10 hz horn design phase problems - diyAudio
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Old 18th February 2010, 09:53 AM   #1
oublie is offline oublie  United Kingdom
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Default 10 hz horn design phase problems

Hi folks,

I think i have finally settled on the design for my subwoofer. I've gone through a lot of different designs from close to llt to ib to horn. I have a pair of dayton 15" 385-88 dvc drivers. fs 18.8 hz, pe 350w the rest of the info is in the pictures.

My problem is the phase with my design, you will see what i mean from the pictures. I'd really appreciate it if someone could explain why it is the way it is I'm assuming it would cause major issues when built.

Secondly, do you have to fold such a design? most of the tapped horn or similar designs i've seen all seem to be folded is it necessary?


Phase

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Inputs

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Schematic

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1 pi Response

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0.5 pi response

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Also when you model a horn and then use the wizard to set the max power and xmax of the drivers the results end up nothing like the basic design should i model with the the xmax and max power set to get a flat response so the the results i model take these two things into account?

Max spl 1 pi

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Spl issues with xmax set to 15.1 and p max at 23 (watts or volts?)

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Thanks.
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Old 18th February 2010, 03:50 PM   #2
MaVo is offline MaVo  Germany
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Ignore the phase plots, because...

... they look different in reality (as tom has said several times)
... you wont hear phase problems this low.

About your design... Two drivers with a sd of 850 in a box with a mouth of 260cm, thats just about a factor of 6. I dont have experience with this layout but maybe it could make noise from the air flow around the mouth corners. Another thing to think about is the max spl at the low corner. I think you barely hit the level required to actually hear something this low. Maybe the low extension is wasted, because it doesnt have enough output.

Last edited by MaVo; 18th February 2010 at 03:55 PM.
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Old 18th February 2010, 03:59 PM   #3
bjorno is offline bjorno  Sweden
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[QUOTE=oublie;2089602]...I think i have finally settled on the design for my subwoofer. I've gone through a lot of different designs from close to llt to ib to horn. I have a pair of dayton 15" 385-88 dvc drivers. fs 18.8 hz, pe 350w the rest of the info is in the pictures.

My problem is the phase with my design, you will see what i mean from the pictures. I'd really appreciate it if someone could explain why it is the way it is I'm assuming it would cause major issues when built.

Secondly, do you have to fold such a design? most of the tapped horn or similar designs i've seen all seem to be folded is it necessary?...[QUOTE]

Hi oubile,

Ive checked your simulations and think you are mixing issues/ results that have to be dealt separately.

First your main screen, your picture # 2 is ok.

The main default screen should exactly reflect whatever you have been manipulated in the following posted pictures or in former phase plot if not commented as to be a deviation from default.

This is not the case for the picture prior to the main screen: The main screen suggests a 0.5xPI environment but the phase picture is for a 1xPI space that you assume is not good.

You cannot draw any conclusions from the first presented picture # 1 alone, if not in detail knowing what phase response you really are aiming for.
See the picture.

You have to fold your enclosure at least once.

Rek: Dont use the pmax plot unless you know what it represents.

b
Attached Images
File Type: gif 10Hz_T-TQWT-rev.GIF (170.0 KB, 73 views)

Last edited by bjorno; 18th February 2010 at 04:06 PM. Reason: bad english
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Old 18th February 2010, 04:24 PM   #4
oublie is offline oublie  United Kingdom
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Quote:
Originally Posted by MaVo View Post
Ignore the phase plots, because...

... they look different in reality (as tom has said several times)
... you wont hear phase problems this low.

About your design... Two drivers with a sd of 850 in a box with a mouth of 260cm, thats just about a factor of 6. I dont have experience with this layout but maybe it could make noise from the air flow around the mouth corners. Another thing to think about is the max spl at the low corner. I think you barely hit the level required to actually hear something this low. Maybe the low extension is wasted, because it doesnt have enough output.
thanks MaVo,

I figured out by delaying it slightly it changed the phase completely so good point.

6X may as you say lead to port noise is there any recommended guidelines for noise from this i know its a very important factor with bass reflex boxes.

As for spl, if i high pass at 11 or 12 hz i can go to around 117 db before xmax. Truth be told i'm only expecting to 'feel' the bass at this level rather than hear it but its nice to have it there for movies etc.

looking at what a lot of folks have done i really don't see the need to got beyond about 110db even at this low level particularly if there is a certain amount of the alleged cabin gain when use in room.
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Old 18th February 2010, 04:36 PM   #5
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Phase only becomes a problem when you're trying to integrate drivers. For example, standard 2-way speaker, XO 3kHz. If the phase (after XO) is the same for both in the crossover region (one or two octaves each way), you'll be fine. If one's very choppy, it will cancel at some frequencies, and re-enforce others. At high frequencies, the tweeter's phase can do what it likes - there's nothing it has to match to. The same applies at low frequencies. I assume you'll be crossing over somewhere between 60 and 100Hz. You'll be fine if you are.

Chris
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Old 18th February 2010, 07:18 PM   #6
oublie is offline oublie  United Kingdom
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Yes chris,

X over around 60 to 80 not decided yet still playing with open baffle line arrays or i may just go boxed eventually. btw 20 4 inch drivers per side with 3 X 8 for surround duties.

Tweeter temporarily a 1 inch dome but going to 7' high 1" wide electrostatic.
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Old 18th February 2010, 09:54 PM   #7
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By the time you get down to 10 Hz, your ears' loudness response is more linear than logarithmic. So a 110 to 112 dB level will be just barely audible, whereas a 120 dB level will be quite loud. Also, even at those levels, your ears are more sensitive than your body - you will hear it before you feel it. The net result is, you won't hear or feel much directly. But you will certainly notice the walls creaking, windows rattling, and your chair vibratnig.
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Old 18th February 2010, 10:18 PM   #8
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Quote:
Originally Posted by Don Hills: 2090262
By the time you get down to 10 Hz, your ears' loudness response is more linear than logarithmic. So a 110 to 112 dB level will be just barely audible, whereas a 120 dB level will be quite loud. Also, even at those levels, your ears are more sensitive than your body - you will hear it before you feel it. The net result is, you won't hear or feel much directly. But you will certainly notice the walls creaking, windows rattling, and your chair vibratnig.
HI there Don: At what frequency does "linear loudness" effect become noticable. I'm planning a TH with a low corner of 27.5 hz ( lowest note on piano ). Will I need 120db to hear 27.5 hz?
...regards, Michael
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Old 18th February 2010, 10:52 PM   #9
oublie is offline oublie  United Kingdom
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Don,

I would also be interested, i was alway under the impression according to what i've read the below a certain threshold sound is no longer audible and merely there for effect please bear in mind i don't want or need 130db at 50hz?

Why do so may go for LLT, IB and other designs down to 15hz and below where i'm sure they are not getting 120db (i modeled a few designs but the number of drivers is stupid e.g 8 of the daytons i have in a 650 cubic foot infinite baffle gets 109db at 10hz or 116db at 20hz )
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Old 18th February 2010, 10:55 PM   #10
oublie is offline oublie  United Kingdom
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Quote:

Hi oubile,

Ive checked your simulations and think you are mixing issues/ results that have to be dealt separately.

First your main screen, your picture # 2 is ok.

The main default screen should exactly reflect whatever you have been manipulated in the following posted pictures or in former phase plot if not commented as to be a deviation from default.

This is not the case for the picture prior to the main screen: The main screen suggests a 0.5xPI environment but the phase picture is for a 1xPI space that you assume is not good.

You cannot draw any conclusions from the first presented picture # 1 alone, if not in detail knowing what phase response you really are aiming for.
See the picture.

You have to fold your enclosure at least once.

Rek: Dont use the pmax plot unless you know what it represents.

b
Hi Bjorno,

Thanks for the reply and for an earlier suggestion you gave me for this type of tapped horn

I noticed afterwards that i posted a 0.5 and 1 pi screen but the issue with phase and with pmax xmax is true in both scenarios.
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