Why do you not see this in plans?
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Topic: Why do you not see this in plans?
Posted By: Teppic
Subject: Why do you not see this in plans?
Date Posted: 29 March 2007 at 1:22pm
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When building any kind of ported bass cab, could you cut each port to a different length and thus tune it to a subtly different frequency to produce a smoother responce across a range? For example, with four ports why not tune one to 20hz, one to 24hz, one to 28hz and one to 32hz? -Like organ pipes?
Any reasons either way? Seen this done? |
Replies:
Posted By: _djk_
Date Posted: 29 March 2007 at 10:03pm
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Sorry, it's been tried and it doesn't work that way. It does work to build two cavites into the box with a port between the two cavities and each cavity ported to the outside at different frequencies. (search on Weems or Marsh double cavity) ------------- djk |
Posted By: Cuppa Joe
Date Posted: 30 March 2007 at 12:42am
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Meyer Sound double-tunes several of their subwoofer models within the same cavity. I can't tell you how far apart the tunings are, but I'll bet that it's closer to an octave than not.
The David Weems double-chamber reflex tunings are also about an octave apart (see above). It's in his 1990 book called "Great Sound Stereo Speaker Manual". |
Posted By: _djk_
Date Posted: 30 March 2007 at 11:34pm
Multiple tuned high power bass reflex speaker system "separate and acoustically isolated bass reflex chambers. Each bass reflex chamber is tuned to a separate octave such that the bass reflex modules formed by each bass reflex chamber and its associate cone driver produces a complex acoustical signal comprised of different frequency components in the low frequency range at high sound pressure levels, but with minimum driver cone excursion and distortion. " ------------- djk |
Posted By: Teppic
Date Posted: 31 March 2007 at 5:38am
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I see. Meyer Sound in particular seem to use ports of varying sizes on single subs, but then obviously we can't see their length or how the enclosures are subdevided inside. Although interestingly they do mention spanning octaves.
Thanks for the insight, I've been wondering about this for a while 
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Posted By: Cuppa Joe
Date Posted: 01 April 2007 at 1:55am
| Oops, pardon the ignorance! I wasn't aware that Meyer was using separate chambers for the tunings. So, they're essentially using the ol' double chamber reflex with patent-worthy modifications? |
Posted By: _djk_
Date Posted: 04 April 2007 at 6:22pm
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"So, they're essentially using the ol' double chamber reflex with patent-worthy modifications? "
Actually, no.
The Meyer cabinet has a 6 cu ft box tuned to 32hz, a 4 cu ft box tuned to 64hz, and a 2 cu ft box tuned to 128hz.
The cabinet is driven with three channels of amplification with the 18 below 45hz, the 15 from 45~90hz, and the 12 from 90hz up. Steep slopes are employed.
------------- djk |
Posted By: tb_mike
Date Posted: 07 April 2007 at 1:54am
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Looks like jbl do something like this with the everest.audioheritage.org talks about it. Two drivers,two enclosures of different volumes,and different tunings. I dont see any advantage because you always get the pros with the cons of each tuning. |
Posted By: Teppic
Date Posted: 07 April 2007 at 4:54am
| And surely this is just like sticking two seperate subs together? I was wondering about different tuning in the same enclosure |
Posted By: gazman
Date Posted: 07 April 2007 at 7:50am
| If you put two reflex cabs with widely different tuning frequencies next to each other it'll sound like crap because the of the phase flip taking place at tuning frequency. The two drivers won't interact together well around their tuning frequencies and will probably cause big peaks/troughs. |
Posted By: Cuppa Joe
Date Posted: 07 April 2007 at 10:55pm
| That sounds like the MTS-4A, a full range cab. I was under the impression that several of their subwoofers were double-tuned within the same cavity. |
Posted By: Tom Umney
Date Posted: 17 April 2007 at 1:30pm
This is double tuned and uses six drivers, 2 18's and 4 15's.
http://www.meyersound.com/products/concertseries/psw-6/ - http://www.meyersound.com/products/concertseries/psw-6/
  But the different tuning is probably like two enclosures in one.Otherwise it would sound weird.
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Cuppa Joe wrote:Posted By: tb_mike
Date Posted: 19 April 2007 at 1:28am
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That meyer multi sub above probably is setup for a cardoid polar. gazman - is that in theory or to your ears? Sure,we have out of phase 'late'bass emanating from the port,but does it matter at that frequency. The phase wrapping on a graph looks bad,but one has to confer with psycho acoustics to see what the ear can hear. |
Posted By: gazman
Date Posted: 02 May 2007 at 7:41pm
| Hi Mike, sorry for late reply! I'd say its both the theory and the practice..think about using multiple types of sub over the same frequency range and all the horribleness that causes, same problem basically. As far that Meyer sub, obviously set up for cardiod use, weird they've used 1x 18" at the front with a 15, then 2 more 15's to provide the cancelling waves. Wonder how the 15 and 18 are setup to coherently sum together... |
Posted By: Cuppa Joe
Date Posted: 24 May 2007 at 3:14am
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Gazman- The 18's and the 15's on the front baffle cover different frequency ranges and have separate subenclosures. The pair of 15's on the rear also have their own subenclosure and tuning.
Tom- Did my homework: Each 18" driver in the PSW-6 IS double-tuned within its own cavity (via employing 2 sets of vents with differing lengths and Sv), as are the following Meyer Sound enclosures: MTS-4A, 18" driver subenclosure (only) 650P double 18" sub 700-HP double 18" sub 600-HP double 15" sub CQ series 2-way, fullrange cabs (This might not be a complete list.) EAW does the same thing with at least one of their older designs. This is not a new design tactic, but it's tricky to get the tunings right. John Meyer can be contacted through the Meyer Sound website (www.meyersound.com). |
Posted By: jcasti1226
Date Posted: 25 June 2007 at 4:04pm
This contains the descripcion of the box MTS-4. It even tells you the size and lenghth to each chamber.http://www.patentstorm.us/patents/5602367-de0scription.html - http://www.patentstorm.us/patents/5602367-de0scription.htmlI was wondering. I have heard stacks of meyer 700HP subs and i see different port size i can assume they are double tune also.Anyway how can we acomplish our own designs double tune. What are the tools we need to do it?
I don't think john meyer will answer questions on port size and length on the 700hp or other cabinets they produce.
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Posted By: Ibex
Date Posted: 15 November 2009 at 3:32pm
Whereon do you relate to this fact? I can't find any information concerning your claim... ...maybe the diverse sized ports have different lengths to get the same tuning frequencies for each one?! |
Posted By: DjMidKnight
Date Posted: 15 November 2009 at 9:02pm
| hermm.. i might be overstepping my self here BUT from what i understand that if you put ports in a common cavity of varying lengths and sizes the combind volume of air that can push through them all will set the tuning of the box. of course there will be differing amounts of resistance through each port but the sum of exchange would be the calculated frequency. |
Posted By: _djk_
Date Posted: 16 November 2009 at 3:06am
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Double tuning still gives only one resonant frequency per tuned chamber.
http://www.gedlee.com/ - http://www.gedlee.com/
------------- djk |
http://www.diyaudio.com/forums/members/gedlee.html - gedlee vbmenu_register("postmenu_1832150", true); 
Posted By: Ibex
Date Posted: 16 November 2009 at 7:11am
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Posted By: Ibex
Date Posted: 16 November 2009 at 8:28am
Maybe Cuppa Joe was talking about such a system design?! DCR - Double Chamber Reflex http://www.claudionegro.com/projects/speaker/dcr/dcr.html It's obvious that the Meyer Subs have different sized ports, it possible that they are utilizing the DCR technology:  
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Posted By: Ibex
Date Posted: 16 November 2009 at 8:51am
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...but there is nothing mentioned on their web site in the sound lab: http://www.meyersound.com/support/forums/talkshop/subs.htm Myth still busted! |
Posted By: MusicXtra
Date Posted: 16 November 2009 at 9:44am
| Each bass reflex cabinet is a simple Helmholz resonator, so it is impossible to give it two resonance frequenties. |
Posted By: G-Man
Date Posted: 17 November 2009 at 4:02pm
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There was a HiFi speaker company a few years ago, that used round ports that were put in at an angle and the ends were cut at an angle, with the idea being similar to what you are talking about here (one port with a variable length). But when you look at the geometry of the thing, all you have in the end is a straight oval port. You are better off using multiple ports (of any length) simply because of the reduction in port velocity and port noise, but other then that, not much benefit. As a side note, even though they are mostly used in HiFi market, flared ports are the best way to go. ------------- If it was easy, everyone would do it! |
Posted By: adambomb
Date Posted: 17 November 2009 at 7:44pm
If you put a horn on the front of the driver... I wonder what you could achieve?  ------------- http://www.freespeakerplans.com" rel="nofollow - www.freespeakerplans.com |
Posted By: Ibex
Date Posted: 17 November 2009 at 9:16pm
...a STAndard port assisted horn SYStem with eXtrem cone control ;) |