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Imperial SO has problems, need help (Read 34212 times)
dank
Ex Member



Imperial SO has problems, need help
10/18/05 at 19:09:54
 
Hi Guys

I know a lot of you are waiting for a report on the Imperial SO I'm building and a comparison to the standard Imperial.  I got the first Imperial SO up and running, but what a disappointment!  Something is wrong!  I'm hoping someone can figure out what it is, because I can't imagine what could cause such a severe problem.  If I had to guess I'd say the speaker back radiations are contained in the sealed compression chamber (like they should be).  And the speaker front radiations are being delayed 180 degrees by the horn so the horn and the speaker are out of phase with each other and canceling big time.  I can pump a lot of watts into this thing and no sound comes out.  Here are 3 pictures that, I hope, show someone what it is that I did wrong (are you out there Steve?)
http://www.mninter.net/~kuechle/impso_1.jpg

This picture shows the front panel before the slot was cut.

http://www.mninter.net/~kuechle/impso_2.jpg

This picture shows the speaker when the front panel is removed.


http://www.mninter.net/~kuechle/impso_3.jpg

Here are some graphs I took:
http://www.mninter.net/~kuechle/1.JPG

http://www.mninter.net/~kuechle/2.JPG

http://www.mninter.net/~kuechle/3.JPG

http://www.mninter.net/~kuechle/4.JPG

http://www.mninter.net/~kuechle/5.JPG

http://www.mninter.net/~kuechle/6.JPG

http://www.mninter.net/~kuechle/7.JPG

Disregard the blue line on the graphs, its the green line that has the information.

Graphs 1 and 2 compare the new Imperial SO to the standard Imperial when driven with a sine sweep.  The peak amplitude is 10 db down for the Imperial SO, which might not be too unexpected as we are comparing 1 speaker to 2 speakers, but at 30 hz the Imperial SO is 24 db down from the standard Imperial.  Whats up with that?

Graphs 3 thru 7 all have the same, lower volume, sine sweep input.  3 is the Imperial SO as it should be.  4 is with the front cover removed.  This is the board with the Karlson shaped slot in it.  According to the graphs, this K-slot makes no difference at all!  5 is a picture of what happened when I covered up the K-slot with a solid board...higher volume by 6-7 db across the frequency range, but that nasty steep slope (looks like almost 30 db/octave to me) is still there from 20 all the way to 50 hz.

Graphs 6 and 7 are with a different speaker...pretty much the same results.

Well, I'm open to suggestions.  Right now I'm thinking how hard is it going to be to turn these guys into a second pair of standard Imperials?

DanK

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JimP
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Re: Imperial SO has problems, need help
Reply #1 - 10/19/05 at 00:22:36
 
DanK,

Are you building from plans?

JIm P
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gexter
Ex Member



Re: Imperial SO has problems, need help
Reply #2 - 10/19/05 at 02:20:04
 
Wow that is not what I expected
my "SO" works pretty good
I will look at the pics and info later and compare it to my Hack version. I will say that mine does not have that boom that everyone associates with "bass". Mine does seem to require more power but not a whole lot more. I attributed it to a cheap car sub.

I will take a look at it later. I am just getting a start bulding a small  light table out of a trashed 17 lcd monitor. thought I would check in. Not so good buddy! got to be something simple.

Gex
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gexter
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Re: Imperial SO has problems, need help
Reply #3 - 10/19/05 at 06:20:42
 
Hey!
Its a little hard to figure things out when I have not built a real ImpSO.
I cannot believe it is performing that bad. Maybe its a lot of little things that all together is causing grief.
But I doubt it by looking at the pics. It looks pretty good to me.
but here I go without a clue.

1.below the bottom of the dirver where it meets the front face that has the Kslot is it tight and no air blowing past.

2. at the top of the driver where the beginning of the mouth. is it big enough ( to steves specs) I think mine is close to 4 inches.

3. the slot is huge compared to my version the points are correct but the curve is pretty big compared to mine.
What I am trying to say is the opening is too big?

4. of course your sealed chamber is not leaking air
5.The driver your using is designed for a sealed enclosure?

the driver is good and wiring etc etc.
Did you try to swap dirvers?

I don,t think your feeding ( loading the horn) enough. and the imbalance is creating the cancellation. Or that is the only thing I can come up with.
I can't imagine that you did anything wrong to be honest. and Steves design is considerably differant than mine.
however I used a 12" driver and changed the dimensions and modified a Imperial corner cab

I don't think I was much help at all, but maybe I can spark a new train of thought at the very least.

Good luck and give Steve a call before you give up. sometimes if you walk away for a day or two it will come to ya.

Gexter

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Circlomanen
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Re: Imperial SO has problems, need help
Reply #4 - 10/19/05 at 07:55:33
 
In my opinion the K-slot seems a bit large. It doesnt give the loading it should. It should direct some pressure into the horn and equalize the pressure seen by the back and front of the driver.
You have probably checked that the sealed chamber is airtight but it never hurts to do that again. Especially for leakes into the horn.

Try cover the k-slot partially so you can tune the response. (?)

Thats my five cents of thought.
Johannes.
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gexter
Ex Member



Re: Imperial SO has problems, need help
Reply #5 - 10/19/05 at 16:01:12
 
I agree with  Johannes
as that is what I was trying to say in point 3.
and about feeding / loading the horn.
gex
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dank
Ex Member



Re: Imperial SO has problems, need help
Reply #6 - 10/19/05 at 16:31:32
 
Just a couple of responces:  1)  I am working from the standard Imperial plans, the first look picture Steve posted a while back, a sketch Steve made for me at Decfest 2005 showing the differences, and a bunch of pictures I took of Steve's Imperial SO's.  2)  Everything is sealed properly and not leaking.  3)  The front board with the K-slot has a gasket under it so it seals correctly with the compression chamber.  4)  I have tried 2 different, working, speakers from 2 different manufactures.  Results were the same.  5)  I agree the K-slot seems big, but covering up parts of it doesn't seem to make much difference...hell removing the slot entirly makes no difference, and covering the slot completly does increase the output but does nothing to reduce the terrible steep rolloff below 50 hz.

Heres a question for you guys:  In the standard Imperial the output of the horn and the output of the front of the speakers MUST be in phase.  The only way to do this is for the horn to add an additional 180 degrees of phase shift to the back rediations of the speaker giving 360 degrees of total phase shift.  In the Imperial SO the horn hasn't changed, so it is still probably adding 180 degrees of shift.  Where are the other 180 degrees of phase shift comming from?  The k-slot? - I don't see how.  Is there a design flaw here?

DanK
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DirtDawg
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Re: Imperial SO has problems, need help
Reply #7 - 10/19/05 at 17:20:06
 
[quote author=dank  link=1129662594/0#6 date=1129735892] .........................  Heres a question for you guys:  In the standard Imperial the output of the horn and the output of the front of the speakers MUST be in phase.  The only way to do this is for the horn to add an additional 180 degrees of phase shift to the back rediations of the speaker giving 360 degrees of total phase shift.  In the Imperial SO the horn hasn't changed, so it is still probably adding 180 degrees of shift.  Where are the other 180 degrees of phase shift comming from?  The k-slot? - I don't see how.  Is there a design flaw here?

DanK
[/quote]

This assumption is flawed because the original Imperial uses a vented chamber AND the horn to increase efficiency. The actual phase of the output of the horn will be different at every frequency. The horn loaded vent is so efficient that the direct driver output is almost insignificant in the bottom octave and so the phase difference between the two is also insignificant.

What happens if you correct the slot dimensions and put 2 watts or so on it and compare it to an efficient full range speaker, instead of another Imperial?
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Circlomanen
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Re: Imperial SO has problems, need help
Reply #8 - 10/19/05 at 20:28:52
 
A wild thought crossed my mind.
What about making the sealed chamber a vented one instead.
Say tuned to 18 - 20 hz with the vents fireing into the very beginning of the horn, but with the open "coupling" of the Imp SO ?    ??? ??? ???
That will say, keep the K-slot and everything like it is now but put 4 tubes/vents from inside the previous sealed box, that fires into the horn. That should still only excite resonanses in the horn in the lowest octave and filter away everything else.
That would probably retain the high efficiency, or at least partly.(?)
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Steve Deckert
Administrator
*****


If the 1st watt
sucks why continue?

Posts: 2425
Re: Imperial SO has problems, need help
Reply #9 - 10/19/05 at 22:55:49
 
I am almost finisihed with the SO plans.  They will also include some pics of the actual speaker with the front panel removed.  I would hang on until I get at least the pdf file done and see what you can do to get yours a bit closer.  At the same time, what size and type box did the computer model for each of the two drivers you selected?  You need to find drivers that will hit 25Hz a sealed box of around 5 cubic feet.

Steve
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gexter
Ex Member



Re: Imperial SO has problems, need help
Reply #10 - 10/20/05 at 00:59:37
 
Mine was 4 cubic feet @ 27 Hz
I used a sealed chamber and no vent. I was going to use a bass relex Square port into the horn, when I started designing it.
I went with a basic karlson with a Imperial horn instead.

I really would like to see a real one, Still like to build one. I am not in a hurry because My hack works well. I would like a driver with a higher sensitivity instead of 86Db for my first change.

I disgarded the port loaded horn because something JohnF said a while ago. wish I could remember where in this forum it was.

So! does it have a port?

Glad Steve stopped by, So don't give up yet.

Gex
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« Last Edit: 10/20/05 at 01:01:15 by gexter »  
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Braggi
Ex Member



Re: Imperial SO has problems, need help
Reply #11 - 10/20/05 at 04:45:30
 
My thought was that you might need a driver with a lower Fs. Then Steve chimed in. Hmmmm. Worth checking out.

Thanks for letting us know how it's working out.

Hope you get it to your satisfaction soon.
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dank
Ex Member



Re: Imperial SO has problems, need help
Reply #12 - 10/20/05 at 23:25:11
 
Well, just when you start to think you know something about this field of science something happens to remind you that you really don't know much of anything at all.  After playing around with the size of the k-slot for a couple hours I decided that there was no tuning involved.  It simple doesn’t matter.  The only thing that made any difference at all was covering up the slot completely.  So, I covered it up.  Now all the energy is going into the horn.  It sounds ok, not as good as the standard Imperial, but ok.  Then as I was moving things around and swapping Imperials in and out I happened to face the boarded up Imperial SO into the corner while it was playing.  Wow.  +10 db instantly.  Clear as a bell.  Effortless bass.  I then tried facing a standard Imperial into the corner, just barley an audible improvement, no where nears as much as with the Imperial SO.  One  boarded up Imperial SO facing into the corner is sounding better than my pair of standard Imperials.  That’s one 18” speaker smoking four 18’s.  I’m rethinking my system now.  Perhaps more is not always better.

The speaker I’m using doesn’t seem to model well in a sealed 5 cubic foot box (if I’m using the s/w correctly).  Perhaps some nice person out there can check my results to see if I’m doing it right.  Fs = 30.5 hz, Qts = .227, Vas = 8.6 cubic feet, 8 ohm, 18” diameter.  I was under the impression that the high Fs / Qts (30 / .227 = 132) makes it a very good horn driver.  When I model it in a sealed box of 5 cubic feet my s/w says Fc = 50, Qtc =  .37 and Cutoff(F3) = 116.  It also gives a pretty sorry looking graph, looks more like a hi pass filter than a speaker.

DanK
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gexter
Ex Member



Re: Imperial SO has problems, need help
Reply #13 - 10/21/05 at 00:02:29
 
Er this sound strange but mine is modeled around a sealed driver not a horn.
and mine is in a corner. laying down on its side.
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stvcmty
Ex Member



Re: Imperial SO has problems, need help
Reply #14 - 10/21/05 at 00:22:46
 
For a sealed box, you want a fairly high QTS driver.  For the SO, you want a low FS.  Moving air is good, so a 18 or 21” driver would be fair game.

If you can find a fast woofer (high QTS), but the FS isn’t low enough add mass to lower the FS.

A lot of the Gold Wood woofers are starting to look good.

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=290-386

The FS might be a bit high, but mass could be added to the cone fairly easily.

Stv
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