Impedance & Sensitivity of a Speaker, & Damping Factor

[p902]

@Big Daddy; Thanks for the input. You kind of reiterated what was explained in the initial post. I guess I have to give this more of a think.

I probably won't go down the pre-amp/amp route because (to be honest) I can't be bothered to start researching and getting extra kit. I think I'll stick with the receiver and get only 6 ohm speakers although conventional wisdom tells me to get the best speakers I can get now (the 4ohm polks) as they will be fixed in the wall and think about a possible upgrade of receiver down the line.

Great forum though - pity I don't have enough hours in the day to read through all this wonderful information

[p902]

Me again....

Decided to go ahead with the 4-ohm polk audio speakers and upgrade my amplifier. The setup is now polk audio lc265i for LCR and RC60i as surrounds in a 5.1 setup.

I have shortlisted two amps; The onkyo tx-nr1007 and the pioneer sc-lx72 (sc-25 in the US).

Anyone have any thoughts on these two amps? Will be used for a 50/50 mix of movies/music.
I am not getting a separate amp as I want the setup as simple as possible.

[jomari]

will both of these amps handle 4ohm resistance tho?

this would be my only question.

[Fors*]

I have the Pioneer SC-05 (previous model to the SC-25 and basically the same specs) and I don't think it would be a good idea to run 4 ohm speakers off of the amp for this receiver, as it is rated only down to 6 ohms. I think it will be quite strained and you'll be pushing it to it's limits, and I don't think you'll like the results. However, I do see the Onkyo can handle a 4 ohm load. In this case, I would take the Onkyo based on this alone.

[kingofgrills]

Originally Posted by Fors*

I have the Pioneer SC-05 (previous model to the SC-25 and basically the same specs) and I don't think it would be a good idea to run 4 ohm speakers off of the amp for this receiver, as it is rated only down to 6 ohms. I think it will be quite strained and you'll be pushing it to it's limits, and I don't think you'll like the results. However, I do see the Onkyo can handle a 4 ohm load. In this case, I would take the Onkyo based on this alone.

I agree. I looked at both user manuals, and while the Onkyo clearly states it can run 4 ohm loads (certifies it, actually), I couldn't find any info on 4 ohm loads or adjusting speaker impedance in the Pioneer manual.

If you're set on getting 4 ohm speakers, I would recommend the Onkyo over the Pioneer. Also, if you end up wanting to upgrade in the future, you can alway add an external amplifier and use the receiver as a pre/pro.

[jomari]

also make sure that your AVR or pre/pro of choice is properly ventilated.

[p902]

Thanks jomari,kingofgrills and fors* for your input. I think it bodes well for me then, as I can get the onkyo cheaper.

I do like my music loud once in a while, but won't be running them at full whack all the time...

Originally Posted by jomari

also make sure that your AVR or pre/pro of choice is properly ventilated.

I saw earlier while researching, someone had connected a computer fan via 12v trigger and placed it on the vent of his receiver to help with cooling. I guess I can do this in addition to good spacing to help cool the unit. I have read onkyos are known to run hot generally so any additional cooling can only help.
Just don't know how distracting the fan noise will be as I assume it will always be on while the receiver is on.

[Fors*]

Originally Posted by p902

Thanks jomari,kingofgrills and fors* for your input. I think it bodes well for me then, as I can get the onkyo cheaper.

I do like my music loud once in a while, but won't be running them at full whack all the time...

p902, have you gotten a chance to listen to the Onkyo 1007 in action? I always like to try to listen to the gear and it sonic limitations before I buy it. Different AVR's will sound different, and some you may like and others you may not. There are other variables like type of speakers, external amplification, etc..that may affect the sound you hear, but it doesn't hurt to listen to the AVR first before buying. Just adding my 2 pennies.

[BigAl87]

Originally Posted by Fors*

p902, have you gotten a chance to listen to the Onkyo 1007 in action? I always like to try to listen to the gear and it sonic limitations before I buy it. Different AVR's will sound different, and some you may like and others you may not. There are other variables like type of speakers, external amplification, etc..that may affect the sound you hear, but it doesn't hurt to listen to the AVR first before buying. Just adding my 2 pennies.

+1, I have found Kef IQ50 and 807 to be an atrocious pairing for instance, lacked alot of detail separation and dynamics and those speakers came to life on an HK 3600 not because I own an HK but honest truth is that even the salesman was quite shocked and the difference in sound.

Some people don't like HK in HT setups because they feel they are too boomy, sound is subjective which is why I always recommend to audition before buying and as much as possible audition with what you are planning to pair the receiver with.

[p902]

Originally Posted by Fors*

p902, have you gotten a chance to listen to the Onkyo 1007 in action? I always like to try to listen to the gear and it sonic limitations before I buy it. Different AVR's will sound different, and some you may like and others you may not. There are other variables like type of speakers, external amplification, etc..that may affect the sound you hear, but it doesn't hurt to listen to the AVR first before buying. Just adding my 2 pennies.

Actually, I haven't, mostly because I haven't had or made the time. I did listen to the onkyo 608 and the Denon 2311, but that was before I decided to get the Polk audio speakers. I am currently in the process of a house build/renovation so time and money are very precious to me.

I chose the Polk audio LC265's after listening to them, but I also got them at less than half price.

The problem I have with Polk listening tests is that very very few dealers here in the UK stock them so it's hard to get a demo with different amps.

I currently have a Denon 3802 running the KEF KHT2005.1 'egg' system. I bought those also only via reviews/research without listening and they paired well. I am hoping (with all your help) I'll have the same kind of luck with the onkyo/polks.

Thanks.

[Automission]

quick question, I have three speakers in my 5.1 setup rated at 6 ohms, and the two front towers rated at 4 ohms, both bi wired. For the last two years I've been running the amp at an output of 6ohms rather than the option of 4 ohms. I've not had any problems.

Should I change it to 4 ohms and over power the other speakers, or stick with 6 ohms? What will happen if i keep them running at 6 rather than 4?

[Big Daddy]

Originally Posted by Automission

quick question, I have three speakers in my 5.1 setup rated at 6 ohms, and the two front towers rated at 4 ohms, both bi wired. For the last two years I've been running the amp at an output of 6ohms rather than the option of 4 ohms. I've not had any problems.

Should I change it to 4 ohms and over power the other speakers, or stick with 6 ohms? What will happen if i keep them running at 6 rather than 4?

I responded in your thread.

[Mirage29]

I am confused on weather it's a good or a bad thing that I am using 6 ohms speakers with 8 ohms ampilifer. From what I have read that fact my speakers are 6 ohms means that they are taking extra power from the amplifer which can be a good thing if the amplifer has the extra power to spare without clipping. But I read a article about oscillation and speaker ringing didn't really understand it that well but from what I read it seemed like not have matching Impedance is a bad thing it causes what is know as ripple. Can somebody help me undertand this. When I turn my speakers up loud they start to hurt my ears am I hearing what is know as ringing?

[Big Daddy]

Impedance Matching:

In most cases, it is important for the receiver/amplifier to be able to handle low impedance loads. However, most mid to high level receivers made these days should be able to handle 6-ohm speakers without any problems as long as you don't turn the volume too high for too long. If the volume is turned up too high for an extended period, the speakers may distort, the receiver may get too hot, and they may fail in the long run.

Impedance matching may be important, but not always easily accomplished. Impedance matching simply means that we should make sure the input impedance of the load (destination) is approximately equal to the impedance of the source in order to maximize the power transfer and/or minimize signal reflections from the load.

Impedance mismatch can cause signal attenuation, standing waves, ringing and other effects because of signal reflections. Signal reflection occurs when a signal that is transmitted along a copper cable or an optical cable may be reflected back to its origin rather than being carried all the way along the cable to the destination. When a returning reflection strikes some of original signal direction it can create multiple echo effects. These echoes reach the load (destination) at different time intervals making it difficult for the load to accurately detect data values of the signal. The effects can be ringing and resemble those of jitter. This effect is compounded if multiple additional portions of the signal is reflected back to the source. This can also be a big problem when multiple electronic devices are daisy chained to one another and is one of the reasons why I do not generally recommend daisy chaining multiple subwoofers in a room.

Remember that the impedance, as reported by the maufacturer, is simply an average number. Other factors such as cable and frequency can affect impedance. Furthermore, damage to the cable, particularly optical cable, can also cause signal reflection and ringing.

With DC current, we only have to make sure the resistance of the source is equal to the resistance of the destination as there is no reactance in DC circuits. With AC current, impedance matching is more of a problem as there is additional capacitance and inductance that varry with the frequency. As a result, we may get an unwanted oscillation of the current or voltage that will resonate at their characterstice frequency. This occurs because of unwanted capacitances and inductances in the circuit that are not part of the original design, but they are due to the materials used and the design of the circuit) to resonate at their characteristic frequency and cause ringing.

Ringing is undesirable because:

• it causes extra current to flow from the source to the load;
• it wastes energy;
• it causes over-heating of the components;
• it can cause unwanted electromagnetic radiation;
• it can delay reaching the final steady state as it increases settling time.

Mechanical ringing of loudspeaker/subwoofer frequency waves in a small home theater room is perhaps more of a problem, but that is another story. Also, the ringing that you hear in your ears has nothing to do with impedance matching. Just turn down the volume. However, if you have continuous ringing in your ears, you should consult a doctor or an audiologist.

[Mirage29]

thanks a lot big daddy it's amazing what you know

[Big Daddy]

Originally Posted by Mirage29

thanks a lot big daddy it's amazing what you know

Thanks, but I am just a noob.

Your XPA-2 amplifier should be able to handle your 6-ohm speakers easily. If the speakers distort at very high volume, it means you are over extending them. This happens with many speakers and is not due to impedance matching problem.

You may get better performance, if you set the crossover of the front speakers to 60Hz-80Hz and redirect the ultra low frequencies to the more strategically placed subwoofer. Also, move the front speakers away from the walls. The mirage omni-directional tweeters need some space in all directions. Make sure all the speakers are calibrated properly and level matched. Some room treatment may be helpful.

Finally, don't turn the volume too high. Not only can you damage the speakers, but you can also damage your hearing.

[Mirage29]

Originally Posted by Big Daddy

Thanks, but I am just a noob.

Your XPA-2 amplifier should be able to handle your 6-ohm speakers easily. If the speakers distort at very high volume, it means you are over extending them. This happens with many speakers and is not due to impedance matching problem.

You may get better performance, if you set the crossover of the front speakers to 60Hz-80Hz and redirect the ultra low frequencies to the more strategically placed subwoofer. Also, move the front speakers away from the walls. The mirage omni-directional tweeters need some space in all directions. Make sure all the speakers are calibrated properly and level matched. Some room treatment may be helpful.

Finally, don't turn the volume too high. Not only can you damage the speakers, but you can also damage your hearing.

How do I go about setting the crossover of my front to 60-80hz? And how do redirect the ultra low frequencies to my subwoofer?

[HAMP]

Stop reading that Mitsubishi DLP manual and read a few threads on things….

Just kiddin.


Big daddy said to select a setting between 60hz and 80hz, not set your receiver hz to 60-80….

Setting the hz on your receiver is redirecting the low frequencies. Depending on what you set your crossover to, will decide how much is sent to the low end. Or you can say, it will determine what part of the audio is played with your subwoofer and/or your speakers

[Mirage29]

Thanks for the help

[Big Daddy]

Connecting Three (3) Speakers:

If your intention is to connect three speakers to one mono amplifier, you have several options:

Option 1. Connect all three speakers in series. The net impedance will increase and you should be safe.

Option 2 (Not generally recommended). Connect two speakers in series (assuming the impedance of each speaker is 4 ohms, the net impedance will increase to 8 ohms) and the third one in parallel to the other two. The problem is that the single speaker will draw more current and you may end up with speakers that have uneven levels.

You could connect a 4-ohm resistor to the third speaker in series to create a dummy load and make the net impedance of the third speaker and the resistor into 8 ohms and the final impedance to 4 ohms.

If your intention is to connect several speakers together, an odd number of speakers is not generally recommended.


Additional Wiring Diagrams: