Axiom Home Page Forums General Discussion Technical Questions 4 ohm towers Hooked to 6 ohm amp

I am a new user and have just completed my HT. Speakers Axiom system 80 hooked to Pionneer Elite vsx94txh,Elite Blue-ray
BDP-05FD,Epson Pro Cinema 1080UB front projector on Goo-system
screen.It "ROCKS MY SOCKS".I have the AV set at 6 ohms The towers
from Axiom are 4 ohm. I think this quality amp can handle it or Am I wrong.Cannot push the amp(140RMS) to the limits without blowing the door off the dicated HT Room. ( 12.1W x 20L X 8.5H )
Do I run the risk of damaging the amp and/or speakers.
Thanks

If your amp is not shutting down, you're cool. Congrats!

You could also try the AV in 8ohm mode as the 6ohm setting is just limiting the amps output to prevent it from overloading.

Either way glad you are liking the new system.

Thanks: I am working on sound panels to deal with the reverb in this lively room.

What those guys said. Unless your amp distorts (sounds bad) or shuts down, just enjoy it.

Sirquack had a really good pictorial essay about his adventure with room treatments (corner bass traps and other panels). Do a forum search on "Room Treatments" and you'll probably find more than you want to know.

I would turn your receiver back to the 8ohm setting, no matter the ohm rating of your speakers.

I'll just put my 2 cents in here...

P=I2R.

The amp is rated for a power level at 8 ohms. If you cut the ohms in half, you must increase the current by SQR(P/R). So, if your amp is 100W rated, in normal 8 ohm operation, it would supply SQR(100/8)=3.5A. Change the load to 4 ohm, it would have to supply SQR(100/4)=5A. 43% more current.

Some amps can handle it, some can't.

I know that some of you may believe that "if the amp doesn't trip" it's okay, and I also know that most of you know that the 8/6 setting will reduce the current limit, thereby reducing your peak power. But, it's there for a reason... Distortion.

Distortion has a better chance of damaging your speakers than connecting an amp rated higher than your speakers. Notice how all torture test blow the speakers using white/pink noise?

Even if the speaker doesn't blow, it most likely will clip the higher power levels. Not a true reproduction of sound.

I would recommend (albeit in contrast to many on this board) to use the 6 ohm setting.

From Gene at Audioholics...

"NOTE: Some Receivers have an impedance selector switch. DON'T USE THEM! The manufacturer puts them there for UL approvals as well as easing consumer concerns about driving low impedance loads. These switches step down voltage feed to the power sections which will limit dynamics and overall fidelity. Keep the switch set for 8 ohms regardless of the impedance of your speakers and ensure proper ventilation of the Receiver.


Update: 09/06/05



Upon further investigation on this topic we have discovered that in most cases the switch is doing nothing more than reducing the rail voltage. Please check out our measurements on page 2 of the Yamaha R-XV4600 review for more information on this.

As you can see the measurement differences between the "low" setting (less than 8 ohms) and the "High" setting (8 ohms or more). This is the reason I usually recommend keeping this switch in its default "High" setting and using common sense when mating a receiver with inefficient 4 ohm speakers in large rooms.

All the "Low" setting of the switch is doing is stepping the rail voltage down so when UL tests the amp at a specified distortion level, the amp will achieve that distortion level sooner since it runs out of headroom more quickly than it would in the "High" (8 ohm or more) setting. This in turn generates less heat since the amp isn't driven as hard. You really aren't buying any protection for driving low impedance loads as you actually risk clipping the amplifier more since it can run out of headroom more easily. The switch is there more for certification purposes. The reason you don't see this switch on separate amps is twofold:

They typically have more heat sink area, and bigger power supplies and can better manage the heat
They aren't UL certified and don't have to meet the requirement. "

I was just looking for that very same article.

Another explanation.

Audioholics comments on this switch:

......." What Doesn't Matter?

Impedance Selector Switches
This so called feature, used by some manufacturers, is designed to prevent overheating of the receiver or damage to its output transistors because of excessive current flow. The manufacturer accomplishes this in one of 2 ways: 1) Stepping down rail voltage supplied to the power amp or 2) feeding half the signal strength to a voltage divider of power resistors. Both of these methods severely limit dynamics and current capability of the power amp. This results in an audible decrease in bass capability and dynamics transient sound because the 4 ohm setting effectively increases the receiver's output impedance. Unfortunately many manufacturers put these features on their products to ease customer concerns with driving low impedance loads and for safety reasons when getting UL approvals. Note: In order to meet UL requirements, a receiver cannot be rated down to 4 ohms without having this switch onboard. Receivers without this switch are usually rated down to 6 ohms. In most cases, well designed receivers can easily handle 4 ohm loads safely and efficiently. It is highly recommend to keep the impedance switch set to 8 ohms regardless of your speakers impedance and make sure your receiver has plenty of ventilation."

And another reason.

Because we say so

As I said, if you think your amp can handle it, go for it. Want to roll the dice and take a chance at blowing your amp or speakers, go for that too.

If you want to do things the "right" way, get an amp rated for 4 ohm load.

By the way, I can detect clipping with my Denon 3806 when I play it loud. It's severe (to the point that I am damaging my speakers) when playing things like William Tell's 1812 Overture.

It's one of the reasons I want a separate amp for the M80s.

What's driving your M80's wid?

I have a Rotel RB 1080 with 330 watts @ 4 ohm. I think it can handle the M80s .

How big is your room?

Note: In order to meet UL requirements, a receiver cannot be rated down to 4 ohms without having this switch onboard.

I don't know of any Denon's that have this switch, but they have certainly proven to drive 4 ohm loads without a problem. Because a receiver does not have this switch it should not be implied that it cannot drive a 4ohm load. Sure there are some receivers that have problems with 4ohm loads and Axiom has been pretty specific about which ones, personally I'll stay away from the ones that have the switch.

Man you must play it really loud

I know, it was kinda a rhetorical question (Nice amp!) But that is kind of the focus of my point. A couple of the posters here that say it's okay have beefier amps driving the M80's. Nothing wrong with that, I want to do the same...

My room is 2600 ft3, but that has no impact on the amp clipping.

And, yes, I do like to play it loud sometimes.

I kind of figured so, I like posting the power rating. I have been a big advocate of large beefy amps ever since I joined here but I have pretty much been in the minority. It's always been my motto to buy as much power as you can comfortably afford.

Rick, I'm one of the minority that will agree with you on more power. I ran ran my M80's off an Aragon amp for about a year and really felt there was a difference, unfortunately I started to run out of room with all the other toys I have in the setup, so I went with a more powerful receiver. If Axiom ever makes a low profile 2 channel amp, that will be my next purchase.

I thought it does in that the further you get from the speakers, the more power you need to maintain the same volume. Is this wrong?

You are right.

His playing a classical piece at high volume levels for the quieter pieces then puts the amp into clip for the loud sections.

I did that one test awhile ago where I was listening to The Planets and I had a dynamic range over 20db, IIRC, so if you are listening at the quiet sections at 85 db then they hit the dynamic high parts at 105db, the power requirements are huge especially as you move farther away.

I can relate, when I'm shooting a game of pool 25ft+ away and listening to the planets, my Odyssey monoblocks make my 80's really shine. The Denon alone did OK, and I would not say the clipping was that noticable if at all, however, it is nice to have the extra HP in my close 8,000 cu ft room.

BJ, your 94 supplies what is likely to be more than enough power(including at 4 ohms, see test )to meet your needs, but you're unnecessarily handicapping it with the 6 ohm menu setting rather than the standard 8 ohms. This setting serves to reduce the maximum voltage that the power supply section of the receiver can output and thereby also reduces the maximum current and power available. The maximum power capability is roughly cut in half, and although this helps prevent overheating it also(contrary to what one of the earlier replies stated)makes the possibility of encountering distortion or even clipping at very high levels more likely. Reset to 8 ohms.

Steve - approximately how loud (SPL) are the peaks you're referring to before the M80s start distorting with your Denon? Clearly I haven't pushed mine hard enough if I haven't heard the clipping, but I just can't imagine listening much louder than I have (and I'm in a medium-small room like you are).

Jason

And what is the dynamic range of the material you are listenng to.

Jason - I never hooked up the meter when listening, but it was comfortably loud during most of the piece, and WOW loud when the cannons shot off. I know a clip when I hear it.

DG - I don't make it a habit to check those things when I put a disc in the player. It was an SACD though.

I agree that a much more powerful amp is of benefit with the M80's, although most of the Denon's, HK's and even the 94TXH can probably handle them reasonably well, it's nice to have the extra power available.

I have the 3808 but use an ATI-1506 in bridged mode for the front 3 channels. In bridged mode the ATI is rated at 450 watts per channel X 3 into 8 ohms. Me Likey!

I did a quick test with SPL meter in hand awhile back checking for the dynamic range of the various tracks on The Planets, I found it to have about a 25 db range, so if this is representative of most classical music then the M80s at 80db for the low parts would have to hit 105 to cover the range and this could put the Denon into clip. Check the amp calculators out there and put in the 20-25 db range for the Dynamic range part, this takes the watts required to a whole other level, especially when the distance goes up.

I also wonder if the 3806 is as strong as the 3808 into 4 ohms? I know there are only 10watts difference into 8ohms in favor of the 3808. I haven't been able to find any actual lab tests of the 3806 to see if it is close the 3808's ~225Watts into 4 ohms.

Jason, the dynamic range on a recording is usually considered to be the range from the lowest level to the highest peak, not from the average level to the highest(which is often said to be about 20dB on some highly dynamic compositions). There are quite a few classical compositions which require a dynamic range of about 50dB or even slightly more when properly performed and recorded(e.g., about 50dB when the volume is set so that the lowest level is audible, which then might hit 100dB on brief peaks). Even these peaks, however, don't require anything which isn't easily within the capability of typical receivers with a rating anywhere around the 100 watt area.

Some of the online power calculators are grossly inaccurate(on the high side)when they take into account a factor such as distance, but fail to fully account for the contribution of room reflections. Notable is the one of a maker of high power amplifiers whose initials are Crown, which drew some praise here last year, but I pointed out that the calculator came up with a number about four times higher(about 140 watts compared to 35 watts)than I'd measured and calculated for a certain high level. A statement that it was only accurate for anechoic conditions, and giving an arbitrary correction number was somewhat buried at the end, and reduced the prior result to less than a third of the previous value.

John. From the Crown page that links to the calculator:

"The calculations discussed here apply to anechoic or outdoor conditions. If the sound system is inside a venue, the room reverberation will increase the SPL typically by 6 dB. You can use this room gain as extra headroom."

While they don't explicitly include the adjustment in their calculator, they are certainly very clear that room gain needs to be taken into account.

I still think the page linking to the calculator is excellent. It was the first place I found that all the elements relating to power requirements were gathered together in one tidy package.

As to the numbers I originally posted using the calculator, that was operator error (me), not an inacurate calculator. A separate box for room gain would simplify the calculator though.

I can't imagine hitting 105db in my room. I suspect that has as much to do with the fact that the room is highly reflective as it does with me not listening to music at reference levels.

I do wonder how that would change if I had a more well behaved room though.

JohnK, I see what I did wrong in my examples, for the calculators to work correctly you would be using the average finding as the listening SPL value, I should be using 92-93db from my previous example, for the main listening SPL level; as the Dynamic Range is made up of the low and high on either side which then drops the required power output from the amp considerably.

I just had it in my head that while listening to Holsts': The Planets, the tracks are very quiet for a large portion of them but have large peaks, I found myself turning the volume up considerably to hear the quiet passages. This had me thinking of the lowest points of the range as the average(desired SPL on most calculators) listening level, which it really isn't.

It's late or early depending on your time frame, does this make sense?

Fred, it apparently isn't all that clear since both here and elsewhere I've seen the calculator used without adding the 6dB correction for room reflections(which is adequate for the typical listener distance of about 3 meters, but would still result in an inaccurate power number at significantly longer distances) which is found only in "other considerations". There's been a lot of "operator error" beside yours.

Jason, sure the composer sometimes intends part of his composition to be heard at a very low barely audible level. Turning the low level parts up louder defeats that intent and is a form of self-imposed volume compression as to those segments(and if not corrected before a sudden loud segment comes, you might get blasted out of your listening chair). On The Planets the volume setting for Neptune should be the same as for Mars and Jupiter.

OK, I guess I'll just like the site all by myself then.


I'm envisioning Jason flying out of his chair and smacking into the wall Ironman like.

Damnit! I haven't seen the movie yet and now you spoiled it for me.

I was thinking more like stuck to the chair as in those old Maxell(?) ads. ala jakeman's avatar.

I'm usually the last person on the face of the planet to watch a movie!

So we won't tell you what "Rosebud" mean!

As it happens I don't think I have ever watched Citizen Cain.

It's Kane.

Not that I've ever seen it either.

What has made you un-Abel to see it?

*GROAN*

How do you make a groan man sigh?

Make him a member of the Axiom Community.