SpeakerTalk

[kandlbarrett]

Hello all,

Help needed with 100hz attenuation. Linn Index Mk1 Plus - I blew my original B200 SP1014 drive units. My fault using too much volume from the Pioneer A66.

I found a good condition set of B200 SP1039 (reported to be a "better" B200 driver) and enjoyed the increased base (it goes much lower in the frequency range) and crisper edge to instruments - especially drums. In all other respects the existing original crossover seems to have integrated them well.

However, after some more listening I realised there is a small base frequency that is very much louder than all others and rather annoying. It is from about 75 - 125hz and clearly centred on 100hz. I assume the cabinets were better tuned to the original SP1014 or the 1014 didn't go that low with the same energy. It could of course be room acoustics but this is my lounge and no capacity to juggle furnishings or positioning. I have tried moving these sealed speakers away from the wall but it has little impact attenuating this frequency. The lounge is 17ft x 11ft x 9ft. Hifi and TV are at one end facing across the room, speakers are at the same end also firing across the room and 6ft apart. both speakers are in corners; one in the corner of the room but that has heavy curtains hopefully stopping reflections and other in the corner of the chimney breast but that can't be changed and 6ft apart.
Note: the chimney breast is not between the speakers they are both on one side of the chimney breast and 6ft apart.

Using Audacity software I made a WAV track that steps 5Hz and played that through the speakers. I then played around attenuating the signal at different frequencies so that it sounds flat and even. Maybe unscientific because everyone's ears are different but both my 28 year old son and my wife agree that my attenuation has levelled the volume around this frequency.

From that I can see that the attenuation required is almost 9db at 100hz with the slope each side fairly steep starting at about 70hz and ending at about 130hz.

The cabinets are HxWxD 435 x 280 x 195 and construction appears to be front baffle 18mm MDF and sides 18mm chipboard. There is no internal bracing and no sound deadening or sound absorption on the cabinet walls. The speakers are stuffed top to bottom with an off white wool like material. From the dimensions and allowing for wall thickness I make internal volume 15.5litres.

Also note that I haven't discovered how to remove the crossover from the cabinet. they are fixed to the incoming terminals and I have tried unscrewing them but they are very tight and I didn't want to break anything.

Yes I am new to this but a very, very long time ago (40 years) did complete one year of C&G225 (electronic servicing) but never used it in earnest but do understand basic circuit diagrams and the operation of components and transistors etc in simple circuits. I have also done lots of reading to try and understand likely causes.

I know in the Linn world these speakers are scoffed at but they do have sentimental value and replacing them is an option that I won't pursue.

So my question is how do I attenuate this. Is it sound deaden and add sound absorbing material to the cabinet walls, add a notch filter to the base driver, completely replace the crossover and build the notch filter into that, return to B200 SP1014 (not a favoured option because they lack base extension even when tight against a wall), all of these or something else?

If the answer is a notch filter (twin T?) can someone help with recommended design, value of components and component type to use. Cost is not currently a significant concern.
_________________
All the gear but no idea. Trying to learn!

[speakerguru]

[kandlbarrett]

Speakerguru, thsnk you for this and understand the difficulty with design. Maybe I'll do a bit of trial and error with cheap components and see what happens. Certainly passive components will be a bit tricky to get a tight attenuation over a relatively narrow band.
I do assure you that despite the higher Bl the 1039 the bass definitely goes far lower.
In the B200 range KEF also do a 1054 with a small magnet but lower Q that is used in KEF sealed cabinets - maybe I will try some of those.

[speakerguru]

[audiolabtower]

Guru is spot on
https://us.kef.com/explore-kef/kef-museum/1970s/corelli-calinda-and-cantata-1976-81