Can the RMB-1095 drive 2.5 ohm speakers?

[hired goon]

G'day,

I've got an opportunity to demo the following speakers at home for a week:

http://www.equinoxaudio.com.au/products/speakers/apogee.php

I've heard these speakers before on other equipment, and they sound wonderful, but I'm worried about driving them with my RMB-1095 200w amp. Rotel recommends a minimum of 4 ohm nominal, and these speakers are rated at 2.5 ohm nominal, with a minimum of 1.8 ohm.

So can I drive these speakers with my RMB-1095, or not?

--Geoff

[Aussie Geoff]

Hired Goon,

Personally - I would not recommend it. The 1.8 Ohm minimum has the potential to either trip the 1095's protecion curcuits or blow the fuses. Either way the amp is likely to struggle with Audible results... THe 1090 is more capable into lower ohm loads (people have driven 2 ohm speakers with it...

Geoff

[Cracking Oboe]

In the Feb/Mar 2000 issue of Audio Magazine, the tester:

"terminated the front channels (of the RMB 1095) in 2 ohms and cranked up the IHF tone burst, the amp pumped out more than a Kilowatt a side with no sign of fatigue." :E


Cracking!

[Andrew Pratt]

Who would make a speaker with an ohm rating that low? Most amps aren't going to like that at all which must really limit your target audience.

[Cracking Oboe]

Who would make a speaker with an ohm rating that low? Most amps aren't going to like that at all which must really limit your target audience.

It does seem a little crazy... kinda like an ultra expensive tube amp that's rated 6 watts @ 8 ohms and can't handle a 4 ohm load.

Cracking!

[Fraise]

Who would make a speaker with an ohm rating that low? Most amps aren't going to like that at all which must really limit your target audience.

the martin logan ascents are 4ohm with an impedence of 1.2ohms @ 20khz.
i know they're tough speakers to drive but the classe equipment i have doenst seem to have much trouble.

[hired goon]

The 1.8 Ohm minimum has the potential to either trip the 1095's protecion curcuits or blow the fuses.

How do the protection circuits get activated? Is it based on the load, or the operating temperature? These speakers have 94db efficiency, so I'm wondering how warm the amp will get, compared to an equivalent volume when using inefficient 8-ohm speakers.

--Geoff

[eelco74]

The 1.2 ohms at 20hz is not uncommon, even for other large speakers. I know the RHMB-10 from Rotels Michi line had a way to bypass the protection, especially for panel speakers like the Martin Logan.

I had a set of transmission line speakers, wich behaved just like that, having a 2 Ohm impedance at around 23Hz. I have had a RA-840bx4 (class A) on it and later my current RB-981. I have never blown a fuse on either amps.

remeber the 1090 is build to drive nasty speakers. All speakers on the market have impedance load as high as 50 ohms and as low as 3 ohms. Some are a bit lower like the Martin Logans or the apogees. So try it and have the Apogees for a demo at your equipment. I guess it will sound wonderfull....

[Andrew Pratt]

There's a difference between having a minimum resistance for a high freq at 20 khz as there's very little material that actually goes that high and its only for a brief moment...the ones in question are 2.5 ohm nominal which means that virtually all the freq's are going to be demanding on the amps power supply. Still it would be interesting to try those speakers on the 1095 and see what happens.

[hired goon]

G'day,

...Still it would be interesting to try those speakers on the 1095 and see what happens.

Just this morning I bought some beaut speakers: VAF Signature I-93 that are rated at 3 ohm nominal, but the bloke I bought them off also sold me a Rotel RB-1090 2x380w amp, which should be sufficient to drive these babies.

I could try running the I-93's with my 1095, but it's probably safer not to risk it.

BTW here's what Rotel tech support have to say on running 2.5 ohm speakers with the 1095:

Rotel does have conservative power ratings but that does not apply to the
impedance rating. I would not recommend connecting these speakers to the
amp. These speakers would operate at a very low impedance all of the time
which would put a lot of stress on the amp and potentially put it in thermal
protection or cause it to overheat and blow up some output devices.

--Geoff

[Taito]

Wow Geoff, congrats on the purchase! Looks like the bigger brother of what I'll end up with - I expect to order the I-66s next week. You're lucky to find a private seller willing to let such a combo go. Let me know how they turn out (and good luck moving them). I'd be very surprised if the 1090 can't do those puppies justice, the I-66s sang with my 1080.

-Ben

[hired goon]

G'day,

Wow Geoff, congrats on the purchase! Looks like the bigger brother of what I'll end up with - I expect to order the I-66s next week. You're lucky to find a private seller willing to let such a combo go.

The bloke selling these was getting rid of all his gear -- he also had JMFocal.Lab Utopia speakers and a massive sub, and Electrocompaniet CD/DAC/pre-amp/monoblocks, and $2000 speaker cables, all going for a fraction of the cost (but still beyond my budget -- sigh).

I got a *very* good price for the I-93 and 1090 (cheaper than your I-66, probably). Too good to resist.

Let me know how they turn out (and good luck moving them).

Apparently they've only had a couple of hours use. They did sound nice through the Electrocompaniet gear.

Moving them was a bugger, though (100Kg each).

--Geoff

[Taito]

Sounds like the guy has decided to pay off his mortgage instead . The 1090/I-93 combo wouldn't be given the role of 'second' in many people's homes! He had (has?) some serious equipment!

I look forward to hearing some sort of review. Until then, Cheers and enjoy!

-Ben