Reflex enclosure vent as port

Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic

   Looking at my 4x8 + 1.4 top (combined) , the cab is a reflex I assume, there are metel grills with perforations, i am trying to understand the concept as someone on here said that in absence of a port (pipe), effectively the cab has been designed to use the thickness of the panel say 22 mm as the effective port length with the grill I guess providing the correct opening, anyone?

Author	Message Topic Search Topic Options Post Reply Create New Topic Printable Version Translate Topic
70,s hero Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 14 December 2014 Location: bristol Status: Offline Points: 637	Post Options Post Reply Quote 70,s hero Report Post Thanks(0) Quote Reply Topic: Reflex enclosure vent as port Posted: 06 April 2017 at 10:25pm
	Looking at my 4x8 + 1.4 top (combined) , the cab is a reflex I assume, there are metel grills with perforations, i am trying to understand the concept as someone on here said that in absence of a port (pipe), effectively the cab has been designed to use the thickness of the panel say 22 mm as the effective port length with the grill I guess providing the correct opening, anyone?
	Top banana

Conanski Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 26 January 2006 Location: Ottawa, Canada Status: Offline Points: 2537	Post Options Post Reply Quote Conanski Report Post Thanks(0) Quote Reply Posted: 06 April 2017 at 11:09pm
	A speaker cabinet is either sealed or it isn't.. so any purpose made openings will act as a port. Figuring out what the tuning is requires knowing the internal volume of the box and the dimensions of the port.

markie Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 31 October 2005 Location: Sunny Liskeard. Status: Offline Points: 4570	Post Options Post Reply Quote markie Report Post Thanks(0) Quote Reply Posted: 07 April 2017 at 12:22am
	As far as I'm aware the factor of the port is it's internal volume, i.e PiRsquared x port length. Thus if the diameter of the port is reduced the port length increases. It is therefore possible to have a large rectangular opening (usually) at the bottom of the cabinet. Usually it's simply a fact that the baffle is made "too short. Then the port volume then becomes length x height of the opening x thickness of the ply. Then again I often get these things wrong so I'm sure an adult will be along soon to correct me. Edited by markie - 07 April 2017 at 12:26am
	If it's got wheels or tits it's gonna cost a fortune

_djk_ Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 23 November 2004 Location: United States Status: Offline Points: 6002	Post Options Post Reply Quote _djk_ Report Post Thanks(0) Quote Reply Posted: 07 April 2017 at 1:11am
	"Thus if the diameter of the port is reduced the port length increases." Backwards.
	djk

matty w Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 27 August 2008 Status: Offline Points: 798	Post Options Post Reply Quote matty w Report Post Thanks(0) Quote Reply Posted: 07 April 2017 at 2:53am
	Correction .. If the diameter of the port increases the length must also to achieve the same tuning !!
	Black to black , red to red , blue to bits ....

70,s hero Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 14 December 2014 Location: bristol Status: Offline Points: 637	Post Options Post Reply Quote 70,s hero Report Post Thanks(0) Quote Reply Posted: 07 April 2017 at 6:17pm
	Thanks, and so the question, is there a different calculator for this type of port or is it just the same calcs, reason why I ask is, the port is a perforated grille. Edited by 70,s hero - 07 April 2017 at 6:18pm
	Top banana

Elliot Thompson Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 02 April 2004 Location: United States Status: Offline Points: 5175	Post Options Post Reply Quote Elliot Thompson Report Post Thanks(0) Quote Reply Posted: 07 April 2017 at 7:59pm
	Having a perforated grille over the port is a matter protection. For the home, it prevents babies from putting things inside such as toys. For sound reinforcement, it prevents rodents living in the cabinets. All loudspeaker software aimed for reflex designs will offer the option of using a rectangular vent or circular port. Best Regards,
	Elliot Thompson

70,s hero Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 14 December 2014 Location: bristol Status: Offline Points: 637	Post Options Post Reply Quote 70,s hero Report Post Thanks(0) Quote Reply Posted: 08 April 2017 at 2:23pm
	Thanks to all, still none the wiser
	Top banana

mobiele eenheid Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 15 August 2004 Location: Netherlands Status: Offline Points: 1568	Post Options Post Reply Quote mobiele eenheid Report Post Thanks(0) Quote Reply Posted: 08 April 2017 at 3:16pm
	I think a picture would help a lot. Unless you mean the port is the same thickness as the baffle, in which case the length of the port is the same as the thickness of the baffle ;) Whilst the surface area of the port, in that case would be the same as, well, the surface area of the port. Ignore the grill for now.

cravings Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 30 January 2007 Location: Ireland Status: Offline Points: 7442	Post Options Post Reply Quote cravings Report Post Thanks(0) Quote Reply Posted: 08 April 2017 at 3:39pm
	yeah just ignore the grill, the hole behind it is the port, thickness of the ply is the length of the port.

70,s hero Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 14 December 2014 Location: bristol Status: Offline Points: 637	Post Options Post Reply Quote 70,s hero Report Post Thanks(0) Quote Reply Posted: 08 April 2017 at 8:31pm
	I will upload a pic, thanks, perhaps the combined cross sectional area of the grill perforations give a predetermined resistive air flow effect?
	Top banana

JonB67 Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 22 April 2016 Location: UK Status: Offline Points: 1376	Post Options Post Reply Quote JonB67 Report Post Thanks(0) Quote Reply Posted: 09 April 2017 at 11:32am
	I understand what you're asking as I has to do the same thing to try to sim my peavey subs. As long as the grille over the ports is relatively open, ignore it. Use the same software as normal. I used winISD. Put the box parameters in as normal. Then, as you originally suspected, put the port length in as the thickness of the panel the port is drilled through. In my case it was 18mm. Marvel at your graph then go get a beer to celebrate.