With today's quoted powers it's hard to say but to me anything under 10 watts rms coupled to low sensitivity speakers and as you say it's the guy controlling the volume. Parties are typical tweeter destroyers. Generally though I see lots of car radios blowing tweeters and that is because the guys crank full volume on their little 5 -10 watt radios. I started off building 250 watt rms amps (the transformers alone weighed a ton) and could never find suitable speakers except for Phillips mids and tweeters rated at 5 and 15w and we never had problems. The old adage was that over powered amps rattle woofers and underpowered ones blew tweeters. My current moscodes are only rated at 80w rms and that's enough power for me, but I guess each to his own.
At least one manufacturer out there recommends the amp be rated at 3X the driver rating.
That is the idea...
However since the quality of this cap is of reasonable importance, if you're going to use it I think it's better to make it part of the actual crossover, and therefore as small as the design will allow.
Going the other way, the cap shouldn't be large enough that the time constant formed with Re and the capacitor would allow the amp's supply rails to fry the tweeter (if that were to happen).
Which probably won't be any of us
Then again a person might blow a tweeter if...1. Performing an experiment.
2. Had a particularly bad day, need music.
3. Interference from cats, or from those with a similar level of audio knowledge.
or 4. "I think a year is long enough to be trying to get good sound out of this tweeter, it must be eliminated."
The "under-powered" amplifier theory does not apply to active speakers. Clipping the bass/mid does not transfer power to the tweeter.
Most tweeters can only handle a few Watts, so even a 25W amplifier would benefit from some sort of average power limiting and peak current limiting, weighted to reduce low frequency current to avoid too much coil travel
Most tweeters can only handle a few Watts, so even a 25W amplifier would benefit from some sort of average power limiting and peak current limiting, weighted to reduce low frequency current to avoid too much coil travel
That's the way I see it. If it is that big, it's only for DC (being active, there's no bass down there anyway). Why make it large unless you're trying to stay away from an already finished crossover.
There are other ways to protect tweeters from DC, but it might become a personal choice. E.g. I may like the idea of electrostatic headphones driven by a valve amp without an output transformer but I doubt I'd be able to relax while listening to them.
Keep in mind that an active crossover is always BEFORE the amp. As long as everything works perfect, that will prevent low frequencies to reach the tweeter, yes. But in case of any malfunction, without a protection device between amp and tweeter, the poor thing is exposed to anything the amp might throw at it, such as DC, pop because some idiot pulled a cable, 60Hz hum because some ground wire got disconnected, etc., etc.
I think it is a wise insurance to have that cap there. We don't live in a perfect world.
(Been to enough parties, blown enough speakers in my life ;-)
"it's only for DC (being active, there's no bass down there anyway). "
I have blown two ribbon tweeters with an active 4-way design, by faulty connections of pa to speaker (bass signal fed to tweeter or dis-/connecting preamplifier wires with power amp on! These connections will be done tens of times during prototyping and measurement sessions. Accidents will happen! Someone with beter mathematical skill can count the number of misconnections af a stereo active 4-way' RCA and speaker wires! I use 4-pin speakon connectors to speaker to avoid misconenctions.
Yes, we need tweeter protection specially in active designs of diyers. Think of someone using an expensive RAAL ribbon or something like that.. I just blew 60€ Founteks...
I have blown two ribbon tweeters with an active 4-way design, by faulty connections of pa to speaker (bass signal fed to tweeter or dis-/connecting preamplifier wires with power amp on! These connections will be done tens of times during prototyping and measurement sessions. Accidents will happen! Someone with beter mathematical skill can count the number of misconnections af a stereo active 4-way' RCA and speaker wires! I use 4-pin speakon connectors to speaker to avoid misconenctions.
Yes, we need tweeter protection specially in active designs of diyers. Think of someone using an expensive RAAL ribbon or something like that.. I just blew 60€ Founteks...
It happened to me when i got my new DCX2496. I played around with it and used the PC-Software to move crossover points.
At one point the DCX answered my action with a nice loud "BLOP".
The Amps clipping indicators illuminated the scene.
Stupid me had no protection on the drivers. So, now I know what happens when a Manger moves far behind X limit.
They could be repaired in the factory for about 300 $ each. I have more than one waiting to be sent.
At one point the DCX answered my action with a nice loud "BLOP".
The Amps clipping indicators illuminated the scene.
Stupid me had no protection on the drivers. So, now I know what happens when a Manger moves far behind X limit.
They could be repaired in the factory for about 300 $ each. I have more than one waiting to be sent.
They will. I recently blew four good output transistors due to a slip of the hand.
I was implying that a passive capacitor is a good thing. I typically use at least one order of passive filter with an active crossover and in this case it should be better for it to be a part of the crossover than just for DC.
lower the value of the cap the higher the cut off point will be with just a cap no coil you will have a 6 db drop so if you have the rated response be one half octave lower then the peek response of your woofer or mid range and you cut if off at the edge of your woofer response with a 6 db drop your fine as most woofers have enough inductance to block off the highs for witch would damage them unless your driving high voltage and low amp without allot of speakers in series some like using 2 back to tweeters if you are using 2 tweeters in series do not put the caps in line put the caps in parallel as bundle then put the bundle in series with the tweeters half the impedance double the double the cap if you put the caps in series with one another you will divide them now this can be useful as it reduces any stray inductance you get at high frequency but you have to account for this reduction so if your tweeters say they are rated for 20 khz and they are only doing 17 khz take the cap out of the cross over replace it 3 caps in series all rated for three times what the original was rated for and the voltage will rating of the caps will go up by a factor of 3 as well so if you had some caps explode or start leaking then try this fix state above
One assumes that the balance between the woofer and the tweeter will be controlled by the separate amplifiers.
But in principle you are correct. Tweeter and treble are usually louder than Mids or Bass, so the amps driving the tweeters would need to be turned down relative to the bass driver to strike a functional balance.
In that sense, you are reducing the power to the tweeter. I think the Original Poster is trying to protect against more catastrophic occurrences. Though the tweeters are under 'attack' from multiple fronts.
To stop power on POP, typically some type of time delay reed relay is used, or some type of soft or slow power on circuit is used.
To stop over-current from excess volume, something has to act as a limiter, though in my opinion, user discretion is the best safe guard.
A catastrophic failure of one of the amps, could cause DC to appear on the driver, and in time that would be a catastrophic failure of the driver. Typically some type of DC blocking device, like a capacitor in the tweeter path, is needed.
Further, depending on how the speaker/amp system is configured, over-driving or clipping the INPUT can be a problem. Most Active speakers like Studio Monitors have a volume control on them. I suspect this volume control turns DOWN the INPUT rather than turning UP the OUTPUT. That control is more of an input attenuator rather than an output amplifier.
Currently, I assume the goal is to protect the tweeter from a catastrophic failure of the driving amp. Likely a capacitor will do that in most cases. However, no solution comes without its own problems.
Think of the Front Speaker Audio Outputs of a Subwoofer. To crossover so massively low, they need a gigantic capacitor is in series with the Front Speakers. That gigantic capacitor comes with its own problems, which is why virtually no one uses the pass through feature.
So the underlying question is - What are you willing to sacrifice to gain what you feel you need to gain? Only the Original Poster can answer that question.
For what it is worth.
Steve/bluewizard
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I'm thinking of doing the same mod on my Spica-50's. If you don't mind, how exactly did you enlarge the hole for the new cup?
Thanks.
Nicco
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