I'm looking into buying a 15" BTL fully loaded. My question is, can I tune my box lower than the recommended fs frequency? If I did, would it affect the sub in a bad way? Poor sound quality? Just wondering if there would be a negative effect on the sub. I think the fs frequency on the 15" BTL is 37.9. I like low frequency hip hop and want to tune my box

low like 30 hz (at the lowest 25 hz). Is this not a good idea, what would be the result?

It would be fine playing in a box tuned below it's FS, try a box that is at 34-32hz.

if your CDs contain info that goes below 30Hz a 25Hz tune would be pretty sweet, though you would probbly lose overall output

Ok, I get it. I would be losing output. Basically becoming less efficient. At least I wouldn't be damaging the sub. Thanks for the help.

Fs is not a "recommended" frequency. It is the resonant frequency of the driver in free air.

It is definitely OK to tune below this frequency. If you go too low, you can get dips in the frequency response, but 32-35 Hz for the BTL works great.

Like everyone else said, you should be fine. If you are not using a box program, a nice FREE (well, it is pretty nice for free) program is WinISD. Google it and get it. Input your driver parameters. Then load your driver and begin working!

Yyou can model basic enclosures, watch your output, impedance, relative phase, excursion with given input relative to frequency, port velocity, etc. It's a pretty useful tool and is much better than most free box programs.

Here read this:

BTL Enclosure Recommendations - SSA Car Audio Forum

Tuning to 30Hz wont be a problem at all since it is recommended, I just wouldnt go down to 25hz unless you listen to a lot of pipe organ music or chopped and screwed tunes.

Tuning lower than recommended will yield output in the higher frequency ranges but give it the ability to dominate the lows and vice versa as well.

Like everyone else said, you should be fine. If you are not using a box program, a nice FREE (well, it is pretty nice for free) program is WinISD. Google it and get it. Input your driver parameters. Then load your driver and begin working!

Yyou can model basic enclosures, watch your output, impedance, relative phase, excursion with given input relative to frequency, port velocity, etc. It's a pretty useful tool and is much better than most free box programs.

IIRC Fi Woofers don't model to well in WinISD.

You will be fine as long as your SSF is set right.

I foresee a blown BTL. SET that subsonic right under box tuning.

nope, subsonic filter is dependent upon an install, not sub in general.

I've done setups where the subsonic needed to be set HIGHER than the tuning frequency and i've done setups where NO subsonic was needed at all tuned in the low 30s.

You set the subsonic filter by mechanical means using test tones.

You don't want the sub bottoming out so don't let it. Set it at the limit you want to.

Maybe you want pure quality so u set it to prevent the sub from jumping out of it's xmax rating or u just want plain loud and you would set it to right before it starts bottoming out.

Subsonic filter is a preference filter like a low pass filter but is more important than a LPF because it has safety purposes as well. Adjust it by install because going by a rule of thumb can still allow a sub to bottom out or reduce potential out of your install.

Also, box modeling programs do NOT work with car audio. Due to how a car is laid out, a program cannot even attempt to accurately tell you anything right... and depending on what you are using it for, even calculating port tuning can be WAY off if competing!

Box modeling programs may work a lot better if your setup is installed in an environment with the least obstacles in the music room which means in an environment with the least "room gain" and attractions that can influence how the sound is reproduced.

these software programs can't account for things like that and anything that can cause a gain in pressure or a room that resonates at a or certain frequencies or one that is full of obstacles will have acoustical properties that will change what any box modeling software will tell you.

Shizz --

For setting a SSF through "mechanical means using test tones". What is the best way to do this? What do you listen / watch for?

Also, box modeling programs do NOT work with car audio. Due to how a car is laid out, a program cannot even attempt to accurately tell you anything right... and depending on what you are using it for, even calculating port tuning can be WAY off if competing!

Box modeling programs may work a lot better if your setup is installed in an environment with the least obstacles in the music room which means in an environment with the least "room gain" and attractions that can influence how the sound is reproduced.

these software programs can't account for things like that and anything that can cause a gain in pressure or a room that resonates at a or certain frequencies or one that is full of obstacles will have acoustical properties that will change what any box modeling software will tell you.

Actually, this couldn't be further from the truth.

Vance Dickason did a complete experiment with this (as written up in his 6th edition) by measuring the complete T/S and enlclosure parameters of a few subwoofers in and out of vehicles. He also placed them in many positions. He could not get changes in the box parameters of more than 5% or so..... In other works, tuning, Q, impedance all stayed the same.

The biggest difference in a car is cabin gain, but that doesn't alter the original box behavior/parameters in the least....

FI drivers are no different than any other drivers, if you have accurate T/S parameters, you can get predicted response just as you can with any other driver....

Edited June 11, 201015 yr by 95Honda

Geez Mike I only have the 5th edition

maybe i should say not get consistent results with the software...

I can tell you plenty of setups where the peak note was different than the predicted note, impedance rise was never right, actual amp power wouldnt be right either, etc...

Here recently for competition, I've seen the software is impossible to accurately get port tuning right.

Example- box tuned to 43hz peaks at 39hz...

Subsonic filter is a preference filter like a low pass filter but is more important than a LPF because it has safety purposes as well. Adjust it by install because going by a rule of thumb can still allow a sub to bottom out or reduce potential out of your install.

errr, sort of, sounds like you almost understand the right use but it isn't at all based on preference but mechanical limitations of your driver. 10 minutes with any decent modeling software will help you understand this.

maybe i should say not get consistent results with the software...

I can tell you plenty of setups where the peak note was different than the predicted note, impedance rise was never right, actual amp power wouldnt be right either, etc...

Here recently for competition, I've seen the software is impossible to accurately get port tuning right.

Example- box tuned to 43hz peaks at 39hz...

Maybe you should just say that you have no idea how to use software, don't understand what the parameters actually mean and are just making up stuff based on limited experience. Just like the woofer is dumb and will only do what you tell, the same holds for the software. If you don't understand what you are inputting and do something incorrectly the results will of course also be incorrect.

My focus is more towards competition usage. Perhaps daily and competition differ when using modeling software.

What i do know is you cannot expect modeling software to accurately tell u things in the competition world.

the way how a vehicle loads and how a box is fired can change the tuning very easily and the way how a sub moves.

Depending on a daily setup, it can happen as well...

Of course competition is more extreme but i have witnessed it plenty of times where a box's specs do not equal what a program like WinISD says it should be doing... even as something as simple as port tuning.

Here is another example-

A buddy of mine had a box that was 2.1cuft NET with a 12"x9" port 56" long... WinISD says it would be tuned at ~47hz and peak, of course, higher than that...

His box peaked at 39hz and his car's resonance peak is at 46hz so not even cabin gain effected this scenario.

This was a box used for competition but could easily be used for daily so weird things happen...

It's pretty hard to miscalculate port tuning and the software can definitely be way off in the real world comparison.

It's not the software's fault... it's because once u drop it in an environment with lots of obstacles and different gains like a vehicle... it's not as accurate.

The whole point Vance Dickason made, installling the enclosure in an automobile did not change the tuning, Q or impedance in any signifigant way. It is cabin gain that really introduces the changes in response.

Additionally, there probably isn't anyone on here that has measured cabin gain accurately (including myself). This would require a refence source and accurate measuring equipment.

So when we are talking about changes in the few dbs or Hz, we are pretty much taking a stab in the dark when we blame it on anything but cabin gain.

There isn't anything magical about loudspeaker response. T/S parameters can accurately predict the response of a loudspeaker. These calculations have been refined over literally millions of man hours over the last few decades....

When I hear things like "you can't model these drivers" all that tells me is that when modeled either the response is missunderstood, or, they have just been modeled wrong or all the modeled parameters have not been taken into account (like group delay and phase magnitude).

This is also where a huge amount of the subjective sound quality of vented vs sealed debates stem from..... Or, more precisely, the missunderstanding of the whole subject...

Edited June 11, 201015 yr by 95Honda

Additionally, there probably isn't anyone on here that has measured cabin gain accurately (including myself).

I haven't, but JBL has Here's a plot of a dozen or so vehicles from Andy Wehmeyer;

http://farm4.static....0d155d5ac_o.jpg

When I hear things like "you can't model these drivers" all that tells me is that when modeled either the response is missunderstood, or, they have just been modeled wrong or all the modeled parameters have not been taken into account (like group delay and phase magnitude).

Unfortunately when people say "you can't model these drivers", they mean don't use the programs suggested enclosure and tuning. But people take the statement literally and think the drivers somehow defy physics and aren't capable of being modeled I recently tried to explain this in another thread; Win ISD parameters for BTL 15 - SSA Car Audio Forum

Also, box modeling programs do NOT work with car audio. Due to how a car is laid out, a program cannot even attempt to accurately tell you anything right... and depending on what you are using it for, even calculating port tuning can be WAY off if competing!

Box modeling programs may work a lot better if your setup is installed in an environment with the least obstacles in the music room which means in an environment with the least "room gain" and attractions that can influence how the sound is reproduced.

these software programs can't account for things like that and anything that can cause a gain in pressure or a room that resonates at a or certain frequencies or one that is full of obstacles will have acoustical properties that will change what any box modeling software will tell you.

Actually, this couldn't be further from the truth.

Vance Dickason did a complete experiment with this (as written up in his 6th edition) by measuring the complete T/S and enlclosure parameters of a few subwoofers in and out of vehicles. He also placed them in many positions. He could not get changes in the box parameters of more than 5% or so..... In other works, tuning, Q, impedance all stayed the same.

The biggest difference in a car is cabin gain, but that doesn't alter the original box behavior/parameters in the least....

FI drivers are no different than any other drivers, if you have accurate T/S parameters, you can get predicted response just as you can with any other driver....

Put a pair of btl 15's in a 2.5 cube ported box with very little port area as the box programs suggest and see how it sounds

It's going to sound like shit..and it's going to model 'fantastic'

Which is why we say..put them in X volume range..with Y port range..

Using what Winisd or any other box program 'suggests' for volume and port size isn't going to work so well..it has a LOT of issues trying to predict higher and higher motor force woofers..and it simply misses the mark.

If you look at it as just a reference point then it's fine. But using what is suggested works best...

another problem i see with these programs is changing port area doesnt influence the amplitude graph at all.

When one graph doesnt change, others won't follow either...

Impedance graphs are WAY off. It's too hard to predict impedance rise because even if the box was the exact size and Q as plotted, there are millions of ways to design the same volume box which will alter the impedance rise in an install anyway.

I just don't agree with you guys.

I have modeled many drivers similar to the BTLs over many years (mostly MTs) and I have never gone with a small box with a small vent, when I run the paramters of the early MTs I always ended up with large volume vented enclosures, never the "crappy small box with a little port" or sealed like I always hear will be modeled. Maybe it is because I know the programs well and have built many, many enclosures over the past 20 years and measured a fair share of them rarely getting results that were way, way off of the predictions. I just know from experience that you can model drivers, and if you know how to interperet the results, you can succesfully design something that meets your goals without surprises.

As far as system impedance (this isn't "impedance rise" as this incorrect term is always used) you know what determains a majority of it is the various resonances as a whole the system has. If the resonance points aren't changed, enclosure shape and proximety to nearfield items does little to change anything... This is always true unless you have a gross change in shape or something so extreme that is doesn't behave correctly at all in the first place.

I think too often in car audio where many people don't fully understand what is going on (I am defiently NOT refering to NDMstang here) and they fall into the "it just works that way" or it is some kind of magic BS... When in reality it isn't, in fact many things can be reliably predicted, again, if you know how to properly use the equipment at your disposal.

But hell, even back in the early 90s when friends of mine had MLSSA and IMP to measure, we used to build subwoofers and bring them into our audio meetings and measure them, hell Dan Wiggins used to build stuff and bring it in... And even back then, when we didn't have anything close to what we have now, we were still able to reliably design and build stuff. I just don't see how this has changed.

Anyway, we'll probably never agree on this, but that is OK, we are here to offer our different points of view.

This is all I have for this thread.

-Mike

I just don't agree with you guys.

I have modeled many drivers similar to the BTLs over many years (mostly MTs) and I have never gone with a small box with a small vent, when I run the paramters of the early MTs I always ended up with large volume vented enclosures, never the "crappy small box with a little port" or sealed like I always hear will be modeled. Maybe it is because I know the programs well and have built many, many enclosures over the past 20 years and measured a fair share of them rarely getting results that were way, way off of the predictions. I just know from experience that you can model drivers, and if you know how to interperet the results, you can succesfully design something that meets your goals without surprises.

As far as system impedance (this isn't "impedance rise" as this incorrect term is always used) you know what determains a majority of it is the various resonances as a whole the system has. If the resonance points aren't changed, enclosure shape and proximety to nearfield items does little to change anything... This is always true unless you have a gross change in shape or something so extreme that is doesn't behave correctly at all in the first place.

I think too often in car audio where many people don't fully understand what is going on (I am defiently NOT refering to NDMstang here) and they fall into the "it just works that way" or it is some kind of magic BS... When in reality it isn't, in fact many things can be reliably predicted, again, if you know how to properly use the equipment at your disposal.

But hell, even back in the early 90s when friends of mine had MLSSA and IMP to measure, we used to build subwoofers and bring them into our audio meetings and measure them, hell Dan Wiggins used to build stuff and bring it in... And even back then, when we didn't have anything close to what we have now, we were still able to reliably design and build stuff. I just don't see how this has changed.

Anyway, we'll probably never agree on this, but that is OK, we are here to offer our different points of view.

This is all I have for this thread.

-Mike

Fair enough, do what works well for you. I just won't condone anybody that buys our product to model it and use it..because it ends up a terrible tragedy of broken stuff because of stupidity.

Trying to get somebody to keep their packaging material and figuring out what a subsonic filter is...is simply hard enough as it is.

Fair enough, do what works well for you. I just won't condone anybody that buys our product to model it and use it..because it ends up a terrible tragedy of broken stuff because of stupidity.

I wouldn't condone it if I were you either, but the problem isn't in the software it is in the user. If you think you can hit the "easy" button and have it "design" the enclosure for you, you are wrong. You have to understand your goals, the environment, but most importantly what the software tells you.

Your analogy is perfect here. Just like a sub is dumb and it will do what you tell it, so is the software. It will do the EXACT calculation you tell it to do. If you mis-direct it your results will be poor. Shizzon's problem is obviously not at all understanding the software, the variables and his inputs.

what's hard about it?

If i design a box and input the specs of the box, tuning and T/S parameters of a sub in it and the software is way off, how is that my fault?