What makes the Magnum 12 a great MBM? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 17 Old 11-04-2015, 06:57 AM - Thread Starter
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Question What makes the Magnum 12 a great MBM?

Hi Guys,

I've been reading about how the Magnum 12 is the amazing midbass monster. I'm wondering what exactly in it's characteristics that makes it so? Some of the description was saying the VA load at the critical midbass frequency is very low, which makes it very efficient and therefore very dynamic at those frequencies?

I previously bought the NHT surplus driver AR 12 clone. I ran some sims for it in WINISD for QB3 vented alignment, and at first glance, it seems quite comparable with the Magnum 12 sims. Does this make the AR-12 also a good Midbass woofer? I have listed the parameters below.

Appreciate your thoughts and comments!

Magnum 12 AR-12
Re: 7.09 Ohms 3.55
Fs: 41.9 Hz 19.8
Xmax: 9.15mm 5.0
Vas: 68.9 liters (2.43cuft) 269 Liters
Le: 1.55mH unknown
Sd: 520cm² 481.9cm2
Bl: 20.7 Tm 13.4
Qms: 13.09 4.095
Qes: 0.35 0.205
Qts: 0.34 0.195
Mms: 80.3 grams 87.8
Cms: .180mm/N 0.8166

EDIT : Magnum 12 in GREEN, AR-12 in RED in the charts.
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Last edited by rhapsodee; 11-04-2015 at 06:59 AM. Reason: Clarification
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post #2 of 17 Old 11-04-2015, 08:13 AM
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The magnum 12 is an 8ohm drivers, but in the MBM bandwidth it's more like a 12 or 16ohm driver, which is why it's so easy on amplifiers. It has also been optomized for the 35hz and up range with high sensitivity and good xmax to go with it. That's not a typical combination as most pro drivers favor sensitivity above all else.

In your comparisons, I'd tune the Magnum 12 a little lower. I'd personally use 35 or 40hz. The AR-12 looks like a fine MBM but it will take more amplifier power to match the Magnum 12. You can see in the impedance plots that the red line is quite a bit lower. For instance, at 200hz the Magnum 12 is 9ohms and the AR12 is 4ohms. So, the AR-12 will take more than double the wattage for those outputs. That makes the Magnum 12 twice as effecient at 200hz. At 80hz it's many times more effecient.
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post #3 of 17 Old 11-04-2015, 09:37 AM - Thread Starter
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Hi Tux, many thanks for your insight. Some of the difference, appears to be because the magnum 12 is 8ohm while the AR12 is 4ohm nominal? Example at 200hz, the difference is basically 8 vs 4 ohm?
I understand the high impedance peak on the magnum at 80hz makes it very efficient there, so similarly the AR12 is most efficient at 70hz?

What does the VA chart mean? It seems to equalise out the 8 vs 4 ohm drivers, because one takes more voltage, the other more current, to achieve the same power or VA output? Here they are both much more equal, main difference being the higher tuning of the magnum in this sim?

On a scale of 1 to 10, where would you put the AR12 vs the magnum 12, if the magnum is a full 10 as a MBM?

Thanks!!

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post #4 of 17 Old 11-04-2015, 01:07 PM
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The nominal impedances are a large part of it, but the magnum 12 is higher impedance than a typical 8ohm. If both drivers in your model are at the same drive voltage, than the magnum 12 is 3db more effecient, or higher even. Though their sensitivities are the same. That's if I'm reading your simulation correctly.

The VA chart is power. If you increase V or A you're using more P. P is watts. The more you increase Z (impedance) the less A will pass through the voice coil. Thus output will go down as you increase Z. So then high Z is bad right? Well no, because if the output is still high even though Z is high, then that means you're using less P for a given SPL and your efficiency is high. And if Z is high, you can add drivers without working the amp to much.

I'm not sure I've read your charts right, so I don't think I can offer an answer to your last question. The parameters you listed show nearly half the xmax and it also looks like it'll require a much bigger box. I'm sure it's a fine MBM and I'd use it if I were you.
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post #5 of 17 Old 11-04-2015, 02:50 PM
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I modeled it and it does look like the NHT AR-12 would make for a decent mid bass driver. The impedance peak is a bit lower in frequency and since it has slightly less motor strength the impedance is not quite as wide but response does match fairly well with the Magnum-12.

When comparing two similar drivers I always try and use the same enclosure volume and tuning. Also make sure you look at the SPL tab in WinISD not just the transfer function. I do wish WinISD had an SPL by input voltage option, it calculates SPL based on the Re of the driver so you have to remember take that into account.

I can't seem to dig up the other specs for that driver but the other thing the Magnum-12 has going for it is its 3" VC which helps further reduces power/thermal compression.
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post #6 of 17 Old 11-04-2015, 11:27 PM - Thread Starter
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Many thanks for the insights Tux and mtg90. I just completed a pair or fusion 8 to match my fusion 8 mtm center, and also a pair of ultimax 15s sealed in 4cuft. Just ordered a pair of volt 6 for surrounds.
Now I'm getting ready to move into my new place next week. The system will be in a spare bedroom, 9x12 feet, 10ft high ceilings.
I've been debating if I need the extra midbass, I probably won't have time to build the mbm for a while. I'm sure the fusion 8 will be plenty for my tiny room.

Still, it's great to know I have a pair of good mbm on my shelf waiting for sawdust!

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post #7 of 17 Old 11-05-2015, 03:34 AM
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What makes the Magnum 12 a great MBM?

Quote:
Originally Posted by mtg90 View Post
I do wish WinISD had an SPL by input voltage option, it calculates SPL based on the Re of the driver so you have to remember take that into account.
It does. Just plug a number into the voltage field instead of the wattage field. When you plug in a wattage number, it's just calculating voltage from that. You can enter a value into either field.

There was also discussion in one of the other threads on apparent power vs true power that's actually dissipated into the voice coil. Not sure if you saw it: https://www.avsforum.com/forum/155-di...l#post38510233

But it makes a driver like the Mag, with the nice wide impedance peaks, even more impressive.
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post #8 of 17 Old 11-05-2015, 08:58 AM
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You should also try and sim at equal voltage level. Depending on the amp chosen, with a high impedance woofer like the magnum you might well run out of amplifier voltage before anything else. Especially if you tune high (like 45 - 50 Hz)

What im trying to say that, Yes Magnum is an easy load but the down side to that is that it requires more voltage to do the same thing. Not saying thats a bad thing. Its just something to be aware of. Maybe these drivers er too different to clearly see the effect, because the AR-12 sacrifices some sensitivity for a bit more bass extension.

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EDIT:

Eminence Delta A and Delta B shows the difference better. Again 10V:

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post #9 of 17 Old 11-05-2015, 10:13 AM
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Hi,
I'm no expert, but I have built quite a few diy speakers. And I have always thought that woofers with higher QMS values sound better than those with lower. They seem a lot punchier and more articulate, especially inn the midbass area.
And if you pair that with a really, really good BL to MMS ratio I think you will find much of the secret to why these sound soo good. I have obviously not heard them myself, but if Erich should start making knock-down cabs for these I will build some too!

Cbarth
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post #10 of 17 Old 11-06-2015, 06:32 AM - Thread Starter
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The magnum 12 has high Qms. Is the high mechanical Q the reason for its high impedance peak, which makes it very efficient at that frequency?
High BL to Mms means a strong motor and light cone. Makes sense the the driver will be punchy with these characteristics.
Thanks!

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post #11 of 17 Old 11-06-2015, 06:39 AM - Thread Starter
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Hi Splotten, thanks for your sims. Which lines should I be comparing, and what do I focus on? The f3 is different despite similar fb?

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post #12 of 17 Old 11-06-2015, 08:21 AM
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Quote:
Originally Posted by rhapsodee View Post
The magnum 12 has high Qms. Is the high mechanical Q the reason for its high impedance peak, which makes it very efficient at that frequency?
High BL to Mms means a strong motor and light cone. Makes sense the the driver will be punchy with these characteristics.
Thanks!

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I'm rusty in this area, but Qms more dictates the height of the impedance peak. Qes dictates the width of the peak (lower Qes should be wider iirc, high Qms should be high peak iirc). So if you have a high Qms and low Qes you'll have a tall and wide impedance peak at Fs.
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post #13 of 17 Old 02-26-2016, 09:11 PM - Thread Starter
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Looking around, the delta pro 12A and the Sigma 18-4 ohm used in the 1899 both have similar high Qms and low Qes, they should have similar punchy midbass quality as the magnum 12?

Could the Sigma 18-4 be crossed over at about 650-800Hz active, to the top half of the JBL 4722? The 2432 driver in the 2384 horn? Would I need 1 or 2 Sigma 18s?

Thanks!

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post #14 of 17 Old 02-27-2016, 09:58 AM
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Could be similar, though the Magnum-12 has about twice the excursion capability of the Delta Pro-12A and the suspension is very linear and mechanically quiet making it better for bass. The Sigma 18 could make an excellent midbass woofer. It looks like it has some breakup starting around 1k so I would cross as low as you could, 650hz with a steep crossover (at least 4th order) should be ok. One driver does minimize the CTC distances giving you a wider vertical sweet spot at the crossover where some off axis lobbing will occur.
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post #15 of 17 Old 02-27-2016, 06:49 PM - Thread Starter
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Sorry to go OT, but would it be better to go with a dedicated mid and woofer, TMW style?
Will a side by side dual 10in mid be able to match directivity at 650hz with the 2384 horn?
Then xo the Sigma 18-4 ohm in at 200-300hz below. Kind of like the 1899.
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post #16 of 17 Old 05-01-2016, 06:01 AM - Thread Starter
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Hey Guys,

I've still been on the lookout for other great mbm woofers. Just came across this. It has high Qms of 16.33, and lowish Qes of 0.32.

Does it mean it will be a mean MBM? Is 3.5mm xmax enough if it's crossed at 60hz or 80hz to a true subwoofer? I'm actually thinking of using it as a woofer to match up to the jbl 2384 horn at 650hz XO.

There is a strange 5db dip in the datasheet FR curve between 400-500hz, any idea what is going on?

http://www.parts-express.com/seleniu...river--264-370

Cheers!

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post #17 of 17 Old 05-01-2016, 06:55 AM
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I don't think that woofer would do very good as a midbass module and would be quite a bit different than the Magnum-12.

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