Impedance of ported 5jr's

Crashdot
Crashdot Posts: 182
edited May 2011 in Vintage Speakers
Greetings,

I seem to recall that some of the early ported 5jr models were 4 ohm, but wonder if there is some way of determining this based on some specific design feature such as which tweeter is used, etc... I have recently seen some orted 5jr's up for sale with the silver faced SL1000 tweeters, and wonder if these may be 4 or 8 ohm.

Thanks
Post edited by Crashdot on
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  • pitdogg2
    pitdogg2 Posts: 25,450
    edited April 2011
    multi-meter
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  • Crashdot
    Crashdot Posts: 182
    edited April 2011
    It is my understanding that placing a multimeter across the terminals of a speaker is not an accurate means of determining impedance, and that an audio oscillator or other equipment is also required:

    http://www.installer.com/tech/sit.html
    http://www.fixya.com/support/t174447-measure_speaker_impedance
    http://www.audiokarma.org/forums/showthread.php?t=100951

    I tried to test two sets of speakers that I have that are known to be 4ohm and 8ohm, but they both read as 4ohm resistance using a multimeter.

    In addition, I am asking this question in advance of buying speakers that are 100's of miles away, so I can't test them. I was hoping that there might be manufacturing cues to look for.

    Thanks
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  • dorokusai
    dorokusai Posts: 25,577
    edited April 2011
    It isn't reliable but why does it really matter? It's one woofer and a tweeter, both of which have decent efficiency at either ohm rating. Neither would tax or overload a power source to boot.
    CTC BBQ Amplifier, Sonic Frontiers Line3 Pre-Amplifier and Wadia 581 SACD player. Speakers? Always changing but for now, Mission Argonauts I picked up for $50 bucks, mint.
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  • Crashdot
    Crashdot Posts: 182
    edited April 2011
    My amplifier cannot safely handle 4 ohm speakers, so I am trying to stick with 8 ohm models, but don't know how to tell the difference between the ones that are up for sale. Thanks
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  • dorokusai
    dorokusai Posts: 25,577
    edited April 2011
    Honestly, I wouldn't worry about the impedence for that loudspeaker.
    CTC BBQ Amplifier, Sonic Frontiers Line3 Pre-Amplifier and Wadia 581 SACD player. Speakers? Always changing but for now, Mission Argonauts I picked up for $50 bucks, mint.
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  • Joe08867
    Joe08867 Posts: 3,919
    edited April 2011
    I am about 95% sure they are 4ohm speakers but like Doro said they should be fine for your amp.
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  • skrol
    skrol Posts: 3,378
    edited April 2011
    Here are the specs. for the ported Monitor 5Jr.

    Monitor 5 Jr
    1984 – 1985 $260

    Midrange 1 - 6-1/2" Diameter (16.51cm) drivers MW6502
    Tweeter 1 - 1" Diameter (2.54cm) Polk SL2000 silver coil dome tweeter

    Overall Frequency Response 30Hz - 26kHz
    Crossover Frequency 3000Hz
    Nominal Impedance 4 ohms
    Recommended Amplifier Power 10-100 w/channel
    Efficiency 92 dB
    Max Output Level 114 dB

    Dimensions Cabinet Size 17" H x 9" W x 8.875" D
    Weight 45. lbs./ pair
    Stan

    Main 2ch:
    Polk LSi15 (DB840 upgrade), Parasound: P/LD-1100, HCA-1000A; Denon: DVD-2910, DRM-800A; Benchmark DAC1, Monster HTS3600-MKII, Grado SR-225i; Technics SL-J2, Parasound PPH-100.

    HT:
    Marantz SR7010, Polk: RTA11TL (RDO198-1, XO and Damping Upgrades), S4, CS250, PSW110 , Marantz UD5005, Pioneer PL-530, Panasonic TC-P42S60

    Other stuff:
    Denon: DRA-835R, AVR-888, DCD-660, DRM-700A, DRR-780; Polk: S8, Monitor 5A, 5B, TSi100, RM7, PSW10 (DXi104 upgrade); Pioneer: CT-6R; Onkyo CP-1046F; Ortofon OM5E, Marantz: PM5004, CD5004, CDR-615; Parasound C/PT-600, HCA-800ii, Sony CDP-650ESD, Technics SA 5070, B&W DM601
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  • Crashdot
    Crashdot Posts: 182
    edited April 2011
    Hmmm... I didn't know there was an SL2000 model that was 4 ohm. This may explain why my mother's amplifier is always 200 degrees. Any idea if the impedance changed at a certain point? Thanks for the specs!
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  • nadams
    nadams Posts: 5,877
    edited April 2011
    I ran my 5jr's on an old Pioneer SX-450 receiver, and also a newer JVC receiver. Both were rated 8ohm, and neither gave me any problems.

    Rock on...
    Ludicrous gibs!
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  • Joe08867
    Joe08867 Posts: 3,919
    edited April 2011
    Crashdot wrote: »
    Hmmm... I didn't know there was an SL2000 model that was 4 ohm. This may explain why my mother's amplifier is always 200 degrees. Any idea if the impedance changed at a certain point? Thanks for the specs!

    Your mom's amp was hot cause you were running it to loud all the time. Moderation is key with Receivers.

    I think all Monitor 5's are 4ohms.
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  • pmlewis
    pmlewis Posts: 100
    edited April 2011
    I've got a pair of the 5JRs with the SL1000 and have never had a problem running them of a receiver. I have used an old Pioneer, Marantz and a NAD and did not have any issues. IMHO they sounded much better than a pair of Monitor 5 II that I sold. FWIW I also ditched the pioneer and kept the NAD and Marantz.
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  • Crashdot
    Crashdot Posts: 182
    edited April 2011
    Joe08867 wrote: »
    Your mom's amp was hot cause you were running it to loud all the time. Moderation is key with Receivers.

    I think all Monitor 5's are 4ohms.
    Ha! No, I'm pretty sure that she doesn't run her speakers too loud under any circumstance, but I have noticed the amp running quite hot at low volume. She is running four 5jr's so perhaps the way the amp is wired the load is presenting as 2ohm. If all 5jr's are 4ohm, that helps a great deal to know.
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  • Crashdot
    Crashdot Posts: 182
    edited April 2011
    pmlewis wrote: »
    I've got a pair of the 5JRs with the SL1000 and have never had a problem running them of a receiver. I have used an old Pioneer, Marantz and a NAD and did not have any issues. IMHO they sounded much better than a pair of Monitor 5 II that I sold. FWIW I also ditched the pioneer and kept the NAD and Marantz.
    I am currently running a Denon AVR-4306, but am concerned that I will start to trigger its protect circuitry and/or stress the amplifier, as Denon says this is likely with 4ohm speakers. My intention is to run RTA-12C as front speakers, and 5jr's as center and surrounds. I got an impedence matching unit to run the RTA-12C's as 8ohm, but if all the 5jr's are also 4ohm, I may have to look into a newer amp such as the AVR-4311CI that has official support for 4ohm speakers.

    Thanks
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  • Crashdot
    Crashdot Posts: 182
    edited May 2011
    Okay, I got my answer today.

    I've been tripping the protection circuit on my amp when using the RTA 12C speakers, and resigned to the fact that I would have to get a different amp to run those. I switched to the Monitor 5jrs and tested for a little while, and tripped the protection circuit with those too. I then switched to the 8ohm speakers, turned up the volume, and didn't have any issues.

    Cheers
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  • kappclark
    kappclark Posts: 136
    edited May 2011
    pmlewis wrote: »
    I've got a pair of the 5JRs with the SL1000 and have never had a problem running them of a receiver. I have used an old Pioneer, Marantz and a NAD and did not have any issues. IMHO they sounded much better than a pair of Monitor 5 II that I sold. FWIW I also ditched the pioneer and kept the NAD and Marantz.

    Had a pair of 5jr's using a NAD 3150 .. never a plm
    *************************
    ** Bill Clark Windham, VT **
    *************************
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  • Crashdot
    Crashdot Posts: 182
    edited May 2011
    I don't know what to say except the Denon is a $2000 (originally) 130w/channel AV receiver, which has been great aside from being overloaded by the draw of 4ohm speakers. I am now in search of a replacement. From what I have read NAD models are 4 ohm stable, although I could not find any Marantz that support lower than 6 ohm.
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  • heiney9
    heiney9 Posts: 25,165
    edited May 2011
    Joe08867 wrote: »

    I think all Monitor 5's are 4ohms.

    Later Monitor series were 8 ohm nominal, IIRC. It is possible to have one model 5B 4 ohm and one 8 ohm depending on year of manufacture or it's a typo in the literature.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass Pass Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
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  • dorokusai
    dorokusai Posts: 25,577
    edited May 2011
    I'm not sure why you experienced the level of problems that you did Crashdot as I've run many 4ohm loudspeakers on less than rated gear....BUT, it's the exception not the rule. Good luck.
    CTC BBQ Amplifier, Sonic Frontiers Line3 Pre-Amplifier and Wadia 581 SACD player. Speakers? Always changing but for now, Mission Argonauts I picked up for $50 bucks, mint.
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  • skrol
    skrol Posts: 3,378
    edited May 2011
    I have found that there were changes to the 5B over the years. I just picked up a set from 1984 which have fuses on the tweeters and are rated 4 ohm. Later years of the 5B had poly-switches and were 6 ohm. The advertised frequency response and sensitivity also changed.


    Monitor 5B spec. Later year specs are in ( )
    Subwoofer 1 - 8" Diameter fluid coupled subwoofer (sub bass radiator)
    Midrange 1 - 6-1/2" Diameter (16.51cm) drivers
    MW6502
    Tweeter 1 - 1" Diameter (2.54cm)
    Polk SL2000 silver coil dome tweeter

    Overall Frequency Response 28Hz - 26kHz (30Hz – 26KHz)
    -3 dB Limits (43Hz – 20KHz)
    Crossover Frequency 60Hz and 3000Hz
    Nominal Impedance 4 ohms (6 ohms)
    Recommended Amplifier Power 10-125 w/channel
    Efficiency 91 dB (90 dB)
    Max Output Level 116 dB

    Dimensions Cabinet Size 21.5" H x 10.5" W x 8.5" D
    Weight 29. lbs.
    Stan

    Main 2ch:
    Polk LSi15 (DB840 upgrade), Parasound: P/LD-1100, HCA-1000A; Denon: DVD-2910, DRM-800A; Benchmark DAC1, Monster HTS3600-MKII, Grado SR-225i; Technics SL-J2, Parasound PPH-100.

    HT:
    Marantz SR7010, Polk: RTA11TL (RDO198-1, XO and Damping Upgrades), S4, CS250, PSW110 , Marantz UD5005, Pioneer PL-530, Panasonic TC-P42S60

    Other stuff:
    Denon: DRA-835R, AVR-888, DCD-660, DRM-700A, DRR-780; Polk: S8, Monitor 5A, 5B, TSi100, RM7, PSW10 (DXi104 upgrade); Pioneer: CT-6R; Onkyo CP-1046F; Ortofon OM5E, Marantz: PM5004, CD5004, CDR-615; Parasound C/PT-600, HCA-800ii, Sony CDP-650ESD, Technics SA 5070, B&W DM601
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  • dorokusai
    dorokusai Posts: 25,577
    edited May 2011
    Agreed Skrol, as I have 3 different charts for the Monitor5.
    CTC BBQ Amplifier, Sonic Frontiers Line3 Pre-Amplifier and Wadia 581 SACD player. Speakers? Always changing but for now, Mission Argonauts I picked up for $50 bucks, mint.
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