# How many db does a second sub add?



## Talley (Dec 8, 2010)

Rewatched "Fury" yesterday and had the SPL logger going during the tank scene where it was the 4 tanks vs. the one. I had the volume set to 0db on the x4000 and here was my results below.

I'm pretty flat response down to 12-13hz in the current single sub scenario. This is with the sub centered between the center channel and right speaker. I moved it to the corner and re-ran Audyssey and only picked up 1db at the peak but this was also without cranking up the sub either. comparing the same audyssey center vs. corner. The corner did offer the flattest response but I did not like the result there compared to center. 

Possibly by adding the second sub and moving both into each front corners then I would have better integration.

My question is if I just added a second VTF-15H MK2 how many db do you think this would add on the low end?

(note: audyssey had all front speakers set to large, rear as small and crossover at rear was 40hz and LFE was 90hz)

peaks are right at the 107.2-107.8db range


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## NBPk402 (Feb 21, 2012)

I believe it will be 3db.


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## Blacklightning (Nov 22, 2011)

I believe it would be 0db. if your current sub is not maxed out adding a sub and then matching the level will still get you to the same level.


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## Talley (Dec 8, 2010)

Blacklightning said:


> I believe it would be 0db. if your current sub is not maxed out adding a sub and then matching the level will still get you to the same level.


ya I can see that.

Then how do I calibrate my system for reference. it's the peaks yes? 105db for speaker and 115db for bass...

I need to read up on how to calibrate the system for reference then maybe. Find out where the limit is.

what do you think


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## Blacklightning (Nov 22, 2011)

I'm new to this too but as far as I know reference is really loud. It takes a beefy system to get there. External amps, multisubs, etc.

Reference should not be a goal if you value your hearing.
http://www.hometheaterhifi.com/volume_13_1/feature-article-thx-1-2006-part-1.html


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## GCG (Aug 22, 2013)

Not sure about subs but adding the ".5 woofer" in a 2.5 way speaker is used to compensate for the ~6 dB stop loss in those designs. If you were adding an identical sub it seems fair to expect +3-6 dB. 


...but don't quote me.


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## GCG (Aug 22, 2013)

Blacklightning said:


> I'm new to this too but as far as I know reference is really loud. It takes a beefy system to get there. External amps, multisubs, etc.
> 
> Reference should not be a goal if you value your hearing.
> http://www.hometheaterhifi.com/volume_13_1/feature-article-thx-1-2006-part-1.html



AW, what are talking about? I still have my hearing. In fact I hear that ringing just about all the time now.

Joking aside, if you value it - protect it - turn it down.


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## willis7469 (Jan 31, 2014)

I believe between 3-6 also. When you calibrate them, each subs gain will just be reduced. So each sub might read 72db separately, but 75-77db together. This equals out to be more headroom basically.


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## Talley (Dec 8, 2010)

willis7469 said:


> I believe between 3-6 also. When you calibrate them, each subs gain will just be reduced. So each sub might read 72db separately, but 75-77db together. This equals out to be more headroom basically.


Well thats my main desire. Just headroom. Ya I'd love to be able to play reference but it's not needed. But the more headroom I add the better imho.

-5db produced max peak of 102db while 0db on the volume produced the results above (107db)

I think the -5db was too loud and really -8db is just about perfect for me personally.

...but when I wanna scare kids I need all the headroom I can get MWUAHAHAHA


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## GCG (Aug 22, 2013)

Talley said:


> ...but when I wanna scare kids I need all the headroom I can get MWUAHAHAHA


You think its fun scarring kids? Try cats.


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## Talley (Dec 8, 2010)

GCG said:


> You think its fun scarring kids? Try cats.


my one cat has a cord chewing problem............


doors remain close into my HT room and cat not allowed. Here's praying that this remains true.


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## willis7469 (Jan 31, 2014)

GCG said:


> You think its fun scarring kids? Try cats.


 Lol! My cat sits with me and watches the sounds "move" around the room.


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## Insearchof (Oct 21, 2014)

willis7469 said:


> I believe between 3-6 also. When you calibrate them, each subs gain will just be reduced. So each sub might read 72db separately, but 75-77db together. This equals out to be more headroom basically.


I concur and will hopefully have time to test this theory tonight. 
I added a 2nd sub recently and immediately noticed more impact but never thought to check the output at the main LP. :coocoo:


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## willis7469 (Jan 31, 2014)

Insearchof said:


> I concur and will hopefully have time to test this theory tonight. I added a 2nd sub recently and immediately noticed more impact but never thought to check the output at the main LP. :coocoo:


 How'd it go?


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## b bos37 (May 30, 2011)

Adding a second sub should produce more db but usually that is not what we should look for.A 2 sub home theatre system should produce more flat bass response if tuned properly.Which in turn improves the total surround envelope of your system.A single sub system will have peaks and dip in the bass response which muddles the surround experience.


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## TomFord (Jul 15, 2014)

Put simply 3 dB.

Wouldn't view the benefits of an additional sub in terms of dB for the purpose/logic of doing it. You already have a world class sub operating in rare range of 12-13 Hz. You can't even feel the bass until it gets to 15 Hz becoming audible at 20 Hz. The 12-13 Hz measurement is impressive, but if the range below 15 was removed at random you wouldn't know which one still had 0-15 Hz in it. None of our 5 senses can detect frequencies or changes in them below 15 Hz. Audibly at 20 Hz. 

When you add another subwoofer you're providing the proper stage needed for the 'best'. 
While the quality of a subwoofer and it's importance in a system are essential for my the representation of the audio I desire the sub is overemphasized and overhyped. 
It's job is to produce the first 3 octaves. 20-50 Hz is where she thrives, also helping every midwoofer out there as they don't being to produce until 40-50 Hz (Low-mid 30's on that speaker costs more than a Benz range) on up to 80 Hz. 
Mids take over around 200 Hz and handle 80% of all audio your system can play. 

With the MKII it's safe to say you're good on the bass at 108 dB.
Note on volume level. Try to run sub near 50% volume, and never operate it above 75%. 

Put that money on better quality speakers and the results will be better than any other improvement you can do every time


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## Talley (Dec 8, 2010)

TomFord said:


> Put simply 3 dB.
> 
> Wouldn't view the benefits of an additional sub in terms of dB for the purpose/logic of doing it. You already have a world class sub operating in rare range of 12-13 Hz. You can't even feel the bass until it gets to 15 Hz becoming audible at 20 Hz. The 12-13 Hz measurement is impressive, but if the range below 15 was removed at random you wouldn't know which one still had 0-15 Hz in it. None of our 5 senses can detect frequencies or changes in them below 15 Hz. Audibly at 20 Hz.
> 
> ...


I just put money on better quality speakers. The SVS Ultra system and the towers are no slouch. My towers produce down to mid 20hz range by themselves.

So far the single sub plays loud enough for my needs and leaves nothing to be desired. I do agree a second sub would help create a better surround. When I place the single sub in one front corner I love the smoothness I get but can still localize it due to the rumble. My room is on the second story so you can source the "vibration" very easy and that is what is causing me to localize the sub... not the audio. Yes I cannot hear hardly at all below around 22hz for me but I can still feel the bass down to 15hz. I don't care to get lower then that however I want maximum headroom. With my current single sub the best spot for me is the center so it integrates better.

With me wanting dual HSU subs crossed at 60hz (two octaves 15-60hz) and then letting the Ultra towers handle the 60hz+ range leaves me with a great headroom. So far to my ears crossing them over at 60hz sounds really good. Especially once Audyssey does it's testing. My testing with audyssey at 85hz of pink noise produces a very flat response from 12hz to 85hz.

My problem beyond this is my room has some major dips/peaks from 100hz to 200hz range (see the photo).


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## willis7469 (Jan 31, 2014)

I think your plan is fine. Get the 2nd one, put em where they're best(corner?). Look forward to around 6db, do some treatments, and scare your family members....maybe the cat too. Lol


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## phillihp23 (Mar 14, 2012)

In general the idea of two subs is to equally pressurize the room, get rid of any localization. The added bonus is a slight increase in dbs. :hsd:


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## Talley (Dec 8, 2010)

Ya I think I should just pull the trigger and order the second HSU and call it quits. No need for more.


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## Tom V. (Jul 12, 2012)

2nd identical woof won't increase extension but it will usually increase headroom by 4-6dB. In rare instances you can see >6.0dB(following along Stan?)..

If you are within 1/4 wavelengths it should be a full 6dB. 

Wavelengths shorten as frequencies increase so you might see 6dB <40hz and 3-4dB >40hz(for example) and that is fine as subwoofers usually have ample headroom in the upper bass anyway.

Tom V.
Power Sound Audio


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## Talley (Dec 8, 2010)

Tom V. said:


> 2nd identical woof won't increase extension but it will usually increase headroom by 4-6dB. In rare instances you can see >6.0dB(following along Stan?)..
> 
> If you are within 1/4 wavelengths it should be a full 6dB.
> 
> ...


Well I can put two HSU subs between the center channel and right speaker no questions at all. So what your saying is putting two side by side with only 1" of clearance between them is better then having one in each corner.... from an output side?

My response after audyssey from 80hz to 10hz is fairly flat +/- 3db with the single sub in this same location. This is after audyssey and no smoothing (which is why I crossover at 60):


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## Wayne A. Pflughaupt (Apr 13, 2006)

Assuming matching subs, 6 dB gain if located in the same corner as the first, or in symmetrical room in “matching” corners, e.g. the two front ones. Any other scenario, 3 dB gain.

Regards, 
Wayne


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## Wayne A. Pflughaupt (Apr 13, 2006)

Blacklightning said:


> I believe it would be 0db. if your current sub is not maxed out adding a sub and then matching the level will still get you to the same level.


Adding the second sub means you have the _capability_ for an additional 3-6 dB. Of course, it doesn’t mean you have to, or will, actually use it... 

Regards,
Wayne


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## Talley (Dec 8, 2010)

Wayne A. Pflughaupt said:


> Adding the second sub means you have the _capability_ for an additional 3-6 dB. Of course, it doesn’t mean you have to, or will, actually use it...
> 
> Regards,
> Wayne



Exactly. But I do like the idea of a more immerse surround experience by having dual subs one on each side of the screen.


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## TomFord (Jul 15, 2014)

Talley said:


> Ya I think I should just pull the trigger and order the second HSU and call it quits. No need for more.



Not sure what context you meant it in, but had me wondering is there such a thing as calling it quits in Home audio/theater? Particularly with an audiophile like myself.

Did a lot of research and my results led me to do what the major Japanese corporation (blanking on name) is doing by skipping 4K and going to 8K. They're the ones with the only (at time I read it) 8K camera that studios are lining up to use. To keep it brief, my analysis led me to 8K TV's becoming available within 6-8 months of 4K content being throughly available on cable/satellite. Reason I didn't get 1 last year and went with the Samsung 7150 which I couldn't be happier with. Friends with projectors say "word I can't say here apparently, big one called Hoover, when did you get 4K?" Haven't seen the high end projectors, yet from looking at the 2-3k models the pic quality isn't even close to the Samsung. Not even remotely. 
Once Moore's law ends I could see an end in sight on upgrades for a longer period, yet to call it quits.... I don't know. 
Then again haven't even had mine a year and have started to build some speakers that have exceeded my expectations tenfold. Show you guys some pics after I get them painted with veneers added if anyone wants to see. Just add that the top end drivers from Audison and Hertz are very impressive to say the least. SQ is on another level

What are the SVS towers and your rear speakers crossed over at internally? When do the midrange take over?
Your measurements looks outstanding to 70 Hz. The drop at 100, especially the last reading in blue I find a bit odd.


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## Talley (Dec 8, 2010)

TomFord said:


> Not sure what context you meant it in, but had me wondering is there such a thing as calling it quits in Home audio/theater? Particularly with an audiophile like myself.
> 
> Did a lot of research and my results led me to do what the major Japanese corporation (blanking on name) is doing by skipping 4K and going to 8K. They're the ones with the only (at time I read it) 8K camera that studios are lining up to use. To keep it brief, my analysis led me to 8K TV's becoming available within 6-8 months of 4K content being throughly available on cable/satellite. Reason I didn't get 1 last year and went with the Samsung 7150 which I couldn't be happier with. Friends with projectors say "word I can't say here apparently, big one called Hoover, when did you get 4K?" Haven't seen the high end projectors, yet from looking at the 2-3k models the pic quality isn't even close to the Samsung. Not even remotely.
> Once Moore's law ends I could see an end in sight on upgrades for a longer period, yet to call it quits.... I don't know.
> ...


Well... I say good enough and call it quits because with most anything you do to upgrade to better is exponential in costs. Right now I really call myself an entry level audiophile setup. I think the sound is great even without room treatment. I'm tickled because the sound CAN only get better with getting the "Room" dialed in. So when I say good enough for the equipment is meaning it's good enough within a reasonable amount of financial investment. The next upgrade would probably have me spending 20k to get the next level of something better. I don't want anything to do with spending more on that.

I still have maple blocks/brass to put under the equipment and room acoustics and such. Honestly I think it'll take me a year or so to get the room like I want it.

The SVS Towers midrange are crossovered at 160hz... there are two woofers and one gets crossover at 700hz and the other at 2khz I think. The center woofers are cross over to midrange at 500hz and then at 2.2k. the bookshelfs crossover from the woofer to tweeter at 2k

The dip in the graph above is the sub and room placement. I put the sub in the corner and I gain more flatness and 8db more output around the 70-100hz range and it is indeed more flat but I don't like the sound from the sub in the corner. The sound of a single sub in the center of the room to me is perfect so thats where it stays.

The crazy thing is I always had the sub facing the room... I turned the sub so it faces the center channel and the one port open is the port closest to the wall and smokin' joes... it can hit hard now. Picked up a bunch... I need to test it but it's probably close to reference now. I need to check.

I'm pretty set on just crossing over the sub at 60hz. Here is the response of all speakers in direct mode w/o processing... yes 1/6 on smothing but it's so you can see the response. The first two lines on the left that are highest are the mains and I have those sealed right now. If I take the plugs out of the port then I pick up like 8db and it's flat down to about 28hz just like advertised but I like them sealed. The blue line is the center channel and the red/green are the surrounds.

Based on the sub response and the speakers I think 60hz is good. I wish there was a way to test all speakers at once. On these tests the volume was set to pink noise at 78db. you can see how they are "bass" heavy and this may be something the Krell attributes to as well. Krells are known for better low end. 

It really makes for nice smooth audyssey results though... I just have a issues in the 80-200 range and I think it's my speaker placement/room stuff.


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