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Help choosing Dual Opposing subwoofer driver

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#1
As I mentioned in this thread (https://www.audiosciencereview.com/forum/index.php?threads/dual-opposed-subwoofer-theory.19186/), I'm considering to build Amphion type DOS tower that also could work as speaker stand. I found out there is no complicated theory in DOS so I feel free in choosing driver. But driver needs to fulfills some conditions.

1. Under 400$ per driver - I have to use 4 driver so I have to cut price...
2. Depth under 12cm - my speaker is 7" MTM build, sealed Qtc 0.707 so has 24cm width. Double driver need to be shallower than 24cm.
3. 10" or 12"
4. Purpose well in sealed design. - I want to match to my main speaker Qtc .707
5. My subwoofer poweramp is 4ohm, RMS 300W for each channel. Power output compatible...

Any recommends?
20180204002248_AmphionLowExtensionsFrontWeb.jpg

20180204002248_AmphionLowExtensionsFrontWeb.jpg
 

somebodyelse

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#2
That depth requirement will probably rule out most conventional drivers, and it needs to be even shallower if the magnet has a vent in the middle. I can see why you're asking for suggestions!
 

digitalfrost

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#3

headshake

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sloth_kwj
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Thread Starter #6
Not sure if you can still get it somewhere, but Tang Band WQ-1814S should be suitable. Very flat, and good Qts for closed box.

Another option https://www.parts-express.com/wavec...-foam-sandwich-cone-subwoofer-4-ohm--298-1078 but it's kinda expensive

https://www.parts-express.com/dayton-audio-ls10-44-10-low-profile-subwoofer-dual-4-ohm--295-251

Another option could be to put the drivers on the front and back und use multiple smaller chassis.
Thanks for recommendations. Wavecor and Dayton might be good option.

https://audioxpress.com/article/test-bench-the-l26roy-10-subwoofer-from-seas

it is a bit bigger but can go in a small space. I just got two of these a couple of months ago and am happy with the bass.

Why not rock 8"? sb23cac It will fit.
https://www.madisoundspeakerstore.c...oustics-sb23cacs45-4-8-ceramic-woofer-4-ohms/
I also looked for seas L26roy but it is deeper than my expect. 8” is to small to produce 20hz well in sealed box.

I found that Amphion use SB SW26dac76 and here are measurements by @hardisj . Good priced, nice design, fulfills all of my conditions, but I want to know price/performance of driver is pairly good enough. How about comparing to Wavecor and Dayton?
https://www.diymobileaudio.com/thre...ac76-4-shallow-subwoofer-klippel-test.115336/
 

MrPeabody

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#7
As I mentioned in this thread (https://www.audiosciencereview.com/forum/index.php?threads/dual-opposed-subwoofer-theory.19186/), I'm considering to build Amphion type DOS tower that also could work as speaker stand. I found out there is no complicated theory in DOS so I feel free in choosing driver. But driver needs to fulfills some conditions.

1. Under 400$ per driver - I have to use 4 driver so I have to cut price...
2. Depth under 12cm - my speaker is 7" MTM build, sealed Qtc 0.707 so has 24cm width. Double driver need to be shallower than 24cm.
3. 10" or 12"
4. Purpose well in sealed design. - I want to match to my main speaker Qtc .707
5. My subwoofer poweramp is 4ohm, RMS 300W for each channel. Power output compatible...

Any recommends?
View attachment 105585
View attachment 105585
I'm not clear on whether what you intend to build will have two woofers arranged vertically as shown in the picture, or whether you intend to use two woofers directly opposing each other. Since you emphasized "DOS", my inference is that you intend to build two stands/subwoofers each with two woofers directly opposing each other (such that the reaction forces mutually cancel), which is not like what is shown in the picture. But this isn't consistent with your statement that the depth of driver needs to be less than 24 cm. If they are arranged in a true opposing configuration, the depth of each will need to be no greater than 12 cm. Perhaps what you intend is to offset the woofers slightly as needed, so that each woofer can use the entire 24 cm if need be. But even if you do this, what you are going to find is that any pair of 10" or 12" woofers that are suitable for use as sealed enclosure subwoofers are going to individually need at least 40 liters of enclosure volume. If I am correct in estimating that your enclosure be in the ballpark of 50 liters, there will need to be an adjustment of your design goals.

By the way, a good place to find drivers is by using loudspeakerdatabase.com.

There are lots of subwoofer drivers that are optimized for ported enclosures, which unfortunately makes them less than ideal for sealed subwoofer use. For a subwoofer, I would want the F3 point to be below 40 Hz, ideally down around 35 Hz. Of course it would be better if it were lower still, down around 25 Hz, but this is practically impossible with a sealed subwoofer. Of course it will be helpful if the amplifier you use has built-in equalization, but even if so, it is still desirable for the speaker to require only minimal EQ, and possibly get by without it.

A good formula that I've found for estimating the theoretical F3 point for a sealed subwoofer is .73 * Fs/Qts. The multiplier .73 is good for Qtc values in the customary range, which you indicate will apply. There are drivers with Fs adequately low, down around 20 Hz, and even after multiplying by .73, it is when dividing by Qts that you discover the difficulty. As an easy hypothetical example, if Fs is 20 Hz but Qts is .4, you end up with a theoretical F3 of about 36 Hz. It is easy to see that Qts needs to be no less than .4, but it will most likely need to be bigger than this, because a driver that is suitable in other respects will probably have Fs a good bit higher than 20 Hz.

And with a high Qts value, you run into the problem of the required volume being too great, unless Vas is unusually small.

Following is a list of drivers that I had come up with when doing a paper exercise several months back:

Brand/model Size Fs/Qts F3 Vas SPL Cms Bl Mms
(inch) (Hz) (Hz) (liter) (dB) (mm/N) (T-m) (gm)
Scan-Speak
25W/8565-00 10 20/.41 35 225 88 1.5 8.2 43
Dayton Audio
RSS265HF-8 10.5 25/.49 36 52.5 84 .31 15 131
SB Acoustics
SW26DBAC76-4 11.4 22/.46 34 54 86 .39 10.8 134
Scan-Speak
30W/4558T00 12 17/.32 38 197 89 .65 11 135
Peerless XXLS-
300F50AL01-04 12 22/.41 39 113 85 .37 11 138
Dayton Audio
RSS315HFA-8 12.4 22/.45 35 97.2 86 .26 18 194
Scan-Speak
32W/4878T05 12.6 17/.32 38 180 89 .52 13 165
SB Acoustics
SB34NRX75-6 13.6 19/.40 34 260 90 .71 11 99


If you really want to arrange the two drivers directly opposing each other, the SB SW26DBAC76 would fit. Each of them will need about 40 liters. This is probably the lowest required enclosure volume for any drivers on this list, but when you put two of them together, you'll need about 80 liters. Since I'm more accustomed to thinking in traditional English units, I convert this to a number a little less than 3 cubic feet. If the interior dimensions are 2/3 foot in width and one foot in depth, the enclosure would need to be about 4.5' in height. When you put the small speaker on top, they will be higher than you'll want them to be. If you were willing to make the enclosures wider or deeper front-to-back, you just might be able to pull it off using this driver.

If you use a pair of smaller 8" woofers, this will resolve the problem with enclosure volume, however the smaller woofers are not going to have the same low Fs value, and will not give you the same deep bass extension. The end result would likely be less desirable than going with a single 10" or 12" driver, since F3 will be lower with the single 10" or 12" driver, due to the lower Fs.

If it were me and I was set on this being a sealed enclosure, I would be content with a single woofer in each enclosure. Given that you'd still have a pair of them, it does not seem likely that you'd find the bass lacking. There is possibly another way to solve the conundrum, which is to use EQ to suppress the big peak in the mid-bass that will be associated with the high Q and due to the enclosure being too small for a pair of larger woofers. I suppose you could do this, but I would carefully calculate the theoretical Q and compare it to the EQ capability that will be provided by the amplifier. And even if the amplifier's EQ would be able to flatten the big peak and allow you to use a pair of 10" or 12" woofers, either from this list or something similar you find elsewhere, I'm not sure whether this is what I would do.
 
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sloth_kwj
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Thread Starter #9
I'm not clear on whether what you intend to build will have two woofers arranged vertically as shown in the picture, or whether you intend to use two woofers directly opposing each other.
Picture I attached is exactly DOS. DOS on top and PR are also opposing on bottom. 2 Sub, 2 PR for each channel. I want to use DOS because subwoofer also need to work as speaker stand. IMO stands should not vibrate in anyway to isolate speakers well, so I consider DOS.
Thanks for sharing your list. I also found sw26dbac will works well in good price. Subwoofer outer H*W*D would be at least 100*24*33 so 80L in pair enough I think.
 

MrPeabody

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#10
I like the approach. Very practical. Would ask you to build me a pair while you are at it.

I didn't realize that the lower drivers in the picture were passive. Nor was the other side of the speakers visible.
 
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sloth_kwj
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Thread Starter #12
I didn't see that spec. Don't you need to a 12-15" for that?
12" is also possible. Also I'm having hard time for making 20hz f3 in sealed box.. Room gain must be needed.
Please recommend 12" for me.

Here is my prototype modeling in shapr3D. 4 version of rounding.
KakaoTalk_Photo_2021-01-14-22-55-51.jpeg
 

jhaider

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#13
12" is also possible. Also I'm having hard time for making 20hz f3 in sealed box.. Room gain must be needed.
Please recommend 12" for me.
Are you expecting a small closed box to reach down to 20Hz without EQ? If so that’s a pipe dream and fool’s errand.

Focus on getting enough volume displacement to reach whatever SPL you’re targeting (or simply maximize SPL) and let the EQ handle the shape of the response curve.
 

Zvu

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#16
12" is also possible. Also I'm having hard time for making 20hz f3 in sealed box.. Room gain must be needed.
Please recommend 12" for me.
............
Here is my prototype modeling in shapr3D. 4 version of rounding.
Whatever driver you choose, move the sub drivers lower, close to floor and more to the back of the cabinet to get more boundary reinforcement.

As for looks i wouldn't round top of the sub and bottom of the mtm to get it look more like one cabinet.
 
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sloth_kwj
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Thread Starter #17
Are you expecting a small closed box to reach down to 20Hz without EQ? If so that’s a pipe dream and fool’s errand.

Focus on getting enough volume displacement to reach whatever SPL you’re targeting (or simply maximize SPL) and let the EQ handle the shape of the response curve.
How about JL Audio f110? Small cube box but go very deep. Did they use EQ and DSP? Or just their driver doing great job?
 

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