What type of load is the AR10Pi ?

[DavidR]

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.

[Pete B]

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.

[JKent]

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"

[DavidR]

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.

[JKent]

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

[DavidR]

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.

[DavidR]

Found this article>>>  https://www.proaudioland.com/news/difference-resistive-reactive-loads/

The bass these put out is incredible.

[Stimpy]

41 minutes ago, DavidR said:

The bass these put out is incredible.

I take it that both crossovers are now complete?  

[DavidR]

Yes

[AR surround]

All AC circuits containing inductors (a.k.a. coils or chokes) are reactive loads.    See the following:

https://www.electronics-tutorials.ws/inductor/ac-inductors.html

So it is a bit confusing as to why Bob Latino would ask if the 10pi was a resistive or reactive load.

[DavidR]

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

Thanks for the link.

[frankmarsi]

This might be helpful:

http://sanderssoundsystems.com/technical-white-papers/52-esl-amp-white-paper

[DavidR]

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

[frankmarsi]

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.

 

[genek]

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.

[frankmarsi]

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

[DavidR]

thank you Gene

[THD+N]

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.

 

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.

 

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

[DavidR]

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!