Got Acoustic Research AR6 - honky nasal tone?

Discussion in 'Speakers' started by duckrabbit, Jun 7, 2018.

  1. duckrabbit

    duckrabbit New Member

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    Could anyone with experiece with the AR family of speakes give me advice please?

    Got these for testing from a local secondhand hifi dealer. So far I've only had modern speakers (mostly studio monitors, Adams, Genelecs, Neumanns). For my hifi I have Usher S-520 and also currently have the Quad 12L for testing (they are actually worse than the Ushers in my setup).

    I like many aspects of the AR6, the tightness, snap and grip, light flow. They are nicely revealing and very musical. But there is one thing that really bothers me: the mids (piano, horns etc) do not sound natural but nasal and honky. At least compared to all those other speakers that I've had. This honkiness worsens when turning down the treble pot on the rear of the speaker. Both speakers have the same tone.

    The AR6s seem to be in a pretty good shape. The woofer foam seems to have been replaced recently.

    Is this' nasal' tone normal, do I just need to get accustomed to the "70s" sound? Or does it seem like there is something wrong with the speakers, bad caps maybe?

    I really want to like them. The basic character is great. So I'm wondering if I should buy another pair of ARs in better shape, keep and try to refurbish the ones I have now, or just accept that this nasality/honkiness is part of their character and get used to them or try something else.

    Thanks.
     

     

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  2. RxDx

    RxDx Speaker collector Subscriber

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    First thing I'd check is the caps. If they're original, they probably need replacement.
    Then evaluate the sound.
     
  3. duckrabbit

    duckrabbit New Member

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    That's what I thought but people seem to like the AR series in their original state (at most refoamed). I'm still thinking whether it's just my ears or is the pair of AR6s I have really so much out of spec. Anyone who has compared the ARs with modern speakers care to share their experience?
     
  4. R Swerdlow

    R Swerdlow Active Member

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    Mid range that sounds 'nasal and honky' is the classic description of a speaker that suffers from baffle step loss. It varies with the type of music, but is most noticeable with piano, horns, and human voice. Speakers with narrower cabinets seem to suffer from this mid range overemphasis while lacking bass. They require a baffle step compensation (BSC) circuit in the crossover to correct for it. BSC circuits do the job, but it often comes at the expense of lower speaker sensitivity.

    Read more about baffle step loss (also known as diffraction loss) and BSC here:
    http://www.salksound.com/wp/?p=42
    https://www.trueaudio.com/st_diff1.htm
    https://app.box.com/s/f2jt7sjokm
    http://www.quarter-wave.com/General/BSC_Sizing.pdf
    It's been a number of years since I heard AR6s, but I do remember hearing the same sound as you described. That's probably how they sounded when they were new. Bad crossover design, not bad caps.
    Don't keep them. If you do keep them, design and build new crossovers that include adequate BSC. Find someone capable of DIY crossover design who understands BSC.
     
    Last edited: Jun 7, 2018
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  5. WaynerN

    WaynerN AK Subscriber Subscriber

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    If they have the brown "cigarette size" Chicago capacitor, it has huge odds of being way out of tolerance. My 20uf in my AR-4X actually measured 36uf. (Yes, sometimes caps will change with the value going up...........which means the cross-over point lowered. Replace cap. (I am not a cap replace automatically advocate, but those style caps have a history.....
     
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  6. R Swerdlow

    R Swerdlow Active Member

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    Coming from you, I'd agree about that cap. But replacing an out of spec cap with a proper one will not address the baffle step loss problem.

    I found one more good explanation of baffle step loss and how to compensate
    http://www.quarter-wave.com/General/BSC_Sizing.pdf
     

     

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  7. ra.ra

    ra.ra Super Member

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    The AR-6 is a terrific vintage bookshelf speaker with great proportions and excellent drivers. During its production run, it employed at least two versions of woofer, two versions of tweeter, and three versions of crossover. I am not familiar with the BSC concept advocated by RSwerd (but will read up) but it is possible that cap replacement is in order per Wayner's note. Some of the original caps I've encountered in AR-6's, however, did not require further attention. If you have any pics to describe your version, please upload. (Actually, if you have variable pots, you most likely have the earliest version with serial numbers 35XXX or lower.)
     
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  8. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

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    If the woofers were refoamed that means someone was potentially inside them. They could have changed caps or even altered the crossovers. Or just hooked up the woofers in opposite polarity to the original design, creating a peak at the woofer-mid crossover point instead of a dip. I'd check out everything and make sure they are actually put together correctly.
     
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  9. R Swerdlow

    R Swerdlow Active Member

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    I found a good illustration of the frequency response curve with and without baffle step compensation. See this page http://speakerdesignworks.com/speakerbuilder.html

    The example is a 2-way speaker with a 17 cm (6½") aluminum woofer in a 9" wide cabinet. The crossover frequency to the 1" dome tweeter is 2350 Hz.
    [​IMG]

    The blue trace is the frequency response of the woofer, mounted in the cabinet, without any crossover or BSC. Notice the bumped up response that begins about 400 Hz and continues to above 1000 Hz. That's what baffle step looks like. It's what causes that 'nasal and honky' sound. See how the bass below 400 Hz drops off in a big way.

    The other traces (pink, green and black) show the frequency response of the woofer with BSC. That 400-1000 Hz bump is flattened to the same level as bass below. It also results in lower overall sensitivity.

    All this takes place well below the crossover frequency of 2350 Hz. So fixing an out-of-spec cap in the crossover will not affect sound in the 400-1000 Hz range.
     
    Last edited: Jun 7, 2018
  10. slimecity

    slimecity Super Member

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    Interesting as that sound characteristic you describe can also be found sometimes in badly designed speakers featuring a "quacky" poly mid/woofer. Although you have a paper cone driver in this case
     
    Last edited: Jun 7, 2018
  11. R Swerdlow

    R Swerdlow Active Member

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    Any woofer with paper, plastic, metal, or other cones can do this. It is more noticeable with woofers 5 to 7 inches (15 to 18 cm) in diameter in narrow cabinets. The baffle step occurs in the mid range where our ears are more sensitive. With larger woofers in wider cabinets, baffle step still occurs, but at lower frequencies where we don't notice it as much.

    Ignoring baffle step compensation makes for a less expensive crossover – fewer parts. And proper BSC does result in lower sensitivity. Many commercial speaker designs deliberately chose to ignore BSC.

    If I remember correctly, one of the reasons behind the first MTM speaker designs was to compensate for the baffle step with two woofers instead of the reduced sensitivity of a BSC circuit.
     
    Last edited: Jun 7, 2018
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  12. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

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    Excellent info RS, thanks.

    The only comment I would make is that in the example, it's happening below what the crossover frequency SHOULD be. If the cap is doing what it's supposed to. But clearly BSC can be an issue even when the speaker is working like it was designed.
     
  13. duckrabbit

    duckrabbit New Member

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    Thanks a million everyone, very valuable info! RS, I will look into the links you provided.

    Since I know virtually nothing about electronics and unable to recap or do mods, I think I will probably just return these.

    But if anyone can confrirm that the nasality is not part of the ARs character, I will keep looking for another pair (AR2, 4, 5, 6 or 7s). Their basic tone (excluding the nasality) is really superb.

    Here are a couple of pics. They really look gorgeous with that patina.
     

    Attached Files:

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  14. ra.ra

    ra.ra Super Member

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    Now I am even more curious about these speakers. We still do not know if they have original drivers or if there has been any "work" done inside, but I see two interesting things. First, it's not often you see AR-6's with a blonde finish; and second, I've never seen a grille badge with AR-6 spelled out on a square badge. Rectangular badges are the norm.

    Why not carefully remove a grille cover, examine drivers, then remove woofer and take a peek inside?

    AR-6 badge.jpg
     
    Last edited: Jun 8, 2018
  15. imral3

    imral3 Super Member

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    And fix that almost shorted out speaker wiring!!!
     
  16. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

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    Couple of spade lugs and an inexpensive crimper/stripper tool would make you some nice cable ends with no more worries about shorted strands.

    The problem with vintage speakers is they quite often need capacitors and many of them sound less honky after they are replaced. It's actually pretty easy to do, even with a $10 soldering iron.
     

     

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  17. duckrabbit

    duckrabbit New Member

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    Ha, saw that one coming.

    Here in Finland the blonde finish seems to be common (like Finnish blondes).

    Here are pics of the grill removed. This is as far as I go (If you wish to see more, please insert coin).

    IMG-1461.JPG IMG-1462.JPG

    Yeah, I should start learning this at some point but not sure if it's worth it now. These are a fine looking pair though...

    IMG-1460.JPG
     
    Last edited: Jun 8, 2018
  18. R Swerdlow

    R Swerdlow Active Member

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    Even if replacing a capacitor is easy to do, this is misleading. It has clearly been shown that any smaller woofer, new or old, can produce this distorted sound if it’s mounted in a narrow cabinet. The effect can be heard or measured without any crossover network at all.

    The blue trace in the figure below shows a 17 cm woofer’s response when mounted in a 9” wide × 20” tall cabinet. See the raised response between roughly 400 Hz and just over 1000 Hz. There is no crossover at all. How can a capacitor, good or bad, be involved?
    [​IMG]
     
  19. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

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    That comment was based solely on the idea that an old cap that is out of spec can affect the response curve by itself, totally aside from BSC. I went on to say that BSC is clearly also an issue, which I thought was clear enough, but perhaps not. Fixing one issue will not fix the other, or vice versa.
     
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  20. R Swerdlow

    R Swerdlow Active Member

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    Thanks for clarifying that. It makes good sense.

    Maybe it was my tired eyes that misinterpreted what you meant earlier. I was up very late last night, watching the Stanley Cup final game. Washington won 4-3 over Las Vegas. The entire game was fierce & intense – nerve wracking for a Washington fan (me :biggrin:) to watch. Late in the game, the Caps took a 1 point lead and went on to win the game and the series :rockon:. I couldn't go to sleep for hours, and was kind of groggy this morning. I know most people don't much care about hockey, but that's my story and I'm sticking with it.
     
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