I have seen in a YouTube video a few months ago how they reduce the center to center spacing of a subwoofer array by covering each driver with a plate with two oval holes.
This is supposed to turn one driver into two separate point sources.
Is there a technical term for this? I scoured the net for an hour without any result.
I am trying to find out if;
....it really works
.....can it be done to midrange array
drivers too?
I have a pile of wonderful 12cm full range drivers that I want to cross over quite high ( around 6Khz) to a tweeter array.
This is supposed to turn one driver into two separate point sources.
Is there a technical term for this? I scoured the net for an hour without any result.
I am trying to find out if;
....it really works
.....can it be done to midrange array
drivers too?
I have a pile of wonderful 12cm full range drivers that I want to cross over quite high ( around 6Khz) to a tweeter array.
Subwoofers, low frequency long wavelengths.
At mid frequencies and going up to 6KHz you may have lots of interesting effects coming into play.
At mid frequencies and going up to 6KHz you may have lots of interesting effects coming into play.
It turns the front of the cone into a bandpass enclosure, the effects of which can be modelled in hornresp.
Rob.
Rob.
Could it be called a diffuser?
Slot diffusers were once used to 'spread' the upper frequencies of single cone 8", 10" or 12" drivers, hence increasing treble dispersion and avoiding 'beaming'. The introduction of dedicated tweeters rendered the use of slot diffusers unnecessary.
In his book 'Loudspeakers', G.A. Briggs gives details of slot diffusers. The modified diffuser shown on the right of the image below avoids restriction of output at lower frequencies.
Slot diffusers were once used to 'spread' the upper frequencies of single cone 8", 10" or 12" drivers, hence increasing treble dispersion and avoiding 'beaming'. The introduction of dedicated tweeters rendered the use of slot diffusers unnecessary.
In his book 'Loudspeakers', G.A. Briggs gives details of slot diffusers. The modified diffuser shown on the right of the image below avoids restriction of output at lower frequencies.
The BBC used slotted baffles and following in that tradition, Graham audio use them in some of their designs See info here for some further words from Graham audio.
https://www.grahamaudio.co.uk/technology/slotted-baffles/
https://www.grahamaudio.co.uk/technology/slotted-baffles/
Slots or holes will do nothing at typical bass and sub bass frequencies...wavelength is the determining factor. 200Hz has a wavelength of about 1.7 meters or about 5.5 feet, increasing as frequency decreases. So it won't affect directivity in any significant way.
Mike
Mike
Study the JBL EON with mid/woofer waveguides, and you might get a clue as to how it affects the speaker.
SImilar concept as using a diffraction slot in a horn. Some info to find on the subject if you look around on google i'm sure.
Here are some threads dipping into the subject at some point.
And some documents
https://www.diymobileaudio.com/threads/improve-your-midbass.322554/
https://www.diyaudio.com/community/threads/jbl-m2-for-the-poors.247050/
https://www.diyaudio.com/community/threads/diy-woofer-wave-guides-they-work.274647/
https://www.me-geithain.de/en/rl-901k2.html
https://web.archive.org/web/20130201144500/http://www.tgpwebzine.com/?page_id=424
SImilar concept as using a diffraction slot in a horn. Some info to find on the subject if you look around on google i'm sure.
Here are some threads dipping into the subject at some point.
And some documents
https://www.diymobileaudio.com/threads/improve-your-midbass.322554/
https://www.diyaudio.com/community/threads/jbl-m2-for-the-poors.247050/
https://www.diyaudio.com/community/threads/diy-woofer-wave-guides-they-work.274647/
https://www.me-geithain.de/en/rl-901k2.html
https://web.archive.org/web/20130201144500/http://www.tgpwebzine.com/?page_id=424
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Study the JBL EON with mid/woofer waveguides, and you might get a clue as to how it affects the speaker.
SImilar concept as using a diffraction slot in a horn. Some info to find on the subject if you look around on google i'm sure.
Here are some threads dipping into the subject at some point.
And some documents
https://www.diymobileaudio.com/threads/improve-your-midbass.322554/
https://www.diyaudio.com/community/threads/jbl-m2-for-the-poors.247050/
https://www.diyaudio.com/community/threads/diy-woofer-wave-guides-they-work.274647/
https://www.me-geithain.de/en/rl-901k2.html
https://web.archive.org/web/20130201144500/http://www.tgpwebzine.com/?page_id=424
Thank you so much Arez for this wonderfully helpful reply. Sometimes forums can be tiering and full of rude or weird characters...... But with replies like this it is all worth it!
I really like the idea of the open cell foam donuts. In my case I will try it with two oval cutouts per driver....
With a solid plate with slits ala JBL you need fairly high EBP. My drivers are low excursion with small alnico motors. The foam could be a brilliant solution and also less prone to diffraction than a solid plate.
When I have some more time I will go through all your links in more detail.
I did a quick and dirty test with some stuff I had at hand. I didn't have acoustic foam so I tried it with automotive felt. That didn't do much but muffle the sound. Then I tried some rubbery closed cell foam and to my surprise that seems to work really well.
My laptop died so I cannot measure at the moment. But I listened to it with white noise while changing listening angles and it does seem way more even. It doesn't reduce the highs off axis but does on axis. It also seems to extend the bass a little.....maybe mild slot loading.....?
I will need to wait until I get a new laptop before I can verify that it also reduces comb filtering in a line array.
Thanks again @Arez for the great information in your reply
My laptop died so I cannot measure at the moment. But I listened to it with white noise while changing listening angles and it does seem way more even. It doesn't reduce the highs off axis but does on axis. It also seems to extend the bass a little.....maybe mild slot loading.....?
I will need to wait until I get a new laptop before I can verify that it also reduces comb filtering in a line array.
Thanks again @Arez for the great information in your reply
Trace Elliott had a bass combo amplifier which used this technique.
content://com.android.chrome.FileProvider/images/screenshot/17192238092309066826837466567883.jpg
The lower slot is for bass reflex port.
The vertical one was used to modify directivity behavior in mid/high. As Galu explained.
DJK ( rip) once gave the equation to define freq at which it start to be effecctive but it was on an other forum. Can't remember where it was but if i found it, it should be accessible ( it was related to ppsl type enclosure discussion about the effect slot have).
content://com.android.chrome.FileProvider/images/screenshot/17192238092309066826837466567883.jpg
The lower slot is for bass reflex port.
The vertical one was used to modify directivity behavior in mid/high. As Galu explained.
DJK ( rip) once gave the equation to define freq at which it start to be effecctive but it was on an other forum. Can't remember where it was but if i found it, it should be accessible ( it was related to ppsl type enclosure discussion about the effect slot have).
Attachments
Some historical information:
The Kolster Brandes patent for slot loading dates back to 1947.
659,063. Loudspeaker baffles. KOLSTER BRANDES, Ltd. Sept. 10, 1947, No. 24849. To improve high frequency response and diffusion, the aperture (6) in a loud-speaker baffle is reduced to a slot having a width no more than half the length.
Gilbert Briggs' experiments showed the diffuser to be effective between 2 kHz to 6 kHz.
He said that the length of the aperture should be the same as the piston diameter of the cone, the width being less than the smallest wavelength involved. Hence a 4" wide slot would be good for 3 kHz.
By altering the shape of the slot and adding extra holes, obstruction at low frequencies can be overcome.
The Kolster Brandes patent for slot loading dates back to 1947.
659,063. Loudspeaker baffles. KOLSTER BRANDES, Ltd. Sept. 10, 1947, No. 24849. To improve high frequency response and diffusion, the aperture (6) in a loud-speaker baffle is reduced to a slot having a width no more than half the length.
Gilbert Briggs' experiments showed the diffuser to be effective between 2 kHz to 6 kHz.
He said that the length of the aperture should be the same as the piston diameter of the cone, the width being less than the smallest wavelength involved. Hence a 4" wide slot would be good for 3 kHz.
By altering the shape of the slot and adding extra holes, obstruction at low frequencies can be overcome.
The acoustic lens is another device for high frequency diffusion, but its operating principle relies on the refraction of sound waves rather than diffraction.
Horns are very directional at high frequencies, and an acoustic lens widens their dispersion.
Below is the optical analogy:
https://www.tnt-audio.com/clinica/acoustic_lens.pdf
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