1st order cross-overs, phase and tweeter protection

[Jonathan Bright]

This is a "fishing expedition" to get other people's feedback. I am intersted in exploring a triamped system with first order filters to see if the benefits of low phase change are worth pursuing.
My concerns are for the safety of the tweeter.

Now I have some hi-frequency units with a resonance of less than 600c/s. I don't want to fry them electrically or overstress them mechanically so I was thinking about the following idea.
It is easy to arrange for the active opamp to provide a first order high pass at 6kHz. (this will feed the power amp.) Then I was thinking of a second cap' after the amp with a break point at about 600s/c. This way I get a 12db/octive slope below the resonance frequency which will help my paranoia about blowing it up.

Now none of this is rocket science. But will it be a stupid idea and I end up losing the benfits of 1st order networks?

Thanks Jonathan

[Loren42]

"My concerns are for the safety of the tweeter. "

You always should put a cap in series with the tweeter to protect it from extraneous DC form the amp.

[Moondog55]

Hi Jonathon, the first question I have to ask is Why?? seems like a waste of time and effort to tri-amp a first order system unless it is to utilize a very low XO on the woofer.

second order slopes? usually with a second component in parallel

[Jonathan Bright]

THanks guys. Probably didn't make myself 100% clear.

1. Loren 42.
There WILL be a cap in series with tweeter, I'll have a low level cap prior to the amp (passive, small signal) and as I am using Class JLH's (1969) amps I'll run a second cap (passive high level) at the amp output.
I am hoping to enjoy the low phase change advocated by its proponents with the 6k break point and achieve a degree of tweeter protection with the earlier 600cycle cap. What it means in practise is that the second phase change will occur about 20db below reference level. Hopefully it is less noticable there.

2. Moondog55.
Hope the above makes more sense. As to the reason, well the reading I've done on IMD puts the fear of God into me and I want to explore bi (tri) amping. I am looking for clarity and so low IMD and possibly low phase change are areas to explore to get to that gaol. I'm just shooting the breeze with these posts and if someone tells me the lower reactance will stuff the whole thing up then I'll abandon the plans.

Re; the IMD. The E&WW article was very persuasive about the cumalative effects of running mutilple frequencies through a non linear element i.e. a power amp. The following is an interesting exercise. In a full range power amp with a spread of 30 to 15,000 cycles the ratio is 500:1. With a triamped system and appropriate x-overs freqs the ratio can drop to 8:1. that is a huge change and possible explains why the subjective benefits of multi amping impress people so much.

As I said at the beginning its an exploratory question. Just shooting the breeze.

Thanks again.

[Moondog55]

OK then I would be using a second cap one octave above resonance.
I am a big proponent of Bi-amping but for me it is probably more a power handling/clarity thing on the midrange

[rabbitz]

The key to success with 1st order electrical is careful driver selection. Get it right and you end up with nice 2nd order acoustic slopes.

BTW, have never fried a tweeter with a 1st order passive and that includes one where I accidentally crossed over below the tweeter's Fs.

[skeptic43]

You should be pretty safe crossing over the tweeter at > 4 times its resonant frequency with a 6 dB HP filter.