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Author Topic: How accurate is...  (Read 9074 times)

Aaron Weidner

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How accurate is...
« on: August 09, 2014, 01:56:25 am »

Sorry for the length, started off as a question, but I thought I would add some background. I am very passionate about sound; I try to follow Tony Andrews

(owner of Funktion One) teachings even if he sounds a bit crazy at times. Knowing what I do now after the past few years, if I had known about Bassboss, I

would have bought a system from them. I have been thinking about building subwoofers for my system for quite some time. My current subwoofers are two B-52

PA18s (that have magically been given a narrower frequency response since I've owned them) powered by one Crown XTI2002 bridged mono @ 4ohm. For tops,

I have 2 X B-52 PA-315s (that have magically been downgraded in "power handling" by b-52 since I've owned them, 650W down to 400W) with a Crown

XTI1002 bridged mono @ 8 ohm for each (running in stereo). The system sounds pretty good overall, but, IMHO the subwoofers are not worth the money I

spent on them. But, itís what I ended with as my first system. Over the past few years, I now know that 1000W is subjective (to the manufacture) and that

B-52's marketing team must be making some very fat paychecks. First I found out that  that I had 2 different drivers in my subwoofer enclosures, one was a

selenium (that I believe was discontinued more than a couple years ago), and the other was a b-52 branded Celestion (FTR18-4080F). Would there be any

adverse effect from having two different drivers in the same box? I thought I was getting something that could handle "1000W" but they both create audible

distortion before the amp even clips and in theory (manufacturer theory) each sub should be getting "1000W." I soon after found out it was because they are

only 600W aes RMS. I'm just now learning how to use limiters to try and keep them happy. I am now curious as to how I can increase my systems low-end

performance and just recently had time to mess with WIN ISD. I plugged the TS parameters for the factory Celestion driver just to see what it would show me

(not fully understanding how to know what it would show me). Then, just for fun, I plugged in the TS parameters for the Celestion FTR18-4080HDX, which is a

1000W aes RMS driver. A mild upgrade in power handling. The pictures below are what I ended up with using the box parameters shown (interior PA18s

dimensions and port size). Yes, from what I have read it is an audio sin to use a pre-existing box and put different drivers in it. Normally you start with a driver

then the box and then power them if I am incorrect please correct me. I would like to use some Faital Pro 18s to build new subs, but when it comes to designing

a box for them I feel as if I am in over my head, and I have not been able to find box designs online for them. I am more than willing to learn. I do own some of
 
the necessary tools and am willing to buy what I donít have. I am looking for something no bigger than the exterior dimensions of the bassboss SSP218. Is

subwoofer design modeling software reliable? More specifically, how accurate is WIN ISD compaired to other programs? What other programs are their? What

should I expect from the pictures below? Any questions, comments, tips, suggestions, or point me in the right directions would be greatly appreciated, I am a

sponge and only want to learn more   :D. I apologize in advance for peppering this paragraph with questions  :-\.
« Last Edit: August 09, 2014, 12:59:09 pm by Aaron Weidner »
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Ivan Beaver

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Re: How accurate is...
« Reply #1 on: August 09, 2014, 10:57:46 am »

Sorry for the length, started off as a question but i thought i would add some background. I am very passionate about sound, I try to follow Tony Andrews (owner of Funktion One) even if he sounds a bit crazy at times. so... is subwoofer design modeling software accurate? More specifically, how accurate is WIN ISD? I have been thinking about building my own subwoofers for my system for quite some time. My current subwoofers (2 X B-52 PA18s (that have magically been given a narrower frequency response since I've owned them) powered by 1 X crown 2002 bridged mono @ 4ohm) sound pretty good, but, IMHO are not worth the money i spent. Being so new to PA systems and pro audio its what I ended up starting with. I wanted 3 way tops and decent low frequency extension. I now know that 1000W is subjective (to the manufacture) and that B-52's marketing team must be making some very fat paychecks. For tops i have 2 X B-52 PA-315s (that have magically been downgraded in "power handeling" since I've owned them (650W down to 400W)) with a Crown 1002 bridged mono @ 8 ohm for each (running in stereo, primarily pre-recorded audio, recently electronic music) First i found out that (buying the subs a couple months apart) that i had 2 different drivers, one was a selenium (which i believe was discontinued more than a couple years ago) and the other was a b-52 branded Celestion (FTR18-4080F). Putting them side by side, would their be any negative effect from have two different drivers in the same box? Ive had them for a while now and I'm just learning how to use limiters to tame them. I thought i was getting something that could handle "1000W" but they both create audible distortion before the amp even clips and in theory (manufacturer theory) each sub should be getting "1000W"... imagine that, because they are 600W aes RMS. Anyways, back to the topic at hand. I found this software and plugged the TS parameters for the Celestion driver just to see what it would show me (not knowing how to read what it would show me, but knowing that simulations are probably not always accurate). Then, just for fun, i plugged in the TS parameters for the Celestion FTR18-4080HDX which is a 1000W aes RMS driver. The pictures below is what i ended up with using the box parameters shown (interior PA18s dimensions and port size). I know it is an audio sin to use a pre-exhisting box and put different drivers in it, because from what i read you start with a driver then the box and then power them, if i am incorrect please correct me. Knowing what i do now after the past few years, if i had known about Bassboss, i would have bought a system from them. I would like to use some Faital Pro 18s to build my own subs, but when it comes to designing a box for them i feel as if i am in over my head, and i have not been able to find box designs online for them. I do own the necessary tools and am willing to buy what i need to build boxes if i need to. Something along the dimensions of the bassboss SSP218 would be alright, but no bigger. What should i expect from the pictures below? are they accurate? Any questions, comments, tips, suggestions, or point me in the right directions would be greatly appreciated, i am a sponge and only want to learn more   :D . I apologize in advance for peppering this paragraph with questions  :-\.
Spaces between lines is a VERY NICE THING.  It makes it MUCH easier to read and understand.

To be honest-I could not read through your post-without a lot of "effort".  So I did not.

Any modeling program is based on a number different different assumptions and the accuracy of the data that is put into it.

The honest answer is "Your milage will vary".

And if you expect the end result to measure close to the predictions-then you will be sadly mistaken. 

I have never seen a woofer measured response even come close to being as smooth as that is shown in the models.

Models are used for designers to get certain ideas-not to be real accurate-except in some parts of the model.
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Ivan Beaver
Danley Sound Labs

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Aaron Weidner

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Re: How accurate is...
« Reply #2 on: August 09, 2014, 01:01:41 pm »

Spaces between lines is a VERY NICE THING.  It makes it MUCH easier to read and understand.

To be honest-I could not read through your post-without a lot of "effort".  So I did not.

Any modeling program is based on a number different different assumptions and the accuracy of the data that is put into it.

The honest answer is "Your milage will vary".

And if you expect the end result to measure close to the predictions-then you will be sadly mistaken. 

I have never seen a woofer measured response even come close to being as smooth as that is shown in the models.

Models are used for designers to get certain ideas-not to be real accurate-except in some parts of the model.

Thank you for the response. I have edited my initial post and hope it is now easier to read. I also thought that it looked a little to good to be true. Is the software used to get a baseline and then trial and error building afterwards? What hardware and software is used to measure frequency responses?
« Last Edit: August 09, 2014, 01:15:40 pm by Aaron Weidner »
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Ivan Beaver

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Re: How accurate is...
« Reply #3 on: August 09, 2014, 01:15:23 pm »

Thank you for the response. I have edited my initial post and hope it is now easier to read. I also thought that it looked a little to good to be true. Is the software used to get a baseline and then trial and error building afterwards?
The line spaces are supposed to be AT THE END of sentences-NOT in the middle.

It is better-but still does not make logical sense.  Sorry.

All prediction software is a guideline to help you and for you to use YOUR knowledge to come to the final result.
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Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Barry Singleton

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Re: How accurate is...
« Reply #4 on: August 09, 2014, 01:16:50 pm »

  Ivan I don't think many people type like this. When I post on this and one other site it often bunches all the text together like this and I have to go to preview post, and then go back and seperate it all back out which is a big enough pain that I rarely post on these sites. It's just not worth the time it takes to attempt to make it readable.

Barry.
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Aaron Weidner

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Re: How accurate is...
« Reply #5 on: August 09, 2014, 01:23:52 pm »

I dont understand how its not readable or logical so i shortened it for people who have no need or care for a more personalized version.

I found out that I had 2 different drivers in my subwoofer enclosures.

Would there be any adverse effect from having two different drivers in the same box?

Normally you start with a driver then the box and then power them if I am incorrect please correct me.

Is subwoofer design modeling software reliable?

More specifically, how accurate is WIN ISD compaired to other programs?

What other programs are their?

What should I expect from the pictures shown?

Any questions, comments, tips, suggestions, or point me in the right directions would be greatly appreciated, I am a
sponge and only want to learn more.
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Paul G. OBrien

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Re: How accurate is...
« Reply #6 on: August 09, 2014, 11:14:28 pm »

Quote from: Aaron Weidner

I found out that I had 2 different drivers in my subwoofer enclosures.

Would there be any adverse effect from having two different drivers in the same box?
Two different drivers in a single dual driver enclosure would be bad, but while having two different drivers in separate enclosures isn't ideal from a system perspective it's not necessarilly the end of the world if those drivers offer similar performance. It is not uncommon for manufacturers to change drivers in enclosures that have been in production for some time, sometimes it is done to increase performance but it is also done if the previous driver was discontinued or if proved to be unreliable.

Quote from: Aaron Weidner
Normally you start with a driver then the box and then power them if I am incorrect please correct me.
No,, the right way is to design a box that delivers the performance you want and then find a driver that works in it.

Quote from: Aaron Weidner
Is subwoofer design modeling software reliable?

More specifically, how accurate is WIN ISD compaired to other programs?
In he big scheme of things a reflex enclosure is a pretty simple speaker so yes you can trust that the software isn't totally lying to you, but it may not be telling you he whole story either. This software assumes the TS specs for the driver are accurate and that is usually the case for products from major manufacturers, but in most cases these are small signal specs and system(driver and box) performance can vary a little or a lot at higher drive levels. To that end you should download and use the Pro version(WinISD Pro) because it also simulates driver excursion, port air velocity, and the effects of low and high pass filters... all of which become important at higher drive levels and will affect your design and how much power it will handle.

« Last Edit: August 09, 2014, 11:23:01 pm by Paul G. OBrien »
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Aaron Weidner

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Re: How accurate is...
« Reply #7 on: August 09, 2014, 11:43:51 pm »

Two different drivers in a single dual driver enclosure would be bad, but while having two different drivers in separate enclosures isn't ideal from a system perspective it's not necessarilly the end of the world if those drivers offer similar performance.
No,, the right way is to design a box that delivers the performance you want and then find a driver that works in it.
In he big scheme of things a reflex enclosure is a pretty simple speaker so yes you can trust that the software isn't totally lying to you. The software assumes the TS specs for the driver are accurate and that is usually the case for products from major manufacturers, but in most cases these are small signal specs and system(driver and box) performance can vary a little or a lot at higher drive levels. To that end you should download and use the Pro version(WinISD Pro) because it also simulates driver excursion, port air velocity, and the effects of low and high pass filters... all of which become important at higher drive levels.

Thank you very much!! I didn't realize i did not put pro. I'm using WinISD Pro Alpha currently. Im still trying to understand everything it is showing me with the different graphs. Im having some confusion when it comes to max power and cone excursion with my current boxes. The box construction is limiting me on driver selection due to cutout and mounting dimensions. I will post some of the other graphs and my questions tomorrow if that is alright? Im out of time tonight.
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Ivan Beaver

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Re: How accurate is...
« Reply #8 on: August 10, 2014, 12:20:30 pm »

Thank you very much!! I didn't realize i did not put pro. I'm using WinISD Pro Alpha currently. Im still trying to understand everything it is showing me with the different graphs. Im having some confusion when it comes to max power and cone excursion with my current boxes. The box construction is limiting me on driver selection due to cutout and mounting dimensions. I will post some of the other graphs and my questions tomorrow if that is alright? Im out of time tonight.
The max power is the point at which the coil "burns".

The max excursion is the point at which the cone/suspension etc will be damaged.

You can easily have one without the other-depending on the freq and the tuning of the cabinet.

There are no "one size fits all" answers.
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Ivan Beaver
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Aaron Weidner

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Re: How accurate is...
« Reply #9 on: August 10, 2014, 01:03:39 pm »

The max power is the point at which the coil "burns".

The max excursion is the point at which the cone/suspension etc will be damaged.

You can easily have one without the other-depending on the freq and the tuning of the cabinet.

There are no "one size fits all" answers.

Ah ok, that makes sense.

I thought that max power was showing how much power the speaker can handle at a given frequency without exceeding xmax.

So, when looking at max excursion, the line being drawn is the drivers excursions at those frequencies?

The objective is to try and keep that line from passing the drivers xmax?

Is the excursion graph equal in its increments or is it calculated some other way?

I ask because even the driver that comes with the box is over 8mm xmax in its operating frequency.
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Re: How accurate is...
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