Dean's Super AA

[Deang]

In a constant impedance filter the value of the high pass is in part determined by the impedance of the woofer. In other words, the high pass of the SAA like the ALK is based on a 6 ohm in series with .10mH inductance (voice coil) - and you are running at 2 ohms, yes? You are at an impasse here with this. You want the additional sensitivity of the parallel connection so you can run tubes - but you will not be able to run tubes with a 2 ohm minimum impedance! I say run those woofers in series. You'll have a sensitivity of 101dB which means you can still drive yourself out of the room with 60 good push-pull tube watts.

Follow my notes -- it's a 20 minute fix. Bring the squawker and tweeter down to match the woofer section. I suspect taps 4 (pos) and 1 (neg) for the squawker and 3dB of attenuation for the K-77. Your choice on how you decide to do that.

[jwc]

Thanx Dean. I guess I will take the plunge and try the series.

I follow your instructions there. I assume I should leave out the diode?

Didn't realize I would need a resistor on a second autoformer to provide the -3dB. I was considerin using that idea on another project and I guess I would have screwed that up. I will need to purchase a resistor.

Well, I will assume it was put together correctly but won't work for my application.

For your suggested changes of the network for a series woofer connection; it essentially is this: leave the the low pass the same, leave the bandpass filter the same except to not use common ground on the squawker, place another autoformer behind the tweeter filter to obtain -3dB on the tweeter.

Will try it. Will have to wait on a 20 ohm 10 watt resistor.

Your the man

[Al Klappenberger]

Dean,

You need to post a CADD drawing of the layout for the Super AA network. A lot of people have a very hard time following a schematic diagram.

AL K.

[Deang]

[Al Klappenberger]

Dean,

I' can draw it for you. How much money have you got?

Al K.

[jwc]

So it looks like the original schematic I had seen with the diode has been ditched.

[Al Klappenberger]

JW,

I looked carefully at the two pictures. It looks to me that you have it wired correctly. Of course, the squawker connections are not shown. They connect directly to the transformer between taps X and 4 or between 2 and 5. Neither squawker lead connects to common ground (tap 0).

AL K.

[Al Klappenberger]

Here's a doctored picture that I hope will make the wiring easier to see.

Note the jumper AROUND the squawker terminals. Neither one connects to common ground.

Al K.

[Deang]

!

[Deang]

?

[tofu]

hey dean, got the package today.

i'm sure glad everything was double boxed otherwise we would've had parts falling out! usps sure did a number on the outer box, they even somehow managed to snap one of the plastic holders off the inductors off. those woofer inductors are hefty suckers. the 10 guage version must be enormous.

well, i'll start putting them together in a temporary fashion (wire twisting) until the weekend. have to run to radioshack and buy some rosin core solder and a new iron.. can't find mine.

i will paypal you the $13 shipping later today, just leave me your paypal address.

thanks again.

-chris

[jwc]

Here's a doctored picture that I hope will make the wiring easier to see.

Note the jumper AROUND the squawker terminals. Neither one connects to common ground.

Al K.

oooh. So there is no common ground for the squawker. I think Dean was trying to point that out to me on the previous photo. There you go. That was my mistake (other than trying it on my dbb's). I didn't pay enough attention to that for this constant impedance design.

Notice you selected X and 4. That is the same ones I used for my late La Scalas.

I will fix the ground problem and try one more time. However, I believe I will try the mod to this network that Dean suggested to try my dbb's in series. Just need to get a 20 ohm resistor.

I am bummed I no longer have my La Scalas to test this thing out.

So AL. I guess all those parts I have to build a pair of your ALK universal A's is useless too. Boy...how fun. I'll have a basement full of networks with no personal use. I think I bought the stuff for AL-3's too...can't remember.

Been A/B'in the ALK B (Dean's) with Type B's and B-3's with new caps and inductors on my Cornscalas. So I have that crap laying around too.

I expect to make more mistakes. Bear with me.

jc

[Al Klappenberger]

JC

"So AL. I guess all those parts I have to build a pair of your ALK universal A's is useless too. "

That's silly! If you have the parts for my Universal you should build that instead. The "Super AA" is a cut-down version of my universal. If you have the parts go for the real thing!

AL K.

[jwc]

Well, my plan was to do one big A/B of all these networks. If you all are telling me that the Super AA won't work with my dbb's, then I can Assume the ALK won't either. May be I could also change the tweeter portion of the ALK's as Dean has mentioned to work...not sure.

I had the confidence to try this due to the fact that my dbb's sound unbelieveable with the TypeA's with a duplicated low pass filter. This is also the reason I held off on swithching the parallel loaded K33's to a series hookup due to the great sound.

Maybe the more complex networks just won't work unless I customize them.

[Deang]

JC -- I agree with Al. I'm leaving for home, when I get there I'm calling Al -- after we have our chat I'll PM or post.

[tofu]

so, i'm getting no squawker or woofer output...

any trouble shooting tips? i'm pretty sure i have everything wired correctly...

tweeter seems to be working fine

[tofu]

i don't see how i'm not getting output from the woofer.. all it is is an inductor. i even tried removing the fuse (and holder of course) from the circuit.

[Deang]

Need a picture.

[tofu]

okay.. i'll see if my cameraphone comes out clear enough.

[Deang]

Al, this from http://www.linkwitzlab.com/faq.htm#Q21

Why does SPL increase 6 dB for two drivers in parallel, when the electrical power consumed only increases by 3 dB?

The acoustic power P_a radiated from a small source at long wavelengths is the product of the radiating piston area A_p, the square of the piston velocity v_p, and the real part of the piston's radiation impedance Z_p:

P_a = (v_p)² A_p Re{ Z_p }

Since the real part of Z_p is also proportional to the radiating area A_p, it follows that the radiated power is proportional to the square of piston velocity and the square of piston area:

P_a ~ (v_p)² (A_p)²

When two identical drivers are connected in parallel, each piston moves with the same velocity as the single driver, because the current through each voice coil is the same as before. The total radiating area has doubled, and the radiated acoustic power has increased fourfold (10 log (4) = 6 dB) over that of the single driver. The electrical power consumed by the two drivers has merely doubled (+3 dB).
With 4x acoustic power for 2x electric power you have a 3 dB increase in power conversion efficiency.

The sound pressure p at some distance from the source is proportional to the square root of radiated acoustic power.

p ~ (P_a)^1/2 ~ v_p A_p

When the piston area A_p is doubled and the piston velocity v_p stays unchanged, then the pressure doubles (20 log (2) = 6 dB).

In summary, when two identical drivers are connected in parallel and driven with constant voltage, then twice the electrical power is consumed (+3 dB), the radiated acoustic power is increased by a factor of four (+6 dB), and the free space sound pressure level is doubled (+6 dB) at a given distance.

Note that piston velocity and displacement are proportional to each other and both are directly related to the current through the voice coil. With two identical drivers connected in series, piston displacement and velocity decrease to 1/2, but the piston area doubles, which leaves the sound pressure and radiated power unchanged (0 dB) compared to a single driver connected to the same voltage. Electrical power dissipation is now 1/2 (-3 dB) and again the power conversion efficiency has doubled.

A source that is small compared to wavelength and radiating 1 W acoustic power into free space generates a sound pressure level of 109 dB SPLrms at 1 m uniformly around it. The SPL is 103 dB at 2 m and 89 dB at 10 m.
If the source has a power sensitivity of 86 dB SPL/1m/1W, then it takes 10^(109-86)/10 = 200 W of electrical power to generate 1 W acoustic and 109 dB SPL/1m. The power conversion efficiency is 1W / 200W = 0.005 = 0.5%.

Two drivers with 86 dB SPL/1m/1W connected in parallel will produce 92 dB SPL/1m when driven with the same voltage, but consume 2 W. At 1 W input the driver combination generates 89 dB, and it takes 100 W to produce 1 W acoustic power, thus the efficiency is now 1%.

The two drivers could be a tweeter and a midrange and have very different piston areas A_p. If they have the same 86 dB output for 1 W input, then the tweeter must have much higher piston velocity v_p than the larger piston area midrange. The volume velocity U = v_p A_p , though, is the same for both drivers when they have the same sensitivity.



Good discussion here as well: http://www.diyaudio.com/forums/showthread/t-67348.html