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  1. #1
    GV#27
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    Default Experimental Mid bass module

    Im building this little fella to augment the subs Im using for HT,its purpose is to reproduce the middle bass from 50-80hz.For reasons of restricted placement options my main HT subs are located directly in the corners of my room.Corner loading means they will be exciting every room mode.

    Because of this I have found that they sound best when crossed over at a rather low 50hz.These subs only handle the LFE signal (the LCR bass is not mixed in with it)but the LFE channel can contain info up to 120hz,so by rolling them off at 50hz means Im likely missing out on some parts of the bass track that can add some punch and impact.

    Instead of comprimising the sound of my main subs by moving the crossover higher ,Im going to try adding a small box to handle the the upper part much like Hsu's MBM12. This box will be small enough to sit directly beside the listening chair.The fact that it will be in the near field of the listener and away from room boundries means it be less affected by response altering room modes.

    I chose a 10" Infinity Kappa Series car subwoofer as it perfectly fit my reqirements.
    It will work great in a small sealed box.
    It has good sensitivity and power handling.
    Price was right,got a great deal on ebay.

    I will build a control unit for it that will have a 50hz hi pass filter to remove the low bass and match the crossover of the main subs.It will also incororate a 80hz low pass filter,level control and a 360 deg phase adjustment.The phase adjustment is essential to get the module to blend seamlessly with the other subs.

    The pics show the tiny 11.75" square box with one side removed.It will get a skin of real wood veneer when assembled.
    Last edited by GV#27; 08-10-2008 at 07:45 PM.

  2. #2
    GV#27
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    Heres the pics.
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  3. #3

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    Sounds like a real neat project. I've always wondered about the mid-bass module. I've read good things about the Hsu unit. I'm sure yours will be even better.

    Keep us posted.
    HT/2-channel Rig: Sony 50 LCD TV; Toshiba HD-A2 DVD player; Emotiva LMC-1 pre/pro; Rogue Audio M-120 monoblocks (modded); Placette RVC; Emotiva LPA-1 amp; Bada HD-22 tube CDP (modded); VMPS Tower II SE (fronts); DIY Clearwave Dynamic 4CC (center); Wharfedale Opus Tri-Surrounds (rear); and VMPS 215 sub

    "God grooves with tubes."

  4. #4
    GV#27
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    Quote Originally Posted by Early B. View Post
    I'm sure yours will be even better.
    He He probably not:) but at least I can customise it to get the exact response I want.If it does'nt work out I can just use it as sub for my PC.

  5. #5

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    I think you'll dig it. I've been using two small Energy passives for this for several years.(I split them off the L/R main pre-outs, running full range, and let the internal x-overs do their thing) Definitely something missing when they aren't on.

    Thumbs up, your box looks great.

  6. #6
    GV#27
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    Quote Originally Posted by LessisNevermore View Post
    I think you'll dig it.
    Im hoping so.
    Thumbs up, your box looks great.
    Thanks.

  7. #7
    Audiophile
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    Nice project and I'm always impressed by your wood working.

  8. #8

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    Very nice. I would consider bracing the back wall if at all possible. I'll keep an eye on it;)
    Ben
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben

  9. #9

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    Bracing the back wall in this case risks leading to an increase in box vibration modes. As it is, there are very few sides with the same dimensions which will spread out the reverberant modes.

    Quality construction as always.

  10. #10
    GV#27
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    Thanks for the comments gentlemen.

    Quote Originally Posted by ben62670 View Post
    Very nice. I would consider bracing the back wall if at all possible. I'll keep an eye on it;)
    Ben
    Thought of it but my dado blade will only cut from side to side.:D
    I guess doubling up the back panel might have been a good idea as well.

    Quote Originally Posted by ShinAce View Post
    As it is, there are very few sides with the same dimensions which will spread out the reverberant modes.
    Yep, thats why the brace is offset from center to break the panel into different dimensions so they will have disimilar resonances.

  11. #11

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    It's not going to play full range, not an issue.

  12. #12

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    Quote Originally Posted by GV#27 View Post
    ...I guess doubling up the back panel might have been a good idea as well.

    ....
    I one hundred percent agree with this. My big SDA are designed to use double thickness on the side walls. I did not want a bunch of bracing inside for such a long run.
    As always I'll be keeping an eye on the DIY stuff.
    Ben
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben

  13. #13
    GV#27
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    Quote Originally Posted by ShinAce View Post
    It's not going to play full range, not an issue.
    as in reference to panel resonances?

  14. #14

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    Correct. If this was for a full range bookshelf, I'd say brace the crap out of it.

  15. #15
    GV#27
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    Quote Originally Posted by ShinAce View Post
    Correct. If this was for a full range bookshelf, I'd say brace the crap out of it.
    While I agree to some extent that with the limited bandwitdh of low frequencies involved panel resonances may not be an issue.However while bracing will move the panel resonances to a higher frequency and put them well outside the indended bandwitdth of this unit there is another benifit to be had by bracing.

    The smaller a sealed box gets the greater the air pressure is built up within.When the woofers are moving inward the air gets heavily compressed and in turn exerts pressure on all the panels.With bracing installed it will lessen the tendancy of the box to want to expand and contract (like a balloon)as the woofer moves in and out.

  16. #16

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    This idea works really good in theory. I've been mulling this over for a long time also. I am no scientist by any means but doesn't most chest-thumping bass occur between 60-100Hz? My BFD sub crosses@50Hz and I expect the LS90's 2-6 1/2"s to reproduce these low frequecies. The Denon I was using had an internal Sub Xover @80Hz. I'm sure there was some material I was missing too.
    Keep me informed on what you find!

  17. #17
    GV#27
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    Quote Originally Posted by Jeff Beaird View Post
    doesn't most chest-thumping bass occur between 60-100Hz?
    I believe you are correct.Im hoping that adding in this missing portion of the LFE channel will give me more of an impact or kick in the chest ,especially on soundtracks like the final gun fight in Open Range.
    Keep me informed on what you find!
    Yes I will post my results after I get it completed.

  18. #18

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    Quote Originally Posted by Jeff Beaird View Post
    I am no scientist by any means but doesn't most chest-thumping bass occur between 60-100Hz? !
    Hmmmm. I'll try this. I grabbed a cheap sub recently mainly for the cabinet. My plan was to replace the driver. The stock unit has a POS driver that only goes down to about 35 Hz. If I hook it up to my HT system and run it from 35 Hz to 80 Hz or more, will it effectively be functioning as a mid-bass module?
    HT/2-channel Rig: Sony 50 LCD TV; Toshiba HD-A2 DVD player; Emotiva LMC-1 pre/pro; Rogue Audio M-120 monoblocks (modded); Placette RVC; Emotiva LPA-1 amp; Bada HD-22 tube CDP (modded); VMPS Tower II SE (fronts); DIY Clearwave Dynamic 4CC (center); Wharfedale Opus Tri-Surrounds (rear); and VMPS 215 sub

    "God grooves with tubes."

  19. #19

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    My stereo crosses over from a 12" sub to two 10" woofers at 85 Hz.

    The tingle in your shirt is due to the 10's. Your pants vibrating against your legs comes from the sub.

    Pick your poison. For kick bass in music, it's the 10's at 85 Hz+.

  20. #20
    GV#27
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    I gave it a new skin of white birch veneer.Now I have to find the right colour of stain to get it to match the floor.
    Attached Images  
    Last edited by GV#27; 08-23-2008 at 12:04 PM.

  21. #21

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    Sweet. I need to do some veneering to my big speakers when I get a chance. I was going to stay black for the HT thing, but I am now 99% music. The 1% HT is for the kids, and they are happy with the 19" color TV on PBS;)
    Please. Please contact me a ben62670 @ yahoo.com. Make sure to include who you are, and you are from Polk so I don't delete your email. Also I am now physically unable to work on any projects. If you need help let these guys know. There are many people who will help if you let them know where you are.
    Thanks
    Ben

  22. #22

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    WOW, that looks nice. Good job!:D

  23. #23

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    Quote Originally Posted by GV#27 View Post
    I gave it a new skin of white birch veneer.Now I have to find the right colour of stain to get it to match the floor.
    Looking good.
    I would say a straight clear lacquer, or polyurethane, no tint, will match your floors pretty closely. If you want that glass finish, use sanding sealer first, sand it smooth, then a couple coats of clear should get you there.

    I did this with all lacquer, and it took much longer to build up, then sand back smooth. Both will get you there though.

  24. #24
    GV#27
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    Quote Originally Posted by ben62670 View Post
    I need to do some veneering to my big speakers when I get a chance.
    Yeah Ben give it a try its not hard to do.Those monsters of yours (your speakers not kids)would look even better with some real wood on them.;)

    Quote Originally Posted by Jeff Beaird View Post
    WOW, that looks nice. Good job!:D
    Thanks Jeff
    Quote Originally Posted by LessisNevermore View Post
    I would say a straight clear lacquer, or polyurethane, no tint, will match your floors pretty closely.
    Beautiful work on the drums there LN.Achieving a finish like that is beyond my skill level.

    Although it does'nt appear so in the pic the floor is actually quite abit darker than the veneer.So I think I will need to find a stain to darken it some to match.

  25. #25

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    Quote Originally Posted by GV#27 View Post
    Beautiful work on the drums there LN.Achieving a finish like that is beyond my skill level.

    Although it does'nt appear so in the pic the floor is actually quite abit darker than the veneer.So I think I will need to find a stain to darken it some to match.
    Thanks for the compliment!

    What if I told you you can get a gloss like that with a brush? All it takes is some wet sanding, working up to around a 1500 grit. (automotive sandpaper) You have already demonstrated enough skill in building the box, to easily achieve a finish like that.

    As far as to stain, or not: take a water dampened sponge, and wipe the cabinet down in one spot. That will show you what things will look like with just clear.

    What kind of wood is your flooring? It looks like quarter-sawn oak, or maybe hickory. Birch has a fairly nondescript grain, and will be tough to truly match the floor. If you have a leftover piece of flooring and a scrap of the birch veneer, you could take them to the store, and see what they can mix up for you.

    Keep up the good work.

  26. #26
    GV#27
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    Wow you did that with a brush and not spray gun.What kind of brush foam or bristle?

    Quote Originally Posted by LessisNevermore View Post


    As far as to stain, or not: take a water dampened sponge, and wipe the cabinet down in one spot. That will show you what things will look like with just clear.
    Guess what?I tried this and the result looked to be very close to some of the lighter areas of the floor. I will finish a big test piece and see how that turns out.If not I might see if I can get a somone to mix a closer match.

    What kind of wood is your flooring? It looks like quarter-sawn oak, or maybe hickory.
    I wish but its just laminate,its supposed to be the species that the cute little bears in Australia eat the leaves of.
    Birch has a fairly nondescript grain, and will be tough to truly match the floor.
    True I already had a roll so wanted to use it up,but I guess I should have sprung for some oak as this would likely have gotten me closer to a match colour and grain wise.

    Thanks again for your valuable tips.

  27. #27

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    Quote Originally Posted by GV#27 View Post
    Wow you did that with a brush and not spray gun.What kind of brush foam or bristle?

    In all honesty, it was sprayed, but spraying, is not required. You can get equal results with a brush. (just takes a bit more time, and resist the urge to do it all in one thick coat) Wet sanding is the KEY. Once you start wet sanding, the goal is to get rid of the shiny spots, which are the low spots. Using a good, square cut block to wrap the sandpaper around will help keep the finish flat. Sand with the grain, and gradually move to finer grits. Once it's flat, it should appear almost shiny, kind of hazy. Bust out a good car wax, apply, and buff like hell.

    Guess what?I tried this and the result looked to be very close to some of the lighter areas of the floor. I will finish a big test piece and see how that turns out.If not I might see if I can get a somone to mix a closer match.

    I wish but its just laminate,its supposed to be the species that the cute little bears in Australia eat the leaves of.True I already had a roll so wanted to use it up,but I guess I should have sprung for some oak as this would likely have gotten me closer to a match colour and grain wise.

    Thanks again for your valuable tips.
    Oh, a foam brush will do fine, just make sure it's compatible with your choice of finish chemicals. Can't wait to see it done.

  28. #28

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    ;)
    Quote Originally Posted by LessisNevermore View Post
    Oh, a foam brush will do fine, just make sure it's compatible with your choice of finish chemicals. Can't wait to see it done.
    1. Foam brush
    2. 000 steel wool
    3. Tack rag
    4. And a ton of patience
    Good luck!

  29. #29
    GV#27
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    I have the boards for the crossover/controller partially done.I will be using 3 dual op amps ,2 xOPA2134's and 1 OP275. For the 1 or 2 interested in such things, the functions of the 6 op amp sections are.

    1.)Input buffer with a gain of 5 that can be adjusted by a pot at its input.

    2.)Inverter.this can be switched in and out as needed with a front panel mounted toggle allowing the phase to be reversed 180 degrees.

    3.)Variable phase.this will allow the phase to be adjusted by a pot in fine increments anywhere between 0 and 180 degrees.In conjunction with the phase switch this will allow complete 360 degree adjustability.This is extremely important for achieving a good blend between the Mid Bass module and the other subs.

    4.)50hz 12 db hi pass filter.This will roll off the Mid bass units response below 50hz which is the upper operating point of the main subs.The actual rolloff will be closer to 24 db because the Mid bass driver in the small box has a natural 12 db roll off of its own in the 45hz range.

    5&6.)80hz 12 db low pass filter.These 2 sections in series will produce a 24 db per octave roll off above 80hz.I chose 80 hz and the steep 24 db slope as it should be low enough in frequency and have sufficient attenuation so that localization is not an issue.
    Attached Images  

  30. #30

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    Quote Originally Posted by Early B. View Post
    Hmmmm. I'll try this. I grabbed a cheap sub recently mainly for the cabinet. My plan was to replace the driver. The stock unit has a POS driver that only goes down to about 35 Hz. If I hook it up to my HT system and run it from 35 Hz to 80 Hz or more, will it effectively be functioning as a mid-bass module?
    Update --

    I got the sub and hooked it up in the front of the room (main sub is in the back of the room just behind the seating position). Wow! I didn't expect this cheap sub to make such a big difference. Of course, it doesn't dig deep, but it fills in very nicely. My main sub is no longer localizable (is that a word?). For the price I paid ($129 NIB with free shipping), it is a great tweak for HT.
    HT/2-channel Rig: Sony 50 LCD TV; Toshiba HD-A2 DVD player; Emotiva LMC-1 pre/pro; Rogue Audio M-120 monoblocks (modded); Placette RVC; Emotiva LPA-1 amp; Bada HD-22 tube CDP (modded); VMPS Tower II SE (fronts); DIY Clearwave Dynamic 4CC (center); Wharfedale Opus Tri-Surrounds (rear); and VMPS 215 sub

    "God grooves with tubes."

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