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Discussion Starter · #1 ·
Hi there,

Got my sub up and running and I am having nightmares trying to sort out REW. Here is my graph. I cant get the levels high enough to work. I have just re calibrated my sound card and it still isn't playing ball.

It is dropping like a brick from 40hz.

cheers
Graham
 

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Elite Shackster
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The sound card cal curve is taking account of your sound cards deficiencies, so dont worry to much about the shape of that curve, it wont affect what your trying to do.

When you say you cant get the levels up, does REW just tell you the levels are to low or does it say levels are ok. I have seen a couple people getting stressed over the levels being in the minus figures when thats how it's supposed to work. FYI, my levels are usually at about -17 IIRC.

I take it your looking at the subs response dropping off though, it could well be that the new drivers need to loosen up quite a bit before you will see good levels quite low down.

BTW, did you apply 1/3 octave smoothing to your graph, it looks to me like you didnt.
 

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The measurement looks OK - though there may be some mains hum breaking through at 50 and 150Hz (I guess you are in the UK). What input level do you see when you make a measurement?
 

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Elite Shackster
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BTW Graham, did you ever measure the response of any of your previous subs, you might find the generally character of the curve is pretty much the same as your previous subs, like the slight dip for instance.

BTW John, we are based in the UK :T

EDIT: it seems the dip is the result of filters cutting the low frequencies on the Behringer amp.
 

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Discussion Starter · #5 ·
Heres a couple more graphs. There is a mode switch on the behringer 4000 amp to cut frequencies for 30 and 50hz. Or you can switch it off. Made a huge difference. I have a graph to show off and one to show 30hz. Is it ok to turn it off completely as I don't want to loose tones below 30hz. The off graph looks much better. There is a massive peak at 40 hz which I presume the BFD will sort out. **** does it scare me when it does its measuring.

cheers

Graham
 

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Elite Shackster
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Thats a fairly ideal response, with most of it being above the reference line. Applying cuts with the BFD is going to get that looking sweet. Its interesting to note the bottom end is inferior to the PB13U you have replaced, at least for the minute.
 

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Discussion Starter · #7 ·
John,

I still new to REW. I did get low levels when you check levels before you do the measuring. Can you tell me what you mean and how I check it.

Dan,

Yes 10 and 20hz test tones you don't hear or feel. Not sure I will sort that out. Will the fiberfill help?

If not how would I get the low frequencies up.

cheers
Graham
 

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Elite Shackster
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The fibre fill will almost certainly help bring up the bottom end a little, but how much only trying it out will tell you.

With the levels check, what level does it give. Is it saying levels is low in red, or does it say levels ok in green. Again, a minus figure is fine as long at the level check passes. Your graphs look to show speakers and sub separately. Apply the proper graph limits, run a sub only sweep, then a speakers only sweep, then a combined sweep. Apply the smoothing to your graphs then post up a graph showing all three response. This way we can see what your sub is doing, what your speakers are doing, and how the final response is with the effects the sub and speakers have on each other.
 

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Once the drivers are run in then you will see a lot more output low down, just keep the sub running for long periods to get them moving...and then you will start to see better measurements.
 

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Discussion Starter · #12 ·
Recruit,

Cheers for that. I played the Bassotronics album yesterday and boy does it rock. So much more clean and deep bass than I ever got with the PB13. It breezed through track 6. Apart from the low end where I am hearing nothing for 10 and only just hearing 20hz it is amazing. No rattles at all.

I am going to run them in for a couple of weeks and then add the fiber fill to see if it makes a difference. With the fiberfill I take it I just loosely put it in. With the amount of air inside will the subs blow it around and if so will it get near the drivers.

cheers

Graham
 

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Elite Shackster
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The fibre fill needs to go in and rest in place under its own weight, but it needs to take up all the space in the box so you need enough to fill that requirement as minimum. You can add more to build its density and thats what the experimentation is about.

Once the box is sealed, there wont be any movement inside the box, not even the air will move. There will only be and increase and decrease of pressure as the driver move in and out, and the movement will cause the fibres to resonate. That amount of movement wont be visible to the eye though.

My company install ventilation systems, and back when I used to fit them I once did a job in a Nuclear power plant. They had a vent system that used a 6meter x 6 meter ish corridor to vent air. When you were in the room you didnt know anything was happening really apart from a slight breeze, but when the access doors where opened the pressure change popped your ears. Its a strange feeling, but inside the sealed enclosure, nothing much happens at all really.
 

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Discussion Starter · #14 ·
Dan,

Your a star, thanks mate. So I can fill all around the drivers or should I leave that bit clear. I was going to put the fiberfill in the two middle compartments and the bottom parts of the outer compartments below the drivers and leave the bit where the drivers alone. Do you think that will be ok.

cheers
Graham
 

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Elite Shackster
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Leaving a little space around the drivers will be fine. What ever you use, the chances of it getting inside the basket are slim at best, especially if your using the sheet/roll style fibre. Once you finish with experimenting and know how much you are going to use. You can borrow the idea from some manufacturers if you wish, and squirt a little glue on the mdf inside, then use this to hold the fibre fill in place and out of danger so to speak.
 
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