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LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll

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Chris Grimshaw:
Thought I'd make a new thread. There was some interest in developing a compact but loud subwoofer for rock 'n' roll gigs, where low-end extension isn't particularly important.

So far, here are the goals I'd consider sensible. Happy to chop/change them by popular demand, though.

- 4ohm (maximises power with 1 sub per amp channel)
- Flat to 55Hz
- Can be lifted with one hand by Average Joe
- Loud as possible while keeping the above
- Sensible money
- Beat a KW181


In my experience, more expensive drivers are worth the money. They typically allow more output in a smaller box than a cheap driver, meaning output density (which is a priority here) is high.

So, my first simulation was with a https://www.bcspeakers.com/en/products/lf-driver/15-0/4/15sw115-4 - it's about as good as it gets for 15" subwoofers, and is conveniently available in 4ohm impedance. I simulated a simple ported box.

With 90v RMS input (about 2KW input) and a highpass filter to cut out-of-band excursion, we're at 128.5dB at 55Hz, 130dB at 60Hz, dropping slowly to 128dB at 100Hz.
Port velocity is a little high at the bottom end, but that will only be a problem if 55Hz comes along at full power - not likely to come up with the intended program material.

The cabinet volume is 62L net, which is nice and compact. Once built, it'll be a bit bigger - wood thickness and bracing all add to the overall external volume.

It's worth noting that a KW181 will manage 128dB at 70Hz, and dropping off to each side. In theory, then, this compact 15" ought to do quite well.


I do have some other ideas:
- 2x 12" mounted for force-cancellation could be interesting - stops the cabinet walking around
- Investigate bandpass and/or other designs - tapped horns etc.

Chris

Tim McCulloch:
Rock goes down to 44Hz (open E string on a conventional bass guitar, and the pants-ruffling kick drum hits; the chest cavity part is around 60-80.

I generally have disliked band pass designs although Nexo has gradually convinced me they can be done "more right" than I've previously experienced.

I don't care about 1-hand speaker management as I still have 2 hands attached to me.  What I want is balance, poise, and no awkward dimensions.

Truck/van pack-friendly dimensions.  Handles on at least 5 sides.  Optional pole cup for those who desire such things.

Chris Grimshaw:
Tim,

Open E is 41Hz. Low B (on a 5-string) is around 30Hz.

My current subwoofers (which I'm happy to share the designs for) are compact 15" boxes which are flat down to 40Hz. They beat a KW181 by around 6dB at 40Hz, but lose out at 70Hz.

They tick most of the boxes in the design spec. However, if we're willing to sacrifice some low-frequency extension then it would be possible to make a much louder box.

Tradeoffs, as always.

Chris

John Halliburton:

--- Quote from: Chris Grimshaw on August 31, 2019, 08:49:56 am ---Thought I'd make a new thread. There was some interest in developing a compact but loud subwoofer for rock 'n' roll gigs, where low-end extension isn't particularly important.

So far, here are the goals I'd consider sensible. Happy to chop/change them by popular demand, though.

- 4ohm (maximises power with 1 sub per amp channel)
- Flat to 55Hz
- Can be lifted with one hand by Average Joe
- Loud as possible while keeping the above
- Sensible money
- Beat a KW181


In my experience, more expensive drivers are worth the money. They typically allow more output in a smaller box than a cheap driver, meaning output density (which is a priority here) is high.

So, my first simulation was with a https://www.bcspeakers.com/en/products/lf-driver/15-0/4/15sw115-4 - it's about as good as it gets for 15" subwoofers, and is conveniently available in 4ohm impedance. I simulated a simple ported box.

With 90v RMS input (about 2KW input) and a highpass filter to cut out-of-band excursion, we're at 128.5dB at 55Hz, 130dB at 60Hz, dropping slowly to 128dB at 100Hz.
Port velocity is a little high at the bottom end, but that will only be a problem if 55Hz comes along at full power - not likely to come up with the intended program material.

The cabinet volume is 62L net, which is nice and compact. Once built, it'll be a bit bigger - wood thickness and bracing all add to the overall external volume.

It's worth noting that a KW181 will manage 128dB at 70Hz, and dropping off to each side. In theory, then, this compact 15" ought to do quite well.


I do have some other ideas:
- 2x 12" mounted for force-cancellation could be interesting - stops the cabinet walking around
- Investigate bandpass and/or other designs - tapped horns etc.

Chris

--- End quote ---

If you go with the vented design, I'd still enlarge the port area(which of course also lengthens it) to reduce vent velocity, and lower that distortion which to me is more audible than one would think.

It is what would separate this project from typical commercial versions. 

Yes, likely larger overall, but IMO worth it if it still fits in the Yugo. ;>)

If more bang for the box is desired, I'd certainly consider going with a bandpass design. 

Best regards,

John

Tim Weaver:
With today's megawatt-handling extra-excursion having super woofers, should we be revisiting linkwitz-transform type enclosures? Or Maybe the Carver Sunfire type?

If you aren't savvy, they are basically undersized sealed boxes that use power and lots of EQ to make up the extension. The benefits are that you can essentially "choose your Q" of the finished product. Also they are very well controlled having a massive air spring in the cabinet. The downside for PA use is it uses tons of power and your HP and limiting needs to be spot on or you'll be launching voice coils.

For a while Bag-End was using this method but that was before modern drivers and amps were common.

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