EAS/ELF doubt

[rs1026]

Hi
In Rod Elliot's Sub woofer controller project
http://sound.westhost.com/project48.htm

Can any one let me know about the dual ganged pot? The connection was not very clear to me. Should I short the varaible point with one of the terminals before connection.Totally there are six connection points in the pot. But schematic diagram shows only two for each pot so I assumed that it should be shorted.
Am I right?

Whats the exact function of VR1 what will be the consequence If i remove it.

[Tube_Dude]

Originally posted by rs1026
Hi
In Rod Elliot's Sub woofer controller project
http://sound.westhost.com/project48.htm

Can any one let me know about the dual ganged pot? The connection was not very clear to me. Should I short the varaible point with one of the terminals before connection.Totally there are six connection points in the pot. But schematic diagram shows only two for each pot so I assumed that it should be shorted.
Am I right?

Yes you are right!

Whats the exact function of VR1

Quoting the text in Rod Elliot site:

[[ While the dual pot seemed like a good idea when I built my unit, it actually only changes the gain. Now, having experimented some more, this is a very good thing, since it means that the level through the controller can be set to make sure that there is no distortion - there can be a huge amount of gain at low frequencies, and if the gain is too high, distortion is assured!]]

what will be the consequence If i remove it.

You can overload the circuit with consequent high distortion

Regards

[Grandma´s_SUB]

So about EAS/ELF(I wont open new thread)
I searched the forum, so I found:
-It is device, which operate driver below resonance(peaks are left to upper freq. )
-trade off is more power to suply and "smearing"


If I properly understand, that works like EQ and active low pass filter.
At lower freq. gain is high and at higher freq. is gain lower, to reach 0db.It is very familiar to linkwitz transform(thats diffirent story, its more complicated; how can be Q transformed???-loses are loses. )

-thats all OK, but why is more power needed?
-Most woofers are 250W RMS....so If you have 250W woofer, you cant drive it with 400W RMS amp(I define RMS, no peaks...P=V^2/R ), because Rod Elliot said,that 400W amp should be good enough, fpr his 250W driver...

Dean

[richie00boy]

Grandma's_SUB,

Love your avatar

You are spot on on all your thinking so far, well done for searching The reason EAS/ELF is power hungry is that it is boosting the output of a speaker whose output is rolling off at 12dB/octave. Thus the power requirements climb very quickly as you go down. Because the speaker is so far down at low frequency, a lot of power is required to bring it up to the same level as the main speakers.

With EAS/ELF you can get deep loud bass from a small box, but your driver voicecoil must be able to take the power needed to get the driver moving. Rod says a 400W amp is OK for his 250W sub because it will only be peaking up to that level occasionally, and it's better to have power spare so that the amp doesn't clip, which causes massive power dissipation due to the harmonics generated.

[Grandma´s_SUB]

Tnx dude! (Its cool that to,that you love my avatare)

-About cliping,you need just 20% more powered than speaker,to prevent the it, not almost 1 time more(250W...400W )



Dean

[richie00boy]

But 20% more power is only 0.8dB more power, pretty negligible. Typically 3dB more power as a burst will not harm a voicecoil. 3dB is double the power.

[Grandma´s_SUB]

example:
We have xy driver which has that characteristics at Vb=10,4L, Fs=60hz
So the power of driver is 250W.That mean,if we deliver more power,than rated power, membrane will break...(there will be mechanical damage).So the very important parameter is SENSITIVITY in free air.In this case its about 83db@1m/W.So that means:
1W...........83db
2W............86db
4W............89db
8W............92db
16W...........95db
32W...........98db
64W...........101db
128W.........104db
256W.........108db

As we can see, this speaker can make 108db SPL+usually 6db of room gain
-This is "standard" speaker attachement.

In the smaller box, sensitivity should rise.we can see from graph,that for 20hz is needed 20db boost, to reach 0db.
For that 20db is needed some power,I DONT KNOW HOW MUCH,
but think the SPL(eas) is defined like this :SPL(eas)=P(delivered)-P(needed to boost)
So,If the result for example is 64W,that means the driver will produce 101db+6 to 8db(room gain+smaller box gain)

thats it

-The big question is:How to calculate; how much power does "eat" boosting?

[Cro maniac]

Hi !

As you said the driver sensitivity will be 20dB down on 20Hz. So, its sensitivity on 20Hz in the box will now be something like 65dB.
So:
1W - 65dB
2W - 68dB
4W - 71dB
8W - 74dB
16W - 77dB
32W - 80dB
64W - 83dB
128W - 86dB
256W - 89dB

So you need 64W to get to the 83dB sensitivity.

Because this driver has Xmax of 16mm (at least in WinIsd), I would put it in 20L box to use all of driver's excursion. Then you would be able to get 94db SPL with full power which will feel like twice as loud, and box will still be quite small.

[Grandma´s_SUB]

So If I understand right, 64W is needed to catch up that 83db@1W/1m(peak sensitivity).So calculate follows:
P(to reach 0db)+P(power to get WANTED SPL)+30%(to prevent cliping)=AMP POWER

-these things are quite hard to me,so I need some time.....

Dean