Will the Dayton Audio UM15-22 15" Ultimax work well in an OB? - diyAudio
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Old 25th December 2013, 05:45 AM   #1
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Default Will the Dayton Audio UM15-22 15" Ultimax work well in an OB?

These are the specs:

http://www.parts-express.com/pedocs/...ifications.pdf

Im interested in building something like this type of baffle:

Theatre woofer

Just using 2 of them per side. (2 subs, 2 drivers each). Any idea what 4 of these will be able to do SPL wise Eq'ed flat to 20hz.

FS: 19.5
Qtc: .47
Xmax 19mm
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Old 26th December 2013, 10:56 AM   #2
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Not interesting enough?
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Old 26th December 2013, 04:57 PM   #3
DUG is offline DUG  Canada
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What I found interesting was the inclusion of the ears' response curve in the low frequency distortion results and how it will SEEM greater because of the roll-off of the ears' response curve.

I never thought about it before.

Learn something every day.

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Old 26th December 2013, 05:47 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

SPL depends on volume displacement and OB roll-off.

EQ'd to flat is very different to say EQ'd with a 10dB
dip at the rooms major mode frequency, it will go
relatively very loud at that frequency.

20Hz though your looking at just VD and baffle loss.

OB's can do low bass. but just not very loud, relatively.

http://www.quarter-wave.com/OBs/OB_Design.pdf

Even though its a 15" driver bass capability is near
equivalent to a good 6.5" or mundane 8", and they
don't do 35 Hz usually, which it does, but not loud.

rgds, sreten.

Last edited by sreten; 26th December 2013 at 05:58 PM.
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Old 26th December 2013, 05:54 PM   #5
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What benefit is there with a dipole at 20 Hz?
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Old 26th December 2013, 06:55 PM   #6
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Quote:
Originally Posted by SpinMonster View Post
These are the specs:

http://www.parts-express.com/pedocs/...ifications.pdf

Im interested in building something like this type of baffle:

Theatre woofer

Just using 2 of them per side. (2 subs, 2 drivers each). Any idea what 4 of these will be able to do SPL wise Eq'ed flat to 20hz.

FS: 19.5
Qtc: .47
Xmax 19mm
I am in the process of building some U-frame type subs using four of the 12" version of that driver. Compared to a true open baffle (mounted to a flat board) the U-frame does have a resonance that will impose a maximum on the operating frequency, however, stuffing the back line can help to eliminate this.

The size of the baffle or length of the U-frame is just as important in determining just how much SPL can be generated at a given frequency, as is driver volume displacement. That link you provided to the "theater sub" got around this by using a large number of drivers and a short U-frame type loading. You would be surprised just how inefficient that setup can be at low frequencies, but the bass can be stunning in terms of its naturalness if not its raw SPL. If you are looking for loud SPL at 20Hz, a dipole is not the answer.
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Old 26th December 2013, 11:09 PM   #7
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Quote:
Originally Posted by CharlieLaub View Post
You would be surprised just how inefficient that setup can be at low frequencies, but the bass can be stunning in terms of its naturalness if not its raw SPL. If you are looking for loud SPL at 20Hz, a dipole is not the answer.
I built dipole mains and I'm stunned. I wanted to experience the naturalness of OB bass as described by so many. SPL wasnt a concern for concert levels. I just didnt want to be limited to 84db because a 15 is bottoming out. Hence I asked if it was a good candidate for OB use. I never quoted a required SPL. I asked for a guesstimation of what SPL it would hit.

Your project sounds interesting.

Last edited by SpinMonster; 26th December 2013 at 11:11 PM.
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Old 27th December 2013, 01:35 AM   #8
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Quote:
Originally Posted by SpinMonster View Post
I built dipole mains and I'm stunned. I wanted to experience the naturalness of OB bass as described by so many. SPL wasnt a concern for concert levels. I just didnt want to be limited to 84db because a 15 is bottoming out. Hence I asked if it was a good candidate for OB use. I never quoted a required SPL. I asked for a guesstimation of what SPL it would hit.

Your project sounds interesting.
Unless you give the "width" (For a baffle) or "length" (for a U-frame) you can't answer the question about SPL because these determine the level of cancellation between the front and rear waves at any given frequency and thus the SPL at Xmax.

Since you didn't mention the size of the baffle you had in mind I will just pick a few:
FRONT TO REAR PATHLENGTH OR BAFFLE WIDTH --> MAX SPL @ Xmax @ 20Hz FOR ONE DRIVER:
40cm / 16 inches --> 87dB
80cm / 32 inches --> 93.7dB
120cm / 48 inches --> 97dB
160cm / 60 inches --> 99.7dB

These distances are from the center of the cone on one side to the center of the cone on the other, so the 16in value is for the driver used nude. For each additional driver an identical open baffle (including both in the same baffle), add 3dB to the total SPL. The frequency response will have a shape something like the blue line in the attached plot (of the 60in wide baffle). Note that for some frequencies the SPL of the dipole is as much as 6dB higher than for an infinitely large sealed box. This happens between 37Hz and 180Hz in the plot.

Here is how I modeled the OB response:
I used a Thiele Small box model of the driver in a closed box of infinite volume. I then adjusted the input power until Xmax was reached at the frequency of interest, which you mentioned was 20Hz, giving 104dB. This calculates the SPL from one side of the driver cone in free air. I will assume that the front and rear output is the same (a good approximation at low frequencies). Then I generated an FRD file of this response. I created two "drivers" in the Active Crossover Designer, one to represent the front of the cone and the other two represent the rear of the cone. The phase of the rear cone is inverted and the "acoustic delay" of the "rear cone" is set to a delay that correspond to one of the lengths listed above. The "System Sum" is the sum of the SPL generated by the two sides of the cone and represents the response of a open baffle when positioned in front of the baffle.
Attached Images
File Type: jpg OB response shape.JPG (72.9 KB, 236 views)
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Old 27th December 2013, 03:40 AM   #9
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Quote:
Originally Posted by CharlieLaub View Post
Since you didn't mention the size of the baffle you had in mind I will just pick a few.
In my first post, I posted a link to a build specifying the U frame application I was trying to emulate using this driver.

Thanks for the detailed response. It was excellent and answers all my questions. The 15 in question appears to be more than I was expecting performance wise.
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