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BioBrian

Gestating large sensitive passive 15" augmenting subs

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2 hours ago, davewantsmoore said:

When you take your deep breath.... there is one thing you should meditate on.

Arghh no! That is my resting state, that I need to get away from! Have to build speakers to escape the dreaded OM 😧

 

My questions are more about how to source and measure the parts, so I can know that I'm actually building the filter that these magic formulae have designed, eg 309 pF, or 14.3 milliOhms.

 

With regard to Anthony's coils, in the passive world, the larger the value, the lower the frequency affected. Values of eg 1241 mH would seem to be on an inter-planetary scale - not sure if my gear will even measure such, and it needs to make sense for me to carry on.

 

2 hours ago, davewantsmoore said:

If you implement a filter with PLLXO, speaker level XO, or DSP, or whatever..... and they have the same curve - they will sound identical.

I know what you mean, but will take it with salt (or sandalwood). There are many variables, including DACs/cables/amps/impedances. They can only measure the same under one circumstance - one specific input.  Isn't that the essence of the Active-Passive debate?

Edited by BioBrian
missing word

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28 minutes ago, BioBrian said:

My questions are more about how to source and measure the parts, so I can know that I'm actually building the filter that these magic formulae have designed, eg 309 pF, or 14.3 milliOhms.

 

With regard to Anthony's coils, in the passive world, the larger the value, the lower the frequency affected. Values of eg 1241 mH would seem to be on an inter-planetary scale - not sure if my gear will even measure such, and it needs to make sense for me to carry on.

 

Filter caps I purchased in bulk multiple values from a US firm (0.001uF-0.68uF), but I was after a particular breed of polypropylene and foil high voltage capacitor (valve amps).  They averaged something like $5 each and I spent a few hundred dollars all up,  But I can mix and match and change to my hearts desire.

 

The pF level air caps are modern production from a mob called OrenElliot.  They are not  inexpensive but you should shield them.

 

Lucas Cant of Black-Art Audio wound and shielded my inductors to my specifications.  He hated doing them because it is an iterative process.  When an inductor is wound its values are pretty close but not quite perfect so he leaves a few taps up and down in say 1% intervals.   Then they are potted into a steel and mumetal sarcophagus  and the inductance values change again, and you just have to hope that they don't change so much that all the taps are outside the target range, otherwise it is back to the start to wind another inductor.  Inductors are imperfect beasts, and are expensive and take up a lot of room in a build.   Buy an unshielded inductor and shield it yourself and you will most likely change its inductance.   

 

Regarding measurement of inductors, capacitors, resistors, I use this meter.    

 

EDIT:  Brian, you can parallel resistors to trim to exact values if you require.  It's easy to calculate and measure.  Air caps of course are adjustable within their range...you just have to measure them out of the circuit.

Edited by acg

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Excellent info, thank you!

 

I  couldn't get far with the Oren Elliot value ranges - looks like 5 or 10 uF might be well out of their range of air-caps (for passive filters).

 

 

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1 hour ago, BioBrian said:

Excellent info, thank you!

 

I  couldn't get far with the Oren Elliot value ranges - looks like 5 or 10 uF might be well out of their range of air-caps (for passive filters).

 

 

Oh yeah, air caps are for treble only, and then really only with line level filters.

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4 hours ago, BioBrian said:

My questions are more about how to source and measure the parts, so I can know that I'm actually building the filter that these magic formulae have designed, eg 309 pF, or 14.3 milliOhms.

Yes, the parts tolerance can become quite important for the resulting filter curve.

 

4 hours ago, BioBrian said:

There are many variables

Yes, but it is ONLY the resulting filter shape which matters.

 

4 hours ago, BioBrian said:

They can only measure the same under one circumstance - one specific input.  Isn't that the essence of the Active-Passive debate?

I'm not quite sure what you mean.

 

Yes.... you will need to put a known signal into the filter to be able to calculate how the filter changes the output vs input..... ie. to know what filter shape you have actually constructed.

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1 hour ago, davewantsmoore said:
Quote

They can only measure the same under one circumstance - one specific input.  Isn't that the essence of the Active-Passive debate?

I'm not quite sure what you mean.

 

The 3 scenarios you mentioned - DSP, PLLXO, and hi-level passive, are all so different that the only way to say if the outcome is the same is to measure the output of the speaker(s), ie, in the room.

 

You take the high road  (active)

And I'll take the low road (passive) 😉

And I'll be     ......   able to tell the difference if it's other than a sine wave sweep.

 

Chuck 'Ein Heldenleben' or whatever through the different systems, and the differences will be quite apparent to interested ears.

 

For further clarification, I'll suggest that nobody with an active system will have 4 Accuphase or Gryphon amps, but many with passive systems will have (or wish for) a Gryphon or Boulder or Holton monoblocs.

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16 hours ago, BioBrian said:

The 3 scenarios you mentioned - DSP, PLLXO, and hi-level passive, are all so different that the only way to say if the outcome is the same is to measure the output of the speaker(s), ie, in the room.

Yes, or measure the output of the filter itself.

 

If the filter outputs (or the speaker outputs) are different, then they might sound different.

If the filter outputs (or the speaker outputs) are identical, then they won't sound different.

 

Focus primarily on the result, not the method.

 

 

16 hours ago, BioBrian said:

able to tell the difference if it's other than a sine wave sweep.

If you are trying to imply that test tones (which by that I mean more than just 'sine waves') are an inferior substitute to music, then you couldn't be more wrong;) 

 

16 hours ago, BioBrian said:

For further clarification, I'll suggest that nobody with an active system will have 4 Accuphase or Gryphon amps, but many with passive systems will have (or wish for) a Gryphon or Boulder or Holton monoblocs.

"Focus primarily on the result, not the method"

 

The filter responses you create for your speaker drivers, have a zillion times more effect on the sound than the amplifier(s) (within reason) you use to drive the speaker.

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I found a source of Baltic Birch in Hobart, and they have 30 mm in stock - have never seen this available before. I really dislike laminating panels, so expect to be getting some of it.

 

And the drivers got posted today.

 

Looks like it will happen after all.

 

Tense up...

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I found a source of Baltic Birch in Hobart, and they have 30 mm in stock - have never seen this available before. I really dislike laminating panels, so expect to be getting some of it.
 
And the drivers got posted today.
 
Looks like it will happen after all.
 
Tense up...
The bunker?

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Yep, you got it. Last time they had to get it in for me. Seems to be more popular now. And I think a bit cheaper, without special freight.

 

30 and 24 mm etc in stock, no 18 at the moment.

 

Are you interested too?

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Yep, you got it. Last time they had to get it in for me. Seems to be more popular now. And I think a bit cheaper, without special freight.
 
30 and 24 mm etc in stock, no 18 at the moment.
 
Are you interested too?
Not at this stage but it's always handy to know where to go.

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How much for the 24mm sheets ?

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On 07/05/2019 at 10:13 AM, jasonphilip said:

How much for the 24mm sheets ?

$267 for the 24 mm, $344 for the 30 mm (Edit: confirmed 7/5/19, when I bought some).

Edited by BioBrian
correction

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36 minutes ago, BioBrian said:

This seems a very timely gift!

http://www.troelsgravesen.dk/High-Pass-Filter.htm

Those filters aren't steep enough for most uses

 

Troells is using them to augment the rolloff of a box....  If you need to do something else, eg. a low pass filter ..... or to high pass a box where it wasn't already rolling off - you will need steeper filters to get good performance.

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24 minutes ago, davewantsmoore said:

If you need to do something else, eg. a low pass filter ..... or to high pass a box where it wasn't already rolling off - you will need steeper filters to get good performance.

Yes, I realized after posting that Troels' filters as presented are OT for this thread.

 

But it's perfect for my 4-way project, as I found the small sealed boxes as HP filters aren't really steep enough on their own.

 

What I was so buoyed about was that it brings passive line-level filters into the real world for me - the type of spoon-feeding I need. Pictures too!

 

I might continue it "over there", but it means accepting bi-amping, which is another mental shift. (Not against it, but it changes long-term amplifier choices).

 

In this thread, I'd still be looking at line-level Low Pass options. The choices seem wider here, and these subs will certainly get their own amp: much easier.

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 Line level analogue active would be nice and an option I will consider but for now purely passive.  

 

Thanks for the price of the ply. Up this way Bunnings are doing a 25mm construction ply (I think 9 plys) for $100. Have used it in the past to very good effect, although the cabs. get painted, rather than varnished.

 

Edited by jasonphilip

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1 hour ago, BioBrian said:

This seems a very timely gift!

 

http://www.troelsgravesen.dk/High-Pass-Filter.htm

Meh. First order, not much better than nothing.

Second order here is a much better idea. Anything above that will require going active and then if you want to keep it to just opamps, then Elliott's kits are very well engineered..

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3 minutes ago, jasonphilip said:

Good idea, passive or active ?

What I'm used to, and would be easiest for me, is a 2nd or 4th order "passive" filter at speaker level. It works well in my other project. (Some may disagree, but it sounds good).

 

The other choice, that @acg and others have inspired, is line-level "passive", which looks like a resistor - inductor job before the amp.

 

As in previous builds, I want to avoid a 2nd digitization (AD-DA), (and use of SMPS, which is banned from my music area as much as possible).

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If you have a big box full of spare inductors/caps left over from your 4 way speaker effort (must have a few :) ) and wanted to stick with 2 channel amplification (which would be fine)  speaker level components all the way 

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27 minutes ago, jasonphilip said:

25mm construction ply

I wonder how the density compares with BB? I suspect the inner plies aren't as complete. But the price helps.

 

Yes, I'd be using paint on the backs of mine too, but the BB is lovely to work with (bruises easily but) and usually flat. Warping would be a disaster for me to deal with.

7 minutes ago, jasonphilip said:

If you have a big box full of spare inductors/caps left over from your 4 way speaker effort (must have a few :) ) and wanted to stick with 2 channel amplification (which would be fine)  speaker level components all the way 

A big box, indeed. Sticking to the theme here!

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47 minutes ago, BioBrian said:

I might continue it "over there", but it means accepting bi-amping, which is another mental shift. (Not against it, but it changes long-term amplifier choices).

It really is worthwhile, if you are designing a bespoke speaker as you are, to move that way.   The whole speaker sound/performance is dominated by what the driver basic frequency responses are.

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Have a look at the 25mm pine construction ply, it's normally flat (normally) 

24 minutes ago, BioBrian said:

A big box, indeed. Sticking to the theme here

:) sounds like fun and all you need to get into the ballpark with the sub augment. Yea stick to the theme. 

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23 hours ago, BioBrian said:

Baltic Birch in Hobart

Denman Marine.

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22 hours ago, BioBrian said:

Are you interested too?

Yes - I've never seen it stocked, so'd be interested to see the quality ...... and, <ominous music> the price.

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