Does this Rotel RB-985 amp has enough power to move a one pair of: AR 3a + two pairs of Ar 2ax

[Guest shafan4]

Does this Rotel amp has enough power to move one pair of: AR 3a + two pairs of Ar 2ax ?

The Power amp I'm talking about is a Rotel RB-985 a five channel amplifier.

Here are it's specs:

"Five channels of amplification, THX certified, 100 watts rms output per channel at 8 Ohms, Frequency response 10 Hz - 80 kHz plus or minus 0.5 dB, harmonic distortion less than 0.03%, input impedance 27 kOhm, damping factor 180, size 5 1/2"H x 17 3/8"W x 15 5/8"D, weight

34 pounds. Black metal chassis, non-grounded AC plug"

I have a home theater system:

Main Speakers: AR 3a

Center Speaker: AR 2ax

Rear Speakers AR 2ax

I want to add a 5 channel power amp. I ran across the Rotel RB-985. I can't audio test it at my home only after I purchase it. I wanted to know whether the amp will open up the speakers (could it be enough for the Ar-2ax but not for the AR-3a) or should I aim for an amplifier that rated more than 100 watts rms output per channel.

If anyone have recommendation about this amp or a diffrent one I would be happy to hear from.

Thanks in advance to anyone who helps

[Steve F]

I have used many Rotel products over the years and they're usually excellent. The 985 is a fine amplifier.

The big question (aside from the usual questions about the size and acoustics of your listening room, your personal preferences for loudness levels, etc.) is whether or not you're going to be using an outboard powered subwoofer or not.

If you are using a sub, then your pre-amp/processor will high-pass your AR's at 80Hz (or some other frequency of your choosing, if your pre-pro has an adjustable HP/LP section). This means that the 985 will only have to deal with 80Hz on up, which is pretty light duty. I wouldn't expect the Rotel to have much problem driving two 3a's and three 2ax's from the mid-bass on up.

On the other hand, if you're using the AR's full range, then you might be stretching the 985 a little thin, especially in a large room at high levels.

There are a whole host of reasons (I can refer you to some past posts of mine if you're really interested) why you'd probably be better off using a really good outboard powered sub with your five AR's, in which case the 985 will undoubtedly prove to be a good choice.

Steve F.

[Guest shafan4]

Hi Steve !

Thanks for the help

The measurements of the room are: width:17 and length: 20.

The setup is

Speakers:

pair of AR-2ax

pair of AR-3a

one AR-2ax

Subwoofer a Definitive 15"

all connected to a Reciver: Yamaha rx-v 1000

I like to hear in loud levels

I'm planing too use the Yamaha as a pre-amp/processor.

all of the speakers are in full range mode and the yamaha is set so the LFE/BASS OUT mode too speakers + Subwoofer ( all frequency 90 Hz and below are directed to the speakers and the subwoofer.

I can't adjust the HP/LP.

so should I start looking for a much powerfull 5 channel amplifier ?

somthing like 150/200/300/????/watts rms output

one more thing the AR-2ax is 8 Ohms and the AR-3a is 4 Ohms. the rotel is a 8 Ohms in all channels would that be a problem ?

[Steve F]

Many AR aficionados want to use Classic AR speakers for Home Theater, probably because they want to have that "tight, accurate" AR bass in their HT systems. While that is certainly understandable, bear this in mind (reprinted from a post of mine in May of 2005):

"A few additional things to keep in mind regarding Home Theater in general, whether using AR speakers or any other brand:

The LFE channel (Low Frequency Effects) does indeed contain different bass information than the regular front channels. Even if the L/R speakers are selected as “Large,” they will be sent full-range material, such as music, that is different than the material contained on the LFE (the “.1”) channel. The LFE channel usually contains the explosions, crashes, earthquakes, etc. effects that are different than the normal soundtrack.

Now, when you select “Subwoofer—Yes, LR speakers-Small” from your set-up menu, most receivers/processors gather up ALL the bass below 80Hz (or whatever electronic crossover frequency you’ve selected, if yours is selectable) from the LCR, surround, AND the LFE channels and then routes it to the “.1” subwoofer output. Therefore, the bass coming from your sub output (assuming you’ve selected “L/R speakers—Small”) is a combination of the 45Hz music tones in the LCR channels and the 22Hz warp engine rumblings on the LFE track.

Two things happen when you select “Subwoofer—No” from your set-up menu. First, you lose the ability to control (via the receiver’s or processor’s remote control) the LFE/Sub level from the convenience of your listening chair. One of the best things about using a powered sub is that your receiver’s remote lets you raise or lower the sub level remotely from your seat, while the program is playing. Very handy.

The other thing that happens when you select “Subwoofer—No” is that on Dolby Digital DVD’s, the LFE channel is folded back into the L/R channel signal, at a –10dB level compared to what it would have been on the separate “.1” channel. Dolby’s rationale for this was that when using regular speakers (no subwoofer), the LFE level should be reduced so as not to damage non-subwoofer speakers, but still present nonetheless (at a –10dB level) so you don’t miss any content.

As far as HT requirements for low-frequency extension are concerned, THX’s manufacturer’s requirements originally called for a response of –3dB at 35Hz with a 12dB/oct rolloff below that. Coincidentally, this is exactly the response of the AR 12”-woofer bookshelf models. However, THX’s requirement is for 105dB at the listening position (which can easily be 10-15 feet away from the physical location of the sub—do your inverse-square law SPL calculations!) in a 3000 cu. ft. room (pretty darn large—25 x 15 x 8’) without objectionable audible distortion. That’s a VERY stringent requirement, and a tall order for a pair of 3a’s or 11’s. THX’s latest “Ultra 2” standard calls for –3dB at 25Hz in a 6000 cu. ft. room, under the same distance and distortion conditions. I’m presenting the THX standards as an objective reference of performance level, not to be construed as an endorsement of THX one way or the other. However, this is representative of how loud some people expect their HT system to play.

Bear in mind that the AR-3, 3a, 11, 10 Pi, and 9 woofers were designed to reproduce the lowest musical notes on commercially-available recordings of the day (vinyl LP’s), at SPLs that were logical to expect at the time (about 100dB max. in a normal-sized living room). While these products can be used in HT systems with very good results, they are ‘70’s-era musical reproducers first, and slam-bang special effects reproducers second. Unless you have some overwhelming desire to keep Bill Miller very busy while making UPS even richer, I’d exercise a sane amount of caution and common sense when using 40-year-old classic speakers to play exploding Death Stars at deafening levels."

In your HT situation, I'd select the LR, C, and Surround speakers as "Small," and let your Definitive sub handle the bass chores, especially in a 17 x 20 room at loud levels. HT is one thing; accurate music reproduction is another thing altogether. You can always re-set your pre-pro's bass management when using your AR's to listen to music. It just doesn't make any sense to beat a 35-year-old 3a to death at 30Hz-105dB levels to listen to Arnold crash his truck into the bridge.

Steve F.

[dynaco_dan]

Excellent write-up Steve, thank you.