Axiom Home Page Forums General Discussion Technical Questions Mixing 4 ohm centre with 8 ohm left and right?

Sorry if this has been asked before in the message board, I just couldn't make the search engine work for me.

I am considering a VP180ow for a centre with a pair of M5HPow for the left and right front, behind an acoustically transparent screen. The 180 is 4 ohm impedance and the M5's are 8 ohm each. Can I do this, mix the impedances? Does the receiver need any special features or setting applied to do this or should i just get an 8 ohm centre?

No problem mixing, you just need to set your channel levels correctly ...

Which receiver, how far away will you be sitting and will you be crossing all fronts to a sub?

Onkyo TX-NR757, 12' away, yes there is a 12" Velodyne sub. thanks for the reply.

No problem. Cross all fronts to the sub at 80Hz to give the Onk less of a workout. Set the Onk to 8 Ohms and not 6.

Consider the 160OW though. There is nothing wrong with the 180 but the 160 is very good and less expensive.

Check refurb and B stock. You may find them there.

Or even another M5hp. Save the dough if you can place it behind the screen. No advantage to a horizontal center if you arent forced to place it under/over a screen.

Use your left over cash on a nice universal remote or a 4K bluray player or gaming console. Or the new LOTR 4K release.

Hey Trevor. You should see what I did with an M5 as a centre at my buddy's. It's the most %$cked up thing ever but it sounds so damned good. I'm sure it's the only installation of its kind in the universe.

I have been considering the M5HPOW for a while. I already have the VP180OW with M60's. The VP180OW is a beast of a centre speaker! What I really want to do is move the M60's to the games room and get the M100's next fall (Black Friday $$).

Thank you all for the responses, The only reason I am considering the 180 is because there are a couple in the Refurb/B stock stores and the saving is significant. My original intent was three matched M5HPOW for behind the screen. Last night I checked my screens construction and the two centre supports/studs are only 36" apart , the 180 won't fit unless I rebuild the frame!

I guess the horizontal centres are really only for systems that use tall L/R fronts like the M60 or M80 then?

The horizontal centers are for those who can't fit a regular speaker into their space.

BTW, the M5s are 6 Ohm. Look at the impedance curve (on the M5 bookshelf page). This is of no practical significance to your Onk and the advice I gave you still stands. Axiom specs them as 8 Ohms to avoid a ton of calls from prospects who don't know what an Ohm is and what it means.

Cross them at 80Hz, turn it up, your Onk will be fine. I have the Onkyo 838 and it has a power supply and amplification similar to yours. In 2-channel, driving M5s, it's practically no different than an ADA-1000-2. I know, because I've measured. I freakin' love my Onk and Visions for the deep discount they gave me on it.

what happens to the sound when you change a speaker from 6 to 8 ohms mojo? I've been listening to my 5's in 8ohms. Does axiom make a speaker terminal for the on wall brackets?

If you change the receiver setting to 4 Ohms, the voltage for the amplifier circuits is decreased. The amplifiers will clip sooner, robbing you of dynamics, soundstage, imaging and emotional impact. The 4 Ohm setting increases the risk of blowing your tweeters because clipping increases thermal stress in the tweeters. It does so because high frequency content is introduced from the harmonics that comprise the clipped signal. This high frequency content carries more energy than typical music and ignites the tweeters.

The reason receiver manufacturers have a 4 Ohm setting is so they can pass safety certification tests and stamp their receivers as 4 Ohm capable. They are indeed 4 Ohm capable but to a lower performance standard. If a receiver puts out 100W per channel into 8 Ohms, a 4 Ohm load would squeeze 200W out of it. But then, the heat sinks on most receivers would get too hot and the safety certifier would give it a fail. The 4 Ohm switch prevents this overheating by robbing the speaker of power. It's not inconceivable for a 4 Ohm speaker to sink only 40W max from a receiver rated 100W into 8 Ohms when set to 4 Ohms.

Practically, the 8 Ohm setting for a 4 Ohm speaker is of no concern unless you listen at very high levels. If so, the best thing to do is get an amp like an ADA. Any ADA doubles its output power when the load is decreased from 8 to 4 Ohms. But even if you don't, a well-designed receiver will self-protect. Of course if it's always self-protecting, you need an amp for sure.

My Onk has multiple modes of protection. It starts to compress the output and if I keep pushing it, it shuts the channel down. I like the ADA protection better. It doesn't try to fool you by compressing the output. It keeps going until it hits its limit and then gently shuts the channel off. It brings it back when the problem goes away.

Regarding speaker terminals for the OW, Axiom can make the speakers with terminals but not the brackets.

What do you think about playing the 5ow's at 6 ohms?

Do you think the smaller M2ow need the back wall or will FMB work?

Don't do it. Why rob them of power?

The M2OW definitely need to be against a wall. I chastised Ian for how shitty they sounded and then took it all back and sang hosannas after crucifying them.

Why do you want to FMB them? How off-axis will they be bolted against the wall?

And if you have a newer Denon turn energy saving off (and its onscreen graphic.)

As for on wall vs FMB, google “Baffle Step”. Use speakers as designed for best result.

https://www.css-audio.com/single-post/2018/09/14/Understanding-Baffle-Step-and-Diffraction

"If you were to lay a circle centered on both the x-axis and y-axis and trace around it’s perimeter, you would have gone... 4Pi when you get back to your starting point."

No. Once around a circle is 2pi which is the ratio of the circumference to the radius of the circle. 4pi refers to a sphere which is the ratio of the surface area to the square of the radius. 2pi is the surface area of a half sphere.

4pi is called full space. 2pi is called half space. Both refer to how radiant intensity is measured. When a bookshelf or floor-stander is spinoramad, the radiant sound power is computed from the intensity incident on the area of a sphere. When a wall-mount is spinoramad, the radiant sound power is computed from the intensity incident on the area of a half sphere. This radiant sound power is referred to as the "sound power" curve. It's a curve because the sound power strength varies with frequency.

One thing I don't understand is why some manufacturers install the tweeter faceplate flush with the baffle and others, like Axiom, stand it a bit proud. Perhaps this is a tradeoff between reduced baffle edge diffraction and higher faceplate edge diffraction? The faceplate edge diffraction would take place at higher frequencies than the baffle edge. Perhaps diffraction at higher frequencies is less objectionable or easier to compensate for.

Which mojo posted this? I'm confused. I just want the M5ow's to purr like the other axioms.

There is only room for one Mojo on this planet and some would say that is one too many.

They'll purr if you crucify them on their wall-mount bracket.