4.1 (Phantom Centre) Nearfield HT setup advice

[essence]

So I have an Okto Research dac8 PRO + Audiophonics 4x purifi amp on the way in preparation for this setup. To be paired with Dynaudio C1s as fronts/rear and PSA V1500 sub.

Originally I had planned for 5.1 setup however the centre speaker is awfully hard to position, our ears and eyes are roughly the same level hence its a choice between either a screen or centre at eye/ear level.

I did clear space underneath my monitor for the centre channel to be positioned with tilt but I've read its important to match your centre with your fronts to match the tonal balance. The matching Dynaudio confidence centre is a hard find, costs just as much as a pair of bookshelves and since committing on a four channel amp means I would have to get separate purifi module to power it.

So the next thought is why not just go phantom centre? The downsides of a phantom centre from what I've read on avsforum seem to be the lack of dispersion and imaging being a issue for everyone other than the sweet spot, which doesn't matter as this setup is designed for single user. From what I understand the downmix from 5.1 -> 4.1 seems to be very easy, just split centre between left-right, pre-amp accordingly to prevent clipping which all can be easily done in EQ-APO.

At this point adding an extra sub seems to be more enticing than adding a centre channel. Looking at the Rythmik Audio G25HP. Can one have too much sub?

 

[Promit]

If your seating area is small, throw the center out the window.

As for too much sub ... well you can have overkill and diminishing returns. That point is farther away than most people think though. It depends on the size of your space, but it’s unlikely that a G25HP is going too far.

 

[Senior NEET Engineer]

I'm running phantom center right now, but it is a bit disappointing. In music I get a precise center image, but movie vocals sound too diffuse. Need to figure out if it is because of low movie volume, interaural crosstalk dip, the mix, or something else.

As for whether a sub is overkill is really hard to say. Room size, how loud you listen, and placement restrictions will have significant impact on how much sub is needed. For sealed subs in my 3000 cubic feet room, PSA recommended dual 15-18" and Rythmik recommended dual dual 15". I'm probably going to add dual E15HP2's to help with my SBIR dip (I'm 8 ft from front wall).

 

[TankTop]

I run Special 40’s 2.1 for mostly home theater. Dyn’s do an uncanny perfect job with dialogue, sometimes too perfect but you’ll never miss a word! You’re correct about the sweet spot but my wife doesn’t care so it’s all about me. I’m looking forward to your opinion 6 months down the road.

 

[rccarguy]

Are you using a AVR? Or quad surround? I have a 4.1 system of pc/dvd/console system upstairs using a avr?


I wouldn't recommend using quad surround, use a avr with prologic IIx music or similar

 

[essence]

I'm running phantom center right now, but it is a bit disappointing. In music I get a precise center image, but movie vocals sound too diffuse. Need to figure out if it is because of low movie volume, interaural crosstalk dip, the mix, or something else.

How much do you need to pre-amp after splitting centre between left and right? And is it really as easy as splitting it left right then matching spl of the three channels?

edit: Okay just tried this, only -3.5dB preamp required, should have plenty of head room.

I run Special 40’s 2.1 for mostly home theater. Dyn’s do an uncanny perfect job with dialogue, sometimes too perfect but you’ll never miss a word! You’re correct about the sweet spot but my wife doesn’t care so it’s all about me. I’m looking forward to your opinion 6 months down the road.

Yeah I find the Dynaudios quite articulate in the vocal region, especially good low volume performance. I still enjoy turning it up for movies though.

Are you using a AVR? Or quad surround? I have a 4.1 system of pc/dvd/console system upstairs using a avr?

I wouldn't recommend using quad surround, use a avr with prologic IIx music or similar

Not a fan of AVRs as I have very little experience with them. It'll be strictly pc-based source. I plan to run R/L + RL/RR 120 degrees.


Choose the Okto as you get more precise control over each output channel. The spare/extra channels I can also use to integrate multi-sub.

Speaker placement is roughly real trap 38 percent rule. My room roughly 44m^3 which is 1500~ cubic feet. I lucked out with ratios, my room fits within the "Bolt Area" in amrocs calculator, with the room modes decently spread out and not so much of a issue to deal with.

Currently running a 2.1 system, DAC -> Y-connector output to speakers + sub. My speakers are running full range as I cannot EQ them separately from my sub. I did try a dbx 223xs crossover unit but it added unwanted noise into my system and the unit's transformer buzz was audible.

After consider the costs of adding a centre is more than going 6.1 makes me very hesitant about it, after all the Okto does have more than enough output channels!

 

[rccarguy]

Bleh. Try using soundcard DSP to encode to decent processed surround.

 

[ernestcarl]

downmix 5.1 -> 4.1 seems to be very easy, just split centre between left-right, pre-amp accordingly to prevent clipping which all can be easily done in EQ-APO.

At this point adding an extra sub seems to be more enticing than adding a centre channel. Looking at the Rythmik Audio G25HP. Can one have too much sub?

or pseudo 5.1ch as I prefer to call it...

This is pretty much what I do for my nearfield desk setup. There's only one main listening position so center channel isn't absolutely required. For me, the phantom center is perfectly fine, although there is a 'critical distance' where I am able to get the "best", most solid sounding center. Gotta experiment with adjusting the angles and distances. Since I use different speakers for my rears, it's not enough to match the FR of the fronts and rears, get correct delays, and volume... I found it very useful to use pink noise to make sure the 'timbre' of the rears match as closely as possible with the fronts (even if the FR already closely match with measurements).

Before rears were 'timbre' matched

In my case, cutting a dB and a half more and applying some additional HF shelving to the rears did the trick. If you're rears sound just even a bit louder than your fronts for whatever reason, this can affect the front image by making stuff sound more diffuse/unfocused than they ought to be. As I'm always upmixing stereo to 4.1ch by default, it was crucial to get just the right balance.

Having done the above, and yet, you still think the 'virtual' center channel sound for movies lacks volume, you could always just use more EQ to boost the vocal region for said virtual center speaker...

 

[Aerith Gainsborough]

If your seating area is small, throw the center out the window.

Tried it ... well the removing the center, not the throwing part.
Works really well in a nearfield setup.

Only caveat is that the sweet spot is really small. I used this track: https://www.tacet.de/download/audio/01546/154_34_il.wav
to test it. If I move my head 10cm to the side, the center image collapses completely. Not a problem for music, where you sit still and listen intently but for a 3 hour movie, you might prefer the ability to shift seating position now and then. Having a center speaker is definitely more robust, so I'd keep it in case you need it.

 

[Promit]

Yeah, how flexible it is probably depends on your speakers and room - and your attention to imaging.

 

[essence]

Okay thanks for all the advice, I'll stick to centre-less setup for now but will add one if necessary. I've also just found out you can customise the voltage of individual channels of your okto unit meaning I'll be able to run my purifi modules in bypass mode! Less is more.

Too bad accessing DTS:X/Dobly Atmos candy is so exorbitantly expensive. Trinnov and Storm Audio being the only two providers that provide post-processed digital outputs.

 

[ernestcarl]

If I move my head 10cm to the side, the center image collapses completely. Not a problem for music, where you sit still and listen intently but for a 3 hour movie, you might prefer the ability to shift seating position now and then. Having a center speaker is definitely more robust, so I'd keep it in case you need it.

Just 10cm and the center collapses completely? Hmmn.. This probably depends on your speakers, the channels setup, as well as its placement and the acoustics in your room. I find my Sceptre S8s at the listening distance of 2m somewhat more forgiving.

If you want to be able to sit elsewhere besides the center listening position while watching a movie or listening to well-defined stereo music, and still have the center image balanced in between your L&R speakers, you can do so effectively with the use of DSP presets.

My couch music listening/movie watching area is wide, and I'm not necessarily in the mood to sit in only one main listening position. Sometimes I prefer to sit in the far right side of the couch, but I get the ff. response:

Besides the displaced phantom center image, there is an interaural time and volume level imbalance.

Since my miniDSP does not have enough buttons for presets, I use JRiver instead to switch quickly to the ff. DSP settings:

Six filters for the left monitor, and just three filters for the right to completely fix the ITD and ILD discrepancy.

Stereo image, timing and volume is now perfectly balanced for the listener sitting in the far right side of the couch -- and since it's usually just me on this couch at any one time, anyhows, it's all good!

 

[Aerith Gainsborough]

Too bad accessing DTS:X/Dobly Atmos candy is so exorbitantly expensive. Trinnov and Storm Audio being the only two providers that provide post-processed digital outputs.

Just get a standard AVR for movies. Even the low cost models should have Atmos decoding capabilities.

People will probably brand me a heretic but IMHO it's useless to fuss about obscenely high SINAD when you are bombarded with synthesized effects done in ADR recording, an LFE channel that makes the house shake and being dazzled by visual effects on a big screen.

Just 10cm and the center collapses completely? Hmmn.. This probably depends on your speakers, the channels setup, as well as its placement and the acoustics in your room. I find my Sceptre S8s at the listening distance of 2m somewhat more forgiving.

Do keep in mind, we were talking about nearfield setups. If I move 10cm, the change in angle, relative to the speakers, is much larger than when sitting further away. So you are not only getting delay but are basically fighting the off-axis response of the speakers too. On top of that, I can only run multichannel sources uncorrected. The sweet spot is a bit larger when I use Dirac Live for 2 channel material.

Very interesting idea with the delay DSP in order to "open up" more seating positions. Also, you couch looks cosy.

 

[essence]

My 4 channel purifi amp for the build has arrived from Audiophonics, very happy with service provided, a few issues here and there but it was more in regards to the shipping company TNT.

They promptly switched out the opamps (from OP275 to LM4562) when requested. Shouldn't matter too much as I plan to run these in bypass mode via Okto dac8 with custom voltage upgrade.

For those unaware, Pavel from Okto Research confirmed that the custom voltage on the Okto dac8 PRO can be customised for specific channels, very useful as I have not seen any subwoofer that accepts high line level voltage.

 

[phoenixdogfan]

My 4 channel purifi amp for the build has arrived from Audiophonics, very happy with service provided, a few issues here and there but it was more in regards to the shipping company TNT.

They promptly switched out the opamps (from OP275 to LM4562) when requested. Shouldn't matter too much as I plan to run these in bypass mode via Okto dac8 with custom voltage upgrade.

For those unaware, Pavel from Okto Research confirmed that the custom voltage on the Okto dac8 PRO can be customised for specific channels, very useful as I have not seen any subwoofer that accepts high line level voltage.

Let me know what voltage you use for the Purifi channels. My plan is to pair an Octo 8 pro with the Purifi Eval 1 i'm putting together, and bypassing the input stage is something I want to do while using the remaining channels for sub, surrounds, center, and for my headphones as well. And yes I would be interested in doing only two channels on the OCTO for that purpose while having the remaining channels set for 4v.