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BackBum Buster Sub


derrickdj1

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Placement is based on availability.  But, with 8 subs spread around the FR never has any dips to worry about.  I EQ them as one sub.  This second Deep Invader will be in a corner around 28 ft. from the MLP.  The real treat is that these large subs produce effortless bass which is a plus for music.  You do need large Mains with this number of big subs.

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Placement is based on availability. But, with 8 subs spread around the FR never has any dips to worry about. I EQ them as one sub. This second Deep Invader will be in a corner around 28 ft. from the MLP. The real treat is that these large subs produce effortless bass which is a plus for music. You do need large Mains with this number of big subs.

so when are the large mains happening ? ;)
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Placement is based on availability.  But, with 8 subs spread around the FR never has any dips to worry about.  I EQ them as one sub.  This second Deep Invader will be in a corner around 28 ft. from the MLP.  The real treat is that these large subs produce effortless bass which is a plus for music.  You do need large Mains with this number of big subs.

That's awesome. Having that many subs distributed around the room increases the modal density and consequentially flattens the response in more and more positions throughout the room. This has to be the ultimate way to go. It is at least from what I have learned.

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Getting near finishing the second Deep Invader.  Three subs this summer.  That's enough for this HT, lol.  I left clamp hanging off the sub.  I need to mount the driver and line the sub.  Then, glue everything together before sanding and painting.

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The bass system: (2) Deep Invaders 17 cu ft, (2) Full Marty's 11.5 cu ft, (2) Mini Marty 10 cu ft, BackBum Buster 12 cu ft, and sealed nearfield 4.5 cu ft.  Next summer, I will convert the last sealed sub to a ported one next year  for a completely ported system.  All the subs have the UM 18 driver except the two Deep Invaders.  They have the SI HT 18 drivers.

 

The goal of the project was to place some dedicated nearfield subs in the main listening area.  The bass system is still a distributed one for a nice FR and great tactile Response (TR) without significantly elevated spl.  The system as a whole is tuned to 15 Hz.  The tactile Response is greater for nearfield ported subs than with sealed subs.

 

ULF in the HT can  be percieved in several ways, the room shaking, what you feel interacting with the seat, what you directly feel like chess vibration, hair movement, ect. and pressure or the weight of the ULF in the room.  The goal is to get some good ULF and not go overboard: it can take away from a movie.

 

TR can be achieved by high spl but, it can still be lacking if in a basement and who wants to go deaf.  This is where a focus on TR comes in.  How to get it, nearfield subs or Tactile Transducers (TT's)  may be needed.  Yes, TT's can feel natural.  The key is a linear response.  Great TR can be achieved using a combination of things.  The end result is a great night at the movies. :)   Now back to listening to music, lol.

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What a fun build! Your system is quite awesome Derrick! It's been great seeing all your monster subs come together. I'm sure anyone who hears your system will leave with a grin from ear to ear.

Edited by Shodrewken
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What a fun build! Your system is quite awesome Derrick! It's been great seeing all your monster subs come together. I'm sure anyone who hears your system will leave with a grin from ear to ear.

 

Thanks, it's a lot of work, lol.

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What's up with such a big sub like the Deep Invader, LLT(large and low tuned)

 

First you have to look at the advantage of sealed, and ported subs.  Ported are relatively flat thur most of the FR compared to sealed.  Ported subs are not as musical as sealed subs.  This happens for two main reasons, 1.) Group delay and 2.) 24 db roll off, 4th order.  The group delay causes a hump in the response near tuning and a phase switch, muddy bass.  The shift to the port predominate output is occurring in the audible range for most ported subs.  Sealed subs don't suffer these drawbacks.  They are also not loosing output at 24 db due to hpf in the audible range

 

Sealed subs suffer from not as flat a FR, increase power needs for higher spl.  At some point the pressure inside the sealed sub starts to fight driver excursion.  This increase in power demands causes more VC heating and in THD.  There are good and bad things on all the sub designs including IB and horn.  But, this is a discussion on why LLT subs for some people.

 

What is an LLT sub.  Well, it is very big and not for everyone.  An LLT should meet certain criteria:

 

1.)  Tuned to 15 Hz or lower

2.)  No discrete hpf

3.) First  port resonance higher the 190 Hz

4.) Very large ports

5.)  FR with a ~4db/octave rolloff between the tuning frequency and the lowest room node

6.) Minimal resonance enclosure.

 

LLT does not have the drawback of regular ported and sealed subs.  No fighting back as in sealed subs due to the spring nature on the box resistance.  Group delay is below the audible range and they don't suffer from port cuffing due to the large port size.  LLT's have higher sensitivity, use less power and have a flatter FR than sealed and ported subs. 

 

An LLT trades headroom at higher frequencies for lower extension.  Is the LLT for HT, music or both.  It can be used for both.  It will play cleaner, lowe and with less THD than sealed subs.  Due to the large box, it can play lower than most ported subs, not suffer group delay problems in the audible range and virtually, no port cuffing.

 

Taming a beast like an LLT on the low end can be problematic is some rooms even with DSP and PEQ.

Edited by derrickdj1
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  • 2 weeks later...

Here are a few graphs using the Vibsensor on the iphone 6.   The first image is the EOT, Edge of Tomorrow wave form.  It starts at 30 Hz and goes down to roughly 10 Hz.  Note the 10-15 Hz region on the VS graphs.  The shakers fill in the low end.  I still can't achieve this on concrete with just subs.

 

The addition of the nearfield subs and shakers adds a more 3 dimensional TR.  I had weights on the iphone to keep it from bouncing around during testing. :blink::P

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Edited by derrickdj1
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Today, tweaking for a nice house curve to finish the major setup of the bass system for HT.  I also have presets to straight PEQ or a flat response and another house curve using an LS 12 shelf filter.  The graph is the HS 12  shelf filer to set the hpf on the subs to 15 Hz since the I Nuke stops at 20 Hz. 

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More on the use of LLT subwoofers

 

I have these subs integrated into the system and have to say they are the most musical and best HT subs to date for my room.  Read a bit more and some things will become clear.  There are many metrics to measure and gage a subwoofers performance.  In our rooms, it comes down to two things: 1.)  Frequency response and 2.) non-linear distortion.  I listed some drawback to typical seal and vented subs above. 

 

First lest look at subwoofer roll off for a seal sub.  This  usually starts somewhere between 40-60 Hz.  A lot of music can go down to the 30's Hz region or lower.  Some people like sealed subs due to punchy bass.  This is due to the roll off and a emphasis in the subs higher portion of the passband.  There is also more non-linear distortion in the low bass: this is not accuracy technically speaking.  Most 10-15 in ported subs roll off 25 Hz or higher and it's 4th order and the use of  a hpf (so called muddy bass region). 

 

Disadvantage of Sealed: Less sensitivy, need more power and diver excursion, increase distortion

 

Disadvantage of Ported:  Group delay, hump near tuning, hpf and 4th order roll off (24 db slope) and port noise

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No matter how you look at it, roll off = increasing distortion as seen in the above diagram.  The IB sub is in between the ported and seal.  It also has greater low end efficiency due to the large box/room/attic ect.  The drawback is the amount of power to reach driver excursion.  Care must be used in this regard.  Output can be limited by the low power use.  Use of several drivers is common with IB subs to overcome this problem.

 

For ported subs, how to do away with the Group delay/transient response problem, port noise and r.oll off?  Lower the tuning.  Below are two example of what lowering the tune accomplishes.  Note the spectral decay around the same sub with a lower tuning.  The above problems are pushed way down in the sub passband.  This simply results in better bass.

 

First graph 20 Hz tune, second 12 Hz tune

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Edited by derrickdj1
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Coupled with the group delay and transient response, the number of cycle for the signal or what we are hearing to reach full amplitude is affected by the use of a hpf.  For example the signal may take 7 or 8 full cycles to reach full amplitude by using a filter.  Without the use of a hpf, it may only take 2 to 3 cycles.  LLT's don't use a hpf.

 

If looking for a good low response and sensitivity the LLT is one of the most common subs.  There are some disadvantages of the LLT, size is the biggest, no pun intended.  LLT's take more material to build and harder to build since they need to have minimal box resonance. For a sub box to go 1 octave lower, you need a box 4x the size. LLT's average 20 cu ft. or more similar to many horn subs.  This is hard to pass the WAF and acceptance factor for many people.  What you will accomplish with an LLT over a typical ported or sealed sub:  lower THD, lower extension, increase spl especially in the lower frequencies, increase headroom with the amp, a flatter un-EQ'ed FR and better bass.

 

There are pro's and con's to all the sub designs including horns, which I did not discuss.  Designing a bass system take time and thought.  It may also take a lot of trial and errors to find what works in your room.  All the designs are good depending on the application.

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An interesting side note, people wonder are tactile transducers reproducing the movie LFE as well as subs.  I hear comment that with all those subs, you don't really need tactile transducers and  subs are more natural.  Some us have been looking in the tactile response (TR) over the last couple of years and seeing how well various system reproduce the TR as in the movie.  What we found is that this is very difficult to accurately mimic the movie soundwaves no matter what type or strength of subs you have.  It is just hard to reproduce what the director had intended.

 

Here are some of my recent results.  The clip used is Edge of Tomorrow.  The one diagram is from AVS memeber desertdrome, http://www.avsforum.com/forum/113-subwoofers-bass-transducers/2118090-vibsensor-accelerometer-test-thread.html

 

The second and third are subs only and shakers only in my system.  Note how close the shaker Vibsensor diagram is to the movie.

 

The addition of TT's can be a very natural extension of the bass system.  The clip starts at 30 Hz and goes down to 10 Hz.  The 10 Hz portion of my graph is small and should be expanding. The reason the 10 Hz is different, I have a vented system that tapers at 15 Hz .  Also note the peak raw z value, the shakers have a higher Z  or give greater TR than the subs.  When using the subs and the TT's, well it extra fun. :)

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Edited by derrickdj1
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I would like to respond to these posts, but unfortunately I don't understand a lot of what you are doing. Most of it is simply over my head....  :(

 

Your subwoofer system must be a thing to behold. Great work, and I am sure those results you are getting are phenomenal. Keep on truckin!

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Thanks Mustang.  The VS and ULF thread on the AVS forum are fun.  You don't need to drive into to deep but, it just gives you a way of telling how your system is doing.  We could have identical systems but one in the basement and one on a wood floor will be vastly different in what you feel and hear.

 

The goal is not trying to bust your ear drums out but, just to reproduce the movie as intended.  Just like people talk about music and speaker accuracy. :)

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