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Old 27th March 2009, 05:14 AM   #1
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Default speakers operating near their resonant frequency

There is something I find annoying about all my speakers:

For signals approaching the speakers resonant frequency there is a peak in response in a muddy/boomy/annoying way. It only vaguely resembles the original sound and it continues for a fraction of a second after the input signal stops.

From what I have read it looks like too high Q, or not enough damping.
Any help on how to fix it?
A parametric equalizer / notch filter to cut down the offending frequency?
Does adding more soft stuff inside the box increase mechanical damping? What materials can be used?
Is there a way to increase electrical damping? Can I add a parallel 8Ohm resistor to 8Ohm speakers when used with a 4Ohm-capable amplifier?

I don't want a lot of bass, just reasonably flat response down to a point and then smooth roll-off. Is this too much to ask?

Thanks
kanguru007
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Old 27th March 2009, 05:43 AM   #2
infinia is offline infinia  United States
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Hi
1) plug or stuff the port.

2) No port then add increasing amounts of acoustic stuffing fiberglass or polyfill>
3) Still not enough then add increasing amount of series resistance 0.5 - 2 ohms.
4) Still not enough and don't want to do step 3), then drill a few smaller holes in back panel and cover with a few layers of cloth.

heehee or we can get a load of more info from you and get our calculators out.
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File Type: jpg put a sock in.jpg (84.3 KB, 386 views)
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Old 27th March 2009, 06:42 AM   #3
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That was quick... Cal just posted that pic in another thread.

There are better things than socks. I like using low-medium density foam (i have lots), Same for the aperiodic ports in option 4. BTW 4/ is a more rigorous application of 1/. Probably be a good idea to seal the port.

Click the image to open in full size.

My feeling is that 3/ will probably take you in the wrong direction.

dave
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Old 27th March 2009, 07:21 AM   #4
infinia is offline infinia  United States
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Quote:
Originally posted by planet10
That was quick... Cal kust posted that pic in another thread.


My feeling is that 3/ will probably take you in the wrong direction.

dave

Saw the pic and thought it fit the shoe so to speak.

Option 3 raises Qes and thus Qts and higher Q for a fixed enclosure volume is not needed here.
Also stuffing too close to the cone raises Qms and usually more slightly Qts too.

Q is inversely related to damping ie higher Q is less damping.



Dave how do you get that 104K image to display large (ie not a smaller thumbnail)
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Old 27th March 2009, 07:44 AM   #5
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Quote:
Originally posted by infinia
Q is inversely related to damping ie higher Q is less damping.
Right. And higher Q is more boom.

dave
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Old 27th March 2009, 07:58 AM   #6
infinia is offline infinia  United States
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Quote:
Originally posted by planet10


Right. And higher Q is more boom.

dave

and i just thought it was Fpk/BW for a 2nd order system.


Dave how do you get that 104K image to display large (ie not a smaller thumbnail)

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Old 27th March 2009, 08:29 AM   #7
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Quote:
Originally posted by infinia
Dave how do you get that 104K image to display large (ie not a smaller thumbnail)
It is sitting in some of my webspace (in this case on some of Apple's servers)

http://p10hifi.net/tlinespeakers/FAL...odic-FR125.jpg

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Old 27th March 2009, 11:31 AM   #8
Helmuth is offline Helmuth  Netherlands
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A to small bass reflex port can sound boomy, or a to long pipe.

Because the pipe ads acoustic resistance on its tuning frequency and so prevents the speaker to resonate.

When the port is to small the pipe will not add enough load to the resonating speaker and the damping will be poor.
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Old 27th March 2009, 12:33 PM   #9
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Default speakers operating near their resonant frequency

Sorry, I should have been more specific. I'm using closed speakers, a pair of 1969 Nivico GB-1E speakers (with 4 small but good-looking paper cone, cloth surround, cast aluminum chassis woofers). They resonate at a low frequency so boomy is not the word to describe their peak but they still have a peak at resonance.
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Old 27th March 2009, 12:59 PM   #10
Helmuth is offline Helmuth  Netherlands
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Default Re: speakers operating near their resonant frequency

Quote:
Originally posted by kanguru007
Sorry, I should have been more specific. I'm using closed speakers, a pair of 1969 Nivico GB-1E speakers (with 4 small but good-looking paper cone, cloth surround, cast aluminum chassis woofers). They resonate at a low frequency so boomy is not the word to describe their peak but they still have a peak at resonance.
Then increase the volume of the box,and then stuff it loose till the right sound is there.

Do not place them near floor or corner or wall but a few meter of the wall.

Place them on a stand about 40cm > of the floor.

Sound like the perfect excuse to build a new set speakers.
Here a design of pair very tight sounding speakers.tight
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