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Author Topic: Typical transient response  (Read 4020 times)

Too Tall (Curtis H. List)

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Re: Typical transient response
« Reply #10 on: August 22, 2005, 10:37:06 am »

Peter wrote on Sun, 21 August 2005 20:01

The LAB horn is about 10 feet long, so the resonance associated with its length will be at about 30Hz.  Thats what you are seeing, resonance, the cone or anything else for that matter including the box, keeps vibrating after the signal has stopped.  What you see as time goes on (the Z axis in this case) is an ever decreasing amount of energy, mainly at 30 Hz and some at 60Hz, which is exactly what you would expect in this case.  There is some at 40, this maybe the box, the wall, don’t know.

As you put more of the LABs in a stack and the mouth becomes bigger it will begin to behave more like a horn and not a resonant length of pipe at these low frequencies.

Having said that – that’s a very good plot in any case, but they are loaded in 1 / 4 space.



The descriptions of the setup on those graphs are incorrect.

That particular batch of data was a failed attempt to measure the change in freq response and impedance as you make bigger stacks. The project was cursed from the start and right through to the end.

It started out with a hum when I hooked the laptop up to the power amp rack. From there it went to an argument with my help on stacking. I wanted to measure a box by itself. My help insisted that it was good enough to stack all four subs in a block at the beginning and just hookup first one, then two, etc.

We know this is wrong, but the help would not be convinced.

The final nail in the coffin was that the NL4 input panel on the back of the amp rack had bad solder connections so I don’t know just how many speakers were actually working at any one time.

So that graph WAS just one LAB working, but it was part of a stack of four where the other three were not driven.

I found another set of data that I believe was from the very first LAB that was built here. It is a ground plane at 1 meter outdoors.

Sorry about the confusion. As you can see the graphs are fairly similar.

Too Tall
        Curtis H. List    
             Bridgeport, Mich.   
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Independent Live Sound Engineer (and I'm Tall Too!)


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Re: Typical transient response
« Reply #11 on: September 20, 2005, 09:36:16 pm »

Gareth James wrote on Wed, 17 August 2005 05:33

Can anyone tell me any real figures for a typical transient response (not sure if my wording is right here) or the time for the emitted sound from a basshorn or other bass speaker to decay by for instance 6 or 10dB after receiving a given impulse.

I realise this is quite a complex question to answer properly but if anyone has any general ideas they would be greatly appreciated! Razz

Peter Morris

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Re: Typical transient response
« Reply #12 on: September 21, 2005, 09:03:30 pm »

There is one point to note.  When you use one LAB its mouth is not big enough to produce 30 Hz properly and it behaves a bit like a resonant 10 ft pipe. What you see on Brads plots is the resonance decay at about 30Hz and the next harmonic 60 Hz associated with its length.

I have not measured it but when you stack about 6 LABs together in half space the mouth is big enough and I would expect things to improve.

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