ported HE15 revisited

Discussion in 'Archived Threads 2001-2004' started by Jeff Rosz, Mar 17, 2001.

  1. Jeff Rosz

    Jeff Rosz Second Unit

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    ok, im opening up this can o worms again. feel free to add your 2 cents, but please explain your 2 cents too. music and HT are getting closer to 50/50 from mostly HT. my room is about(from memory) 12x20x7. im using BB6pro and here what i have so far:
    Vb=10 ft3
    Fb=16 Hz
    1 6" vent @ 21"
    modeled input power @ 500 W seperate coils
    F3=~25.5 Hz
    F6=~16 Hz
    GD=< 19 msec @ 20 Hz
    VV=< 20 m/sec from 14 Hz and up
    its got about a 2dB/oct slope in a BW from ~16 to ~50 Hz
    i also tried Fb @ 17-18 Hz that resulted in the slight expected changes in GD and output. btw, BB6 suggests 18 Hz
    now to the questions i have:
    1.what are the pros and cons of seperating the coils?
    2.is group delay really noticable
     
  2. Chris Hoppe

    Chris Hoppe Stunt Coordinator

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    Well, a large ported HE is a great idea! That's really the way to go if you have the room.
    A couple suggestions...
    Your choice of box volume and tuning is good. However, a single 6" port is in my opinion and experience...insufficient. I would say that two 6" or four 4" ports would be the minimum. Not only will this avoid chuffing, but you'll get less port compression and more whallup at the low low frequencies!
    I don't see any real pro or con to separating the coils from a performance angle, but they do allow you more flexibility in matching the load to your amp.
    Most people have found that GD at very low frequencies is not much of an issue. I wouldn't worry about it.
    Another thing... you should use a subsonic filter on this if you can. It helps tremendously! In fact, in my model, if you set the Q to 1.3 with a center of 18Hz, it will get you that 2db back and give you more output at 20Hz while keeping the cone in control. (you can model that in BassBox by selecting 'Vented box with Active HP EQ filter')
     
  3. Jack Gilvey

    Jack Gilvey Producer

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  4. Jeff Rosz

    Jeff Rosz Second Unit

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    thanks for the replies fellas.
    chris:
    i must have been looking at a different model when i wrote down the port info and posted it. do you believe that?, er ah, i mean thanks for catching my error [​IMG] i agree two six inchers are the way to go here. the vents then become really long though [​IMG] tradeoffs tradeoffs...
    i plugged in the subsonic filter info and i see what you mean. a very nice improvement, great tip. that bad boy is dead flat and slamming 115dB @ 1 meter to 20 HZ. thanks. looks to me like this monster will scare termites (but possibly do as much damage) tradeoffs tradeoffs.... [​IMG]
    jack:
    thanks for the link, very informative thread. i found the values of the components for the filter there. BB6 has a utility for adding filter component values, but at this point with my limited experience using the prog, i am not quite sure how to plug them into BB6. can anyone help me out here? however, the prog has on its box design window, 2 boxes to input the freq and Q of a filter. i input 17 hz and .96, and get a response very simular to the response chris modeled. not enough difference to warrant trying to modify the HS500, or no? looks like adire has got their hands on a nice amp.
    ------------------
    *why build one when you can build two for twice the price*
    jeff
     
  5. John E Janowitz

    John E Janowitz Second Unit

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    Jeff, there are a few things to take into consideration with the enclosure size. First of all, the very large enclosure, 10 cubic feet is really the only way you can fit adequate vents in the enclosure. This large enclosure will give you more output in the sub 20Hz range on a small signal level.
    Here is a graph comparing the recommended 22" cube in red to your 10 cubic foot ported in green:
    [​IMG]
    You can see that the larger enclosure does have much more output below 20Hz, however the response is not flat by any means. With room gain your 16-18Hz output will be much louder than your 20-30Hz output if no subsonic filter is used.
    The other issue to look at is the max output capability. Going with the larger enclosure limits your output in the 18-30Hz range much more than the smaller 22" cube. This is where the excursion is at it's highest levels above Fb. Just as an example, at 20Hz your acoustic power will be limited to about 6dB less with the 10cf enclosure, compared to the 22" cube. However, you will have capability for much more output in the region below 18Hz with the larger enclosure. Here is a graph showing this, again the large enclosure is in green:
    [​IMG]
    In most cases, the 20Hz to 30Hz region is much more important than the region below 18Hz. This is one of my main reasons for suggesting the 22" cube, or other enclosure about 4 cubic feet. Enclosures larger than this seem to be past the point of diminishing returns. You can get more output below 20Hz, but at the expense of you your output above this point.
    Regarding using the subsonic, you can use a Q such as 1.3 that Chris suggested to get a few dB back. This will flatten your response, however you will still be limited in max output. If you plan to use a subsonic at 18Hz, there is really no advantage to the larger enclosure. You will be losing the 20-30Hz output capability, and because you are then using the subsonic at 18Hz, you will not get any of the gains from the larger enclosure.
    John
     
  6. Chris Hoppe

    Chris Hoppe Stunt Coordinator

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    John, I don't get that "ski jump" looking curve, and I am also using Bassbox. I get a little ski jump, but not nearly that severe... Not sure why it's different.
    Also, even if you do have a ski jump, that can be corrected for by setting the subsonic filter to a frequency a little higher than the peak occurs and giving it a higher Q that will mirror the shape of the trough.
    The cool thing about this is that you can get tremendous output at and below Fb with very little excursion. In fact, it will be less excursion for a given SPL than above port resonance. Excursion above Fb is about the same as it is for a small box. Also, this reduces your risk of bottoming the driver.
    Setting the HP to a frequency higher than Fb in this situation does not even cause you to lose much low bass extension either. You are just taming an excessive response down there...
    ...or so I theorize... We'll see when I get my 16cuFt 4HP Sonotube done eh?
     
  7. Jeff Rosz

    Jeff Rosz Second Unit

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    thanks for the input john. it is highly regarded. as you may know, i have a 22" cube built and ready to go. just waiting on the PR's. i just wanted to explore a ported system perhaps more in depth than previously done on this forum. i wish i knew how to grab those graphs off the prog like you. also when i asked about getting 2 dB/oct back, perhaps i should have added "with room gain", but i'll take it anyway i can get it. please bear in mind i have limited experience with this prog (a month) and i use a kind of learn as you go approach, and cover my mistakes with "its only MDF, i'll buy more". [​IMG] but i, like chris, cannot duplicate the response graphs, except when i make the enclosure much much larger than 10cuft. or by adding in some room gain into the "room acoustic properties". is this what i am missing? again, thanks chris and john for the input.
    ------------------
    *why build one when you can build two for twice the price*
    jeff
     

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