"Attenion" All Subwoofer Smart Guys!!

Discussion in 'Speakers & Subwoofers' started by terence, May 18, 2004.

  1. terence

    terence Supporting Actor

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    Can This Be Done!!

    I’m about to ask something kind of out there, now I want you to work with me on this. I’m sure it’s some science or physics or something that will keep this from ever happening. How this crazy thought of mind came about is, different tunes on subs have compromises. This now brings me to my question.

    Can one design a HT with (powered or not) subs, @ different tunes, to all work with each other putting out maximum SPL’s?

    For i.e. (collocated or not) [​IMG]

    Sub A: tuned 25hz
    Sub B: tuned 20hz
    Sub C: tuned 15hz
    Sub D: tuned 10hz (i know i'm asking a lot on this one)

    X them to overlap for a seamless transition, and Equed from 100hz all the way down to 10hz or lower! Remember no compromises far any loss of SPL! So can this be done or am I a dreamer??!

    Oh, and of course the subs most sound good and be articulate.

    What would be perfect, if one sub could do it all. This thread is for educational and fantasy of the a perfect sub/sub's, that could do it all. Now let's have some FUN! [​IMG][​IMG]
     
  2. Stephen_Ponte

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    By having multiple vents in your enclosure, each with a 'different tuning', the system will sum all of the vents, and you'll end up with a summed vent resonance.

    If you're thinking of having 4 different vents, each at a different length, for a different tuning - it won't work.

    What you're looking for, is a sealed subwoofer, with extensive EQ available. Look toward the DD series from Velodyne.


    Physics dictate otherwise.
     
  3. steve nn

    steve nn Cinematographer

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    Terence buddy! What have you been ingesting for the past few days?[​IMG] Blotter? Pink barrel?[​IMG] You just set the hurdle for the perfect sub though. I'll go change tunes in my trio and see how it does you funny guy you. [​IMG]
     
  4. Chu Gai

    Chu Gai Lead Actor

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    Maybe you're looking for one sub with 4 separate enclosures?
     
  5. John Tami

    John Tami Stunt Coordinator

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    Get a B4+ and just enjoy it..............
     
  6. Dennis Gardner

    Dennis Gardner Stunt Coordinator

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    One big (4-15s or bigger) IB setup with EQ to give flat response to 10hz will do what you want.

    You don't need multiple tunings from multiple boxes, just a flat response from one!

    It's done all the time.

    DG
     
  7. terence

    terence Supporting Actor

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    Thx for the suggestions guys, and info. I'm fine for now. I was just asking for fun.

    Got to admit that, a sub designed with no compromises would be cool.
     
  8. Craig Chase

    Craig Chase Gear Guru
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    Tee - A Pair of B4+ and a really Big Crown Amp (I don't feel like looking it up) will give 120 dB bass at the listening position to 10 Hz, will sound great, and set you back about $8000 ...

    I would estimate about 15 Tempests in IB would do the same, If you had the empty room to use...

    Either way, you would qualify for the Asylum...
     
  9. Craig Chase

    Craig Chase Gear Guru
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    Tee - A Pair of B4+ and a really Big Crown Amp (I don't feel like looking it up) will give 120 dB bass at the listening position to 10 Hz, will sound great, and set you back about $8000 ...

    I would estimate about 15 Tempests in IB would do the same, If you had the empty room to use...

    Either way, you would qualify for the Asylum...
     
  10. Craig Chase

    Craig Chase Gear Guru
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    Is anyone else seeing double ?[​IMG]
     
  11. Mark Seaton

    Mark Seaton Supporting Actor

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    Hi terence,

    No compromises? No size restrictions? No question. The answer is a large bass horn with flat response in free space to maybe 16Hz with significant loading below that point to about 10Hz. In most any real home theater this would yield flat response to 10Hz at truly startling levels such as about 140dB @ 1m. A horn very much is the "work smarter, not harder" approach, as such a monster could run off of only 2-8 drivers and need less than 5kW to acheive such response.

    Interestingly, a horn very much parallels what you are thinking with multiple tuned boxes tuned to specific ranges. What you describe is also the similar concept to a bandpass. The issue with both of these are that they are far from trivial to execute well, and "misalignment" can be quite audible. EVERY solution has it's compromises in size, efficiency, and potential non-linearities. Don't forget that every solution has a point of non-linearity. Ports, horns, drivers and passive radiators all have points of non-linearity or overloading. The big question is how much is enough? Most people I know as well as myself would agree that clean dynamic capabilities to about 125dB to the listener would cover just about anything we could desire to be reproduced. My take is that the ultimate would be to extend this response to 5Hz, or even nearly enabling a DC offset if we could make the room vault like. Of course the concept of DC will only come from a system which is ultimately sealed. Many trade offs to consider...

    Cheers,
     
  12. terence

    terence Supporting Actor

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    I forgot about size, i guess one could always build a house around the sub! [​IMG] I wonder what wife is going to go for that! Thx Mark, Craig for the great info, it's fun learning about this stuff. [​IMG]
     
  13. Bruce Hall

    Bruce Hall Agent

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    Our experiences tuning the DD Signature 1812 relates to the topic and might make interesting reading.

    As some background, the 1812 consists of two DD-style sealed servo-controlled woofs - you guessed it, an 18 and a 12. We designed the 18 to handle from infrasonic to about 50 Hz, and the 12 to handle above that to whatever the low pass crossover point is set to. This means that the 18 has a subsonic of as low as 15 with the slope set by the user, and the low pass of the average of the woofer’s subsonic and low pass settings (default is 15 + 80 / 2 = 47.5 Hz), fixed at 24 dB per octave. The 12 has a “subsonic” of the average described above (again, default 47.5 Hz), with a 24 dB/octave slope, and the low pass of whatever the low pass is set to to mate with the main speakers (often 80 Hz, but sometimes higher or lower depending on the main speakers and how they are crossed over).

    This might seem pretty straightforward, but it turned out to be a much larger can of worms than we expected. The 18 and 12 subs’ crossover point (default 47.5) changed as the subsonic or low pass changed – easily calculated when you have a DSP’s processing power. However, this wreaked havoc with the phase angles between the two woofs, and caused suckouts at the crossover frequency. Add to this the fact that the overall phase of the woofer can be adjusted, not to mention the slopes of the subsonic and low pass, and you have a multi-dimensional array of combinations of subsonic, low pass, phase, and slopes, all of which affect the response of the woofer in its playing range.

    Now, there aren’t exactly textbooks that tell you how to solve this problem. So, we went through an incredibly tedious process of testing each combination and coming up with an internal lookup table that is referenced whenever any of the above parameters changes. The phase of the 12 is determined by this table and set on the fly to ensure that it stays flat with its 18 counterpart.

    This took us literally months to sort out, but we had to do it. I tell this story because any multi-drivered deployment faces this challenge, and it’s pretty important to get it right if you’re interested in flat response.

    Bruce
     
  14. terence

    terence Supporting Actor

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    Thx Bruce,

    For chiming in, very good stuff you posted. When i first saw the 1812, i always thought it was an interesting design far as subs go.

    Do you have any measurements of what the 1812 can do, that you can share?
     
  15. Bruce Hall

    Bruce Hall Agent

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    Hi Terence,
    It really depends on what you want it to do. All management of the signal and the amplifier are digital, and there is an 8 band EQ (plus the one with the presets, making 9 total) that are settable by the user, in addition to the subsonic and low pass crossovers, phase, presets, and servo loop gain setting which are also user controlled. Each EQ can be set for frequency, Q and level, from 15 to 120. I've seen people "stack" EQs at 15 and jack them up, providing unbelievable low end performance (the filters jack not only the primary frequency they're set at, but also surrounding frequencies according to the Q value - the higher the Q the more narrow the band of the EQ's effect). So if someone is interested in playing below 15 it will do so quite obediently.

    To summarize the above, an infinite number of frequency curves can be created by using the computer/onscreen controls other than the ones we preprogram with the unit.

    Regarding overall capability, let me put it this way. From my office I hear lots of woofer testing in the lab (usually followed by a request to change the DSP software). I always know when the 1812 is being tested. It is truly the scariest of beasts, with 2500 watts RMS (6000 peak) power, 1.75" throw drivers, and huge magnets/voice coils. Divvying up the load on which driver plays what frequencies is just icing on the cake.

    Bruce
     
  16. Mark Seaton

    Mark Seaton Supporting Actor

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    Indeed, matching multiple subwoofers in a optimal manner really does require measurement and awareness of different interactions. I've done more than a few "multi-way" bass/subwoofer setups in professional applications, and this weekend I will have the fun of integrating one of our B-DEAP-32 subwoofers with a ContraBass. There was a little discussion of this over on AVS Forum. Readers should realize that this interaction with the high pass/subsonic filter is not limited to a multi-way subwoofer setup, but significant changes to a subsonic high pass in slope or frequency can certainly affect the interaction with the mains. I have a major advantage in that I'll be attacking this with a TEF 20 to really see how the two are interacting and quantify what needs to be altered and by how much.

    There are many benefits and detriments to adding such complexity. In the end it mostly boils down to more opportunities to screw it up, so you better know what you are doing! That said, simplicity will typically only get you so far. In reality, if you had free reign to properly execute multiple subwoofers for multiple frequency ranges, you would likely find optimal locations for their placement to better work around issues with the room. Again, not something you can optimally execute in a plug 'n play manner.
     
  17. Mark Seaton

    Mark Seaton Supporting Actor

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    Hi Guys,

    Pulling up an old thread here as I had meant to post some measurements of what we did with a 2 way bass system compromising a ContraBass and a B-DEAP-32. I finally took some time to export some images. While the B-DEAP was not used in its preferred orientation for low frequency extension, in this location/configuration it gives very smooth and rediculously powerful response above 40Hz. As such, we then used a QSC DSP-4 to integrate the two based on the measurements I made using the TEF analyzer. While a slight shift in the seating location helped some, the space limitations of placement at either side wall made for a few problems, particularly a nasty dip near 30Hz. Even more interesting was finding that opening or closing french doors to and adjacent basement office at the back left of the room would suddenly suck 10-20dB out in the 28-32Hz range! The measurements linked below are with the door closed.

    The first image is a before and after (single ContraBass with EQ vs. ContraBass plus B-DEAP integration). Note that for all of these, I still need to double check the absolute value of the levels, which can be adjusted after the fact in the TEF software, but the scale is accurate. All measurements here were taken at the primary, center seat at ear height. Here is a look at what we started(white curve) with vs. what we ended with(magenta curve):
    Anthony's system - Before(white curve) /After (magenta curve)

    Here are some measurements of the system at progressively louder increments, with the top curve being a louder sweep where I only started at 25Hz as the room was making lots of its own noise below that point.

    Increasing levels at the seat

    So yes, you can most certainly integrate multiple units, but I have to say that doing this in-room was quite the interesting trick, and I came to some very non-obvious settings with the DSP-4. I would strongly recommend someone having more measurement capability than just an RTA for such a setup, but it could certainly be made to sound ok.
     
  18. frank manrique

    frank manrique Supporting Actor

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    quote:

    "So yes, you can most certainly integrate multiple units, but I have to say that doing this in-room was quite the interesting trick, and I came to some very non-obvious settings with the DSP-4. I would strongly recommend someone having more measurement capability than just an RTA for such a setup, but it could certainly be made to sound ok."

    Umm...so that's exactly what I'll be faced with when I finally attempt to integrate the eight 16-46 and two B4+ subs within the same sound system, eh? [​IMG]
    And cannot even avail the use of an RTA or DSP-4 since I don't have neither. [​IMG] Phew!...

    -THTS

    "...hi, my name is Frank...and am an SVS bassaholic..."
     
  19. Mark Seaton

    Mark Seaton Supporting Actor

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    Frank,

    Implementing such a 2 way setup is more work to get a good blend vs. just running multiples. In the end, it is a matter of taking a few measurements to see where you are starting. I should probably re-state the comment above in that without a hi-res RTA like TrueRTA or similar, it could be a long process. A time sensitive measurement system will make the process much quicker. I would strongly recommend you invest in something like TrueRTA, especially in light of everything else in your system. This way you can immediately see where there are good and bad interactions with the room or between different subwoofers.

    Cheers,
     
  20. frank manrique

    frank manrique Supporting Actor

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    quote:

    "A time sensitive measurement system will make the process much quicker. I would strongly recommend you invest in something like TrueRTA, especially in light of everything else in your system. This way you can immediately see where there are good and bad interactions with the room or between different subwoofers."

    Thanks, Mark...I was afraid of that! [​IMG]

    Seriously, really appreciate your wisdom, in-depth comments and suggestions. They're very valuable to me.
    Now, where would I have to go to get stuff like TrueRTA?...

    -THTS

    "...hi, my name is Frank...and am an SVS bassaholic..."
     

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