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Speakers - Displacement


tonyclaret
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It's the volume of air displaced by the speaker - the area of the cone multiplied by the distance that it moves.

Assuming that the dimensions you've given are speaker diameters, it's not possible to say - you need to know what Xmax is for the speaker (that's the maximum distance that the cone can move before mechanical damage starts to occur to the voice coil).

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3 hours ago, tonyclaret said:

if I have one cab A at 200cm and cab B at 450cm, is cab B louder? Is it moving more air?

chees

As a complete amateur in these matters, I think of it as being surface area x excursion (i.e. the amount that the cone moves to & fro). If you think of the entire speaker cone moving forwards and backwards then the volume it occupies is a cylinder and that's something you can measure. While I typed that, Pete gave the same answer.

Thing is, very few manufacturers publish excursion figures, and you've got this thing called "efficiency" which incorporates the idea of not losing too much power to heat (through friction) so I never feel that I either can work out displacement properly or estimate potential volume either.

What I can do, though, is a quick mental calculation when comparing cabs. Since the only variable that I know for sure is the radius of the speakers, I can do a quick & dirty comparison of, say, a 1x15 -v- 2x10. Radius squared for a 15 is 56.25; radius squared for a 10 is 25, but there are two of them so that makes 50. So if someone tells me that a 1x15 is about as loud as a 2x10 that doesn't upset me.

If someone tells me that their 1x10 (that's a 25) is as loud as someone else'e 1x12 (that's a 36) then I expect them to explain how they've achieved that ... more efficient speakers, greater excursion than usual, cab filled with magic smoke, whatever.

And chees has nothing to do with it.

 

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2 hours ago, Happy Jack said:

 

If someone tells me that their 1x10 (that's a 25) is as loud as someone else'e 1x12 (that's a 36) then I expect them to explain how they've achieved that ... more efficient speakers, greater excursion than usual, cab filled with magic smoke, whatever.

 

Step 1. Convince the gullible crew on an Internet forum.

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2 hours ago, Happy Jack said:

What I can do, though, is a quick mental calculation when comparing cabs. Since the only variable that I know for sure is the radius of the speakers, I can do a quick & dirty comparison of, say, a 1x15 -v- 2x10. Radius squared for a 15 is 56.25; radius squared for a 10 is 25, but there are two of them so that makes 50.

 

I'm not trying to be a smartarse here, but the area of a circle is given by Pi x R x R.  So your answers will be approximately three times more area.

But there are lots of other factors as you probably know well enough. :)

Frank.

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1 minute ago, machinehead said:

I'm not trying to be a smartarse here, but the area of a circle is given by Pi x R x R.  So your answers will be approximately three times more area.

But there are lots of other factors as you probably know well enough. :)

Frank.

I think he was demonstrating the sort of maths that cab manufacturers use to derive their published specs. ;)

  • Haha 1
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7 hours ago, tonyclaret said:

Hi,

What does this actually mean?

if I have one cab A at 200cm and cab B at 450cm, is cab B louder? Is it moving more air?

chees

Cab B will be louder, by about 7.5dB. In fact, Cab B will be more than the equal of a pair of cab A. This assumes that you're actually driving both cabs to their full excursion. If their sensitivities and frequency response are similar and both are driven with the same voltage swing they'll be equally loud. What gives Cab B the ability to go louder is that it can take over twice the voltage swing, which is more than four times the power, as Cab A.

Quote

Assuming that the dimensions you've given are speaker diameters, it's not possible to say

True, because speaker diameter is not a measurement of displacement. But displacement would not be stated as 200cm anyway. Cone area (Sd) is stated as square cm, displacement (Vd) is stated as cubic cm. As the OP specifically asked about displacement I assume that's what he means. The main issue with trying to compare displacement of different cabs is that almost every cab manufacturer won't reveal it. One can rightfully assume that those very few who do publish displacement specs don't feel the need to hide it.

Edited by Bill Fitzmaurice
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On ‎13‎/‎03‎/‎2018 at 05:17, tonyclaret said:

Hi,

What does this actually mean?

if I have one cab A at 200cm and cab B at 450cm, is cab B louder? Is it moving more air?

chees

I hope this hasn't been too confusing so far :)

All of the information given so far is good but I'm not sure how easy it is to follow. I think you may have a mistake in your question, if you change it into ' if I have one cab A at 200 cubic cm and cab B at 450 cubic cm, is cab B louder? Is it moving more air' then it makes sense. Displacement is the volume of air displaced when the speaker cone moves through it's full undistorted range. In this case the answer would then be yes, it moves more air.

As to how important this figure is, well it's one figure amongst many, it's important but not without all the other figures. Barefaced use it a lot in their adverts because their drive units are very good in this area and Alex Claber regularly posts in this forum so it has become a significant quality factor for many people. To be fair I don't think he has ever claimed it's the only important factor or made false claims but some of his fans have jumped upon it as being the key figure by which speakers should be judged. Over the last couple of years it has become a figure people on BC have fixated upon.

I'm going to use the car analogy I'm afraid. The volume displacement of the speaker is like the capacity of the engine, it's the piston area times the stroke length. But , the cubic capacity of the engine won't tell you its power and the cubic capacity of a speaker won't tell you how loud it is. That also depends upon how efficient the speaker is, not all it's movement is converted into sound. A 2 litre engine is likely to be more powerful than a 1litre engine but you will know that isn't always true, I've just traded in my 1.6 litre VW for a more powerful 1.0 litre Vauxhall. If Vd is too low then your speaker isn't going to be able to make lot's of undistorted bass. If your goal is a small loud lightweight speaker then high excursion and therefore Vd becomes very important. If you can't displace enough air then you can't make sound above a certain volume and bass frequencies need a lot of air shifting. If I was designing a 10" high performance speaker I'd be proud if it had Vd :) 

Another factor though is efficiency. If you double the cone area and keep everything else the same then you'll get an extra 3dB for the same power. It's quite possible for example that if you took two 10" speakers with Vd of 200cm3 they might be louder at 300W than a single 10" speaker with Vd of 450 cm3.'t I couldn't tell you for sure without all of the figures.

The physics of speakers isn't that hard, if you've got 'A' level science or maths you'll have no trouble, GCSE maths is enough if you are interested enough but plucking any single figure out of the air isn't going to explain much, you have to do the maths. I the end I don't think Vd is very helpful to the average bassist. Yes it's particularly important that small speakers have good excursion but in the end that won't tell you how they sound. You wouldn't buy a car without a test drive or choose the engine size without considering other factors first and I don't think you should choose a bass speaker like that either.

 

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23 hours ago, pete.young said:

Assuming that the dimensions you've given are speaker diameters, it's not possible to say - you need to know what Xmax is for the speaker (that's the maximum distance that the cone can move before mechanical damage starts to occur to the voice coil).

That would be BIG drivers!  @ 79" and 178" xD

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23 hours ago, machinehead said:

I'm not trying to be a smartarse here, but the area of a circle is given by Pi x R x R.  So your answers will be approximately three times more area.

But there are lots of other factors as you probably know well enough. :)

Frank.

What I know, Frank, is that Pi is not a variable.

:dash1:

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Assuming that the 237cc displacement of the first and 496cc displacement of the second does in fact refer to woofer Vd (odd they can't find anyone to translate their spec explanation into English) the second would equal two of the first in maximum output capability. I'd bet pence to pounds that the first is loaded with an Eminence Beta 12, the second with an Eminence 3012LF.

 

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15 hours ago, Bill Fitzmaurice said:

The same percentage who know what it means.

Nope. Although we know on paper brand X is technically better, the reality is that in practice it doesn't make for a more suitable product for all. 

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