Two crazy home theater epiphanies – could this elevate your home theater sound?

[High Power Dude]

Years ago while auditioning a friend’s home theater, his ceiling exploded. Literally. The 8 inch full-range Atmos mounted marine speakers (he got them cheap) had bass, and lots of it. This messed me up because the Atmos spec doesn’t call for sounds below 170Hz. So what was going on? Well, he changed the frequency on his AV receiver and wham! Bass from explosions in the sky. Who knew? Rocked my world. I did some homework and got Heco 44f speakers, mounted them on the ceiling and ka-blam – the sound donut is now the cone of sound and things blowing up in the sky ain’t no joke. Years have passed, and now I’m about to try something new with rear channels.

In my 18’ x 14’ x 7’ home theater, It’s time to ditch my floor standing rear channel speakers for a much better option. As most of you know in medium sized rooms, rear channel floor standing speakers can have unforeseen drawbacks. First, they are often too close to listeners, second, the bass can be wasted by the cone of dispersion blocked by seats or other obstacles. So I thought, what’s the purpose of rear channel speakers? Professional sound editors use rear channels for environmental ambience in world-building. Most of that is mid-bass frequencies and up. They create space and support a 360-degree soundfield. Although 80% of our sense of sound comes from the front and sides, rear channels come into play when something moves from the rear to the front or vice versa. From directional effects and flyovers to panning and acoustical reflections – such as gunshots in a warehouse, sound editors want you to feel like you are there. They employ off-screen sound cues and wrap-around music spatial metadata but never direct dialogue. They like to put creepy sounds from the darkness behind you while you watch in the dark because they want you to feel scared. When it comes to deep bass, they generally keep it up front but in movies it’s wherever it is. So what speaker is designed optimally for the mid-bass to vocal range and higher? The answer lies in the center of my question.

That’s right. I am about to buy 2 center channel speakers that reach down to 70 Hz, placed, as they should, horizontally at ear height in the corners of the room angled into the primary listening position. Do I add subs below for the full effect? Maybe. But not just yet. Think about it and let me know your thoughts. Cheers!

The equipment depicted in the bathroom signage has changed, but it's a great way to inform the uninitiated.

 

[90sNintendoKid]

I wouldn’t personally go for two center channels unless maybe a Kef centre speaker.

What’s your reason for centre speakers and not book shelves that go down to 70 hz?

Might I suggest nearfield and MLP measurements to investigate if your current rear speakers are being compromised?

 

[90sNintendoKid]

Do you have front wide speakers?

I would personally experiment with different positions for those rear speakers.

Also, I noticed you have high backed theater seats. Have you thought about using a coaxial speaker for the rear speakers, slightly higher than the height of the seats? Something with good vertical dispersion like a Kef or Ascilab?

 

[Oddball]

I am a bit lost in your post. There are centers that go down to 30hz in the room if your are looking for that. Two centers can't be done properly unless your processor has option to EQ two centers, which is few.

As to the bass management, it depends what you use. Rather than buying 2 new centers, you might want to buy gear compatible with Dirac ART that will brighten your day and manage the bass like nothing else available at that price.

Atmos specs are for full range BTW. What is in the mix is really up to the mix. Theoretically it should not matter if you are bass managing your Atmos.

 

[popej]

That’s right. I am about to buy 2 center channel speakers that reach down to 70 Hz, placed, as they should, horizontally at ear height in the corners of the room angled into the primary listening position

Many center speakers are MTM type, symmetric with tweeter in the middle. The better position for these speakers is vertical, because it gives better spatial characteristics.
Do you really need new speakers? Why not set the crossover to 70Hz for your rear floor standing?

 

[EJasonC]

They employ off-screen sound cues and wrap-around music spatial metadata but never direct dialogue.

One exception is Bane's dialog in the opening sequence of ‘The Dark Knight Rises’ - virtually all channels used for his dialog only no one else. In full range and to excellent effect by the way! One’s system needs to be very highly resolving to render the sound design in many of Christopher Nolan’s work.

 

[Soundmixer]

Atmos mounted marine speakers (he got them cheap) had bass, and lots of it. This messed me up because the Atmos spec doesn’t call for sounds below 170Hz.

There is no such limitation in the Atmos spec. The ceiling channels, much like all of the other channels, are spec'd from 20-20kHz.

 

[High Power Dude]

I wouldn’t personally go for two center channels unless maybe a Kef centre speaker.

What’s your reason for centre speakers and not book shelves that go down to 70 hz?

Might I suggest nearfield and MLP measurements to investigate if your current rear speakers are being compromised?

Good points. I've owned nearfields and as you know beyond a few feet they surprisingly lose coherence, so they don't cover the audience uniformly. Bookshelves are a great option too. The perspective I have is dual woofers horizontally placed provide a wider dispersion for the audience. It's very easy to go back to the bookshelf option. I do have measurements of my Induction Dynamics rear speakers and elevating them is an option. Thanks for your insight. Good stuff!

 

[High Power Dude]

Do you have front wide speakers?

I would personally experiment with different positions for those rear speakers.

Also, I noticed you have high backed theater seats. Have you thought about using a coaxial speaker for the rear speakers, slightly higher than the height of the seats? Something with good vertical dispersion like a Kef or Ascilab?

I don't have front wide although I have experimented with that in the past (photo). I've had every imaginable iteration out there and it's always fun. I even had dual center channels, one low, one above the TV. I always felt that was something I'd like to return to. Thanks for the coaxial tip. I overlooked that option.

 

[High Power Dude]

I am a bit lost in your post. There are centers that go down to 30hz in the room if your are looking for that. Two centers can't be done properly unless your processor has option to EQ two centers, which is few.

As to the bass management, it depends what you use. Rather than buying 2 new centers, you might want to buy gear compatible with Dirac ART that will brighten your day and manage the bass like nothing else available at that price.

Atmos specs are for full range BTW. What is in the mix is really up to the mix. Theoretically it should not matter if you are bass managing your Atmos.

Center channel speakers that go low invariably get larger or wider. So space is a factor. The Atmos upfiring or downfiring spec is 100Hz minimum, so many speaker manufacturers design them in that range. I thought that was the limit but you are correct, it is not and that's where one can be lulled into thinking "that's what they make so that's what Dolby wants," which is not the case. As for Dirac ART, I took the painfully expensive route of building a room from the ground up to be as acoustically neutral as I could. It is double-walled, green glued, employs mass-loaded vinyl between the walls, over a quarter ton of Roxull Safe-N-Sound, acoustic putty, etc. Nothing rattles or produces sound from bass, etc. The Dirac ART option I haven't explored. Thanks!

 

[High Power Dude]

One exception is Bane's dialog in the opening sequence of ‘The Dark Knight Rises’ - virtually all channels used for his dialog only no one else. In full range and to excellent effect by the way! One’s system needs to be very highly resolving to render the sound design in many of Christopher Nolan’s work.

True. I use the airplane sequence in 'The Dark Knight Rises' as a demo. Being a skydiver myself, that's an awesome scene.

 

[sander]

The perspective I have is dual woofers horizontally placed provide a wider dispersion for the audience.

I am a bit late to the party here, just found this thread by accident. I sense a misunderstanding here. Dual midwoofers horizontally give a horizontal comb filtering effect that effectively narrows the horizontal dispersion! Like @popej said it would be better to use them vertically (that is, if you need horizontal dispersion more than vertical dispersion).
(For some reason - looks good and logical to the uninformed, symmetrical, fits nice below the tv - the horizontal MTM is the most common center design, but it is also happens to be the most stupid! Three way with vertical mid and tweeter arrangement between two woofers, or coaxial mid-high would be better.)

 

[High Power Dude]

I am a bit late to the party here, just found this thread by accident. I sense a misunderstanding here. Dual midwoofers horizontally give a horizontal comb filtering effect that effectively narrows the horizontal dispersion! Like @popej said it would be better to use them vertically (that is, if you need horizontal dispersion more than vertical dispersion).
(For some reason - looks good and logical to the uninformed, symmetrical, fits nice below the tv - the horizontal MTM is the most common center design, but it is also happens to be the most stupid! Three way with vertical mid and tweeter arrangement between two woofers, or coaxial mid-high would be better.)

The most stupid. Really? So all the MTM manufacturers of center channels, stupid. When people give explanations using Acoustics theory as to why something won't sound good, but never bother to listen themselves, is that all you need? Or do people actually know that despite the comb filtering, dispersion can be sufficient and still sound amazing? Compromise is what loudspeaker engineers grapple with daily. All designs have compromise like comb filtering. You'll never hear me throwing out buzzwords suggesting the person or the idea is stupid when, guess what, it can actually sound really good despite an acoustic pitfall. They still sell tens of thousands of down-firing subwoofers don't they?

 

[sander]

Well, I may have worded it a bit harsh with 'most stupid', but it is certainly not the most logical design from a pure sound perspective.
I have listened to a few MTM center speakers. Walking from the center line to the side I could often hear the sound change. More than with most normal speakers and center speakers with a vertical tweeter-midranger configuration. And that is unfortunate because the center is most important and most needed for people not sitting on the center line. Sure some horizontal MTM's are better than others. But why not simply do it compeletly right from the start and use a vertical tweeter-midrange configuration or a coaxial unit?
Manufacturers want to sell stuff and they know people will buy horizontal MTM center speakers (and I think most of them have no idea about the potential downsides, they just assume there is nothing wrong with it because they are the most common, and look and fit nice).
I see your actual center speaker (jbl?) has its mid-woofers placed angled to the outside a bit. That surely helps. (I have heard horizontal MTMs with outward angled midwoofers that did have better dispersion indeed than most horizontal MTMs).
Some horizontal MTMs are actually a three-way or two-and-a-half way in disguise, where only one of the woofers is doing the upper midrange, there the dispersion is better (although not left-right symmetrical).
Those MTMs that you have high up on the stands don't seem to have outward angled drivers, and the woofers are fairly large and further apart than necessary, so unless they are not working in paralell over the full midrange band physics dictate that there will be a horizontal comb filtering pattern and loss of high mids of axis horizontally. Maybe it isn't enough to bother you, but it is easily avoided by using a different design.
I am convinced that really the key reason why horizontal MTM is the most common center design is consumer acceptance / form factor.