Bass reflex port question - Page 2

clem_o · 11th April 2006, 12:51 AM

Oops, to add one more thing: At the port resonant frequency, the driver and the port output (or passive radiator) are in-phase, but it may be a bit difficult to verify this since a well-designed box with low losses will case the driver motion to be reduced very significantly - in other words, most of the sound pressure is actually emanating from the port.

Cheers!

Javachip · 11th April 2006, 11:01 AM

Thanks again for the very helpful information. I am considering building a speaker with an MTM open baffle dipole configuration, with an integral bass enclosure consisting of a woofer and PR firing in opposite directions at about a 60 degree angle from the listening position. (The cabinet would have a somewhat pyramidal shape.)

I was wondering if that design would create a dipole-induced null space for the woofer output at the listening position, but based on your comments, it appears that such a design would actually be a bipole, since the woofer and PR are in-phase at and above the resonance frequency.

I plan to do some more reading before I go any further with this idea.

clem_o · 11th April 2006, 12:11 PM

Just remember that they move in-phase only close to the resonant frequency. Above resonance, the mass of the PR (and mass of air in a port) moves a lot less, acting more like a cover or plug so that the box works similarly to a sealed enclosure. So, very dependent on the crossover frequency you choose going from the Midrange to the bass driver, you may find that the "bipole" radiation you hope for may not be there. The argument of course is that LF tends to be omnidirectional anyway, so at LF would there be a difference between a bipole and a monopole?...

Cheers!

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Quick bass reflex port question...	revans	Everything Else	26	8th March 2009 06:36 PM
Bass Reflex Port: 46mm where to buy?	maf_au	Multi-Way	9	28th October 2005 08:41 PM
Tuning bass reflex port	beamnet	Multi-Way	0	28th September 2005 01:03 PM
Q-factor of bass reflex port	SSassen	Multi-Way	6	26th March 2005 08:26 PM
what the max Air velocity of bass reflex port?	Audist	Multi-Way	4	7th February 2005 08:43 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

11th April 2006, 12:51 AM	#11
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	Oops, to add one more thing: At the port resonant frequency, the driver and the port output (or passive radiator) are in-phase, but it may be a bit difficult to verify this since a well-designed box with low losses will case the driver motion to be reduced very significantly - in other words, most of the sound pressure is actually emanating from the port. Cheers!

11th April 2006, 11:01 AM	#12
Javachip diyAudio Member Join Date: Dec 2005 Location: CA	Thanks again for the very helpful information. I am considering building a speaker with an MTM open baffle dipole configuration, with an integral bass enclosure consisting of a woofer and PR firing in opposite directions at about a 60 degree angle from the listening position. (The cabinet would have a somewhat pyramidal shape.) I was wondering if that design would create a dipole-induced null space for the woofer output at the listening position, but based on your comments, it appears that such a design would actually be a bipole, since the woofer and PR are in-phase at and above the resonance frequency. I plan to do some more reading before I go any further with this idea.

11th April 2006, 12:11 PM	#13
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	Just remember that they move in-phase only close to the resonant frequency. Above resonance, the mass of the PR (and mass of air in a port) moves a lot less, acting more like a cover or plug so that the box works similarly to a sealed enclosure. So, very dependent on the crossover frequency you choose going from the Midrange to the bass driver, you may find that the "bipole" radiation you hope for may not be there. The argument of course is that LF tends to be omnidirectional anyway, so at LF would there be a difference between a bipole and a monopole?... Cheers!

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)