impedance v freq. charts

[farmerjack61]

Hello all. I was hoping that someone could tell me the difference between the speaker model and the delta model in all the frequency v impedance charts I've been looking at:- Phil E.

[Ron E]

Originally Posted by farmerjack61

Hello all. I was hoping that someone could tell me the difference between the speaker model and the delta model in all the frequency v impedance charts I've been looking at:- Phil E.

have you got a link, or some context?

[john k...]

Originally Posted by farmerjack61

Hello all. I was hoping that someone could tell me the difference between the speaker model and the delta model in all the frequency v impedance charts I've been looking at:- Phil E.

I think what you are referring to is the difference between the added mass approach,(delta mass) compared to the volume or box method of determining Vas Is that correct? If so, in theory both should yield the same results as both yield a shift in frequency at resonance from which Vas can be found. The delta mass method is usually preferable because the tester has good control over the change or added mass. With the box method the problem is that there are unknown factors such as leaks in the box, leaks around the seal between driver and box, other possible leaks, stiffness of the box, and other box losses. These generally make the box method less reliable.

[farmerjack61]

Hello again, boy-o-boy, nothin is ever simple is it? I will firstly apologise for my cynicysm and frustration. I have been mucking around with speakers for a while now but, only rarely get it right. It really sod's me from an awkward angle because the whole idea of this passtime is to make it easier to listen to music, but alas!...all I hear are annoying tones transmitted down a copper wire from my signal generator through a 10r resistor to some bloomin' woofer or tweeter [tweeters really have a taste of cabbage to me].

I think you John, have got a handle on my question, but I will start at the start:

I like big speakers but can only afford little ones from the corner store.

Despite this I buy 'big' speakers for basement prices and generally get what I pay for.

Despite even this I have two good speakers; a sound dynamics 100s (pair) and a dog I built myself from an old bass amp box. The latter canine contains two old 8" jaycar 'vanilla-flavoured' speakers with a soft dome tweeter. The dog speaker outperforms my SD spkrs (which I have always admired fondly).

The other day I was looking at a Jaycar catalogue and saw a little 8" woofer that outperformed all of their other speakers bar one or two. At first I thought "those buggers are just exaggerating" but then I remembered just how stupid I actually am. I already have a couple of these speakers CW2196 (or similar) in my old bass combo box, and Lo, they sound most excellent indeed.

I'm almost there, so I'll get to the point and paste a picture in to explain. I'll just save this gabble first so I don't ime out.

OK the picture should be there somewhere, so John! here's my next question,

Q. When you say "Weighted" (this is the joiner coming out now!) do you mean they stick a bit of blu-tac in the centre of the cone before they run their tests or is there some kind of witchery-pokerey with the numbers to get a pretty looking chart?...AND b). Why show that plot on the graph?

I feel as though I am about to have a stroke. So I'm going for a beer and a bite to eat.

Yours sincerely, Phil E.

[speaker dave]

John had it right.

Weighted and delta refer to adding mass to the woofer to be able to figure out its parameters. The Thiele Small (TS) parameters will help you predict how the woofer performs in any box you might put it in. Primarily you look at the impedance curve to see numbers around resonance. Along the way you also have to change resonance to figure out the final numbers. The easiest way is to add mass to the woofer, and yes, that is usually some modeling clay smooshed into the apex.

As an example, if you added some amount of clay and the resonance dropped to 70% of what it previously was, then you must have added mass equal to its usual moving mass. (1 over square root of 2 = 70%) For any mass and any drop there are formulas to help you calculate woofer effective mass.

David

[farmerjack61]

That makes sense. I will have to get around to reading up on these t&s parameters. My dad got it right - in his own 'sarcastic' way, when he said; "If all else fails, read the instructions son!

Cheers and thanks to all three of you. Have a good week and l will try to hit the books soon!

[buggsson]

Isn't the new value supposed to differ by at least 50%?

Some use magnets instead of sticky stuff, no problem?, or problems?

[farmerjack61]

Hi Buggsy! You're dead right. 50% is the exact position of the derived peak - at least that's my take on what I have learnt.

And....you have just taught me something else.

The 12" CW2199 I purchased actually had an extra magnet glued on - piggy back style. It was different to the original CW2199 which only had the one.

I wonder if this was an attempt by the manufacturers to move the 28hz peak to the left? - I reckon so, but I am often mistaken!

Is it warm or cold up there in the Northern Extremities, dark or light? Tasmania has been blowing and pouring with rain (non stop) for almost 3 Days. I have tiny little plants growing inbetween my toes, and will have to take a bath this week if the rain doesn't stop.

Nice to meet you - hope to talk again soon - Phil E.

[speaker dave]

Originally Posted by buggsson

Isn't the new value supposed to differ by at least 50%?

Some use magnets instead of sticky stuff, no problem?, or problems?

I was giving a hypothetical, but you are correct. A greater weight percentage difference will give a bigger shift and greater accuracy from your numbers.

I wouldn't use magnets because they would likely be attracted to the woofer's magnet structure and add some bias or position shift. I've always used modeling clay, but sometimes the residue it leaves is a little nasty. I've heard heavy plumber's solder suggested. Whatever it is, it needs to be firmly attached so that it doesn't set up a secondary resonance.

David S.