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In at the deep end - SB 15 inch for sensitive bass


BioBrian

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Hi Russell, I'd love to come over and check out your latest activities. Still a bit hamstrung over transport though (can drive, need a car).

 

I've been sort of preparing for the inevitable by concentrating on the mid-tweeter passive area, so this could make a "3-way" with the 2 woofers. This yielded a little surprisey-poohs the other day, after fitting the Scan tweeter:

 

5980489f9ac1f_ScanspeakD3004-6620andSBmidinclphase.JPG.b0c873661138086af1a9323740897846.JPG

 

This seems to show good phase match and symmetry at crossover, so, damn, might mean another $400 for a 2nd tweeter. These were at 70 cm, mid-tweeter axis.

 

(The SB tweeter-mid show a slight phase difference, but this may well be correct with a lowered or raised mic position).

 

I think I have all the wiring and amps ready for a miniDSP orgy. How long can I put this off?!

Edited by BioBrian
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21 minutes ago, Upfront said:

Happy to give driving lessons and loan you the minidsp Brian. Can drop it off with the Pre if you'd like?

 

Linc, you're too kind! Such seduction is not unnoticed. miniDSP I may do one day, but can I kick and scream a bit longer?

 

Please deliver the Pre, but leave the driving lessons in the letterbox. Nah, I'll be in town at the right time soon, surely?

 

The Pre might save the day WRT the sensitivity imbalance at the moment. Pre and Parasound A-21 on bass (grunt with control), Cyrus for 3-way. But maybe we can wait to see if I hit the red button on the AT drivers first.

 

 

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10 minutes ago, Upfront said:

 my bum into gear

 

I knew my gut feeling about the driving lessons was up to scratch ;)

 

Will be in town again on Wed, maybe late enough to drop in. But if you're missing my angular birch numbers, you're most welcome!

 

I don't have the energy to learn miniDSP alone, so you or Russell or Dave might have to join forces, or straws, or something. Farmer's time here - let's not rush. (Little prayer for the passive).

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14 hours ago, BioBrian said:

 

Thanks Matt - all encouragement gratefully received!

 

It should be fairly clear that I've found it quite a challenge to create what my wishes are, especially as they change with new learning. Progress has been slow, but I'm getting quite a lot out of the journey. Your suggestion is on board, but I reckon it'd be a long day's work, even with somebody who knew wtf they were doing, to get the anticipated good result, with miniDSP or DEQX.

 

To be honest, I don't think I could come close to replicating what these could do, using passive components. Nobody could, especially boosting desired frequencies,  like down toward 20 Hz. Or matching phase. They are just too different.

 

I'm very wary of being seduced - it may be too much of a shock in my delicate state...

Cheers Brian 

You have done amazing things with the speaker build at every level and personally getting back on your feet over time, congratulations. 

Mastering the passive like you have would most certainly be a very rewarding achievement and a massive challenge initially.

Not being serious and thinking stave off the passive filter blues (we have all been there I believe)   for your continued (fun and learning something) enjoyment is to give the old digital a run one day and have play for no other reason than to give it a run :) for a jolly. 

 

Sounds like a a good excuse for a GTG, can just imagine a hoard of blokes rolling up to the quiet Farm under the Mountain, with a car load of "special" amps, beer and DSP's ready to have an arvo in molesting your speakers with frequency sweeps, dialling in some crossovers and EQ. Might even get a pop track in although would guess I would get rugby tackled if I go near the CD player. :P

 

Have another suggestion as well as a solution that I have to show rather than tell next time we GTG for that amazing speaker set. Will come prepared.

 

Have a good one

Matt 

 

 

 

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47 minutes ago, 125dBmonster said:

Have to say @Upfront is a dab hand at the DSP :thumb: clever bugger and @soundbyte 's system blown what's left of my hair back 

Thanks Matt, nice to hear you still have some hair. :unsure:

 

The DSP software is relatively easy to drive, setting the xovers and PEQ's not so much.

 

REW was not so easy, but I got through it.

 

The difficult part was getting everything in phase one spectrum at a time, then WOW, no other word for it!

 

Brian let me know if you have time to call in tomorrow on your way home?

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Well I got a nice potted 'driving lesson' on miniDSP from Linc @Upfront today - thanks mate!

 

It was a lot more straightforward than I'd thought, but then watching somebody else doing it is not quite the same. Setting volume levels of each driver (4 per side possible in this case), then XO target frequencies, and roll-off rates - incredible really, and all in a few seconds. I'm sure there's a lot more, and knowing me I'd want the Dirac software too, then REW etc, but the rewards look to be many and quick.

 

But for now the prize has been the loan of a nice preamp, so I can stay passive, but set different volume levels for bottom woofers and top 3-ways. Bi-amping cuts out all the interaction that goes on when changing XO components. The 4th order LP filter the other day really put a dampener on the top drivers, and understanding the details and ramifications and working out corrections gets all very overwhelming.

 

Now I just have to make a shelf, so everything can fit on the bench.

 

What an amazing community this is.

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On 8/2/2017 at 10:59 PM, BioBrian said:

The 4th order LP filter the other day really put a dampener on the top drivers, and understanding the details and ramifications and working out corrections gets all very overwhelming.

Never a truer statement been uttered.

4th order passive crossovers will always severely dampen driver output. Bass drivers require current to "breath" the music into life. Each reactive component added will suck out its' share of power, so the driver will end up with what's left over.

 

This is why with multi-driver speakers, the active miniDSP/DEQX/multiamp setups have it all over the passives in regards to ease of construction, electrical and acoustic parameter corrections.

This also explains why creatures like this  Upfront  can slap something together in no time and make it sound decent, whilst purists like us will curse endlessly.

 

Disclaimer: Any references to persons passed or living that feel that they resemble any of these remarks should look in the mirror less often. Should offence be taken by any remarks held within, was sheer fluke on my behalf, and bad luck on yours...

 

 

                                                                                Honey!  Have I taken my medication tonight?

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Hi Sam, good to see you've hit the ground running, and are recovering fairly well from the jet lag :unsure: :).

 

I'm not sure if the post on the 4th order filter made sense - there's always an "assumed understanding" and I'm never quite sure how much detail to go into, for people to make sense of my rabbiting.

 

Firstly, the 4th order filter has less DCR than the previous 2nd order ones, due to the ginormous C-coil, and will drop even more when Nigel (Speaker Bug, @Green Wagon) gets his new C-coils in. So the net result is, that the bottom woofer actually got louder, and the top 3-way therefore relatively quieter. I fiddled a bit with mid attenuation which made a big difference, but still for the top 3-way to be balanced within itself, the sensitivity of its woofer will be critical. Otherwise, I'll have to attenuate the bottom woofer, which is contrary to the whole thrust of this thread.

 

The other issue I've been concerned with is phase shift. When using 2nd order filters through the whole 4-way, I understand that each driver has to be reversed in polarity. compared with the one below it. I've not been doing this. All along, the drivers have been like this:

 

Tweeter +

Mid -

8" woofer +

15" woofer +

 

At one point I tried reversing speaker wires, and do remember at one point a sound of unusual clarity and integrity, but as usual, there were too many other variables for me to remember just what made this big improvement.

 

I'm led to understand that there's a phase shift of 90 degrees with each "order", but is this when changing BOTH drivers' filters, or just one? Suppose I could just measure it. But because the phase on the 4th order one was flat in the working range, I presume it's gone the full circle, and is just delayed by one cycle. (But at what frequency? How far do I move the box to correct that?).

 

Whatever, the bottom woofer is having a ball, being slightly dominant at the moment, and with the 4th order filter, as is, it's doing close to 2.5 octaves (crossing about 110 Hz). Running with both vents open, as designed, it has a really open, relaxed presentation. Bass extension seems adequate in the large open room, which now has some reflection control and damping.

 

@Upfront's lovely Bel Canto Pre and the Parasound A-21 power amp are driving the whole 4-way, through new (I feel so grown up) balanced cables, and it's the best I've heard so far.

 

I don't want to waste too much more time fiddling (learning's fine), until I settle on the new drivers.

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The Pre 1 is a real pleasure. Especially that huge openness and apparent headroom in the bass. It's set about Vol 68 for most listening, so plenty of abundance there. Not surprised it's a keeper for you.

 

The balanced cables were ordered from Blue Jeans last Wed, and arrived Monday arvo! I enjoyed that slight textured feel as the new plugs slid into virtually-virgin* sockets: lots of contact area, and after a couple of days, I think they allowed more of that awesome bass accuracy.

 

* That's a thing, isn't it?

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I've been agonising on how to give you an informative response, since I'm not sure on your depth of knowledge pertaing to filter network theorems and associated mathematics.

I will start with a few basic facts hopefully without getting too heavy.

Filter networks usually come in the form of T or TT (pi). The quasi parallel sections will tend to want to "resonate" and form peaks (Q) and troughs (nulls) before the attenuation commences, -IF, of course, that is what the application requires, otherwise, the incorrect component values have been chosen. If the application is audio, then that peak/trough should not be a desired outcome. It is actually distortion, and it is audible. Some manufacturers use this trick on cheap subwoofers (they have a wild and woolly sound when played on their own).
Consider this; if you are attenuating, how can you have more out that what you are putting in?

These types of issues forced me to formulate calculators that allow me to instantly see the changes in curves for each component swap. This has made my crossover design process so much easier and quicker with not many corrections. I can also tailor-make stepped slopes if required.

The other bits of info I can offer are:-

* With large amplitude signals, metalically cored inductors will saturate and cause audible distortion. Try large air-cored units instead (place them outside and make them a feature).

* Ruler flat frequency responses will never be achieved with passive crossovers. Only digital manipulation can achieve this.

* If someone thinks they can hear variations less than 2dB, they are deluding themselves. Yes, it's a harsh reality, and it gets worse with age. Consider that the tolerances of the components will give you that alone.

---------------------------------

Some of this information you may like, and some you will not. But they are the results of my experiments and experiences, and will stick by them. These days I realise that the time I have left is precious and prefer to enjoy listening to the music ( yes, yet another cliche') on a nice system rather than the system. Also, having just returned from a developing country, one sees things that put our first-world lives into perspective. I think most readers will understand what I mean. So yes, spend on what makes you happy, but always know your limitations.

 

Cheers

 

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Hello Auracle, thanks for your reply. Sorry to have caused you to 'agonize' - not my intention, of course! It would seem that in trying to clarify what I meant, discussion of these complex issues might have caused more misunderstanding.

 

Some of your post I understand, some not.

 

"Filter networks usually come in the form of T or TT (pi)" - no idea - I try to avoid jargon until it becomes 2nd nature. Due to others' never-ending quest for mathematical understanding of speakers, I stick with a "do this, and hear/measure what happens" approach. This is safer for me than relying on eg internet calculators, which are a bit of a farce. What I would trust is good software, but at well over $1000, I've left that to the people who are capable of affording, using, and interpreting it. I'm glad you have your calculators, but you also have the knowledge to use them. I can only trust the tools I have, and my fairly strong taste in a satisfactory outcome.

 

The word "quasi" is meaningful to me in other contexts, but I don't know why you've used it here. I am guessing "quasi parallel" refers to all elements parallel to drivers? eg LCRs, LRs and CR (Zobels)?

 

"Peaks/troughs" would refer to variations in the FR curve?

 

By "attenuation" I mean anything resistive in the signal path, eg a resistor, or the DCR of an inductor, in series with a driver. Please say if this is incorrect! (Eg the DCR of an air-core 3.9mH is 0.59, where the same value in C-core is 12 times less, at 0.05 Ohms. I have found differences caused by less than 0.5 Ohms in series to be readily heard).

 

The saturation issue is not something I can have an opinion on, but I hear Jantzen (OK, they make the things ;)).From their website:

 

"If the stated maximum wattage is not exceeded the core will never saturate.      [Rating for my coil is 2000 Watts - Brian]

The C-Coil is designed for the bass section of crossovers and for passive Sub-Woofers, available in different core and wire sizes".

 

The Jantzen P-core ones I use for testing also have high saturation, and are recommended for the low frequencies only used by bass drivers. From the Speaker Bug website: "Power handling before saturation is 400 Watts."

 

"Ruler flat frequency responses". I've spent about 5 years, in various projects, getting closer to ruler-straight (as opposed to ruler-flat, on account of needing a gradual fall toward high frequencies - I don't think anyone disputes that this is better for educated ears). This is a goal, not an expectation, for me. Enjoying the thrill of getting closer is something I'm sure I'm not alone in.

 

I have to graciously disagree about the 2 dB thing. The graph I posted on August 1 (p 10) shows the 'improvements' made by changing the tweeter baffle shape. These appear to be less than 2 dB (admittedly 'improving' a rise followed by a dip) but to me are definitely audible, and I'm sure even reasonably elderly ears other than mine would pick it up. Then, I did spend 30 years as a violinist, playing with extremely fine differences in often very strained interpersonal environments, so I can't even guess what other people hear. I presume you would agree with me that sometimes it can takes days, or weeks, of listening to be able to hear not just "2 dB difference", but how that affects all the different recordings we listen to - it'll show up much more on some.

 

Hopefully this has left us slightly less 'out of phase'. I feel it would be much quicker and easier to progress if we got together again some time.

 

and yes - I agree totally that all the above is very much a '1st World Problem'! I'm actually hoping the maniacs give us peace for long enough at least to finish my speakers. Not that I need any more disincentives.

 

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It definitely does seem like it's time to make a live appearance. I do need to find my whiteboard however. I still haven't unpacked my gear due to red-tape.

 

And, since you asked nicely, I will give a primer on attenuation.

Definition: "the reduction of the amplitude of a signal, electric current, or other oscillation".
=>The DC resistance component of an inductor is but a small but inclusive part of what makes up attenuation when placed in an AC circuit. The coil "resists" the directional changes of Alternating Current as a function of frequency. It's value is calculated using complex number mathematics, and contains an angular component. It's name changes to "impedance" and notation is usually "Z".

 

A "T" filter is image.png.0d01d27754c449114aba5c65519e6191.png

"TT" is.....       Image result for 4th order filter,

 

and so on... Image result for 4th order filter,

 

 

I also like your parting comment.

I should listen to more music before that nutter reduces this world to a smouldering radioactive wasteland.

 

Hope to see you soon.

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Oh good. Here was me thinking a TT was a round thing with an arm, so a T must be just an armless round thing.

 

I have a whiteboard. Choice of coloured pens. Or maybe you'd prefer in town?

 

Just need to polish up me tinfoil hat (lying - but I'll take building one as nice as yours seriously, if necessary).

 

Thanks; look forward to it.

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No tin hat necessary, -you have proven your mettle (no pun intended).

 

I remember somewhere that your driving situation is somewhat curtailed?

If so, we just need to arrange a convenient time. I'm actually "working" up north of the state until next week. I'm also dropping in and annoying poor Matt.( Dunno why he hasn't told me to P!$$ off yet.)

 

Cheers

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No tin hat necessary, -you have proven your mettle (no pun intended).
 
I remember somewhere that your driving situation is somewhat curtailed?
If so, we just need to arrange a convenient time. I'm actually "working" up north of the state until next week. I'm also dropping in and annoying poor Matt.( Dunno why he hasn't told me to P!$$ off yet.)
 
Cheers
Happy to be the half way point if it helps guys.
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Thanx Linc. I'm OK to take up your kind offer.

 

An idea:-

If anyone else wishes to attend this class, let us know so we can accomodate numbers. (aka GTG)  -please bring an apple for the teacher though.

 

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Well this is looking productive. Perhaps we could continue as PMs, and if any other Tassie Tinhats want to join in, please let us know. GTG with a difference!

 

Let us know what format, venue, and variety of apples, please Sam.

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