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Tannoy HPD 315 Questions

Discussion in 'classic' started by jonathanmorbin, Oct 15, 2020.

  1. So the red one is as you suggest is harsh when the energy is up but sounds to my ears nice/correct when i turn the energy down.

    The grey one just sounds a bit fizzy toppy in comparison and almost a bit phasey sounding.
  2. Tony L

    Tony L Administrator

    Hmmm, given one has likely been replaced have you actually checked the phase is correct? Nothing to say some previous owner didn’t wire one in backwards!

    PS Frank can better comment on the specific units as to whether they are right for the unit.
    cooky1257 likes this.
  3. cooky1257

    cooky1257 pfm Member

    They look to be the correct diaphragms. Clean the gaps- use postit notes or masking tape, then carefully re instal and by trial and error get one to sound and measure reasonably flat with a rising response/ bump above 12-13 kHz . Using the same crossover unit install and tweak the other dia in terms of position and tightness to get a good match. It's a bit of a dark art so be prepared to spend between an hour and a day or so to get this optimum as if you get dia 2 better than dia 1 you may want to go back and try to improve dia 1!
  4. ok thanks i will give that all a go today. Is there any science behind the paper spacers in terms of how many? i.e what does adding/taking away spacers achieve sonically?
  5. cooky1257

    cooky1257 pfm Member

    Use the number as supplied, they set the voice coil height in the gap and compensate for manufacturing variations, only start messing with them if you can't get a good result with the previous advice from Tony et al. I've sometimes had to change them in the past but it's after all else fails.
  6. Tony L

    Tony L Administrator

    Again I can only speak for Golds and the era before, but the paper spacers were added at assembly/testing to compensate for any tolerance issues in manufacturing as these were still at this stage hand made items. The distance between the pepper-pot and the diaphragm is hugely critical and makes a heck of a difference to the treble response, but unless someone has really been messing about in there it should be right, you shouldn’t need to change it as it was defined at the factory for that particular basket/pepper-pot assembly. You should’t need to alter the number of spacers when swapping a diaphragm, though if anyone forgot to put one back in the past you’ll never get them pair-matched! I’m lucky in that to the best of my knowledge I was the first person into my current Golds so they haven’t been messed with at all. I only needed to give a very gentle nudge to the diaphragm centring to get an acceptable (though not perfect) pair match. It is exceptionally hard to find a pair of Silvers, Reds or Golds that are truly pair-matched the way one would expect of a modern mass-produced driver (e.g. within say +/-1db). It is just the price of owning these superb sounding classics. They are magical things, but imperfect. Even so I am talking tiny differences here, not the gross imbalance you are describing.

    Again I can’t over-emphasise the importance both of centring and of bolt tightness (use very little!). Another trick if you end up with one that sounds good and the other just doesn’t sound as open, free or clear then try the poor one in a different orientation in the voice coil. Given the four bolt fitting there are four possible 90 degree orientations, try each as you may well find it is far happier in one position than the other three. Just take it really slow and careful and really listen to what position and tension produces which result. As I say this takes me many hours with Golds to get to the point I am really confident I have the best result that particular speaker/diaphragm combination can produce.
  7. cooky1257

    cooky1257 pfm Member

    There's a definite hand made aspect to the original gold hf drivers.
    In the 205 ,the standard set of spacers is one glued to the diaphragm assembly and 2 more, one thick one thin, the hard plastic cover 205 diaphragm assemblies do vary, as does the pepper pot machining (rear and throat)particularly in some HPD's.
    if they were all 'wrong' in the same way you wouldn't need 3 spacers of different thickness, you'd need just one of the correct thickness or as in the case of the later k series units tighter machining tolerances in the drivers and in the diaphragm assembles so no spacers required at all.
    My advice is to leave them as they are as in the vast majority of cases careful cleaning,
    screw tensioning and position will get you where you need to be. I warn against just rotating the Dias whilst in position as you can scrape the voice coils so remove /rotate 90'.
    If I was installing the 'new' replacement ones I'd still initially re-use the 2 loose original spacers in case I had to to account for variations in the original pepperpots/top plates.
  8. Wow I’m surprised by how much alignment effects the frequency response of these speakers!

    I seem to have got the HF a little better. There A few areas around roughly 1.7k, 3.5k, 11k that are about 5db off but I shall have some more playing I think. The big one is around 18k where it’s about 10db off.......but I’m not sure that’s particularly a frequency I can actually hear anymore!

    The LF I think is where I may have a problem and possibly the reason for my perceived “One being louder“ as there seems to be a constant 10db or more difference in volume between 2.2k and 4k. And a 5db difference around 1.2k.

    I’m guessing I can do a similar thing aligning the LF. Loosen the bolts and wiggle it about a bit?
  9. cooky1257

    cooky1257 pfm Member

    Interesting, that 2.2-4khz difference is right where the notch filter operates or at least should be. The Crossover freq is 1.2 kHz so I suspect the 5 dB issue could be phase cancellation due to a wrong driver polarity , i.e. The LF and hf drivers are cancelling rather than summing at the crossover frequency. If the LF drivers aren't rubbing I'd leave them alone.
  10. Forgot to mention for these tests I was testing the LF and HF separately just to see what was going on.

    But you have just reminded me about the phase canceling between the LF and HF when playing together. I will do a few measurements with everything together.
    cooky1257 likes this.
  11. Raoul Duke

    Raoul Duke pfm Member

    A few months on, just wondering if the OP managed to get a better match? I am just about to take a look at my own HPD315s as I am noticing one does not sound right. The notes here from Cooky and Tony L re HF alignment are very helpful. Can someone possibly describe what I should be seeing in terms of a correctly wired HF unit? I seem to remember that the HF unit is opposite phase to LF?
  12. cooky1257

    cooky1257 pfm Member

    You will get a cancellation/ notch at the crossover frequency if they are wired incorrectly. Note though it's relative so first make sure both the bass drivers are in phase with each other before you start or you can end up with LF/HF correct but L/R out of phase.
  13. Raoul Duke

    Raoul Duke pfm Member

    I have been using a test CD to check phase, this also has pink noise bursts alternating between left and right channels. I had previously noticed a different quality between left and right with the pink noise, and so was extra careful when I went over my speakers a few months back to make sure they were wired exactly the same all the way through (as well as a proper clean out of HF magnet gap and very careful HF realignment with a tone generator) Since then I had still been bothered by a channel imbalance and so this afternoon I quickly went in and flipped the wires around on the HF unit of the perceived weaker speaker. I have to say this seems to have done the trick!

    Cooky I just grabbed a pair of your HPD Labels today as well for my Eatons :)
    cooky1257 likes this.
  14. cooky1257

    cooky1257 pfm Member

    Cheers Jonathan, I'll pop an extra one in incase of mistakes;-)
    Raoul Duke likes this.
  15. Raoul Duke

    Raoul Duke pfm Member

    Well it seems logical to continue here discussing mysteries of the HPD315....

    I have just done measurements on my speakers (which are 100 liter Bass Reflex tuned to about 40Hz) with Room EQ Wizard and a calibrated USB mic and now have a visual representation which confirms what I have been hearing. Wondering now if HF alignment, paper gaskets, or pepperpot machining (or a combination of all!) could account for the differences. From a bout 1.4kHz to about 7kHz there is up to 5dB difference in response. Then Cabinet 2 shows a more pronounced 10kHz resonance peak.

    [​IMG]HPD315 by Jonathan Chiles, on Flickr
  16. ToTo Man

    ToTo Man the band not the dog

    This has to take the biscuit for the most useless y-axis scale posted on pfm! :rolleyes:

    Tip: if you click the button at the top right of the graph that looks like two intersecting arrows, you can change the lower and upper limits of the y-axis. I'd recommend +40dB as the lower limit and +90dB as the upper limit. I'd also recommend changing the lower and upper frequency limits to 20Hz and 20kHz, respectively. Also, if you click the button at the top right of the graph that looks like a cogwheel, you can change the amount of smoothing applied to the graph. I'd recommend 1/12, any smoother and you won't get enough detail to accurately determine the frequencies that are diverging. HTH. :)
    Fatmarley likes this.
  17. Raoul Duke

    Raoul Duke pfm Member

    Apologies for that horrible plot! Literally my first day playing with REW, thanks ToToman for the pointers..

    [​IMG]HPD315 Plot by Jonathan Chiles, on Flickr
    cooky1257, Fatmarley and ToTo Man like this.
  18. ToTo Man

    ToTo Man the band not the dog

    That's better, now we're in business! If you're new to REW then, forgive me if I'm teaching granny to suck eggs, but it's essential that the conditions for the two measurements are as identical as possible. Ideally this means keeping the mic in a fixed location and moving each speaker into the exact same position in the room for the measurement. IME this is the only way to guarantee consistent results, especially in the bass.

    It looks like this is the technique you've used because the two drivers have excellent matching below 1kHz. Above 1kHz there is an obvious disparity, but this is common in Tannoy HF units. You might be able to improve the matching by re-centering the HF units and/or changing the number of paper shims (assuming your HF unit has paper shims), you'll only find out by trying. I've never attempted to re-align the HF units so am not the best one to give advice on this.

    If the thought of this daunts you, then I recommend playing with the Energy switches on the crossover instead. Boosting the Energy of the Green driver by +1 and lowering the Energy of the Red driver by -1 should get you a closer match between 2kHz-8kHz and 12kHz-20kHz. This will make the matching between 8kHz-11kHz worse, but hopefully you might not notice a mismatch here as much as you notice it between 2kHz-8kHz. This won't be of much help to the large disparity at 1.9kHz, I suspect the only way to improve that is to experiment with re-aligning the HF units.

    PS - Have you checked the distortion measurements? Are they similar for both drivers?
  19. Fatmarley

    Fatmarley Agnostic

    How difficult is it to swap one crossover to the other? If it's easy, that's what I'd do first. Take a measurement of one of the speakers with the microphone and speaker in a fixed position (preferably off the ground and as far away from boundaries as possible), and then without moving anything or adjusting the amplifier volume, swap the crossover from the other speaker, and take another measurement. If the measurement doesn't change, then you know both crossovers are identical, and it's got to be a problem with the compression driver.
    cooky1257 and ToTo Man like this.
  20. Raoul Duke

    Raoul Duke pfm Member

    Thanks gents for your comments! Obviously you are lacking background to my situation... but yes I did measure the 2 speakers in the exact same position in the room. Also the same amp channel and crossover used for both measurements. I am also no stranger to fiddling with the HF unit alignments, having done this previously on these drivers as well as my HPD295s. Both of the HF units in these HPD315s have 2 paper gaskets fitted, and the screws are just finger tight. Have aligned as best I can with tone generator initially.
    Things get a bit confusing here as I am using my own external DIY crossovers. I may need to return to using the factory crossovers until I iron out this mismatch between drivers just in case a crossover problem is throwing me off here.

    ToToman.. interesting to note that the HF units are often mismatched.. I understand the pepperpot machining also plays into this. Will also do some distortion measurements as you suggest.
    Fatmarley likes this.

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