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ZOD Audio M.A.U.L. Test Results and Discussion

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The Alpha B3 sub is an already obsolete product from that brand. It's a company known only in Europe, more precisely Germany and Romania. I don't know the correct term for the alignment but the sub port is inside that straight horn. Big, heavy and expensive kicksub. Nothing under 40 hz really,because of drivers with only 7 mm xmax

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Thanks Mark.

 

Yes...Much head scratching and cursing. Mostly over how to fit everything together. Think I started on it almost 4 years ago and settled on the bastard 6th order type maybe 2 years back. Time flies. Whipping up a simulation is the easy part! I thought about contacting you to discuss things a few times because I knew you had some experience with unusual bandpass loadings.  

 

Agreed about using some sort of slot or horn loading up top versus a port. Those are the same conclusions I came to. A positive expansion also gives a chance to use a bit more area at the exit than possible with a port which can help keep airspeeds down while also avoiding issues with the internal vent opening placement and loading. It was also easier to fit this type of short expansion than a vent in a space starved design like this one. Overall it was a win/win.

 

You can also get some interesting results by getting a little more LF loading with longer slots by tapering down where effectively the "port" is the in one dimension of the path, but narrows slightly, and ideally opens again near the exit.  I've landed at the same point from both directions of starting with a chamber and port that kept growing to be the same cross section as the end of the chamber, to starting with a longer line/horn that you reduce the horn segments to model it like the line/column it really is.  When I last experimented Hornresponse couldn't load 2 of the same drivers at different points on the pathway, so it was an average and a double check with models from each separate location to insure acoustic resonances don't line up.   It does open up some interesting options if you can direct all the output from a large box to a relatively modest sized opening.

 

 

On a side note your buddy Jeff is starting to sell me on slim profile slot ports.

 

 

 

Slot ports certainly work, they just need a little compensation as the aspect ratio increases.  The one hurdle they all face is noise/turbulence near the small ends.  Of course it's then a question of do you really care if it lets you get 6dB more from larger area or a tuning you might never build with round ports.  The big bandpass designs can work well, with the caveat that any non-linearity in the high frequency system sets in motion all sorts of gross response modulation.  In my early investigation with the Terraform design I first spent a lot of time making sure I got a handle on why there were so many bad sounding examples of bandpass designs.  Shift the BL and Cms on a driver in a bandpass design and you can quickly see what happens to those short Xmax, long Xmech pro drivers which used to be so common.  Next look at an undersized port and the changes that occur and you can get an idea of what is happening dynamically.  Most of it isn't a big deal below 30Hz, but at 50-100Hz, it's highly audible, with some driver non-linearities probably responsible for 6-10dB high-Q peaks if they are producing that range when the driver gets past Xmax.  Having free tools like the recent incarnations of Hornresponse opens up possibilities which would have been largely guesswork not that long ago.

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All in all Josh is using 16 of those RF drivers...

 

Good start. Can load up each corner with.... pfft, just one MAUL each. :P

 

Wake me up when he has two stacked in each corner. :D

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Good start. Can load up each corner with.... pfft, just one MAUL each. :P

 

Wake me up when he has two stacked in each corner. :D

 

Then we will hear about how the jaws of life had to extricate him from the rubble that was his house; the smile welded to his face unfazed even when they had to amputate the hand that was unable to be pried from the volume knob.

 

Popalock will be forever harmed (and may succumb) shortly thereafter from the heretofore unheard of magnitude of bass-envy.

 

JSS

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Luke and I were discussing offline and I think we both pretty much made the call....

 

Josh Ricci has won the bass. All of it.

 

Winning it makes it sound like there was a choice involved. I'm kicking the bass's ass and taking it by force. :angry:

 

Now I just need to find someone to put one of these in their Suburban or mini van and go to the local car audio competition. See if we can get that 155 at 14Hz.

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The Alpha B3 sub is an already obsolete product from that brand. It's a company known only in Europe, more precisely Germany and Romania. I don't know the correct term for the alignment but the sub port is inside that straight horn. Big, heavy and expensive kicksub. Nothing under 40 hz really,because of drivers with only 7 mm xmax

 

Noted. I'll check it out anyway. It does seem like lately the Pro sub designs are beginning to change and become more creative. I think they are starting to take advantage of the improved drivers on the market now.

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Winning it makes it sound like there was a choice involved. I'm kicking the bass's ass and taking it by force. :angry:

 

Now I just need to find someone to put one of these in their Suburban or mini van and go to the local car audio competition. See if we can get that 155 at 14Hz.

 

I'd guess they'd need to seal the car quite well or they might have windows bent off their hinges with that thing....

 

Put it in a Uhaul and see what she does!

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You can also get some interesting results by getting a little more LF loading with longer slots by tapering down where effectively the "port" is the in one dimension of the path, but narrows slightly, and ideally opens again near the exit.  I've landed at the same point from both directions of starting with a chamber and port that kept growing to be the same cross section as the end of the chamber, to starting with a longer line/horn that you reduce the horn segments to model it like the line/column it really is.  When I last experimented Hornresponse couldn't load 2 of the same drivers at different points on the pathway, so it was an average and a double check with models from each separate location to insure acoustic resonances don't line up.   It does open up some interesting options if you can direct all the output from a large box to a relatively modest sized opening.

 

I have done some playing around with weird vent shapes and sizes like bowtie's. Anything for the last little bit of performance. HR still cannot do drivers at different locations in the model. I still keep Akabak on an old XP laptop for those cases. I tried ABEC and have a license but it is daunting to say the least. 

 

 

Slot ports certainly work, they just need a little compensation as the aspect ratio increases.  The one hurdle they all face is noise/turbulence near the small ends.  Of course it's then a question of do you really care if it lets you get 6dB more from larger area or a tuning you might never build with round ports.  The big bandpass designs can work well, with the caveat that any non-linearity in the high frequency system sets in motion all sorts of gross response modulation.  In my early investigation with the Terraform design I first spent a lot of time making sure I got a handle on why there were so many bad sounding examples of bandpass designs.  Shift the BL and Cms on a driver in a bandpass design and you can quickly see what happens to those short Xmax, long Xmech pro drivers which used to be so common.  Next look at an undersized port and the changes that occur and you can get an idea of what is happening dynamically.  Most of it isn't a big deal below 30Hz, but at 50-100Hz, it's highly audible, with some driver non-linearities probably responsible for 6-10dB high-Q peaks if they are producing that range when the driver gets past Xmax.  Having free tools like the recent incarnations of Hornresponse opens up possibilities which would have been largely guesswork not that long ago.

 

The comment about "do you really care about a little vent noise if it gets another 6dB" or allows the vent to fit in the cab is spot on.

Vent noise doesn't bother me so much as usually I find it's almost totally masked by other content in use.

 

Most of the bandpasses I've ever heard were kinda bad I have to admit Either they were used to get more out of a weaker driver that wasn't very good to begin with or they were used to make a lot of gain over a small bandwidth resulting in a lot of ringing and peakyness. The stereotypical one note boom. Add in a healthy dose of underdamped operation, undersized ports and sometimes bad integration and it's not surprising they have such a bad reputation.

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Josh, when you made the slot, why did you choose to make that slight horn profile? It looks to me like weight, volume, and construction time could have been (barely) reduced by having the baffle run straight from the bottom to the top. The baffles would then be pushed toward the hatches a little, and the whole rear-chamber extension under the front chamber wouldn't be necessary. Was it to make more room for hatch bracing?

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It extends the length slightly. Improves the airspeeds at the mouth exits. Produces a bit more extended top end response and output. I wanted the bump right in the middle of the 60-100Hz range. Easiest way is to model it. I still would have used the offset to get airspace back in the vented volume and reduce the area of the slot.

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Ah I see it now. Without it you don't really get that full 100Hz extension on the top end. I guess you could have just angled the baffles, but then you're sacrificing some of your force cancellation. Not a great tradeoff when your total moving mass is nearly 10lbs. I'll bet those 4 woofers could walk a 500lb cab if they were all facing the same direction

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Exactly. With roughly 9lbs of mass oscillating I thought force cancellation might be worth a look! 9lbs! Just one of these drivers produces a lot of vibration on a cab. 4? Forget about it. On a suspended floor just down fire them. No shakers needed.

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Damn, the design is cool to work with if one has the right drivers.

I know probably now I sound like I am trying to promote the M-force design (which I am not) but for now, in these types of applications, I cannot find something to beat it if you know how it really behave in use.

Using a simple fold like the one in the picture bellow, in large box, 60*60*35.5 " (not quite double the volume of the MAUL) one could put 2 M-force with custom 34 " drivers.Why custom? Because they produce this driver with whatever parameters one wants, even diaphragms with SD up to 6500 sq cm made on specs.

post-3306-0-54150700-1469967272_thumb.jpg

The vent would be tuned to around 21 Hz so the efficiency would get much better. Also the vent surface would be huge so the compression would be reasonable even at huge SPL.post-3306-0-00688500-1469967250_thumb.jpg

The port inlet could be guided so the air flow to be right over the motor assembly so that at very high power levels the turbulent air would cool it down. Also, the driver has a very large inertia and an Xmech of 35 mm and right over the port fs, one can use a bit of eq to flatten out the FR, easily with only a small amount of power asked from the amp.

Considering also the DPC tech, the distortions and accuracy would be fenomenal. 

Because it would use only 2 M drivers which weigh less than one  RF T3 19, Using 18mm Ply and extensive 15mm bracing, this would weigh around the same as a single MAUL, but would output the same as 2 of them from 19 hz up.post-3306-0-97994700-1469967250_thumb.jpg

then, if you add the cost, a driver + module is around 4.5k, so the factory retail price for an active would be around 12-18 k. 4L-acoustics KS28 with amp would be north of 30 K and this would be smaller and would go 5-10 hz lower.

Cool for touring or instals, even for pro Cinema's.

post-3306-0-36488100-1469968234_thumb.jpg

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It could also be made smaller, a lot smaller because of the possibility of changing parameters, but it would then use smaller vent and it's main purpose is efficiency down to lower 20's, so no compression is allowed. Look at the F132 from Funktion 1 and there you will see how large a horn has to be to get those numbers with this driver

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Hey Paul.

60x60x35.5! This is absolutely huge. Can no longer fit through most common doorways. Not a big deal since these would be destined for arenas and box trucks and forklifts but that is a big honking cabinet. I do wonder about the M-force vibration of the cabinets as they have 2 to 3kg mms. That has to vibrate the hell out of single driver enclosures. I believe the weight in this bigger cabinet would be closer than suspected after all of the extra wood needed for the larger cab and extensive bracing. Not to mention the Mforce amplifier and plate. I know you have probably looked at the drawings and all of that. The depth and diameter of the drivers plus the built in motor mounting and bracing required could cause logistical issues. A 34" driver hatch and clearances needed to access and bolt up the driver and motor? This is a big chunk of real estate and how to adequately brace these huge hatches? The amplifier recommended plate and layout is very large also. It has to go somewhere. This would be the difficult part. Could be done of course but will take some acrobatic design work to fit it all together. Total displacement is about the same actually for 4 19's vs the 2 M-force 34's. I wouldn't count on using the 35mm xmech range. I think linear xmax is rated at 15mm so perhaps 20mm or maybe 25 would be "useful". Probably not enough amp to get there anyway though. No doubt about it the motor system is CRAZY efficient. Way beyond anything else available. That is the part that makes me want to try the MForce and the DPC circuit of course. I wish it wasn't so difficult to obtain. Unless you are a big manufacturer or have some very good connections you can forget about it. Sounds like you have an "in" so perhaps you will be getting hands on with it? I really want to see someone independent who will post data and impressions of using it.

 

EDIT:The drivers behave so much different due to the efficiency that traditional cabinet sizes and designs result in a peaky and odd response shape. The drivers want unreasonably small volumes to produce naturally flat or smooth response shapes that are a physical impossibility. That's why it is called the Mforce system. It really requires advanced DSP to shape the response into something that sounds good when using a cab that actually fits the driver and has enough area to deal with such a huge driver and displacement. You cannot run it "raw" and expect it to sound good. Actually the T3 19 and even more so the 21 and 18Ipal drivers are already this way, but the MForce is even more extreme. It's the price you pay for ever higher conversion efficiency. I see it as a strength not a detriment. So I cannot run the MAUL without some processing...Big deal I don't ever plan to, DSP is cheap and powerful these days. ;)

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The processing is a must in this design. As you probably saw I put the amp resistivity at 0.03 Ohm and that smoothed the response especially at port resonance. Probably that is the correct way to change RE in the adaptive parameters and sim it in HR, without having to calculate the parameters if I would change the driver's.

The Xmax of the driver is given by the linearity of the motor force and of the magnetic suspension but even if the motor has only 30%force at 25-30 mm, it still has over twice the power of an Ipal driver.

But not just that. The fact that this driver has a very reactive load, it stores a large amount of kinetic energy. The amp will deliver a HUGE current at the start of the motion ,then less is needed to keep it going. At the end of the stroke, the DPC processing will tell exactly what signal to generate to stop it because the magnetic brake is very strong at large excursions, so again, the energy consumption is much smaller than in a normal driver. It wil not hit 35 mm but it will be close. Also, it is quite immune to nonlinearities even at those strokes because of that magnetic centering. The more it exits the 0 point position,the more powerful that centering gets.

In one of their white papers they compared a single 30" short transmission line vs a dual 18 and they measured up to 147 dB at 40 hz or so,and when I tried to see what the excursions would be needed, the number is huge!

It is a large enclosure but if a contractor has to use 4 of these instead of 32 of another brand it would be in fact quite compact!

 

Another cool thing about this system is if you simulate multiples (2,4,8) in HR keeping the amp res at 0.03, it will not scale as it shout, but if you then change it to 0.02 or 0.01, then the response improves.I bet the DPC system would sense the boundary change and would modify the damping accordingly.

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I would have a way to get my hands on them if I can get a sponsor here.I would probably need to build 10 to get past some minimum requested order if I decided to do it but we have a good distributor here with a good reputation in Powersoft company that could get them for me for tests. The price being what it is, it's also a barrier.

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As with the hatches, they would need to be as big as the diaphragm on her side. The other parts would come after. One can make the driver "basket " as it feels suited so it can be build from wood or custom Al or steel parts from the beginning,mounted inside and then trough the hatches to put the other parts.in fact, the membrane could be punted trough the horn, with only small hatches to screw it in place. Because is modular, it is much easier.

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I think the magnetic braking kicks in prior to 35mm actually from looking at the exploded motor shots and the patent filings. Also from what I've read and heard the system is sensitive to alignment of the cone assembly to the motor. A small percentage of offset in the angle will magnify itself as excursion grows so this must be nailed. I'd assume this would impact the 2nd order distortion a bit if it is off a little. You cannot only look at BL^2/Re being down a certain amount. You also have to consider the performance of the surround, the stiffness of the suspension and its linearity, the amount of MMS, etc. Not only that but the way the changes in the drivers behavior at the limit will impact its loading into the enclosure. I expect that the performance is extraordinary but I want to see more hard data at high power in a finished system.

 

I really need to get ahold of one of these. B)

 

Also DPC won't tell the driver to stop because of the magnetic braking. You will have to define within the software what the driver excursion limits are and that will act as the limiter in the amplifier based on the simulation data using the driver specs compared against the recorded data.

 

It is modular but like I said it is still huge and is a complicated system. You still have to assemble in the cab, access bolts and screws and possibly make some adjustments to the motor and cone assembly alignment.

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I doubt delaying the pairs of drivers individually will do anything good. This will then cause them to load the common vented section in a delayed manner.

 

Not to be an armchair engineer, but I did run a few numbers on this one before posting....from my armchair even, haha ;)

 

The aspect I find curious is how the same acoustic design exhibits very different excursion qualities when the drivers are changed. The magnitude of the difference here is quite large - and it's probably testament to just how powerful the T3 motor is.

 

Anyways - the point I wanted to make is that the drivers are not loading the front chamber in a balanced manner. If you were to convert this to a normal vented alignment (essentially by removing the access panels), then you're not going to see the staggered excursion behavior shown in your akabak model. This means your front loaded offset horn acoustic impedance is the source of this imbalance. Danley talks about how the effective Fc of the horn changes as you get closer to the mouth of a conical horn....I believe the same thing is basically happening here.

 

All that to say - delaying the drivers relative to each other does in fact change the acoustic loading that they impart on each other because it changes their relative phase. The thing about phase is that it rotates slower as you go lower in frequency - which means a fixed time offset imparts more phase difference at higher frequencies than it does at lower frequencies. An allpass filter may be more appropriate so you don't affect high frequency performance, but I think it may be possible to get the 21-IPAL drivers to exhibit an excursion characteristic more similar to the T3. You are right that it will affect rear chamber loading, but that can be mitigated by isolating the rear chambers (which in theory wouldn't use much volume to achieve).

 

In other words - is it possible with a little DSP help to be able to use a much less potent woofer in this alignment? I know less potent is less exciting, but does it also in turn improve the efficiency of the system by a few dB? The IPAL drivers look to have another 3dB of sensitivity above the T3, and most of your max SPL was amplifier limited. I didn't run a full blown sim on it - just a few napkin calculations. Is it even possible to drop the 21-IPAL drivers into the existing design? I'm also curious how the load spread across the face of the driver affects the simulations (I believe the sims assume all the energy emanates from one location centered on the face of the driver). It'd be interesting to see if that dip existed in real life.

 

Anyways - just thinking out loud to spur some discussion.

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