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Additional wooferage


derrickdj1

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The thing with transducers is that you can have the feel/shake with out the volume being very high.  They are not for everyone which is OK.  I can't wait to get the I Nuke 6000 to give these things full power.

 

Metro I am not surprised the near field ported performed so well.  The ported will have higher particle velocity compared to the sealed.  I'm a fan of ported subs for HT.  My ported have 10-12 db more output than and single sealed from 15-40 Hz.  That's a lot of extra output for the ported subs.  If I didn't have a couple of ported subs I would need 3 more dual cab subs.  You can't go wrong with ported for HT in a large room.

Edited by derrickdj1
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I got the new  I Nuke 6000 and had some time to play with the new sub location which is 20+ ft from the MLP around a corner and out of sight.  They are delivering an addition 5-6 db from about the upper 20 Hz and down region.  The shape of the FR graph is unchanged for the most part.  This may be a modal problem that I can't readily fix.

 

I have tried them with different PEQ settings and the one I like the best is an LS 12 filter to boost the low end from 35 Hz and down.  These copper cube subs will be almost exclusively just for movies and they add nothing to the music experience in their role.  Nearfield placement would most likely be off the hook but, it may be to distracting.  More experimenting over the the next month or two.

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Here is what a LS 12 filter graph looks like.  It is used for a house curve and puts and emphasis on the 20-40 Hz region.  This is great for HT and also for music.  People talk about not liking a flat FR for music.  A gradual 3-6 db declining slope is what is recommended.  The bass is slightly higher and declines between 30-100 Hz. This is different than a bass boost with the trim which is a universal boost of the LF and not selective.  This graph is +/- 7.5 between 10 and 200 Hz.  DSP and PEQ are powerful tool to assist with tailoring the bass to fit the room.

 

The first graph include the RF 7's XO at 80 Hz and ran as small.  I have included a 2 graph of just the RF 7's as LARGE for comparison at the same volume.  The do hold their 3 db point as listed in their specs down to 34 Hz.

 

The 3 graph has RF 7's as LARGE with subs.  Note the cancellation and phase issues has resulted in a less desirable FR.  All graphs were ran at the same volume.  All graphs have autocalibration active.

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Edited by derrickdj1
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All 5 subs optimized for 15 Hz extension and performace.  Omnimic use for optimum phase and bandwidth adjustments.  RF 7's as Small.  Effect of placement  in the graphs.

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Edited by derrickdj1
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Play time again.  I will lower the 20 Hz filter in the I Nuke amp.  The filters natural lowest point is 20 Hz but it does extended pass that from looking at FR graph.  I will employ a high shelf filter for the next graphs.  I need to tweak things a bit before posting graph.  The goal is to set the filter to 15 or 16 Hz and shift the entire FR to the left on the graph.

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No filters on any of the subs for now.  I only use filters on the vented subs when they are not plugged.  I am away for a few days so playing with the I Nukes is on hold.  What I will do is use a high shelf filter to bring up the low end.  This will eat up some headroom and require more power.  The I Nukes stop at 20 Hz so PEQ below that is not an option and using a High Shelf Filter(HS) is a work around.

 

I would like to compare using HS with higher lower end spl vs straight PEQ vs LS(low shelf filter) house curve LFE.  The I Nuke has 20 presets so I can save these modes for comparison.  The HS filter works similar to a Linkowitz transformer.  See attachment:

 

Red line natural sub FR

Black line in LK transformer FR of the same sub.

Care needs to be taken to avoid over stepping Xmech. 

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Edited by derrickdj1
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I have mention that the effects go beyond 20 Hz.  Yes, the lowest filter stops at 20 Hz.  Hopefully sometime next week I can start playing around with resetting the filter lower on the I Nuke using the HS filters.  This is one area the MiniDSP is better using REW than the I Nukes DSP amp.  Although placing filters below 20 Hz I would recommend proceed with caution.The problem with the I Nuke filters not going lower than 20 Hz is that it is hard to tell what the amp is contibuting vs room gain.  One way to track some of this is with voltage and spl readings. Preliminary results show a flat graph down to around 10 Hz after I EQ out some peaks.

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  • 3 weeks later...

Exploration of lowering the HPF using a HS filter on the I Nuke DSP amps:

 

The I Nuke's lowest filter is 20 Hz.  The amp extends beyond 20 Hz with PEQ.  For increased output in the lower registry a HS filter will be used to change the HPF to around 15 or 16 Hz.  The technique will use negative gain with a HS filter. 

 

 

 

Post MCACC the combined sub level is 73-74 db at the MLP with a trim of -1 in the avr.  All graphs are from the MLP using the subs and RF 7's set to small.  The first graph is at -15 on the avr .   The first and second  graph has a filter gain 6 db.  The bass is way to high for safe use with a movie. The response is peaky to say the least.  The second graph uses a combination of HS/LS filters with no bass boost as before.  This brought up the low end slightly and is less peaky.  The trick will be trying to get a flat FR since some of my usual PEQ technique don't seem to have much effect.

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First attempts at shifting the LS without changing the HS was unsuccessful.  Next the HS was shifted to the right (up) and the LS 6 was not changed with marginal if any benefit in flattening the FR +/- 7.5 to 10 Hz.  Music lovers would hate the bass, lol.  I will try a few movie clips with the ear plugs when the wife goes out this evening, lol. B)

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Edited by derrickdj1
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Due to the Large humps in the FR, I PEQ'ed the subs into two groups, sealed and vented.  Using an HS 12 filter fits the natural roll-off of the sealed drivers.  Maximizing the sealed drivers is the only  to get sub 15 Hz  increase spl and meaningful extension.  The vented subs have a much steeper roll-off and the HS 12 filter was of little use and did not fit the driver's natural roll-off.  I combined the use of HS filters in the sealed boxes with LS filters in the vented boxes.  This gave a much smoother FR and should sound better to the ears.  Music sound great with the new FR.

 

The FR is still around +/-7 due to the limitation of further reduction in the peaked portion of the graph.  More sophisticated PEQ will include a peak filter in addition to the HS and LS filters.  Overall I am pleased to have accomplished 3 settings for HT, Flat, House curve using all LS filter and Deep extension by changing the sealed subs f3 and setting the I Nuke lowest 20 Hz filter down to 15 or 16 Hz.  The final step will be to re-adjust the entire systems gain structure and run MCACC to make time domain corrections and standing wave corrections.  This will allow for amp reference level at 0.

 

Care must be taken in doing these type of advance PEQ techniques due to available headroom, amp damage, or driver damage can occur.  As can be see in some of the graphs, the spl's are at the extremes using Omnimic and may not be applicable for movies with re-directed bass at these levels.

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Where did all the low bass output come from:

 

The increased output was based on a Linkwitz Transform.  This is a mathematical formula for sealed subwoofers that does two things:

1.)  Change the frequency of the sealed driver roll-off

2.) Q or quality factor of the driver.  It will make the box appear larger

 

The response of a sealed box will roll-off at 12 db per octave.  This will lead to the driver's native FR curve.  This is how the Q and F are determine for a driver or it can be obtained from the manufacture of the driver specs.  The sealed box roll-off is why I used HS12 filter for the sealed subs.  This is also why the HS 12 was not effective with the vented subwoofers.

 

Results:  Dramatic increase in extension and output occurs with the use of the Linkwitz Tranform.  The first figure below show the result of changing the F and Q.  The results show an 11 db increase at 10 Hz.  The second figure shows how a HS and LS filter works.  The LS filter was employed for the vented subwoofers in the system.

 

Things needed to do this:

1.) PEQ

2.) Sealed sub/s

3.) F and Q of the driver

4.) Enough amp headroom

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Edited by derrickdj1
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  • 3 weeks later...

I was in error that the HS filter can't work with the vented subs.  The filter will set the tunning lower.  The peaky response that I was having up top was related to the xo, MCACC.  The work around was to lower the xo to 50 Hz.

 

The LS and HS filters are more abrupt in the cut-off than, LPF, HPF, and PEQ manipulation.  This is a new graph using HS filters on the vented and sealed subs with xo adjustment.

 

On a funny note, MCACC set the sub trim to +4.5, lol.  It has to do with the way I calibrated everything.  The spl from them is not that low or the sub amps turned way down.  This is the first time in 4 years MCACC was not on the money.

Edited by derrickdj1
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