Driver choice for a shallow subwoofer

[xarkkon]

There is much discussion about the minimal space behind the driver magnet and the rear wall of the box. Opinions vary from 1,25-1,5cm to twice the diameter of the vent. From images of UM10-22 I have found, the latter would imply 6-7cm behind the magnet, with the box at least 22-23cm deep. This is clearly well beyond my geometry constraint. Life is not easy...

That being said, I wonder if such ventilation is needed for the driver which will hardly ever receive more than 10W of RMS...

my current plan for the UM10-22 is to have 1.5 inches between the rear wall and the driver, and to have the front baffle 2 inches off the ground. mind you, i don't really know the right answer to this and only selected those numbers because (1) front of the driver + xmax is around 1.6 inches so i added a bit of clearance off the ground on top of that at 2 inches, and (2) i needed to fit the downward firing sub within 10 inches for my space constraints (2 inches off ground, c. 5.75 inches for depth of woofer incl. front baffle, 1.5 inches of space, and 0.75 inches rear wall). hopefully someone more knowledgeable here would be able to comment if this even works to begin with

i do realise 10 inches is beyond your geometry constraint. what sort of height are you limited by?

 

[ai1]

Sounds reasonable. That being said, we are not sending a probe to Jupiter, but sticking to the same units may still help;-)

I see that um10-22's total height is 178mm. When adding 4cm below (I do not know how far it may reach--its Xmax is 19mm, but the maximal excursion may quite a bit more) and 5cm above (30mm from the rear wall plus 21mm of the wall itself) we arrive at 27cm. Certainly quite a bit too much, indeed, 25cm being the absolute maximum I can stand.

 

[Chrise36]

https://www.soundimports.eu/en/dayton-audio-ls10-44.html

Sounds reasonable. That being said, we are not sending a probe to Jupiter, but sticking to the same units may still help;-)

I see that um10-22's total height is 178mm. When adding 4cm below (I do not know how far it may reach--its Xmax is 19mm, but the maximal excursion may quite a bit more) and 5cm above (30mm from the rear wall plus 21mm of the wall itself) we arrive at 27cm. Certainly quite a bit too much, indeed, 25cm being the absolute maximum I can stand.

Look at the shallow subs:
https://www.soundimports.eu/en/dayton-audio-ls10-44.html
https://audioxpress.com/article/Test-Bench-Dayton-Audio-LS10-44-and-LS12-44-Shallow-Mount-Subwoofers

 

[Chrise36]

This one is 159mm deep high quality driver and simulates well in 38 ltr vented https://www.thomann.de/gb/bms_12n630_8_ohms.htm

 

[Wolf]

I would think a half inch would be enough pole-vent breathing room.

I can also tell you this- in 18ltrs sealed, yields an F3 of about 42Hz, and +6dB of boost at 25Hz is about right there.

 

[ai1]

https://www.soundimports.eu/en/dayton-audio-ls10-44.html

Look at the shallow subs:
...

Thanks! Ls10-44 does not seem to be a great performer. I believe that SB Acoustics SW26DAC76-4 of similar dimensions looks better.

This one is 159mm deep high quality driver and simulates well in 38 ltr vented https://www.thomann.de/gb/bms_12n630_8_ohms.htm

Very interesting driver. Yet, I am probably doing something wrong when simulating--I typically get rather high excursion at 20-30Hz, more than 8mm Xmas for this driver. Maybe not a problem due to its >100db of max SPL at 25Hz. In any case, could you share the parameters of your vented simulation?

 

[Chrise36]

Thanks! Ls10-44 does not seem to be a great performer. I believe that SB Acoustics SW26DAC76-4 of similar dimensions looks better.



Very interesting driver. Yet, I am probably doing something wrong when simulating--I typically get rather high excursion at 20-30Hz, more than 8mm Xmas for this driver. Maybe not a problem due to its >100db of max SPL at 25Hz. In any case, could you share the parameters of your vented simulation?

Vb 39ltr fb 31.6 under 20 hz use filter to keep driver displacement in control group delay is good in this configuratiom

 

[ai1]

I would think a half inch would be enough pole-vent breathing room.

I can also tell you this- in 18ltrs sealed, yields an F3 of about 42Hz, and +6dB of boost at 25Hz is about right there.

Good news! Ok, with +6dB boost it will be at -3dB at 25Hz, right?
Because you know well this driver, do you think that 3cm of below space (below the rubber surrounds, 55-58mm below the front baffle) will be enough in the down firing position? If this is the case, when doing my maths, 30+178+12,5+22=242,5mm. Indeed, this is about right there...

 

[Wolf]

I have not done the measurement to yield the actual F3 with this boost, but chicken scratching with an added +6dB at 25 Hz yields about an F3 of 22Hz. BTW- I'm using the boosted curve of the Yung SD500-6 as my benchmark against the driver. I use that amp with the UM10 and the RSS315PR in my Overdrive10 bandpass design. Of course- this theoretical 22Hz F3 is considered anechoic, and you actually yield a lower F3 when placed in room.

I think 2.3" (equivalent) should be plenty fine.

One more word of caution- These are high-mass drivers. They can shake a LOT on their own. I would make sure the box/enclosure is heavy enough that the driver doesn't 'throw its weight around', if you catch my drift. I need spikes on my O10 so it doesn't move too much. Someone else built the O10, and made it upfiring. It shook violently and rattled against his floor. Anchoring the sub to its location could also be a good option.

 

[ai1]

Vb 39ltr fb 31.6 under 20 hz use filter to keep driver displacement in control group delay is good in this configuratiom

What is this? I tried 50,4L vented box with Fb=26.6Hz and obtained the results below. It would not go below 22-25Hz, but -6dB at 25Hz with 105dB of max SPL looks interesting. And it weights just 4,5kg and sells at every corner...

 

[ai1]

One more word of caution- These are high-mass drivers. They can shake a LOT on their own. I would make sure the box/enclosure is heavy enough that the driver doesn't 'throw its weight around', if you catch my drift. I need spikes on my O10 so it doesn't move too much. Someone else built the O10, and made it upfiring. It shook violently and rattled against his floor. Anchoring the sub to its location could also be a good option.

Using the suction cups? 10mm excursion at 25Hz with 0,230kg moving mass would give ~36N (3,7kgf) and 163N(16,7kgf) at 5mm/100Hz.
But this is at 500w. I really doubt I will ever try that. I mean, will the beast jump even when fed with <10w RMS?

 

[xarkkon]

Sounds reasonable. That being said, we are not sending a probe to Jupiter, but sticking to the same units may still help;-)

I see that um10-22's total height is 178mm. When adding 4cm below (I do not know how far it may reach--its Xmax is 19mm, but the maximal excursion may quite a bit more) and 5cm above (30mm from the rear wall plus 21mm of the wall itself) we arrive at 27cm. Certainly quite a bit too much, indeed, 25cm being the absolute maximum I can stand.

ha! I'm from a country that uses cm as well and typically hate inches. Unfortunately, everything that I've purchased, from tools to drivers to my MDF boards, all come in inches. I've given up and fallen to the dark side.

I have not done the measurement to yield the actual F3 with this boost, but chicken scratching with an added +6dB at 25 Hz yields about an F3 of 22Hz. BTW- I'm using the boosted curve of the Yung SD500-6 as my benchmark against the driver. I use that amp with the UM10 and the RSS315PR in my Overdrive10 bandpass design. Of course- this theoretical 22Hz F3 is considered anechoic, and you actually yield a lower F3 when placed in room.

I think 2.3" (equivalent) should be plenty fine.

One more word of caution- These are high-mass drivers. They can shake a LOT on their own. I would make sure the box/enclosure is heavy enough that the driver doesn't 'throw its weight around', if you catch my drift. I need spikes on my O10 so it doesn't move too much. Someone else built the O10, and made it upfiring. It shook violently and rattled against his floor. Anchoring the sub to its location could also be a good option.

To clarify, by 2.3", are you referring to the empty space from the front baffle to the floor? Thanks!

 

[Wolf]

Yes, his stated gap = 2.3".

 

[Chrise36]

The results vary with the port configuration i get 37 to 39 ltr with vented at 25 hz -9db f3. You can try another program to calculate this just to be sure.

 

[xarkkon]

btw, have you thought about what plate amp you're going to use and how you'll mount it? Looking at the available 500w options, they all look a little too tall. I'm thinking of mounting the amp on the front baffle to maintain the low height requirement.

 

[ai1]

I am using minidsp-pwr125 modules, the size--153x216mm (fits 135x200 slot)--is just fine. I particularly appreciate AES-EBU input. Otherwise, Fusion FA251 which is 135x360mm or FA501 which is 135x280 should also work.

 

[ai1]

The results vary with the port configuration i get 37 to 39 ltr with vented at 25 hz -9db f3. You can try another program to calculate this just to be sure.

I get similar results with VituixCAD enclosure tool: (I measure w.r.t. SPL at 60Hz, +1dB at 100Hz)
60L fb=26Hz: -5dB at 25Hz
50L, fb=27Hz: -6.3dB at 25Hz
39L, fb=26Hz: -8dB at 25Hz
However, people observe large variations of real driver parameters, cf. http://www.cinetson.org/phpBB3/viewtopic.php?f=16&t=34761

 

[Chrise36]

That is why i have my drivers measured before i build the subwoofers.If you dont you have to build a test box and play with tuning it. Or build a closed box and let the room do the rest. Anyway the nulls wil still be the problem. No matter how much you spent or what driver you choose.

 

[ai1]

You cannot count on German rigor anymore I will try to rely upon EQ then.
Small size will be an advantage if I need to move the boxes around the place.

 

[xarkkon]

I am using minidsp-pwr125 modules, the size--153x216mm (fits 135x200 slot)--is just fine. I particularly appreciate AES-EBU input. Otherwise, Fusion FA251 which is 135x360mm or FA501 which is 135x280 should also work.

ah yes, those look like good options! i was only looking at the dayton / yung options before off the parts-express website.

let us know when you have a finalised box design, i'm very interested in following your build!