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Why do my reflexes sound so...honky?

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dmr View Drop Down
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    Posted: 16 June 2016 at 5:16pm
I just freshly built 4 reflex subs and i'm having great trouble in getting it sounding acceptable. I'm not even sure if honky is the right word, but its really boomy/resonate-y and hard to make out anything musical.

I have tried messing around with EQ, xover points and slopes with no avail.

Specs are:
180L MDF cab (that's 180L after subtracting driver/port volumes) tuned to 43Hz
Loaded with some 2nd hand 18pzb46 (one odd thing, when in the cab and I lightly flick the cone it wobbles back and fourth a few times before coming to a rest)
4 corner ports of 200mm length with an area of 9800mm^2 per port
Foam damping on sides & back, not covering the entire panel but placed in the middle of each one with a ~4 inch gap around each foam sheet
Driven by a bridged  crown/amcron MT1201 per pair
Crossed over at 97Hz 
Tested outdoors, elevated off a grassy floor by about a foot
Simulated FR graph, for what its worth:


And a semi-finished picture because who doesn't like pictures eh


Any idea what could be causing it to sound like this?
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Teunos View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Teunos Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2016 at 5:57pm
that cab is never, never 180L.
Looking at it from the front its about 4cm wider than the 18'' woofer, minus side walls it will probably be about 45-47cm internally. Top to bottom about 50cm internally. It looks to be about 60cm deep, but lets just say its 70. Minus a few cm due to the baffle and rear panel that leaves at max +-65cm internally
. Thats only 145 litres and we have not deducted the ports or speaker yet.
Best regards,
Teun.
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dmr View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dmr Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2016 at 6:16pm
I just measured it, inside dimensions -  495mm wide, 570mm tall, 709mm deep
so 495*570*709 / 1000000 = 200L gross

unless i'm making some mistakes somewhere...
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Teunos View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Teunos Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2016 at 6:26pm
internal dimensions?
hmm....
Then i guess it looks bigger than i thought it would be.
However, you say 4 ports of 9800 mm2, thats a triangle with sides of nearly 20*20.


Edited by Teunos - 16 June 2016 at 6:29pm
Best regards,
Teun.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Crashpc Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2016 at 6:33pm
It would be good to measure impedance characteristics in that enclosure to see what's the tuning. 18PZB46 would be little happier in larger enclosure, but I believe it is not the only or even main problem here. Are you sure these speakers are original, and not reconed/recoiled by somebody who didn't know what he's doing?

If I count well, these ports are 14x14, not 20x20cm. That is about okay, on the low side.

Edited by Crashpc - 16 June 2016 at 6:35pm
Nikon and Canon people should not be married to each other. Why did you let this happen?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shortrope Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2016 at 7:10pm
What kind of Foam?....some kind of polyester wadding or Fibre glass would be better.
My Tinnitus is coming along nicely!!
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dmr View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dmr Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2016 at 7:59pm
Originally posted by Crashpc Crashpc wrote:

It would be good to measure impedance characteristics in that enclosure to see what's the tuning.
Ill have a go at this later and post up the results, I don't have any fancy equipment so its going to be pretty rudimentary.
 

Originally posted by Shortrope Shortrope wrote:

What kind of Foam?....some kind of polyester wadding or Fibre glass would be better.
I'm not sure, it was packing foam I chopped up, about an inch thick - to be honest it looks pretty skimpy and I cant tell the 
difference between un-padded and padded cabs so it could do with some more.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2016 at 8:08pm
180L is perfectly fine for the 18PZB46, in fact D&B used it in much smaller cabs in the C4 Sub.  It's a very light cone for an 18".

What cab are you running as the mid-top above it.  Subs running on their own or much louder than the mid-top can sound very odd.

Outdoors, with the cab off the ground you are essentially running in free space which will reduce the bass response somewhat.  Try running it in a different location, on the floor.

Worthwhile checking the tuning experimentally.  If the tuning is based on a simulation, without compensating for the ports being in the corners, it could be a long way out from what you expect.  Been there, got the t-shirt, retuned the cab etc etc...  Also, what is the bracing like in the cab?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote dmr Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2016 at 9:10pm
Originally posted by ceharden ceharden wrote:

Also, what is the bracing like in the cab?
The mid tops are some crazy creation of 6x 6" drivers and a CTS/powerline piezo in a 75L ported cab. No idea on any of the details as they are not my work but they are the next upgrade. The snare from them will rip you in half but they really struggle to go low. 

Maybe I need something that can go lower to meet the subs? And what i'm hearing is a giant gap between sub and top?

Originally posted by ceharden ceharden wrote:

Also, what is the bracing like in the cab?
Pretty minimal - the corners are braced well but the main panels aren't; I didn't get time to add it in before taking them out. How would you suggest bracing without weighting it down? One 18mm wide  by 60mm tall batten down the middle of each side?

Edit:
Crashpc / Teunos: the ports are triangles of 140x140 (not sure of the hypotenuse) so 140*140 / 2 = 9800mm^2 each? (maths is really not my strong point!)


Edited by dmr - 16 June 2016 at 9:15pm
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Teunos View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Teunos Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2016 at 10:03pm
Sorry, i was having a brain fart > Sqrt(9800)*2 = +-200 OuchDead
This is not my day LOL


Edited by Teunos - 16 June 2016 at 10:09pm
Best regards,
Teun.
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Teunos View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Teunos Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2016 at 10:21pm
Okay so please tell me i wont make another mistake here.
But i just quickly plugged your numbers into bassbox pro
Are you sure that graph you posted is tuned for 43Hz?
If i insert 180L, 43Hz, 4 ports of 9800 mm^2 it should be 21.0cm long, but it gives me the yellow graph.
If i insert 180L, 34Hz, 4 ports of 9800 mm^2 it should be 43.0cm long, but it gives me the red graph.
The red graph is very similar to yours.


Best regards,
Teun.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 16 June 2016 at 11:27pm
From experience, whatever the simulation says, it'll come out at least 5Hz lower with corner ports.  You get a massive amount of effective length increase due to the position.

If the mid-tops aren't meeting the subs then that definitely won't help because you'll probably end up turning the subs up more to try and compensate.

Bracing-wise, corner ports do help to brace quite well.  What I've done in similar cabs is a brace against the bottom, maybe 150-200mm high between two of the panels, then another one between the other two further up the cabinet.  If you're intending to put handles in, bear that in mind before you choose where to put the braces.

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