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Discussion Starter #1
Do TS parameters mean much for SPL subwoofers. The reason I ask is because I was always under the assumption that TS parameters were small signal parameters. How do those numbers hold up when you are feeding a sub with 5Kw?
 

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Discussion Starter #3
That is kinda funny but I think I'm right. The parameters are taken using small low level signals. There are also large signal parameters. But I'm focusing on the question. How do you predict the behavior of a subwoofer using TS parameters when dropping massive amount of power into it?
 

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How do you predict the behavior of a subwoofer using TS parameters when dropping massive amount of power into it?
Skills. You need to come up with a model that takes into account both the mechanical movement and the thermal system involved. I haven't seen enough on thermal models and tests to say anyone is right (or close, especially at very high power levels).

And yes, they are small signal parameters as they are assumed to be constant (not position dependant). Usually a very small signal is applied - less than 1V.
 

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Not really... the only thing I really look at is BL^2 / RE and MMS :) I have found direct correlations between those and peak SPL output.

For example... my Monster sub prototype has double the motor force (BL^2/RE) of my Nightshade -- it literally has nearly 3dB more peak SPL output. Even with a much higher MMS (I think the lower thermal compression made up for the MMS).

On a given woofer like the Nightshade - going from a stronger (heavier) paper cone to a bit thinner (lighter) cone yielded a direct 0.4 dB gain at equal power.

Maximum excursion is also a consideration... but it doesn't need to be linear. A 42mm coil is louder than a 50mm and a 56mm in our Nightshade regardless of power input -- we use the longer coils only for better "daily" power handling and low frequency output.

We use a 42mm tall coil in the Monster where "linear" x-max by overhang is only 8.5mm but one of them got up to 154.9dB in my Jeep... it was "throwing" 30mm easily despite a low linear x-max.

So... basically... most T/S specs and even excursion specs don't mean a whole lot in raw SPL output.
 

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Thiele/Small parameters are just as useful for SPL subs as they are for any other driver as they decribe certain physical characteristics of the driver. It is not enough information to describe the driver in full, but does allow us to identify drivers that might be more useful than others.
 

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Thiele/Small parameters are just as useful for SPL subs as they are for any other driver as they decribe certain physical characteristics of the driver. It is not enough information to describe the driver in full, but does allow us to identify drivers that might be more useful than others.
Yes, but unfortunately even posting what you wrote on some of the other more SPL-oriented forums still won't deter people from chosing one sub over another because of one or two simple parameters.

As Jake pointed out, he has seen through testing that Mms alone has an impact on the SPL ability of a subwoofer with everything else remaining constant, even though by common belief Mms doesn't matter. Unfortunately too many people still rely on Xmax and BL figures to determine what driver will produce the most SPL for their application. Vas and Mms are often overlooked, but like you and Jake said (and I agree) that looking at a few T/S parameters isn't the only thing to look at when determining whether or not a particular driver will produce the most SPL in your vehicle. Box size, actual power available, and a clearly defined goal (broad-band high SPL or "I don't care as long as it hits hard") are often overlooked.
 

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We use a 42mm tall coil in the Monster where "linear" x-max by overhang is only 8.5mm but one of them got up to 154.9dB in my Jeep... it was "throwing" 30mm easily despite a low linear x-max.
But you know why that is, right? It doesn't mean that Thiele/Small parameters are any less useful.

So... basically... most T/S specs and even excursion specs don't mean a whole lot in raw SPL output.
Of course Thiele/Small parameters don't tell you frequency response vs amplitude. They're still very useful; as useful as they are for any application.


Yes, but unfortunately even posting what you wrote on some of the other more SPL-oriented forums still won't deter people from chosing one sub over another because of one or two simple parameters.

As Jake pointed out, he has seen through testing that Mms alone has an impact on the SPL ability of a subwoofer with everything else remaining constant, even though by common belief Mms doesn't matter. Unfortunately too many people still rely on Xmax and BL figures to determine what driver will produce the most SPL for their application. Vas and Mms are often overlooked, but like you and Jake said (and I agree) that looking at a few T/S parameters isn't the only thing to look at when determining whether or not a particular driver will produce the most SPL in your vehicle. Box size, actual power available, and a clearly defined goal (broad-band high SPL or "I don't care as long as it hits hard") are often overlooked.
OK. But what does any of this have to do with how relevant Thiele/Small parameters are for the application? Misuse of statistical data never invalidates the potential for use of said data.
 

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OK. But what does any of this have to do with how relevant Thiele/Small parameters are for the application? Misuse of statistical data never invalidates said data.
I never said that the data was invalid. I said that people tend to look at the wrong one's (or just a few and not enough of the others) when analyzing drivers for their non-defined goals and/or applications.
 

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Yeah, that was very badly worded. Edited it accordingly.
 

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Discussion Starter #12
WOW! I step away for a couple days and low and behold someone responds. Thanks for all the useful information. I posed this question because I know many enclosure design programs base their design off TS parameters. As said before, I know the behaviour can be predicted when using low level signals but when using really high levels things change. I want to be able to design an enclosure that will work well with the specific sub of choice and from what I'm understanding, the TS parameters cannot really in the design of the box. Am I understanding this correctly?
 

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I forgot to add one more... CMS - also useful to an extent in SPL.

Although, still doesn't tell you much without knowing CMS vs. excursion. I've tested equal at-rest CMS drivers and one is substantially louder than the other as one has a linear compliance and the other tightens up. Besides the suspension they were otherwise identical.

So you have to have a the same "type" of suspension to use CMS as a comparison figure.

The most compliant (softest) suspension that I can get away with without having the driver break apart is the loudest in all my testing -- I am not a fan of overly stiff suspensions.

I am going to further my testing into the mass correlation by building a driver with equal BL^2 / RE to the Monster but over 100 grams less moving mass in the coil.
 

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Discussion Starter #14
I forgot to add one more... CMS - also useful to an extent in SPL.

Although, still doesn't tell you much without knowing CMS vs. excursion. I've tested equal at-rest CMS drivers and one is substantially louder than the other as one has a linear compliance and the other tightens up. Besides the suspension they were otherwise identical.

So you have to have a the same "type" of suspension to use CMS as a comparison figure.

The most compliant (softest) suspension that I can get away with without having the driver break apart is the loudest in all my testing -- I am not a fan of overly stiff suspensions.

I am going to further my testing into the mass correlation by building a driver with equal BL^2 / RE to the Monster but over 100 grams less moving mass in the coil.
Great info! Now, how do you go about making an appropriate SPL/StreetBass enclosure for the Monster?
 

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2.5 - 3.5 cubes works great for box volume... if you want a mix of both SPL numbers and response that is acceptable for daily you want to tune to 35-40 Hz.

For maximum SPL my tuning is nearly 50 Hz as my vehicle peak is 50 Hz.

Same enclosure specs work for the Nightshades.
 

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Hey Porky,
Sorry for my '*******-ish' first reply to your post. I guess reading the question wrong + some of my own ignorance about what you were saying caused me to make a fool of myself. :p

I'll add some more to that ignorance here --> If there are "small" signal parameters and "large" signal parameters, is it possible to measure said subwoofer under "large" signal parameter conditions to get a better idea of the performance of the sub at that level?? Like instead of Thiele-Small you get Thiele-Large? :laugh::laugh: I mean, there has to be a more scientific way to go about it that just building 50 different boxes or trying 50 different subs in a box you've built... right?
 

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Discussion Starter #17
Hey Porky,
Sorry for my '*******-ish' first reply to your post. I guess reading the question wrong + some of my own ignorance about what you were saying caused me to make a fool of myself. :p

I'll add some more to that ignorance here --> If there are "small" signal parameters and "large" signal parameters, is it possible to measure said subwoofer under "large" signal parameter conditions to get a better idea of the performance of the sub at that level?? Like instead of Thiele-Small you get Thiele-Large? :laugh::laugh: I mean, there has to be a more scientific way to go about it that just building 50 different boxes or trying 50 different subs in a box you've built... right?
Hey dude, I didn't take it as being rude. I actually found it pretty amusing. Now thinking about it Thiele_large is funny as hell too. Mr Thiele would love to know that we are having a discussion about his large parameter.

I don't know if I am asking the right question or not. It seems to me like the parameters mean nothing in box design(for spl and streetbass). FI does not list their parameters, they will just tell you to build to their spec. DD says build a big box and use 16 square inches of port area per cubic foot of box. It doesn't sound scientific but it seems to work. Maybe Jacob could chime in here and enlighten me.

One more question: An 15" SPL sub with a Vas of .88 cubic feet. That seems extremely low for a sub. Does that make sense. If I measured the sub correctly, what benefit do a really low Vas serve?

Thanks
 

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Low VAS is a result of a stiff suspension for SPL - you have to have a certain amount of stiffness so the sub doesn't blow apart. You don't want TOO much stiffness or you won't be able to get the sub moving and you'll simply lose SPL even if you try to jam more power into the driver.
 

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Reading the book by David Weems gives you a better understanding of what the parameters are for. I always understood that these were used to compare speakers side by side first, and determine enclosure type and volume second. With that, fine tuning the box to your personal preference was a separate issue. I also thought that it was a constant thru the measurements and providing the surroundings did not change the outcome was similar at large volumes.

This is still available at
Amazon.com: How to design, build, & test complete speaker systems…
 
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