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Author Topic: Sub design for a 18 Sound 12" subwoofer  (Read 3999 times)

Dave Jackman

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Re: Sub design for a 18 Sound 12" subwoofer
« Reply #10 on: March 07, 2018, 08:00:04 am »


Pm me with what you have to offer.
Thanks david
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Chris Grimshaw

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Re: Sub design for a 18 Sound 12" subwoofer
« Reply #11 on: March 07, 2018, 09:11:52 am »

Pm me with what you have to offer.
Thanks david

Might as well write it up here in case anyone else wants it doing.

What I'll do is a couple of measurements of the driver, both free-air, one with mass added to the cone. Using REW, I can then get a set of the T/S parameters to you.
I don't have the equipment to do the Klippel testing for Xmax etc, but what I usually do is feed a sine wave into the driver and listen for when there's a slight knocking sound (NOT the sound of the coil hitting the backplate), which is distortion as the driver reaches its limits. I'll note the cone travel available from that test. NB - this isn't Xmax as such, since Xmax is often derived from the physical sizes of the voicecoil and magnetic gap. That definition is of limited use, though, as the suspension might lock up well before the motor goes non-linear. My test isn't particularly "official", but does give a good idea of what the driver can do.

If that all sounds good, put a Sheffield (UK) postcode into your shipping planner and see what it quotes you. For fairly obvious reasons, I'm not going to post my full address online.

If I start to get a huge influx of drivers I'll have to add a small charge, but for the odd one per year like this, I'm happy to help.

Chris
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Dave Jackman

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Re: Sub design for a 18 Sound 12" subwoofer
« Reply #12 on: March 07, 2018, 12:50:49 pm »

Measuring T/S parameters is the way to do it. Happy to help once you've got those.

Chances are there's someone nearby that has the equipment to do it, even if they don't realise. I use a pair of guitar cables cut in half, a resistor, and a USB soundcard. Needs two matched inputs (ie, both XLR, or both 1/4" jack - some have one of each and the jack is often high-impedance, which will screw up your measurements).

Chris

I managed to track down the specs. Hopefully I can some suggestions for a relatively compact vented enclosure.
Thanks, David
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Dave Jackman

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Re: Sub design for a 18 Sound 12" subwoofer
« Reply #13 on: March 07, 2018, 12:53:18 pm »

I managed to track down the specs. Hopefully I can some suggestions for a relatively compact vented enclosure.
Thanks, David

 
Fs 53 Hz
Re 2.6 Ohm
Sd 0,053 sq.mt. 
Qms 9,7
Qes 0,384
Qts 0,37
Vas 36 lt. 
Mms 93 gr. 
BL 19,7 Tm
Linear Xmax 8 mm 
Le (1kHz) 0,9 mH

Copied and pasted as given to me by the tech.
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David Morison

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Re: Sub design for a 18 Sound 12" subwoofer
« Reply #14 on: March 07, 2018, 02:52:32 pm »


Fs 53 Hz
Re 2.6 Ohm
Sd 0,053 sq.mt. 
Qms 9,7
Qes 0,384
Qts 0,37
Vas 36 lt. 
Mms 93 gr. 
BL 19,7 Tm
Linear Xmax 8 mm 
Le (1kHz) 0,9 mH

Copied and pasted as given to me by the tech.

I had a quick google for the driver and the pic I found looked a lot like the 12NW530. Those specs are virtually the same as the 530, which is a slight problem. Normally, when you make a 4 ohm version of a driver, both Re and BL reduce, but on those specs BL has stayed exactly the same as the 8 ohm version. That in turn means it couldn't have the same Qes. I suspect a careless cut'n'paste job at play, to be honest.

So, if it really is just a 4R version of the 530, something around 30l tuned to 55Hz for the small end of what's reasonable, up to 50l tuned to 45Hz at the lower/deeper end of the scale. The larger & lower you go, the less power it takes to reach Xmax so that affects how loud you can get while maintaining sound quality.

The pic below shows predicted output (for the 530 version as I already had those spec's entered in WinISD) for the above 2 setups, the 50l in green and the 30 in blue. Green takes 350W to reach Xmax and blue 550. That's just over continuous and just under program respectively.

One 12.7cm dia vent will be enough to keep vent airspeed to about 30ms-1 in either case, for the big box it needs to be 28.1cm long, and for the small box 32.5cm.

Excursion & Xmax have been calculated assuming 24dB Butterworth HPF's in each case, at 39Hz for the bigger box and 45Hz for the smaller.

HTH,
David.

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Dave Jackman

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Re: Sub design for a 18 Sound 12" subwoofer
« Reply #15 on: March 08, 2018, 01:32:28 pm »

I had a quick google for the driver and the pic I found looked a lot like the 12NW530. Those specs are virtually the same as the 530, which is a slight problem. Normally, when you make a 4 ohm version of a driver, both Re and BL reduce, but on those specs BL has stayed exactly the same as the 8 ohm version. That in turn means it couldn't have the same Qes. I suspect a careless cut'n'paste job at play, to be honest.

So, if it really is just a 4R version of the 530, something around 30l tuned to 55Hz for the small end of what's reasonable, up to 50l tuned to 45Hz at the lower/deeper end of the scale. The larger & lower you go, the less power it takes to reach Xmax so that affects how loud you can get while maintaining sound quality.

The pic below shows predicted output (for the 530 version as I already had those spec's entered in WinISD) for the above 2 setups, the 50l in green and the 30 in blue. Green takes 350W to reach Xmax and blue 550. That's just over continuous and just under program respectively.

One 12.7cm dia vent will be enough to keep vent airspeed to about 30ms-1 in either case, for the big box it needs to be 28.1cm long, and for the small box 32.5cm.

Excursion & Xmax have been calculated assuming 24dB Butterworth HPF's in each case, at 39Hz for the bigger box and 45Hz for the smaller.

HTH,
David.

Thank you so much.
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Dave Jackman

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Re: Sub design for a 18 Sound 12" subwoofer
« Reply #16 on: March 10, 2018, 06:00:50 am »

I had a quick google for the driver and the pic I found looked a lot like the 12NW530. Those specs are virtually the same as the 530, which is a slight problem. Normally, when you make a 4 ohm version of a driver, both Re and BL reduce, but on those specs BL has stayed exactly the same as the 8 ohm version. That in turn means it couldn't have the same Qes. I suspect a careless cut'n'paste job at play, to be honest.

So, if it really is just a 4R version of the 530, something around 30l tuned to 55Hz for the small end of what's reasonable, up to 50l tuned to 45Hz at the lower/deeper end of the scale. The larger & lower you go, the less power it takes to reach Xmax so that affects how loud you can get while maintaining sound quality.

The pic below shows predicted output (for the 530 version as I already had those spec's entered in WinISD) for the above 2 setups, the 50l in green and the 30 in blue. Green takes 350W to reach Xmax and blue 550. That's just over continuous and just under program respectively.

One 12.7cm dia vent will be enough to keep vent airspeed to about 30ms-1 in either case, for the big box it needs to be 28.1cm long, and for the small box 32.5cm.

Excursion & Xmax have been calculated assuming 24dB Butterworth HPF's in each case, at 39Hz for the bigger box and 45Hz for the smaller.

HTH,
David.

David,
Forgive me if this is too simplistic, but I am very new to this and want a small sub to compliment a pair of tops in order to do some light DJ work. Could I have your, or anyone else's opinion, on the following enclosure. All measurements are in inches. L-17, W-16.5 and H-20.5. The vent on the bottom measures 2.5 by16.5 and has a shelf that is 13 inches deep. I wish I knew more about this topic, but that is why I am here seeking advice.
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Dave Jackman

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Re: Sub design for a 18 Sound 12" subwoofer
« Reply #17 on: March 10, 2018, 06:45:38 am »

David,
Forgive me if this is too simplistic, but I am very new to this and want a small sub to compliment a pair of tops in order to do some light DJ work. Could I have your, or anyone else's opinion, on the following enclosure. All measurements are in inches. L-17, W-16.5 and H-20.5. The vent on the bottom measures 2.5 by16.5 and has a shelf that is 13 inches deep. I wish I knew more about this topic, but that is why I am here seeking advice.


Here are the specs on the speaker again so that other people may have a look at it also.

Fs 53 Hz
Re 2.6 Ohm
Sd 0,053 sq.mt. 
Qms 9,7
Qes 0,384
Qts 0,37
Vas 36 lt. 
Mms 93 gr. 
BL 19,7 Tm
Linear Xmax 8 mm 
Le (1kHz) 0,9 mH

Copied and pasted as given to me by the tech.
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Chris Grimshaw

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Re: Sub design for a 18 Sound 12" subwoofer
« Reply #18 on: March 10, 2018, 08:54:15 am »

Looks reasonable. What does the simulation look like?

For what it's worth, bracing can be particularly effective when you join opposite panels. In subwoofer use, the forces acting on the panels will try to blow the cabinet up like a balloon, so physically connecting the opposite panels strengthens against that very well.

Chris
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David Morison

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Re: Sub design for a 18 Sound 12" subwoofer
« Reply #19 on: March 10, 2018, 10:01:30 am »

David,
Forgive me if this is too simplistic, but I am very new to this and want a small sub to compliment a pair of tops in order to do some light DJ work. Could I have your, or anyone else's opinion, on the following enclosure. All measurements are in inches. L-17, W-16.5 and H-20.5. The vent on the bottom measures 2.5 by16.5 and has a shelf that is 13 inches deep. I wish I knew more about this topic, but that is why I am here seeking advice.

It's approximately 59.5l net internal volume which should leave it tuned to about 45Hz.
That's actually not too bad at all for your driver.

However, the bigger question raised is what you mean by "light DJ work" please?
One 12" sub on its own will not produce enough bass to keep up with most of what I understand DJ'ing to be about, so you may very well still end up disappointed even if you build a box that gets the best out of this driver.

What size audiences will you be playing to, and what main PA speakers will you be using? Those 2 factiods should help narrow down what you might actually need, in case it doesn't match what you've bought.

That said, here's the predicted plot for your driver in the fEarful box. It will take around 340W to reach Xmax; at this power level vent airspeed is very good at 16.5ms-1. A 39Hz Butt24 HPF is again needed.

Cheers,
David.
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