Axiom Home Page Forums General Discussion Home Theater Ideas on 31'L x 23'W room for fronts, 7.1 backs

Hi davekro,

I've been following this thread and here are a couple of points. Get rid of this idea that matching woofer sizes between different speakers, especially different brands, will somehow creat a better timbral match. Slight adjustments in the crossover of a given speaker create far more audible differences than any combination of different woofers. And I urge you not to use the BIC speakers in an Axiom-dominated system. From my experience as an audio-video magazine editor for many years, in the course of which several BIC models were tested, I can assure you that a BIC will audibly stick out or make its presence known because of inherent coloration.

The reason that Axiom does not make a dedicated in-ceiling speaker is first, that isn't how movies are mixed and meant to be played back and our hearing is much more acute to side-generated and front-generated sound and reflections. Most movies are mixed in 5.1; the decoder will interpolate material for the additional two channels at the rear from the discrete left and right surround channels. Two extra surrounds certainly improve coverage and envelopment in large rooms, however, the QS8s are so effective in their side locations, that often adding two more surrounds yields only a marginal improvement. I don't know why Brent suggested M2s at the rear; if you want 7.1, then add an extra pair of QS8s. They don't need to be 16 feet apart. Ten feet will certainly be enough for ample separation.

Axiom has made provision for mounting a W22 in the ceiling if that's the way you want to go. I also advise against swivelling tweeter designs. After measuring some of these in our anechoic chamber, they had intrinsic flaws large enough that we rejected that design approach.

As to impedance, even entry-level Denons will drive our 4-ohm M80s with no problems so long as you don't drive the Denon into clipping or distortion. The sensitivity differences between the M60 or M80s and the QS8s are not so great that you can't compensate easily with the individual channel levels in the Denon setup.

And in terms of power requirements, I always urge buying as much power as you can afford so there's no danger of exceeding the output limits of your amplifier and damaging the speakers. Your existing Denon should have ample power for very loud playback (95 dB to 100 dB SPL peaks) given your listening distance. If you are into extremley loud (above 100 dB SPL) playback, you could always add a powerful outboard amplifier later on. And has been pointed out, if you want a "slightly noticeable" increase in volume levels (3 dB), you'd need twice as much power (180 watts per channel, assuming your Denon would be driven to near-clipping to achieve 100 dB SPL). To subjectively increase playback volume to "twice as loud" requires ten times as much power.

A note on distortion: virtually all amplifiers have measurably greater distortion driving a 4-ohm load because more current runs through the output section, and it runs hotter. That said, we are talking about fractions of a percent, minuscule levels that are inaudible with music or movie programming. Distortion has to rise to greater levels than 1%--often 3% or more--before it becomes clearly audible. Those levels of distortion do not happen with modern well-designed solid-state audio amplifiers when they are not driven into clipping. They do happen with some tube amplifiers and are quite common with vinyl playback--and it's clearly audible when it occurs.

Regards,
Alan

Great info Alan. I'm not surprised testing of angled tweeters did not yield good results. I would not recommend them for critical listening. But in this case, where in-ceiling is needed and placement may not be optimum, I found (in my case) the ability to aim the surround off a back wall helped increase the perception of distance from the back wall and helped the dominance of a down firing woofer near the seating position. Accuracy, not great, but for surround presence, it helped and here it will be for real fill only with the QS8 taking the heavy lifting. Again, I'd try 5.1 before going through all this, but 7.1 seems be a done deal here.
I have the Klipsch 5800 if that helps you, but the pale in comparison to the QS8s that replaced them.

Alan,

Thanks for sharing your knowledge. I'm especially glad I saw your comments before investing a bunch of time researching in-ceiling speakers.

I was surprised the 1909 would be ok with 4 ohm M80 fronts. I had concerns of the heating issue, especailly since the specs in the manual only mention a watts/ ch rating down to 6 ohm. I think I still feel M60's are my preference. The price, 8 ohm rating and I do not know if the dual tweeters and dual mids, may contribute to some perceiving the 80's to accentuate the highs. I have never heard any of these, though I have hopes that Twelly in Newark, CA will contact me after Axiom sent my info to them. Thanks again.
Dave

Hi Zimm,

Thanks for your feedback. Look, I'm not saying that in-ceiling surround speakers can't work. Of course they can; in fact, part of the reason for the QS8's excellent delivery of an enveloping surround sound field is the top-firing woofer and the off-axis dispersion of the two tweeters--a good chunk of the radiated energy from those drivers is reflected from the ceiling in a side- or rear-wall mounted QS8. It's also why QS8s installed about three to five feet above ear level can create a very convincing sense of height on helicopter flyover effects.

However, I'm a bit of a purist when it comes to movie and music playback and the way our hearing system operates. If ceiling-mounted surrounds worked well, they'd be used in Dolby Digital and THX movie theaters--and they aren't. I understand if there's no other solution than using some type of ceiling mount, but I always advise side and rear-wall mounting if at all possible.

Cheers,

Alan

Davekro,

Virtually all AV receiver manufacturers specify not using impedance loads of less than 6 ohms in order to comply with the UL and CSA product testing, and also to err on the side of caution. Some brands include an impedance switch that actually limits the power output and current flow to a lower impedance load to prevent the output devices from running too hot. Doing that also reduces the available power output dramatically into a 4-ohm load.

In the real world, however, some amplifier sections of some AV receivers tend to be more stable than others driving 4-ohm loads, Denon and Sherwood Newcastle being a couple that Axiom has had long experience with. Some other brands, as I've previously noted in the forums, have overly sensitive protection circuitry that immediately upon sensing greater current flow or increased heat from the output transistors, will shut down the AV receiver or put it into "current limiting", a mode that limits power output.

Also, it is not the number of midrange drivers and tweeters that will determine the timbral (tonal) balance of a loudspeaker. Using dual midranges and dual tweeters in the M80 gives it huge power handling in large rooms. It is subtle adjustments in crossover design and driver selection (among many factors) coupled with careful anechoic measurements and listening tests that will ultimately determine the tonal balance and neutrality of a loudspeaker. Over the years, I've tested some small bookshelf speakers from other manufacturers that are almost unlistenable because of excessive treble emphasis and wonky tonal balance.

Actually, in double-blind tests, the M80 is a slight bit smoother on female and male vocals than the M60. These differences are tiny, barely noticeable except in the instantaneous switching between the two speakers. You'll be fine with the M60s in your size of room and as other M60 owners have noted, they are capable of very loud, clean playback in very large spaces.

Also, your notion that sound from the rear speakers has to "travel" a long way--16 feet--to your listening area is not a significant factor. Sound travels at one foot per millisecond, so the sound from the rears in your room would take 16 milliseconds--that is 16/1,000ths of a second--to reach your ears. The setup on your Denon will insert digital delay quite a bit longer than that to prevent your ear/brain from hearing the rear surround signals before the sound from the front speakers.

Regards.

Alan

Alan,

Thanks for the discussion of M60s in my environment.
On the QS8's...
7.1 Backs: Due to the left rear back wall having kitchen cabinets, I'd like to know how a 3 1/2" top clearance (at 6' rt of center and best aesthetically) or 6 1/2" top clearance (at 4' rt of center). These assume mounting so QS8's extend out so their back is flush with cabinet fronts, but flush with cab. top. I assume mounting to back wall between cabinet and ceiling with only 4" above and below AND only 3 1/2' rt. of sound center would be a no go. Right rear wall top clearance could be up to 16". sound wise differing locations is OK, but aesthetically, being closer to left speaker height would 'look' better.

Side surrounds (8' ceiling ht. at wall slopes up to sound stage center 12' in to 10' ht.):
In order to cover the old in-wall covered holes, 13 1/2" top clearance would be best. How far from optimal is that? Since these sides are more listener critical, I'd be willing to place them lower to achieve closer to optimal sound here.
Thanks again.
Dave

[quote=sirquack][/quote]

Sir Q,
I just saw your HT set up. Very nice. What are those ceiling mount brackets for your QS8's? I may need to press the WAF factor and consider mounting 8's on ceiling mid room. (just to make Tom happy ;o)

Thanks, Dave

No argument there, and good info - love to learn the whys of the rules I've heard. This would be a purely aesthetic solution in a less than "pure" set up. For anyone mining this thread for info, I want to be clear, having used both in the same position, the QS8 is in a whole different league than the good in-ceilings. Not even close.

OK, I'm going to try to change my perception of QS8's mid ceiling as an aesthetic 'feature', not a fau pau... Then to sell it to the wife. ;o) Though I am amazed at the leeway she is willing to show after her elation of moving the Klipsch Cornwall out of the living room.

For mid room ceiling mounting for MS8's, what is minimum top clearance and a good distance back primariy list. pos./ side surrounds? Due to sky light closest possible is 6' behind list. pos. Futhter back has no physical constraints.

and now....



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