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21" reflext enclosure needed

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Mel_Gibson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 04 December 2020 at 3:13pm
Right I received an email reply from Beyma about the ports on the 21LEX1600nd enclosure plans supposedly being too small as said on this forum and they said word for word :

Good morning

 

I paste below the answer from our R+D Department.

 

Thanks a lot for your interest in our products and for your question.

We can assure you the cabinet is tested and the ports size is 100% correct. If there is any doubt we would appreciate a reason to claim the ports design are “too small”.

According to our measurements and listening tests the ports are correct.

We hope this information helps.

 

Kind regards

Rebeca Rodríguez



Edited by Mel_Gibson - 04 December 2020 at 3:14pm
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Noyzmunky View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Noyzmunky Quote  Post ReplyReply Direct Link To This Post Posted: 04 December 2020 at 3:56pm
''We can assure you the cabinet is tested and the ports size is 100% correct when you consider the compromises inherent in the design...''


There, I fixed their reply for you. I can well imagine your email to them having read your replies on here... Were you expecting anything else to come back from them than ''it's fine''
my name is Inigo Montoya...you killed my father, prepare to die!.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 04 December 2020 at 7:13pm
Originally posted by Noyzmunky Noyzmunky wrote:

''We can assure you the cabinet is tested and the ports size is 100% correct when you consider the compromises inherent in the design...''


There, I fixed their reply for you. I can well imagine your email to them having read your replies on here... Were you expecting anything else to come back from them than ''it's fine''

This.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 04 December 2020 at 7:52pm
Originally posted by Noyzmunky Noyzmunky wrote:

''We can assure you the cabinet is tested and the ports size is 100% correct when you consider the compromises inherent in the design...''


There, I fixed their reply for you. I can well imagine your email to them having read your replies on here... Were you expecting anything else to come back from them than ''it's fine''

Well they tested the enclosure and got peaks of 137db with pink noise with a 6db crest factor so all I can say to you is :





Edited by Mel_Gibson - 04 December 2020 at 7:58pm
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Mel_Gibson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 04 December 2020 at 9:57pm
By the way I was joking with that little kid and her face, lol. But seriously ok if the ports ARE too small what size ports would be ideal? Plus also i'm rubbish at carpentry so would getting a cabinet maker to make me up the enclosure be a good idea? If I had a decent plan for him to follow I mean. I've tried using WinISD and I have no idea so rather than take months to learn how to use it and learning to understand the results i'm seeing i'd rather get an enclosure designed as well as made. 

Edited by Mel_Gibson - 04 December 2020 at 9:59pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Contour Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 9:39am
The ports indeed may be perfectly sized for the required optimal reflex tuning, but same tuning can be achieved using larger area, but longer port. The larger port area results in less port losses and higher output. In some cases however, the ports are designed so small on purpose, it effectively changes the cabinet tuning to a higher frequency when the driver warms up and it T/S parameters change, resulting is a more optimal design when the driver is working on its limit.  

Best regards,

Walter
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 11:01am
Thank you Walter for your excellent detailed reply that helps me a lot, one problem I have is, Beyma measured the peak SPL output at 137db using pink noise with a 6db Crest Factor I can't see how you could get more output from a single 21" reflex sub than that. So making the ports bigger would you say it's reasonable that even doing that would result in SPL output being not even noticeably higher? Unless it's gonna get 3db or more higher output it's probably not worth taking the time to design an enclosure with bigger ports as it'd mean pretty much re-designing the whole enclosure and testing it out once built then adjusting all for less than for example 3db output. 

Edited by Mel_Gibson - 05 December 2020 at 11:02am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chris Grimshaw Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 12:49pm
Originally posted by Contour Contour wrote:

The ports indeed may be perfectly sized for the required optimal reflex tuning, but same tuning can be achieved using larger area, but longer port. The larger port area results in less port losses and higher output.


... With the compromise that the larger ports directly mean a larger cabinet.

There's also the potential for 1/4-wave resonances to mess up the top of the bandwidth.


The time when under-sized ports become obvious is when you're demanding full output at/near the port tuning frequency. Whether that's likely to happen will depend entirely on the program material.

Example: https://www.youtube.com/watch?v=UnQY3swM4tA (caution - lyrics are nsfw)
Has a very compressed bass line which gives subs a hard time. If your port is tuned to 36Hz, you better make sure it has lots of area. You'll also need to make sure the magnets on the drivers are adequately ventilated.

Most program material isn't so demanding, and you can "get away with" smaller port areas without suffering much/any compression.

Chris
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www.grimshawaudio.com
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Mel_Gibson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 2:07pm
Originally posted by Chris Grimshaw Chris Grimshaw wrote:

Originally posted by Contour Contour wrote:

The ports indeed may be perfectly sized for the required optimal reflex tuning, but same tuning can be achieved using larger area, but longer port. The larger port area results in less port losses and higher output.


... With the compromise that the larger ports directly mean a larger cabinet.

There's also the potential for 1/4-wave resonances to mess up the top of the bandwidth.


The time when under-sized ports become obvious is when you're demanding full output at/near the port tuning frequency. Whether that's likely to happen will depend entirely on the program material.

Example: https://www.youtube.com/watch?v=UnQY3swM4tA (caution - lyrics are nsfw)
Has a very compressed bass line which gives subs a hard time. If your port is tuned to 36Hz, you better make sure it has lots of area. You'll also need to make sure the magnets on the drivers are adequately ventilated.

Most program material isn't so demanding, and you can "get away with" smaller port areas without suffering much/any compression.

Chris

In your opinion Chris which ports are the best overall shape? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Contour Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 2:11pm
Round, has the best ratio port area versus port wall surface. Use a very big radius at start and end of the port, google intertechnik jetset for an example. 
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Mel_Gibson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 2:46pm
Don't round ports suffer more from the chuffing sound? I heard the chuffing sound on some old hi-fi speakers years ago and it sounded unpleasant. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jammin75 Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 3:04pm
Originally posted by cravings cravings wrote:

it's yet another account for djteknovibe / Jack_The_Ripper / richard stringer / Fred_Dibnah / richardstringer1993... so he's in Boston in Lincolnshire.


Originally posted by Fred_dibna Fred_dibna wrote:

I have a quick port question, are circular, triangular or under driver slot ports best? The driver will be the RCF LF18X401, cabinet tuned to 36hz and i'll be powering a pair with a bridged QSC RMX4050HD giving the subs a combined 4k.

I was just curious, thanks.




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