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BioBrian

Gestating large sensitive passive 15" augmenting subs

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6 minutes ago, almikel said:

have you considered Infinite Baffle?

Thanks for your post, and welcome back! Hope those pesky distractions aren't too disruptive for too long.

 

Interesting about the IB15. I didn't follow through with the idea of this in a vented box. A little swayed by the presence of a pair of used TD15Hs for sale locally.

 

I was going to respond to one of Dave's posts about baffle shape, which would elicit much the same words as this:

 

My intended wall-ceiling box placement, with a 45 degree angled baffle, would effectively be an infinite baffle - ie no baffle step loss, in fact I'd expect a net gain over IB (on a flat wall) - approaching "corner placement" - huge room gain.

 

But IB implies a virtually infinite air space behind the baffle, doesn't it? It's all looking fairly similar though - my vented box size is 320 litres, so I'm guessing they won't get many Watts thrown at them.

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Posted (edited)
13 hours ago, davewantsmoore said:

Personally, I'd want a steeper cutoff.    (It's too loud at 200Hz)

 

... but more so, the idea of putting 36w (perhaps even double that) through a huge inductor and a capacitor... on the way to my speaker driver - doesn't seem like a very good plan.

 

People argue about the distortion these components create even when they are much smaller, and the energy transfer is much lower.    If we accept the views (I'm not 100% sure) that there is something to these people claims  (for example, different components sound different) .... then using them at all - let along in this situation - seems like a bad strategy.

 

It's only 6 and a bit litres.  ;) 

The 105 dB is also a little loud!!   But yes, I could do the same as my other SB42 woofers (vented 240 l) - use a 4th order passive. Easy. I'd call that fine-tuning, and I suspect room-tuning will predominate those decisions.

 

Not sure that the parallel capacitor sound 'thing' is an issue with large bass drivers - much more a tweeter issue. Happy to do some tests. There is a new generation of electrolytic caps, but Jantzen Cross-caps aren't that much dearer (I have a couple of 150 uF here).

 

Huge inductors?  No idea how they affect sound.  Not at all, from my listening. From all the emotive stuff on "damping factor" threads, I have sort of gleaned that R is the only relevant issue there, and these C-coils have almost none. Thick, short wire. Phase and group delay may be important, but that's unfortunately something I'll have to swallow with these design parameters.

 

I had modelled the vents using 2 lengths of 102 mm ID sewer pipe, as in my previous build. At the GTG on Saturday, we played a 24/192 version of "Hotel California" through them, appreciably louder than my normal tolerance, and I held a tissue over one of the vents. It only flapped about a centimetre. I have zilch worries about a 150 mm vent chuffing, as its area is larger than the 2 x 4" pipes (177 cm^2 vs 163 cm^2).

 

Further on "passive" inductors - did you see what I think I saw, of the mH values on @acg's line-level filters?? I seriously want to know more about this approach.

 

Edited by BioBrian
GTG on Sat, not Sunday. Wish sun'd been there.

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3 minutes ago, BioBrian said:

Thanks for your post, and welcome back! Hope those pesky distractions aren't too disruptive for too long.

I've been learning how to play harmonica - a fantastic distraction!

6 minutes ago, BioBrian said:

But IB implies a virtually infinite air space behind the baffle, doesn't it?

correct - but drivers designed for IB alignments can work in sealed boxes if the box is big enough - when you sim a driver meant for IB in a sealed box you'll see it peak before roll off - the bigger the box the lesser the peak...

...if you're considering a 320 litre vented box and haven't purchased a driver yet, then consider the AE IB range, and run them in a large sealed box...or proper IB - they don't have to be on a flat wall to be IB...most IBs have a manifold (that the drivers mount on), with the manifold exiting outside.

 

IMHO I would avoid ported alignments if sound quality is the goal - too many things go awry as SPL changes - much less so with sealed or IB subs.

 

cheers

Mike

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9 hours ago, BioBrian said:

The 105 dB is also a little loud!!

Not in a max SPL sense.

 

If you think about what you measure on a SPL meter with music .... You need to add the crest factor of your content on top.    Is that 4dB?  10dB?  30dB????  ;) 

 

Otherwise what happens, is that on the "short, sharp, loud" bass tones ....  You get some sort of linear or non-linear distortion....  which typically results in either a raised noise floor (from non-linear), or a reduced level (from linear) .... both results in "indistinct" bass.

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9 hours ago, BioBrian said:

Huge inductors?  No idea how they affect sound.  Not at all, from my listening. From all the emotive stuff on "damping factor" threads, I have sort of gleaned that R is the only relevant issue there, and these C-coils have almost none.

No, it isn't a "damping factor" thing.

9 hours ago, BioBrian said:

Phase and group delay may be important

They're directly related to the frequency response in this instance ..... so, just the FR is important.

 

9 hours ago, BioBrian said:

but that's unfortunately something I'll have to swallow with these design parameters.

Yes, I guess that's my point.  :) 

 

9 hours ago, BioBrian said:

I have zilch worries about a 150 mm vent chuffing

I didn't mean to imply that was the primary problem.    It's more a "compression" issue, when you look at how the driver responds at LF vs time.

 

9 hours ago, BioBrian said:

did you see what I think I saw, of the mH values on @acg's line-level filters??

Yes.    You'll see some comments from me in his thread  ;) 

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10 hours ago, BioBrian said:

My intended wall-ceiling box placement, with a 45 degree angled baffle, would effectively be an infinite baffle - ie no baffle step loss, in fact I'd expect a net gain over IB (on a flat wall) - approaching "corner placement" - huge room gain.

At the frequencies you are talking about, the concept "of baffle step loss" is kinda nonsensical.    At LF essentially anywhere in the room you place the subwoofer it is approaching being "in the corner".

 

10 hours ago, BioBrian said:

But IB implies a virtually infinite air space behind the baffle, doesn't it?

Yes.

The practical effect of doing that is reduced power requirements vs SPL at LF.

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Looking at the drivers frequency response in a box, before you have shaped the response to your needs - is not the right way to evaluate a driver.

 

Need to mould their response to be the same (whatever your target is), then look.    A lot of the differences will go away, others will become more obvious.

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13 hours ago, BioBrian said:

Further on "passive" inductors - did you see what I think I saw, of the mH values on @acg's line-level filters?? I seriously want to know more about this approach.

It's pretty simple Brian, you jam the filter at the input of the amplifier where the voltages are much smaller, let's say 2V max (4V in my case) and use the input impedance of the amplifier as the load for the filter rather than the reactive impedance of a speaker level crossover network and transducers.  Then you direct connect your transducer to the amplifier.  It keeps the filter component values much smaller, so tiny caps and inductors.

 

In some circumstances you may even be able to build part of the filter into the amplifier itself.  For example an interstage coupling capacitor can be sized such that it creates a first order high pass filter at the desired frequency.  Couple that with a low pass filter  before the amplifier and you have a bandpass filter.

 

I've not yet read your thread Brian but the speaker photos on the front page look excellent.

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2 hours ago, acg said:

For example an interstage coupling capacitor can be sized such that it creates a first order high pass filter at the desired frequency. 

Yes, that works, but a 1st order filter is woefully inadequate in almost all situations. You can do a 2nd order PLLXO easily enough, but 3 order and above are much harder, pretty much impossible without a lot of parts and adequate measurement gear.

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@A9X, yeah the bits add up.  I have a 4th order highpass set at 10kHz using two air-caps and two inductors.  It takes lots of space. ...like twice as much space as all the filters for the other five channels.   3rd or 4th order RC filters take next to no room.  The caps are tiny and the resistors only need to be quarter-watters.

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Posted (edited)
On 01/05/2019 at 12:30 PM, acg said:

It's pretty simple Brian, you jam the filter at the input of the amplifier where the voltages are much smaller, let's say 2V max (4V in my case) and use the input impedance of the amplifier as the load for the filter rather than the reactive impedance of a speaker level crossover network and transducers.  Then you direct connect your transducer to the amplifier.  It keeps the filter component values much smaller, so tiny caps and inductors.

Yes, I've a handle on the concept, but how to calculate the values, and how to find the values seems less easy.

 

By "smaller, so tiny caps and inductors", I guess you mean like this (small by acg standards 😊)

 

1785549132_HFBoxfilter.jpg.10112bdfab75ec6972fb8b99ea151966.jpg

 

With the cable ties, i can only guess, but the values look humongous. (I'd expect only 0.1 uF and less than 0.1 mH if it were passive).

 

Thanks for your kindness re my speakers.

Edited by BioBrian
spelling

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Posted (edited)

Yeah @BioBrian, that's the 4th order high pass filter set at 10khz.  How to calculate them....that's easy.  I have the "Electronic Filter Design Handbook" and I took the equations for calculating that particular "CLCL T High Pass Filter with unequal terminations - Fourth Order Butterworth - Infinite Termination"  (simple when you say it like that haha) from within its pages and put it in an Excel spreadsheet, which also includes all the other types of much simpler filters that I have employed:  low pass RC; high pass RL; bandpass RCL; low pass RRC; and the high pass coupling capacitor filter.  Subtractive filters only.

 

With those larger shielded inductors in the photo 1.241H and 0.298H are also two air capacitors set at 346pF and 490pf (yes picofarad).  The filter is loaded by a 30k ladder type LPad.  Do not fear the inductor...the inductor is good... capacitor is bad...reduce or eliminate the capacitor. 

 

EDIT:  I should add that the caps used in my other passive line level filters range from  0.0047uF to 0.068uF with the large low passing at 78Hz.  Tiny little suckers.

Edited by acg

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11 hours ago, acg said:

capacitor is bad...reduce or eliminate the capacitor. 

Oh good grief.

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Posted (edited)

capacitor not bad

room is bad

room can make mega buck speakers into pretty average speakers

room is bad, very bad...must fix room

Edited by afa

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23 hours ago, afa said:

room is bad, very bad...must fix room

Hi Arthur, not sure if you mean generally, or my room in particular.

 

It's had some treatment, and I anticipate more in conjunction with this present project.

 

Of course, you are still most welcome to visit. I'd appreciate any help with this complex situation.

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