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Imperial SO has problems, need help (Read 35269 times)
J_Rock
Ex Member



Re: Imperial SO has problems, need help
Reply #30 - 01/31/06 at 23:38:50
 
Cancel that above. foudn the graphs

Looking at the graphs in pairs, i.e. 3 and 4 or 6 and 7.  The response in the bass region is practically the same with or without the front baffle on.  This would lead me to assume the k slot isn't loading the speaker's front wave into the horn portion at all.

so your K_slot is either, a) not working properly or b) the sealed portion of the box is what is causing the reduced lower output.  


Okay, i actually figured out what the problem is.

Spec wise, the JBL and the Cerwin Vega are vented box only subs, the barely reach into the 80 hz range when sealed.  I assume the madison one is also since I couldn't model it.

The reason the subs work fine in a normal imperial is the fact that there is no sealed chamber.
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DirtDawg
Ex Member



Re: Imperial SO has problems, need help
Reply #31 - 02/01/06 at 01:52:44
 
[quote author=J_Rock  link=1129662594/30#30 date=1138750730]Spec wise, the JBL and the Cerwin Vega are vented box only subs, the barely reach into the 80 hz range when sealed.  I assume the madison one is also since I couldn't model it.

The reason the subs work fine in a normal imperial is the fact that there is no sealed chamber. [/quote]

I can remember Steve saying you need a driver that can get into the 20's in a sealed cabinet. I know the JBL won't do that without copious amounts of EQ'ing. You mat be onto something J_ROCK.
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gexter
Ex Member



Re: Imperial SO has problems, need help
Reply #32 - 02/01/06 at 04:52:32
 
I don't think that the sealed area is the problem.
I think J rock may have it.
As far as we know Dank has built it correctly and is an experianced builder. So the K slot is out as well as the sealed area.

That would leave the type of driver suspect.
In my hack I built the sealed area around the driver specs and the driver specs were 25Hz in a sealed enclosure.

When I converted my So into standard Imp configuration the output was greater in volume.

I have a pair of 12"s that will do 20Hz in a sealed enclosure but I can no longer test that theory because my last mod is not reversable.
I have no idea if that is of any help but I thought it was worth mentioning.


At the present I am using the IMP hack on its side as a sturdy table for some other projects. as some may remember it is reinforced carboard and the sealed chamber was wood ( now the Compression chamber).

It may sound strange but for me it has much more output than usable and it's too big.

I don't think I need an Imperial even if I did have the room. if my hack works that well, I have no need for a real  Imp sub that will most likely blow mine away.

Well okay!!!  if I did have the room maybe I would just to say I did.



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dank
Ex Member



Re: Imperial SO has problems, need help
Reply #33 - 02/01/06 at 16:08:45
 
Here is a new graph of the slp vs frequency:

http://www.mninter.net/~kuechle/graph1.jpg

The Imperial SO is being driven with a signal generator through an amp.  The slp meter is a Radio Shack unit about a meter in front of the Imperial SO.  I had a volt meter and current meter hooked up and calculated the power going to the speaker at each frequency, as well as recording the slp.  Since the power was all over the map, I took (10 log power) and used that to normalize the slp meter reading.  That is what the graph uses:  the normalized slp vs frequency from 20 hz to 250 hz.  

I find it VERY hard to believe that a JBL E-140 would preform so poorly in a 5 cubic foot sealed cabinet.  This speaker produces close to 100 db (1w/1m) when sitting on a sealed standard volume box (3 cubic feet) that I use for measuring speaker parameters.  Now its producing 65 db (1w/1m) at 60 hz??  Thats barely above room ambient!!! I just can't believe that every speaker I've tried (there have been at least 4 different ones) is that much of a mis-match.

Dank

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DirtDawg
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Re: Imperial SO has problems, need help
Reply #34 - 02/01/06 at 17:36:27
 
I agree Dan,

I've used them in 4 cuft boxes sealed in a system before and they get into the 50's flat. There has got to be some mysterious cancellation gremlin at work here.

I sure hope you figure this out!
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J_Rock
Ex Member



Re: Imperial SO has problems, need help
Reply #35 - 02/01/06 at 18:57:12
 
modeling in winISD Pro and Beta show a very steep rolloff at 90 hz for both drivers, pics in an hour or so.
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Brian
Ex Member



Re: Imperial SO has problems, need help
Reply #36 - 02/01/06 at 19:35:05
 
Is it possible one of the panels is unbraced?  Would this vibrating panel cause the cancellation?
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J_Rock
Ex Member



Re: Imperial SO has problems, need help
Reply #37 - 02/01/06 at 22:50:59
 
heres a JBL E140 in 5 cubic foot sealed enclosure.  Response drops off before 100hz and is down almost 6 db at 100hz.



If you got a different JBL E140, perhaps....

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« Last Edit: 02/01/06 at 22:51:16 by j_rock777 »  
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gexter
Ex Member



Re: Imperial SO has problems, need help
Reply #38 - 02/02/06 at 04:40:56
 
You guys are going places I don't bother going with this.

Or at least until I get a spare PC set up in my garage.
I have a bunch of old 68Kmacs stiing around but no audio software that old.( So on a side note if anyone knows of any old Macintosh 68K pre PowerPC audio software out there let me know)

Anyway this is my wierd side speaking:
what would happen if you shimmed up the horn without taking the whole thing apart.
sliding a sheet of 1/4 ply up the back of the inside and making the whole horn shallower in a way. as a temp way to change the horns tuning.
so just changeing the horn tuning without taking the whole thing apart.
Would that accomplish anything?
Or would it because you had sealed off the front and the diff was marginal.

and a stupid question, the chamber behind the driver is completely sealed right?


When you get this figured you are going to start a new thread (Imperial SO problems solved) and detail the problem or at least let us poor saps that are trying to help know what is going on.

I am still waiting for the plans to show up on line just to have them.

and waiting

and waiting

and waiting
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J_Rock
Ex Member



Re: Imperial SO has problems, need help
Reply #39 - 02/02/06 at 16:15:31
 
I don't know that the sealed chamber is the problem, But I do see it being one of few possibilitys.  The original imperials were ported versions, and a driver like the jbl e 140 would do well, considering theres a single larger port firing into the horn.

I could only recommend trying a driver that excels in a sealed enclosure/  Perhaps you could give us a list of anyt drivers you would be willing to throw into the SO and we could suggest the best one.  If you had specs on them too would be nice, since a few subs aren't in winISD and I would need to program them inorder to model them.
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J_Rock
Ex Member



Re: Imperial SO has problems, need help
Reply #40 - 02/02/06 at 16:25:40
 
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dank
Ex Member



Re: Imperial SO has problems, need help
Reply #41 - 02/02/06 at 17:39:30
 
To J_rock
You might have something there.  I did not see your yellow line in my graph, but it fits pretty well.  I questioned the drop off rate though, until I saw it was 6 db/octave, its just that it goes on (and on and on) for about 4 octaves and 24 db.

Heres some more info...I boarded up the Imperial SO and re-did the frequency response the same way.  Heres the graph:

http://www.mninter.net/~kuechle/graph2.jpg

Now this is the same speaker, in the same 5 cubic foot sealed enclosure, its just that now its only firing into the horn.  These slp numbers are more like what I'd expect.  

One last thing I noticed is that since I had the V and I figures for the different frequencies, I also had the speaker impeadance.  When I graphed this it came as a surprise to me.  Maybe it will give someone out there another clue as to whats going on.  Here are the 2 graphs:

http://www.mninter.net/~kuechle/graph3.jpg

http://www.mninter.net/~kuechle/graph4.jpg

Dank
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Zygi
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Re: Imperial SO has problems, need help
Reply #42 - 02/02/06 at 23:40:43
 
Dan,

  I keep looking at your IMP's and I see something that just doesn't look right, I just can't place my finger on what it is.

 I just built a pair for Changeout, I took a lot of pictures as I built them, I keep going back and forth between your pictures and mine, it puzzleing me.

 What changes did you make to the originial (Steves) drawing?

            BobZ
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dank
Ex Member



Re: Imperial SO has problems, need help
Reply #43 - 02/03/06 at 14:19:28
 
Hi Zygi, remember me from Decfest 2005?

I have a couple dozen build pics that I will move up to the web tonight and post links to.  Lets see if you can spot anything.

As far as mods go, its for an 18" instead of a 15" and I didnt have the ImperialSO.gif drawing when I built it so none of the brace B's, brace D's, or brace E's are in it.  Also the origional front panel cutout was cut too big, so I made a new front panel just recently...so a couple of the build pics will have the old front panel.


Dank
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Jet-Lee
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Re: Imperial SO has problems, need help
Reply #44 - 02/03/06 at 16:19:30
 
[quote author=dank  link=1129662594/30#44 date=1138976368]...I didnt have the ImperialSO.gif drawing when I built it so none of the brace B's, brace D's, or brace E's are in it... [/quote]

That has my vote for the reason!
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