BBC LS S/5 loudspeaker

Tyimo · 14th August 2007, 06:22 PM

Hi!

Could some body tell me where can I find detailed infos about the attached loudspeaker??? (sorry for the bad quality picture)
I am most interested for this "diffusor" panel.

Tyimo

Geoff · 14th August 2007, 07:03 PM

Have a look at the following BBC document for the LS5/8 which uses a similar principle:

http://downloads.bbc.co.uk/rd/pubs/reports/1979-22.pdf

I cannot remember if it covers the design of the front panel cut-out for the bass unit.

Salas · 14th August 2007, 08:14 PM

It widens the midrange dispersion of the 300mm woofer. Its the same principle as with slot tweeters.

Tyimo · 15th August 2007, 06:33 AM

Hi!

Thanks!

About the slots: if the slots opening is smaler than the out coming sound wave, than will be a kind of spatial sound?

Tyimo

sreten · 15th August 2007, 09:37 AM

Hi,

As alluded to in that article, if you make the slot too narrow you
will effectively turn it into the front chamber of a bandpass cabinet.

Which is not what you want .........

Also remember to leave enough clearance for the units max excursion.

/sreten.

Tyimo · 15th August 2007, 10:20 AM

Yes.

Thanks.

What could be the min. slot for an 6.5" (18cm) driver?
13cm =2600Hz?

Tyimo

Salas · 15th August 2007, 11:14 AM

It can't be accurately decided by wave formulas alone. It takes experimentation and measurements for individual transducers. There are many things to balance. One is the off axis behavior of each 6.5'', since the dispersion is dependable on its cone flex and phase plug or dust cup. Then, the cavity behind the slot interacts with the cone shape and movement. The material and thickness of the slot baffle contributes also. Crossover frequency and slope is essential too. The goal is to get better off axis integration and certain desired dispersion without extra cavity and mechanical resonances coloring the area. In pro speakers that many such tricks are used, much wood is cut and many measurements are taken. Subjective evaluation and trial on error, is the order of the day despite the theory. I would try your 130mm starting point, it sounds logical.

Tyimo · 15th August 2007, 01:04 PM

Thanks!

I will try it soon.

Tyimo

ente · 15th August 2007, 09:42 PM

.. maybe this helps to find something more

http://home.wanadoo.nl/dezaire/LS3-5a/LS3-5a_clone.htm

Regards
Heinrich

Tyimo · 16th August 2007, 09:27 AM

Thanks Heinrich!!!

Very good links!

Greets:

Tyimo

15th August 2007, 09:42 PM	#9
ente diyAudio Member Join Date: Aug 2004 Location: NNW of Rome	LS3-5a .. maybe this helps to find something more http://home.wanadoo.nl/dezaire/LS3-5a/LS3-5a_clone.htm Regards Heinrich

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14th August 2007, 07:03 PM	#2
Geoff diyAudio Member Join Date: Apr 2001 Location: UK	Have a look at the following BBC document for the LS5/8 which uses a similar principle: http://downloads.bbc.co.uk/rd/pubs/reports/1979-22.pdf I cannot remember if it covers the design of the front panel cut-out for the bass unit.

14th August 2007, 08:14 PM	#3
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	It widens the midrange dispersion of the 300mm woofer. Its the same principle as with slot tweeters.

15th August 2007, 06:33 AM	#4
Tyimo diyAudio Member Join Date: Nov 2002 Location: Hungary	Hi! Thanks! About the slots: if the slots opening is smaler than the out coming sound wave, than will be a kind of spatial sound? Tyimo

15th August 2007, 09:37 AM	#5
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, As alluded to in that article, if you make the slot too narrow you will effectively turn it into the front chamber of a bandpass cabinet. Which is not what you want ......... Also remember to leave enough clearance for the units max excursion. /sreten.

15th August 2007, 10:20 AM	#6
Tyimo diyAudio Member Join Date: Nov 2002 Location: Hungary	Yes. Thanks. What could be the min. slot for an 6.5" (18cm) driver? 13cm =2600Hz? Tyimo

15th August 2007, 11:14 AM	#7
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	It can't be accurately decided by wave formulas alone. It takes experimentation and measurements for individual transducers. There are many things to balance. One is the off axis behavior of each 6.5'', since the dispersion is dependable on its cone flex and phase plug or dust cup. Then, the cavity behind the slot interacts with the cone shape and movement. The material and thickness of the slot baffle contributes also. Crossover frequency and slope is essential too. The goal is to get better off axis integration and certain desired dispersion without extra cavity and mechanical resonances coloring the area. In pro speakers that many such tricks are used, much wood is cut and many measurements are taken. Subjective evaluation and trial on error, is the order of the day despite the theory. I would try your 130mm starting point, it sounds logical.

15th August 2007, 01:04 PM	#8
Tyimo diyAudio Member Join Date: Nov 2002 Location: Hungary	Thanks! I will try it soon. Tyimo

16th August 2007, 09:27 AM	#10
Tyimo diyAudio Member Join Date: Nov 2002 Location: Hungary	Thanks Heinrich!!! Very good links! Greets: Tyimo

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