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I built a sub - the Overdrive10

MrPotatoHead

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Over a year ago I posted here that was searching for a design for a DIY sub. There were several great suggestions, but I ended up going with the Overdrive10 designed by @Wolf. It's a bandpass design with a 10-inch Dayton driver and a passive radiator. I bought the hardware a year ago and finally got around to putting it together.

I already have a Hsu black cube so I decided to mix it up a little. Rather than making a black body with a speaker grille, I went with a plywood top and bottom with 1/4-inch aluminum rods that cage in the PR. I don't like designing things that people have seen before so this is where my brain went. My friends just say, "Huh. Okay..." so I know it's not for everyone.

I think it sounds great but, honestly, I don't really know how to evaluate a sub. It seems to do what it's supposed to do. With two subs, the presentation is just so much bigger and for HT the change is impressive. The first film I watched was Dune and I was blown away in the first ten seconds.

I'm hoping @Wolf will hop on to answer any technical questions.

Brett

PS Here's a photo of the stereo rack I built last year.

Overdrive-10-sm-1.JPG
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Overdrive-10-sm-19.JPG
stereo-rack-1-sm.JPG
 

Slayer

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Over a year ago I posted here that was searching for a design for a DIY sub. There were several great suggestions, but I ended up going with the Overdrive10 designed by @Wolf. It's a bandpass design with a 10-inch Dayton driver and a passive radiator. I bought the hardware a year ago and finally got around to putting it together.

I already have a Hsu black cube so I decided to mix it up a little. Rather than making a black body with a speaker grille, I went with a plywood top and bottom with 1/4-inch aluminum rods that cage in the PR. I don't like designing things that people have seen before so this is where my brain went. My friends just say, "Huh. Okay..." so I know it's not for everyone.

I think it sounds great but, honestly, I don't really know how to evaluate a sub. It seems to do what it's supposed to do. With two subs, the presentation is just so much bigger and for HT the change is impressive. The first film I watched was Dune and I was blown away in the first ten seconds.

I'm hoping @Wolf will hop on to answer any technical questions.

Brett

PS Here's a photo of the stereo rack I built last year.

View attachment 185064
I think it looks pretty cool if not unique. My only concern (possibly invalid) would be any possible resonance from the aluminum rods.
 
OP
MrPotatoHead

MrPotatoHead

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I think it looks pretty cool if not unique. My only concern (possibly invalid) would be any possible resonance from the aluminum rods.
I had planned to use adhesive if there was any chance of buzzing but they tapped in nice and tight.
 

Blumlein 88

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The rods do look nice. You could have filled them with sand or even foam. Or something like these golf club shaft dampeners.

You've done nice work there. You should be proud. I like your equipment rack too.
 

JayGilb

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Why the 12" passive radiator driven by the 10" sub ?

The design allows for the sub and radiator to be in phase, but why not just a 12" sub ?
 

Angsty

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I think it looks pretty cool if not unique. My only concern (possibly invalid) would be any possible resonance from the aluminum rods.
Easy enough to calculate the resonant frequency of a straight metal rod. Having them better clamped at the ends does not really change the resonant frequency, but may reduce buzz associated with the resonance. Having several of them makes it more likely that resonance would be detectable, but it’s possible the frequency is so low to be irrelevant.
 

Wolf

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Why the 12" passive radiator driven by the 10" sub ?

The design allows for the sub and radiator to be in phase, but why not just a 12" sub ?

If you use a PR in general, it is supposed to be capable to sweep 1.6-2x the volume of air of the active driver. This is so the PR is not taxed, stressed, or over-excursed to damage or failure. This is why you see PR sub/woofer designs with 2x of the same size PR as of the single active driver. Usually, a next-larger size PR vs the active driver does enough in increasing Sd (cone area) to keep the PR and driver happy when using one of each.

In relation to this bandpass design-
You have to be able to mount the active woofer through the 12" PR hole. If you can't do this, then it has to go through the amp-cutout, or you have to have a removable section of box to facilitate the active driver mounting. Well, more reasons herein-
1- The amp hole is not large enough.
2- Rear-mounting it would make the amp hit/collide the magnet when it was mounted due to there only being 0.75" between the magnet and the amp's heatsink internally as it is designed.
3- As stated above you need 1.6-2x more swept volume from the PR vs the active driver, so 2 elements of the same size would require 2x of the Xmax from the PR over that of the active driver, and that is not easy to come by. This is the reason the James Loudspeaker design of this type is not as good performing. Their PR is taxed.

Now- why the bandpass over say a sealed 12" sub with 25Hz boost (Yung inherent boost on 500W model)?
1- Bandpasses are inherently low-HD, as the output from the terminus (or PR in this case) has no motor induced distortion, nor will it have cone breakup. Since I am using a PR, there is also no port turbulence.
2- A bandpass is an extremely efficient system (I don't mean sensitive or higher output over say a conventional sub) and has other benefits.
3- The dual chamber design rolls off the bandwidth of the sub on both ends acoustically, so you can optimize the design from both ends. This means you can tune for one-noted output like in a car at immense sensitivity gain vs tune for broad bandwidth and take a loss in sensitivity. When I design a bandpass, I tend to try and keep sensitivity roughly the same or just higher than that of a sub's spec output with the same driver running conventionally. This yields a 12dB highpass and a 4th order lowpass, both acoustically. Lower the tuning, and the bandwidth shifts lower as a whole. It also has an inherent brace right in the middle of the cab.
4- Then you add in the active lowpass, and the lowpass rolloff can be 8th order to really just get out of the way of the loudspeakers it is adding thump to. This is without requiring DSP.
5- The sealed highpass volume controls the Xmax due to the air-spring, and the tuned PR helps in the same way; both of these limit Xmax usage a bit and the driver operates in an easier alignment than if it were alone. Not that high Xmax is not required, as this is a subwoofer after all.

In a conventional sub, you do not have the front chamber to optimize the upper-end's lowpass, and the motor HD may actually come into play. Say you have this as a PR-vented system, then the driver will unload below tuning, and a lot of mass is required on the PR to do so. If you use it in a bandpass, the tuning gets shifted almost to the upper-corner of the response, and is applied to a really small volume to get it there. This allows for a very tight volume coupling, and minimal mass added to the PR. It takes less pressure/motion to get a lighter PR moving.

These are all advantages, one way or another.

The volume of the Overdrive10 (soon to be rebadged Kilauea in kit form) is only 26 ltrs. 18/8ltrs respectively. The boost yields an F3 close to 22Hz, and the natural bandwidth is 30-65Hz with a 50Hz PR tuning.
 

JayGilb

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If you use a PR in general, it is supposed to be capable to sweep 1.6-2x the volume of air of the active driver. This is so the PR is not taxed, stressed, or over-excursed to damage or failure. This is why you see PR sub/woofer designs with 2x of the same size PR as of the single active driver. Usually, a next-larger size PR vs the active driver does enough in increasing Sd (cone area) to keep the PR and driver happy when using one of each.

In relation to this bandpass design-
You have to be able to mount the active woofer through the 12" PR hole. If you can't do this, then it has to go through the amp-cutout, or you have to have a removable section of box to facilitate the active driver mounting. Well, more reasons herein-
1- The amp hole is not large enough.
2- Rear-mounting it would make the amp hit/collide the magnet when it was mounted due to there only being 0.75" between the magnet and the amp's heatsink internally as it is designed.
3- As stated above you need 1.6-2x more swept volume from the PR vs the active driver, so 2 elements of the same size would require 2x of the Xmax from the PR over that of the active driver, and that is not easy to come by. This is the reason the James Loudspeaker design of this type is not as good performing. Their PR is taxed.

Now- why the bandpass over say a sealed 12" sub with 25Hz boost (Yung inherent boost on 500W model)?
1- Bandpasses are inherently low-HD, as the output from the terminus (or PR in this case) has no motor induced distortion, nor will it have cone breakup. Since I am using a PR, there is also no port turbulence.
2- A bandpass is an extremely efficient system (I don't mean sensitive or higher output over say a conventional sub) and has other benefits.
3- The dual chamber design rolls off the bandwidth of the sub on both ends acoustically, so you can optimize the design from both ends. This means you can tune for one-noted output like in a car at immense sensitivity gain vs tune for broad bandwidth and take a loss in sensitivity. When I design a bandpass, I tend to try and keep sensitivity roughly the same or just higher than that of a sub's spec output with the same driver running conventionally. This yields a 12dB highpass and a 4th order lowpass, both acoustically. Lower the tuning, and the bandwidth shifts lower as a whole. It also has an inherent brace right in the middle of the cab.
4- Then you add in the active lowpass, and the lowpass rolloff can be 8th order to really just get out of the way of the loudspeakers it is adding thump to. This is without requiring DSP.
5- The sealed highpass volume controls the Xmax due to the air-spring, and the tuned PR helps in the same way; both of these limit Xmax usage a bit and the driver operates in an easier alignment than if it were alone. Not that high Xmax is not required, as this is a subwoofer after all.

In a conventional sub, you do not have the front chamber to optimize the upper-end's lowpass, and the motor HD may actually come into play. Say you have this as a PR-vented system, then the driver will unload below tuning, and a lot of mass is required on the PR to do so. If you use it in a bandpass, the tuning gets shifted almost to the upper-corner of the response, and is applied to a really small volume to get it there. This allows for a very tight volume coupling, and minimal mass added to the PR. It takes less pressure/motion to get a lighter PR moving.

These are all advantages, one way or another.

The volume of the Overdrive10 (soon to be rebadged Kilauea in kit form) is only 26 ltrs. 18/8ltrs respectively. The boost yields an F3 close to 22Hz, and the natural bandwidth is 30-65Hz with a 50Hz PR tuning.
Excellent - Thank you for such a detailed response.

Since a majority of subs on the market do not utilize a PR or use a rear/side mounted PR, what are the disadvantages to this design ?
 

Wolf

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The only bad placements for a PR are up or down firing. This is because the mass of the cone causes the suspension to sag and be less efficient at their task. When using them side-firing, this is not of any concern. Even larger active drivers should not be up or down firing as the suspension will sag and hamper the Xmax abilities to a smaller number than previously capable. Anything larger than a 10" is usually better to be side-fired.

As to the PR being a disadvantage? It costs more than a port, and sometimes a LOT more depending on the requirements. PRs allow a lot lower extension in much smaller boxes than ports can be utilized. The ports in the same application would need to be 4-6" in diameter, and longer than the box multiple times over. PRs can really help in a lot of areas vs a vented/ported/bass-reflex box.

Now- the disadvantages of this particular PR-bandpass design? It uses a driver with a very small Vas (compliance) component as well as high Xmax (throw) and power handling (Pe). This generally means a pretty expensive driver, or something that starts in the realm of $150 for the driver alone. It is also a driver better optimized for a sealed box, which is better for the 4th order bandpass type like this is.
Another issue is that the plate amp is really powerful, and could likely destroy the driver with an unfamiliar hand on the knob. The reasons for the 500W plate amp come with; where the boost frequency is centered, how much headroom the amp has to avoid clipping out with power on tap at stated frequency, and the size/form-factor in that it fits the box intended.
Another disadvantage is that the boost is required for the lowest extension for HT or movies, but with music or placed carefully in the room it may not be that large of a requirement. The lesser powered amps have frequencies above 30Hz, which would not help this design in the extension. This is why I chose the SD500-6. Apparently, the Dayton 500DSP could work and use it to boost the 25Hz spot +6dB- with one caveat. The Dayton amp cannot be adjusted to a center frequency low enough without using the PC-interface to get it there. If you use the on-board features, you cannot adjust down to that frequency. It seems that this was not well thought out in that regard, and makes me question the Dayton amp's usefulness.
Sensitivity is kinda low due to the type of driver used, and that the bandpass was not designed for maximum output and narrow bandwidth. Since it was for bandwidth and extension, this is where the 500W amp power also helps to deal with the shortcomings due to Hoffman's Iron Law. Pick 2 of the following, you cannot have the third as physics will not allow it to also occur:
1- lowest frequency extension. (I think 22 Hz is pretty low.)
2- smallest box size. (Yeah- 26 ltrs is pretty small!)
3- highest sensitivity. (Nope- it's a power hungry beast!)
 

ABall

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Over a year ago I posted here that was searching for a design for a DIY sub. There were several great suggestions, but I ended up going with the Overdrive10 designed by @Wolf. It's a bandpass design with a 10-inch Dayton driver and a passive radiator. I bought the hardware a year ago and finally got around to putting it together.

I already have a Hsu black cube so I decided to mix it up a little. Rather than making a black body with a speaker grille, I went with a plywood top and bottom with 1/4-inch aluminum rods that cage in the PR. I don't like designing things that people have seen before so this is where my brain went. My friends just say, "Huh. Okay..." so I know it's not for everyone.

I think it sounds great but, honestly, I don't really know how to evaluate a sub. It seems to do what it's supposed to do. With two subs, the presentation is just so much bigger and for HT the change is impressive. The first film I watched was Dune and I was blown away in the first ten seconds.

I'm hoping @Wolf will hop on to answer any technical questions.

Brett

PS Here's a photo of the stereo rack I built last year.

View attachment 185060View attachment 185061View attachment 185062View attachment 185063View attachment 185064View attachment 185065View attachment 185066View attachment 185067View attachment 185068View attachment 185069View attachment 185070View attachment 185071View attachment 185072View attachment 185073
Hello! many thanks for including the pictures of your build, Ive just received the parts to build this, hell I wish I had your workshop! I was wondering if you changed the box dimensions and re-calculated the internal volume because you appear to have a larger front baffle than in Wolf's design?
 

Wolf

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He built it truthfully, and only lengthened the bottom and top to facilitate a grill.
Looks great, methinks....
 

ABall

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He built it truthfully, and only lengthened the bottom and top to facilitate a grill.
Looks great, methinks....
Thanks Wolf, is your picture of a prototype then, just using the old box from your 8" build because your PR baffle has its edges cut all the way to the sides by the looks and this one has about an inch of timber from what I can see. I'm gathering info before I start measuring and cutting. I am also curious about the rear chamber volume because I want to make the walls 50mm thick, gluing 2x 25mm together, this will put the amp 25mm further away from the main driver and so increase the volume ever so slightly. Alternatively I can drop the amp in 25mm to maintain an exact distance. Mind you I dont even know if you used 25mm mdf.
 

Wolf

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I used 3/4" MDF. My PR is surface mounted, and I have used the same box. I believe he made the front panel thicker to accommodate the flush mounting and retain original spacings.
 

NiagaraPete

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Nicely done. Though you say passive radiator. If its internal is it not Isobaric?
 
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