Hi everyone.
After several incidents, destruction and repair I decided to replace and maybe upgrade my really bad tweeters on my very average old pair of Fostex PM 0.5 active monitors.
I'm thinking of buying a new pair of Sica ones with similar faceplate dimension (85 -90mm) and 8 ohm impedance. The only ones I found with the same faceplate. Better quality I guess since they are quite more expensive ones.
I don't go back to the original tweeters of Fostex since they sound horrible anyways. I have even replaced their woofers some years ago with much better Monacor ones.
The thing is that Sica has a recommended crossover point of 2.5k on their average priced ones (even if the tweeters are capable of lower freqs according to the data sheet) and my speakers have their crossover point at 2k. Only their more expensive ones have a recommended point at 1.5k (but they are 3 times the price)
Will this gap be audible and if yes should I experiment with small inductors or capacitors along the positive side ?
Are there any alternative mid priced suggestions for 2khz recommended crossover point tweeters, 8ohms and a faceplate around 90mm (3,5in)?
Thanks in advance
After several incidents, destruction and repair I decided to replace and maybe upgrade my really bad tweeters on my very average old pair of Fostex PM 0.5 active monitors.
I'm thinking of buying a new pair of Sica ones with similar faceplate dimension (85 -90mm) and 8 ohm impedance. The only ones I found with the same faceplate. Better quality I guess since they are quite more expensive ones.
I don't go back to the original tweeters of Fostex since they sound horrible anyways. I have even replaced their woofers some years ago with much better Monacor ones.
The thing is that Sica has a recommended crossover point of 2.5k on their average priced ones (even if the tweeters are capable of lower freqs according to the data sheet) and my speakers have their crossover point at 2k. Only their more expensive ones have a recommended point at 1.5k (but they are 3 times the price)
Will this gap be audible and if yes should I experiment with small inductors or capacitors along the positive side ?
Are there any alternative mid priced suggestions for 2khz recommended crossover point tweeters, 8ohms and a faceplate around 90mm (3,5in)?
Thanks in advance
I see your speaker has an active crossover, 40W to woofer and 30W to tweeter.
I shouldn't think the slightly lower crossover frequency than recommended for the average priced Sica would be problematic, provided the resonant frequency of the Sica is suitably low.
Can you supply the Sica's spec sheet for all to see?
here is a link. The speaker value is 20 euros per unit. The resonant frequency is around 1.1k that's why I decided on this one.
Dome tweeter Sica LP85.25/95, 8 ohm, voice coil 25 mm
then there is this one with 1.5khz crossover point but it's way more expensive (70 euros per unit):
Dome tweeter Sica LP90.28/N92, 8 ohm, 28 mm voice coil , 90 mm front plate
Dome tweeter Sica LP85.25/95, 8 ohm, voice coil 25 mm
then there is this one with 1.5khz crossover point but it's way more expensive (70 euros per unit):
Dome tweeter Sica LP90.28/N92, 8 ohm, 28 mm voice coil , 90 mm front plate
It really depends on the slope of the active crossover. If it is no steeper than 12dB/octave then things are looking tight for the LP85.
The LP90 has a resonant frequency of 550Hz, so would be the safer choice. However, it's the low resonant frequency that makes it expensive.
Alternative tweeters with a similar low resonant frequency are likely to be equally expensive.
A knowledge of the resonant frequency of the original Fostex tweeters would give more certainty.
The LP90 has a resonant frequency of 550Hz, so would be the safer choice. However, it's the low resonant frequency that makes it expensive.
Alternative tweeters with a similar low resonant frequency are likely to be equally expensive.
A knowledge of the resonant frequency of the original Fostex tweeters would give more certainty.
Thank you Galu. Fostex is really horrible with the specs. They don't even give speaker impedances.
But I'm pretty certain that their tweeter (and also the woofers) on this series of cheap monitors is really cheap (I mean in the 10 euro category...really poorly constructed, with the cheapest chinese diaphragms) so if low resonant frequency makes tweeters expensive, I bet it doesn't go low at all.
Even the crossover doesn't seem active to me. It's just a bunch of components on the same pcb along with the class d amplifier. No pots or anything to adjust it. The only other pcb in the speaker is the power supply unit.
But I'm pretty certain that their tweeter (and also the woofers) on this series of cheap monitors is really cheap (I mean in the 10 euro category...really poorly constructed, with the cheapest chinese diaphragms) so if low resonant frequency makes tweeters expensive, I bet it doesn't go low at all.
Even the crossover doesn't seem active to me. It's just a bunch of components on the same pcb along with the class d amplifier. No pots or anything to adjust it. The only other pcb in the speaker is the power supply unit.
The original Fostex tweeter certainly doesn't look anything special:
Fostex 8578004000 Tweeter For PM0.5 And PM0.5 MKII | Full Compass Systems
At its price, it's worth taking the gamble with the LP85 tweeter.
If it sounds harsh, you could experiment by placing a bipolar capacitor in series with its positive lead. As a guesstimate, 10uF may be a reasonable value.
Fostex 8578004000 Tweeter For PM0.5 And PM0.5 MKII | Full Compass Systems
At its price, it's worth taking the gamble with the LP85 tweeter.
If it sounds harsh, you could experiment by placing a bipolar capacitor in series with its positive lead. As a guesstimate, 10uF may be a reasonable value.
+1, especially since the way I look at it the 2.5 kHz XO is no doubt due to its 40 W peak rating, so [20*40]^0.5 = ~28.28 W mean and with most drivers requiring at least a 1/2 octave above Fs/2nd order = [1.1*2.5]^0.5 = ~1.56 kHz XO mean meets it close enough to the original's 1.5 kHz, though a good plan to hard limit it to ~30 W in case you need the 105 dB/m peak rating.
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Thanks GM. Could you please explain to me a bit better the math (cause I would like to learn basic things on how these work)?
[20*40]^0.5 = ~28.28 W mean
[1.1*2.5]
and how can I hard limit it to 30W (even if I never play both monitors combined above 70 db - that's what I've measured)?
[20*40]^0.5 = ~28.28 W mean
[1.1*2.5]
and how can I hard limit it to 30W (even if I never play both monitors combined above 70 db - that's what I've measured)?
Formulae are often the reserved property of audio wizards!
The two formulae GM has used are:
mean power = square root of [rated power x continuous program power]
mean crossover frequency = square root of [tweeter resonance frequency x recommended crossover frequency]
I am using the terms from the tweeter's data sheet: https://en.toutlehautparleur.com/media/catalog/product/datasheet/sica/Z009040.pdf
P.S. To be pedantic, [1.1*2.5]^0.5 = ~1.66 kHz and not ~1.56 kHz.
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Thanks Galu for the thorough explanation. Always good to learn something new. And not to forget to remind GM that the original's crossover frequency is 2khz and not 1.5khz
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The drivers are bi-amped with 30W maximum going to the tweeter.
So, the tweeter should be operating within GM's suggested limit.
hey tedsorvino,
my fostex tweeter broke down and i couldn't fix it anymore. The original spare parts are out everywhere, so i stumbled across your post from 2 years ago and am wondering how the sica-tweeters turned out in your system. Did you experience any issues or were they really an upgrade to your monitors?
Also, which monacor woofers did you choose?
i would be glad hearing from you
Maemmel
my fostex tweeter broke down and i couldn't fix it anymore. The original spare parts are out everywhere, so i stumbled across your post from 2 years ago and am wondering how the sica-tweeters turned out in your system. Did you experience any issues or were they really an upgrade to your monitors?
Also, which monacor woofers did you choose?
i would be glad hearing from you
Maemmel
I bought the Sica LP85.25/95. To replace it:
Form factor: the new tweeter dome protrudes slightly, I'd now avoid laying the speaker on its front.
I haven't done extensive audio tests.
- from the front, remove the black foam + rigid plastic to uncover the 5 screw. Some alcohol behind the rigid plastic helps dissovling the glue.
- unscrew the 5 peripheral screws. Beware the screw drive are fragile. I replaced the screws (they are hidden anyways).
- from the back, unscrew the peripheral screws. Add alcohol in the slit between metal plate and wooden box, let it dissolve the glue for ~1min, pry it open.
- push on the tweeter from inside the box
- unplug the faston terminals from the faulty tweeter. Enlarge one faston terminal a bit. The other one is too small, but it's possible to crimp a larger one directly on it.
- I had to cut a small square roughly 5x5mm from the wooden box to make space for the onnectors on the new tweeter (Sica)
- plug the new tweeter, set it in place, screw it (preferably drill a smaller hole first for each screw, since the screw positions have changed), put the black foam cover, screw the back plate.
Form factor: the new tweeter dome protrudes slightly, I'd now avoid laying the speaker on its front.
I haven't done extensive audio tests.