1. Things you need to know about the new ‘Conversations’ PM system:

    a) DO NOT REPLY TO THE NOTIFICATION EMAIL! I get them, not the intended recipient. I get a lot of them and I do not want them! It is just a notification, log into the site and reply from there.

    b) To delete old conversations use the ‘Leave conversation’ option. This is just delete by another name.
    Dismiss Notice

Tannoy Chatsworth 12" MG rebuild advice.

Discussion in 'classic' started by awkwardbydesign, Feb 26, 2021.

  1. awkwardbydesign

    awkwardbydesign Officially Awesome

    I've just bought some Chatsworths from Mark (divedeepdog), and now I need to build some proper cabinets for them. I took the backs off to have a look inside, and was amused to see the panels are all 1/2", except the back which is 3/4" chipboard. No wonder the cabinets were vibrating so much. I put an accelerometer on the top, and not only was it vibrating up and down, they are so light the biggest movement was backwards and forwards!
    I like the character of the sound, but bigger and stiffer cabs are needed.
    But I need advice on suitable cabinet type. Not horn, I think, as I don't need higher efficiency, plus my valve amps have some residual hum, so that would be amplified. And 110 watts is enough power without greater efficiency. Nor straight reflex, as I want fast bass more than louder bass. So sealed box, aperiodic, or what about distributed port loading? If that is the correct term.
    I can position them fairly close to the front wall, so some boundary reinforcement would be available.
    Any advice or pointers would be appreciated.
    Monitor Gold 10 likes this.
  2. hermit

    hermit obsessive

    I very much like the look of the RFC Canterburys. Perhaps Paul would be willing to sell you the plans?
  3. cooky1257

    cooky1257 pfm Member

    No point in going bigger that 75L if sealed.
  4. divedeepdog

    divedeepdog pfm Member

    I suspect you play louder than I do given your description, funny how listening levels are rarely discussed?

    Looking forward to your build, I was heading towards slightly bigger, braced cabs. The other Tannoy *build thread with panels bonded with PU15 mastic made interesting reading. In ordinary times I’d have liked a listen to those before too much building took place.

    *was it Rockmeister??
    Rockmeister likes this.
  5. s1h1

    s1h1 performing within expectations

    eastone and hermit like this.
  6. awkwardbydesign

    awkwardbydesign Officially Awesome

    Wrong shape. But that is the kind of loading I'm looking at. I doubt Paul would sell me the plans (I wouldn't in his place). But if I can settle on a volume (150 litres looks promising) I can make the distributed ports as a slide in module, and add or subtract as I go. That sort of volume may well work as sealed, reflex, aperiodic or slotted.

    Actually , most of my listening is late at night, so very low level. And during the day my wife doesn't like loud, plus my smallish room overloads quite quickly. My GL75 plinth was made using non-setting acoustic sealant, so I may play with that again.
    BTW, I just measured both drivers. One has a 38 ohm resonant peak at 20 Hz, min impedance 6.4 ohm at 100 Hz, the other is 52 ohm/20 Hz, 8.0 ohm/120 Hz, and a slightly squashed looking surround. The horrible 4 pin connector on that one took some effort (and tape) to get it working reliably. It will be upgraded with the crossover components, though. Such is life with 50 year old drivers.
    At the moment they are set up in the loft, with the rest of the retro gear. And I made those plinths a little more secure, so they won't slide off. :eek:

    Wrong shape again. I'm looking at a rectangular build, although I may curve the sides.
  7. awkwardbydesign

    awkwardbydesign Officially Awesome

    I have tried to calculate an Onken, but the programme I used didn't work with my T/S parameters.
    More research needed, although I am leaning towards an aperiodic loading. I like the speed of sealed box, but a little more extension would be nice. And the difference in impedance measurements would be less critical. But I will re-do the impedance plot with a different sig gen and mV meter, as switching ranges on the current set up causes a jump in readings.
    The small 4mm binding posts have arrived, to replace the horrid spring loaded terminals, and the Mills resistors and Clarity Caps are due today. I have some Russian Teflon caps, but they are somewhat large, and take months to burn in, so they won't be used. I also bought some small RC model connector pins to replace the 4 pin plug too.
    I guess I ought to throw this out over on diyAudio, but I probably won't understand the answers! :D
  8. Fatmarley

    Fatmarley Agnostic

    Aperiodic won't give you any more extension, but if you combine it with a port or ports like the Lockwood cabinets do, that seems to work well for people. I'd rather go for ports without the aperiodic shelf If it were me. It just seems like a bad idea to restrict the air with an aperiodic shelf before it has a chance to reach the port. Although I'm sure the Lockwood way would sound better than a badly tuned port.
  9. awkwardbydesign

    awkwardbydesign Officially Awesome

    Thanks. I was thinking more of a Variovent style, with no shelf, but a restrictive port.
  10. Fatmarley

    Fatmarley Agnostic

    That still won't extend the low frequencies. The best way to add more low frequency extension is with a port.

    As said above, it would be well worth reading Rockmeisters build thread. Perhaps send him a pm?
  11. eastone

    eastone pfm Member

    My Chatsworths had a resistive port when I first got them. I thought they were significantly better when I sealed the port up and I haven’t ever had the urge to go back.

    There may have been a decrease in frequency extension when I went to sealed, but the increase in detail and definition right across the spectrum was very clear.

    YMMV as I have yet to hear a ported speaker i could live with and obviously not everyone hears the same way.
  12. awkwardbydesign

    awkwardbydesign Officially Awesome

    I have an aversion to reflex ports, but do like TLs. As I understand it, an aperiodic design allows for a smaller box for the same bass extension. Or lower bass for the same box size. Is that wrong? Plus the flattened bass peak makes it easier to drive. This is only from reading, not actual experimentation.
    Is that with HPDs? Mine are sealed, with 12"MGs, rubber surround (NOT foam!).
  13. eastone

    eastone pfm Member

    Mine are 12” Golds with the rubber surround.

    Your description of the aperiodic enclosure fits with my understanding of the science but I’m no expert.

    The previous owner of my pair wrote on here that the Chatsworths didn’t really image in a precise way, that it was more of a wall of sound effect. I found that fairly accurate until I sealed the cabinet at which point they sharpened up considerably and are now capable of throwing a cavernous, walk-through soundstage.

    Perhaps I’ll open up the slot in the baffle again one day and see how they sound. It was a little rough and ready looking so maybe you’ll have a better result?
  14. Fatmarley

    Fatmarley Agnostic

    You've only got an aversion to ported speakers because you haven't heard a good one. I agree, most are terrible.

    An aperiodic speaker is just a leaky, sealed enclosure, and can be simulated with software. It doesn't add anything, only takes away. It can be handy if you want to reduce the peak in the low frequencies caused by a high Q driver in a sealed box. In simulations, it doesn't do much to Tannoys, but may subjectively give a more open sound because of the reduced pressure inside the enclosure (that's just my opinion though).

    It's the impedance peak that's flattened.
    Hoopsontoast and eastone like this.
  15. awkwardbydesign

    awkwardbydesign Officially Awesome

    I have just seen this.
    Which may well suit me. The cabinet size would lend itself to experimentation with different bass loading, reflex, sealed, aperiodic or possibly even Onken, if I make the fronts changeable. In my room I would need to reduce the height a fraction, but widening the back would enable me to maintain volume. Curved panels are no problem; I have done them before.
    And the style, with slightly darker sides, is attractive. At least it would be a starting point.
    hermit likes this.
  16. awkwardbydesign

    awkwardbydesign Officially Awesome

    Yes, that's what I meant to say.
  17. eastone

    eastone pfm Member

    Go for it!

    That project looks stunning. Would be very interesting to know if you can replicate Paul’s results.
    Last edited: Mar 3, 2021
  18. Fatmarley

    Fatmarley Agnostic

    As regards to this:

    I don't know if the published thiele small parameters are wrong for the HPD 315A or if it's my software, but with a 160ltr enclosure and 100 x 225 port - When modelled, I get a 3db peak in the low frequencies centred around 33hz (or it could be a dip centred around 55hz depending on what the crossover is doing). How that sounds subjectively, I don't know. Obviously It also depends on the room.
  19. cooky1257

    cooky1257 pfm Member

    Yes , I get that peak too, if you go that large with conventional reflex porting you have an issue with the bass peak that needs fixing, the group delay isnt great either, it( the peak) can be tamed by the use of slotted/ distributed porting.
    In my experience 120 L is on balance the ideal volume and as big as you need to go.
    Fatmarley likes this.
  20. Fatmarley

    Fatmarley Agnostic

    Glad to see it's not me going mad then.

    Interestingly, I found you can fix the problem by adding an aperiodic vent to the cabinet (just model the same 160ltr cabinet with 2 x 4" ports, but with a leak). Would be interesting to hear how that compares to a smaller cabinet. As you say though, it has a large peak in the group delay, so perhaps the smaller cabinet is the best way to go.
    cooky1257 likes this.

Share This Page


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice