Superb job there, Richard! :clap::thumbsup:
They look like new... How are they sounding? I'm a big fan of 66s, as I had a pair myself and very much enjoyed their style of music making!:cool:
Marco.
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Superb job there, Richard! :clap::thumbsup:
They look like new... How are they sounding? I'm a big fan of 66s, as I had a pair myself and very much enjoyed their style of music making!:cool:
Marco.
Cheers, guys! They sounded fantastic. I was actually sad and somewhat reluctant to let them go, but I had already committed to the sale before I'd started the refurb, - I'll know better next time! TBH I wasn't expecting them to sound as good as they did, especially with the original stock caps still in place. This suggests there is something 'magic' about the original caps that is difficult to replicate with modern equivalents.
I decided to replace the T2169 woofers in my 2018 66s with earlier T1600 woofers, and this has brought the frequency response below 500Hz measurably and audibly closer to that of my 2015 66s. The differences that remain between 600Hz-900Hz must therefore be entirely mid unit related.
Before:
https://live.staticflickr.com/65535/...f1a40a6e_b.jpg
After:
https://live.staticflickr.com/65535/...6faf2097_b.jpg
Out of sheer curiosity, I then decided to reverse the polarity of one 2018 66 woofer to see what effect this had:
Amplitude frequency responses:
https://live.staticflickr.com/65535/...f8720150_b.jpg
Phase responses:
https://live.staticflickr.com/65535/...a1c111b7_b.jpg
https://live.staticflickr.com/65535/...46ac133d_b.jpg
Step responses:
https://live.staticflickr.com/65535/...0651eb16_b.jpg
https://live.staticflickr.com/65535/...1fa376ca_b.jpg
The difference in the amplitude frequency response when woofer polarity is inverted is pretty self-explanatory; there is decreased output between 300Hz-550Hz and increased output between 700Hz-900Hz. The mid-range sounds more forward with less upper-bass bleed when the woofer's polarity is inverted; - I think I prefer this new tonal balance.
Regarding the Phase Response and Step Response graphs, I could use a little help to explain the changes in those!
The effect on inverting the polarity of the woofer with respect to the mid driver is even more significant when measured at farfield distance from my listening seat. Instead of elevated output between 300Hz-600Hz, there is now recessed output between 300Hz-600Hz. I think the recessed output is the more 'correct' outcome, because other speakers I have measured in my room usually exhibit recessed output between 200Hz-500Hz, so I think it's a characteristic of my listening room (e.g. floor bounce cancellation). The recessed output definitely gives a cleaner and more transparent presentation (to my ears).
https://live.staticflickr.com/65535/...eee2b7ff_o.jpg
Thought I should update this thread with how my Ditton 66s have been tweaked since my last post. In short, nothing much has changed. I still have the polarity of the woofers inverted to provide a cleaner response through the LF/MF crossover area. I have however since taken time to integrate my subs. I'm running the 66s full range and have set the XO frequency of the subs to where the <40Hz roll-off is minimised but the >40Hz peak isn't added to. Getting this dialled in exactly was finicky but doable with Periodic Pink Noise, an RTA and a steady hand!
I have EQ'd the entire system in 4 areas:
1) notch filter at 48Hz to capture the 42Hz, 45Hz and 52Hz room modes;
2) notch filter at 130Hz to control a response peak;
3) wide notch filter at 750Hz to attenuate mid frequencies;
4) notch filter at 6kHz to smooth MF/HF crossover region.
I used measurements to guide me where to set the centre frequency for each notch filter, but I ultimately used my ears to determine what areas of the frequency response needed to be ameliorated and how much EQ should be used to achieve this. My approach was to use the least amount of EQ possible to obtain an even-handed sonic presentation that is detailed and transparent but has no areas that draw undue attention.
The BBC-esque dip at 3kHz is a classic feature of the 66 tuning, as is the 5kHz-6kHz bump. (The 5kHz-6kHz bump is most noticeable when listening on-axis with the mid unit, which is how I prefer to listen to these speakers). I found that EQ'ing the bump completely flat robbed too much excitement so I left a little lift in.
I verified all EQ adjustments by listening and measuring in several locations around my listening seat to ensure I ended up with a response that was balanced and didn't create more problems than it fixed. Sadly I didn't save all of those measurements so am unable to upload an average of them.
The following graph shows a before & after EQ from my listening seat, with the left & right speakers averaged into a single measurement:
https://live.staticflickr.com/65535/...a8fefe63_o.jpg
Some will no doubt argue I've ended up with a tonal balance on the brighter side of neutral, and they are perfectly entitled to this opinion! As I say, I have not been led by target house curves, I have EQ'd the system so that it sounds both natural and neutral to my ears. :)
This was all done with the speaker grilles OFF. As much as I think these speakers look best with the grilles on, they do have a significant effect on the frequency response, knocking an average of 2dB off everything above 4kHz (the effect isn't entirely linear so I suspect the metal grid structure diffracts certain frequencies more than others), which is detrimental to the transparency/clarity and crispness of the presentation IMO.
Although it took some fettling to get there, these Ditton 66s in the current configuration are probably the most satisfyingly balanced and articulate 'big monitors' I've thus far had the privilege of owning. :)
Impressive work; I wish I had the time, knowledge, and application to do similar.
I should really have gone into the computer measurement of my own design, for which the Xover values were a guesstimate based on numerous calculations, but with no external I?P, and scarce educational resources I was intimidated.
This was also compounded by several people stating that many of the programs are not really very good.
I should confess that I have no EE training and was very much learning as I completed these projects. I found RoomEQWizard an indispensable aid to help corroborate and explain what my ears were hearing and I would have really struggled if I had to rely on just my ears alone. I didn't delve into the software's advanced features, I completed the projects solely based on frequency response and distortion measurements. The 'proper' way to do it would have been to model each driver's impedance curve, as this would likely have provided better insight into how they would behave around the crossover frequency. I instead took the 'suck it and see' approach of trying various driver combinations until I ended up with a frequency response at the crossover regions that my ears agreed with. It would have been much easier if I'd been dealing with modern 'cookie cutter' drive units that have far smaller intersample variations than 40+ year old hand-assembled units!