I have read that the box resonate frequency is 1/2 the wavelength of the longest dimension...is this the longest unbraced dimension or simply the cabinet dimension? Also, is the longest dimension the diagonal from corner to corner or does this assume measurements of parallel edges?
Thx
Thx
Resonant frequency eq'n
AFAIK, it is the longest dimension in Cartesian coordinates (not strictly speaking, but if measuring in Cartesian coordinates then all calculations must be in them). It can be reduced by placing appropriate bracing at .617 times the particular dimension (the Golden ratio, .617:1.00:1.617), braced to the side opposite.
You must also consider whether the enclosure is a bass reflex or a sealed box.
AFAIK, it is the longest dimension in Cartesian coordinates (not strictly speaking, but if measuring in Cartesian coordinates then all calculations must be in them). It can be reduced by placing appropriate bracing at .617 times the particular dimension (the Golden ratio, .617:1.00:1.617), braced to the side opposite.
You must also consider whether the enclosure is a bass reflex or a sealed box.
So what are you asking about?
If trying to calculate possible enclosure resonances, then calculation are easy. If you know the desired volume (calculated in the usual way), calculate the cube root of it. Multiply that by .618. That's the smallest interior dimension. Multiply that by 1.618. That's the 2nd dimension. Multiply that by 1.618 again. The result is the largest dimension.
This is assuming that you are after a Golden ratio enclosure, which is generally thought to be the best rectangular enclosure. The Golden ratio is calculated as follows:
(1+/- (5^-2))/2
An example Volume req'd:=1.5 Ft^3 (or 1728 in^3 x 1.5 = 2592 in^3)
Taking the cube root results in 13.73". That becomes the "middle" dimension. Divide that by 1.618 gives you 8.486". Multiplying 13.73" by 1.618 results in 18.1" . Remember that these dimensions are inside ones and do not take into account any volume losses due to internal bracing.
Do you have any experience with loudspeaker calculations? If not there are very good books available, most noticeably "The Loudspeaker Design Cookbook " by Vance Dickenson.
The only difference between sealed and bass reflex calculations is that the resonant frequency of the enclosure is dominated by the resonance frequency of the port, which is substantial.
If trying to calculate possible enclosure resonances, then calculation are easy. If you know the desired volume (calculated in the usual way), calculate the cube root of it. Multiply that by .618. That's the smallest interior dimension. Multiply that by 1.618. That's the 2nd dimension. Multiply that by 1.618 again. The result is the largest dimension.
This is assuming that you are after a Golden ratio enclosure, which is generally thought to be the best rectangular enclosure. The Golden ratio is calculated as follows:
(1+/- (5^-2))/2
An example Volume req'd:=1.5 Ft^3 (or 1728 in^3 x 1.5 = 2592 in^3)
Taking the cube root results in 13.73". That becomes the "middle" dimension. Divide that by 1.618 gives you 8.486". Multiplying 13.73" by 1.618 results in 18.1" . Remember that these dimensions are inside ones and do not take into account any volume losses due to internal bracing.
Do you have any experience with loudspeaker calculations? If not there are very good books available, most noticeably "The Loudspeaker Design Cookbook " by Vance Dickenson.
The only difference between sealed and bass reflex calculations is that the resonant frequency of the enclosure is dominated by the resonance frequency of the port, which is substantial.
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Hi.Without making a new thread i would like to ask a question about resonat frequencys..how can we reduce them?Dampening the box?(yes im a noob)..asuming my cabinets resonant frequency is at 133hz(peak) starting at @ 128 how can i fix that?(i detrmined that by using a sound generator)
Reducing an enclosures resonance.
There are several methods to reduce a cabinet's resonant frequency
Remember that we are talking about resonances that are cabinet related, not the actual resonance of a port or the woofer cone itself (that's what stuffing is for).
There are several methods to reduce a cabinet's resonant frequency
- brace the enclosure
- use damping material (or constrained layer construction)
- dampen the driver chassis using something like "Dynamat" or a non-hardening putty or sealant
- improve the mechanical fasteners,using T-nuts or threaded inserts
Remember that we are talking about resonances that are cabinet related, not the actual resonance of a port or the woofer cone itself (that's what stuffing is for).
well its a ported box u have any links to a guide or can u explain/guide me to a site on how can i reduce the resonace of the sistem itself?(im prety sure that frequency is of the port..how can i know how much stuffing i need for a paticular freq..i understand u can do more harm than good if done incoreclty)
I do have the book and it mentions spacing the braces unevenly but it does not go into detail on what magnitude of imbalance in spacing is appropriate...maybe it does not matter so long as they are not creating equal spaces?
What speakers(or drivers) are you trying to "fix"?
Izuall : What speakers are you trying to fix? If you provide the internal volume (and dimensions, including the port diameter and it's length), I can work backwards to calculate the resonant frequency and the tuned frequency. Once that is known, then steps can be taken to reduce the magnitude of it and/or shift the resonance. A resonance can also occur if the cabinet is poorly constructed and the drivers are poorly mounted.
Kooshball : The fact that a cabinet is braced is more important as to where it is braced (I know some may disagree). What is important is that opposite sides are connected. This can be quite simple, and can even be used as a means of "tuning" the resonance of the enclosure as per Michael Greene's (of Room Tunes) loudspeaker designs.
There are so many sites explaining basic loudspeaker designs and construction. One that I have seen that seems to cover a fair bit information is The Subwoofer DIY Page. It includes a few projects that should be very good (the DIY version of Rogers AB1 subwoofer intended for use with LS3/5A monitor speakers is a good example). Also check out humble homemade hifi, and Troels
Gravsen's Page.
Izuall : What speakers are you trying to fix? If you provide the internal volume (and dimensions, including the port diameter and it's length), I can work backwards to calculate the resonant frequency and the tuned frequency. Once that is known, then steps can be taken to reduce the magnitude of it and/or shift the resonance. A resonance can also occur if the cabinet is poorly constructed and the drivers are poorly mounted.
Kooshball : The fact that a cabinet is braced is more important as to where it is braced (I know some may disagree). What is important is that opposite sides are connected. This can be quite simple, and can even be used as a means of "tuning" the resonance of the enclosure as per Michael Greene's (of Room Tunes) loudspeaker designs.
There are so many sites explaining basic loudspeaker designs and construction. One that I have seen that seems to cover a fair bit information is The Subwoofer DIY Page. It includes a few projects that should be very good (the DIY version of Rogers AB1 subwoofer intended for use with LS3/5A monitor speakers is a good example). Also check out humble homemade hifi, and Troels
Gravsen's Page.
I have an active speaker system(internal dimentions are Depth of 9.1in/Hight
13.6in/With=9.1in rear ported with a 6in long port and 2.2in in diameter the entire cabinet is made of MDF 0.2in thick)It houses a 6.5in woofer and a 1in dome tweeter.The port is located above the woofer in exact alignment with the tweeter.50Wx2
Some answers.
Izuall:
I tried a calculator located here. The results are an enclosure with a resonant frequency of 45.07 Hz. How does this compare to what you know about the speakers?
Are the walls of the enclosures really made with mdf that is just .2" thick? Typically enclosures of this size should be made with at least 1/2" material, but much better with 3/4"(if using mdf). If using Baltic Birch ply, you may be able to use 1/2" material, as long as it is well braced.
Stuffing can alter the resonance of the driver, damping material on the walls of the enclosures can reduce the resonance of the enclosures. If you are okay making new boxes make them from the best material possible using the best method available told you.
Izuall:
I tried a calculator located here. The results are an enclosure with a resonant frequency of 45.07 Hz. How does this compare to what you know about the speakers?
Are the walls of the enclosures really made with mdf that is just .2" thick? Typically enclosures of this size should be made with at least 1/2" material, but much better with 3/4"(if using mdf). If using Baltic Birch ply, you may be able to use 1/2" material, as long as it is well braced.
Stuffing can alter the resonance of the driver, damping material on the walls of the enclosures can reduce the resonance of the enclosures. If you are okay making new boxes make them from the best material possible using the best method available told you.
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well ive done better mesuremenents and the speakerbox is constructed asimetricaly the back wall is only 0.2in thick but the sidepanels are 0.3in.i was allso able to deterimine that the resonance i was hearing wasnt the cabinets themselfs but rather some old furniture that i tought i fixed by filling them..also the speakers arent all that powerfull and dont go that deep in terms of bass(low frequnecy point is only 55hz)so if they resonate at 45..thats good news.Thank you for ur time and asistance..i guess im only gona buy a pair of good stands to improve them(and later replace them when i can allocate some buget in that direction ..right now i have other priorities)Again thank you.
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