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  1. #1

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    Default will running 4 monitor 70s put a strain on my RR2150 receiver?

    Until such time as I make a decision on what brand surround receiver or receiver/amp combination to purchase eventually, for the time being I have a 2.1 ch receiver (Outlaw RR2150, 100 wpc for 2 speakers or 160 wpc for 4 speakers (A & B)). This is a pretty hefty receiver (28 lbs) and until now I've been using it only to drive 2 monitor 70s plus a powered sub.

    I have just purchased 2 more m70s for a total of 4 (had to get them before they were no longer available new). I intend to run A & B speakers from my receiver using the 4 monitor 70 speakers and also a low-level sub-out jack to my subwoofer, although for the most part even with a sub I don't roll-off the mains except for a little tweak of the bass knob, since I love the upper bass quality of the monitor 70s. Outlaw states that this will be safe. However, in reality, I've heard generic recommendations that a 2.1 channel receiver should not be used for long periods or anything except low listening volumes with 4 speakers. The rationalization is that there will be dips in impedance during certain passages or types of music and HT, particular with heavy bass, which if running 4 speakers will make the individual channel impedance, already at 4 ohms, drop below 4 ohms enough to potentially stress the amp or trigger a shutdown. As my RR2150 has already been through one repair and only has 6 months left on the warranty, I want some opinions on this.

    Has anyone done a serious amount of 2 channel receiver listening using four 8-ohm speakers such as the monitor 70s, and either experienced problems or not noticed any issues at all?

  2. #2

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    "Has anyone done a serious amount of 2 channel receiver listening using four 8-ohm speakers such as the monitor 70s, and either experienced problems or not noticed any issues at all?"

    The answer seems to be "No."

    You might try posting this question at the Outlaw Saloon, their forum, since it's really more a question about the capabilities of the RR2150 than it is about the properties of the Monitor 70.

    My guess is it won't work very well, but this guess is based on pure intuition; it's information-free.

  3. #3

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    Running 4 speakers in a "2 channel" rig is generally a bad idea. It can create phase issues, and rape your stereo imaging.

    Additionally, hooking up 4 speakers to the A&B outputs is going to change the overall impedance that's being presented to the amp. I'm not familiar with that receiver, but if you're going to try it, make sure it's stable at 4 ohms, or even better, lower than 4 ohms.

    Personally, I think you'd be better off just using one pair of the 70's. In my experience, there aren't any benefits at all to be had by running two pairs of speakers up front.


    edit-I just checked Outlaws website. It says nothing at all about a power rating for 4 speakers at one time.

    Continuous Average Power:
    100 watts per channel, 20 Hz - 20kHz,<0.03% THD, both channels driven into 8 ohms
    160 watts per channel, 20 Hz - 20kHz,<0.03% THD, both channels driven into 4 ohms
    What this means is that with an 8 ohm load, the receiver has a rated output of 100 watts. With a 4 ohm load, the rated output is increased to 160 watts. This has nothing to do with running 4 speakers at a time. It has to do with a given speakers nominal impedance.

    If you're running 4 speakers at once, those power ratings are essentially going to be cut in half. With one pair on the A outputs and the second pair on the B outputs, it's going to be presenting a 4 ohm load to the amp. That doesn't mean that it's going to be putting out 160 watts to each of the 4 channels though. In reality, it would probably only be putting out about 80 watts to each of the four channels, so there aren't really going to be any gains. You're still going to have roughly the same volume capabilites, and you might as well forget about stereo imaging. It won't be there anymore.

    Give it a shot...you might like it. I've tried it in the past, though not with Monitor 70's, and found it to be absolutely terrible.
    Last edited by comfortablycurt; 06-21-2009 at 12:55 AM.
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  4. #4

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    Good advice CC. You might consider picking up a separate amp to handle the work on those 4 speakers. I'm not sure though why you want to have four speakers on a two channel system. Stereo surround?
    Last edited by messiah; 06-21-2009 at 03:21 AM.

  5. #5

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    This is just a stopgap until i get true surround. I picked up 2 more m70s cuz they were a steal and pretty soon you won't be able to find them new.

    Meanwhile, some of the tech advice is incorrect IMHO. The m70s are 8 ohm nominal, and while some speakers have drops below nominal at certain frequencies, the whole point of the nominal rating system is to give a safe number across the whole frequency spectrum, and Polk has usually been fair with their specs from what I've seen. When you run A+B you drop 8 ohms to 4 ohms, so the amp performs as if it has a pair of 4 ohm speakers instead of four 8-ohm speakers. Furthermore, all the tech. reading I've done is that amps don't halve their output per channel with 4 speakers instead of 2. On the other hand the output per channel is not double (100 front L + 100 rear L), but somewhere in-between, in this case the cited figure for Outlaw is 160 W per channel, so it would be 80 front L + 80 rear L, etc.

    But what this really boils down to is will the amp heat up, and the only thing I have been able to find is that the Outlaw groupies who hang out on their forum tend to brag that the RR2150 can move mountains without breaking a sweat, yet no one has talked about running A+B. This kind of owner's-bias is what you expect from the regulars on any particular manufacturer's forum, which is why i posed the question here.

    I did find one independent review printed in Stereophile in which a Mr. John Atkinson did test comprehensive test measurements driving a RR2150:

    http://www.stereophile.com/integrate...law/index.html

    "I preconditioned the RR2150 by running it at 41Wpc into 8 ohms (approximately one third the measured clipping power) for one hour. The chassis was very warm at the end of that period, with the area above the internal heatsinks too hot to touch. However, the receiver didn't turn itself off, and the measured THD+noise percentage was the same at the end of 60 minutes as it had been when first turned on."

    "The Outlaw RR2150 exceeded its 100Wpc specification by 1dB, delivering no less than 125W into 8 ohms (21dBW) at clipping, defined as 1% THD (fig.6). It gave 190W into 4 ohms (19.8dB), this 0.8dB higher than the specified 160W, and even managed 310W into 2 ohms with one channel driven (18.9dBW). That this $600 receiver managed to survive this highpower testing without blowing fuses or anything breaking is high praise. The RR2150 is a
    powerhouse!"

    "Fig.7 Outlaw RR2150, THD+N (%)vs frequency at 12.75V into (from bottom to top): 8, 4, 2 ohms (right channel dashed). The spectrum of the distortion is predominantly low-order harmonics, even into low impedances (fig.8)...Fig.8 Outlaw RR2150, 1kHz waveform at 40W into 4 ohms (top), 0.0116% THD+N; distortion and noise waveform with fundamental notched out (bottom, not to scale)...Fig.10 Outlaw RR2150, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 115W peak into 8 ohms (linear frequency scale). ...Fig.11 Outlaw RR2150, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 180W peak into 4 ohms (linear frequency scale)."
    Last edited by rru2s; 06-21-2009 at 09:26 AM.

  6. #6

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    Well, I set everything up and it works about as well as I expected. With such a long (24 foot) living room and most of my HT seating (and much of my day-to-day audio listening) with seating locations at the far end from the fronts (25 feet away), my goal had been to achieve a more room filling sound, which this does quite nicely. And my sub still keeps up, too. My RR2150 2.1 just came back from a warranty repair and in addition to fixing the relay that was broken, they also boosted the subwoofer output which many customers felt was a design flaw. In my case, two different subwoofers booth had to be run from Speaker B high level output until the upgrade was done, meanwhile these same two subs were perfectly matched level-wise with my HK3490.

    I can't comment on the stereo imaging that someone remarked would be non-existent after going to 2.1 x 2 (front and rear) instead of 2.1 (front only). Right now I'm going through a few CDs such as Hiroshima's Odon and find the sound just as well separated as before, even on the long side wall couch (in between left front and left rear). In the center of the room where all four speakers are toed-in focal point, the imaging as as good or better as before.

    I've been playing around with bass management as I can cross-over from the subwoofer out internally on the RR2150 at 50/65/80, and since the m70s have such nice upper bass, cross-over at 50 is all I am willing to give away to the subwoofer, which is a 15" 330W Epik that is sealed and very musical with string bass, jazz, you name it, yet rumbles plenty well for HT. Also, I have a bass-boost at 55Hz that I can use to restore some of the lost signal with the crossover only to speaker B at other end of the room but not Speaker A at the fronts. The designers probably anticipated Speaker B would be a second room without a sub and Speaker A with the sub in the main listening room, so I have options for (A with sub), (B without sub), or (A + B + sub). Rather flexible for a 2.1 system if you ask me. Plus I like the USB for a rapid quick listen to what I pull down off of my PC from Youtube, although the DACs are as high quality as some, neither are most of the compressed audio formats you randomly listen to on the internet, anyway.

    So my original question about the unit getting too hot doesn't look to be a problem as loud as my ears can handle it over a couple hours of listening. Right now I have the unit running pulled out of the shelf so I can check it's temperature (although not really opening the chassis, I can still get some idea). It doesn't really seem to be running too hot.

  7. #7

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    Good to hear you're happy.

    You are dropping the power output to each speaker though. That power rating is a reference to a pair of 4 ohm speakers, not a quad of 8 ohm speakers presenting a 4 ohm load. That 4 ohm rating is with 2 channels driven. You're still drawing 160 watts on both the left and the right, but since the A/B channels are likely on the same circuit from the power amp, that signal is being split between four speakers.

    You aren't putting out 160 watts x 4 channels, you're putting out 160 watts x 2 channels. The two right channels and the two left channels are together on the same circuit, and thus they're sharing the rated 160 watts per channel. Given that, the signal is split between the 4 speakers, effectively halving the amps output.
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  8. #8

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    No misunderstanding, all comments appreciated. In my previous post I just wanted to clarify that when you speak of halving the power it is not 1/2 x 100 W but 1/2 x 160 W, so the net effect IS additional volume (80 x 4 = 320 W total instead of 100 x 2 = 200 W with 2 speakers). So my point is that it isn't a fruitless exercise to get more volume but like we both know, it isn't double. Plus a side benefit is that each speaker is driven with fewer watts to acheive the same decibels listening volume, which means my speakers should in principle have less of a chance of being blown, provide I am not clipping. Also, there is a much increased ambience and spaciousness, albeit nothing like a proper surround, but that is for another year's budget.

  9. #9

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    You're more likely to blow a speaker with less watts, than you are with more watts, so you're actually increasing the possibility of blowing a speaker. That's not something I'd be overly concerned about either way, just an FYI.

    For instance, say you have a speaker that is rated to handle 150 watts RMS. Let's suppose you are driving it with an amp that is 200 watts. This isn't a bad thing, it's actually a very good thing. A speaker is only going to draw as much power as it needs at any given time. That amp is only going to be putting out a fraction of the 200 watt rating the vast majority of the time. When you're driving a speaker with a higher powered amp, you have more head room, which means that when you hit a part in a musical piece that all of a sudden demands a lot more power, the amp is going to be able to provide all of the good clean current that it needs. The speaker won't be working as hard to maintain it's volume level, and the amp is going to be running a lot more efficiently, without fear of clipping.

    Now let's take that same pair of speakers that are rated for 150 watts and power them with an 80 watt amp. The speakers are still only going to be drawing a fraction of that 80 watts the majority of the time, but when you hit a more demanding passage that requires more power, the amp isn't going to have enough power(headroom) to give the speakers as much current as it needs. This causes the speaker itself to have to work harder to keep playing at the same volume, and makes it a lot more likely to blow a driver, or clip the amp.

    A lot of people get confused on that topic. They think that since their speakers are rated for 150 watts, and they're only driving them with 80 watts, they should be able to crank the volume up all the way without any worries. This is not true at all. As I said, an underpowered speaker is more likely to be damaged than an overpowered speaker.

    I wouldn't worry about blowing the speakers, but do be careful with the volume knob. If you start hearing any distortion, back the volume down a few notches.
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  10. #10

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    One question...I think I may have gotten mixed up on something.

    Where do you have the second pair of M70's placed? Are they acting as surround channels, or do you have them up front next to your other pair of M70's?

    If they're in the place of surround speakers, you can forget about my comments regarding soundstaging and phase issues.
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  11. #11

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    I'm running 2 pair of speakers (A+B) up front in my rig. RTi6 and Yammie NS10M's. No phase issues and I think it provides a better soundstage. I'm powering them with the beefy Yamaha RX-797 2 channel receiver. The bookshelves are easy to drive and my receiver doesn't even break a sweat.

  12. #12

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    Quote Originally Posted by comfortablycurt View Post
    One question...I think I may have gotten mixed up on something.

    Where do you have the second pair of M70's placed? Are they acting as surround channels, or do you have them up front next to your other pair of M70's?

    If they're in the place of surround speakers, you can forget about my comments regarding soundstaging and phase issues.
    Yes, they are in the place of surrounds, at back wall of the listening room. I posted a rough drawing of the listening room in another thread, so here is the link to the diagram:

    http://www.polkaudio.com/forums/show...t=83006&page=2

    I ended up moving both rears near the corner (swapped with the recliner), since I didn't want to have any seating located outside of the perimeter of the speaker locations.

    It is interesting that I get a nice concerthall type effect no matter where you sit on any wall. But if you are along the center line, forward of midpoint then you hear the fronts as primary, while if you turn around 180 degrees and move slightly towards the rear speakers, then they become the focal point. The apparent focal point of the soundstage shifts from front to rear as you walk facing towards the back of the room. However, it all sounds very good.

  13. #13

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    Are your speakers close to your front wall? If you have at least a couple feet of clearence between speakers and front/side walls, you could try running a bipole set up. I mention this because you say you like the "concert hall" effect. What you do is place the 2 speakers in each channel back to back. So you have one firing forward and the other firing back. It won't hurt to try.
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  14. #14

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    Quote Originally Posted by organ View Post
    Are your speakers close to your front wall? If you have at least a couple feet of clearence between speakers and front/side walls, you could try running a bipole set up. I mention this because you say you like the "concert hall" effect. What you do is place the 2 speakers in each channel back to back. So you have one firing forward and the other firing back. It won't hurt to try.
    If two cute girls were singing to me, I wouldn't want one of them to be facing the wall instead of me. I treat my speakers the same way.

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    Puts me in mind of my days as an audio salesman back in the mid 80s...this scruffy looking dude is looking around our "high end" room (early days of Best Buy, so almost anything above a rack system was high end ), and he tells me he "needs more power", even though he is running a Kenwood amp rated at 200 wpc. Ask him what he has for speakers, he says "four Small Advents". So of course I have to tell him his problem is not power, it's impedance, as the Small Advents are 4-ohm speakers to start with...

    Anyway, all this discussion about power ratings won't matter if the amp can't handle the impedance drop to average 4-ohms...but I would think the Outlaw is robust enough to push four 8-ohm speakers without issue.
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  16. #16

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    Quote Originally Posted by rru2s View Post
    If two cute girls were singing to me, I wouldn't want one of them to be facing the wall instead of me. I treat my speakers the same way.
    Dude, I was trying to help you on my previous post. Bipoles act like pulsating cylinders and gives more of an omnidirectional sound which is great for filling up large spaces.

    Do you think a violin shoots its sound straight forward? No, the soundwaves flow in 360 degrees. So go ahead and send an e-mail about your cute little girls theory to Def Tech, MBL and a whole bunch of other companies that do omni sound. Didn't know you like to give smart ass answers to people trying to help you out.
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  17. #17

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    If I get a chance I'll try the bipole setup you mentioned. I was being facetious. However, realistically, the room is so long I find there is a need to get more sound 24 feet across to the other end where most people sit. Furthermore, the rear speakers also are in a direct line-of-sight with the opening off of this room to the dining room, which conveys more sound to that room for listening at the same time. But to answer your question, I do have a rather tight room configuration since this is a great room and has the equivalent of both living room and entertainment room furniture all in one area (see the diagram below):



    Note: not everything is to scale. Also, all speakers and the sub are toed-in facing a focal point about 2 feet off-axis from the room center. Also, the rear speakers are closer to the corners than illustrated (I swapped the recliner and right rear speaker).

    To have a right front bipole setup, there is barely 1.0 to 1.5 feet in the right front corner due to a loveseat jammed in between the right front speaker and a woodstove in the center of the wall.

    The left front speaker is also sitting in a tight corner atop a subwoofer that is wedged next to the HDTV entertainment center console. The sub has a larger sound output near the corner, and I'm not sure if I would have the same sound if I pulled it out from the wall enough to put two towers on top of it. I don't want to put the sub elsewhere on the other side of the entertainment center since that is in front of a sliding glass door and over a slate surface, which would not be ideal for a sub.

    Yea, but thanks for the ideas, sorry to joke around. Wasn't one of the first companies to emphasize the omnidirectional sound the early Bose models back in the late 70s? I seem to remember their early models were quite well respected for their ominidirectional character.
    Last edited by rru2s; 06-24-2009 at 10:06 AM.

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    First of all, I need to make an apology. Sorry, I overreacted on my previous post (probably because I use bipoles lol).

    Yeah, your room is quite tough to work with but your current configuration should provide enough energy to fill up the entire room. I can't think of any other way to set them up. However, I would suggest that you look at some towers for your next speaker set up. Klipsch is excellent and can rock out real hard. You might want to take a look at them when you feel like upgrading.

    Yeah, Bose did a quasi bipole with the 901's. Not true bipoles because they had 9 small drivers for the rear and a large one for the front. But the effect is similar. Bose preferred 10% direct sound and 90% refelected while Mirage likes 30% direct and 70% reflected.
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