Anything DIY that can beat the QSub-18? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 28 Old 02-07-2020, 07:27 PM - Thread Starter
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Is there anything DIY that would beat this sub by Magico? It apparently weighs 570 pounds and costs more than $30k.

https://www.soundandvision.com/conte...b-18-subwoofer

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post #2 of 28 Old 02-07-2020, 11:34 PM
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Originally Posted by blake18 View Post
Is there anything DIY that would beat this sub by Magico? It apparently weighs 570 pounds and costs more than $30k.

https://www.soundandvision.com/conte...b-18-subwoofer


Looks like a dual sealed 18” in a small but pretty box. The marketing department had a field day trying to make it sound special though.

Trying to match it diy, there are tons of options.
Lets just take it on with our own dual opposed 18.
Make a well braced box the same dimensions. (Its a bit small, but we’ll keep it fair). Stick a Stereo Integrity HST-18 in each end. Add a Speakerpower sp1-4000. (Or a sp1-6000, if you want to take on their 230v ratings)

Congratulations, you now have a DIY copy. Now what are you going to do with the other $33,000?

Chris
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post #3 of 28 Old 02-08-2020, 06:02 AM
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136db at 20hz. Anyone want to do the math and figure out what excursion would be needed to achieve that?

Maybe they’re measuring this inside a hatchback.
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post #4 of 28 Old 02-08-2020, 09:25 AM - Thread Starter
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Quote:
Originally Posted by a77cj7 View Post
Quote:
Originally Posted by blake18 View Post
Is there anything DIY that would beat this sub by Magico? It apparently weighs 570 pounds and costs more than $30k.

https://www.soundandvision.com/conte...b-18-subwoofer


Looks like a dual sealed 18” in a small but pretty box. The marketing department had a field day trying to make it sound special though.

Trying to match it diy, there are tons of options.
Lets just take it on with our own dual opposed 18.
Make a well braced box the same dimensions. (Its a bit small, but we’️ll keep it fair). Stick a Stereo Integrity HST-18 in each end. Add a Speakerpower sp1-4000. (Or a sp1-6000, if you want to take on their 230v ratings)

Congratulations, you now have a DIY copy. Now what are you going to do with the other $33,000?

Chris
Hah, yes, love it! I knew one of you awesome forum members would know! 🙂

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post #5 of 28 Old 02-08-2020, 09:32 AM
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From their info page,

“The vast majority of subwoofers are manufactured using MDF. But when the woofers move, they cause the cabinet to flex or warp. Those pliable walls absorb a tremendous amount of energy, which leads to distortion and massive group delay, which the listener perceives as a smearing of the sound."

Massive group delay...okay lol
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post #6 of 28 Old 02-08-2020, 10:36 AM
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So the infamous MAUL with 4 RF19s in a bandpass horn gives up to 126.2 dB at 20 hz. This dual 18 sealed outputs as much as 2.5 MAULs.


The highest Data Bass could get at 20 hz with a sealed subwoofer is the HS-24 in a 23 cu ft cabinet. It got up to 110.2 dB at 20 hz. So you would need at least 16 of them. (Talk about massive group delay)


The fact that Magico has managed 136 dB at 20hz with only 2 18s with about 23mm xmax in a less than 10 cu ft enclosure with a shared amplifier proves that they can do Magic(o)!


Why didn't they just round it up to an even 150? Oh... that's right. They want you to buy two.



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post #7 of 28 Old 02-08-2020, 11:10 AM
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What a load of donkey feces! How could ANYBODY come up with such marketing crap and maintain a straight face? It is awesome that they are able to completely ignore the laws of physics.


BTW: all of that energy being lost in your flexible subwoofer cabinet MUST be converted to heat. I am so grateful I have never been BURNED! The amount of energy dissipation is substantial, given how much MORE acoustic energy this sub produces
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post #8 of 28 Old 02-08-2020, 11:12 AM
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I’d bet a kidney those DB’s were measured in a small room. At 20hz that isn’t saying much.

The drivers look nice though, I bet they aren’t fudging numbers with the distortion though. These could probably compete with the HST’s. For 36k I’d rather get two HS24’s with a massive power soft amp and save money.


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post #9 of 28 Old 02-08-2020, 11:22 AM
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Interestingly, it turns out it would actually cost roughly $30,000 to get 136 dB at 20hz groundplane using sealed subwoofers.


16 x HS-24 mk iii @ $1275 = $20,400
16 x NX3000D @ $400 = $6,400


Total $26,800 (with nothing on sale, and no quantity discounts)


That leaves $3200 for 16 23 cu ft cabinets, or $200 each, which is kind of optimistic.

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post #10 of 28 Old 02-08-2020, 11:22 AM
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https://www.audioholics.com/subwoofe...woofer-preview


Here’s a good write up


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post #11 of 28 Old 02-08-2020, 11:36 AM
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Magico brags about their enclosure being able to handle 175dB. My guess is that 136 dB @20hz with 1% distortion is actually being measured inside the enclosure. That would be a ridiculous way to measure equipment, but it sure makes for big numbers for the marketing department to fudge with.

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post #12 of 28 Old 02-08-2020, 11:39 AM
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No independent measurements to verify the marketing bs

For all we know, a dual opposed UM18-22 would equal or best it.

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post #13 of 28 Old 02-08-2020, 11:43 AM
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Second article not much better. Flex in the cabinet ... the FEA they show has measurements arount .000001mm which is NOT going to do much to screw with wavelengths measured in meters. So it must be converted to heat, not just radiating. Think of a large diaphragm moving .000001mm and consider how many dB that could POSSIBLY generate!


Not talking about poorly braced cabinets, I'm talking about a well built DIY. Now, want to really take it up a notch? Then do it in CONCRETE! Shoot, do it in aluminum if that is REALLY your bag. Actually Al is quite resonant. Do it out of ceramic.


Stupidity ...
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post #14 of 28 Old 02-08-2020, 12:37 PM
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Originally Posted by MTBDOC View Post
Second article not much better. Flex in the cabinet ... the FEA they show has measurements arount .000001mm which is NOT going to do much to screw with wavelengths measured in meters. So it must be converted to heat, not just radiating. Think of a large diaphragm moving .000001mm and consider how many dB that could POSSIBLY generate!


Not talking about poorly braced cabinets, I'm talking about a well built DIY. Now, want to really take it up a notch? Then do it in CONCRETE! Shoot, do it in aluminum if that is REALLY your bag. Actually Al is quite resonant. Do it out of ceramic.


Stupidity ...

Adamantium would be the only logical material for such a cabinet.


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post #15 of 28 Old 02-08-2020, 01:05 PM
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Anything DIY that can beat the QSub-18?

I would like to demo one, just to put a hand on and see how dead it really is.

As I was just posting in another thread, I’ve never felt a sub without some vibrations.

My ported HST: Thats a triple baffle too.


Even my Goldenear Supersub xxl has slight felt vibrations under high output. It’s marketed as being completely dead, balanced nickel trick and all.

Chris
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post #16 of 28 Old 02-08-2020, 01:28 PM
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Quote:
Originally Posted by Samps View Post
136db at 20hz. Anyone want to do the math and figure out what excursion would be needed to achieve that?

Maybe they’re measuring this inside a hatchback.
Dual 18", 1.3" Xmax, sealed = 119.3dB at 20Hz

More than 16dB needed to get to their "spec" readings . . .

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post #17 of 28 Old 02-08-2020, 01:30 PM
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Anything DIY that can beat the QSub-18?

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Originally Posted by Will P View Post
Dual 18", 1.3" Xmax, sealed = 119.3dB at 20Hz



Still more than 16dB needed to get to their "spec" readings . . .


Close-mic counts, right?

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Close-mic counts, right?

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The Q-Sub has been around since at least September of 2013, and now all of a sudden there is curiosity about how it actually performs. Exactly no one actually tested it, for some strange reason. Vastly overpriced at anywhere from $36,000 to $48,600.

Give me the JTR 4000ULF any day of the week, 108 db at 10Hz groundplane.
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post #20 of 28 Old 02-08-2020, 09:55 PM
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In their marketing hype, they specify that the sub "goes all the way down to 15hz". That implies a built-in high-pass system to limit your ULF fun. At 10hz, a DIY 15 would stomp it.


Put away your wallets, boys.

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post #21 of 28 Old 02-09-2020, 12:09 AM
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Originally Posted by bimmaguy View Post
In their marketing hype, they specify that the sub "goes all the way down to 15hz". That implies a built-in high-pass system to limit your ULF fun. At 10hz, a DIY 15 would stomp it.


Put away your wallets, boys.


As much as I’m not impressed by their marketing, I’ll give them the benefit of the doubt on this one. FR is listed as 15-150hz, so I’m going to assume thats the -3db point.
I hope they didn’t cut off the ULF, and just didn’t try to boost it.

Chris
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For sealed sub the output will drop -5dB from 20Hz to 15Hz.

The SPL at 15Hz would be 114.3dB.

SPL at 10Hz - 107.3dB

All that for $36,000 !

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post #23 of 28 Old 02-09-2020, 10:34 AM
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As much as I’m not impressed by their marketing, I’ll give them the benefit of the doubt on this one. FR is listed as 15-150hz, so I’m going to assume thats the -3db point.
I hope they didn’t cut off the ULF, and just didn’t try to boost it.

I'm not so sure... 15hz is roughly where you will start to see huge power draw from amps and the biggest excursions from the drivers. If you sell a product with a warranty, you want your product to be absolutely idiot proof to minimize claims. I've owned a few high $ sealed subs, and most have a brick wall filter around 10 - 15hz. The cones don't move at all below that.


Rythmik was the only sealed sub (non-DIY) I've ever had that would do it's best to reproduce a 1hz signal. It was actually a surprise to me.

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post #24 of 28 Old 02-09-2020, 11:55 AM
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I'm not so sure... 15hz is roughly where you will start to see huge power draw from amps and the biggest excursions from the drivers. If you sell a product with a warranty, you want your product to be absolutely idiot proof to minimize claims. I've owned a few high $ sealed subs, and most have a brick wall filter around 10 - 15hz. The cones don't move at all below that.


Rythmik was the only sealed sub (non-DIY) I've ever had that would do it's best to reproduce a 1hz signal. It was actually a surprise to me.
You are correct. Many manufacturers employ High Pass Filter for protection of sealed subs.
The reasons for that are:
1. Driver coil thermal protection when the box is smaller (Qtc>0.7)
2. Driver cone excursion protection when the box is larger (Qtc<0.7) - bigger box size is not likely due to overall design requirements
3. Removing subwoofer load for ULF (<20Hz) which would give some more SPL capabilities at and above 20Hz

Power draw needed for reaching Xmax at different frequencies depends on the sealed sub box size which determines the Qtc.

Pmax and Xmax are the only (2) parameters limiting the sealed subwoofer performance. Ideally you would have them getting reached at the same time so the subwoofer can be used to it's full potential (Xmax at all frequencies for the smallest box as long as Pmax not hitting before Xmax for all frequencies below Fb).

For box size giving Qtc=0.7 the power draw P needed for Xmax remains constant no matter the frequency. With proper TS parameters you will get P= Pmax for Xmax below Fb as long as P=Pmax at Fb when X=Xmax. Above Fb power thermal limit Pmax is the restriction - the driver will hit power limit before getting to Xmax.

Just to give you a reference point - for Qtc=0.7 the Fb = (1.5 to 2)x Fs and depends on the box size and TS parameters.

When you have box with Qtc=0.7 the power will be constant for getting Xmax for all frequencies below Fb. If the box is smaller than that (when Qtc >0.7) then the power limit will limit performance below Fb - that's when you will see HPF employed for protection to limit power to the driver coil.

At box size with Qtc=0.7 the subwoofer power limit and Xmax limit work hand-in-hand and get all performance at any frequency - Xmax at constant P (or Pmax with proper TS parameters) down to 1Hz if you have the amp capable of getting that low frequency out.

Driving the subwoofer to Xmax at any frequency will provide SPL drop of 12dB/oct. That means for sealed sub with SPL 120dB @ 20Hz will give you 108dB @10Hz, 96dB @ 5Hz, 84dB @2.5Hz, 72dB @1Hz.

Type of room - size, air tightness, walls/floor/ceiling structure - would add to the above numbers as room gain which would be dependent on the frequency only, and not the type of subwoofer (sealed, ported, etc) or the Qtc value.

That's the simplified description of the process - not accounting for Le, etc.
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post #25 of 28 Old 02-11-2020, 11:27 PM
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No independent measurements to verify the marketing bs
...
For all we know, a dual opposed UM18-22 would equal or best it.
Double the Data-Bass numbers for their sealed Aura NS18-992-4A test and you'll have a good approximation.

I do not defend the price, but also would not call a DO Utimax 18 comparable.

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post #26 of 28 Old 02-12-2020, 06:01 AM
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Double the Data-Bass numbers for their sealed Aura NS18-992-4A test and you'll have a good approximation.

I do not defend the price, but also would not call a DO Utimax 18 comparable.
I stand corrected. DO UM18-22 blows it out of the water

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post #27 of 28 Old 02-12-2020, 06:45 AM
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Seems like a re-hash of the Krell Master Reference sub from the 90's.

1.3inches of excursion? LOL, the SI-24 has 4inches p-p, and it's a 24!
Even if that was one-way, it's still less than 1/3rd the SPL.

The LMS-18 does 3.2inches p-p, and the RF-19 is up there too!

That sub won't even beat a single 24, let alone a pair of them powered with a K20 or FP14k (real or clone); and STILL well under the price.

As for the box, it's total overkill. It's not hard to DIY a marble or concrete box that weighs more and is better braced, and also dual opposed, with more watts and more cone-area/excursion/displacement.
So yeah, it's possible.

Anyone that has quad 18's, or better, already has this beat.
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post #28 of 28 Old 02-12-2020, 11:48 AM
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All this article and discussion has done is make me really want to build a DO 24" in 1" of MDF. And now I'm drooling.
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