 o'clock and the amp running at -25db - does this have the same effect? Does the bass sound none and void or is it there?

    Also, where is your sub placed?

    Just trying to get a bigger picture.
     
  7. nfordenfield

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    Agree with Brad, does sound high, looked a brother in laws and his is only at 11o'clock and that sounds good in his room, 14x12ft.

    Have you started from scratch with the amp set up with speaker size etc. How is the sub connected? What speaker are used?

    Can you swap subs with a friend to see if the fault follows the sub?

    Rgds

    Nathan
     
  8. Brad_Porter

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    Very good point, Nathen. You could have all the speakers set to large which would explain why the sub has to be at a very high setting to get anything. All the bass is going to the speakers rather then the sub. Also, when your running the sub at the 2 o'clock position, it wont take much to make it distort.

    Come back to us by with answers to Nathen and my questions. Hopefully, we can go from there to finding to a solution.
     
  9. Brox

    Brox
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    Hi Nathen, Brad.

    I'll try to answer all your questions:

    I have never tried the sub volume at the 11 o clock position and the amps vol up to -25 - mainly because listen at -25 would be too loud in my room, it's only about 9/10 feet across and the subwoofer is at the far wall next to the hifi rack firing toward me into the room. i'll try turning up the amp and get back to you.

    I have my main speakers set to small and the sub turned on.

    I have tried the sub will another amp (Sony 930) and you just can't hear it do much unless you turn the o/p from the Sony up to the max, and it gives up and starts 'clicking/ buzzing' long before my friends Yamaha sw90

    It does give a good sound but only when it is really on the edge (of buzzing and making funny noises)

    The sub is sat about 5 ft way from me.

    If you need any more info let me know
     
  10. Brad_Porter

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    The sub doesnt sound well in that case. What you are saying is that it only starts to perform to any level of acceptance only when its on the verge of distortion !!

    This is not correct - I can only suggest taking into a dealer (preferably where bought) and asking them to test in the shop. Thats the only way to be sure whether its broke or its just plain crap.

    I thinking it will more likely by the former. Well, I am hoping its the former!!!!
     
  11. Brox

    Brox
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    I bought it from Hyperfi, don't expect alot of help from them they don't even have any proper demo rooms - it will have to go back to Kef but they do not acknowlege a problem - they do not have any other 20b's to compare mine with and I don't think the staff have actually heard one. But I may ask them to try another amplifier in it.

    However one of the staff I spoke to descibed the Kef as 'a bit of a beast' may go back to him.
     
  12. Brad_Porter

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    I wish I was nearer - I could have popped round and had a listen.

    I am afraid it looks like your only choice; sending it back to KEF.

    It doesnt sound right - and you know if it sounds wrong......just dont take no for an answer.
     
  13. Brox

    Brox
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    where are you based Brad?
     
  14. Brad_Porter

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    Chelmsford in Essex - Too far from Bucks!
     
  15. Brox

    Brox
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    Yes you're probably right Brad.

    nfordenfield Does your brother inlaw have the Kef 20b? What's his experience of it?
     
  16. nfordenfield

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    This is a decent sub for it size and should be alot better than it is.

    Just looked and brother in law has a 30b so amp is the same.

    Take it you have tried on not auto (maybe a sensing issue). His is actually set to 9 o'clock with the phase to 180 and cut of at the lowest point 80 htz. This really does add some bass to his Celestion A compacts.

    He uses a single phono out from the amp and then a single to two phono cable, using both L & R inputs.

    Have you swapped out the cable to see if that is the prob?

    Again if I was nearer, i'll have pop round to help, but Kent is hardly next door.

    Hope this helps

    Nathan
     
  17. Brox

    Brox
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    Cheers Nathan,

    The 20b doesn't have an input sensor so is on all the time.

    I have tried using a high quility interconnect and it does make a small amout of differance but not enough to change my mind about the sub.

    What would be most useful is to be able to compare my sub against another the same to be absolutely sure it's not me, so if anyone has one and they live in travelling distance of Marlow in Bucks please get in contact.

    I don't mind driving a bit of a way to sort this out definitively as I need to go back to Kef with something reasonably solid before they start looking at it again.
     
  18. Brox

    Brox
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    Spoke at length to one of the technical chaps at Kef and told him about my concerns with the sub not performing as it should, he agreed to take it back and completely test it and compare it to one of the 20b subs that they use as a reference. This should get to the bottom of it once and for all.

    Previously they had compared it to a PS1000? a similarly speced sub and they said the 20b held it's own - I ponted out this was not very scientific and that Kefs new range was not very hard hitting unlike the 20b

    Anyway they do appear to be offering a very professional service
    taking into considerarion that they do not think there is anything wrong with my sub.

    Watch this space.
     
  19. Brad_Porter

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    Will do - let us know mate
     
  20. Brox

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    Well I sent the sub back to Kef after speaking at length to one of there technical people who agreed to do a full check on the sub against their reference model. He measured and compared the output at different frequencies against the reference series 2 20b
    and plotted this on a graph which he enclosed with the returned sub.

    The results were that there were no problems with the sub as it was only 1db down from the reference (which has lower tolerances on it's components) but he suggested turning the Xover to max, the volume on the sub to max and setting the o/p from the amp to the flat position - he had found that the o/p went down by 12db when the xover was at the 50 htz position.

    Well i've tried this and i'm happy with the results. It does seem a bit strange to have to turn the subs gain up to max which is why I didn't do it before but he reminded me that this sub was made mainly for pro logic rather that DD. But i am impressed with the qualityof the base it blend in seamlessly with my 601's and goes fairly low especially when you considfer it's only 30cm by 30cm.
    In my opinion it's faster than the Rel 150 when the rel is in Depth mode and sounds very similar to the Rel in Slam mode. The rel goes deeper but it is definately a bit 'one note' and really didn't blend in well with the other speakers (M&K satelites)

    So now i'm happy with no plans to upgrade since i only paid £200 for it I think i've done ok
     
  21. Brad_Porter

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    I am still slightly worried about the fact that you have to turn the sub upto MAX gain for it too be effective. Im sure that sounds really wrong. However, if its working and its ultimately solved you £200, then good luck!
     

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