Could this sub work at 20hz ok?

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cameron paterson

Senior Audioholic
Could anyone please send me to a sub that would work better than this tuned @ 20hz?
 
TLS Guy

TLS Guy

Audioholic Slumlord
Could anyone please send me to a sub that would work better than this tuned @ 20hz?
We have been over this before with you, but you never seem to understand. You do NOT pick a tuning frequency out of thin air. Tuning frequency is dictated by the T/S parameters of the driver. And once more, the tuning frequency is not the low frequency the sub will operate to.

The best guide as to how low a frequency a sub will output is the fundamental resonant frequency of the driver, Fs. In practical terms the f3 point of the driver will be somewhat above that for a ported enclosure, and far above it for a sealed one. However a sealed enclosure can be equalized and a ported one can not. Although equalization is limited by the power handling of the driver and its excursion limit.

The driver you selected has an Fs of just over 26 Hz, so if you model it, you will find that it will probably have an f3 around 30 Hz.

It is the electromechanical specifications of the driver that determine this. If you measure the impedance of a driver in a ported box, you get a trace like the one below.



The tuning frequency is at the bottom of that saddle of impedance. You DO NOT get to determine that, the design of the driver does.

However that tuning frequency is NOT an indication as to how low the driver will play, that is actually always BELOW the tuning frequency.

So in your search for a driver to play down to 20 Hz, you need a driver with an Fs a little below 20 Hz and a Qts in the 0.35 to 0.4 range.

But you have to model it, and the low point of the saddle of the impedance curve has to be the tuning frequency. If you try and make it something else then the sub in fact will not perform well, and not go as low as it would if the tuning frequency was correct as determined by the T/S parameters of the driver.
 
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cameron paterson

Senior Audioholic
Well it doesn't help when I can''t get my winisd to work.
 
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cameron paterson

Senior Audioholic
This sub says it works in a 4.2ft3 box tuned at 22hz.
 
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cameron paterson

Senior Audioholic
What about the Dayton I just posted about? It says 4.2ft3 tuned at 22hz. Here it is:

 
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cameron paterson

Senior Audioholic
Could someone please model that Dayton sub for me at 4.2ft3 and tuned at 22hz? I tried the WinIsd 3 times and can't figure it out! Thanks for your time guys!
 
TLS Guy

TLS Guy

Audioholic Slumlord
Here is your model.

This driver is essentially for sealed application. It does model for a vented enclosure with a port length that is just acceptable.

The cabinet is just over 4 cu.ft, but you need to add driver volume baracing and port volumes to that number.

The F3 is just under 27 Hz, it is slightly lower than the driver Fs of 29 Hz. That is because it is a high Qt driver. That will limit the sound quality for a ported design. It would I fear not have a tight enough bass for my tastes. I really put an absolute limit of a Qts of 0.45 and preferably below o.42 for ported application.
For the record I will state once more that this driver was not really designed with a ported application in mind. Its T/S parameters are optimized for sealed application. It has high power handling and a large xmax to allow for the bass equalization required. In other words it is a brute force driver.

So you should be looking for a driver with Fs as close to 20 Hz as you can get and Qt in the range I indicated. This driver failed on these two counts and produced the expected results.
 

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TLS Guy

TLS Guy

Audioholic Slumlord
The trouble is you do not know how to select drivers, and I have to admit that takes experience. The Dayton alignments in my experience are generally correct.

That last driver you quote, has a low Fs, and is ideal for a ported enclosure. However it has a lighter cone and is a significantly more sensitive driver and low Qts at 0.32.
So an F3 of 30 is what I would expect, and you can not force it to play lower. There is an absolute inverse relationship between bass extension and sensitivity.

However that driver would likely be a very good driver and produce very high quality tight bass.

You are making a massive mistake concentrating on just one aspect of a sub and that is bass extension to the exclusion of everything else. In fact that driver would produce very high quality bass most likely.

You need to purchase a good modelling program and also purchase a textbook, on speaker design, like the Audio cookbook for instance.

You are currently acting like the blindfolded man throwing darts.
 
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cameron paterson

Senior Audioholic
Well this 15" sub asks for everything you mentioned.


Would this work in 4.25ft3 ported, tuned to 22hz?

I cant get Winisd to work so I am in the dark there.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Well this 15" sub asks for everything you mentioned.


Would this work in 4.25ft3 ported, tuned to 22hz?

I cant get Winisd to work so I am in the dark there.
That is a high sensitivity driver. I doubt it will play that low.

For what you are doing this is the driver you need, that will make a really good sounding practical sub of reasonable dimensions. I did this design back in February and plan to use except using two drivers, for our family room system.

This is just the sort of plan you need to make a really nice sounding sub, that will sound excellent. You can build it with confidence. It is just what you are looking for.
I'm not going to sit here modelling drivers all night the you drag up from the back of your neck.

So if you build this, I know you will be very happy, especially as the tuning frequency is 18 Hz.

I guarantee that you, or no one else will tell 24 Hz from 20 Hz.

So please report back when you have built it.
 

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cameron paterson

Senior Audioholic
Why would the first 15" Dayton I mentioned not work at 4.2ft3 tuned at 22hz? Does parts express just make up a box off the top of their heads? They said it was modeled with Bass Box 6 pro high fidelity. And you are wrong that a sub with high xmax should only be used as a sealed subwoofer.
 
highfigh

highfigh

Audioholic Slumlord
Why would the first 15" Dayton I mentioned not work at 4.2ft3 tuned at 22hz? Does parts express just make up a box off the top of their heads? They said it was modeled with Bass Box 6 pro high fidelity. And you are wrong that a sub with high xmax should only be used as a sealed subwoofer.
Parts Express uses basically the same software as TLSGuy- they don't make this up, but you need to understand that the driver doesn't give a crap about what you want it to do, it can only do what its materials and physical characteristics allow. That means the mass of the moving parts, the compliance of the suspension and electrical characteristics determine the box, not the other way around or by your choice. Ever seen a car that was bouncing as it went? That's because the compliance of the shock absorbers was wrong for the weight of the car because they were old and no longer working the way they should or because they were a bad choice. The opposite side of that is noticeable if you have been in a car that made you feel every little bump as if it had no springs or shock absorbers- they were wrong for the weight of the car and its occupants.

Designing a box is a series of compromises- look at the response in Mark's model, then look at the electrical power handling- if you make the box too large, the power handling goes out the window, making it useless in real world applications. In his model, that spec is roughly 150W between 20Hz and about 38Hz- that should be enough.
 
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cameron paterson

Senior Audioholic
This sub has a FS of 18.8hz .


And it says to put in a ported box thats 7.5ft3 tuned at 23hz. Once again shouldn't parts express be right about their box size? They said they used bass box pro...
 
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cameron paterson

Senior Audioholic
And about that 15" again that says it should go in a 4.2ft3 box tuned at 22hz. That box should be fine right? Why would parts express be wrong?
 
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