Brain Teaser: Biamp or biwire w/limited rack space

Woops! Sorry about the redundant posts. I thought my earlier one had gotten flushed when I did a system reset.

08-20-08: Shadorne
110 db spl clean from a 5.5" woofer is rather a lot (assuming you sit 6 feet back) - are these pro type drivers and have you measured this? Very impressive!

I didn't measure; I was extrapolating the OMD-15's sensitivity of 91dB @ 1w input at 1KHz, doubling the power for every 3dB increment until the 70wpc Amber runs out of headroom.

The 5.5" drivers in this ARE special, though. They use a patented ribbed elliptical surround that Mirage developed for their subwoofers to maintain longer excursions without losing linearity. To me, a 5.5" woofer usually means "farty" when pushed, but that's not the case with these.

It's not a single 5.5" handling the bass. It's a 2-1/2 way system, and below 900 Hz there are two active 5.5" woofers in separately sealed chambers; the upper one is reinforced with a passive radiator, the lower one is in a much larger chamber and reinforced with a slot-loaded down-firing port.

Subjectively it works beyond my expectations. This is the highest quality bass I have ever had in my home, and I've seldom heard better in demos. The bass is clean, full, and articulate down to about 32Hz in-room, and these speakers easily sort out all types of bass sources--free-air microphone, transducer, flatwound or roundwound strings, synth, organ pedal tones, tympani, bass drum, gong fundamentals, etc. Most engaging is how they convey musical communication between bassists and the rest of the band or combo, interactions between bass and guitar, bass and left hand figures of a 9' concert grand piano, etc.

These little guys have better quality bass with their 5.5" drivers in a 35-lb. enclosure, driven by a 70wpc amp than my Mirage M5si's, which are 51" tall, weigh 85 lbs. ea. with two 6.5" woofers and 4" dia. ports biamped with a dedicated high current 200 wpc for the woofers.

08-20-08: Shadorne
110 db spl clean from a 5.5" woofer is rather a lot (assuming you sit 6 feet back) - are these pro type drivers and have you measured this? Very impressive!

Are these drivers special? Yes. Have I measured? No. This was just an extrapolation, starting at the OMD-15's sensitivity rating of 91dB at 1w input and doubling the power for every 3dB increment until the Amber runs out of headroom. Mirage rates the power handling at 250w. Does this mean it can put out a clean 115 dB @ 1KHz at 1 meter? Probably not, but I feel safer with a speaker with a 250w max rating than an 80w one.

However, I will say that subjectively the bass performance on these speakers is outstanding. It's a 2-1/2 way system, so it's not just a single 5.5" driver handling the bass. When this loudspeaker dishes out with deep bass, it has 2 active 5.5" drivers in separate chambers, one reinforced by a passive radiator and the other by a slot-loaded down-firing port.

Furthermore, these drivers used a special patented "ribbed elliptical" surround originally developed for their powered subwoofers, that is said to maintain linearity while enabling more extreme excursions.

Does it work? I can't measure its excursion vs. linearity, but this 5.5" driver-based system offers up the most effortless, taut, clean, and extended bass I've ever heard from 5.5" drivers. The OMD-15 excels at revealing the nature and quality of the bass you're hearing. It's easy to identify if an upright bass in jazz was recorded with a mic or a contact transducer, whether Charlie Haden should have changed his strings that day, distinguishing tympani from bass drum in large scale orchestral crescendos, organ pedal tones, synth tones, round wound vs. flat wounds on an electric bass--you name it, the OMD-15 reveals it.

It's also particularly good at sorting out melodies and chords and interactions in the bass. I've played several recordings featuring outstanding bassists (Jaco Pastorius, Charlie Haden, Neils Orsted-Henning Pedersen, Ray Brown, etc.) and I get a greater sense of the bassist interacting with the rest of the musicians than before. This also holds true for what it does with left hand chords and bass lines on a 9' concert grand piano.

They play down to about 32 Hz, which is plenty for any music I throw at 'em. I couldn't believe how they fleshed out the big bass drum and gong (which has a low fundamental) on a CD of Copland's "Fanfare for the Common Man."

And it's doing all this powered by this 70 wpc Amber Series 70 amp I was afraid wouldn't do the job.

The OMD-15s are 91dB sensitive, which means that the Amber Series 70 amp should power them cleanly to 110dB and peaks to maybe 113.

110 db spl clean from a 5.5" woofer is rather a lot (assuming you sit 6 feet back) - are these pro type drivers and have you measured this? Very impressive!

07-07-08: Markphd
I have gone through bi-wiring, passive bi-amping and active-biamping with my equipment, which was designed to be upgraded in this way. Based on my experience, and on what you said, here are my somewhat rambling thoughts.

... However, before you start spending money, make sure that your present amp is not up to the job. The Mirage speakers are quite efficient, and 70 watts is within their recommended range.

Anyway, make sure you need more power before you open your wallet.

Ding ding ding! Well, we have a winner and I'm responding to and bumping this thread to thank Kal (kr4) and Markphd for some great advice.

When I ordered the OMD-15s, I thought they would have the same voracious appetite for power as my old M5si's. Turned out not to be the case. The OMD-15s are 91dB sensitive, which means that the Amber Series 70 amp should power them cleanly to 110dB and peaks to maybe 113. I've never had speakers this efficient before, and it sure is fun getting used to. The speakers have an effortless, open sound and have tightly controlled extended bass that used to take anvil-weight amplifiers to achieve. These little guys merrily sail along on this 70 wpc amp in a vaulted ceiling, open architecture living room, no less.

In the meantime, I was trying too hard. I biamped them using the Amber for the woofers and a 45 wpc Paraound Zamp v2. for the mid/tweets. Then today I got the urge to swap things around and experiment, and tried the Amber by itself, leaving the Mirages bi-wired. Holy moly! When bi-amping, make sure the two amps have not only the same sensitivity but a the same amount of resolution. The Parasound couldn't keep up.

When the Amber took over all the duties, everything bloomed. The soundstage got deeper, wider, and airier. There was clearly more resolution in the midrange on up. Vocals and even acoustic plucked strings had more sense of the notes forming, blooming, and then decaying.

I do have a 150 wpc amp in the shop. It's a VSP Labs Trans MOS and those things are deceptively musical and resolving. They are also bass control monsters. When I get it back, we'll see if swapping it in permanently is warranted.

In the meantime, this modest little Amber, which I picked up for $379 NOS at a former dealer, refuses to get replaced. I think (unless the VSP can supplant it), I'd have to spend a whole lot of money to get a decidedly better sound than this Amber gives. It's amazingly neutral, yet is anything but sterile. Anything run through it is musically engaging.

This amp is a perfect example of those 70 wpc amps that used one pair of transistors per side. They're magic, and when designers add more output devices to increase output, they often lose some of that magic. The B&K ST-140 comes to mind.

Sometimes less is more.

I have gone through bi-wiring, passive bi-amping and active-biamping with my equipment, which was designed to be upgraded in this way. Based on my experience, and on what you said, here are my somewhat rambling thoughts.

You state that you want more power for bass as you will not have a sub. Bi-wiring has nothing to do with this. Bi-amping or single amping with a bigger amp will do what you want.

However, before you start spending money, make sure that your present amp is not up to the job. The Mirage speakers are quite efficient, and 70 watts is within their recommended range. You may find that they are fine and you don't need to spend anything. You can save your money for some other upgrade in the future ..... or buy your wife something. Think of the sports analogy of trading a player for "future considerations". Or maybe you can buy a nice looking new rack with high WAF ..... and more rack space for those future considerations.

Anyway, make sure you need more power before you open yuor wallet.

If you do want to upgrade, bi-wiring doesn't give you more power. It simply helps to separate the high and low frequencies a little bit. So it's not your current objective. But, I have found that bi-wiring is a cost effective upgrade if you use modest cables. And I have found bi-wiring to be effective in my system with very inexpensive cables. It produced a slight, but noticeable, increase in clarity. So, I think bi-wiring is worth doing, even though it's not your primary objective. And you can do it with any amps you use. It doesn't have to be only with the amp in your second option.

Next step up is bi-amping. If your speakers need the extra power, and you haven't determined that with certainty yet, then bi-amping is an option. But then again, so is single amping with a better amp (bi-wired or not). A good single amp is better than two poor amps in bi-amping configuration. Personally, I have not found passive bi-amping to be a cost effective upgrade if you don't really need the extra power. I only recommend it as an intermediary step to active bi-amping. Now that's an upgrade!

So, in conclusion, don't spend on another amp until you are sure you need more power. Save for a more significant upgrade.

In any event, bi-wire. It's cheap and easy to do and should produce an improvement.

If you need more power, and funds are limited, consider single amping rather than bi-amping. It's better to have the limited money in one good amp rather than spread it over two mediocre ones, plus interconnects.

I can't comment on the merits of the particular models/brands you are proposing. However, there is an important point to keep in mind. If you bi-amp with dissimilar amps, they have to have the same gain. So options 3 and 4 may not be feasible depending on the gain. Option 1 would be a good choice though.

2. with or without the biwiring.

Kal