Autotuba measurements, plus shiva

[BassAwdyO]

John, how low is your EBS maelstrom tuned???

In my experience if you tune below 15hz there is no audible difference between sealed and ported enclosures of the same size.

An octave above tuning a port will be at ~-10db and hardly contributing anything. The sensitivity and group delay should be almost the exact same from there on up.

what is a sealed box other than a ported one with 0hz tuning(in other words a port with infinite airmass)

[rcw]

It is my opinion that most of what is talked about subwoofers is nonsense.
There is absolutely no physical basis for saying that bass reflex enclosures are "slow" and sealed ones fast, other than the fact that since most reflex systems have a greater setteling time people concluding therefore it must be audible therefore bad, there is no double blind study that I am aware of that has ever shown this.
The fact is that as shown by Floyd Toole, you can transform a slow one into a fast one by removing the room resonance causing the slowness.
It is also true that most so called fast sealed box subwoofers have considerable amounts of third harmonic distortion and d.c. offset caused second harmonic, not to mention flux modulation effects, and the subjective fastness is just that they are not in fact radiating enough power at the relavent frequencies to activate the slow sounding room resonances, and the so called lack of flabiness is in fact nought but good old 60Hz. punch region bass masquerading as low bass.

[johninCR]

Originally posted by BassAwdyO
John, how low is your EBS maelstrom tuned???

In my experience if you tune below 15hz there is no audible difference between sealed and ported enclosures of the same size.

An octave above tuning a port will be at ~-10db and hardly contributing anything. The sensitivity and group delay should be almost the exact same from there on up.

what is a sealed box other than a ported one with 0hz tuning(in other words a port with infinite airmass)

It's the Adire recommended enclosure for the original maelstrom for which, if I recall correctly, is tuned to 16hz. It's not on their site anymore.

Originally posted by rcw
It is my opinion that most of what is talked about subwoofers is nonsense.
There is absolutely no physical basis for saying that bass reflex enclosures are "slow" and sealed ones fast, other than the fact that since most reflex systems have a greater setteling time people concluding therefore it must be audible therefore bad, there is no double blind study that I am aware of that has ever shown this.
The fact is that as shown by Floyd Toole, you can transform a slow one into a fast one by removing the room resonance causing the slowness.
It is also true that most so called fast sealed box subwoofers have considerable amounts of third harmonic distortion and d.c. offset caused second harmonic, not to mention flux modulation effects, and the subjective fastness is just that they are not in fact radiating enough power at the relavent frequencies to activate the slow sounding room resonances, and the so called lack of flabiness is in fact nought but good old 60Hz. punch region bass masquerading as low bass.

I'm not getting into a fast/slow debate. I do know for a fact that there is a significant audible difference with the ports stuffed. Same room, same placement, and room modes have nothing to do with it. Sure room modes can affect bass quality, however, anyone who thinks that perceived quality in the region below 100hz, has nothing to do with the alignment has:
A. A screw loose
B. Has never heard good quality bass OR
C. Has poor low frequency hearing (probably from listening to too
much high SPL, highly distorted bass).

[rcw]

I assure you Jonin that all of my screws are about as tight as the next mans.
My system uses a 15inch driver in a QB5 class II filter assisted box.
I have measured this and it goes down to 25Hz. at 106dbm. with a cone excursion of 5mm. and I cannot measure more than 5-8% THD, and the roll off Q is almost exactly 0.7, and the setteling time is around 4.2milliseconds.
If you stuff up the port the power handling factor reduces from around 6.4, down to .8, in practicle terms it means that the acoustic output for the same cone excursion is reduced by a factor of 8.
If you increase the power input to compensate for this, not only those distortions due to cone excursion are increased, but also those due to power input, and in practice most of the extra output you get is distortion.
Most professional subwoofers use filter assisted alignments of the QB5 class I or II sort, and they do this for good reason, that is that the quality/extension/size equation reaches an optimum with these enclosure types, they are also very careful to eliminate room resonance effects, this is important for this type of subwoofer since for the same cone excursion they are capable of putting out around 8 times the acoustic power in the range below 100Hz.

[johninCR]

RCW,

I don't doubt that you have a fine subwoofer for a BR sub. Power handling and acoustical output are perfectly valid reasons that ported systems are used in PA. I'll even concede that THD measurements of speakers may be a good indicator to distinguish between cheap junk equipment and the good stuff. These things are not necessarily evidence of sound quality.

Now you can quote measurements until you're blue in the face and I can explain my real world results likewise, but you will never be convinced until you take an appropriate driver and a sealed enclosure that is large enough to give you the extension you want for music. Then port it to provide the extension and LF output necessary for HT. Put whatever filters you deem necessary and play music both with the ports plugged and open. If you can't hear the difference, then you really should get your hearing checked.

Let's put it in a different perpective for the types who only care about meaurements and how things look on paper. Clear your mind of all the technical stuff. Now just think about how you can possibly take the rear, out of phase, radiation of a driver going into a box, and port it out of the box and still think the acoustical energy coming out of that port does not harm the quality of the acoustical energy radiating from the front of the driver. Guess what, you can't. If you could get a high quality signal coming out of the port, then almost all subwoofers would be bandpass enclosures because it's the easiest way to get significant output over a narrow bandwidth.

If your primary emphasis is output then by all mean build a BR sub, but if SQ is important to you, don't, because what comes out of that port mucks up your sound.

[rcw]

Unfortunately Johnin it is impossible to forget technical stuff when one is discussing the reproduction of sound, since it is by nature a technical exercise and as such is goverened by the laws of physics.
The unfortunate thing about these laws is that if you don't like them, and choose to ignore them and substitute your own laws, they just carry on being true anyway, and your laws don't work, we have to accomodate to them, and there is not a thing we can do about it.
The fact is that a Helmholz resonator is inherantly a far more perfect device than a loudspeaker driver, and you provide such a driver with almost a perfect environment for realising its best performance by providing it with a very high acoustic impedance to deliver its energy to, this lowers its excursion and lessens the amount of power we need to put in, both of which greatly reduce the distortion it produces.
We can measure this by comparing the input to the output. The simple fact is that the signal that comes out of a reflex is a much better copy of that one which goes in than you find in a typical sealed box, which in turn means it must sound more like the musician intended it to sound, and as far as I am concerned that is what we are trying to achieve.

[johninCR]

RCW,

You may be correct that a helmholtz resonator is a perfect device. If so, then a typical driver is a substandard mechanism to stimulate it. I'm not saying the laws of physics should be ignored. What I am saying is that if you really understood the physics involved to the extent that you think you do you would understand why a BR enclosure produces a less than optimum sound. I'm sorry that I don't understand it enough to explain it to you, but I'll leave you with this thought. With a BR you are combining apples and oranges to increase the total output and pure apple juice tastes better than the blend.

Also, I as stated before (and it is widely accepted), bandpass enclosures produce a substandard quality of sound. If they were perfect as you say, then they would of course dominate.

I've really grown tired of arguing with know-it-alls like yourself. If you'd get out from in front of your computer other than to stick your head in a book and open up your ears and listen more then you'll learn a few things that will make you more useful in the real world. You should take the time to look at Cheever's work as well. There are valid reasons the THD is one of the most meaningless measurements that guys like yourself have ever come up with.

[BassAwdyO]

I still find it strange that with 16hz tuning you find a major difference between the sealed and ported maelstrom...

I'm not going to argue which sounds better or worse, but I think I'd have a hard time hearing that difference....

What are you crossing at John? Any chance of pipe resonances in the port..... I know a 16hz port is typically rather long

With my setup (for the mids-bass Extremis 6.8 midwoofers in highly stuffed TL's and an adire Tumult in a 6cubic foot enclosure that can be sealed, 10hz tuned 16hz tuned 20hz tuned or 30hz tuned) I dont really hear any audible differences until I get up to the 20hz tuning. The extremises are uncrossed on the low end and have good extension down to at least 50hz. I intregate them by turning the sub down all the way then slowly turning it up until I first notice any difference, then I back off just a hair and leave it there.

The ports have a few bends in them(which I believe damps the pipe resonances somewhat, I may be wrong)

the 20hz port has 2 bends
the 16hz port has 2 bends
the 10hz port has 5 bends

[BassAwdyO]

ohh BTW

For RCW

John is talking about an EBS. Hardly comparable to a Quasi-butterworth alignmemnt. The amount of excursion decrease in an EBS is much smaller compared to the quasi butterworth due to the larger enclosure size and lower tuning.

I think to be fair it would also be wise to neglect electronic corrections here

[rcw]

Your point is taken Bass, but I too get tired of people who claim some intrinsic mystical superior property for a particular method of loading, that other types don't poses.
The lastest double blind testing data in the AES journal indicates that for a cut off below 50Hz. people can't hear the difference between a fourth and second order system, although of course audio nuts, (including me), all think that they are the exception and they can. The same research incidently shows that 3% thd is audible, and this is the research that the THX standards are based upon.
It is also true that since most horn loaded designs used are too small
the much vaunted superor low bass sound is in fact caused by the horn acting as a much despised bandpass box.
This is why this type of testing is so important in audio, to sort out what people can actually hear from that which they think they should.