ribbon crossover question
Beginning a speaker project here.
I've ordered two RT2E-A HiVi isodynamic tweeters that I intend to build into the setup (2 Way speakers)
Has anybody here used these in a two way setup yet?
I would presume, with these tweets I would be using a 3 order filter, crossed over at 3Khz.... Any recomendations as to which type will give me the least nightmares?
My other big concern is that I don't over power these tweeters. How can I limit the power to them? or what should I do with the crossover to avoid over driving them?
Crossovers always drive me crazy, as using the standard formulas it never seems to work properly and I end up with a final design using vastly different values, but still giving a decent response.
If this is the same tweeter they have been producing from inception , my recommendation is that it is only suitable for a 3 way system , not 2 way. If you insist on a 2 way system use 5 1/4 - 6 1/2 , the 6 1/2 will be at the extreme of acceptability when x-over to the tweeter.
There is no easy solution on x-over design, even when using very detailed and extensive equipment a good x-over will take time to truly develope.
Due to the very different radiating patterns of your drivers i would favor an odd-order x-over.......
1) It's an isodynamic speaker, therefore it's (in principle) less vulnerable and less stress-sensitive than a ribbon
2) it can (in principle) be X-overed closer to the resonant frequency
3) Expolinear.de, the German specialist retailer for planars specifies the RT2a at 100 W (12dB slopes) as from 2200 Hz. Should be no problem with an adequate 17cm (7'') or even certain 20 cm (8'') bass-mid in a 2 way set-up. It is true that it can sound a bit harsh at the begining, until the break-in is complete.
4) as regards protective measures, DIY loudspeaker retailers usually have on offer protective devices for tweeters. Can be some kind of fuse or light bulb (alternatively a light bulb of 24V, 50W in series could do the job and absorb part of the excess power); sensitivity of the RT2a seems quite good at 93dB or so); in a classical 2 way set-up and to keep a balance, you will probably end up anyway adding a resistor or dividing resistor bridge to take away a few dB down to 85-88 dB: this should give you some extra headroom if you really tend to listen at very high levels.
5) I think one of the German DIY loudspeaker magazines (hobby hifi, klang und ton) has done some tests and simulations. I might even have it (somewhere).
I hope this helps a bit.
Thanks, that's what I thought.
After realising what's involved with actually getting a passive crossover working correctly, I have decided to go with two way active crossovers and bi-amping. Crossover point chosen will be at 3K
Now that I actually have these tweeters in my hands, they are enormous and preliminary listening tests indicate they should perform well at the reasonable price.
I had also purchased some Hi-Vi TN27 tweeters because they seemed interesting for another project I am working on. They initially sounded real nasty till after much development and fiddling I managed to tame them with correctly designed crossovers, and was quite surprised at the pleasant result.
Lesson learned here was a tweeter with an incorrect crossover can sound really painfull, and it's always worth the time and effort to get the passive crossover correct.
As regards the use of standard formula to calculate Xovers, it is generally admitted among DIYers that this is pure illusion since there is no speaker that exhibits perfect parameters (linear frequency response, impedance curve, distorsion figures etc.); component retailers have to convince their customers that building a loudspeaker is very easy but the filter is probably the most important part of the construction and it ideally requires measures to adapt the theoretical calculation to the reality. I know a few "old generation" and very experienced speaker developers who still adjust the filter only with their ears; needless to say, they spend a lot of time and their criteria as I found out is often an averaged adjustment that accomodates most music styles (as opposed to the modern developer who will aim at the most linear frequency response curve based on measures and computer assisted simulations).
Isodynamics, ribbons and the like may make things a bit easier since the impedance is constant. But if one takes a tweeter that I like very much, the Stage Accompany SA8535 (impedance is the same at all frequencies), it would be illusory to Xover it at 1500 Hz with the standard calculation formula; the frequency response exhibits a much higher sensitivity between 1 and 5kHz than it does in the uper range. The trick is to Xover electrically this tweeter at 4-5 kHz or so, so that the Xover frequency with the (bass-)mids is accoustically at 1500 Hz. Only then does the Nirvana door open... I'm sure you'll get something great with your tweeters; good luck!
I had different results with the SA tweeter, I found it reached ~1500 just fine and was reasonably flat all the way up. It is possible that either your baffle or their receipe has changed since I used them (over a decade ago now).
As far as an xover for ribbons of the Hi-Vi type - "printed ribbon" or "leaf ribbon" - (dunno what "isodynamic" means?) - my experience has been that 4th order is better in terms of power handling near the xover freq, lower THD, and easier to integrate phase wise to the driver that meets it.
"I had different results with the SA tweeter, I found it reached ~1500 just fine and was reasonably flat all the way up. It is possible that either your baffle or their receipe has changed since I used them (over a decade ago now)."
Did you use the SA8535 or one of its precursors (SA8520 - which is in fact still available from the factory - , SA8525, SA8526)? Some are indeed "flater" than others.
"As far as an xover for ribbons of the Hi-Vi type - "printed ribbon" or "leaf ribbon" - (dunno what "isodynamic" means?) - my experience has been that 4th order is better in terms of power handling near the xover freq, lower THD, and easier to integrate phase wise to the driver that meets it."
I'm probably old fashioned; I do reserve the name "ribbon" for the type of technology used by manufacturers like Raven and others (a stripe between magnetic poles), that's why I call isodynamic the technology used by HIVI, SA etc., leaving aside Heil, Mundorf, Beyma TPL150 which is again of another type. I fully agree with you that (true) ribbons definitely need steeper Xovers when cut near the resonant frequency and/or near the area where distorsion is at the highest; 24dB is often the standard.
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