drivers, enclosures and other helpful(useless) knowledge

[squeak9798 5,000+ posts]

This would be a good thread to toss out some formula's aswell //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif Such as;

Theoretical increase in output due to increase in power:

10*log(power1/power2)

10*log(2/1) = 3.0103db

Double power = 3db increase

Increase in output due to displacement:

20*log(Vd1/Vd2)

20*log(2/1) = 6.0206db

20*log(1.413/1) = 3.003db

Double displacement = 6db

41.3% displacement increase = 3db

Resonant Frequency;

Fs = [6.28(Cms * Md)^1/2]^-1

Sensitivity;

SPL = 112 + 10*log(9.64 * 10^(-10) * Fs^3 * Vas/Qes)

Efficiency;

N0 = 9.64 * 10^(-10) * Fs^3 * Vas/Qes

Qts;

Qts = Qes * Qms / ( Qms + Qes )

Sealed enclosures:

Vb = Vas/[(Qtc/Qts)^2-1]

Fb = (Qtc/Qts)*Fs

F3 = Fb*((1/Qtc^2-2+((1/Qtc^2-2)^2+4)^0.5)/2)^0.5

 

[PV Audio 5,000+ posts]

When cutting the cabinet, it is a good idea to cut a few millimeters or 1/8" wide for good measure. This way, you can have over hang OR you will be dead on the correct measurement. The only reason for this is because when using circular saws, or table saws inparticular, most people dont account for the blade which is usally 1/8 or more by itself. By cutting them wide, you have a margin of error and can then just throw in a flush trim bit on the router and go to town for a fine finish.
On my tablesaw, every cut I make is precision and the box is glued to perfection.

It's harder to do with a circular saw, jig saw, hand saw, etc. Tablesaw rules.

I think it's better to train yourself to do precision cuts than to settle for loose

tolerance cutting, eventually you will be happier this way as it's less work.

I mean the plywood that is multiple layers thick and resembles flooring. Baltic birch is a personal favorite of mine, as well as oak.

Baltic Birch at the local lumber store here is 14 ply, $202 for 3/4" , 4x8 sheet. /ouch

It's strong because of the laminations but will resonate in a similar fashion

to ordinary 7 ply wood, knock on it and you'll see [or hear it, hehe}.

Typical oak, birch, maple, etc plywood {$50/sheet} at the home centers

is 7 ply, the only thing 'oak', 'birch', 'maple', etc., about this wood is just the

very thin veneer, the inner layers are usually other types of cheaper

wood, perhaps fir or whatever. Because you pay premium for this 'veneered'

plywood, they try to make the quality of the sheet better with less voids to

because you expect it to be this way. If you don't need the fancy veneer

*and* can find good quality 'construction' grade plywood then it will perform

just as well for less money.

The damping characteristics of the plywood are better and have a tendency to resonate LESS than MDF (as said by Small in an article from the 70's, just so u don't think i'm makin that up //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif ).

30 year old article? /hehe

MDF pros for loudspeakers;

* cheaper than veneered plywoods, marine plywood, baltic birch

* it doesn't warp like plywood

* weights 2x more than typical plywood which gives it a lower resonant frequency, damps higher frequencies better.

* machines well

* smooth surface for painting

Plywood pros for loudspeakers;

* more robust cabinets for other industries {DJ, proaudio, etc.}

* lighter weight + bracing can be very effective too.

* if veneered plywood, will finish well with stains, lacquers, etc.

What else?

When is your book going to be released ? //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I learn something new every day //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

the reason why i said about cutting wide is because not everyone on these forums can afford a good table saw. you might as well cut wide and trim than cut short and make it sloped. my book? naw..i don't know alot //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif gotta learn //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[thylantyr 10+ year member]

I learn something new every day //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Don't assume everything I say is golden //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif If it makes sense, go with the

flow ...//content.invisioncic.com/y282845/emoticons/satan.gif.9c6a335ed7aeeed3ee273e573f1fcaac.gif

 

[thylantyr 10+ year member]

If you can find an old table saw this size

http://woozy.com/coppermine/albums/userpics/tablesaw/DSCN3716.JPG.800.jpg

you can rebuild it.

If you don't have space in the garage for lots of tools you can maybe

make a tablesaw cabinet on wheels like I did. It's a multi-function cabinet,

rectagular in shape with six casters. I removed the saw legs and placed

the saw on the cabinet center and sealed it up so it collects dust and hole

for a shop vac interface to **** dust out later when it fills. To the right side

of this cabinet I installed another box, the router table and it's lined up with

the saw table. On my tablesaw fence I made an attachment that slips on,

this fence is the router fences and it has a chamber that the shop vac

connects to.. to **** dust during table top routing. You can make your

own sleds too. This is a rolling cabinet so I can move it aside when not in use

and the extra dead space in the cabinet is used to store my other tools,

clamps, drills, jigsaw, circular saw, etc. The cabinet has no doors because it's

just easier to leave it without.

If you find an old tablesaw you can upgrade to a better fence, but killer fences

aren't cheap either. I bought the big azz fence so I can rip wider sheets, you

pay premium for a longer throw fence.

If you have a big budget and lots of shop space, I really like those big azz

radial arm saws that have uber stroke to cut 4 x 8 sheets. It's so easy..

To cut a 4 x 8 sheet on the regular saw you need another person to help

hold the wood and you have to slide the wood across the table and to get

a perfect cut is harder because the wood is heavy.

The lumber yard may have one of those radial arm saws, all they do is

place the sheet on the table, clamp it, and drag the saw across the wood

for perfection, and you can do it alone. Pretty sweet. //content.invisioncic.com/y282845/emoticons/yumyum.gif.0556df42231b304b9c995aefd13928a8.gif

 

[PV Audio 5,000+ posts]

pretty good info

 

[thylantyr 10+ year member]

Re: non tablesaw cutting, ie circular saw, jigsaw.

Try this and let me know. If you cut plywood the dreaded chip out happens,

try laying down a piece of masking tape on the cut line, both sides of the wood,

then cut the wood and remove the tape after.//content.invisioncic.com/y282845/emoticons/satan.gif.9c6a335ed7aeeed3ee273e573f1fcaac.gif

[you can do this on a tablesaw too.. but usually people user course blades on

circular saws that give you chipout]

 

[PV Audio 5,000+ posts]

^^ indeed, i noticed that when i got my birch. i had lowes cut it ( //content.invisioncic.com/y282845/emoticons/mad.gif.c18f003ab0ef8a0d9c27ca78d77a6392.gif table saw doesn't work, circ saw blade is green so we don't need green paint on the fine wood //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif ) It chipped pretty good.

 

[ballstothewall 10+ year member]

Routering dovetails in baltic birch trying to minimize chipout is a pain it the ***... That is the one part i don't like about making drawers for furniture. Unless i cut down some walnut down to 1/2" for the drawer, then its all good.

 

[jaygeorge1979 10+ year member]

methinks i like this thread

 

[PV Audio 5,000+ posts]

indeed, there has been alot of contribution.

 

[JimJ 5,000+ posts]

Well, it's early in the morning, and I figure this thread could use something else. So let's talk tube numbers and naming schemes //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

This seems to be a point of confusion for a lot of people starting out in tube audio...and you really need to know the terminology in order to make decisions about what to buy - after all, an EL34 amp and EL84 amp are two very different things. We'll just look at the European (Mullard/Phillips) and the US scheme, because those are the two most common you see on the used and new tube markets.

European system:

First letter: Filament

A 4V

B 0.18A (series)

C 0.2A (series)

D

E 6.3V (series/parallel)

F 12.6V

G 5V (parallel)

H 0.15A (series)

K 2V

L 0.45A (series)

P 0.3A (series)

U 0.1A (series)

V 0.05A (series)

X 0.6A (series)

Y 0.45A (series)

Second and subsequent letters: construction

A Diode (excluding rectifier)

B Double diode

C Triode (signal, not power)

D Power output triode

E Tetrode (signal, not power)

F Pentode (signal, not power)

L Power output tetrode or pentode

H Hexode or heptode (of the hexode type)

K Octode or heptode (of the octode type)

M Tuning indicator

Q Nonode.

Y Half wave rectifier

Z Full wave rectifier

First digit: Basing

1 Miscellaneous

2 Miniature 10 pin

3 International octal (eight pins)

4 8-pin miniature (B8A)

5 Magnoval (B9D)

8 Noval (B9A - nine pins)

9 Miniature (B7G)

Example: If you find a tube and its box is marked "EZ81", then you've stumbled across a full wave rectifier that has a 6.3V filament voltage and fits a standard 9-pin socket. Or the commonly found EL84 is a power pentode with a 6.3V voltage and a 9-pin base. The EL34 differs in that it has an octal base (the 3 shows that) but other than that, it's simply a larger version of the '84. In practice, it works very similar to that - a single ended amp with the tubes wired in triode mode with EL84's does around 3wpc, while the same wiring scheme with '34s will up the power output to 6wpc.

EL34's on the left, EL84's on the right.

American system:

First number: filament voltage

0 Cold cathode (e.g. voltage regulator tube).

1 0.1 - 2.0

2 2.1 - 2.9

3 3.0 - 3.9

n n.0 - n.9

Letter or letters: sequence code

One or two letters to indicate the sequence code. When the single character codes were used up, double character codes were introduced.

Note that U - Z generally (but not always) as the only character, or last character, are used for rectifiers

Final number: Element count

The number of elements in the tube, the filament counting as 1. For example, the 6SN7 has two cathodes, two grids, two plates, and a filament.

Additional letters:

A Controlled heater warmup time, although can also be used to denote increased ratings or performance over and above the non-A model.

B Improved ratings/performance.

C Ditto.

G Glass bulb.

GT Glass tubular.

W Ruggedised version.

X Low loss ceramic base.

Y Low loss phenolic base.

The type designator is a sequentially assigned letter, or pair of

letters. Other than the fact that they started assigning rectifiers

in reverse order, the letter doesn't mean anything. When they ran

out of single letters, they used two. So a 12AX7 is a 12-volt signal input triode that has seven elements and has a 9-pin base. In that tube, there

are two cathodes, two grids, two plates, and a heater that make up the elements.

Furthermore, you can have different types of tube envelopes themselves...you can have a "coke bottle" shaped tube (G) suffix; straight-sided (GB), and a smaller coke bottle shape (GA). However, tubes that are marked like this might have other differences...for example, the 5U4G and 5U4GB are really different tubes, as the 'GB version can supply slightly more voltage. But the two are generally interchangeable in most circuits.

A 5U4GB is shown on the left, and an older style 'G is shown at right.

That's all for now, will include more when I get the urge to...like a detailed listing of all the tubes we're interested in for audio purposes and the different naming games that go on with that. I can't begin to figure it all out. But if you want to get into this sort of thing, it helps to know that a 6CA7 is the same thing as an EL34, or a 6BQ5 means an EL84, or a 6CA4...you get the picture. Can't do anything unless you speak the langauge first.

 

[PV Audio 5,000+ posts]

ok yeah i think this deserves a sticky now. EXCELLENT stuff, and thanks for posting it jack.

 

[JimJ 5,000+ posts]

continuing a little theme here...

Push Pull v. Single Ended amplifiers

and why you should care...

Not found often in solid state electronics (where PP MOSFETs reign supreme), the differences between push pull output stages and single ended ones should be considered when looking at vacuum tube amps, as they're two very different beasts built for different applications. Each topology has certain benefits and drawbacks...PP amps are generally more powerful, but lack some of the tone and "presence" that SETs often have.

Push-Pull:

In a push-pull amplifier the power supply is connected to the center-tap of the transformer and a tube is connected to both the upper and lower end of the center-tapped primary. This allows the tubes to conduct on alternate cycles of the input waveform. A push-pull stage can be biased class A, where current flows in both tubes for the entire input cycle (but in opposite directions), or class AB, where current flows alternately in both halves, but less than a full cycle in each, or class B, where current flows only half the time in each tube. Most designs are biased class AB for best efficiency and power output with minimal crossover distortion (but not necessarily best "tone").

A push-pull stage requires at least two tubes to operate, but can have more connected in parallel with each side, resulting in an amp with four, six, or even eight output tubes for higher-power amps. This is called "parallel push-pull" operation. Another advantage of the push-pull circuit is that there is little or no unbalanced DC current in the output transformer if the tubes are matched and the output stage is balanced, since current flows in opposite directions to each tube, allowing a smaller transformer with less iron (translation: cheaper). Also, even order harmonics and distortion products generated in the output stage are canceled out. In addition, power supply hum is canceled out, allowing the designer to get by with less filtering of the power supply. This stage generally clips symmetrically, resulting in more odd harmonic distortion.

SE operation:

A single-ended amp output stage is always run class A. The output transformer primary is not center-tapped, having only two connections. One connection goes to the power supply, the other to the plate of the power tube or tubes. Tubes can also be paralleled for more power as in a push-pull stage, resulting in what is called "parallel single-ended".

The single-ended stage is found in both modern high-end vacuum tube amplifiers and countless millions of early radios and TV's. It is as inefficient as it is good sounding, putting out very low power levels in comparison to push-pull output stages. Another problem with this type of stage is the transformer must handle a continuous DC current. This results in a physically larger and more costly output transformer, which must be gapped to prevent saturation of the core due to this offset DC current.

Crossover distortion is eliminated in SE operation, because the output devices are always on - only having one per channel elimates switching them on and off. This, however, contributes to the design's inefficiency. Theoretically, SE amps have a maximum efficiency of 25%, but in the real world you're doing well to break 20%.

In a SET design, the transformers are the most expensive part of the amp, with the iron basically the limiting factor on the frequency response. You don't want to skimp here when designing a SE amp.

Disadvantages of single-ended include: no rejection of power supply hum, which mandates heavier filtering to keep the hum to acceptable levels (although there are several workarounds for PSU hum that render it almost negligible), no rejection of even order harmonics, and generally asymmetrical limiting on overloads which further emphasizes even order harmonics (which are more pleasing to the ear than odd order harmonics). These "disadvantages" give the single-ended output stage a unique tone, compared to the push-pull output stage. Whether it is "better" or not is a matter of taste.

 

[ballstothewall 10+ year member]

One question....

WHY ISN'T THIS A STICKY?

 

[PV Audio 5,000+ posts]

Not sure, I think that it should have been.