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Old 4th November 2011, 07:16 AM   #21
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Quote:
Originally Posted by davidsrsb View Post
Music may have more average power at low frequencies, but my own measurements show that many over compressed CDs have digital full scale swing when high passed at 2kHz with 3rd order cutoff. To avoid clipping the HF amplifier needs as much headroom as the LF although the peak to average ratio will be fairly high

It can be argued that clipping the active speaker HF amplifier does not sound too bad and clearly does not have the side effect of increasing HF power that a clipped full range amplifier can
but is not clipping is 'dangerous' for tweeters?
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Old 4th November 2011, 02:53 PM   #22
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Clipping a low frequency signal, while full bandwidth, creates abrupt discontinuities that have a high level HF content, which can fry tweeters in a conventional passive crossover speaker

Clipping a HF signal in an amplifier that is driving the tweeter only will REDUCE the power to the tweeter. Clipping a LF signal in an amplifier that only drives the woofer will generate harmonics, but these will not bother the woofer and have no way of affecting the tweeter

Biamping makes it much easier to protect a tweeter
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Old 4th November 2011, 03:35 PM   #23
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Davidsrsb is dead on about the headroom. However, I feel that clipping should be avoided. PERIOD.

Rod Elliot has some very useful information on his site. The linkwitz-riley crossover is certainly not his IP, and as such you are free to build your own without permission. However if you are incapable of doing the design by yourself, it would be appropriate to get permission from the developer.
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Old 4th November 2011, 09:36 PM   #24
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To drag this topic back onto chip amp choices,a fully active 2.5 way is an ideal application for low cost parts like the TDA2050.
I would have two 8R bass drivers, each with its own amp with one low passed at the baffle step. This solves the problem of driving 4R drivers that most chips have
The tweeter would have its own amp of the same rating
Separating the LF and HF means that there is less problem with the rising HF distortion that the cheap chips have
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Old 5th November 2011, 04:05 AM   #25
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have any body here in this forum tried using/making Rod Elliott's active xover ckt? how does it sound? i will be using the ckt published on his website as it is as i dont have knowledge of active crossovers or filters
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Old 5th November 2011, 09:01 AM   #26
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It works well, but has limitations. There is no facility to delay any of the outputs to time align the drivers, so unless you use a sloping baffle or some other arrangement then you will have some phase issues. Saying that, I have a three way running unmodified for a background music system in my dining room and haven't noticed any real problems.
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Old 5th November 2011, 10:39 AM   #27
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Originally Posted by pinkmouse View Post
It works well, but has limitations. There is no facility to delay any of the outputs to time align the drivers, so unless you use a sloping baffle or some other arrangement then you will have some phase issues. Saying that, I have a three way running unmodified for a background music system in my dining room and haven't noticed any real problems.
Agreed. It is a crossover, not a complete solution.
It is a very good crossover however.

In addition, you will need Baffle step compensation and maybe a delay (all-pass) network.

Frank
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Old 5th November 2011, 11:56 AM   #28
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I'm a bit surprised by the suggestions that we need high power to HF drivers when listening to music. The highest piano note (C8) has a fundamental of 4,186 KHz; Violin same as piano; The highest cymbals in a drum kit (Hi Hat) around 5 Khz. All other instruments and voice are lower: Piccolo 2,951 Hz (B7); a flute 1,976 Hz (B6); Electric or acoustic guitar 1,397 Hz (F6); most others at or below those frequencies (eg Trumpet 988 Hz).

Energy above the fundamental (harmonics) will be well down in level.

There is simply no need to be able to reproduce 100 db SPL at frequencies of the 2nd or higher harmonic; that energy level doesn't exist in the note when the fundamental is at 100 db SPL.

I've done bi-amping at home and sound reinforcement situations, and keeping in mind there are other variables (the speaker, obviously) my rules of thumb go something like this:
Assuming a system that plays at appropriate sound quality and balance with a single amplifier, and your goal is to always have the LF amp clip first, then:

For home listening, with conventional music and voice, 10x is a practical and useful ratio
For home listening with significant synthesized content, use 4x

For sound reinforcement, 4x is a practical and useful ratio
For live music with synthesized content, go 2x


Even if your music consists of significant top-octave instrument notes with an instrument capable of very high fundamentals (rare) these notes are difficult to excite; you have to play very hard to get a lot of energy out of a high piano key and no matter how hard you play, it won't be as loud as even a moderate press on a lower key; and if you're talking about a guitar player working near the neck, well, not only is it essentially impossible to get good volume compared to the open E string, the fundamental can't be higher than 1,397 Hz. Top notes are hard to generate volume on every instrument, period, and that includes the human voice.

In practical terms, very good sounding SS amps on HF content in the 50W range are not difficult to find, while a 200W SS amp with good bass performance is also fairly easy to find, so there is an easy 4x ratio there that won't break the bank.

It's a bit more fine of a line if you go unconventional, but if the top end is vacuum state and the bottom SS, then even at a 10/100 ratio the tube amp's clipping characteristics are not going to be an issue, and to be honest I doubt you would ever get near the knee on the HF amp playing music at home.

Those who've pointed out that the speaker's sensitivity and overall balance may come into play have made a good point, but personally I don't feel the power balance is really that difficult an issue.

The short answer is you don't need gobs of power above 5K and you probably don't need equivalent power even at 100 Hz and 1 Khz.

You need most of your power at or below 1 Khz. I would not hesitate to go 10x even at that crossover frequency in my own home system but if you listen to significant high volumes you could be a bit more conservative.
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Last edited by Johnny2Bad; 5th November 2011 at 12:22 PM.
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Old 5th November 2011, 03:56 PM   #29
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Take a look at this CD: Steely Dan - Katy Lied - Black Friday 1:48.0200
There are sequential samples at almost +/- digital full scale.
This is a fairly well engineered CD, not much of the over compression so common now.
Playing around with the Audacity high pass effect, the signal is still full scale with a 10 kHz 4th order cutoff
One odd thing about this CD is that the spectrum shows the use of a 8kHz notch filter
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Old 5th November 2011, 04:14 PM   #30
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One thing that seems to have been neglected in this conversation is the fact that a crossover doesn't actually occur instantly at one specific frequency. A second order Linkwitz-Riley active crossover produces a -40 dB/decade roll off. That means that if we consider -40 dB to be sufficient attenuation to be insignificant (it isn't really...) That we need our tweeter and woofer to agree on SPL from a decade below crossover to a decade above crossover. For a 2K crossover, this would be the range from 200-20000 Hz.

If our SPL's don't match, it will show in a frequency response. However, these variations can be very difficult to pick up with an untrained ear.

I have not used Rod Elliot's setup, but I have used many Linkwitz-Riley crossovers, and they produce excellent results.
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