Is a sub at the rear better than none at all

[Jone5y]

Morning all,

 

As part of recent renovations i have been granted approval to add a sub to my system, provided it goes "Over there, where it'll never be seen". "Over there" is a concrete and brick lined box, at the back corner of the room, concealed by some wooden doors. The space is approx 700x700x600mm and the room itself is approx 7x7 with ceiling sloping to 4.5m at the rear. The main speakers are VAF DCX35's for the foreseeable future.

 

I realise there are potential issues with localisation, phasing, integration etc. My question is whether these would be able to be overcome to the point of it being worthwhile adding a sub at all, or continue going without one. Music to movies would be a 50/50 split, +- 10% either way. 

 

Have read a lot of conflicting info re: success and failure stories, appropriate crossover level, phase adjustment etc. I don't have the sub to go there yet (will be DIY if i proceed) nor do i have access to one for testing so I want to be somewhat confident of a positive result before i pull the trigger.

 

Does anyone have any experience with rear sub placement? Is the space where it will reside going to cause additional problems, or just exaggerate the effect of putting it in a corner?

[betty boop]

Depends on a few factors, will putting the sub there cause any adverse issues if put there ... likely won’t know till do

 

yes not co-located with mains will add  complexity with integrating with mains... again won’t know whether issue till try

 

do you have means to setup eq and integrate the sub in with room and mains ? Given stuck with location, eq and what do with setup and integration will be your friend

 

as long as not running too high freq range it shouldn’t be localised .. Ie keep below 80hz. If it’s doing something obnoxious bringing attention to self have to deal with that, whether with design (ie ports chuffing or something) or do what can to deal with eq and setup to minimise

[tubularbells]

I have the option to place my sub at either the front or rear of the room for my 2 channel system and after much experimentation find it actually integrates with my mains much better when in the rear position approx 1/3 from the LHS corner.

 

It really comes down to room acoustics and front speaker positioning as to where the best place for a single sub will be.

[Itsmoi]

I have dual subs in the rear, one in each corner, sealed 2x15 inch subs driven by a single plateamp from one sub(Seaton Submersive Master/slave config), simply no room in front anyway and system overall sounds fine. I may blow out the pane of glass next to front door one day as that one can have a right old rattle at certain frequencies though hehe

[Jone5y]

Only option for EQ would be through the AVR plus whatever amp running the sub may bring. No  MiniDSP or DEQX at the moment or in the immediate pipeline. Will run with an established design and plug it into something like WinISD to check for chuffing, but I'm not expecting that kind of issue.

 

Is the general consensus 80 Hertz or below to remove localisation? Setting the upper limit to 80 will probably remove some of the higher end (100Hz+) capabilities  of the sub but I'd prefer to have it not able to be localised than to be able to make output higher frequencies. I assume this'll be best handled by trial and error once its in place

[JohnL]

I would expect things to work best if you set all speakers to "small" on your AVR which will set crossover to sub at 80hz.

Ensure crossover setting on sub is set at max........eg 200hz and volume around halfway.

 

Then run your AVR's Room EQ and fine tune sub Vol and Phase from there if/as necessary.

Hope you have long enough I/C to reach sub from AVR!!!  

Edited August 26, 2020 by JohnL

[betty boop]

3 hours ago, Jone5y said:

Only option for EQ would be through the AVR plus whatever amp running the sub may bring. No  MiniDSP or DEQX at the moment or in the immediate pipeline. Will run with an established design and plug it into something like WinISD to check for chuffing, but I'm not expecting that kind of issue.

what is the AVR? the EQ and setup for most is actually pretty decent. I think only yamaha doesnt do all that much with sub bass, but most others do pretty well  

 

3 hours ago, Jone5y said:

Is the general consensus 80 Hertz or below to remove localisation? Setting the upper limit to 80 will probably remove some of the higher end (100Hz+) capabilities  of the sub but I'd prefer to have it not able to be localised than to be able to make output higher frequencies. I assume this'll be best handled by trial and error once its in place

dont really want to go 100hz plus ! definitely try and see.... will soon know  

[hopefullguy]

"As part of recent renovations i have been granted approval to add a sub to my system, provided it goes "Over there, where it'll never be seen". "Over there" is a concrete and brick lined box, at the back corner of the room, concealed by some wooden doors."

 

so sorry for your situation

 

nothing wrong with the sub at the back of the room, usually "in the room" not a concrete box.

Edited August 26, 2020 by hopefullguy

[Jone5y]

6 minutes ago, betty boop said:

what is the AVR? the EQ and setup for most is actually pretty decent. I think only yamaha doesnt do all that much with sub bass, but most others do pretty well  

 

dont really want to go 100hz plus ! definitely try and see.... will soon know  

The AVR is an old Denon 2311. It has Audyssey but I'm not sure which iteration. I'll only ever require 5.1, maybe 5.2 if this venture is successful (there's a bigger spot in the other rear corner), so when this one dies I wont need anything particularly fancy to replace it. Mains will be driven by an integrated when funds allow

 

[betty boop]

12 minutes ago, Jone5y said:

The AVR is an old Denon 2311. It has Audyssey but I'm not sure which iteration. I'll only ever require 5.1, maybe 5.2 if this venture is successful (there's a bigger spot in the other rear corner), so when this one dies I wont need anything particularly fancy to replace it. Mains will be driven by an integrated when funds allow

 

only base audyssey, I think had to go to the 4311 to get xt32 which is more sophisticated. though even that said the base audyssey likely be fine with doing what's needed for only one sub. otherwise can easily add something as well if needed be.

[Jone5y]

39 minutes ago, JohnL said:

Hope you have long enough I/C to reach sub from AVR!!!  

That's the next task on the list. It'll need to be run under the carpet and that goes down on Monday. That short timeframe means delivery is not an option which means I'll be DIYing the 10-11 metre length i need. Much like the sub placement itself, what is required in a sub IC and how important those things are is a bit of a minefield to sift through. 

[gwurb]

On 26/08/2020 at 8:30 AM, Jone5y said:

concrete and brick lined box, at the back corner of the room, concealed by some wooden doors.

Are you going to open the doors when the sub is playing? Always behind closed doors?

[Jone5y]

Doors will be open when its in use

[davewantsmoore]

On 26/08/2020 at 8:30 AM, Jone5y said:

Does anyone have any experience with rear sub placement?

Make sure the crossover is no higher than 80Hz 24dB/octave ..... and if only 12dB/octave... then consider running it lower than 80Hz

On 26/08/2020 at 8:30 AM, Jone5y said:

Is the space where it will reside going to cause additional problems

Check the doors won't rattle (or fix them if they do).

 

Otherwise, it will be fine..... and it's just the typical issues of "where are the bass sources located in relation to each other, the listener, and the walls"

[Jone5y]

Noted,  thanks.  I'll run the cabling tomorrow before the carpet goes down on Monday and get to building it once the Reno's calm down a bit

[gwurb]

I had a sub between a wall and a couch, at the back of the room. It was the only place I could put it. It worked ok. It was better than no sub.

 

With doors open you will probably get a benefit out of having it in the the space.

[davewantsmoore]

Until the "cavity" becomes a significant size in relation to the wavelength of sound being produced, it will have zero effect.

 

80hz is 4.3 meters long.     Even if some of the sound "bounces around inside of the cavity before it comes out the front opening" ..... it is only a very small fraction of a wavelength out of phase with the rest of the sound.    So there will be no effect.

[Cloth Ears]

On 29/08/2020 at 8:43 PM, davewantsmoore said:

Until the "cavity" becomes a significant size in relation to the wavelength of sound being produced, it will have zero effect.

 

80hz is 4.3 meters long.     Even if some of the sound "bounces around inside of the cavity before it comes out the front opening" ..... it is only a very small fraction of a wavelength out of phase with the rest of the sound.    So there will be no effect.

On 26/08/2020 at 8:30 AM, Jone5y said:

"Over there" is a concrete and brick lined box, at the back corner of the room, concealed by some wooden doors.

I was actually thinking that the "concrete and brick lined box" could be a really nice enclosure for your new sub-woofer. You don't have any photos of "Over there" do you?

 

[Jone5y]

The sub location will be in the back left of this picture. Doors were removed for the carpet to get laid today

[Cloth Ears]

14 hours ago, Jone5y said:

The sub location will be in the back left of this picture. Doors were removed for the carpet to get laid today

That looks like some sizable room! Where you've got back pair of fans - is the floor the same level as the rest of the room or does it go down somewhere else in the house?

 

But, looking at the space in this photo, I would way you are going to need some sizable air movement to fill the space! And, if you're not into designing and building a subwoofer (you have what looks like a couple of great spaces to do that in), then I'd suggest getting the biggest one you can afford and place it just behind the 'door' in the cavity. If it's a ported design, I probably suggest you have the ports and the driver facing in the same direction.

You might be able to use the cavity to re-inforce the bass (but it might just muddy it up or give some weird peaks in bass response - but it's worth a try). I've tried to give an idea below (the bottom two would probably be the least likely to change the response) using the left cavity and guessing at the dimensions.

Have fun!

[Jone5y]

The rooms with the fans in them are elevated compared to the lounge. The slab that forms the roof of where the sub is going is their floor. The openings to them are are approx 1x3 and 2x3. Behind the fireplace is a stairwell that goes down 1 level and up 1 level.

When i last looked at putting a sub in, i think the space on the right was big enough to house Paul Spencer's tapped horn. I also toyed with a mini Marty. Unfortunately i "Don't need a sub that big" so the spot on the left it will have to be. Was thinking of a Marty Cube  but haven't delved too deeply into the actual design I'll go with yet. I reckon you're right though, it'll need to move some air 

Edited September 1, 2020 by Jone5y

[betty boop]

I tend to agree seems to be more like largish open plan and bass doesn’t seem to see boundaries unless getting into concrete bunkers  definitely need to move some air ... 

[Cloth Ears]

23 hours ago, Jone5y said:

The rooms with the fans in them are elevated compared to the lounge. The slab that forms the roof of where the sub is going is their floor. The openings to them are are approx 1x3 and 2x3. Behind the fireplace is a stairwell that goes down 1 level and up 1 level.

When i last looked at putting a sub in, i think the space on the right was big enough to house Paul Spencer's tapped horn. I also toyed with a mini Marty. Unfortunately i "Don't need a sub that big" so the spot on the left it will have to be. Was thinking of a Marty Cube  but haven't delved too deeply into the actual design I'll go with yet. I reckon you're right though, it'll need to move some air 

Not sure what your budget is, but the cavity on the left looks tailor made for a reasonable ported sub. As long as you keep the door closed when not in use! I just wasn't sure what the 'box' on the wall was that's inside the cavity and whether it needed to be accessible.

 

I'm guessing it's about 600-odd litres, which means a pair of Dayton RSS460HO-4 would fit nicely, along with a 5cm x full width (including bracing) slot port of about 60-65cm length. You'd have to choose your amplifier pretty carefully, but there's some pretty high power ones out there.

[Red Spade Audio]

There's always some risk of localisation with a single sub at the back of the room. Simply having a 4th order crossover at 80 Hz won't necessarily avoid the problem. Different subs vary in their tendency to be localised and different listeners vary in their sensitivity. I've ran demos like this countless times and a surprising number of people don't notice a problem, where I'd call it distracting. So there is always some degree of uncertainty.

 

The best solution that I've found to the localisation issue is to have at least one front sub and to limit the rear sub to about 60 Hz. Often the rear sub will help with the midbass where front sub positions might have a major dip. Yes, I know this is not quite what you had in mind.

 

Your DCX speakers could actually be used to run tests. One speaker goes into your listening position, the mic goes into sub positions you want to test.

 

In a room that big with custom DIY on the table, I'd be thinking if you can find a creative solution ie. another position for a sub somewhere along the front wall. Perhaps something stealthy with slim proportions. Don't rule out multiple smaller drivers, or a coffee table sub or something made to look like part of the room. If you are feeling even more daring, there is also IB.

 

The other factor is of course how each position impacts the room response. Sometimes positions like that work perfectly, sometimes they are awful. Sometimes they are so bad that even with plenty of power and EQ, they still behave badly. But in most cases, you could still expect better than no sub at all.

[Jone5y]

Hi @Red Spade Audio 

I fought hard for a sub at the front and, prior to the reno, had an old magazine storage box already up the front that would've done nicely. Alas, it is gone now and any additional speakers will not be permitted . Truth be told the current floorstanders would be gone if the boss had her way. The coffee table idea is a good one but the chosen design for the new table is not enclosed and therefore not an option.  Can't think of a way to incorporate IB. The front wall of the room leads to the exterior, as do the side walls and there is no ceiling space to work with. There is a garage under the floor which would be ideal but a driver mounted in the fresh carpet is unlikely to get the nod.

 

What would i be looking for in the measurements and how would the setup work? Play a tone through the speaker in the listening position and assess the various mic positions for ....?

 

If i could wrangle a sub into the cavity on the other side of the room as well, would that potentially lead to a better result?