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Author Topic: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll  (Read 1867 times)

Chris Grimshaw

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LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« 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
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Tim McCulloch

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #1 on: August 31, 2019, 12:09:46 pm »

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.
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Chris Grimshaw

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #2 on: September 01, 2019, 03:30:53 am »

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
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John Halliburton

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #3 on: September 01, 2019, 09:55:17 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

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
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Tim Weaver

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #4 on: September 01, 2019, 10:36:44 am »

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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Mark Wilkinson

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #5 on: September 01, 2019, 01:15:24 pm »

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.

I tried that, using the same 18" driver in a sealed box, and in a larger vented box. bms 18n862 8ohm, 95dB 1 watt, 1500w AES, 19mm xmax.
The sealed is about a 21" cube, and probably could have been made an inch or so smaller.
The vented is 23"x 23"x 28" deep and is tuned to 31Hz.
The Linkwitz transform needed too much boost to make the sealed reasonable at 31Hz,
but i do believe it would work fine if restricted to say 40-45Hz, and at less than anger SPL.
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Chris Grimshaw

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #6 on: September 02, 2019, 03:26:19 am »

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

I actually tried sealed subs before moving to ported. Over a useful frequency range, the ported box would keep up with 3x sealed boxes. Each box had 1KW on tap. So, you'd need 3x the drivers and 3x the power if you wanted to go sealed.

IMO, not worth it. I was slightly embarassed to find that my (ported) main speakers would happily out-run the sealed subwoofers down to 60Hz.

It's possible to use some clever multi-band limiting to get something that's flat to 20Hz at low SPLs, but cuts off higher as you push the fader. However, that's not how I like to run my PA systems - IMO they should respond linearly as you push the faders. No change in tonality, just louder and louder.
It would also restrict the user base to those that have access to high-end DSPs. Ideally I'd like to keep the filtering as simple as possible: lowpass, highpass, maybe a PEQ to tilt the overall response.



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

Hi John,

Right now I'm simulating a port with 300cm^2 area, for a driver with 855cm^2 of cone area.
Should keep port compression to less than a couple of dB if you hammer it with worst-case sine waves.

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.

Cheers, all.

Chris
« Last Edit: September 02, 2019, 03:35:44 am by Chris Grimshaw »
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Steve M Smith

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #7 on: September 02, 2019, 11:06:37 am »

My current subwoofers (which I'm happy to share the designs for)


I would like to see your design.




Steve.
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Mark Wilkinson

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #8 on: September 02, 2019, 11:25:03 am »

I actually tried sealed subs before moving to ported. Over a useful frequency range, the ported box would keep up with 3x sealed boxes. Each box had 1KW on tap. So, you'd need 3x the drivers and 3x the power if you wanted to go sealed.

IMO, not worth it. I was slightly embarassed to find that my (ported) main speakers would happily out-run the sealed subwoofers down to 60Hz.

It's possible to use some clever multi-band limiting to get something that's flat to 20Hz at low SPLs, but cuts off higher as you push the fader. However, that's not how I like to run my PA systems - IMO they should respond linearly as you push the faders. No change in tonality, just louder and louder.
It would also restrict the user base to those that have access to high-end DSPs. Ideally I'd like to keep the filtering as simple as possible: lowpass, highpass, maybe a PEQ to tilt the overall response.


Chris

Hi Chris, I can't imagine how 1 ported box could keep up with 3 sealed boxes (other than in the frequency range where the port is making the big bulk of the output).
Were you using the same driver? Was the sealed box already rolling off at 60Hz ?

My experiments using the same driver showed near identical response and sensitivity once above the sealed box's rolloff corner.
That may be because i chose a driver known to work well either sealed of ported, I dunno. 
(What is the spec for when a driver works better sealed vs ported?  EBP (fs/Qes) ?  That a value around 90 works for both, lower value for sealed, higher for ported? You know more about that stuff than I do............)

Anyway, below are traces for the sealed and ported boxes as described earlier, with a little processing in place.
The sealed processing was using a Linkwitz transform, but only to get to about 40-45 Hz.  I'm pretty sure the same results  could be done with normal parametric & shelving filters, too.

I played both sealed and ported boxes hard, alot. 1500W into 8ohms. 
Unless content got very strong below mid 40's, it could be hard to tell a difference.
blue=ported   green=sealed   rather obviously  :)
« Last Edit: September 02, 2019, 11:29:29 am by Mark Wilkinson »
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Chris Grimshaw

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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #9 on: September 02, 2019, 01:50:49 pm »

Hi Chris, I can't imagine how 1 ported box could keep up with 3 sealed boxes (other than in the frequency range where the port is making the big bulk of the output).
Were you using the same driver? Was the sealed box already rolling off at 60Hz ?


Hey Mark,

Looks like I mis-wrote. 1:2 is about right when you consider a frequency range of 40-100Hz. At 40Hz (port tuning), the ported box would match 3x sealed boxes.

Same drivers each time. Ported box was around 70L net, sealed boxes were 35L net. 1KW per driver.

FWIW, the sealed boxes were rolling off (gently) at 80Hz, and required a lot of EQ to get flat down low. Even then, the mechanical demands on the drivers were considerable.

Chris

PS - Steve, I'll send them via PM in the interest of keeping this thread tidy.
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Re: LAB Sub 2 - Small 'n' Loud for Rock 'n' Roll
« Reply #9 on: September 02, 2019, 01:50:49 pm »


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