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1802 sub port experiment

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7 hours ago, Chief bonehead said:
On 4/15/2019 at 8:19 PM, jason str said:

 

Sealed subs work better in small rooms because they take advantage of cabin gain to fill in the lower octave.

 

Cinema's or movie theaters are too large to take advantage of any cabin gain thus making them a poor choice.

 

 

so the laws of physics change.....

 

The way I see it any cabin gain available will be applied regardless of which type system is used (ie: sealed, ported, or horn systems) and they all can take advantage of it.

 

miketn

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11 hours ago, mikebse2a3 said:

 

The way I see it any cabin gain available will be applied regardless of which type system is used (ie: sealed, ported, or horn systems) and they all can take advantage of it.

 

miketn

 

Ported subs will have a steeper roll off than sealed models. Ported horns included.

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31 minutes ago, jason str said:

 

Ported subs will have a steeper roll off than sealed models. Ported horns included.

 

Yes but the cabin gain would be equal for all. The air is being acted upon and doesn’t discriminate based on type of system causing the action.

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16 hours ago, AHall said:

I’m sure there is a lot of optimizing in tuning and treatment left on the table. I just have to learn how to achieve it. 

I've been working on my room and loudspeakers for over 10 years now, and I'm still finding things to do to improve the sound.  It doesn't seem to be slowing down either, as I understand the effects of psychoacoustics on the resulting sound--particularly phase response: more on that subject below.

 

16 hours ago, AHall said:

Am I incorrect in my thinking? Trying to get an 1802 to play full spl below what it was designed to do? Why not roll it off at 22-25hz and let sealed subs cover that last 10hz?

You could do that for the LFE of movie tracks in your listening room.  You're right in assuming that any direct radiating (DR) sub will have very high levels of harmonics at sub-25 Hz frequencies, and with that, the potential for modulation sidebands at higher frequencies if it's covering a wider band of frequencies than the one octave (i.e., ~12-25 Hz).  It's best to roll off the lowest frequency subwoofer ("infrasonic woofer") so as to preclude heavy modulation sidebands from appearing at higher audible frequencies.

 

Note that the direct radiating woofers will also introduce other forms of distortion--mainly compression distortion due to the small relative size of the woofers (without horn loading) to the wavelengths being produced, and secondarily due to thermal heating of the voice coils and passive crossovers--if they are used (which I don't recommend). 

 

It's probably worthwhile to experiment with EQing the bottom end of the 1802 in order to see what kind of extension can be had and how much amplifier gain you give up doing that.  I've learned that it's usually better to use the horn-loaded bass bins below their cutoff frequency boosting their output using EQ, than to use much higher distortion direct radiating or even ported (bass reflex) woofers.  Group/phase delay takes its toll in terms of the resulting sound.  The quote below is from Toole's book, 1st Ed., pg. 420:

 

Quote

18.6.2 Phase Response—The Low Bass

In the recording and reproduction of bass frequencies, there is an accumulation of phase shift at low frequencies that arises whenever a high-pass filter characteristic is inserted into the signal path...Finally...is the loudspeaker, which cannot respond to DC and must be limited in its downward-frequency extension...

 

Fincham (1985) reported that the contribution of the loudspeaker alone could be heard with specially recorded music and a contrived signal, but that it was “quite subtle.” The author heard this demonstration and can concur. Craven and Gerzon (1992) stated that the phase distortion caused by the high-pass response is audible, even if the cutoff frequency is reduced to 5 Hz. They say it causes the bass to lack “tightness” and become “woolly.” Phase equalization of the bass...subjectively extends the effective bass response by the order of half an octave...

 

This would seem to imply that the really dramatic phase shift introduced by bass reflex enclosures--through group delay growth alone--loses about a half an octave of subjective bass response. 

 

That's a lot.

 

Chris

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With that in mind, refer to my second-to-last post before this one...

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I just found out that there is a patent for DSP correction of low frequency phase growth--clearly, a bad patent because prior art is clearly provable in this instance by simple internet searches: https://patents.google.com/patent/US9992573B1/en?oq=9992573

 

The Toole book referenced above also shows that the technique was openly discussed years before the patent filing date (2008 publication date, referencing reports going back 15 year before that date).

 

It seems that Meyer Sound thinks its appropriate to patent something that you can clearly find going back many years before the patent application date (29 Oct. 2013).  I don't think this is the reason why patent protection laws came into existence. 

 

Perhaps the USPTO should give its examiners a computer with Google freely accessible for searching through the "prior art". 

 

Chris

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On 4/16/2019 at 1:06 PM, Chief bonehead said:

so the laws of physics change.....

In some people's minds they do, LOL. Not in mine. To the OP, if you really want to get below 20 hz., which statistically, is a rare occurrence in so much program material (Blue Rays). That being said, I've noticed a much stronger LFE channel output in all the Dolby Atmos movies I've rented. So "just in case," I've designed a 22 foot long Tapped Horn that can get down into about 13 Hz. in my small living room. I used to have twin DTS-10's that got down there and this is rectangular box version with Twin MONSTER 12" drivers I got on sale almost 3 years ago. Even IMAX theater specification call out 23 Hz. as the bottom end, which I can easily reach now. I just want to say that going below that with 95 db/Watt efficiency, is an expensive proposition and requires a LONG HORN to do. Crippling your 1802's normal response is not the best answer to your quest, IMHO opinion. I'll post my plans if you want to build one, but trying to get 10 Hz. sub bass out of a horn that is too short, is not the best thing to do. But hey, it's your sonic life, time, and money.

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Not your best posting, Claude.  Issues embedded...and assumptions that are not correct.

 

Chris

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I really think we are totally forgetting what we are talking about in this post. First hornloading vs direct radiator. Boosted response vs non boosted. Isn’t the goal to get clean bass?  A director radiator to 10hz?  How big is the box? What sensitivity, never mind efficiency?  Is it boosted?  Is distortion a desired attribute? Or lack of?  Just wondering. Remember it’s a compromise.......but take the good while reducing the bad. Definitions may vary....

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How low can we go without distortion? When we enter below that threshold how audible is the distortion? Is the low end extension worth the added distortion to provide that wow factor for movie ULF? 

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I think that you're already there in terms of distortion.  The 1802 is not really meant to go much lower than 26 Hz in half space.  Pushing the response lower increases harmonic distortion fairly significantly.  Of course, this is also true of other direct radiating subwoofers, too.  The only way that I know to get relatively clean output below 26 Hz is to use a horn-loaded subwoofer with a horn length of greater than 12 feet of path length, and place the mouth of said horn in a room corner with stiffened/reinforced walls. 

 

As far as how audible that distortion is: if you presently cannot detect harmonic distortion, then your tolerance for it is fairly high at those low frequencies (which is, from my observations, fairly typical of most folks that haven't heard/felt clean output below 26 Hz).  What you get when you boost the output below 26 Hz is lots of harmonics, but little clean output.  My experience is that clean output in this frequency band is almost inaudible, but is mostly felt tactilely. If you can actually hear something when playing a tone or impulses below 26 Hz, you're mostly listening to harmonics (second, third, fourth...9th, etc.)

 

Chris

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23 hours ago, Chief bonehead said:

A director radiator to 10hz?

I can get that with my IB, you can measure it but you definitely can't hear it.  All you hear is windows and doors rattling/flexing.

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The other enjoyable sensation is one of pressure.  The feeling of pressure waves, of the room being pressurized.  My 10" sub rolling off below 40Hz does it in the close confines of the car but in the HT?  DTS10!  There's something primal and thrilling/scary about those sensations - perhaps imprinted in our genes from thousands of years of such natural occurences - waterfalls, ocean waves, migrating herds of beasts, and of course thunder storms!

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11 hours ago, AHall said:

How low can we go without distortion? When we enter below that threshold how audible is the distortion? Is the low end extension worth the added distortion to provide that wow factor for movie ULF? 

If we can't hear below 25 or 22Hz, will we still hear distortion from those frequencies?

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9 minutes ago, CECAA850 said:

If we can't hear below 25 or 22Hz, will we still hear distortion from those frequencies?

 

Likely yes. Second harmonic would be at 50 or 44 Hz, respectively. Third would be at 75 or 66, respectively. And so on. Second harmonic is actually pretty common in woofers at very low frequencies, often called "doubling".

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4 minutes ago, Edgar said:

 

Likely yes. Second harmonic would be at 50 or 44 Hz, respectively. Third would be at 75 or 66, respectively. And so on. Second harmonic is actually pretty common in woofers at very low frequencies, often called "doubling".

I wondered about harmonics but didn't know how audible they'd be.

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