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Author Topic: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll  (Read 1058 times)

John Halliburton

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #10 on: September 03, 2019, 09:06:03 am »

A quick simulation for a 6th order bandpass looks pretty promising - 3-4dB more output above 70Hz. The internal box size goes to 82L, so the net volume would come to roughly 100L.
I'll try running a few other drivers through that cabinet to see how flexible it will be. I don't want to have a design that's nailed for exactly one driver, but terrible for all others.

Although it's been 20 plus years since I designed and used one-and it was 4th order, a 6th order BP IMO would be less bang for the effort than a tapped horn.  I fully expect a good TH design would have more output, lower distortion, and better impulse response(especially this).

I think it's tougher to get a 6th BP design to have enough bandwidth to not sound like a one note wonder as well.

YMMV,

John
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Rory Buszka

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #11 on: September 04, 2019, 11:42:22 am »

Although it's been 20 plus years since I designed and used one-and it was 4th order, a 6th order BP IMO would be less bang for the effort than a tapped horn.  I fully expect a good TH design would have more output, lower distortion, and better impulse response(especially this).

I think it's tougher to get a 6th BP design to have enough bandwidth to not sound like a one note wonder as well.

YMMV,

John

The original LAB Horn Subwoofer was designed for (and delivered) tremendous output, tremendous bass extension, and excellent efficiency, but the tradeoffs were large size, heavy weight, and difficult construction. It sounds like for the One Hand Subwoofer (OHS) the priorities are reversed: Small size, light weight, and easy construction, with the best possible output and efficiency available from such a design, and deliberately limiting bass extension to that required for most music.

Tapped horns are somewhere in the middle. They offer horn-like output from as few as one box, but they are still complex to construct, heavy, and relatively large. Don Keele did a survey during the earliest concept development for the JBL Vertec line array that compared various bass loading techniques and the amount of output that could be achieved from the smallest occupied volume. He found that the most output at low frequencies for a given volume could be achieved using a typical bass-reflex enclosure. I think his survey was limited and it probably deserves to be conducted again using today's designs, including 6th order bandpass and tapped horn configurations. But it does provide some guidance in the direction of a vented box.

I think it would be interesting to look at a Reflex/Horn Hybrid design (not the Martin one, as it would have some of the space-efficiency shortcomings of a horn). As you design a reflex enclosure with minimal chamber volume, you increase the port length necessary to achieve a certain tuning. You also increase the needed length of the port when the cross sectional area of the port is increased. What a few designers have done is designed an enclosure with a port that not only creates a bass-reflex resonance, but also has a quarter-wave pipe resonance in the frequency range of interest. Then when those two resonances are brought close together, they create a reflex enclosure that is very efficient over a narrow(ish) bandwidth. The RCF ESW 1018 subwoofer is an example of this. Then the famous Yorkville LS808 (or LS801p) applied a taper on the port section, turning it into a compromised rear-loaded horn. This doesn't enable the port to truly act like a horn (except for also possessing a quarter wave resonance), but it does add some damping to the port action. The benefit to a speaker like this is it would be easy to construct, and easy to make lightweight, while having more efficiency over a limited bandwidth than a classical bass-reflex enclosure.

To drive adoption, be careful of using a speaker that is either difficult to obtain outside of the EU, or very expensive.
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John Halliburton

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #12 on: September 04, 2019, 09:35:49 pm »

The original LAB Horn Subwoofer was designed for (and delivered) tremendous output, tremendous bass extension, and excellent efficiency, but the tradeoffs were large size, heavy weight, and difficult construction. It sounds like for the One Hand Subwoofer (OHS) the priorities are reversed: Small size, light weight, and easy construction, with the best possible output and efficiency available from such a design, and deliberately limiting bass extension to that required for most music.

Tapped horns are somewhere in the middle. They offer horn-like output from as few as one box, but they are still complex to construct, heavy, and relatively large. Don Keele did a survey during the earliest concept development for the JBL Vertec line array that compared various bass loading techniques and the amount of output that could be achieved from the smallest occupied volume. He found that the most output at low frequencies for a given volume could be achieved using a typical bass-reflex enclosure. I think his survey was limited and it probably deserves to be conducted again using today's designs, including 6th order bandpass and tapped horn configurations. But it does provide some guidance in the direction of a vented box.

I think it would be interesting to look at a Reflex/Horn Hybrid design (not the Martin one, as it would have some of the space-efficiency shortcomings of a horn). As you design a reflex enclosure with minimal chamber volume, you increase the port length necessary to achieve a certain tuning. You also increase the needed length of the port when the cross sectional area of the port is increased. What a few designers have done is designed an enclosure with a port that not only creates a bass-reflex resonance, but also has a quarter-wave pipe resonance in the frequency range of interest. Then when those two resonances are brought close together, they create a reflex enclosure that is very efficient over a narrow(ish) bandwidth. The RCF ESW 1018 subwoofer is an example of this. Then the famous Yorkville LS808 (or LS801p) applied a taper on the port section, turning it into a compromised rear-loaded horn. This doesn't enable the port to truly act like a horn (except for also possessing a quarter wave resonance), but it does add some damping to the port action. The benefit to a speaker like this is it would be easy to construct, and easy to make lightweight, while having more efficiency over a limited bandwidth than a classical bass-reflex enclosure.

To drive adoption, be careful of using a speaker that is either difficult to obtain outside of the EU, or very expensive.

I find most tapped horns almost as easy to build as a vented cabinet.  When I first started working for Tom at Intersonics, my first day involved working on the SDL-4 Servodrive subwoofer prototype, which was the smaller brother of the SDL-5.  Both were horn loaded W designs with close to fifty pieces in each.  I may have slightly skewed take on what is an easy cabinet or hard cabinet to build.

That said, a vented cabinet is still likely to yield the lightest cabinet, and one can easily make high quality designs that are compact.

Best regards,

John
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Tim McCulloch

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #13 on: September 04, 2019, 09:56:24 pm »

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

Okay, I'll take the -10 at 45Hz, reasonably peaky from 55ish to 80, useful to 100ish and combine those with size (transport friendly) and balance (ergonomics).  Oh, wait, that's almost what the JTR Growler does, it just weighs more than "one handed."

I'd take a weight penalty if it means preserving output and handling.  Like I said, I still have 2 hands.

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Michael Thompson

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #14 on: September 05, 2019, 01:28:50 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

As simple DIY goes, the Cubo designs from www.freespeakerdesigns.com already hit pretty much all of these marks and are forgiving enough that you can add handles, pole mounts, casters, etc...  I've built some and find them to be pretty handy boxes to have around.  You get an extra ~3 db in trade for some low end compared to ported box, but they are still plenty low for most things.
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Nathan Riddle

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #15 on: September 05, 2019, 09:04:49 am »

As simple DIY goes, the Cubo designs from www.freespeakerdesigns.com already hit pretty much all of these marks and are forgiving enough that you can add handles, pole mounts, casters, etc...  I've built some and find them to be pretty handy boxes to have around.  You get an extra ~3 db in trade for some low end compared to ported box, but they are still plenty low for most things.

https://freespeakerplans.com/plans/14-plans/basscab/44-cubo15

This seems rather interesting. Also pretty easy & cheap to build.

~130dB peak output...not bad.
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Rich Riotto

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #16 on: September 06, 2019, 02:06:04 pm »

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

If it were me, I'd prefer reasonable flatness down to 40Hz for the bass open E.  Like Tim, I'd be OK with two hands as long as it was under 75 lbs and not an awkward lift.  Also, high efficiency drivers so less power is required to get to full output.  Depending on the power requirements, I might also opt for 8 ohms so I could run two chained at (4 ohms) off of one amp channel.  With that said, definitely as loud as possible from low 40s to low 100s.  It seems like the JTR Cap212Pro checks a lot of the same boxes.  The design seems pretty simple...it's the custom drivers that might be key to making it work.

Full disclosure: Everything I think I MIGHT know about speaker cabinet design has been learned from reading these threads!  Please correct any false assumptions.

- Rich
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Caleb Dueck

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #17 on: September 07, 2019, 01:25:46 pm »

If it were me, I'd prefer reasonable flatness down to 40Hz for the bass open E.  Like Tim, I'd be OK with two hands as long as it was under 75 lbs and not an awkward lift.  Also, high efficiency drivers so less power is required to get to full output.  Depending on the power requirements, I might also opt for 8 ohms so I could run two chained at (4 ohms) off of one amp channel.  With that said, definitely as loud as possible from low 40s to low 100s.  It seems like the JTR Cap212Pro checks a lot of the same boxes.  The design seems pretty simple...it's the custom drivers that might be key to making it work.

Full disclosure: Everything I think I MIGHT know about speaker cabinet design has been learned from reading these threads!  Please correct any false assumptions.

- Rich

I agree with flat to 40Hz at least.  Subs without good low end extension just feel a bit emasculated regardless of SPL. 

Another point that is important to me - quality, neodymium magnet drivers.  Non- neo drivers just sound a bit mushy.  I got to hear pretty much the entire Fulcrum subwoofer lineup side by side a couple times, and the muddy vs tight sound fit with neo vs non difference. 

If you assume 2 people, wheels, and a form factor that can be tilted easily - that keeps the performance from getting hosed.  If you assume carry by 1 person - SPL or extension, or both, are crippled.  Setting up a sound system is real work, that's why there are wheels, paid muscle, ramps, etc.  When I think tiny and light, what comes to mind is a Bose WaveRadio! 
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Bill Hornibrook

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #18 on: September 07, 2019, 04:33:45 pm »

If it were me, I'd prefer reasonable flatness down to 40Hz for the bass open E.  Like Tim, I'd be OK with two hands as long as it was under 75 lbs and not an awkward lift. 

- Rich

Yeah my thinking too. B&C's own recommendation for that 15 is an enclosure size of 3.2 cubic feet tuned to 40hz. That gets me me there, and is still incredibly small and easy to transport.

If any of you guys (who are much better at this than I am) would care to design a simple bass reflex cab for that driver based on B&C's recommendations, I'd be very interested.
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Rory Buszka

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #19 on: September 15, 2019, 08:41:17 pm »

https://freespeakerplans.com/plans/14-plans/basscab/44-cubo15

This seems rather interesting. Also pretty easy & cheap to build.

~130dB peak output...not bad.

I wonder if that number was arrived at through measuring an actual box, or through simulation.

In terms of the physics involved, this seems more like an ElectroVoice Sb180 "SubScoop" style of design - that is, NOT a tapped horn. The horn path is much too short to resonate below about 80-90 Hz, and output below that is provided by a reflex mode of operation where the air in the narrow entrance of the horn starts acting like the air mass in a ported enclosure. Helmholtz resonance cannot be back-driven like a quarter wave resonator can to achieve a second tuning point at the half wavelength, as a tapped horn does.
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