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Discussion Starter #1
I have a couple of questions to help me better understand what I am looking at in WINisd.
Transfer function magnitude graphs for two different drivers tuned to 16Hz.:

1. Is this essentially the modeling of the anechoic response curve?
2. Where does room gain start to kick in? I seem to remember 30Hz, but I'm not sure.

I found the following post by TheEar (thanks to Mike C.) this morning.
Correct,the drivers sound almost too close.Even the MJ-18`s sounds quite close to the LMS-Ultra/Acoupower units.

Only when pushing them,will the more linear and longer excursion of a LMS/Acoupower start to clearly show.

Not to say they sound exactly the same,they do not. But are close,very close.
Is there a 'rule of thumb' I can apply to "pushing them" or is this strictly a trial and error thing? I am guessing this is where Klippel or Dumax tests would be useful (if one knew how to interpret them)??

Thanks all for your help so far.
 

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1. Is this essentially the modeling of the anechoic response curve?
yes
2. Where does room gain start to kick in? I seem to remember 30Hz, but I'm not sure.
No rule of thumb here, no room is like the other...but the smaller the higher it begins. 30 Hz is for a mid-sized room

Is there a 'rule of thumb' I can apply to "pushing them" or is this strictly a trial and error thing? I am guessing this is where Klippel or Dumax tests would be useful (if one knew how to interpret them)??
To my understanding "pushing" is when the driver is at the onset of becoming non linear.
 

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Discussion Starter #3
Cool. So my 20' x 11/20' room would probably fit into the midsize category, maybe small.

To my understanding "pushing" is when the driver is at the onset of becoming non linear
Which would be somewhere around Xmax? Depending, of course, on how accurate the manufacturer's specs are... Hmmm.
 

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Which would be somewhere around Xmax? Depending, of course, on how accurate the manufacturer's specs are... Hmmm.
Most drivers are not linear to rated xmax, sadly. The only way to tell if a driver actually is linear within a specific range is via actual testing.
 

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A lot of this gets over analysed. All any modeling program can do is give a ball park idea of what to expect. Linearity, distortion, compression, panel resonance, etc are all extremely important when talking about critical listening as in music reporduction, but way to much is of this is focused on for a HT environment. Below is an example. I know what this graph "sounds like" because I built it. An IXL-18 in 12 cu.ft. tuned to 16 hz with three 4 inch ports.

My IXL.JPG

I can ship this sub away and have it tested. There will be graphs of distortion, port compression, frequency response, etc. showing how a SDX15 or a LMS18 is superior to my IXL-18. Yet when a canon blast goes off at 120 db at 20 hz and the whole house shakes, it's nothing but pure pleasure on peoples faces. All you need to do to build as great HT sub is pick a decent driver and stay within the manufacturers recommendation for Xmax and power handling. Then sit back and enjoy the experience. For the majority of people it's what it's all about.
 

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Discussion Starter #8
Mike. If it were just HT, I would not be so picky, but I am using this system for critical listening as well so I want clean bass for music.

Playing with models, for music at levels of 75-80db with maybe 95db peaks, any of the drivers I have looked at are going to be at 50% or less of their Xmax and way below max power. I don't know how linear distortion works, but I would imagine that there will be points of excursion where, beyond that point, distortion starts to rise more quickly. I would hope that most drivers are reasonably linear for the first 50% of their travel, but I have no idea.
 

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With your post showing two different drivers tuned to 16Hz, I assumed you were referring to HT. For music applications the only thing you can do to be guaranteed the results you're looking for is go with what has been proven. I would think it's safe to say that using a sub at 50% or less of its capabilities is within the linear range. There will be small differences between subs at those levels that can be seen on a graph, but if you can't hear any differences, there would be no point in persuing it further.
 

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There will be graphs of distortion, port compression, frequency response, etc. showing how a SDX15 or a LMS18 is superior to my IXL-18.
Is this at the same SPL?:scratch:
 

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Discussion Starter #11
For music applications the only thing you can do to be guaranteed the results you're looking for is go with what has been proven. I would think it's safe to say that using a sub at 50% or less of its capabilities is within the linear range.
Yup, Guaranteed costs. Thinking further I suspect linear performance of a driver is mathematically related to the slope of the BL curve. If a BL curve has a flat section, that is the area where the driver operates linear-distortion-free. I need to do some searching/reading to confirm this.

The reason I mention it is that I have seen BL curves that look like an inverted U so there would be some distortion at all levels of excursion.

I know, too geeky. :coocoo:

There will be small differences between subs at those levels that can be seen on a graph, but if you can't hear any differences, there would be no point in persuing it further
From what I understand, 2db down in the most sensitive area of hearing is noticable but subtle. At 20Hz I suspect that it would be very very hard to hear.

Another thought. I have huge room gain centered at 52-56Hz loosing a db or 2 in that range might actually be a good thing. :devil:
 

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Discussion Starter #13
More questions:
Here are two drivers modeled at 16Hz in similar size enclosures.


1. It is my understanding that you want a curve that is flat above say 30Hz, and then rolls off slowly as seen in the top curve in the graph above. Is this correct?
2. At what point do differences or deviations from the ideal curve become noticable? I would think that at 30Hz, two db down would be hard to hear, but what about 4db as with the lower curve above?
 

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Discussion Starter #15
:scratch:

I thought the idea of modeling is to be able to both choose the optimum enclosure for a driver and to be able to compare and choose the optimum driver for your particular application.

I know that room gain will be different from one room to another, but I would think that for a given size gain plots would be similar such that you can make some reasonable assumptions said room gain and matching to driver response.

I also understand that you can EQ, but that it should be a last resort as it can introduce as many or more issues as it resolves.
 

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Not to put a kink in your designs, but I wouldn't design around room gain for providing low frequency extension. Boundary gain, yes, but not room gain. You want to be somewhere inbetween. Also keep in mind that WinISD is providing ground plane predictions...throw things in a corner and you might need to take polars into account as well. I have also found that the shape of the rolloff matters just as much as where the F3 ends up...
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Discussion Starter #18
model the Adire Audio Shiva sub in 2 cu.ft. sealed. Now compare that modeled frequency response to Waynes in room
Actually, it looks a lot like Wayne's in room response. If you smooth Waynes trace from 40Hz down, its a very close match. Hmm.

I did a bunch of reading on room gain last night, and it seems that there is dissagreement on whether or not it exists other than in a perfectly sealed room (perfect theoretical example).

All this has me wondering what the anechoic response of my current sub is.

Not to put a kink in your designs
More like scribbles on the back of a napkin. Never having designed any sort of speaker before I do not claim to know what I am doing here.

MikeC. I do understand the acoustic effects of rooms. If you look at this thread you will see that I have spent a lot of time looking at my room in particular.

What I do not understand, is when modeling diferent drivers, when do diferences in response between drivers become big enough to indicate issues? When I look at the two drivers modeled in the last graph I posted, I see one driver with 4db less response than another at 30Hz. To me, that dosn't look good. BUT, if the two drivers were to play like their theoretical curves, would that 4db actally be noticable??

I also understand that this is only one parameter and that I should look at all the informationWINisd provides me before making a decision, but I do need to make sense of what each parameter on its own tells me. I need to have some sense of what is meaningful and what is not.

I hope I am making some sense here. Maybe I'm just a little :coocoo:

:bigsmile:
 

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A lot of us DIYers use as much testing and modeling as we can find in an attempt to produce a flat frequency response from the driver box combination. Then we apply the driver box combination to the actual listening room only to find that the flat response curve we designed into the driver box combination has turned into a response curve, during actual operation with peaks and valleys that are very noticeable during listening tests. So our final remedy, to again produce an in-room flat response curve, is to apply electronic equalization or speaker placement or a combination of the two to achieve that flat response we think will produce a pleasing sound resembling the original recorded sound spectrum and material.
It has been my experience that in-room response IS boosted at the lower end of the response curve, and THAT boost varies depending on several factors including box placement and type.
Your original inquiry about the two different response curves in the first graph wouldn't necessarily sound (different) but would be louder or softer depending on the specific frequency, possibly with NO noticeable difference in sound quality.
I don't think any of us DIYers would admit to having this speaker building and sound reproduction down to an exact science . . . . it's all still experimental and subjective and in my opinion still an art form.
 

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Discussion Starter #20
Your original inquiry about the two different response curves in the first graph wouldn't necessarily sound (different) but would be louder or softer depending on the specific frequency, possibly with NO noticeable difference in sound quality
Hmm, so 3-4db down should be noticable, but subtle. I wonder if I could possibly simulate this in my room with a single test tone to see what a 3-4db change sounds like.
 
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