Gestating large sensitive passive 15" augmenting subs

[BioBrian]

On 21/05/2019 at 7:25 PM, soundbyte said:

Solved the problem with building a sphere!!

 

Lots of woodworking with plywood!!

That's incredible, thanks Russell! What a beautiful thing.

Might be a bit thin after all the smoothing, but could be lined, or at least strengthened around the driver hole.

It'd be hard to bring myself to cut holes in it though.

Painting would be fun.

(What were the advantages of a sphere again?)

[soundbyte]

3 minutes ago, BioBrian said:

(What were the advantages of a sphere again?)

 

7 hours ago, Auracle said:

Spheres don't require internal bracing as the shape itself does that already.

The hole for the driver may be problematic but I'm pretty sure it would be possible.

 

Look very cool.

[jasonphilip]

..

 

 

Edited May 24, 2019 by jasonphilip

[BioBrian]

Hi Sam, great to have you back!

 

Yes, the DIY thing was getting a bit quiet, so I thought I'd expose myself with some public gestation.

 

Just a pair of augmenting subs, but the thread has definitely pulled in some interesting contributions (just wait, says Sam?).

 

I agree, the 'nasties' shown in the graphs are not important - except in that case, to ask the internal reflection question. They don't show up in 'finished' measurements, and I have noticed that placement of the mic, either right next to the dust cap, level with the baffle, at 50mm from the baffle, etc, can show (or get rid of) these extreme peaks. So they can be reflections within the cone space/surround, etc.

 

But I do worry about what happens to all the energy delivered by the back of the cone. It's almost equal to what comes out the front, that gives us  silly grins and knocks on the door. But it's stuck inside the box, with the only possible escape being by moving the cone. (Let's forget vents for now). That has to be a lot of distortion, my little brain tells me.

 

I've been tossing around the idea of using lots of baffles with smaller-than-usual holes (an extreme would be like a silencer??), making the air have to 'work' a bit harder, and lose more energy; less large reflections from open surfaces. But I suppose that's just 'stuffing' on a larger scale.

 

If there's any sense to this energy dissipation thing, it would apply to spherical enclosures as well, but this is why I'm here gestating. 2nd trimester is yet to begin.

[Grant Slack]

1 hour ago, BioBrian said:

....But I do worry about what happens to all the energy delivered by the back of the cone. It's almost equal to what comes out the front, that gives us  silly grins and knocks on the door. But it's stuck inside the box, with the only possible escape being by moving the cone. (Let's forget vents for now).

 

Hello, Linkwitz described the problem as somewhat intransigent, requiring either impracticably small or impracticably large enclosures to mitigate the effect. He mentioned some chemical-engineering-grade filter materials that have promise, but did not develop the idea much, and was thinking of it as more suited for an open-back woofer than an enclosure.

 

Quote

 

That has to be a lot of distortion, my little brain tells me.

 

IMO the back-energy does not so much present as non-linear distortion, but as an effect on the frequency response. Which it is best to equalise for subwoofers in any case, since the net FR is room-dominated.

 

Quote

I've been tossing around the idea of using lots of baffles with smaller-than-usual holes (an extreme would be like a silencer??), making the air have to 'work' a bit harder, and lose more energy; less large reflections from open surfaces. But I suppose that's just 'stuffing' on a larger scale.

I think that will serve only to increase the problem in the chamber closest to the back of the cone. In the same way as a car muffler increases the pressure between the cylinder and the muffler. Such a device really makes things worse at the start of the pipe in order to make them better at the end -- which is not where you are most concerned.

 

Regards

Grant

 

Edited May 24, 2019 by Grant Slack

[Auracle]

1 hour ago, BioBrian said:

But I do worry about what happens to all the energy delivered by the back of the cone. It's almost equal to what comes out the front, that gives us  silly grins and knocks on the door. But it's stuck inside the box, with the only possible escape being by moving the cone. (Let's forget vents for now). That has to be a lot of distortion, my little brain tells me.

That's what I like about you: -always thinking objectively. 

The eternal dilemma of what to do with the rear energy so that it doesn't effect the front. In all but a few cases, the trade-off has been to stick the driver in a box of some description, and then the "fun" starts. 

If you truly want equal energy front and rear, then cut 15" holes in your walls or ceiling. The rear is then exposed to equal volume (rooms next door or ceiling cavity). If you can weather-proof the drivers, the low frequencies could be shared with your neighbors and wildlife.

Also, keep in mind that you can never really have equal energy from a cone driver as they are physically different on each side. The basket/magnet can also present as spikes, (as per your graph).

In an ideal world, you would have vibrating walls/ceiling (WAF) with infinite power available. The best you could hope for (with no expense spared) is to embed a heap of electrostatics into the walls.

Yes, it's a little out there, but after all this is part of the gestation isn't it?

[soundbyte]

14 minutes ago, Auracle said:

But I do worry about what happens to all the energy delivered by the back of the cone.

This is one of the reasons for me going OB, I did not find an answer to that issue.

I thought I could hear "boxes" in most cases when I went to listen to systems.

So I did something different, there are other solutions apparently, but I took the easiest solution for me, I cannot do woodworking too well.

I feel it works well, others may think not, but that is their prerogative.

 

Your solution/s for your system/s/ situation/s, but gestating ideas is a good thing.

 

@Auracle seems to have solved that issue but I am not aware of how it is/was done, only a few selected people know so far, intriguing.

Edited May 24, 2019 by soundbyte

[almikel]

At the wavelengths/frequencies being discussed, I don't think "reflections" off internal speaker boundaries come into it - if you equate the speaker enclosure to a "very small room", you're way below the modal zone, and into the pressure zone.

There are no "reflections" inside the speaker enclosure, just pressure changes.

 

7 hours ago, Grant Slack said:

IMO the back-energy does not so much present as non-linear distortion, but as an effect on the frequency response. Which it is best to equalise for subwoofers in any case, since the net FR is room-dominated.

^this - is all that matters

 

But to achieve this requires a crossover that matches the sub and mains acoustically.

Not too hard to achieve with measurements and DSP - much harder to achieve it passively...

...if your main woofers are sealed that will provide a high pass 12dB/octave response - adding a 2nd order passive high pass at the appropriate frequency would make it 24dB/octave - a reasonable/achievable crossover between mains/sub .

You would need a 24dB/octave low pass on the subs at the appropriate frequency to match it - keep in mind you want the acoustic responses to match at crossover (irrespective of passive/active electrical circuits)...

...The acoustic summing of the speakers is all that matters.

 

Add to that - all filters create delay - delay increases the steeper the filter and the lower in frequency the filter - this applies regardless of the type of filter (passive, analog active, DSP).

 

At sub/mains crossover freq these delays should be considered in the solution design - but symmetrical hi pass/low pass crossovers will usually have the same delay.

 

...Achieving the best "in room" sound - especially in the low end - requires the ability to "muck" with crossovers and speaker/room EQ and delay based on measurements - IMO not achievable with a passive design.

 

As the frequency drops active/DSP becomes the sensible solution. 

 

cheers

Mike  

[jasonphilip]

On 24/05/2019 at 2:02 AM, Auracle said:

privileged viewing of it's insides whilst I was living there

There was another

 

And out of interest, don't be concerned with reflected standing waves inside a sub enclosure. More importantly internal bracing to get the actual enclosure resonance above enclosure  LP. There is a great thread from over a year ago about how a bloke made probably the best (ultra large) mid bass enclosures in Australia where this was discussed at length, The Twins I recall, some utter nutter with pairs of 10Kw neodymium magnet 150mm voice coil 21' monster bass drivers.

 

Edited May 24, 2019 by jasonphilip

[BioBrian]

21 minutes ago, jasonphilip said:

There is a great thread from over a year ago about how a bloke made probably the best (ultra large) mid bass enclosures in Australia where this was discussed at length, The Twins I recall, some utter nutter with pairs of 10Kw neodymium magnet 150mm voice coil 21' monster bass drivers.

Good one! I think I remember calculating that my box volume/Sd was even greater than his! But you can't argue with 600 litres, or whatever they were.

 

I just love the sound of high-sensitivity drivers. That effortless quality they have, to fill a large room with a natural sound, with no fuss. I have a pair of HPD 315A Tannoys in about 70 litre vented boxes, (mostly playing digital TV these days) and every time I walk past that room I'm amazed. 

 

I've heard 'over-worked' bass from small rubbery drivers in tiny boxes too much, hence this journey. We'll know when we get there, I suppose.

 

 

 

 

[jasonphilip]

34 minutes ago, BioBrian said:

small

Probably going off topic here

[davewantsmoore]

On 21/05/2019 at 7:25 PM, soundbyte said:

Solved the problem with building a sphere!!

Cool! 

[davewantsmoore]

On 24/05/2019 at 9:50 AM, BioBrian said:

What were the advantages of a sphere again?

At these frequencies.   Zero.

[davewantsmoore]

On 24/05/2019 at 10:36 AM, BioBrian said:

It's almost equal to what comes out the front

Almost exactly equal.

 

On 24/05/2019 at 10:36 AM, BioBrian said:

that gives us  silly grins and knocks on the door. But it's stuck inside the box, with the only possible escape being by moving the cone

Perhaps nothing like as much as you think.

 

Sounds transmits through the cone

Sound pressure does not generate enough force to "move the cone" (or at least not as much as you think - given the quote above)

 

These things are not at all the primary concern for the SQ of your sub.    I'd urge you to focus on "what matters".
 

Quote

 

That has to be a lot of distortion, my little brain tells me.

 

If you take measurements of an otherwise identical dipole (open baffle, no box) vs a monopole (box) .... then we can see there isn't a lot going on.

 

On 24/05/2019 at 10:36 AM, BioBrian said:

I've been tossing around the idea of using lots of baffles with smaller-than-usual holes (an extreme would be like a silencer??), making the air have to 'work' a bit harder, and lose more energy; less large reflections from open surfaces. But I suppose that's just 'stuffing' on a larger scale.

Not quite sure I follow what you're suggesting .... but I'm curious.   However I think this "energy dissipation thing", is likely energy which doesn't exist (or isn't a problem) ..... so no matter what neat solution we come up with - it's not going to actually solve a problem.     But like I said, if you can explain the idea a little more!?

 

On 24/05/2019 at 12:22 PM, Grant Slack said:

Hello, Linkwitz described the problem as somewhat intransigent, requiring either impracticably small or impracticably large enclosures to mitigate the effect.

In the end, we kinda got SL around to the idea that this wasn't "no box" sound .... it was "dipole" sound.

 

If you think about the magnitude of "distortion" we are dealing with here, between:

 

The radiation of monopole vs dipole

Reflections, etc .... caused by the box+air attached to one side of the driver

 

 

We're not even in the same universe .... when considering a "reasonable" box.

 

On 24/05/2019 at 12:22 PM, Grant Slack said:

IMO the back-energy does not so much present as non-linear distortion, but as an effect on the frequency response.

YES!   (That's what I'm saying above)

 

On 24/05/2019 at 12:30 PM, Auracle said:

Also, keep in mind that you can never really have equal energy from a cone driver as they are physically different on each side

That's true.... but the differences are surprisingly small, until you reach quite high Hz (and even then).

 

On 24/05/2019 at 12:44 PM, soundbyte said:

solution for me, I cannot do woodworking too well.   I feel it works well, others may think not, but that is their prerogative.

The key (as we've been saying all through the thread and above by Grant) is the frequency response.    OB subwoofers won't work well without EQ (which isn't allowed here).

 

Otherwise, it would be a suggestion .... although I do think that the benefit is in the upper subwoofer to 200Hz odd range.   For a true subwoofer only, I'd go for a box.

[Sub Sonic]

11 hours ago, jasonphilip said:

 The Twins I recall, some utter nutter with pairs of 10Kw neodymium magnet 150mm voice coil 21' monster bass drivers.

 

This one here? Another Taswegian...

Sadly now persona non grata...

 

[soundbyte]

@BioBrian

Anything happening with the new subs as yet?

Entering your second trimester (try mister)?

[BioBrian]

@soundbyte

Hah! Not sure how to continue the analogy - "pregnant pause" is the best I can manage at the moment.

 

Truthfully though, it's been death by a thousand frosts, as dreaming about a heating system has taken priority. I can only manage a few minutes at a time in the Barn (lucky to get over 5 deg lately), and the process of thinking there has proven too much of a challenge.

 

I did put some tape on the floor to try getting an idea of the projected (actual) size, and my present design all looks a bit silly. Too long and thin? 1500mm would make them the same height as my DTQWT-12s, but I doubt they would ever be set up side-by-side seriously. 1200mm would be more practical, especially in cutting from 8 x 4 sheets of plywood; this would mean much wider baffles though, and limit any future option of a floor-standing option, as they'd just take up too much space, especially in their triangular shape.

 

There's also an acoustic question - I'm not really on top of the the whole "augmenting subs" thing, as in: where is the best room placement for them, to fill nulls. Reading today from @Audiophile Neuroscience and his mate "Barry", I started worrying about exciting modes if placed in the ceiling corners. But to counter modes, maybe this is what is needed?

 

I suppose I'd have the option of lowering them down the walls - would make a couple of nice tables/shelves to rest drinks & nibbles on at the next GTG...

 

Hope you're enjoying your new cosiness!

Edited July 21, 2019 by BioBrian
ocd issues, modes/nodes, whatthehell

[BioBrian]

Oh, and forgot to mention, I'm also a bit "shatto Le Tour"...

[Audiophile Neuroscience]

1 hour ago, BioBrian said:

There's also an acoustic question - I'm not really on top of the the whole "augmenting subs" thing, as in: where is the best room placement for them, to fill nulls. Reading today from @Audiophile Neuroscience and his mate "Barry", I started worrying about exciting nodes if placed in the ceiling corners. But to counter nodes, maybe this is what is needed?

I am coming in way too late to this thread but "Barry" is this guy

http://www.discogs.com/artist/389175-Barry-Diament?sort=year%2Casc&limit=500&noanv=1

 

Not sure if this is any use to you but here is a quote from somebody (not Barry)who is an acoustic engineer and who has a masters in physics

"When you build a reverb chamber for acoustic testing, the classic speaker position to stimulate all the room’s resonant modes is in the tri-corner [the point where two walls and the ceiling or floor intersect]. This is a room made from concrete two-feet thick coated by two inches of polished marble, and that has a reverberation time of fifteen seconds. The classic position for the measurement microphone to pick up all those resonances is also in a tri-corner. "

Edited July 16, 2019 by Audiophile Neuroscience

[BioBrian]

25 minutes ago, Audiophile Neuroscience said:

an acoustic engineer and who has a masters in physics

Welcome, David, to my low-key thread. I've enjoyed your posts elsewhere, especially as you favour acoustic rather than DSP solutions to bass issues. Can you lure your mate down this way at all? You never know - one american guy told me the fly fishing here was legendary...

 

Your participation would be much appreciated.

[soundbyte]

Pregnant pause sounds about right.

What was the result of your ultra"sound"?

With two 15 inchers involved they are probably only going to be called boys?

2 hours ago, BioBrian said:

I suppose I'd have the option of lowering them down the walls - would make a couple of nice tables/shelves to rest drinks & nibbles on at the next GTG...

GTG?.......GTG in the snow?........Coldest GTG ever?.......How about next weekend?

Four days should be enough time to build and finish the total build!

 

No need for a beer fridge either it would seem at your place, just place the beer out near the paddock gate.

 

You could always put up a few rails on the walls, use ceiling mounting facilities and mount the boxes so that they are movable (hang the two boxes from 2 or 4 endless chains), then test in different places, you should have enough room?

Welding cables for the sub wiring to reduce resistance on such long runs?

 

Seriously, I hope that you can work out what you are going to do with the build.

I will wait patiently for the birth of the twin subs.

[Audiophile Neuroscience]

20 hours ago, BioBrian said:

Welcome, David, to my low-key thread. I've enjoyed your posts elsewhere, especially as you favour acoustic rather than DSP solutions to bass issues. Can you lure your mate down this way at all? You never know - one american guy told me the fly fishing here was legendary...

 

Your participation would be much appreciated.

Hi Brian,

I cannot be of any help as I would never to presume to offer advice if I have no experience in the area. I have never built subs or incorporated subs into my system apart from one minor attempt many years ago, just for fun.

 

I can only speak from my experience of full range floorstanders, their placement in the room and room treatments/ Eq I have used and researched for bass control .

 

I'm sure you already know that if you want to maximally stimulate room modes and reinforce resonances, place the source bass driver in the corner. Obviously that's usually the opposite of what most want to achieve with floor-standing stereo loudspeakers. If the source is placed out from the corners it cannot stimulate all of the possible room mode resonances, just some of them, depending on that driving location. It is only those stimulated modes that need to be spaced out to give a more even distribution of resonant frequencies ( the ones that are not stimulated obviously don't matter). I only mention the latter as some people think that a particular room may have all sorts of uneven mode distribution based on the room geometry, however it is the speaker placement and how low the speaker goes which will determine if the modes get stimulated at all.

 

Hey good luck with your project, I will be keen to see how it turns out.

 

Oh by the way, I see what you did there with "lure" and "fly fishing" haha

 

Barry would be a huge plus to the forum, such a wealth of knowledge and a true gentleman.

 

Cheers

David

Edited July 17, 2019 by Audiophile Neuroscience

[BioBrian]

17 hours ago, soundbyte said:

What was the result of your ultra"sound"?

Sadly, the radiologist said it's unlikely I can achieve full dilation in 3 days. And a Caesar would be too dangerous. We'll just have to hold our breath for the next GTG date (except me - better get onto those breathing exercises).

 

Meanwhile, I'll just keep feeding the beasts. Need more plywood, BUT... usual story down here - can't do that until you've done this, and you can't do that until you've done this, etc etc.

 

I borrowed a friend's elderly Hilux to get the first load of ply, and had a sore leg (and mild PTSD) for a few days after enduring the perched position and needing several tonnes of force to get the brake to understand my intentions. (Not to mention the near-death experience of getting back in my car, and discovering the brake DID work). So, having a trailer just sitting here, I decided that's how to do the rest. NO - first I had to get a towbar fitted, then re-do the trailer wiring and swap plug type, fit new reflectors, repair lights, re-weld a couple of suss joints, spray some zinc around, take it for inspection, be told someone had stuffed up the original data entry, had to buy a new compliance plate and sets of letter and number stamps, stuff up one and have to buy another compliance plate, spend 4 hours stamping the thing, pay the inspector, pay the new rego, and wonder what the hell was all that about. Now it's raining for weeks on end, with no letup in sight. Hmm.

 

So now I'm starting a flirtation with Daphile on my music server - in an attempt to get DSD-512 happening. Better than cleaning out the bottom drawers, I suppose.

[davewantsmoore]

23 hours ago, BioBrian said:

I 'm not really on top of the the whole "augmenting subs" thing, as in: where is the best room placement for them, to fill nulls. Reading today from and his mate "Barry", I started worrying about exciting nodes if placed in the ceiling corners. But to counter nodes, maybe this is what is needed?

All of the answers depend on each other .... and the best answer depends on exactly what you're trying to achieve.

• Max SPL required
• Frequency range required
• Possible positions in the room where subwoofers can go (be realistic)
• Ideal size of the subwoofer (be realistic)

 

If you don't know the answers to these questions.  Good.  Stop.  Don't avoid answering them.   Figure out the answers ... and they will lead you to clear "you have to do this".

[BioBrian]

I can add to the (above) list of hurdles conquered - fitting new bearings, tyres, and tubes to the trailer. Cost, from tow bar to safe(?) trailer, now over $1300, but it finally did the job.

 

@Upfront  "Stubborn" works, Linc! Thanks again for your kind offer.

 

 

Driving past the sites of 2 previous nasty trailer accidents brought up some vivid memories; I can't describe how relieved and pleased I am to have this lot here.