What's to chat about?

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Bill Fitzmaurice
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Re: What's to chat about?

#1006 Post by Bill Fitzmaurice » Thu Aug 05, 2021 11:01 am

Bruce Weldy wrote:
Thu Aug 05, 2021 10:16 am
We've had more rain than I can ever remember during the summer.
The average rainfall in July here is 4.3 inches. This year we had 16.

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Seth
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Re: What's to chat about?

#1007 Post by Seth » Thu Aug 05, 2021 12:52 pm

I've been taking Celebrex for years. Initially for knee pain and in more recent years for lower back pain too. 1-2 per day, as needed, takes the edge off fairly effectively (usually 2). I don't typically need it daily. But, when I do, acetaminophen & ibuprofen aren't effective. However, I'm very open to natural remedies. I'll give the Turmeric a go, thanks for the mention :thumbsup: If you guys haven't tried Celebrex... it's great with few to no side effects.

Also, this book was recommended to me a few years ago.
Image

Good book to have... Pain Free: A Revolutionary Method for Stopping Chronic Pain
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Re: What's to chat about?

#1008 Post by Bill Fitzmaurice » Thu Aug 05, 2021 12:56 pm

Turmeric isn't a pain killer, it's a low dose anti-inflammory. You don't take it to treat pain, you take it to prevent it. That being the case you have to take it every day. The good news is that it's not expensive on-line. Be sure it's turmeric curcumin, which is better absorbed by the body than pure turmeric.

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Re: What's to chat about?

#1009 Post by Bruce Weldy » Thu Aug 05, 2021 2:24 pm

Seth wrote:
Thu Aug 05, 2021 12:52 pm


Also, this book was recommended to me a few years ago.
Image

Good book to have... Pain Free: A Revolutionary Method for Stopping Chronic Pain
I've been using the Egoscue techniques for a couple of years.....it's helped more that anything else. I wish I could make myself do it every day - I would probably be in better shape with my back. It's very easy and almost all of it is laying on the floor. It's more of a case of letting your body get back into position instead of trying to force it back where it belongs.

Haven't read the book, but spent a couple of hours with a guy who swears by it and he make a huge difference that day.

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Re: What's to chat about?

#1010 Post by Bill Fitzmaurice » Fri Aug 06, 2021 10:43 am

Before I discovered turmeric I did PT for a time and then continued using the techniques I learned there when I had a bout of sciatica. I haven't used them since discovering turmeric, because I haven't had sciatica since then. :hyper:

As far as arthritis goes glucosamine does work. When I was diagnosed with it my doctor said that I'd have to get a knee replacement eventually, but I could try glucosamine as it might help. That was 25 years ago. The glucosamine didn't reverse the arthritis, but it did stabilize it. I've still got my own knee, and it hasn't gotten any worse since then. A week ago I tweaked it a bit, probably playing golf, and it bothered me for two days. Thanks to the turmeric the inflammation was gone by day three.

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Re: What's to chat about?

#1011 Post by Chris_Allen » Sun Aug 08, 2021 7:52 am

Every time I hear the term armchair quarterback, that's the kind of thing I think of :D
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Re: What's to chat about?

#1012 Post by Seth » Fri Aug 20, 2021 12:14 am

A good while back, I recall Bill saying there's a 6dB gain for every doubling of voltage. Up 'til that point, I'd always done the "doubling/halving wattage is 3dB". It got my brain turning a little bit in new ways. Opened new thought processes. Thanks for that (and many other bits of knowledge and insights over the years) Bill. :thumbsup:

Anyway, one of my initial thoughts was, what if we want to figure the gain for a voltage amount other than double and/or what's an easy way to double, then double, then double 2.83 in my head or even manage keeping track of the number of times I doubled on a calculator? That just kinda rattled around in my head since then as an unsolved mystery.

Well, here we are, years later and I experienced a moment of clarity and inspiration to try and figure it out. Tinkering in an excel spreadsheet for an hour or so, I finally just worked out a new-to-me formula for calculating volts required to gain a specific dB and thought I'd share it with you guys. I've never seen this calc anywhere (wish I had), but I can't imagine I'm the first to come up with it. It calcs a final voltage from dB gain instead of my initial curiosity of calculating dB gain from voltage.

I know, for a lot of you this will be really boring stuff. Sorry about that. Don't bother reading any further. But just know... It's pretty damn cool for numbers guys (well... I'm impressed with myself anyway). If any of you guys DO have an audio math reference spreadsheet, you might want to add this equation in there...


The product of 1.122 ^ dB increase, times initial voltage equals final voltage.

(1.122 ^ 20dB) x 2.83V = 28.29V
(1.122 ^ 21dB) x 2.83V = 31.74V
(1.122 ^ 22dB) x 2.83V = 35.61V
(1.122 ^ 23dB) x 2.83V = 39.95V

Any dB number and any initial voltage gives the final voltage required to make that gain.

Say we're already at 35 volts and want to know how many volts is required to gain another 1, 2, or 3dB (or any number dB)...

(1.122^1dB) x 35V = 39.27V to achieve a 1dB gain
(1.122^2dB) x 35V = 44.06V to achieve a 2dB gain
(1.122^3dB) x 35V = 49.44V to achieve a 3dB gain

Since we know 3dB is essentially double the power we can double check and prove the math...
Volts x Volts ÷ Ohms = Watts
35V x 35V ÷ 8 Ohms = 153W
49.44 x 49.44 ÷ 8 Ohms = 306W... twice the initial wattage

Checks out.


Pretty sure I shared this last one already, but I'll mention it again...

1.2589 ^ dB increase over base sensitivity equals watts needed to achieve the specific gain

1.2589 ^ 20dB = 100W
1.2589 ^ 21dB = 126W
1.2589 ^ 22dB = 158W
1.2589 ^ 23dB = 199W

Any dB number gives the watts needed to achieve the gain.

That calc assumes 1 watt is the initial figure. But, just this moment, I realized we can modify the equation to the format of the Voltage equation if we want to know the final power needed to make a specific gain above a number of Watts other than 1. Nice little ah-hah moment of incidental realization I had there. Cool. Anyway, here's how that looks...

If we're running 250W (or any number of Watts) and want to know how many total watts we'll need to realize a specific gain of 1, 2, 3db (or any number of dB)...

(1.2589 ^ 1dB) x 250W = 315W
(1.2589 ^ 2dB) x 250W = 396W
(1.2589 ^ 3dB) x 250W = 499W

Any dB increase over any starting wattage get's you the final wattage.


Anyway, I know I get a little more geeked out in the numbers than most of you. But, figured I'd share for anyone interested and for the sake of posterity. I might need to come back here and find it again sometime. I am creeping up on 50 and all. :mrgreen:
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Re: What's to chat about?

#1013 Post by Seth » Fri Aug 20, 2021 12:36 am

Little note: The first (voltage) equation and last equation appear to also work perfectly well with negative or minus dB too.
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Re: What's to chat about?

#1014 Post by Grant Bunter » Fri Aug 20, 2021 12:59 am

Maybe I missed when Bill said doubling voltage = +6dB.
Do you reckon you could find it?

Time and time again, it’s said a doubling of cabs adds +6dB, but half of that is attributable to power, the other half is from doubling the radiating plane.

While I’m here, BL IIRC is the product of magnet strength and the length of wire in the VC gap.
Since the amount of wire in the gap decreases as the coil and cone move forward, BL will decrease as that happens.
If the coil leaves the gap, BL must then = 0, hence the loss of control...
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Re: What's to chat about?

#1015 Post by Seth » Fri Aug 20, 2021 2:29 am

Grant Bunter wrote:
Fri Aug 20, 2021 12:59 am
Maybe I missed when Bill said doubling voltage = +6dB.
Do you reckon you could find it?

Time and time again, it’s said a doubling of cabs adds +6dB, but half of that is attributable to power, the other half is from doubling the radiating plane.
Like I said, it was a good while ago. But, I'll give a look-see. And also, it's easy enough to verify against the doubling/halving power = 3dB rule because doubling voltage quadruples power.

From 10 to 20 volts...
10V x 10V ÷ 8Ω = 12.5 watts
12.5W doubled to 25 = +3dB, doubled again to 50 watts for another +3dB, total +6dB.
20V x 20V ÷ 8Ω = 50 Watts... twice the voltage, for times the power, +6dB.

While I’m here, BL IIRC is the product of magnet strength and the length of wire in the VC gap.
Since the amount of wire in the gap decreases as the coil and cone move forward, BL will decrease as that happens.
If the coil leaves the gap, BL must then = 0, hence the loss of control...
The conversation in the other thread prompted me to look into it a little further today and you're right, BL is the product of magnet strength and the length of wire in the VC gap. I read just that, nearly verbatim. The gap has a height or thickness to it. Pushed beyond Xmax, the coil doesn't just instantly leave the gap and magnetic flux. It's progressive (or maybe regressive is a better word LOL).

Take the LAB12 for instance, it's gap height is 9.5mm and the Xmax is 13mm. So, at rest, there is 13mm of coil above the gap, 9.5mm of coil in the gap, and 13mm of coil below the gap, which add up to a total coil length of roughly 35.5mm. So, the coil can move 13mm in either direction and maintain the same amount of coil in the 9.5mm gap/flux throughout the entire 26mm motion. Pushed beyond 13mm, say to 15mm excursion, now there's only 7.5mm of coil in the gap for the last 2mm of cone travel in either direction. Less coil in the gap equates to less length of wire in the gap, which further equates to progressively less and less coil in the gap the harder and harder it's pushed, taking more and more input for less and less output. But, again, in this scenario it only occurs at the last 2mm peak at either end of the entire stroke. The coil is still 81% in the gap at that peak and 100% in the gap for the next 26mm of travel until it gets to the other peak. Just on a hunch, I'd have to imagine that's not really that bad of a scenario. Perhaps quite common even. I think it's when people push way past Xmax that it starts to sound poorly and bad things happen. I could be wrong though.

Mathed out, the LAB12 has only 0.5mm of coil in the gap at Xlim.

Here's a cross section to help visualize it all.
Driver cross section.jpg
Close up Cross section.jpg
Xmax, Voice Coil Height, Gap Height

Here's the pages they came from. Really good, quick, easy to understand reads. For sure recommend reading.
Xmax BL



Another little tidbit I picked up today while noodling around the web is... I didn't know and hadn't even considered it before, that surrounds and spiders (the cones suspension) springy-ness isn't linear. The further in/out the cone travel, the more resistance to movement occurs. Sounds like a double wallop of no good if pushing deeply beyond Xmax... progressively lowering BL along with increasing suspension resistance requiring even more power and heat... It really drives home the good sense of staying within the bounds of Xmax. Or, at least, trying to remain relatively close to it for a vast majority of the intended frequency range. Personally, if the cone exceeds Xmax at the low end of the scale as the horn unloads, I'm not too too worried about that. We're not pushing it there with additional power input and the impedance rises swiftly with excursion reducing the wattage (heat) considerably. So long as they don't come too close to Xlim, I don't see a huge issue with it.

Anyway... time to stop the rambling. Enjoying the conversation and learning some new stuff along the way :thumbsup:
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Re: What's to chat about?

#1016 Post by Seth » Fri Aug 20, 2021 3:02 am

Grant Bunter wrote:
Fri Aug 20, 2021 12:59 am
Maybe I missed when Bill said doubling voltage = +6dB.
Do you reckon you could find it?
Found it! October 2018. It's been rattling around my mind for almost 3 years!

Page 6 of 6 Tuba 45s
Bill Fitzmaurice wrote:
Tue Oct 02, 2018 7:59 am
Every doubling of voltage gives 6dB. We don't talk watts here. :cop:
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Re: What's to chat about?

#1017 Post by Grant Bunter » Fri Aug 20, 2021 4:02 am

Cheers!

It's just occurred to me though, if you double cab count and wire them in parallel, then voltage stays the same, impedance decreases, and amperes increases.

In series, you can double the voltage and stay in power handling limits (and impedance will increase and amperes will decrease).

So, it can't always be about doubling voltage for +3dB.
Built:
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T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
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Re: What's to chat about?

#1018 Post by Bill Fitzmaurice » Fri Aug 20, 2021 7:07 am

Grant Bunter wrote:
Fri Aug 20, 2021 12:59 am
Time and time again, it’s said a doubling of cabs adds +6dB, but half of that is attributable to power, the other half is from doubling the radiating plane.
When you double the cabs wired parallel power doubles, but that's not what gives increased sensitivity or maximum SPL. Power doubles because with the halving of impedance current, and therefore power, doubles. It's a side effect, not a causal factor.

Doubling cabs parallel wired adds 6dB because displacement is doubled. Doubling voltage adds 6dB for the same reason, displacement is doubled.

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Re: What's to chat about?

#1019 Post by Seth » Fri Aug 20, 2021 11:36 am

Grant Bunter wrote:
Fri Aug 20, 2021 4:02 am
Cheers!

It's just occurred to me though, if you double cab count and wire them in parallel, then voltage stays the same, impedance decreases, and amperes increases.

In series, you can double the voltage and stay in power handling limits (and impedance will increase and amperes will decrease).

So, it can't always be about doubling voltage for +6dB.
Fixed it for ya.

In either of those cases, if you double or halve voltage from any specific value, the change should be 6dB... assuming Xmax isn't exceeded.
Last edited by Seth on Fri Aug 20, 2021 12:21 pm, edited 1 time in total.
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Re: What's to chat about?

#1020 Post by Seth » Fri Aug 20, 2021 11:43 am

Bill Fitzmaurice wrote:
Fri Aug 20, 2021 7:07 am
Doubling cabs parallel wired adds 6dB because displacement is doubled. Doubling voltage adds 6dB for the same reason, displacement is doubled.
I'm sure it's a horn specific phenomenon that's currently beyond me. But, I've always found it a little interesting that doubling drivers (and therefor displacement) within a single cab doesn't actually add 6dB to the cabs output and you have to actually double the cab count to realize the full 6dB.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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