|13th March 2013, 11:36 PM||#11|
Join Date: Nov 2003
Location: Brighton UK
I've come across it several times, its not a good tweeter.
Throw in a poor crossover design and its much worse.
The latter makes it a poor general DIY tweeter.
Looks suspiciously similar to some old Goodmans tweeters.
Last edited by sreten; 13th March 2013 at 11:39 PM.
|14th March 2013, 12:07 AM||#12|
Considering their vintage in the light of what was available at the time,the Philips dome was a reasonable choice.Yes it has more colouration than the early cloth domes such as the Goodmans DT3 and the Peerless DT 10 HFC,but this should be kept in perspective considering its comparitive cost.It might be of some interest if the experiment could be continued in stages; with a 0.32mH coil and an 8 Ohm resistor for a l.f load in the sweep together with the 5 mFd cap and Philips dome.Then followed with the same components in a series arrangement.Both of these arrangements should give a xo freq of approx 3980 Hz.If you have surplus xover components handy, such as a 0.45mh inductor and a 3.5 mFd cap. then the quasi 2nd order xover could be part of the comparison.
|14th March 2013, 04:28 AM||#13|
Join Date: Apr 2002
Location: New York State USA
I think the issue with this or any tweeter is that if you do not get the energy out of the tweeter below the lower rolloff point you end up with increasing IM and THD as power goes up due to the excess LF excursion.
If I remember properly (doubtful) the first order filter will merely flatten the excursion of the driver below the rolloff point, making it more or less constant as frequency goes lower. This is not a very good choice, since I don't think you want the little dome dishing in and out at bass or even midbass frequencies at all.
The Cauer or Eliptical filter suggestion has some merit, but the implementation will be tricky, in part due to the impedance rise that is there around LF rolloff and also the non flat passband of the filter. Carefully done, it might work fine. Of course, I'd not suggest a trying to get a first order out of such a filter. The dip is very high slope, and the remaining rolloff while down a reasonable number of dB, in a first order implementation (which is something of a kludge arrangement, I expect) it seems to me would potentially have some of the same problems as mentioned at LF with the standard first order filter, as the levels at very LF may not be all that much different... you'd have to run a simulation and see where you end up.
I used a number of these Phillips tweeters back in the day, and they were pretty nice when rolled off more like 2.5-3kHz... and the ones that were original (arguably better) did not have the little black "phase cap". The ones with the phase cap were later models, and I think they went heavier and cheaper with the domes... maybe even they were polycarbonate, and not mylar. Unsure.
Just guessing about the way to do it, based on only the curves, I think I'd try to adjust the Q of the xover for a slight bump and try to set the xover about 2kHz, this would flatten the passband a bit... the rise may be due to the phase cap... and I generally have not heard the phase cap sound quite right... but I think I'd opt for a very small low DCR inductor in series with the tweeter to flatten the rise, just enough... maybe make the coil start to have effect ~10kHz, and drop 3dB by 20kHz, that would give a flat response, you'd have to dork the coil value carefully, and actually a slightly lower freq start, larger coil is likely to have a better result to the ears...
A few cents worth of thoughts dredged off the top of the head...
Btw... it's slightly unclear from the OP's discussion if the intent is to run the tweeter only from say 8kHz up??
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
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