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In my subwoofer design quest, I recently discovered UniBox. I've found that between UniBox and WinISD that their respective calculations are within about 5-10% of each other. My gut feeling is that UniBox is more precise... is that a correct assumption?


I've also found myself confused a bit by the UniBox "Max. Excursion graph." A fair number of the drivers I've plugged in seem to hit the max excursion at relatively low power (100-200 watts) and at seemingly higher frequencies than I would have thought (i.e. between 30-40hz). Does this seem normal?


For example, I modeled the TangBand 12" sub at Parts-Express. It's rated for 500W at 8 ohms. In UniBox, a sealed enclosure of 76.7l (no fill, minimal leaks) shows this driver hitting max. excursion just below 40hz at 200w. Am I doing something wrong or are the manufacturer's wattage claims pure and utter BS?


Thank you for indulging my NuB questions...
 

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The driver power specifications are thermal limits. -That is the power where the voice coil opens up, or the glue holding the former, spider, etc. starts to melt and everything lets go'. This is generally based on a limited range of frequencies applied to the driver.


Excursion limits on the other hand, as I'm sure you've noted, are dependant on enclosure size, type, and the intended passband of the driver in question. For example, a vented woofer design may have a higher SPL at Xmax than a sealed design, but only if it is high passed below the tuning frequency. Likewise, smaller, higher Qtc sealed designs will support higher SPL's than larger, lower Q'd ones.


Which calculation are you referring to that is 5%-10% different?


C
 

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"My gut feeling is that UniBox is more precise... is that a correct assumption?"


I think so; it gave results closer to one of the higher end programs for one driver I've seen them for.


I like that it accounts for box stuffing.
 

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Welcome to the world of engineering trade-offs, and +1 to Curt's comments.


Excursion limits, power handling and low-end extension are a triad; you can have any two, but the third is an outcome. A small, sealed box has horrible low-end extension, but it never gets close to X-max without massive amounts of power (and a little EQ and room gain make up for any low-end loss). A bigger sealed box will give you more low end (in the limit becoming an Infinite Baffle, which has it's own driver designs) but you'll also be closer to X-max. Vent it and you'll get great low end, but the voice coil will bottom at lower power.


The key is requirements:

- how loud do you need

- how low do you need.


A vented design will play lower and louder than a sealed one. If it meets your needs without exceeding X-max (really X-mech), it meets your requirements. In my case, power was cheap and space limited so I went sealed and equalized, and I'm safe to 10Hz in my room at sound levels I can enjoy - it meets my needs.


Conversely, in full-range designs, I routinely design for an extended low end that hits X-max at 1/2 or 1/3 rated power, as I want the low-end extension and I know it's highly unlikely to ever see enough power at or below port tuning frequency to exceed X-mech. I don't care that [email protected] will smoke then as that's not a realistic expectation for music. Home theater is a different story...


HAve fun,

Frank
 

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Quote:
Originally Posted by noah katz /forum/post/17021021


"My gut feeling is that UniBox is more precise... is that a correct assumption?"


I think so; it gave results closer to one of the higher end programs for one driver I've seen them for.


I like that it accounts for box stuffing.

The Alpha version seems more accurate, and is a lot more informative. Still free.
 

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They all use the same math. The only difference is the default assumptions about parameters -- Qa, Ql, Qp, series R, port end correction, etc. If you set everything the same, they give the same results.
 

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Quote:
Originally Posted by catapult /forum/post/17022004


They all use the same math. The only difference is the default assumptions about parameters -- Qa, Ql, Qp, series R, port end correction, etc. If you set everything the same, they give the same results.

Jack Hidley tried WinISD, he said he found several math errors just playing around with it for a few minutes.
 

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Been using WinISD for years. OK, close enough. Been playing with Unibox the last couple of hours. Nifty. One of the games you can play is if you believe Mms, you can adjust VAS to match, and see if Bl ans Cms are closer to spec.

For the driver I was playing with today, the thus calculated VAS was dead center of the range between delta mass and 3 box sizes on delta compliance and within 10% of the spec. Other calculated values closer to spec. So it gets down to what you believe. VAS is not easy to measure that's for sure.


If the errors in WinISD were in the alpha version, I hope he passed that info on so they can be corrected.
 

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Quote:
Originally Posted by cixelsid /forum/post/17022121


Jack Hidley tried WinISD, he said he found several math errors just playing around with it for a few minutes.

I respect Jack a lot but I wonder if a few minutes were enough to find let alone change the default conditions -- all the Q values and the series R.


Also, the power of the input signal is different from the way some do it -- it's the voltage to produce that power into Re + R series. It's not wrong but you need to read the manual to realize what's going on. It would be easy to plug in a driver you knew well (like one of Jack's) and say that SPL isn't right with that much power.
 

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I use Unibox simply because I find it easier to use, less of a PITA than WinISD. The last couple of projects have measured very close to simulated at LF.
 

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I'm about to build two cabinets for dual AE TD15S opposed, and I wanted to reduce the cabinet size. I had been informed that the right size for Qtc 0.707 is nigh on 300L .


For my room, having two 300L cabs is a bit excessive so I worked out my biggest box is 180L (internal) to be reasonable. So I did some modelling with Unibox and then I thought I would check some variants in WinISD 0.50a7.


I keep double checking the parameters but they look the same to me (could be snow blind
). Why is there such a difference between the two programs? I want to go with Unibox as I really like getting a Qtc of 0.75/0.76 from a 180L cab and I don't think this will have a dramatic affect on sound quality in the pass band 70Hz to 350Hz. (opinions and experiences welcomed!)


 

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Quote:
Originally Posted by Antripodean /forum/post/19198379


I'm about to build two cabinets for dual AE TD15S opposed, and I wanted to reduce the cabinet size. I had been informed that the right size for Qtc 0.707 is nigh on 300L .


For my room, having two 300L cabs is a bit excessive so I worked out my biggest box is 180L (internal) to be reasonable. So I did some modelling with Unibox and then I thought I would check some variants in WinISD 0.50a7.


I keep double checking the parameters but they look the same to me (could be snow blind
). Why is there such a difference between the two programs? I want to go with Unibox as I really like getting a Qtc of 0.75/0.76 from a 180L cab and I don't think this will have a dramatic affect on sound quality in the pass band 70Hz to 350Hz. (opinions and experiences welcomed!)

Actually, although the graphs appear very different, it looks like the two results are actually pretty much the same. I didn't go over them real close but I did check that at 10hz they're both about -28dB and the -3dB point is right around 50hz on both. They just look so different because the scales on the graphs are so different. I don't think you can change it in Unibox but in WinISD you could set it to appear in the same format as Unibox by setting the X-axis to 10 - 1000hz and the Y-axis to show +4dB to -56dB.
 

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Antripodean,


There are enough things that vary beyond our control that all box sims should be considered reasonably close approximations, -but still approximations.


A couple of things on your sims:


I see you have the Qa = 5 and Ql = 30 in Unibox. These parameters suggest a heavily stuffed box. WinISD defaults to 10 and 100 respectively for these parameters, and If you didn't adjust them to match the Unibox sim, they may be the reason WinISD suggests larger enclosures.


You've also left Rs (or Rg in WinISD) at .1 ohm. This is fine if a plate amp or an active crossover is used to drive the woofers. If a passive crossover is utilized, the series resistance of the passive network should be added.


Another parameter to consider is voice coil heating. Depending on the design SPL and the driver, the VC heating can potentially add another couple of tenths to Re. -All this additional series resistance unfortunately requires an even larger enclosure, but should be considered in the enclosure model.


A third option you've not considered is to utilize an aperiodically damped enclosure. This is nothing more than a resistively damped hole in the enclosure. See the Scan Speak vario-vents as one example of this concept. Aperoidic damping can utilize a smaller enclosure, at the expense of a higher fs, but the acoustic impedance will lower the Q of the resonant peak at fc, providing better cone control over that portion of the drivers passband.


C


BTW, Juha has written a new version of WinISD, which is compatable with win7. Still in the alpha stages, but fairly bug free, and very similar to the old pro alpha version. Check the Linear Team forum if you want to download and try version 0.7.0.
http://www.linearteam.org/forum/view...7590f811298a2d
 

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Quote:
Originally Posted by cc00541 /forum/post/19199410


Antripodean,


There are enough things that vary beyond our control that all box sims should be considered reasonably close approximations, -but still approximations.


A couple of things on your sims:


I see you have the Qa = 5 and Ql = 30 in Unibox. These parameters suggest a heavily stuffed box. WinISD defaults to 10 and 100 respectively for these parameters, and If you didn't adjust them to match the Unibox sim, they may be the reason WinISD suggests larger enclosures.


You've also left Rs (or Rg in WinISD) at .1 ohm. This is fine if a plate amp or an active crossover is used to drive the woofers. If a passive crossover is utilized, the series resistance of the passive network should be added.


Another parameter to consider is voice coil heating. Depending on the design SPL and the driver, the VC heating can potentially add another couple of tenths to Re. -All this additional series resistance unfortunately requires an even larger enclosure, but should be considered in the enclosure model.


A third option you've not considered is to utilize an aperiodically damped enclosure. This is nothing more than a resistively damped hole in the enclosure. See the Scan Speak vario-vents as one example of this concept. Aperoidic damping can utilize a smaller enclosure, at the expense of a higher fs, but the acoustic impedance will lower the Q of the resonant peak at fc, providing better cone control over that portion of the drivers passband.


C


BTW, Juha has written a new version of WinISD, which is compatable with win7. Still in the alpha stages, but fairly bug free, and very similar to the old pro alpha version. Check the Linear Team forum if you want to download and try version 0.7.0.
http://www.linearteam.org/forum/view...7590f811298a2d

Good catch on the Qa and Ql. I also noticed the enclosure sizes (and Q) of the simulations aren't the same. In WinISD there are three different simulations none of which match either of the two attached from Unibox.
 

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Many thanks CC and Lennon!



I didn't think the models should be so different and I really appreciate your picking up on the variables. It's helping me use the tools a lot better! I also downloaded the new WinISD, thanks



I had heard of aperiodically damped and GM mentions them in the linked post but I need to understand how to design and implement such a cabinet. I have also been a fan of sealed cabs and have steered clear of doing things differently to this. Time to get searching and learn some new tricks
 

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One aspect I like about WinISD is that it requires correlation of the T/S parameters that are input. What I've often found is that manufacturer's use a bit of 'poetic license' in their specs. Of course I'm not saying that they fudge the numbers to promote their drivers in the best possible light. -Let's just call it the occasional 'fortuitous happenstance'.



Consequently, WinISD is somewhat picky about the parameter input order. Don't be disappointed if Vas or Bl for instance don't exactly match the published values. Using values I've generated, I've never had parameter errors, but the manufacturer's values can be another story.


Curt C
 

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Quote:
Originally Posted by cc00541 /forum/post/19201651


One aspect I like about WinISD is that it requires correlation of the T/S parameters that are input. What I've often found is that manufacturer's use a bit of 'poetic license' in their specs. Of course I'm not saying that they fudge the numbers to promote their drivers in the best possible light. -Let's just call it the occasional 'fortuitous happenstance'.



Consequently, WinISD is somewhat picky about the parameter input order. Don't be disappointed if Vas or Bl for instance don't exactly match the published values. Using values I've generated, I've never had parameter errors, but the manufacturer's values can be another story.


Curt C

Thanks Curt


I noticed this with some drivers but provided I do things in the right order
the parameters for the TD15S match up with WinISD. Running lots of comparative models alongside each other is also a bonus.


Have you used WinISD for aperiodic enclosures? From a search "in WinIsd, model a sealed enclosure with a Ql set to 3 and you will have an Aperiodic box model."


And kudos for all your great speaker designs!
 

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I prefer winISD over everything else I've tried so far. I like that it allows you to factor in filter responses so you can actually see what is going on. One person complained that there sub didn't sound right. I had a quick look, and once I put in the filter response of the amp, I could see that the response was ugly.


Ideally to design a vented sub, you need to see excursion, power input, vent velocity with the filter transfer function included.


The only thing that WinISD is a bit finicky about is entering a new driver. I made a little tute on that in my blog:
http://redspade-audio.blogspot.com/2...iver-data.html

That one's for lazy people who don't want to read the help file!


Also a basic tutorial:
http://redspade-audio.blogspot.com/2...inisd-pro.html


And a bit of a tute on designing a vent that won't chuff:
http://redspade-audio.blogspot.com/2...that-wont.html


You need another tool for that, but the link is included.


It's been a while since I looked into other programs, but most of them seem to lack something important that WinISD has.


Now I'm being the lazy one - I can't remember if Unibox does all the same things. Perhaps it does.
 

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I find these types of discussion interesting.


Lets just conclude that many, many, many, many incredible subwoofer builds have used WinISD and have used Unibox.


They are similutions only and really do we need to haggle over any math errors when the sims STILL represent a valid model of the design???


I have yet to read a build thread where WinISD screwed them. WinISD gives us all the basic needs. Volume, port size, excursion, slopes, EQing. No one will ever prove that its not a valid simulation product....the key word here is SIMULATION.


I like WinISD better then Unibox, its easier to manipulate/tweak.
 
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