Amp selection for RTi10s....Need help

[Methodical]

I’ve been researching and reading threads on the addition of amp(s) to HT systems and got good info but wanted to post specifically for my situation/setup. I need advice on the proper amplication for my situation. I am considering at least a 2 channel amp for my Rti10s. My setup is in my signature. My preference is 50/50 for music/movies. But I’d like to get more from my Polk Rti10s for when I’m playing music. The Denon 3805 has 120w per channel but the towers don’t seem to put out bass to my liking so I am relying on my powered sub to produce the thump. According to some of the reviews I’ve read about the Polk’s, they are suppose to put out some good deep bass. Now either those people don’t know what deep bass is or they are Polk staff writing those reviews because they are not putting out deep bass as of now. That is why I am considering at least a 2-channel amp to run just the Rti10s. I assume the towers won’t match the bass reproduction as my powered sub but I do want more from them, especially when listening to CDs or the Tuner.

During my research, I’ve learned that the following:

1. Behringer A500 is a good amp for the money,
2. That I need to at least double the wattage to increase 3db SPL and quadruple to get 6db SPL, and
3. I need an amp that matches the preamp output of my receiver to get the full potential of the am, which I believe is 1.23v.

My system configuration is below if that helps any. (I’ve played with other settings and like this one so far)

Speakers = Large
Subs = yes
Xover = 120
LFE+Mains

1. The speakers can handle up to 300w so I figure I need at least an amp that can produce at least 240 watts. Am I thinking logically here or am I way off base?
2. Which amp do you think I need to properly drive the Rti10s and get good sound quality out of them?

3. Also how can I fit a equalizer in this equation, if possible?

I appreciate any advice and opinions because I need help here. And some of this stuff is just over my head but I'm learning.

Thanks

 

[PENG]

If you do a search you will find that there are people who believe you need more power than the 3805 can provide in order for the RTi10 to sound their best. While it is a safe bet that more power can do a better job, I learnt from experience that you may or may not hear the anticipated improvement in your own listening environment.

Amplifiers are only part of the equation. There are other more important factors such as the room acoustic environment. I added 200WX2 to my 3805 but the bass did not sound any different so I tried another 300WX2 amp and the results were the same. I then took some measurements and found that at up to 105 dB SPL from 11 ft away, the 3805 was sending the same current to my towers with or without those amps connected. My towers are 2 dB less sensitive than the RTi10 and their impedances are 8 ohms nominal, 4 ohms minimum. To be clear though, my 12X17X8 room is quite small. It might have been a different story if the room was much larger.

The fact is that the 3805 is capable of delivering reasonably high currents to even 4 ohm speakers. How big is your room?

 

[mtrycrafts]

I added 200WX2 to my 3805 but the bass did not sound any different so I tried another 300WX2 amp and the results were the same. I then took some measurements and found that at up to 105 dB SPL from 11 ft away, the 3805 was sending the same current to my towers with or without those amps connected.

If you mentioned in the past, I forgot What kind of signal did you use to measure current, a test signal or music/movie soundtrack? If the latter, does that meter have a peak hold feature? Just curious.

 

[PENG]

If you mentioned in the past, I forgot What kind of signal did you use to measure current, a test signal or music/movie soundtrack? If the latter, does that meter have a peak hold feature? Just curious.

I used two music CDs for the tests, one of them being track one of Telarc's Copland Appalachian Spring at around 2m30s to 2m:50s.

Yes, the meter has peak hold and it can read true RMS. Without referring to the manual I believe it is good for up to 3000 Hz signal. During the tests I was getting between 3 to 4A RMS and peaks in excess of 11A in each channel. The external amps did not yield higher current. At the same SPL the currents were almost identical regardless of whether the external amp was in the loop.

 

[mtrycrafts]

I used two music CDs for the tests, one of them being track one of Telarc's Copland Appalachian Spring at around 2m30s to 2m:50s.

Yes, the meter has peak hold and it can read true RMS. Without referring to the manual I believe it is good for up to 3000 Hz signal. During the tests I was getting between 3 to 4A RMS and peaks in excess of 11A in each channel. The external amps did not yield higher current. At the same SPL the currents were almost identical regardless of whether the external amp was in the loop.

Now I remember, thanks.
When you have the same speaker load attached to different amps, they still have to output a power level to achieve an SPL output. If that spl out is fixed, held the same, then the amps must output the same power. I just don't see it any other way. Thanks.

 

[Methodical]

If you do a search you will find that there are people who believe you need more power than the 3805 can provide in order for the RTi10 to sound their best. While it is a safe bet that more power can do a better job, I learnt from experience that you may or may not hear the anticipated improvement in your own listening environment.

Amplifiers are only part of the equation. There are other more important factors such as the room acoustic environment. I added 200WX2 to my 3805 but the bass did not sound any different so I tried another 300WX2 amp and the results were the same. I then took some measurements and found that at up to 105 dB SPL from 11 ft away, the 3805 was sending the same current to my towers with or without those amps connected. My towers are 2 dB less sensitive than the RTi10 and their impedances are 8 ohms nominal, 4 ohms minimum. To be clear though, my 12X17X8 room is quite small. It might have been a different story if the room was much larger.

The fact is that the 3805 is capable of delivering reasonably high currents to even 4 ohm speakers. How big is your room?

More info: My system is in one part of the basement (22X14x8). The floor is berber carpert with 10lb padding, the ceiling is insulated, the walls are drywalled and painted and there's only one small window in the basement.

I did research this topic and read many threads on this subject prior to submitting this thread and they talked about what you stated. The problem is that the threads tend to go off topic. Now, I am no expert in this area, far from it, but I find it hard to believe that if I put 440w to a speaker that is currently getting upto 120w that there would be no sound difference. For comparison, I installed a very nice stereo system in my car and the head unit puts out 30 watts rms/channel and it sounded ok, but when I put an amp (120w/channel) to those same speakers there's 2 worlds of difference in the sound quality and loudness. Now, I don't have those meters you speak of for measurement but my ears told me that there was a differene in sound quality and the db level. Now, maybe home audio and car audio are not equivalent, not sure, but I don't they would be too far off.

I will read some more of those threads to see if I missed something between the lines though.

 

[MichaelJHuman]

This thread confuses me.

It seems to me that 120 watts/ch should be sufficient to drive those speakers correctly at 105Db. What's their efficiency?

Also, assuming you have an HT setup, most experts seem to reccomend sending from between 200hz to 100hz of the bass to your sub(s) even when your mains can handle that bass. I am curious as to why you have an issue letting your subs do their job?

 

[Methodical]

This thread confuses me.

It seems to me that 120 watts/ch should be sufficient to drive those speakers correctly at 105Db. What's their efficiency?

Also, assuming you have an HT setup, most experts seem to reccomend sending from between 200hz to 100hz of the bass to your sub(s) even when your mains can handle that bass. I am curious as to why you have an issue letting your subs do their job?

What's the confusing part?(I can provided add'l info needed) I just want more out of the front channels than the 120w from the 3805. The efficiency rating is 89db. Yeah, I guess the 120w is sufficient but sufficient is not good enough for me though. I have the Xover set at 120hz that's within the 100-200hz the experts recommend, right. I've read on this forum, other forums and the "experts" recommendations, including the Denon manual that says I should set the xover to 80 hz. Now, I here from you that experts say set the xover between 100-200hz. With all of the xperts recommending different settings, which conflicts one another, I (my ears) decided to be the expert for my xover point, which is 120 and for me this sounds good. It just does not sound that good to me at say 40-80hz. Hell, I even have my xover set above 120hz in my car stereo, just sounds better to me.

 

[Nick250]

I don't know who you think the experts are, but your cross over should be 80Hz on all speakers and they all should be set to small. That is the THX standard and the de facto industry standard. There are exceptions, but your setup is not one of them. A side benefit of this is that it will take a huge load off your receiver.

Nick

 

[wire]

Go to a audio store that allows returns and try a 2 channel amp , try it and return and decide what you want to do . There are a ton of older models out there for a decent price range , some you pay reliabilty ( Bryston , will last for most of your life ) , then you can get Carver for a Cheap price ( but not built like a Bryston , both run clean power and lots of it ) .

Opps kinda off topic
I just hooked my TFM-35 into my 5.1 system , I use it for the Center channel and it replaced a JBL amp bridged into mono . Wow , what a difference in sound , the Carver is alot softer and cleaner sounding amp then the JBL , the JBL seemed sharp and loud . The Carver smooth .

 

[Methodical]

I don't know who you think the experts are, but your cross over should be 80Hz on all speakers and they all should be set to small. That is the THX standard and the de facto industry standard. There are exceptions, but your setup is not one of them. A side benefit of this is that it will take a huge load off your receiver.

Nick

OK I will experiment. As far as experts, I was repeating part of what the previous poster stated. Thanks

 

[PENG]

More info: I installed a very nice stereo system in my car and the head unit puts out 30 watts rms/channel and it sounded ok, but when I put an amp (120w/channel) to those same speakers there's 2 worlds of difference in the sound quality and loudness. Now, I don't have those meters you speak of for measurement but my ears told me that there was a differene in sound quality and the db level. Now, maybe home audio and car audio are not equivalent, not sure, but I don't they would be too far off.

I will read some more of those threads to see if I missed something between the lines though.

It is possible that your 120WPC car stereo sound better not only because it is more powerful but more so because it is of higher quality than the 30WPC one.

I read your post again and noticed that your mains are set to large and you selected LFE+Main. Depending on your room acoustic environment, this configuration could sometimes work against you. For example, since your RTi10 is capable of reproducing substantial bass comparable to that of a subwoofer, you could be getting cancellation effects. To make sure this is not happening you need to use a SPL meter and play a series of tones that can go down to say 20 Hz. You will quickly find out how much, if any bass cancellation you may be getting. You could then solve the problem by moving your sub around until you find a sweet spot. Of course you could go by hearing if you don't care about accuracy and have the time to do it.

 

[Buckeyefan 1]

OK I will experiment. As far as experts, I was repeating part of what the previous poster stated. Thanks

How do your towers sound with the subwoofer turned off, and the Denon powering the two towers without any surround? In other words, all power and frequencies to the front two speakers? Try a cd with a lot of dynamics and punch. This is the only way your RTi10's will see a true 120 watts per channel below audible distortion, assuming you're pushing the Denon to reference levels.

Introducing a center channel and surrounds takes a bit of current away from your demanding towers, and will first limit the bass response before anything else. The 3805 is a great two channel power amp, but IMHO an average surround AVR with demanding surround sound in larger rooms. There's been many Denon owners who've stated the move from the 3 series to the 4 or 5 series is night and day.

Something else you may try is increasing the bass output on the 3805 (bass/treble control), as well as boosting the lowest two frequencies on the graphic built in eq for the front speakers.

I've always found it tough to get the twin 7" woofers moving with the 3805 unless I was driving them hard by themselves at full frequency, or (believe it or not), playing LP's on my ancient Pioneer turn table. You can't beat signal to noise on a turn table.

 

[mtrycrafts]

The efficiency rating is 89db.

Is this from the manual? Unless it is stated that this is the sensitivity in room, it is anechoic sensitivity. In room, you can add 3dB-4dB. With a 100 watt amp, that should output 113 dB of spl continuoulsy.

Adding a 400 watt amp will not make it sound any better at 113 dB spl. However, if the speaker can handle 120 dB spl, then yes, those spl will be presented, amp not clipped.

So, the question is how loud do you listen to the setup as that 100 watts should give you THX reference levels, 105 dB spl, at your listening position.

 

[mtrycrafts]

Now, I am no expert in this area, far from it, but I find it hard to believe that if I put 440w to a speaker that is currently getting upto 120w that there would be no sound difference.

Where are you expecting that sound difference, what spl levels? Which amp is outputting 440 watts into those speakers?
That 120 watt amp will output a certain spl from those speakers. Are you demanding spl levels beyond that amps capability? By a lot?

For comparison, I installed a very nice stereo system in my car and the head unit puts out 30 watts rms/channel and it sounded ok, but when I put an amp (120w/channel) to those same speakers there's 2 worlds of difference in the sound quality and loudness.

Well that would also depend on the comparison methodology and bias perhaps.

 

[Nick250]

It is possible that your 120WPC car stereo sound better not only because it is more powerful but more so because it is of higher quality than the 30WPC one.

I read your post again and noticed that your mains are set to large and you selected LFE+Main. Depending on your room acoustic environment, this configuration could sometimes work against you. For example, since your RTi10 is capable of reproducing substantial bass comparable to that of a subwoofer, you could be getting cancellation effects. To make sure this is not happening you need to use a SPL meter and play a series of tones that can go down to say 20 Hz. You will quickly find out how much, if any bass cancellation you may be getting. You could then solve the problem by moving your sub around until you find a sweet spot. Of course you could go by hearing if you don't care about accuracy and have the time to do it.

Just to add, if the speakers are set to small, LFE+Main and other bass modes are rendered moot on the 3805. All bass below the crossover point goes to the sub regardless of the bass mode setting and you can not alter that. This is sometimes misunderstood.

Nick

 

[Methodical]

How do your towers sound with the subwoofer turned off, and the Denon powering the two towers without any surround? In other words, all power and frequencies to the front two speakers? Try a cd with a lot of dynamics and punch. This is the only way your RTi10's will see a true 120 watts per channel below audible distortion, assuming you're pushing the Denon to reference levels.

No I have not played the twin towers without the surrounds. I will experiment to see what it sounds like. Question. If I select small for the twin towers how will that affect them when playing in 2 channel mode (i.e. listening to the tuner or cd player). Will I be losing some of the lower frequencies or will it go down to the crossover point (I set it back to 80hz based on responses here). Or will I have to set it to large everytime I play cds or listen to the radio.

Introducing a center channel and surrounds takes a bit of current away from your demanding towers, and will first limit the bass response before anything else. The 3805 is a great two channel power amp, but IMHO an average surround AVR with demanding surround sound in larger rooms. There's been many Denon owners who've stated the move from the 3 series to the 4 or 5 series is night and day.

I figured that was happening that is one of the reasons why I want a separate 2-channel amp(s) for the twin towers to relieve the 3805 and allow it to just focus on the surrounds. Also, I may possibly get an amp just for the center channel (just thinking out loud right now)

Something else you may try is increasing the bass output on the 3805 (bass/treble control), as well as boosting the lowest two frequencies on the graphic built in eq for the front speakers.

I've increased the frequencies in the eq setting. The 1st thing I did. I reset all speakers to small to experiment with them that way.

I've always found it tough to get the twin 7" woofers moving with the 3805 unless I was driving them hard by themselves at full frequency, or (believe it or not), playing LP's on my ancient Pioneer turn table. You can't beat signal to noise on a turn table.

What is a SPL meter and where can I get one. I see SPL all the time but don't know the meaning of it.

Thanks fellas. I am learning the home audio stuff as I am more in tune with car audio now.

 

[PENG]

What is a SPL meter and where can I get one. I see SPL all the time but don't know the meaning of it.

Thanks fellas. I am learning the home audio stuff as I am more in tune with car audio now.

You can buy a SPL (Sound Pressure Level) meter here:
http://www.radioshack.com/sm-digital-display-sound-level-meter--pi-2103667.html

You should be able to get one with the generally preferred analog display. I still think you should try and set your mains (RTI10) to small XO at 80 Hz as Nick suggested, with the subwoofer on. Then you can set the mains back to large and see if you get more bass (assuming you are still on LFE+MAIN). If you don't, then for sure some of the bass frequencies of the RTi10's 7.5" woofers and the subwoofer are cancelling each other due to the phase differences of the low frequency signals between the towers and the sub. During such tests, especially when you are not using a SPL meter, make sure you use the same bass heavy material and set the volume at a fixed position, e.g. -15 dB.

If you are in fact getting bass cancellation, you can reduce the effect by either moving the subwoofer around until you hear significantly more bass, or setting the mains to small with the sub on for H.T. and to large with the sub off for music. Bass cancellation is only significant (audible) in low frequency signals.

Some subwoofers actually allow you to vary, or reverse the phase, i.e. 180 degrees.

 

[Methodical]

You can buy a SPL (Sound Pressure Level) meter here:
http://www.radioshack.com/sm-digital-display-sound-level-meter--pi-2103667.html

You should be able to get one with the generally preferred analog display. I still think you should try and set your mains (RTI10) to small XO at 80 Hz as Nick suggested, with the subwoofer on. Then you can set the mains back to large and see if you get more bass (assuming you are still on LFE+MAIN). If you don't, then for sure some of the bass frequencies of the RTi10's 7.5" woofers and the subwoofer are cancelling each other due to the phase differences of the low frequency signals between the towers and the sub. During such tests, especially when you are not using a SPL meter, make sure you use the same bass heavy material and set the volume at a fixed position, e.g. -15 dB.

If you are in fact getting bass cancellation, you can reduce the effect by either moving the subwoofer around until you hear significantly more bass, or setting the mains to small with the sub on for H.T. and to large with the sub off for music. Bass cancellation is only significant (audible) in low frequency signals.

Some subwoofers actually allow you to vary, or reverse the phase, i.e. 180 degrees.

Peng I already reset my the XO to 80 and speakers to small and yes my powered sub does allow phase switching. I have tried it on both 0 and 180 and notice some changes. I will need to do more experimentations as you've suggested though.

But to make sure I am clear, the powered subwoofers thumps without issue, it's the twin towers that does not thump to my liking. Again, I will have to experiment though.

Thanks

 

[PENG]

But to make sure I am clear, the powered subwoofers thumps without issue, it's the twin towers that does not thump to my liking. Again, I will have to experiment though.
Thanks

Okay, I know you are clear, but let's try to be even clearer. If I understood correctly you are saying:

1) The towers are now set to small.
2) XO at 80 Hz
3) The phase switch pos. does make a difference.

If you can hear a difference by flipping the phase switch with XO at 80 Hz, you are getting bass cancellation. The cancellation effect will be much more audible if you had the mains set to large because the mains will then be getting full range, i.e. down to 20 Hz and below. Since the RTi10 can reproduce 20 Hz, it will cancel the subwoofer's bass if the signals are not in phase.

Two questions:

1) Have you tried setting the mains to large, and flip the 505's phase switch back and forth and see if you could hear a difference?

2) How did the towers sound if you set the mains to large, or listen in pure direct mode, with the 505 power turn off completely.

The thing is, my Veritas are less efficient than your RTi's, and I have no problem with bass when using the 3805 on its own. The 3805 is not as powerful as a 150WPC power amplifier but it should have no trouble driving a pair of RTi10, especially in two channel music.

One more thing to check, make sure you L&R channels are connected in phase. That is, from the amp output to the speaker terminals, red to red, black to black, for both L&R channels. If not, you will get bass cancellation between the two tower speakers. Good luck!