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Is a sub at the rear better than none at all


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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?

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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 :)

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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.

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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

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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

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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 by JohnL
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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 :) 

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"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 by hopefullguy
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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

 

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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.

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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. 

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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?

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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"

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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

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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.

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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.

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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?

 

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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

20200831_211600.jpg

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!

image.thumb.png.43a1841b923fc5d71189801e46cc2c5e.png

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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 by Jone5y
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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 :D definitely need to move some air ... 

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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.

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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.

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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?

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17 hours ago, Cloth Ears said:

Not sure what your budget is, but the cavity on the left looks tailor made for a reasonable ported sub. 

 

I'm guessing it's about 600-odd litres

I'd be looking to come in at around $1500 for driver, box and amp (or as close to that as possible)
The space is around 500l. 1000x700x800

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1 hour ago, Jone5y said:

I'd be looking to come in at around $1500 for driver, box and amp (or as close to that as possible)
The space is around 500l. 1000x700x800

Look, I'm no expert. I build using an old spreadsheet called Unibox. Quickly running a Dayton Audio UM18-22 through that shows you could use it as a...

  1. Sealed box (about 400litres) with a really solid baffle and you could use that probably without any EQ with a big amplifier (1000W). As this would be driving it to about its limits, you probably wouldn't want to boost below 25Hz, if you did want EQ - but you could always balance it a bit by dropping above 25Hz by 3-6dB. Only after you've listened to it first, of course.
  2. Ported box. Possibly not super musical, but definitely worth it for movies. It would basically be a "Marty Cube" thing, with an 'L' shaped slot-port of about 105cm length, full width (on the floor) and about 6cm high. This would be able to be quite loud (well over 110dB at 15Hz and no issues with the driver excursion) and reasonably balanced.

Here's a UM18-22 thread from AVS forum: https://www.avsforum.com/threads/um18-fully-marty-build.2936768/#post-55206500. Yours would look similar to the first model (on the inside), but you wouldn't need bracing as your 'box' is made of bricks and concrete. The port would not be as long, it would need the 'L', but only about 25cm of the upward pipe (as I've assumed that your 800mm was the front to back dimension). I'd also suggest some sort of cradle to rest the magnet on...

 

16 hours ago, Red Spade Audio said:

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.

Based on experience, I've found it quite easy to find 80Hz (even if it's down 3-6dB - like with a 4th order crossover). So I would look at 50-60Hz as being the highest I'd like to crossover to a sub unless the crossover is 8th order (and I've never used one of those). Since I moved my bass boxes under my main speakers, there is no issue. And the subwoofer I'm building now will be only used with a 50 or 35Hz low-pass (depending on the crossover I decide on).

Edited by Cloth Ears
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13 hours ago, Jone5y said:

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?

"Darling, I promise you, there always was a giant return air duct in this corner! What do you think? That I just added a useless air duct in the corner for no good reason?!"

If the matter goes to the high court of interior design, I had nothing to do with it!

There is a mix of things you can look for, including bottom end extension, avoiding major dips, flattest overall response, highest output. The emphasis changes as you change the number of subs and also the number of listening positions you want to optimise.

For one sub and one seat, the answer is often relatively straightforward. It's mostly about avoiding dips, as you can EQ out the peaks very well in that one position. As you start adding more seats you want to optimise, especially in more than one row and also as you start to consider more subs, the exercise becomes more complex. The answer leans more towards reducing seat to seat variation.

 

 

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Appreciate your input Cloth Ears, i did enjoy playing around with simulations a couple of years ago.  When funds allow I'll probably start a thread specific to the design of the sub

 

Everything will be optimised for 1 seating position, potentially 2 - immediately adjacent to each other. Not entertaining the idea of multiple rows

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47 minutes ago, Jone5y said:

Appreciate your input Cloth Ears, i did enjoy playing around with simulations a couple of years ago.  When funds allow I'll probably start a thread specific to the design of the sub

 

Everything will be optimised for 1 seating position, potentially 2 - immediately adjacent to each other. Not entertaining the idea of multiple rows

NP. I was surprised how well the single UM 18-22 simulated. And for $699 (Aussie) I thought  that was pretty good. Especially considering it can move more than 2 litres of air at a time (3 times the amount it's cheaper cousin can do. If I didn't already have a pair of drivers, I might try to get one of those!

 

Looking forward to the build thread!

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  • 2 weeks later...

Another option is a near field dipole (open baffle) subwoofer. It's light and easy to move. You bring it out of hiding and plonk it 1m in front of you when you are listening and put away when you're finished (or when she sees it)

 

The other bonus is you can listen late at night because its near field and dipole and does not really "leak" in to other part of the house

 

Also being dipole, you don't have to really worry about room mode issues. It sounds VERY clean.

 

I have one and I love it. Will never use boxed subs again BUT its not for everyone I guess

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1 hour ago, logarhythm said:

Another option is a near field dipole (open baffle) subwoofer. It's light and easy to move. You bring it out of hiding and plonk it 1m in front of you when you are listening and put away when you're finished (or when she sees it)

 

The other bonus is you can listen late at night because its near field and dipole and does not really "leak" in to other part of the house

 

Also being dipole, you don't have to really worry about room mode issues. It sounds VERY clean.

 

I have one and I love it. Will never use boxed subs again BUT its not for everyone I guess

For the size of the room (well over 200 m3) it would have to a pretty big OB to provide any sort of bass response in the room. Four to six large drivers, maybe in 'H' or 'S' enclosures might work. But I think it might blow the budget.

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Just now, Cloth Ears said:

For the size of the room (well over 200 m3) it would have to a pretty big OB to provide any sort of bass response in the room. Four to six large drivers, maybe in 'H' or 'S' enclosures might work. But I think it might blow the budget.

Size of room is not relevant if it is nearfield :) 

 

I have one 18” in small H frame and at the volume I listen it is more than enough but it really depends on what SPL and cutoff frequency you are chasing

 

cheers 

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14 hours ago, logarhythm said:

Size of room is not relevant if it is nearfield :)

 

I can't argue with that.

 

But it's not much good for a home theatre...

 

13 hours ago, danrey said:

How about an entertainment unit in tasmanian blackwood with concealed sub like the Vaf Platform 2? 

 

https://vaf.com.au/collections/subwoofers/products/platform-subwoofer?variant=19932601477

 

 

Very pretty! There might be vibration issues unless the woofers were mounted opposing each other at the ends of the unit. "WOW! The whole room seemed to vibrate when the T-Rex put his foot down!" 😁

Edited by Cloth Ears
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5 hours ago, Cloth Ears said:

"WOW! The whole room seemed to vibrate when the T-Rex put his foot down!" 😁

 

"Yeah, new thicker speaker cables did the trick"

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On 15/09/2020 at 7:11 PM, danrey said:

How about an entertainment unit in tasmanian blackwood with concealed sub like the Vaf Platform 2? 

 

https://vaf.com.au/collections/subwoofers/products/platform-subwoofer?variant=19932601477

 

 

Stunning. Would also match the decor as I've laid stringy bark floors in other rooms and the lounge has some stringy in it at the back.  

I actually had something like this in mind at the start, but as a coffee table. the boss didn't want components sitting on top of the ent unit. So I'm in the process of wrapping a couple of ikea carcasses in stringy and decorative moulding. The new coffee table design has been decided and unfortunately it is of an open design 😒

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