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Discussion Starter · #1 ·
I am looking for a reciever that will power my 5 speaker Polk LSi 4 ohm surround sound system. I would prefer to use a single reciever unit if possible(I know an external amp would work better but...) because space is limited. I had not plannned on replacing my current reciever (Onkyo TX-SR705) but was told it would not handle (without an external amp) the LSi's. Ideas?
 

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I am a Huge Harman Kardon fan, I have the AVR745 and it will power even the most demanding speakers, such as your LSi's


What is your budget?

# of HDMI in/out?

Upscaling?

what additional options do you want/need aside of being able to run the speakers?


HK, Denon, Marantz, Pioneer Elite, Integra, Adcom, Krell, NAD etc


P.S For "Onkyo Certified 4ohms performance" you would need an TX-NR905, TX-SR875 or TX-SR805
 

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Discussion Starter · #3 ·
I would prefer not to exceed $1500 (not even that if at all possible) since I had not planned on replacing my reciever in the first place. I need 3 HDMI's in and 1 out and upscaling is not necessary since I run a Toshiba A35 HD and a Sony Blu-ray player through the HDMI's and they upscale already. I have thought about the Onkyo TX-SR805 but I have read threads that claimed it really didn't do the job when it came to the LSi's. I like the Onkyo line but I don't understand in the specs under the amplifier section where it lists speaker Inpedance it says "4 ohms-16 ohms or 6 ohms-16 ohms ". Can anyone explain this to a "short-circuit" minded person? Also they do not list the wattage output using 4 ohm speakers. I read (and I know you can't believe everything you read) that you need at the very least 200 watts/channel output to run the LSi's. Thoughts? Thx.
 

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Try looking at one of the NAD HT receivers. They are all capable of running 4 ohm loads. I believe the T755 is roughly 1500.


nadelectronics.com
 

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Have you tried the 705? Might be worth it just to see if it meets your expectations. The 805 has a very strong amp (THX Ultra 2 certified) so it should drive the Lsi with no problem, particularly if you use a sub. I have driven some pretty diverse (and low sensitivity speakers with the 805) including Totem Mani'2s and Forests, and it has yet to meet its match.
 

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Quote:
Originally Posted by tonygeno /forum/post/14186622


Have you tried the 705? Might be worth it just to see if it meets your expectations. The 805 has a very strong amp (THX Ultra 2 certified) so it should drive the Lsi with no problem, particularly if you use a sub. I have driven some pretty diverse (and low sensitivity speakers with the 805) including Totem Mani'2s and Forests, and it has yet to meet its match.

True, a lot or power problem arise when trying to run 4 ohm speakers full range. if you limit them to 80Hz and run a sub, you should be fine.


I agree that you should try your receiver... (loud !!!) and see if it works first.
 

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There is no way no how that 705 is going to handle the LSi15 and the LSi center. It will hit protect mode as soon as you try to crank it to a decent volume. The LSi line is a 4ohm nominal speaker that I have seen dip to less than 3ohms at peaks. Do not put an unnecessary strain on your receiver which will reduce the life of it substantially. Even in the $1500 range there is no receiver that will live very long powering those speakers. Denon and Yamaha receivers are rated for up to 6ohms so if you try to power the polk and it breaks you will void your warranty on the spot.
 

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I don't think many receivers are going to easily deliver the current you'll need to make those LSIs sing. NAD has a 200wpc receiver which is prob as good as it gets...although at $3k it's not cheap.


Honestly your 705 with its pre-outs and HDMI audio decoding has almost everything you could ask for. A simple 5 channel external amp ($500-1200) would do you better than any receiver you could buy for $1500.
 

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It is interesting to hear a lot of this. Fact all THX receivers must power speakers with a impedance down to 3.2 ohms to levels of 105db. 2,000 sq. ft. for select and 3,000 for ultra certification. I have a Pioneer VSX-55TXi rated at only 100 watts per channel. It powers my LSi 15's, LSi-Center and LSi F/X's just fine. The speakers were purchased after my receiver so I did not buy them specifically for the 55TXi. I have read from many forums about 100 watt or greater THX reicevers powering these speakers just fine. Your 705 should have no difficulty since it is THX certified and it is 100 watts per channel. I am not saying the 705 is the ideal choice but it will work and safely.
 

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Discussion Starter · #11 ·
Thanks for all the input. Now I am throughly confused. I wish I knew more about this technical stuff. I emailed Onkyo about their TX-SR805 reciever and they replied it would power 4 ohm speakers. They just didn't say how well it would do it or how long the reciever would last. I think I will follow the advice of adding an amplifier to my existing TX-SR705 reciever since it has pre outs and is a great reciever. One person recomended the Emotiva XBA-5 or maybe the MPS-2 depending on how much I decide to spend. He seemed to know his stuff and was very helpful. My LSi's are being delivered tomorrow so I need to get on the stick and decide what the heck I am going to do. It takes me a while to decide because I don't want to make the wrong desicion and with so many options I guess it all comes down to personel preference.
 

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JRobin50:


Not sure why you're confused. You have all the elements you need to decide if you need an outboard amp. Before spending any additional dough, why not try the 705 to determine if it will do what you want. You will not blow it up. Worse case scenario: thermal shutdown at which point you'll know the 705 is not sufficient for your use.


Read again this post: http://www.avsforum.com/avs-vb/showp...3&postcount=10


It contains the info to clear up your confusion.
 

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Also, depending on where you are, a Crown XLS402D can be had pretty cheap on craigslist in pretty good condition if you keep your eye out. It might be worth it to you to pick one up. If you aren't happy with it you can relist it.

Quote:
Originally Posted by PRO-630HD /forum/post/14188333


It is interesting to hear a lot of this. Fact all THX receivers must power speakers with a impedance down to 3.2 ohms to levels of 105db. 2,000 sq. ft. for select and 3,000 for ultra certification

Where can you find out what the specifications are? Google wasn't cooperative and I couldn't find it on the THX website. I've been trying to find out what it ultra means for power amps. I was looking at a JBL Synthesis S7150 Amplifier, Ultra Certified, but it says minimum 8 ohms/channel
 

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Discussion Starter · #14 ·
Maybe confused was not the correct word to use. Maybe I should have said overwhelmed instead what with all the suggestions and ideas. I guess it will boil down to trial and error. I just don't want to do any harm to my 705 in case it won't work. I want it in good selling condition or be able to add an amp ( I don't want it to go up in smoke). Thx.
 

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Quote:
Originally Posted by JRobin50 /forum/post/14198900


Maybe confused was not the correct word to use. Maybe I should have said overwhelmed instead what with all the suggestions and ideas. I guess it will boil down to trial and error. I just don't want to do any harm to my 705 in case it won't work. I want it in good selling condition or be able to add an amp ( I don't want it to go up in smoke). Thx.

You don't have to worry about the 705 going up in smoke. A friend of mine runs his LSi15 fronts and the LSiC off a Sony 5200ES receiver (less powerful than your Onkyo). At normal listening volumes it sounds fine. You may need an external amp to get the best sound from your speakers, but you probably don't need an external amp to protect your receiver.
 

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Quote:
Originally Posted by cjm7c /forum/post/14198977


You don't have to worry about the 705 going up in smoke. A friend of mine runs his LSi15 fronts and the LSiC off a Sony 5200ES receiver (less powerful than your Onkyo). At normal listening volumes it sounds fine. You may need an external amp to get the best sound from your speakers, but you probably don't need an external amp to protect your receiver.


Just thought I'd add that of more concern is to protect your speakers.


IF your avr is driven into clipping as you turn the volume up and the LSIs are sucking up more than the avr can deliver, then your avr may go into distortion which will damage your LSI drivers - especially the tweeters.


More damage is done to tweeters with underpowered receivers or avrs when driven to high volumes and into clipping than damage to the avr or receiver.


Been there - done that - not a pretty place to be when your speakers have a permanent crackly sound or if the tweeters blow altogether (done that too).


When it comes to speakers - power is your friend - not your enemy.


fwiw,

Erik
 

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Quote:
Originally Posted by datgai /forum/post/14197173


Where can you find out what the specifications are? Google wasn't cooperative and I couldn't find it on the THX website. I've been trying to find out what it ultra means for power amps. I was looking at a JBL Synthesis S7150 Amplifier, Ultra Certified, but it says minimum 8 ohms/channel
http://www.hometheatermag.com/receivers/104yam/


page 1
 

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Quote:
Originally Posted by Erik Tracy /forum/post/14199945


Just thought I'd add that of more concern is to protect your speakers.


IF your avr is driven into clipping as you turn the volume up and the LSIs are sucking up more than the avr can deliver, then your avr may go into distortion which will damage your LSI drivers - especially the tweeters.


More damage is done to tweeters with underpowered receivers or avrs when driven to high volumes and into clipping than damage to the avr or receiver.


Been there - done that - not a pretty place to be when your speakers have a permanent crackly sound or if the tweeters blow altogether (done that too).


When it comes to speakers - power is your friend - not your enemy.


fwiw,

Erik

The issue with the Lsis is not power (watts) but current. You will not clip the amp, but the amp could run out of current, overheating and shutting down. Clipping should not be a problem with a good 100 to 125 watts. A 200 watt amp will only give you three more db of output compared to 100 watts. However, if the external amp has a more robust power supply, it could supply way more current.
 

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Are you sure you can't clip and amp by drawing too much current? Can you pull down the rail voltage by trying to draw too much current ? E = IR, but at some point, you must reach a point where you can't draw more current. Then what ?


I do understand that you can also reach thermal limits.
 
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