AR 9 Impedance

[dahrich]

Hello:

I have a question about the impedance of my AR9's because I want to bi-amp them.

Per the specs: impedance is 4 ohms but I suspect this is with the imput terminals on the back of the cabinet jumpered.

If I remove the jumpers what is the impednce to just the side facing woofers and the impedance to the front facing drivers?

(Since the impedance with the terminals jumpered is 4 ohms I would think the separate impedances are 8 ohms. Yes/No?)

Thanks in advance.

Richard

[rrcrain]

I'm confident someone will jump in with a more detailed reply, but the fast answer is no, it's still 4 ohms with the jumpers removed. The upper terminals will read open because theres a few caps in series that block DC but the effective impedance of the circuit remains 4 ohms.

[soundminded]

I tried this before but my computer crashed in the middle. Do you think it was trying to tell me something? You would do well to print out the schematic diagram of the crossover network in the library.

http://www.classicspeakerpages.net/ar/ar-9...20Schematic.bmp

For some reason, I could not print out the Word version or open the TIF version but they will be the same as the bmp version.

There are 5 drivers and four filter circuits. You can see the two woofers in the lower right are wired in parallel to the same filter circuit. More about that later. The jumpers on the back of your speaker connect the corresponding red and black terminals in the lower left part of the drawing allowing you to power the entire system with one amplifier or two. Normally in a drawing of this type the jumpers would be shown in dotted lines with a note to that effect but it is understood implicitly that this the user's decision. Each of the three drivers in the "upper range" has its own filter circut in series with it. The three filter circuits with their respective drivers are wired in parallel. Each filter circuit is arranged so that its impedence is very low over the frequency range of its own driver and very high outside that range. Their purpose is to allow current to flow only at the appropriate frequencies to each driver. For example, the tweeter filter circit is near zero above 7 khz so the impedence is the impedence of the tweeter in that frequency range, around 4 ohms. Below that range it is very high so little midrange and low frequency current will flow to the tweeter. If you adjust the program switch for the tweeter to -3db or -6db, it will put an additional resistor in series with the circuit increasing the impedence in that frequency range. This arrangement allows the speaker system to have an impedence no lower than about 4 ohms at any frequency. At any one frequency, the impedence is 4 ohms for the driver intended to operate in that range and high for the circuits in parallel operating the drivers in different ranges. Therefore the overall system impedence remain at about 4 ohms or higher. This is safe for a high quality amplifier but not necessarily for some such as HT receivers which state specifically that their connected load must be at least 8 ohms.

The woofers use a clever filter circuit. Although each driver is nominally 4 ohms, it is much higher at its resonance frequency. With two such drivers in parallel, you would expect the impedence to be well above 4 ohms at resonance but down to 2 ohms or less at other frequencies. But this is altered by the arrangement of inductors and capacitors which increase the series impedence above and below the system bass resonance of 28 hz so that the combined impedence never goes much below 4 ohms at any frequency. This protects the amplifier and flattens the frequency response of the woofers at the same time. It is important to understand that the circuit is carefully tuned for the speakers when they are properly mounted and operating in their enclosure as installed by the factory. This means that the amount of air trapped in the enclosure and the arrangement of fiberglass inside results in the correct air springiness and aerodynamic drag for the speakers to work against. If this is altered such as by not having the enclosure air tight, the system resonance frequency will change and the impedence could go below 4 ohms at some frequencies risking damage to the amplifier depending on how well protected and how well designed it is. Some solid state amplifiers may be particularly vulnerable so be careful. Because there will be no air to work against, the woofers could bottom out as well causing damage to the voice coils so it is important to be careful with them when operating them disassembled or if there is an obvious air leak.

We've had this disussion before but I'm afraid some participants didn't seem to understand it. I hope this explanation helps clear it up for them.

[ar_pro]

It's 4 ohms for each section, with the jumpers removed.

What amplifiers are you planning to use?

[dahrich]

Hello Soundminded and ar pro:

Sorry to be so late in responding but I was gone for a couple of weeks.

I have copy of the schemtic but not savy enought to interpret it.

Thank you for you excellent explanation.

I will be using Adcom GFA 5500 or Adcom GFA 545 amps with the Sony STR DA7100ES as preamp.

I have been bi-amping the AR9's using the A + B speaker connections on the 7100 but this cuts the power to the speakers in half and I will explore a separate amp to the wooofers or the other three drivers.

Thanks again,

Richard

[dahrich]

soundminded:

Hello:

I have been thinking some more about the AR's impedance.

So, I have another question.

If the impendance is 4 ohms for each section does that mean that when the terminals are jumpered the total impedance is 8 ohms since the sections are in parallel?

Or, it's still only 4 ohms because of the unique design of the netwoorks?

Regards,

Richard

[soundminded]

>soundminded:

>Hello:

>I have been thinking some more about the AR's impedance.

>

>So, I have another question.

>

>If the impendance is 4 ohms for each section does that mean

>that when the terminals are jumpered the total impedance is 8

>ohms since the sections are in parallel?

>

>Or, it's still only 4 ohms because of the unique design of the

>netwoorks?

>

>Regards,

>Richard

Richard;

First some basic electrical concepts. When two identical impedences are wired in parallel, the net result the amplifier sees is half the impedence of each one, not twice. Two identical 4 ohm full range speakers in parallel would present an amplifier with a 2 ohm load, not an 8 ohm load. If they are not identical or if there are more than two of them, the actuall equation is 1/Zequiv = 1/Z1 + 1/Z2 +....+1/Zn where Z equiv is the equivalent impedence an external circuit would see in total and Z1, Z2, ...Zn are the individual impedences. Wired in series (end to end in a string) Zequiv = Z1 + Z2 + .....Zn.

But the top and bottom section of the AR9 are not identical impedences at all and this is deliberately so. What I tried to say above and will try again is that below 200 hz, Z of the lower section is 4 ohms and of the upper section is very high (1/Z for the upper section above 200 hz is therefore nearly zero. Therefore 1/Zequiv = 1/4) Above 200 hz, the situation is reversed and the Z of the lower section is very high while the Z of the upper section is about 4 ohms. And this holds true in the same sense from one driver in the upper section to the next. This is the intended function of the crossover network. So at any frequency, the amplifier sees about a 4 ohm load. This is safe for amplifiers designed to handle a 4 ohm load and it is safe for the speakers restricting electrical signals going to each driver to only those frequencies it is designed to handle.

[dahrich]

soundminded:

I was aware of the parallel equation - just can't add fractions in my mind any more it seems.

Thanks for taking the time to explain again.

Regards,

Richard

[dahrich]

soundminded:

Ok, now that I am starting to understand it gives rise to some more questions.

Here is the situation:

A/V receiver has A and B speaker outputs. Either A or B or A + B can be selected. As I understand it when A + B are selected the power to each output is cut in half.

So, if I bi-amp the speakers using A + B each network sees 1/2 the power? Or does it since the power going to each section will depend on the frequency of the signal at the time?

In other words, If A is connected to the high freq drivers and B to the woofers and a signal of say, 100 Hz is generated, it goes to both A + B but no power is sent to A because its load is very high and full power then goes to the woofers.

If what I just said is true than I think there is not reason to bi-amp the speakers using A + B. I might just as well jumper the speaker input terminals and select either A or B to drive the speakers.

I hope all this is clear.

regards,

richard

[soundminded]

Richard;

If you connect the upper and lower sections separately to the A and B speaker outputs of your amplifier, you will not be biamplifying them, you will be bi-wiring them. You still will have only one power amplifier per channel, the only difference this will make is that you will be connecting the upper and lower sections together in parallel at the amplifier instead of at the back of the speakers and of course you will use twice as much wire. In other words, nothing will change.

I think in some receivers, perhaps many(????) when you seclect A+B speaker outputs this puts a low value resistor in series with each speaker so that the total impedence the amplifier sees can't go too low. This is done to avoid possible damage to the amplifier output circuit. This is not desirable for sound quality because it not only wastes power but will lower the electrical damping (control) the amplifier has over the woofers. It may also slightly change the balance between the loudness of the subwoofers and the upper section but if so, usually by a very small degree. I can make a theoretical case for bi-wiring but not the one the advocates of it usually make and frankly, I am very skeptical about it. True biamplification will require another stereo amplifier and the ability to control the relative gain (loudness) of one compared to the other. This means that at least one of the power amplifiers must have its own volume control. It also requires a separate preamplifier or a receiver with a removable jumper between the preamp output and power amp input which allows the receiver's volume control to simultaneously control the loudness of both stereo amplifiers. In some cases this may have advantages but if you are using a high quality amplifier or receiver of sufficient power, even this may be of little or no value improving the performance of your AR9s. I use a high quality 60 watt per channel power amplifier I built from a kit and it will make my AR9s play very loud without distortion over their entire range including window rattling floor shaking bass. My room is approximately 4000 cubic feet, about 30 x 14 x 9.5 and is slightly on the live side, sheet rock, lots of windows, low pile burber carpet.

[dahrich]

soundminded.

Your comments have been very helpful to me understanding my system.

FYI, I have been using a Sony STR DA2ES receiver with a Adcom preamp and two Adcom power amps bi-amping the AR9's.

I recently bought a Sony STR DA7100ES receiver rated 170 wpc and disconnected the Adcom separates.

Experimenting with and without the Adcoms let me to feel that using the 7100ES alone was superior. However, I wasn't sure if I was getting the best performance using only the A speaker output, hence, all the questions.

I understand your coment about bi-wiring.

Interestingly your room is similar in size to mine which is 25' x 14' x 9' with berber carpet and cloth reclining chairs but I don't have a lot of windows.

This room is also a home theater room but I have added some acoustic treatment which helps it being a music room too.

I'm curious as to where your speakers are located. Mine are about 6' from the front wall and 2' in from each side wall.

I originally had the speakers up against the front wall but moving them to this location made a tremendous difference.

regards,

Richard

[rrcrain]

The AR9 and AR90 are intended to be wall loaded, meaning for idea bass response, their back should be placed no more than a few inches from the wall. I'm thinking its 4 inches but don't remember the factor recommended distance. Concerning side clearance, both sides shoud have no less than one foot of clearance, possibly three for ideal bass since both sides contain an active bass driver. A few inches in or out from the wall can make for quite a change in bass response depending on other room variables but it depends on other room acoustic variables to determine the extent and type of change you will experience.

I've had mine in a very lively room (large finished basement, drywall, low suspended ceiling and berber carpet) and the bass was over bearing. Spiking the cabinets to the cement floor was a massive benefit. They are now in a different home in the living room with paneling, vaulted knotty pine wood ceiling, standard carpet and the room sucks the bass out of the speakers.

I absolutely agree with Soundmided on the bi-wiring. The math says it might do something, but experience says it doesn't. If it did, I didn't hear it and if I can't hear it, it isn't worth the time or money.

[soundminded]

I agree, the manufacturer's recommendations are IMO best and they suggest that the speaker be no more than 2" from the wall behind them or there will be a significant loss of bass. Mine are on the short wall about two feet from the side walls. I've found that moving them left or right just a few inches can also make a big difference. I have equalized mine using a ten band equalizer and the program level switches and added (3) 3/8" indirect polys firing upward towards the ceiling to each channel. In this configuration, they are the most accurate speakers I've ever heard. I use them both alone and in conjunction with a special surround system I invented myself. BTW, used placed in this manner I would be hard pressed to name even one other speaker system which can surpass or even come close to equalling it in bass response. I recommend to anyone who owns these speakers to read Tim Holl's excellent technical writeup of them in the library on this site. Moving speakers away from the walls is intended to reduce reflections from the walls to improve "imaging" but at a huge cost in bass reinforcement.

As for bi-wiring, the usual argument among audiophiles is that each pair of wires should be optimal for the frequency bands covered by the connected drives and that this somehow reduces some sort of imagined intermodulation distortion. This IMO is pure rubbish, the ordinary zip cord type speaker wires are more than adequate to cover the entire audio band without perceptable loss at the power levels involved. But a better case could be made for putting the resistance of each set of wires between the respective drivers and the amplifier. In this way, the amplfier's damping factor will be more effective in surpressing back emf from the woofers before they reach the midrange and tweeters. However, in the real world, that emf at frequencies of interest to the upper range drivers is minimal, is well surpressed anyway but the amplifier, and is filtered out by both the woofer's series inductors and the midrange/tweeter's series capacitors. In the real world, it's hard to make a case for the trouble and expense of it. The only real test is to bi-wire them and then A/B the configuration with a jumper at the back of the speakers to see if there is any difference. This would be most effective if it is performed by a pair of relays to facillitate the comparison.

[Guest Bret]

>Moving speakers away from the walls is intended to reduce reflections from the walls to improve "imaging" but at a huge cost in bass reinforcement.<

Would you happen to have any idea how tall the wall must be directly behind the speaker?

There's a physics problem in there somewhere. 1/4 length of the lowest frequency reproduced, or is it okay for the wall to be only as tall as the top of the driver?

Anybody? Ken? Anyone?

Bret

[dahrich]

Hi:

I didn't mean to start a Q & A on speaker placement but When I relocated my speakers about 6' from my front wall I got a tremendous improvement in the sound.

I did this after reading the following article:

http://www.cardas.com/content.php?area=ins...ring=Room+Setup

Thanks to all of you who have commented on my original question. It has been very enlighting for me.

Regards,

Richard

[rrcrain]

Personally, I believe speaker placement of an AR9 is well within context of this forum.

At the end of the day, regardless of anyone elses opinion or the manufacturers recommendations, the best place is where the owner believes they sound best to them. Sharing opinions openly without prejudice or malace(sp) is, as far as I'm concerned, always welcome.

I took a fast look at the web page you linked to, and at first blush, it appears to be addressing front firing speakers only. Speakers with side firing or read firing bass drivers are a different animal.

[soundminded]

I also looked at the site and intend to try this placement scheme although I don't look forward to moving a pair of 125 pound speakers around. It seems to me this idea has the common audiophile goal of achieveing a kind of pinpoint imaging where each instrument is localized to a very specific point. And it only works if you sit exactly where you are supposed to, the so called sweet spot. This was not the philosophy of AR during its heyday, is not typical of the way live performances sound either, and it's not typical of the way most musical instruments generate sound and therefore how it reaches our ears. Even in small rooms, there are many reflections of most of the sound between the time it leaves the instrument and the time it reaches the listener. A careful look at most musical instruments and the way they are played shows why. A piano propagates virtually all of its sound indirectly. Spinnets and uprights completely so and for a grand piano the closest you can get to direct sound is for some of it to bounce off the lid once when it is propped open, even so it is a very broad source. All reed and brass instruments with a bell are almost always played pointed away from the listener, usually nearly vertically down at the floor so that their sound is all reflected. That photo of Al Hirt with his trumpet held horizontally made a good album cover but it is not the way the instrument is played. The player's arms would get tired very quickly if it were. (brief fanfares played on ancient horn instruments to announce the arrival of the king were though. If you sat where a trumpet were pointed straight at you, you'd hear quite a blare.) String instruments are more complicated sending out sound in both cylindrical waves from the strings themselves and in very complex multi-directional patterns from the f holes and the body of the instrument. About the only exception is a human voice which directs most of its energy straight forward but even here, unlike loudspeakers, fundimentals and the harmonics have pretty much the same propagational directivity while loudspeakers become incrasingly directional with frequency. What difference does this make to the perception of music? Arriving over a much broader range of angles and where spectral balance is uniform with direction of arrival and time, real instruments sound larger and have a different timbral character from sound coming from loudspeakers. When you combine this with the fact that most there is a wide range of differences between spectral balance from one recording to the next even on cds so that if a sound system were timbrally accurate with one recording it wouldn't be with another unless the system were re-equalized I think in large measure explains why most loudspeakers never sound like real musical instruments.

[Carlspeak]

>Personally, I believe speaker placement of an AR9 is well

>within context of this forum.

>

>At the end of the day, regardless of anyone elses opinion or

>the manufacturers recommendations, the best place is where the

>owner believes they sound best to them. Sharing opinions

>openly without prejudice or malace(sp) is, as far as I'm

>concerned, always welcome.

EVEN THOUGH THE THREADS HERE HAVE WANDERED A BIT FROM THE ORIGINAL QUESTION, I HAVE TO AGREE WITH YOU ON THIS ONE REGARDING SPEAKER PLACEMENT.

THE ATTACHMENT BELOW SHOWS A UNIQUE SPEAKER THAT MUST HAVE SPECTACULAR *SPECTRAL BALANCE*. THE BOSE 901 GONE SPHERICAL :-)))

I WONDER HOW IT WOULD SOUND IN MY LISTENING ROOM - TALK ABOUT REFLECTIONS!

>

>I took a fast look at the web page you linked to, and at first

>blush, it appears to be addressing front firing speakers only.

>Speakers with side firing or read firing bass drivers are a

>different animal.

It's all about the music

Carl

Carl's Custom Loudspeakers

[tysontom]

>Hi:

>I didn't mean to start a Q & A on speaker placement but

>When I relocated my speakers about 6' from my front wall I got

>a tremendous improvement in the sound.

>

>I did this after reading the following article:

>

>http://www.cardas.com/content.php?area=ins...ring=Room+Setup

>

>Thanks to all of you who have commented on my original

>question. It has been very enlighting for me.

>

>Regards,

>Richard

Richard,

That Cardas article really doesn't take into consideration the individual loudspeaker's specific design criteria -- whether or not it was designed to be used out in the floor or back against a wall. I did not read it carefully, but the article appears to discuss methods to suppress standing waves in a typical listening room. Some speakers are designed to work well when radiating bass frequencies into a larger angle; i.e., out in the room. The AR-9 was definitely *not* designed to work this way, and to do so will definitely attenuate its low-frequency performance and smoothness and, to a degree, upset the spectral balance of the speaker.

I remember going to a high-end audio dealer (not an authorized AR dealer) out in Los Angeles back in the late 70s, and in an effort to disparage the excellent performance of the AR-9, the dealer had set up a pair about eight or nine feet from the facing wall while comparing it to to several expensive tower loudspeakers (of lesser reputation). Predictably, the AR-9s did sound thin, and the advantage of powerful bass reproduction was lost in the method of mounting the speaker on the floor. The dealer succeeded in diffusing the AR-9's great advantage and was able to sell his own line of inferior speakers.

However, if you like the sound of them in this position, that is the most important thing. You are probably losing some realism this way, but it may be your preference.

--Tom Tyson

[soundminded]

>>Personally, I believe speaker placement of an AR9 is

>well

>>within context of this forum.

>>

>>At the end of the day, regardless of anyone elses opinion

>or

>>the manufacturers recommendations, the best place is where

>the

>>owner believes they sound best to them. Sharing opinions

>>openly without prejudice or malace(sp) is, as far as I'm

>>concerned, always welcome.

>

>EVEN THOUGH THE THREADS HERE HAVE WANDERED A BIT FROM THE

>ORIGINAL QUESTION, I HAVE TO AGREE WITH YOU ON THIS ONE

>REGARDING SPEAKER PLACEMENT.

>

>THE ATTACHMENT BELOW SHOWS A UNIQUE SPEAKER THAT MUST HAVE

>SPECTACULAR *SPECTRAL BALANCE*. THE BOSE 901 GONE SPHERICAL

>:-)))

>I WONDER HOW IT WOULD SOUND IN MY LISTENING ROOM - TALK ABOUT

>REFLECTIONS!

>

>>

>>I took a fast look at the web page you linked to, and at

>first

>>blush, it appears to be addressing front firing speakers

>only.

>>Speakers with side firing or read firing bass drivers are

>a

>>different animal.

>

>

>It's all about the music

>

>Carl

>Carl's Custom Loudspeakers

I wasn't able to successfully download your attachment for some reason.

I think when you talk about spectral balance and dispersion you are talking about apples and oranges. I think Peter Snell hit the nail on the head when he said words to the effect that it's not what comes out of the speakers that matters but what reaches your ears. In this regard a constant directivity speaker of limited dispersion could have good spectral balance. I think Audax makes a high fidelity 4 way coaxial system of this type now. Constant or controlled directivity speakers are desirable in sound reinforcement systems because they allow for maximum gain before feedback and uniform loudness and response over the largest area with the fewest number of speaker systems. This would probably be of interest to audiophiles today who are more interested in imaging than anything else or so it seems to me. I'm going to go out on a limb and disagree with Tom, I think this article locates speakers and the listener for the best possible imaging although that may not be inconsistent with reducing excitation of room resonances. What seems critical is the ratio of distances which optimize the tradeoff between maximizing the distance between the speakers and minimizing the side wall reflections. By sitting at just the right point you probably are at an angle which is just shy of creating an audible "hole in the middle" a term you rarely ever hear used anymore. This will make the musicians sound as though they are spread out across the widest soundstage and may also maximize the perceived distance between them and you. Of course the penalty is deep bass and for that, most audiophile systems need a subwoofer which is separately amplified and equalized. I'd say the average audiophile speaker today is a 2 way system with a 1" tweeter and an 8" woofer. The woofers are often ported (the port being in the rear where it is not obvious) and the system having a very high Q tuned to the lowest possible frequency. These have to be very robust woofers for their size and are often of equal or greater cost to high quality 12" woofers. The tweeters deliberately have limited dispersion by virtue of both their 1" size (smaller tweeters like 3/4" AR have greater dispersion all other things being equal) and by virtue of their recess which semi horn loads them in much the same way the half torrus around the AR 9 midrange does. Clearly this is very different from AR's philosophy and my own but this is what many audiphiles prefer.

Bose 901 is a speaker I am very familiar with. It's problem is not dispersion, it radiates almost 90% of its energy indirectly, it is spectral balance, ie frequency response. The original is capable of very deep bass BUT, it not only requires enormous amplifier power, it also requires a further deep bass boost to be flat to 30 hz and below that it is capable of. How much more? IMO about another 10 to 15 db making power requirement rediculous for any but small rooms and requiring multiple stacked systems in larger ones. And it also has a 7 to 8 db peak in many rooms at around 250 hz and it has little response above around 10 to 12 khz which combine to make it unacceptable to audiophiles. It took me about 3 years to improve mine to my satisfaction and now I am very pleased with their timbral accuracy. How does it compare to my enhanced AR9s? In many ways surprisingly similar.

[dynaco_dan]

Hi Soundminded;

I enjoy reading what you write when you display your obvious intimacy with numerous music instruments.

I play no instruments, but it is something that I appreciate when you use those instruments for a reference point though.

Thank you.

[dahrich]

Hi:

One last comment on part:

Soundminded stated: 'By sitting at just the right point you probably are at an angle which is just shy of creating an audible "hole in the middle" a term you rarely ever hear used anymore. This will make the musicians sound as though they are spread out across the widest soundstage and may also maximize the perceived distance between them and you. Of course the penalty is deep bass"

I have to say that this is almost exactly what hear which makes me feel the musicians are right in front of me. I think it's great!

I listen to music only in stereo and there probably is a lack of deep base, no subwooder, but for me, that's ok.

Richard

[soundminded]

>Hi Soundminded;

>

>I enjoy reading what you write when you display your obvious

>intimacy with numerous music instruments.

>

>I play no instruments, but it is something that I appreciate

>when you use those instruments for a reference point though.

>

>Thank you.

I strongly urge anyone who is interested in high fidelity sound reproduction to listen to live music at every possible opportunity. What comes out of musical instruments is music. What comes out of a loudspeaker is a facsimile of music as I see it unless you are talking about electronic music in which case the loudspeaker is part of the instrument. Listen to different kinds of instruments and to the same instrument in different places. Try to notice how the place you hear music in affects the sound. If you have a friend who is in an amateur orchestra, ask him if you can sit in on their rehearsals once in awhile and then attend the concert and hear the difference between the same instruments in a rehearsal room and a concert hall at the actual performace. Colleges often have pretty good orchestras. Sometimes listen from outside through an open door. Watch how the musicians play and see if you can visualize how the sound eminates from their instruments and reaches your ears. Go to a church and listen to organ and choral recitals. Hear what a real pipe organ sounds like. It is even better if you take up playing a musical instrument yourself, you will learn a lot more about music and appreciate what you do hear that much more, even if you never play very well. All of this will make you a better and more critical listener and will increase your enjoyment of both live and recorded music considerably.

[Carlspeak]

Here's a .pdf that you may be able to open. I really want you to see this picture.

It's all about the music

Carl

Carl's Custom Loudspeakers