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Old 15th July 2003, 08:19 AM   #11
7V is offline 7V  United Kingdom
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Default Re: Re: Qt

Quote:
Originally posted by planet10
I like a design that starts rolling off fairly high (~100 hz) and slopes gently down from there (ie Qt=0.5). Often this isn't achievable with a reasonable size box in which case i go aperiodic (which i prefer anyway).
Dave, please would you explain exactly what you mean by "go aperiodic" in this context?
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Old 15th July 2003, 08:38 AM   #12
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Default Re: Re: Re: Qt

Quote:
Originally posted by 7V
please would you explain exactly what you mean by "go aperiodic" in this context?
ake the sealed box. Add some holes as far from the driver as feasible, and then restrict the air flow thru the holes (ie compressed fiberglass). I've found that long thin slots like in the Dynaco A25 are easier to deal with.

Tune by ear, the click test, or flattest impedance curve.

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Old 15th July 2003, 09:34 AM   #13
Kay is offline Kay  Germany
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Hy,

if you are looking for a more intelligent setup, read some papers:

http://www.harman.com/wp/index.jsp?articleId=65

best regards
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Old 15th July 2003, 09:49 AM   #14
7V is offline 7V  United Kingdom
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Default Re: Re: Re: Re: Qt

Quote:
Originally posted by planet10
Take the sealed box. Add some holes as far from the driver as feasible, and then restrict the air flow thru the holes (ie compressed fiberglass). I've found that long thin slots like in the Dynaco A25 are easier to deal with.

Tune by ear, the click test, or flattest impedance curve.
Thanks Dave.

Websters describes "aperiodic" to mean:
1 : of irregular occurrence <aperiodic floods>
2 : not having periodic vibrations : not oscillatory

In the last few days I've seen the term used to describe 'Daline' bass loading, egg-shaped enclosure design and restricted ports.

As it's such a general term I guess we should be specific about exactly what we mean.
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Old 15th July 2003, 12:38 PM   #15
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Default Re: Re: Qt

I am really surprised that a project of this magnitude did not receive more attention from this board until now.

Quote:
Originally posted by planet10:
If you design for flat anechoic response (ie in your modeling program) and then you put them into a room with gain of 3-6 dB/octave below a certain point you end up with a really lump at the bottom.
Your ability to hear these deep frequencies drops off dramatically as well. What's wrong with a little extra "ooph" down there?

Quote:
Originally posted by Planet 10: I like a design that starts rolling off fairly high (~100 hz) and slopes gently down from there (ie Qt=0.5).
dave
A Qtc of 0.5 is considered the best for transient response. A Qtc of 0.7 is considered critically damped. His Qtc is about midway between these two. He is not far off from Qtc = 0.5 now. Are attempts to bring it all the way down to Qtc = 0.5 really necessary?

If he wants to experiment, I was going to suggest he go in the other directiion-port these things for extra "oomph". Use a 4" pipe with a pipe cap on it and make one of the subs a "convertible". See how it sounds. He can always put the "convertible" sub's capped port hole in the back of the enclosure so nobody will see it.

Just a suggestion to mull over.
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Old 15th July 2003, 01:16 PM   #16
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Just thought I would throw in a simulation of proted and sealed box. A fair amount of extra output down to 16 Hz, the tuning frequency. Again, not advocating ported, just putting up some options.
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Old 15th July 2003, 01:20 PM   #17
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why not just buy an Aeolian Skinner pipe organ?
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Old 15th July 2003, 04:10 PM   #18
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Default Re: Re: Re: Qt

Quote:
Originally posted by 7V
2 : not having periodic vibrations : not oscillatory

In the last few days I've seen the term used to describe 'Daline' bass loading, egg-shaped enclosure design and restricted ports.
It any TL is heavily stuffed it approaches or becomes aperiodic.


Quote:
Originally posted by kelticwizard
A Qtc of 0.5 is considered the best for transient response. A Qtc of 0.7 is considered critically damped. His Qtc is about midway between these two. He is not far off from Qtc = 0.5 now. Are attempts to bring it all the way down to Qtc = 0.5 really necessary?
But if room gain rasies the system Q (in the room) to above 1, that isn't very good. With that many drivers in such a small room they become a VERY significant part of the "box".

dave
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Old 15th July 2003, 04:11 PM   #19
jmiyake is offline jmiyake  United States
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Default the harmon paper

Hi Kay,

Kay said:
if you are looking for a more intelligent setup, read some papers:
--------------------------------------------
Well I have read this paper. It is a very directed work, and seems somewhat sparse in providing enough rules or theories to follow the conclusions.

One of the recommended configurations has you sitting practically top of the multiple subwoofers, which will have the flatest frequency response at the seating position. This may be true.

In an earlier concept I proposed imbedding a subwoofer in the raised seating platform of the theater. (I mean there is all that space, ~25 cubic feet.)
However I rejected it since such a configuration would seem to be very difficult integrate the subwoofer with the rest of speakers. Although for home theater, this may be fine, for music listening, it is considered important to have the sound generated from a uniform location.

One of my goals in having a sealed array with an enormous sd, is to have a very musical bass setup. Setting up subs below or behind the listening position would seem to be counter to this end.

James
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Old 15th July 2003, 06:32 PM   #20
jmiyake is offline jmiyake  United States
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Default Port vs sealed

Hi kelticwizard ,

kelticwizard chanted, in part:
I was going to suggest he go in the other directiion-port these things for extra "oomph" ... He can always put the "convertible" sub's capped port hole in the back of the enclosure so nobody will see it.
---------------------------------------
Well this is a very interesting notion.

The reason I have been leaning towards sealed, is less distortion and a shallower drop off at the very lowest frequency. Also I am looking for tightness, and low boom. Musicality. I seriously doubt that I will require more boom, or that it would be desirable.

However you bring up some very interesting ideas, on making it adjustable.

I shall ponder this some more.
James
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