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DavidR

What type of load is the AR10Pi ?

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What type of load does the AR10Pi present to an amplifier? Is it considered a reactive or a resistive load?

I'm thinking it's a reactive  load due the the autoformer.

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Do we have input impedance measurements for all the old AR systems?

10Pi,  11, 5, 2ax, etc.

I have the AR3a but I think that it is for the early version only not the later.

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23 hours ago, DavidR said:

What type of load does the AR10Pi present to an amplifier?

Is this what you're looking for? http://www.classicspeakerpages.net/library/acoustic_research/add_series_1975-1978/add_series_brochures/ar-10pi_brochure/ar-10pi_brochure_pg4.html#previous-photo

It says "4 to 16 ohms nominal, depending on switch position"

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I knew that. So it's just a resistive load to an amp? If that's the case I'll have no issues using my tube amp BUT if the autoformer makes it a reactive load that could cause issues.

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Oh--sorry. Should have realized your question was more complex. 

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I was speaking to the guy who builds the amps for Bob Latino and was asking if he thought it would drive the 10Pi. He asked if it was a resistive or a reactive load. To be honest I don't know what a reactive load would be in a speaker, thus my thread.

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It was Bob's builder and he suggested I confer with Bob about driving the 10Pi speakers.

Thanks for the link.

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Not related to my original question but at what point did AR begin using ferrofluid in tweeters?

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I felt it was useful information on a few different levels and I spent the time searching for it as common courtesy but, so what, the culture has changed, rite?

AFAIK common AR knowledge says that AR included ferro-fluid  with their AR-9 and no doubt also with the AR-11 and 10Pi in the new series.

I run AR-LST's with an even bigger transformer in the X-over along with nine multiple drivers in each cabinet and never experienced any grief because of it while using transistors. Tubes may not be that different.  I don't recall ever hearing folks complaining of difficulties as many folks were still using tubes when the AR-11 variant was released.

 I believe if you're using a fuse as you should, a blown fuse or 'open' would create problems for tubes.

A good web-search with time will probably offer more info to you.

 

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A transformer is just two or more cleverly arranged inductors.

Even without a transformer, speaker crossovers contain capacitors and inductors, which are reactive components.

Driver voice coils have inductance.

The only truly resistive load is a bunch of resistors.

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Thanks for the clarification gene.

I sort of knew the answer but, it's not good to answer a question when one is not fully sure of the answer.

I'm sure DavidR will work it out.

FM

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I think the question should have been; Does the 10pi have a (fairly) constant impedance? The auto-former will more than likely introduce a huge impedance swing into the impedance curve somewhere. The only way to know is to measure it. My Klipsch La Scala's use an auto-former and the factory crossover had a large impedance swing. I rebuilt them into ALK clones.

The impedance plot below is from an OLA with news caps (and incorrect surround. Notice the high Fs = 52Hz). The impedance peak at 600Hz is not a problem for any solid state amp. However, a vacuum tube based amp prefers a constant impedance for best performance (especially SET Class A amps, with no global feedback).

The peak at resonance can be tamed as well, but it will require a huge inductor . The peak at resonance is not really an issue (a compromise) as long as the rest frequency range is fairly flat.

image.thumb.png.0f85c67f84a8f466a22ac0d50600a9bd.png

 

The below impedance plot (DATS2 software) is from the same woofer (with correct surround; Fs = 39Hz) with a series notch filter. I have several SET Class A amps and they sound better with speakers that have a near constant impedance.

image.thumb.png.a54d0654c05649de2bdfd12f5e449ea2.png

 

If you tinker with speakers even for one project, the DATS2 software from Parts Express is worth every penny.

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Thanks for the great input but its not an issue. The amp drives it just fine and I leave the switches in the 4 ohm position (0 dB or 4 pi) as my tube amp is wired internally for a 4 ohm load. They sound fantastic!

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