Rti12 impedance

pbullblue

The RTi12 is an 8 ohm speaker. When the jumpers are removed for the purpose of bi-amping what is the impedance of each pair of input terminals? I was told that it remains 8 ohms, that doesn't seem right to me. Anyone know for sure.

thanks
Bradley

wizzy

Good Question. What I would like to know is how bi-amping works with the internal crossover.

ShinAce

When you build an 8 ohm 2-way, you take an 8 ohm woofer and an 8 ohm tweeter and use an 8 ohm crossover. Because a certain frequency is only handled by a single speaker(ignoring the crossover region), the amp always sees 8 ohms.

When you bi amp, the amp still sees an 8 ohm speaker(whether it be the tweeter or woofer). It just has a limited frequency response.

Bi-amping should(ideally) bypass the internal crossover completely.

jakelm

Hmm.. Interesting Shin. If Bradley had a multimeter, easy way to find out.

Bradley, if you have an ohm meter, disconnect the jumpers and see what the meter reads.

wizzy

ShinAce wrote: »

When you bi amp, the amp still sees an 8 ohm speaker(whether it be the tweeter or woofer). It just has a limited frequency response.

Bi-amping should(ideally) bypass the internal crossover completely.

So, if you just do it the slacker way and don't bother bypassing the internal crossover ... you would simply crossover your amps at a point near the internal crossover value?

Let's say your woofer<->midrange speaker crossover is 125Hz, one could send everything below 150Hz to the low freq amp, and everything over 100Hz to the high freq amp?

My thought is overlapping covers the speaker's crossover rollover (it's not an exact cutoff) -- if you cut each amp at exactly 125Hz you might introduce weirdness when you combine rollover of two crossovers - your external, and speakers internal.

Is that wrong?

jakelm

wizzy wrote: »

So, if you just do it the slacker way and don't bother bypassing the internal crossover ... you would simply crossover your amps at a point near the internal crossover value?


Let's say your woofer<->midrange speaker crossover is 125Hz, one could send everything below 150Hz to the low freq amp, and everything over 100Hz to the high freq amp?

My thought is overlapping covers the speaker's crossover rollover (it's not an exact cutoff) -- if you cut each amp at exactly 125Hz you might introduce weirdness when you combine rollover of two crossovers - your external, and speakers internal.

Is that wrong?

Treat it as if it were a normal connection. If your running full range on the amps, then keep them that way. Using internal xover, there is no need to xover amps. If I understand you correctly.

If you have 2 amps to one speaker, bi/wired. Your pre is set the same way as if there was only one amp and not bi/wired. Let the internal xover do the rest of the work.

ShinAce

jakelm wrote: »

Hmm.. Interesting Shin. If Bradley had a multimeter, easy way to find out.

Bradley, if you have an ohm meter, disconnect the jumpers and see what the meter reads.

Will read Wizzy's post and reply later....

Reading resistance with a meter might only give you a reading for the woofer. If the tweeter crossover remains in the signal path when trying to bi-amp, the series capacitor will prevent any DC readings.

If a reading anywhere keeps giving you 6.7 ohms, you are probably reading the woofer's voice coil resistance.

jakelm

ShinAce wrote: »

Will read Wizzy's post and reply later....

Reading resistance with a meter might only give you a reading for the woofer. If the tweeter crossover remains in the signal path when trying to bi-amp, the series capacitor will prevent any DC readings.

If a reading anywhere keeps giving you 6.7 ohms, you are probably reading the woofer's voice coil resistance.

But if the jumpers are removed, then it is straight wire to the drivers? Wether it is or isnt, he will still find out what the load is, that the amp sees?

ShinAce

wizzy wrote: »

So, if you just do it the slacker way and don't bother bypassing the internal crossover ... you would simply crossover your amps at a point near the internal crossover value?

Let's say your woofer<->midrange speaker crossover is 125Hz, one could send everything below 150Hz to the low freq amp, and everything over 100Hz to the high freq amp?

My thought is overlapping covers the speaker's crossover rollover (it's not an exact cutoff) -- if you cut each amp at exactly 125Hz you might introduce weirdness when you combine rollover of two crossovers - your external, and speakers internal.

Is that wrong?

That is correct. As Jake is saying, you could feed each amp with a full range signal and then let the internal crossover do its magic. This assumes that you knwo the internal crossover is still there when bi-amping.

Or you could do as you are suggesting and allow a little bit of overlap knowing that the internal crossover will handle the crossover region.

The absolute best is an active crossover, multiple amps, and then no passive crossovers at all. Have faith in the active crossover, they are very exact in their function.

By the way, typical crossover frequencies are 60-80 Hz(sub to bass driver), 400 Hz(bass to midrange), 2-4 KHz (mid to tweeter).

wizzy

Thanks!

pbullblue

I don't have a ohm meter, maybe I should get one.
Shin that makes a lot of sense, I was thinking differently and assumed the wrong thing. It might now be time to buy another amplifier.

thanks for the answers
Bradley

ShinAce

Even a digital ohmmeter from your local electronics shop will do the trick. Expect to pay $ 40 for a digital one that can even read frequency and small capacitance. They just keep getting better and better.

No need to go with a Fluke on this one.

jakelm

ShinAce wrote: »

.

No need to go with a Fluke on this one.

My father gave me his about 10 years ago, havent used it yet.

ShinAce

I don't think that model checks frequency.

By the way, I bought a $ 60 (CAN) meter about 5 years ago that reads capacitance, frequency and even harmonic distortion. It is so great I ended up throwing out my B&K scope I got from a high school shop.

GSRBOB

If its any help, i have the Rti10's and they meter 4ohms with the jumpers.