Gestating large sensitive passive 15" augmenting subs

[davewantsmoore]

2 hours ago, Grant Slack said:

I have also used EQ since day 1, which is considered mandatory for sub bass... but really I thought we were talking about locating it by ear, and that was what my story was about. 

 

Yep that's what s being discussed.    Like having 5 subwoofers in circle around you..... and not being able to sense which one was playing.

[frednork]

3 minutes ago, davewantsmoore said:

I think what many people seem to miss, is that the point of bringing that up isn't "to be right"..... it is because finding and figuring out what that "something else" is..... is often pivotal in building a better playback system

Yes definintely interested in the above, (or, a nobel prize)

[davewantsmoore]

33 minutes ago, frednork said:

Yes definintely interested in the above, (or, a nobel prize)

 

Rooms can make it very complex.

 

Perhaps something happening outside your time window.... although you probably don't have enough SNR to see (to make it longer)   

[frednork]

2 hours ago, davewantsmoore said:

 

Rooms can make it very complex.

 

Perhaps something happening outside your time window.... although you probably don't have enough SNR to see (to make it longer)   

 

How long do you want it to be ? (said the priest to the parishioner. boo boom)

[davewantsmoore]

2 hours ago, frednork said:

How long do you want it to be ?

 

I would just look at everything (like right out to 1.5s) .... and I'd also largen the IR right window.

 

.... but you probably won't be able to see much that is not noise.

[frednork]

12 hours ago, davewantsmoore said:

 

I would just look at everything (like right out to 1.5s) .... and I'd also largen the IR right window.

 

.... but you probably won't be able to see much that is not noise.

Is this of any use?

[davewantsmoore]

2 hours ago, frednork said:

Is this of any use?

Yep.

Did you also lengthen the IR window?

Anything obvious in the opposite channel.

Does the noise (eg. around 100) look different in the opposite channel?

 

 

Anyways... all that being said.... it's all the more likely to be the red (loud) bits, than the blue/purple bits (almost inaudible).

[andyr]

On 07/05/2021 at 9:02 PM, davewantsmoore said:

 

Ah, yes... I remember you posting about this bench top before..... doesn't seem like a good idea... but rooms are tricky with all the practicalities of life.

 

 

I've just done another sweep, after moving the Maggie panel away, Dave.

 

Unfortunately, this did't change the graph - still a 2nd spike at just over 1.2 msec.  So it would seem to be the benchtop?

 

I then did another sweep, moving the spkr out more into the room - and, yes, the spike moved to the right.  So it would seem to confirm that the reflection is  due to the bench-edge.  

 

Andy

 

[frednork]

On 10/05/2021 at 2:25 PM, davewantsmoore said:

Yep.

Did you also lengthen the IR window?

Anything obvious in the opposite channel.

Does the noise (eg. around 100) look different in the opposite channel?

 

 

Anyways... all that being said.... it's all the more likely to be the red (loud) bits, than the blue/purple bits (almost inaudible).

 

other channel , window is set at 1000ms but default is 500 doesnt seem to change much  though

 

[Grant Slack]

On 27/04/2019 at 11:10 PM, BioBrian said:

The best option would seem to be in the joint of wall/ceiling.... A "sub-crawl" would necessitate a reversal of gravity.

 

Hi Brian,

 

plasterers disagree! 

 

cheers

Grant

[BioBrian]

10 hours ago, Grant Slack said:

On 27/04/2019 at 11:40 PM, BioBrian said:

The best option would seem to be in the joint of wall/ceiling.... A "sub-crawl" would necessitate a reversal of gravity.

 

Hi Brian,

 

plasterers disagree! 

 

Thanks Grant, a lovely example of humans with highly developed spatial awareness, and complete confidence in a stereo (bipedal) bass!

 

Although speaking of reversal, screwing my 125 kg monsters into the plaster would be more like going into Stilton than 'on stilts'.

 

And to all other enlightened stereo bass adherents,   ".... therefore never send to know for whom the Nobel tolls; it tolls for we."

[BioBrian]

A bit off topic, but my Elektra 7-channel amp was posted yesterday, so I got this project finished (if that's a possibility in this game).

 

It's a 6-channel attenuator, designed to save me spending $6k on a Parasound P7, or similar HT preamp. It also saves 12 plugs and 12 sockets, another power cable, more LEDs, power use, etc. The Jaycar zinc die-cast box eventually came up OK, after a few awful weeks of trying to get the paint right.

 

6-channel because the Front L & R will be handled by the normal system.

 

The RCA outlet doubles the Sub outlet, in case I want to use a 2nd LFE off the same attenuator. (Don't want any bare unused plugs lying around).

 

 

[BioBrian]

As this is a DIY section, the above "Brian built a pretty box" might not have been terribly useful, so I'll add a bit of the how and why.

 

The Potentiometers might seem a bit "last century" compared with Muse chips and even resistor ladders, but these ones are supposed to be a bit special. A link to their source contains another link that explains how they sort of incorporate a ladder: it's best if you have a look rather than me try to explain:

 

https://www.hificollective.co.uk/potentiometers/tkd-potentiometer.html

 

The WBT-0114 gold-plated plugs with their fantastic chuck-type tensioners are not cheap; I happened to have built 3 pairs of cables with them in 2017, so they were just lying around after my Luxman update, which saw me build some super-exy silver Neotech/ETI balanced cables - another story. So I had 12 available - perfecto.

 

The glands were from Jaycar, and have a similar chuck-type clamping system, which means the cables can't pull out or twist, but can be undone any time. They did cause a lot of grief - some had different washers, necessitating a trip to find o-rings to match the others. Then some had different dome nuts, requiring another trip to town to swap for the other type. Then, on assembly day, I found some of the tightening nuts were a different size, needing another, even bigger, spanner to fit into a very tight situation. Grr...

 

The WBT RCA socket was bought for another project a while ago, so finally it found a good home.

 

All the WBT plugs and sockets have low mass and high quality metals and plating - I like them a lot - but they are certainly not cheap!

 

The holes needed to be pretty accurately spaced, so after centre-punching I used a sharp 4 mm drill, then corrected any wandering with a small rat-tail file. This meant that when I brought in the stepped drill, they ended up in the right place, and with the added bonus of a neat rounding off of the outer hole. 16 mm diameter is quite big in thin metal - glad I didn't have to rely on the old-style drills.

 

Inside these boxes there are ridges for mounting PCBs, etc, so I had to cut them off to allow the glands to sit flat. After a fair bit of fiddling (mistakes could be a bit fatal) I made up a jig at the required (not 'right') angle to slide the router along, and trim them off. Long straight bit, low speed, and in small increments.

 

The cable chosen is Belden 3079A, which has 2 solid-core 22 AWG copper cores, and a common shield of al-foil and tinned copper braid. It has low capacitance of 28 pF/m, and outer diameter of 8 mm.

 

The 2 cores make the cable 'balanced', carrying +ve and -ve, and the outer shield is connected to only the plugs at the power amp end. The shielding goes continuously through each cable in the pot box, and the box is only earthed by the Centre cable shield. This is my take-away from a fair bit of discussion in other threads on this forum.

 

The box started with epoxy paint, but despite keeping it quite warm (on fire bricks over a wood heater) for quite a while, it never got really hard. Eventually I sanded it back and used a more common type of black satin spray, which not only dried much quicker for re-coating, but set harder.

 

The knobs looked really nice in the HFC catalogue, and I thought they would mean I didn't have to have numbers on the panel, but in reality, it's quite hard to read the numbers on them, and I don't know a (reversible in case I stuff up) way to make the grooves visible. They also said they had 6 mm diameter holes, but as we know they are all 1/4", so are quite sloppy, and the SS grub screws are so hard that it's almost impossible for them to grip the hard pot shafts! Hard to win.

 

The 4 knobs do Centre; Side surround x 2; Back surround x 2, and LFE sub. The LFE/Sub output has one fixed cable, doubled by a socket for an auxiliary cable/sub.

 

The Dynamat Extreme was added more for weight than vibration control - I had lots of scraps, and may add more next time it gets opened, as it needs to not slide away every time it gets touched. It does have a good solid feel now, though. Little stick-on clear silicon feet help too.

 

Anyway, that's my pretty box. Last century perhaps, but very first world.

 

The bad news is that the Elektra amp wasn't mine after all, and had to do a boomerang up to Qld. I heard they have a large damping factor . Mine's apparently still on the bench, so it looks like I have time to build a proper rack. (Now, how does one do that? Maybe this time, not 'build now, think later'?). Lots of interest in CLD.

 

Cheers.

 

 

[davewantsmoore]

52 minutes ago, BioBrian said:

The glands

Looks tough

 

32 minutes ago, BioBrian said:

The 2 cores make the cable 'balanced', carrying +ve and -ve

There's no -ve signal.  It's "ground".

 

54 minutes ago, BioBrian said:

and the outer shield is connected to only the plugs at the power amp end.

What is the reason for this?

 

54 minutes ago, BioBrian said:

This is my take-away from a fair bit of discussion in other threads on this forum.

Is there some interesting / special reason why not coaxial cable?

 

(Using "not-coaxial" cable for unbalanced with shield-lifted can be the "right" way to do things if any of the equipment is not internally grounded / wired properly)

[BioBrian]

Yes, as I said, this is my take on it. Maybe you don't like me calling -ve something different from ground, but I see  the signal as being the difference between the + and -, so I don't see that the practicality of what I've done is wrong. I don't like the idea of the return being considered inferior - it's just as important, so in my case, it can enjoy its own bit of wire.

 

There was talk of the shield being a Faraday cage, and also it acting as an antenna; I think earthing it at both ends is asking for trouble - eg earth loops. I prefer the idea of a single earth. I've chosen the amplifier as the preferred earth, as it's a good Aussie design which is solid and predictable and down to earth. When it arrives. (The OPPO has no earth mains wire).

[davewantsmoore]

1 hour ago, BioBrian said:

Maybe you don't like me calling -ve something different from ground

It's not about "what I like" .... I'm not that precious  

 

It was more the "balanced" comment (it doesn't do anything like that).

 

1 hour ago, BioBrian said:

but I see  the signal as being the difference between the + and -, so I don't see that the practicality of what I've done is wrong.

That's a common misconception about how unbalanced audio works.

 

1 hour ago, BioBrian said:

I don't like the idea of the return being considered inferior - it's just as important, so in my case, it can enjoy its own bit of wire.

"Inferior" is the wrong way to think about it.

 

It is a different wire with a different purpose.   The purpose in unbalanced audio of the "ground" / "return" wire... is to

• stop noise getting to the signal conductor
• be low resistance
• be in a geometry that reduces the capacitance between the signal and "ground"

A coaxial cable is (or can be) very superior in all of these regards... 

 

By only connecting the shield at one end, it makes the shield less effective.... by having a 3rd conductor it increases the capacitance  (and the core metrics of good unbalanced audio are shielding and low capacitance).

 

Anyways... sorry, I honestly don't mean to always be the one to rain on the parade.  

 

1 hour ago, BioBrian said:

I think earthing it at both ends is asking for trouble - eg earth loops.

This depends on whether your equipment is correctly designed or not.    You shouldn't "expect" it will be a problem.... as I said.  To counter specific problems you can use a custom cable.... but it is not ideal.  It's never optimal to connect the shield at only one end, unless you are solving a specific issue.

 

1 hour ago, BioBrian said:

I prefer the idea of a single earth.

It's not uncommon (to see people say that) ...... but (most usually) due to a misunderstanding.

 

1 hour ago, BioBrian said:

The OPPO has no earth mains wire

The in that case arranging the shield like that, is probably "no worse" .... not that you'd probably have issues with noise anyways (although you might, it depends).

 

... basically you just end up with lots more capacitance (due to the big conductors, closer to the shield) , and a smaller shield.... then a cable designed for unbalanced audio.

[davewantsmoore]

8 hours ago, davewantsmoore said:

BioBrian said: The OPPO has no earth mains wire

 

The in that case arranging the shield like that, is probably "no worse"

 

Thinking about this more... I don't think I should make this generalisation.   It's too confusing.

 

The main point is everyone thinks something like "I want to 'keep the -ve wire pure... because my signal wire is referenced to it" .... but this isn't the right approach (unless trying to use a cable to fix some type of specific problem).

[davewantsmoore]

11 hours ago, BioBrian said:

There was talk of the shield being a Faraday cage, and also it acting as an antenna;

 

Owh, missed this bit.    Antenna increases exponentially when only one end is connected