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My experience with RS-4.5s and biamping (long)

kmanusa

kmanusa

AK Subscriber
Subscriber
I've had my RS-4.5s for several months now and have used them in various configurations. I still believe this is an outstanding speaker. I'd like to pass along my experience with biamping since it would appear to be at odds with what others have reported here on AK.

I have biamped my 4.5s with various combinations of the following SS amps:

McIntosh 2205
McIntosh 7270
Bryston 4B-ST
SAE A-201
SAE 2401
Adcom GFA-555

I have used the Infinity external crossover, Bryston 10B Sub crossover, and Marchand XM-26 tube crossover. In addition, I have passively biamped as well using a single amp to power the 4.5s.

My experience boils down to this: if the amp is powerful enough, I prefer using a single amp with these speakers. I am still experimenting but for now I prefer using the SAE 2401 full range to any of the bi-amp combos I have on hand.

I have tried identical Adcom GFA-555s for top and bottom. I have not yet tried using a tube amp on the top as some suggest. But, my experience generally has been that biamping tends to make the speaker sound slightly discontinuous, even with identical amps top and bottom. Perhaps my external crossovers are to blame. I have tried 6, 12, 18, and 24 dB/octave slopes in the external crossovers as well as various crossover frequencies.

This is a speaker that can occasionaly sound a little thin in the lower mids. Male voices for example, don't always have the weight they do on other speakers I have used. No amount of adjusting the crossovers in biamped configurations has affected this perception. Still, I am not sure the speaker is at fault and the pink noise measurements I have made show no suckout in the lower mids, biamped or single amp.

I know many folks here prefer to biamp these speakers. One possible explanation for my preference is that I can't really push the 4.5s too much in my present domestic setup. Also, my room is only medium size and does not require huge power to fill-up with sound. The SAE 2401, in particular, has no trouble driving the Watkins woofers of the 4.5s in a full range set-up.

I also feel that biamping these speakers does not take full advantage of all that biamping can offer. This is because the passive crossover components remain in the loop and the external crossover is added to set the crossover point between EMIMs and woofers. In classic biamping, you would remove the passive crossover and power the speaker drivers directly, thereby eliminating the need for the amps to drive the large caps and inductors in the passive crossover. By the way, my 4.5s use what I believe is the last revision to the passive crossover.

For now this has been my experience. I wonder if any of the other 4.5 users have had similar experience with their systems?
 
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People tend to forget that what sounds good to one person doesn't necessarily sound good to another. I am not as technical as most of you "smarties" here (I mean that in a good way) but I know what I like to hear. I felt that biamping my 4.5's would be the way to go but may not be so sure now. I have biamped my 2.5's and the RSIIb's I had as well. Both horizontally and vertically (thanks to info from here). The amps I have used are as follows:

Kenwood Basic M2, Carver TFM-45 (2), Aragon 4004 (2), Parasound 2205A, Parasound 3500 and 2 Manley 120w tube monoblocks. Right now I have the Parasound 3500 powering the lows and the tube monoblocks for the mids and highs. So you could say I am running a hybrid bi-amp setup.

How each amp performed with the 4.5's was more the factor than how the 4.5's sound. To some extent an amp would perform differently in a horizontal setup than a vertical one.
Here's what I believe - regardless of the setup type, single or bi-amp, that if you get the right power source you maximize the potential of your speakers, for your ears. I have never heard bass from the 4.5's like I now hear with them being powered by the 3500.

You may not ever get the correct transition from lows to mids because that just might be an inherent characteristic of the speaker. Reviews of this speaker note that fact. I don't know if removing the passive crossover of the speaker from the signal path would correct that "dysfunction" because it might just be a characteristic of the EMIMs. It would be interesting to know if this is possible - not only removing the passive crossover from the path but whether the speaker components are capable of "fixing" this problem.

I think alot of the fun (curiosity) here is trying different setups and getting opinions from others as regards to what other possibilities lie out there. Thank you for sharing your opinion.

I am going to try the Parasound 3500, single amp, to run both speakers fully. I have a feeling it will perform well. Might have some tube amps for sale soon.

One note for me - as far as one single improvement goes for making a big difference - going from run of the mill $25 speaker cable to higher end cable. Wow, that opened the speakers up!
 
I've a pair of RS2.5s which are very similar albeit lesser speakers with fewer drivers and no external factory crossover.

I've tried a couple bi-amp combinations and share your opinion - one good and big amp sounds best. My Sony TA-N80ES is good enough although I have been daydreaming of a pair of 500 wpc monoblocks instead.

I've used an op-amp-based external crossover too (24 dB slope) and found the op-amp artifacts nullify any advantages.

There remains the discontinuity between the dynamic woofers and the ribbon mids. My mods to the insides of the woofer box and spikes helped a bit but there is a residual.

The internal crossover is rather complex and I think there are different slopes between the drivers.
 
"People tend to forget that what sounds good to one person doesn't necessarily sound good to another."

Absolutely!

"I think alot of the fun (curiosity) here is trying different setups and getting opinions from others as regards to what other possibilities lie out there."

I agree!

"I am going to try the Parasound 3500, single amp, to run both speakers fully. I have a feeling it will perform well."

It can't hurt to try, you can always go back!

"One note for me - as far as one single improvement goes for making a big difference - going from run of the mill $25 speaker cable to higher end cable. Wow, that opened the speakers up!"

The 4.5s are very revealing, aren't they! Also, with their low impedance in the bass, cable resistance might become a factor.

Make sure your connectors are in good shape too. When I opened up one of my Adcom amps to replace the on/off switch, I noticed the RCA input jacks were cracked (they are mostly made of plastic)!
 
There was mention of this bass-lower midrange discontinuity in the original Stereophile and TAS reviews which can be found at

http://www.infinity-forum.de/rs_4_5.html

I don't know if you can completely fix this problem as it is an issue when trying to mate a monopole speaker with a dipole speaker. It's a compromise which Infinity chose to make in order to improve other aspects of the system. You'll find the same issues with the bigger IRS system.

I am interested in this myself because I am looking at buying a pair of these ;)
 
Whitehall said:
The internal crossover is rather complex and I think there are different slopes between the drivers.
Click to expand...

I agree, the 4.5 is similar. I find it interesting that the EMIM to woofer passive crossover in the 4.5 appears to be second order but Infinity used first order crossovers in their external processor.
 
rabbit said:
There was mention of this bass-lower midrange discontinuity in the original Stereophile and TAS reviews which can be found at

http://www.infinity-forum.de/rs_4_5.html

I don't know if you can completely fix this problem as it is an issue when trying to mate a monopole speaker with a dipole speaker. It's a compromise which Infinity chose to make in order to improve other aspects of the system. You'll find the same issues with the bigger IRS system.

I am interested in this myself because I am looking at buying a pair of these ;)
Click to expand...

I don't mean to over-emphasize the discontinuity issue, it is not a showstopper for me and I still think this is the best speaker I have ever owned!

I hope you get a chance to hear the speaker, it can sound superb. Unfortunately, there were so few made!
 
In mine I also feel there is more to be had then what I am getting from the speaker.
The Passive Xovers in mine are the very first version no revs at all.
I do not have the active crossover I used the one from my RSIIbs with mixed results.
I have tried it without an Active Xover also.
I have thought of going with a TriAmp configuration using a Beringer Active Crossover.
In this mode I would leave the LC network in the woofer circuit for the dual voice coils I think this is a must because of the design of the Watkins woofer.
Never tried this but I feel this would allow for the maximum settings of the Xover points.
Another thing I wonder about is the foam on the front it seems to almost be to absorbent and it attenuates the mids.

I to have a smaller room with 8 foot ceilings I am thinking the room mode also
is coming into play.

Hard thing is they are big and moving them and the amps furniture etc around is a weekend project.

Still the best pair of speakers I own and yes they do reproduce the good and the bad. (Sh&t in Sh&t out)
 
kmanusa said:
My experience boils down to this: if the amp is powerful enough, I prefer using a single amp with these speakers. I am still experimenting but for now I prefer using the SAE 2401 full range to any of the bi-amp combos I have on hand.
Click to expand...


I've come to the same conclusion with my Infinity Quantum-2's. I'm driving them with a Yamaha MX-10000 amp.
 
Has anybody tried putting the acoustic foam on the back of the midrange/tweeter baffle as well as on the front ??
 
rabbit said:
Has anybody tried putting the acoustic foam on the back of the midrange/tweeter baffle as well as on the front ??
Click to expand...

Interesting, someone mentioned doing that in one of the reviews from years ago I think. It might have an interesting effect since the back has fairly deep side panels and there might be some kind of "cavity resonance" formed by this construction.

It looks like a previous owner re-did my front foam, someone here pointed that out when I posted the pix. My foam is real thick in the front and I sometimes wonder about whether it is too thick and whether the original stuff so deep.
 
kmanusa said:
I've had my RS-4.5s for several months now and have used them in various configurations. I still believe this is an outstanding speaker. I'd like to pass along my experience with biamping since it would appear to be at odds with what others have reported here on AK.

I have biamped my 4.5s with various combinations of the following SS amps:

McIntosh 2205
McIntosh 7270
Bryston 4B-ST
SAE A-201
SAE 2401
Adcom GFA-555

I have used the Infinity external crossover, Bryston 10B Sub crossover, and Marchand XM-26 tube crossover. In addition, I have passively biamped as well using a single amp to power the 4.5s.

My experience boils down to this: if the amp is powerful enough, I prefer using a single amp with these speakers. I am still experimenting but for now I prefer using the SAE 2401 full range to any of the bi-amp combos I have on hand.

I have tried identical Adcom GFA-555s for top and bottom. I have not yet tried using a tube amp on the top as some suggest. But, my experience generally has been that biamping tends to make the speaker sound slightly discontinuous, even with identical amps top and bottom. Perhaps my external crossovers are to blame. I have tried 6, 12, 18, and 24 dB/octave slopes in the external crossovers as well as various crossover frequencies.

This is a speaker that can occasionaly sound a little thin in the lower mids. Male voices for example, don't always have the weight they do on other speakers I have used. No amount of adjusting the crossovers in biamped configurations has affected this perception. Still, I am not sure the speaker is at fault and the pink noise measurements I have made show no suckout in the lower mids, biamped or single amp.

I know many folks here prefer to biamp these speakers. One possible explanation for my preference is that I can't really push the 4.5s too much in my present domestic setup. Also, my room is only medium size and does not require huge power to fill-up with sound. The SAE 2401, in particular, has no trouble driving the Watkins woofers of the 4.5s in a full range set-up.

I also feel that biamping these speakers does not take full advantage of all that biamping can offer. This is because the passive crossover components remain in the loop and the external crossover is added to set the crossover point between EMIMs and woofers. In classic biamping, you would remove the passive crossover and power the speaker drivers directly, thereby eliminating the need for the amps to drive the large caps and inductors in the passive crossover. By the way, my 4.5s use what I believe is the last revision to the passive crossover.

For now this has been my experience. I wonder if any of the other 4.5 users have had similar experience with their systems?
Click to expand...

I know it isn't easy to try and audition, but these things sound about 25% better w/ tubes on the midrange when bi-amped. SS works very well for the bass.

You also need the big wattage tube amps and nobody exactly gives them away. But the same principal applies to these Infinites as with other electrostactic or ribbon speakers where that tube matchupis a thing of beauty. The maggies/apogee/even old accoustats all get that magic from tubes. Once you've heard that magic tho, there's no turning back. It'd be like reaching back into the toilet > you've finished.

Tube monoblocks are even better but the costs are considerably higher than
the speaker investment. See if there is a way you can try and audition some high end tube amps like audio research or CJ (what Nudell used) and then listen to them.
 
robertk said:
I know it isn't easy to try and audition, but these things sound about 25% better w/ tubes on the midrange when bi-amped. SS works very well for the bass.

You also need the big wattage tube amps and nobody exactly gives them away. But the same principal applies to these Infinites as with other electrostactic or ribbon speakers where that tube matchupis a thing of beauty. The maggies/apogee/even old accoustats all get that magic from tubes. Once you've heard that magic tho, there's no turning back. It'd be like reaching back into the toilet > you've finished.

Tube monoblocks are even better but the costs are considerably higher than
the speaker investment. See if there is a way you can try and audition some high end tube amps like audio research or CJ (what Nudell used) and then listen to them.
Click to expand...

I do have a Melos 200 Triode Plus amp which I have been trying to fix up. I have not used it with the Infinity's although I did use it for a while with my Martin Logan CLS. It was a nice sounding amp on the MLs but I had problems with tubes and caps failing.

I have since got the thing back up and running (I think!) and that will be my next attempt at biamping using the Melos.
 
Dredging up history here...

As at least Kman knows, I'm now running his 4.5's as my mains :yes: Bi-amping with tubes aside, I have to agree that single amping works awfully well with these guys/gals. Balance seems very good overall as-is, except for perhaps that (pretty) slight thinness in the midrange/midbass that's been mentioned many times. I tried active bi-amping at the Fest with a Yamaha M-2 and Classe CA-400 and compared to single amping with the Classe - the top end seemed just a bit harsher with the crossover in-line, but otherwise it was somewhat of a toss-up. Nice to be able to adjust the crossover point "fill" and the bass gain, but did I really need that in the first place?

At home now I'm listening to the PC5002M, which is a bit more "exact" than the Classe and slightly leaner in the bass - a very nice match with the rest of my electronics. I also swapped in some OCC interconnects that seem to be working some strange but wonderful black magic. In fact, I like the sound so much that I'm going to rebuild the single-amp version of the crossover on the spare crossover chassis Keith included with the purchase (with point-to-point wiring and bypassing most of the switches).

I will try bi-amping again when I get the B-1 and BX-1's back, but I honestly don't feel like I'm missing anything (an overused phrase, I know). I haven't tried passive biamping yet either - that might be interesting with the B-1 since it's got plenty of power.
 
Chris-- you might also try biamping with something other than the Infinity crossover. I tried the Marchand XM9 and XM26 (tube). The Marchands use plug-in boards to fix the crossover frequency. Both feature 24 dB octave Linkwitz Riley crossover slopes (the 26 can do other slopes too). I ended up using 24 dB octave slopes at 220 Hz in my room.

The Infinity only uses 6 dB octave slopes which, because of their broad overlap region, can add a bit of thickness to the bass that may not be a benefit in some rooms.

I still think that single amp mode is the easiest way to get good sound with these speakers; my smallish room was a tough challenge for these speakers and, in the end, I had to biamp just get reduce the bass level. But, in the right room, all you need is a single amp with lotsa power!
 
Just an observation (not a disagreement), but it seems like most of the people in the Infinity forum (not just this thread) who prefer a single amp over biamping are mixing and matching their amps. I suspect part of the issue they have over biamping may arise from this.

When you have two non-identical amps, you get into issues of gain differences, different amp topologies and voicings, output impedances, etc. When using a single amp, that doesn't arise. Personally, I biamp everything, but always with amps that are either identical or higher/lower powered amps from the exact same amp family with identical designs (eg, SAE A301/A501).

Again, just an observation, but I wonder if using significantly different amps for the highs and the lows doesn't create some of the issues people experience with biamping.

David
 
This is a very good point. I also Biamp and use similar amps which have the ability to adjust the volume individually per channel.
 
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