RM7200 and Onkyo receiver

rmhughes0711

I have an RM7200 system with subwoofer connected to an Onkyo TX-SR 701 receiver. My rear and center speakers are connected directly to my receiver and my front speakers connect to the subwoofer with the subwooker connecting back to the receiver. With this configuration, my receiver goes into "protect mode" at about 50% volume.

If I take the subwoofer out of the picture and connect my front speakers directly to my receiver, I can raise the volume and rattle the rafters. What is causing the subwoofer to limit my volume?

What can I do to diagnose further and ulltimately resolve this problem?

Help!!!!

Skynut

Your subwoofer is pulling power out of the onkyo and causing a fault.
I had the same problem with my pos sony and my rt2000p's.
The sub needs to be hooked up to a lfe output.

John K.

RM, when a receiver shuts down at a moderate level that it should handle easily(your direct speaker connection shows that your 701 can do this and isn't the problem), the cause is often a loose strand of wire which is causing a short and activating the protection circuit of the receiver. The sub actually draws no power from the receiver in normal use. If you haven't already done so, rewire the sub to speaker connection, taking special care that there's not even a single strand of wire loose. If this doesn't resolve the problem, it's possible that there's a short in the internal sub wiring when the speakers are wired through it. So, wire the sub and the front speakers in parallel from the front speaker outputs of the 701(i.e. one set of wires directly to the sub and another set directly to the speakers), trimming strands off the ends if necessary so that both sets of wire fit the receiver terminals.

rmhughes0711

John K, you suggest a wiring issue. Skynut, you think it may be a power issue and I may need to evaluate lfe output. What do you think of the other person's response?

I'm going to run a short speaker run to the subwoofer so I can evaluate the wiring issue.

If I do the the LFE scenario, does my wiring basically stay the same?
(front speakers to sub
sub to receiver)

Dennis Gardner

I responded to your other post also, but lets clear this up.

The Polk sub can be hooked up 2 ways.

1. Speaker wires, from receiver's front speaker hookups into high level inputs on the sub, and then into your front speakers. This uses 2 stereo pairs of speaker wires.

2. LFE uses an RCA cable. The sub is run from the subwoofer output on your receiver to the low level or RCA input on the sub.
The speakers are run directly from the front speaker wire post on the receiver to your front speakers using speaker wire.

If your receiver is working good with the fronts hooked directly, then I would use an RCA cable from your subout to your subwoofer to handle the low bass.

We all know that Polk has long suggested the way that you hooked yours up, but many have found that the receivers find the load hard to handle this way. It is a load problem that the receiver doesn't like. Polk satelites are already 6 ohm models, and the sub may lower this somewhat into areas that the receiver can't handle.

John K.

Dennis, using the line level connection to the sub may be generally better from the standpoint of flexible bass management, but regardless of what "many have found" regarding the speaker wire type of connection, if the wiring is done correctly no load problem results. The input impedance of sub amps is in the tens of thousands of ohms(the sub driver itself may be 4ohms, but the receiver isn't powering it). When the sub amp and the speakers are connected in parallel with speaker wire the resulting net impedance is equal to the reciprocal of the sum of the reciprocals of the speaker and sub amp impedances. For example, with 6ohm speakers and a 30,000ohm amp input impedance the calculation is 1/6 + 1/30,000= 5,001/30,000, the reciprocal of which is 5.999 ohms. No appreciable difference.

Dennis Gardner

John,

I agree that a short is the most logical cause of his issue.

How do you come up with the high impedance measurements since a direct measurement across speakers input posts show a 4 ohm measurement?

rmhughes0711

OK, I have the problem resolved. I basically re-wired the whole shooting match, verifying each connection as I went. It seems to be working fine now. Thanks for all who contributed to my question.

Now, that I have this resolved, I am still thoroughly confused on my method of hooking up my speakers via LFE or the way I originally configured them. In another post, someone said that digital playback would be an issue connecting them my way. Does this mean digital cable and DVD? What am I losing my keeping them this way. What are my gains by changing them. If I do change to LFE, do my front speakers still connect to the sub or do they go directly to the front speakers input on my receiver?

Any help is appreciated.

John K.

Dennis, from what RM now reports, it appears that one or both of the speaker wire connections had a loose strand which was shutting down the receiver. On the impedance matter, note that although sub drivers themselves typically have a 4ohm impedance, the receiver isn't "seeing" the sub driver. If the sub driver and the 6ohm speaker were actually connected in parallel the resulting impedance seen by the receiver would be 1/4 +1/6= 5/12, the reciprocal of which is 2.4 ohms. However, the parallel connection is instead between the speakers and the input to the sub amp, all of which have impedances in the tens of thousands of ohms, so the result is as was described before; the impedance seen by the receiver is essentially unchanged and no receiver power is used by the sub. The parallel nature of the connection is apparent when separate speaker wires from the receiver terminal go directly to the sub and directly to the speaker. It's less apparent when the feed to the speakers comes instead from the sub output terminals, but this is simply dividing the receiver output just inside the sub input terminals(then out through the sub outputs) instead of at the receiver output terminals. The two arrangements are essentially identical electrically.

John K.

RM, glad to see that you resolved the situation. It's unclear what was meant by this "digital playback" comment that you mention. Regardless of whether the source material is digital or analog, all information, including low bass from "small" speakers and LFE(low frequency effects sometimes present in 5.1 movies), is sent to the sub with the speaker wire connection when the mains are set "large" and the sub "none". The alternate connection using a cable from the sub output of the receiver to the LFE input on the sub is probably preferable in most cases. It allows you to have flexibility in assigning bass between the speakers and the sub. Polk cautions against having the receiver filter(active through the sub output)conflict with the internal sub crossover filter, and this is a valid point, but any conflict is totally avoided by using a switch or LFE input which bypasses the internal sub filter. A sub not having such a bypass provision can have any conflict minimized by turning the sub's crossover control all the way up, so as to get it as far out of the way as possible.

It may not be of much advantage with the RM7200 speakers, but you should at least try the alternative line-level connection. You don't have to buy anything; just temporarily use any cable that you have with an RCA plug on each end. All speakers would be set "small", the sub yes, and because of the limited low frequency response of the RM7200 speakers a crossover of about 120Hz on the 701 would be appropriate.