Best amp for Polk Rti series and Yam 2500

[PENG]

Have you ever even used an Ohmmeter to measure the resistance of a driver or speaker? I have, and when they are rated at 8 ohms, they measure 8 ohms or slightly less. Just to let you know units like the Denon 3805 can’t drive a 4-ohm load. They are current limited, at least that’s what their tech support told me.

Yet according to http://www.usa.denon.com/support/faqs_ht.asp#Q9

It should be able to drive 4 ohm loads.

Regardless, I would have no concerns with the 3805 driving a pair of 4 ohm speakers, but certainly not all 5 or 7 speakers.

 

[mtrycrafts]

I meant it couldn’t be lower; I made a typo in my second sentence (it has been edited).

It happens to the best of us

I am not saying that the speaker circuit is a resistive load. It is a complex load that contains resistive, inductive, and capacitive components. You are right, the inductive and capacitive components of the speaker load are frequency dependent but its resistive component (such as the resistance of the coil) is not.


OK, I can go along with this


If you measure it with an ohmmeter, you get its resistance, or D.C.R., because the ohmmeter's measuring signal is D.C., i.e. 0 Hz.

Yes, of course.

If it is found to be say X ohms, then the resistance of the circuit is X ohms regardless of the frequency of the signal. Skin effect does make the resistance somewhat frequency dependent but it will be negligible, and in any case, will make it higher, not lower.

OK. But, does that amp sees a DCR load, outputting DC current into the speakers? Or, it sees the Z component? Since the Z of the low section is isolated from the high section by the crossover networks, will the amp see this two loads as a parallel Z circuit? How would it since the frequency is the factor and in essence isolator?

But, I may be all wrong. I have been known to be wrong, from time to time

I did send this question to an industry expert on speakers. I'll see

 

[mtrycrafts]

The man made an error, he meant lower. You know that, yet you insist on instigating.

Are you a mind reader? You know what he meant? Good for you.

I don't know what he meant. He explained, now I know what he meant. Problem solved.

 

[PENG]

Z is the total impedance of the circuit that includes all 3 components. Z is the vector (or phasor, in E.E. terms) sum of the 3 components in any series/parallel combination). I assume Mac measured the resistance of the speaker itself. If you are talking about the influence of the crossover netwrok then it could be a different story. I have no idea what the value of the overal Z (impedance) of the speaker system that includes the crossover network.

Please share what you find out from your expert source.

Thanks in advance.

 

[mulester7]

.....and once again, next to nothing is accomplished with an attempted discussion that gets technical with meters and scopes being used....most of us can at least keep up, but who really wants to?.....

.....EARS, EARS, EARS, EARS, EARS, EARS....we need to experience products, combine products, tweak products, and then give a report, imo....and.....

.....I have now been conditioned to detest the winking faces, and I suspect I am not the only one.....

.....I just saw on the Weather Channel the high temperatures today in Washington state were in the 60's....mercy, here in Little Rock, it was right at 100 with HIGH humidity....this afternoon I saw a dog chasing a cat, and they were both walking.....

 

[Buckeyefan 1]

3805 and 4 ohm

Yet according to http://www.usa.denon.com/support/faqs_ht.asp#Q9

It should be able to drive 4 ohm loads.

Regardless, I would have no concerns with the 3805 driving a pair of 4 ohm speakers, but certainly not all 5 or 7 speakers.

Denon should update that. If you call Denon tech support, they'll tell you they don't recommend running 4 ohm speakers on the 3805 or lesser units. In fact, it says right in the 3805 manual that they don't recommend running 4 ohm speakers. Unfortunately, I'm running Polk 4 ohm speakers (yes, I measured the resistance of these speakers, strapped and unstrapped. Macs measurements are dead on). The Denon pushes them alright, but no where near what the speakers can handle. How much more proof does one need?

If you own 4 ohm towers with the 3805, I highly recommend a separate two channel amp. A 120 watt Denon 3805 and a separate two channel 120 watt quality power amp are not the same. The huge heat sinks alone will keep the separate power amp running cooler, longer, with less distortion. There's not room in the 3805 for massive heat sinks. You'll also find much larger capacitors and transformers in separate power amps.

IMHO, manufacturers tend to use the ceiling on receiver specs, and the floor on quality power amp specs. The 3805 may be able to attain 120 watts for a few milliseconds in 2 channel mode, but a separate quality power amp will maintain those levels much longer. That's true at 10 watts, 25 watts, or 100 watts. That's why you'll hear a difference in the sound.

Mtry, there are no insane levels with my setup, especially when running digital music such as TWC's Music Choice. You're welcome to stop by and listen for yourself.

 

[MacManNM]

Are you a mind reader? You know what he meant? Good for you.

I don't know what he meant. He explained, now I know what he meant. Problem solved.

I guess I am a mind reader

 

[PENG]

Denon should update that. If you call Denon tech support, they'll tell you they don't recommend running 4 ohm speakers on the 3805 or lesser units. In fact, it says right in the 3805 manual that they don't recommend running 4 ohm speakers. Unfortunately, I'm running Polk 4 ohm speakers (yes, I measured the resistance of these speakers, strapped and unstrapped. Macs measurements are dead on). The Denon pushes them alright, but no where near what the speakers can handle. How much more proof does one need?

If you own 4 ohm towers with the 3805, I highly recommend a separate two channel amp. A 120 watt Denon 3805 and a separate two channel 120 watt quality power amp are not the same. The huge heat sinks alone will keep the separate power amp running cooler, longer, with less distortion. There's not room in the 3805 for massive heat sinks. You'll also find much larger capacitors and transformers in separate power amps.

IMHO, manufacturers tend to use the ceiling on receiver specs, and the floor on quality power amp specs. The 3805 may be able to attain 120 watts for a few milliseconds in 2 channel mode, but a separate quality power amp will maintain those levels much longer. That's true at 10 watts, 25 watts, or 100 watts. That's why you'll hear a difference in the sound.

Mtry, there are no insane levels with my setup, especially when running digital music such as TWC's Music Choice. You're welcome to stop by and listen for yourself.

I agree with you, that's why I would not recommend using the 3805 to drive all 4 ohms speakers. I was only talking about 2 channel stuff. I have compared my 3805 with my separate amps, an Adcom and a Bryston. In two channel music, the Denon came very close in both Jazz and Classical music. So for those who are not ready to add an external amp, they can relax, enjoy their CD's more, and wait until they are ready. The 3805 can deliver some high current if it only drives 2 speakers.

I almost forgot to mention that when I was shopping for receiver last year I also checked out the Yamaha. In one high end store I was able to AB compared a RX-V2400 to an Anthem preamp/power amp using my own CD's, one classical with lots of dynamics and the other was one of Patricia Barber's. To my surprise, the RX-V2400 held its own against the Anthem. It showed no sign of strain or lack of headroom even at very loud volume. Again, that's just two channel Stereo. I am sure in multi-channel situation the receiver would more readily expose its limit. The speakers used for the demo were the Paradigm Studio 100's. The Studio 100 may not be as power hungry as the big RTi towers, but they are quite demanding too. I thought I should mention this because this thread is more about the Yamaha 2500.

 

[mtrycrafts]

I agree with you, that's why I would not recommend using the 3805 to drive all 4 ohms speakers. .

But remember, while the speaker measures 4 ohms DCR, its actual Z is higher.

 

[mtrycrafts]

.....and once again, next to nothing is accomplished with an attempted discussion that gets technical with meters and scopes being used....most of us can at least keep up, but who really wants to?...

Nothing? No one learns from this??

.....EARS, EARS, EARS, EARS, EARS, EARS....we need to experience products, combine products, tweak products, and then give a report, imo....and.....


Yes, but only if audiophiles would rely only on their ears. They don't. They are not comfortable with that concept, so they also involve their eyes to judge what they hear. How could ones eyes hear?? Interesting trick.

No faces included

 

[mtrycrafts]

Z is the total impedance of the circuit that includes all 3 components. Z is the vector (or phasor, in E.E. terms) sum of the 3 components in any series/parallel combination).

Yes, but speakers have these crossover networks that limits the speakers impact to frequency bands, no? So how would the high frequency driver impact the others outside its frequency band? The high frequency Z would be high to frequencies outside of its crossover bands. The crossover filters are integral part of the system, not bypassed. Not as if you had 3 drivers in parallel with no crossover filtering, right?

And, the vector is the Z and always greater than R unless the phase is 0, no?




I assume Mac measured the resistance of the speaker itself.


Yes, the DCR, from the sound of it.


If you are talking about the influence of the crossover netwrok then it could be a different story.

In a 3 way speaker system, even with this one that can be biamped, you cannot get away from the crossover filters that blocks out of band signals, no current, or miniscule depending on the slope of the crossover.


I have no idea what the value of the overal Z (impedance) of the speaker system that includes the crossover network.

That is the whole issue. That is what the amp sees, a Z value, right?

Please share what you find out from your expert source.
Thanks in advance.

Yes, of course.

 

[MacManNM]

My whole point was to show that biamping them is a much easier load on the amp. I think we can all agree on that. Yes?

 

[mtrycrafts]

To Mac and Peng

My whole point was to show that biamping them is a much easier load on the amp. I think we can all agree on that. Yes?

I received my answer from my trusted friend, Dr Toole's office, passed on my Q to one of his engineers this time

You cannot assume a simple speaker Z that an amp sees, especially a Z that is but a DCR measurement. I am getting further clarification to this though to be sure.
I received a spreadsheet that shows speaker Z for each 1/3 octave and this is what an amp sees in reality, not a simplistic parallel DCR value. The Z in the chart has a low of 5.3ohms at 20Hz, a max of 18.5 at 50Hz, another low of 6.2 at 160Hz and up from there.

What is being calculated is the real Z at each 1/3 octave that each section has, low and high, due to the frequency dependence. At low ferquency the low section has a low impedance and the high section has a high impedance. The parallel calculation of the two section at that frequency is what the amp sees, independent of the impedance at other frequencies.

Now to your point, Mac.

Being easier on an amp is a subjective value. As long as the amp can deliver the power at a specific Z point at a specific volume and acceptable low level of distortion, then this is a moot point. If the amp cannot, then that is what needs to be discussed.
In the final analysis, that published Z for the Polk RTI 12, 8 ohms, is fine as it is a nominal Z only with more bands being closer to it than going below it to the minimum Z at some point.

I have nothing against bi amping, only for the wrong reasons because then there is incomplete information for the choice.

 

[MacManNM]

I received my answer from my trusted friend, Dr Toole's office, passed on my Q to one of his engineers this time

You cannot assume a simple speaker Z that an amp sees, especially a Z that is but a DCR measurement. I am getting further clarification to this though to be sure.
I received a spreadsheet that shows speaker Z for each 1/3 octave and this is what an amp sees in reality, not a simplistic parallel DCR value. The Z in the chart has a low of 5.3ohms at 20Hz, a max of 18.5 at 50Hz, another low of 6.2 at 160Hz and up from there.

What is being calculated is the real Z at each 1/3 octave that each section has, low and high, due to the frequency dependence. At low ferquency the low section has a low impedance and the high section has a high impedance. The parallel calculation of the two section at that frequency is what the amp sees, independent of the impedance at other frequencies.

Now to your point, Mac.

Being easier on an amp is a subjective value. As long as the amp can deliver the power at a specific Z point at a specific volume and acceptable low level of distortion, then this is a moot point. If the amp cannot, then that is what needs to be discussed.
In the final analysis, that published Z for the Polk RTI 12, 8 ohms, is fine as it is a nominal Z only with more bands being closer to it than going below it to the minimum Z at some point.

I have nothing against bi amping, only for the wrong reasons because then there is incomplete information for the choice.

The lowest Z is what the amp is going to have problems with. As I said the Z can't be less than the DCR. These receivers can't drive those loads, so additional help is needed.

 

[PENG]

"In the final analysis, that published Z for the Polk RTI 12, 8 ohms, is fine as it is a nominal Z only with more bands being closer to it than going below it to the minimum Z at some point."

I agree. The DCR of that speaker may be lower than 8 ohms as MacManNM indicated, but that's at 0 Hz. Within the 20 to 20,000 Hz range, its impedance should be closer to 8 ohms most of the time, otherwise Polk Audio should not specify it as an 8 ohm speaker. That said, from my own experience, even the RTi10, can do better with more power. They are definitely power hungry.

 

[mtrycrafts]

The lowest Z is what the amp is going to have problems with. As I said the Z can't be less than the DCR. These receivers can't drive those loads, so additional help is needed.

And where is that lowes Z? Which frequency? Why is it so hard if the frequency is so narrow and the music so dynamic and changing constantly?

You don't get the DCR unless you have zero phaseshift at a certain frequency, hence, everything is above the DCR, right? So, what is there to worry, especially without seeing a Z chart for the speaker spectrum.

 

[mtrycrafts]

I agree. The DCR of that speaker may be lower than 8 ohms as MacManNM indicated, but that's at 0 Hz.

Or, if a frequency happens to eliminate some sort of phaseshift, not likely

Within the 20 to 20,000 Hz range, its impedance should be closer to 8 ohms most of the time, otherwise Polk Audio should not specify it as an 8 ohm speaker.

That would certainly make sense. I called Polk as well as I missed their Z spek at the web page
The person didn't have a Z plot for th ewhole speaker range but the engineering dept may

That said, from my own experience, even the RTi10, can do better with more power. They are definitely power hungry.

If that speaker is rated for 8 ohms, regardless where it dips lower, its sensitivity of 90 dB, published, 10-12 dB for the 4 meter distance to the listening position, 117 dB real output for reference levels, yes, you would need a real dynamic capability indeed. But, this would apply to any speaker then with 90dB spl sensitive, 12 ft listening distance. No ifs about it.

 

[MacManNM]

And where is that lowes Z?

Lowes is on the corner of Juan tabo and Candeliera in Albuquerque

Which frequency? Why is it so hard if the frequency is so narrow and the music so dynamic and changing constantly?

All freq. Amps can drive the upper z without a problem, the lower without, that’s why this is an issue.

You don't get the DCR unless you have zero phaseshift at a certain frequency, hence, everything is above the DCR, right? So, what is there to worry, especially without seeing a Z chart for the speaker spectrum.

Plot it and we’ll discuss it.