You seem to have cornered the market in HF2000's Richard. :)
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You seem to have cornered the market in HF2000's Richard. :)
I'm surprised by how many I have TBH as I certainly don't remember buying that many! I did have a pair of B&O 5700 and B&O 5702 which I shamefully stripped for parts, which accounts for almost a third of the units I have. Once I have completed this 66 project I think I will be offloading a few, and also my 1st pair of 66's as owning 3 working pairs of 66's will indeed be the very definition of greed! :DQuote:
Originally Posted by walpurgis
Oh dear. I like those. ;)Quote:
Originally Posted by ToTo Man
Me too, but keeping them would have been the straw that broke the camel's back in terms of domestic harmony with my parents! All is not lost as the B&O's will live on in my 66's. ;)Quote:
Originally Posted by walpurgis
Thanks Barry, I intend to use solid core copper wire to link the components in the crossover as it will be easier to wrap around the contact posts without splaying, and use stranded copper wire from the crossover to the drive units.Quote:
Originally Posted by Barry
However I'm not sure whether to go with plain copper or tinned or silver-plated copper. Van Damme Studio Blue has been recommended to me (which is funny as this is actually what I use between my amp and speakers!), however I'm leaning towards tinned or silver plated copper because the original stock cable was plated and I'm presuming it resists oxidation more effectively? This could be important for the wire-to-wire solder connections required to join the ends of the crossover cabling to the ends of the driver cabling, given that I cannot depend upon my dad to successfully flood 100% of the exposed wire ends with solder (soldering is not his forte!).
I'd be grateful for recommendations and links to suitable wiring, as I don't know where to shop for this. Cheers!
Regardless of the plating, or whether it is plated or not, it is important that the wire ends are properly 'tinned' with solder (or "flooded" as you put it). If not, a 'dry' joint can form which with time will fail and/or become noisy.Quote:
Originally Posted by ToTo Man
I would go for 1.0mm diameter solid tinned copper wire to wire up the crossover: https://www.amazon.co.uk/Tinned-Copp...ed+copper+wire, and insulated stranded wire to connect between the crossover and the drive units; maybe something like this: https://www.amazon.co.uk/THIN-WALL-F...win+core+cable, or perhaps twin core 10 amp rated lighting flex.
it makes perfect sense to use the same cable inside and out if your using van damme blue already,i used the 4mm
Progress on my restoration ground to a halt for a while, hence no updates to this thread. However my local tech returns from holiday next week so I'll be dropping off the crossovers to him to rewire and recap. Once I get them back it should be a simple case of re-installing them and the drivers.
I went with Van Damme Studio Blue 1.5mm for the internal hookup wire on the basis that it will be easier for a numpty to solder than the heavier gauges. I also had the supplier completely strip off the outer jacket which has really helped to shed the weight.
While I await the return of the crossovers I'm going to prepare the cabinets. Luckily they are in mint condition so all I need to do is replace the stock binding posts with some nice solid brass ones.
On the last pair of 66s I refurbished, I lined the top and bottom panels with 2mm bitumen dedshete like Ken did. For consistency I suppose I should do the same this time, or am I better not to? The top and bottom panels seem to be the least resonant areas of the enclosure, the knuckle test seems to excite the side and back panels more. I don't want to do anything that's going to mess with the voicing too much, so I'd be grateful to hear from someone who has experimented with dedshete or any other forms of damping in their 66s and what the outcome was?
Any thoughts on the pros and cons of adding dedshete to the 66 cabinets?
I'm looking for information on the Celestion MF500 and MD500 domed midrange units, specifically what the difference is between them?
AFAIK, Celestion first introduced the MF500 sealed dome mid unit with 50W power handling and later replaced it with the MD500 with increased 80W power handling.
Anecdotal reporting suggests the two units had slightly different frequency responses, the latter MD500 apparently had stronger mid frequencies but rolled off sooner at the bottom and top (perhaps this is the reason it was able to achieve a higher power handling).
Having measured a selection of MF500 and MD500 units (in free-space without a baffle), these are my findings:
1) The response is nowhere near flat/linear, it is around 7dB louder at 1kHz than it is at 3kHz-5kHz.
2) Left/right matching between all pairs of MF500 and MD500 units is excellent (within 1dB across most frequencies).
3) One pair of MF500 and one pair of MD500 units have identical frequency responses.
4) Two pairs of MF500 have different frequency responses between 3kHz and 5kHz (SEE GRAPH BELOW).
5) There is not a significant difference in lower/upper frequency roll-off between the MF500 and MD500 until it reaches 14kHz (SEE GRAPH BELOW).
https://live.staticflickr.com/7866/4...b246149b_o.jpg
I appreciate my sample size is small, and that measurements can be notoriously unreliable out of context, but finding #3 contradicts the anecdotal reporting that the MD500 has a different tuning to the MF500.
Possible explanations?
- Perhaps there was a there was a transition period during which Celestion mis-labelled MD500 units as MF500.
- Perhaps there was originally inherent and unavoidable manufacturing variation in the tuning of MF500/MD500 units.
- Perhaps the ageing process / deterioration is responsible for the apparently different tunings between the MF500 and MD500.
- Perhaps Celestion made a different tuning of MF500 for other loudspeaker makers (the pairs of MF500 I tested that displayed weaker output between 3kHz and 5kHz were taken from B&O Beovox speakers).
Interestingly, once installed into a Ditton 66 loudspeaker, I find the differences in tuning in the upper mid frequencies pale into insignificance in the frequency response measurements of the complete loudspeaker. This could be due to:
1) Overlap with the tweeter. The crossover frequency is 5kHz so the tweeter's response likely still makes a significant contribution between 3kHz and 5kHz. (I have measured a total of thirteen HF2000 units and all exhibit a rising response below 4kHz, though the sharpness of this rise varies greatly from unit to unit).
2) The fact that 30uf capacitance is used in the MF500 circuit vs 24uf in the MD500 circuit. (I've just learned that reducing the capacitance from 30uf to 24uf shifts the crossover frequency from 500Hz to 600Hz, so perhaps this is responsible for the MD500's increased power handling?)
3) Baffle-step effect might mean the raw frequency response measurements I made of the MF500 and MD500 in free space are irrelevant.
4) A combination of all of the above!
Are there any other plausible explanations I've missed?
It would be great to step into a time machine to find out how an MF500 and MD500 measured when it left the production line in the mid-1970's!