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#339422 - 02/22/11 03:51 AM Denon 2808 bi amp m80's?
markmd Offline
regular

Registered: 02/14/11
Posts: 5
I got my 2808 in today and wont be getting my emotiva for quite some time unless another ebay auction pops up.

Anyways I would like to know if I would benefit much if I bi-amped the m80's? Also how would I do that?

Thanks.

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#339434 - 02/22/11 10:05 AM Re: Denon 2808 bi amp m80's? [Re: markmd]
SirQuack Offline
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Registered: 01/29/04
Posts: 13572
Loc: Iowa
you will not notice any difference as that is not true biamping. Also, what version of the m80's do you have and what amp are you looking at from Emo, there have been past issues with Emo's shutting down driving the m80v2's, haven't heard about the v3's.

I talked to Lonnie at Emo and he said he discussed this with Axiom engineers about a year ago, and it has to do with the Axiom crossover not rolling off in some situations, which causes the Axioms to dip below 4ohms long enough in certain situations to put the amps in protect mode.

The v3's may be different, not sure.
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#339484 - 02/22/11 01:44 PM Re: Denon 2808 bi amp m80's? [Re: SirQuack]
Jc Offline

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Registered: 06/27/06
Posts: 526
Loc: Sherbrooke, QC, Canada
Hi,

The Axiom M80v3 is an easy 4 Ohm Impedance audio speaker. Here is a link showing its Impedance Graph. M80v3 Impedance Graph

Alan, in a previous post, has indicated how a Nominal Impedance of an audio speaker is calculated. If I remember correctly it puts the Axiom M80v3 actual Nominal Impedance over 4 Ohms.

By the way, the Emotiva issue was not exclusive to the Axiom M80 model but all audio speakers having a 4 Ohm Nominal Impedance
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#339493 - 02/22/11 02:01 PM Re: Denon 2808 bi amp m80's? [Re: Jc]
SirQuack Offline
shareholder in the making

Registered: 01/29/04
Posts: 13572
Loc: Iowa
JC, that is not totally true. There are lots of people with speakers a lot harder to drive than Axioms and less efficient and way more expensive that do not have issues with any of their amp line. I was one of the people that had issues a few years back with their MPS-1 monoblocks, so I know the whole story, believe me.

I talked to their Chief Technical Officer/Design Engineer who states he was in contact with Axiom Engineers about a year ago, not sure who that is, maybe Ian. Anyway, below is some of the details.

"The problem results because Axiom's crossover design does not have a roll off filter on its drivers. It allows them to run untethered far below their ability to produce useful output, but under some combination of circumstances this design allows the impedance to drop below 2 Ohms.

At high volume levels, when the M-80 presents a sub 2 Ohm load, the XPA-2 will go into protect mode to keep from melting the voice coils in the speaker. What happens is that the XPA-2 responds to the drop in load by trying to provide the increased power needs of the load and senses that the wall outlet is incapable of providing enough juice to meet the need... protect mode jumps out to save the speakers from damage.

This would never happen, if Axiom had elected to use a crossover design that would provide a roll off filter to prevent the drivers from impeding on each others designed frequency outputs.

If you want a more detailed explanation of exactly what happens, why it happens, and when it happens call Lonnie at Emotiva. He is the man who designed the amp and is very familar with this problem. He has been in touch with the Axiom engineers and is fully aware of what is going on with the M-80.

We do not current limit our amplifiers. If I was to put a current limit in the amp it would pretty much play into a crow bar but that would suck the life out it and it wouldn't have the headroom it has now. Sure it would play loud (loud and lifeless), but that would in my opinion destroy what makes it special. When dropped into a 2.4 ohm load the amp will try to draw a boat load of juice but won't be able too (it is going to try and produce in excess of 1500 watts per channel). The end result is that the rails will dip, distortion goes up and the protect will shut off the amp to protect the speaker from damage.

So are you saying I should limit the amp just so it will play on any speaker???? I mean if you really want it I can have it added to design from now on."
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#339496 - 02/22/11 02:04 PM Re: Denon 2808 bi amp m80's? [Re: SirQuack]
SirQuack Offline
shareholder in the making

Registered: 01/29/04
Posts: 13572
Loc: Iowa
Anyway, I am considering jumping up to the V3 M80's some day with different internals, and may entertain giving Emo another shot. There are 1,000's of people around the world loving their amps and comparing them to very expensive offerings costing many thousands more. Also, they are driving speakers much harder to drive than Axioms, with no problems.

You all know that I love Axiom, been around a long time. Just wish we could resolve this, maybe it already has.
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#339500 - 02/22/11 02:35 PM Re: Denon 2808 bi amp m80's? [Re: SirQuack]
BlueJays1 Offline
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Registered: 09/19/08
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The shutdown issues with the M80's were previous versions of the M80's (V1 or perhaps early V2) that had a different crossover design than the V3. Emo's contention I believe is that Axiom designed the crossover where the midrange drivers were running full range without a HP filter. This would lower the impedance and in the lower frequencies creating high current demands where the midrange drivers are not producing any meaningful output. If this is true than perhaps is the reason for the earlier M80's shutting down their amps and why there is no problem now.

The EMO problems with the M80's do not seem problematic with the later V2 and V3 models.
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#339508 - 02/22/11 03:00 PM Re: Denon 2808 bi amp m80's? [Re: BlueJays1]
SirQuack Offline
shareholder in the making

Registered: 01/29/04
Posts: 13572
Loc: Iowa
That is good to know mine are about 4 years old and had the problem, but not with other amps stable below 4 ohms.
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Anthem AVM60 Outlaw 7700 Emotiva A500 Epson 5040UB



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#339534 - 02/22/11 04:25 PM Re: Denon 2808 bi amp m80's? [Re: SirQuack]
Adrian Offline
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Registered: 12/27/08
Posts: 6888
Loc: It's all about the location.
Not wanting to open the bait can here, but could it be the Emo amps had their protection circuit set too high considering so many people have used relatively inexpensive AVR's which technically aren't as powerfull, and had no issues?
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#339544 - 02/22/11 04:33 PM Re: Denon 2808 bi amp m80's? [Re: Adrian]
BlueJays1 Offline
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Registered: 09/19/08
Posts: 4116
Loc: Porch,enjoying Bombay Sapphire
Emo's explanation on why their amps shutdown is because they do not current limit their amps like sirquack posted above. Are receivers designed this way?
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#339548 - 02/22/11 04:40 PM Re: Denon 2808 bi amp m80's? [Re: BlueJays1]
ClubNeon Offline
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Registered: 02/06/09
Posts: 3466
Loc: Western Maryland, USA
Most amps have a current limiter, either by design, or by simple function of not being able to draw more because some component is limiting it.

Amps in receivers are usuallly a bit of both. A protection circuit that guards against shorts (or nearly shorts, like one stray wire in loose contact). And then a heat protection, which will kick in pretty quickly when running into 1 or 2 Ohms. Plus the power supply simply cannot deliver enough power from the wall (that's one thing that'll cause clipping).


Edited by ClubNeon (02/22/11 04:40 PM)
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