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Open Baffle woofer what is important?
Open Baffle woofer what is important?
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Old 12th February 2015, 09:09 PM   #1
Kjeldsen is offline Kjeldsen  Denmark
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Default Open Baffle woofer what is important?

I love my open baffle, but i actually don't know thiele small parameters. Since they now sound really good, I'm planning to begin a new design.

I would like to know more.

I'm thinking of two 15" per speaker. Some eq is ok, but I would like to minimize it in the low end. There is a lot of woofers, some available i EU some are not. Therefore I would like to know if there is something that simply do not work.

Xmax - That is important - I'm thinking at least 10 mm?

Qts: I know what Qts does. I know there are lot of opinions. I would like fairly high Qts around 0,7-0,8. Am I wrong when I assume a low Qts woofer will suffer from distortions because massive eq is needed. And I need more woofers to compensate for that? I have 200 decent watt 8 ohm. I don't want 1000 watt PA amplifiers.

Fs - I guess as low as possible, but is it 30 Hz or 20 Hz. Right now I have nothing usable below 40 Hz

Vas - does it matter? High or low Vas

Qms - ?

Maybe we could take this 15" woofer - Two in series = 8 ohm. Can you identify something that will not work, or is not optimum.

SPL15.1

Revc = 3.6 Ohm
Fo= 30.642hz
Sd= 779.310 CM Sq
BL= 12.970 TM
Qms= 6.151
Qes= 0.748
Qts= 0.667
No= 0.477%
SPL= 88.8db
Vas= 128.173 Ltr
Cms= 148.624 uM/N
Krm= 9.174mOhm
Erm= 0.777
Mms= 181.61g
MMd= 169.006g
Kxm= 47.238mOhm
Exm= 0.657

I have searched for the info, but I can't find much. I allwais end up in IB woofer discussions.
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Old 12th February 2015, 09:16 PM   #2
woody is online now woody
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Have you read this ?


http://www.quarter-wave.com/OBs/OB_Design.pdf
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Old 12th February 2015, 09:18 PM   #3
Kjeldsen is offline Kjeldsen  Denmark
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One more thing

I focus here on low bass. I would be in a 3 way, so The woofer will not go higher than 200 - 300 Hz. So emphasis is on low bass.

This woofer could be some kind of reference

Dipole15 - But what I'm after is why and what is important.

Fs: 21.66Hz
Qms: 15.16
Qes: 1.002
Qts: 0.94
Vas: 623L
Mms: 90g
Xmax: 13mm peak
Voice coil height: 12.4mm
Air gap: 38.4mm
Sd: 855cm2
Re: 12.3 ohms
Le: 0.3mH
Z: 16 ohms
Bl: 12.26Tm
1W SPL: 90dB
Pmax: ~100W
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Old 12th February 2015, 09:27 PM   #4
Kjeldsen is offline Kjeldsen  Denmark
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Quote:
Originally Posted by woody View Post
No I have missed that one. Thanks a lot. Really good info here.

I need to find a +90 dB woofer with fs below 30 Hz high excursion and a Qts around 1. I still need to play with some simulators.

I'm still not sure about the importance of Qms and Vas (what does a very low Vas do compared to high Vas in an open baffle)
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Old 12th February 2015, 10:43 PM   #5
evershumi is offline evershumi  Portugal
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try to find this speakers Speaker Detail | Eminence Speaker
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Old 12th February 2015, 11:53 PM   #6
woody is online now woody
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Again Martin King has written several articles on open baffle systems reading them would be an excellent start. You might start with this one. I built it and am very happy.

http://www.quarter-wave.com/OBs/OB_Design.pdf
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Old 13th February 2015, 04:17 AM   #7
mor2bz is offline mor2bz  United States
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two might color the mids more than one. a low fs is important but it is really hard to
go lower than 40 on open baffle, so I don't know is fs below that is very useful.

lots of people like this one: Goldwood GW-1858 18" Pro Woofer

I am pretty happy with the one beta 15 per channel in large H baffles, but am not a headbanger.
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Old 13th February 2015, 08:01 AM   #8
markbakk is offline markbakk  Netherlands
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Dayton offers a nice open baffle woofer, the IB385-8. Seems to meet most of your requirements, apart from efficiency. But on that aspect one should really consider the real efficiency on low frequencies, not the number on the spec sheet.
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Old 13th February 2015, 08:23 AM   #9
bzfcocon is offline bzfcocon  Romania
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Quote:
Originally Posted by Kjeldsen View Post
I need to find a +90 dB woofer with fs below 30 Hz high excursion and a Qts around 1. I still need to play with some simulators.
That sounds as if you tried to go very low.

IMHO, there is little point in trying to play 30Hz through OB in an acoustically small room. In theory (which typically assumes free space !), you can get it with enough driver area, Xmax and amplifier power. In practice, a normal living room induce very significant additional boundary losses below lowest mode (dipole can't pressurize the room). See: Boundary effects

Later edit: this also happens to be one reason why OB bass is hard to get right. At the end of the day, in-(your)-room equalization is going to be the only accurate way.

40Hz is a more realistic target - and for some people, like me, quite enough for music. If you do movies, multiple subwoofers are your friends.

Quote:
Originally Posted by Kjeldsen View Post
I'm still not sure about the importance of Qms and Vas (what does a very low Vas do compared to high Vas in an open baffle)
I think Vas has in itself less relevance in OB context, because Vas is a measure of equivalent air compliance that determines the a driver + enclosure Fs and Q. For OB, there is no enclosure. See this discussion: Vas Question

Thiele/Small parameters are not independent, but interrelated (Thiele/Small - Wikipedia, the free encyclopedia).. Vas is given by the driver's stiffness and the latter is linked to the driver's Fs via it's mass. In the context of open baffle, it makes more sense to look at things from Fs and Qts perspective.
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Last edited by bzfcocon; 13th February 2015 at 08:33 AM.
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Old 14th February 2015, 01:03 AM   #10
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by Kjeldsen View Post
I love my open baffle, but i actually don't know thiele small parameters. Since they now sound really good, I'm planning to begin a new design.

I would like to know more.

I'm thinking of two 15" per speaker. Some eq is ok, but I would like to minimize it in the low end. There is a lot of woofers, some available i EU some are not. Therefore I would like to know if there is something that simply do not work.
Will you have DSP EQ?

If so then the only really thing that matters is the volume displacement (sd*xmax) and the distortion performance. (Assuming you have enough watts to drive the subs over planned the operating range).

L26RO4Y for example are great subs, used among others by Linkwitz in the LX521.

Best is if you can use two drivers per speaker where you invert one of them. Also keep in mind that two 15" makes for a huge speaker, I thought I did when I got 2x 15" per side but then I realized I didn't

I initially bought 2x AE IB15 but then downsized to 2x L26RO4Y instead. two high excursion 15" subs is just massive overkill unless you really need crazy SPL below 40 hz. There is very little actual musical content below 40 hz unless you listen to electronic music which I don't so I realized I didn't need that SPL capability.
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