Hi guys this is indeed a very noob question, but I have read stuff all over the net and on this forum but haven't found any simple explanation of why an open baffle has a low frequency roll off ?
Could someone please explain this phenomenon ?? Graphically please ??
Is it just because the waves from the back of the speaker collide with those of the front of the speaker and cancel out due to their difference in phase ??
Why doesn't it happen with wide baffles ??
Why don't front ported or bass/reflex have this problem?? as they are adding the waves from the front to the waves coming from the back of the speaker via the port
Do open baffle with narrow panels(obviously small speakers 3"-5") or zero-baffle constructions(again using 3" to 5" speakers) which have extended bass exist or it's physically impossible to have bass from them WITHOUT adding an EQ ?
Is the bass from an open baffle speaker sound like a sealed box ?? or is it really something else ?? describe please
Thanks again for your time guys!!
Could someone please explain this phenomenon ?? Graphically please ??
Is it just because the waves from the back of the speaker collide with those of the front of the speaker and cancel out due to their difference in phase ??
Why doesn't it happen with wide baffles ??
Why don't front ported or bass/reflex have this problem?? as they are adding the waves from the front to the waves coming from the back of the speaker via the port
Do open baffle with narrow panels(obviously small speakers 3"-5") or zero-baffle constructions(again using 3" to 5" speakers) which have extended bass exist or it's physically impossible to have bass from them WITHOUT adding an EQ ?
Is the bass from an open baffle speaker sound like a sealed box ?? or is it really something else ?? describe please
Thanks again for your time guys!!
Yes you do have it right...The two waves meet at the the baffle edge out of phase & cancel out....the phenomenon was called Doublet operation or an Acoustic short circuit. The wider the baffle the lower the frequencies of 'cancellation' soon however the width of the baffle becomes entirely too big.
Assuming you want to get it down to 80Hz & have a sub-woofer take over from there......do the calculations & prepare. Often times, Super-sized loudspeakers don't go over too well with our Wives/GFs!!!
Ported enclosures are a whole nother' ball O' wax.
________________________________________________________Rick.......
Assuming you want to get it down to 80Hz & have a sub-woofer take over from there......do the calculations & prepare. Often times, Super-sized loudspeakers don't go over too well with our Wives/GFs!!!
Ported enclosures are a whole nother' ball O' wax.
________________________________________________________Rick.......
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Hi,
The waves from the front and back combine and cancel. The bass
rolls off at 6dB/octave, and note that driver excursion doesn't.
(its the most important thing to understand, baffle loss throws
away driver excursion, reducing the drivers SPL capability a lot.)
It happens with wide baffles as well, except the frequencies it occurs
are lower, the transition frequency is lower, so wider baffles have
less baffle loss at a given low frequency than narrower baffles.
Vented boxes do have this problem below the port tuning. Above
tuning the output of the port is in phase with the driver output.
(Consider playing with a toy that is weight on the end of a spring,
moving it up or down slowly it will follow your movements, but at
the clearly obvious resonance, your hand and the weight move in
opposite directions, and if you wiggle it fast, nothing much happens.)
For narrow panels even with EQ extended bass is not possible due to
the ludicrous driver excursion requirements to overcome baffle loss.
Bass from a sealed box is not like an open baffle as it is not dipolar.
rgds, sreten.
The waves from the front and back combine and cancel. The bass
rolls off at 6dB/octave, and note that driver excursion doesn't.
(its the most important thing to understand, baffle loss throws
away driver excursion, reducing the drivers SPL capability a lot.)
It happens with wide baffles as well, except the frequencies it occurs
are lower, the transition frequency is lower, so wider baffles have
less baffle loss at a given low frequency than narrower baffles.
Vented boxes do have this problem below the port tuning. Above
tuning the output of the port is in phase with the driver output.
(Consider playing with a toy that is weight on the end of a spring,
moving it up or down slowly it will follow your movements, but at
the clearly obvious resonance, your hand and the weight move in
opposite directions, and if you wiggle it fast, nothing much happens.)
For narrow panels even with EQ extended bass is not possible due to
the ludicrous driver excursion requirements to overcome baffle loss.
Bass from a sealed box is not like an open baffle as it is not dipolar.
rgds, sreten.
As usual...
...a good explanation sreten (hi Cal).
One way to increase bass with an OB is to create sides and a top shelf (that can be used as a stand to hold the OB). The modified OB then is a very short "U" with much deeper bass as a result. The great thing about the OB types is that there does not exist box colourations.
The resultant bass produced via OBs is what I would consider "deep" but without much impact. The low frequencies are there, they just don't hit you like a good box type subwoofer.
...a good explanation sreten (hi Cal).
One way to increase bass with an OB is to create sides and a top shelf (that can be used as a stand to hold the OB). The modified OB then is a very short "U" with much deeper bass as a result. The great thing about the OB types is that there does not exist box colourations.
The resultant bass produced via OBs is what I would consider "deep" but without much impact. The low frequencies are there, they just don't hit you like a good box type subwoofer.
I have to disagree. An OB, be it flat,curved U, H can all have just as severe coloration from the baffle as you do with the baffle closed on itself. If you take an OB to the extreme, as in an IB, I can assure you some very strong bass is possible with the proper driver ( large, stiff suspension ) A point well argued by "The cult of the IB" Management of the impedance is far harder than a compliant box.
I have been trying to deal with the same issue from the opposite side of the coin.
Namely, too much bass from an OB.
Worried about a potential lack of bass from a pair of PHY-HP sand filled baffles I am building, I got a pair of 12 inch full rangers.
Trial assembly and testing was disappointing with way too much bass response, even down into the mid 20hz region.
I have tamed them by reverting to a pair of old 8 inchers and raising the baffles off the floor a bit. Also, folding the wings back and fitting a bass trap has helped.
Have lost the very lowest notes of a pipe organ since they back off significantly below 35 hz.For any normal music, reggae, dub, electronica etc there is more and better bass than I have heard before. Fast, detailed, delicate and warm.
I can't understand what I did wrong to get this result. I think the NOS tubes I am using must take some responsibility along with the 80kg of sand I managed to squeeze in.
I should have been more skeptical of statements that OBs do not make good bass.
That is not always true.
Namely, too much bass from an OB.
Worried about a potential lack of bass from a pair of PHY-HP sand filled baffles I am building, I got a pair of 12 inch full rangers.
Trial assembly and testing was disappointing with way too much bass response, even down into the mid 20hz region.
I have tamed them by reverting to a pair of old 8 inchers and raising the baffles off the floor a bit. Also, folding the wings back and fitting a bass trap has helped.
Have lost the very lowest notes of a pipe organ since they back off significantly below 35 hz.For any normal music, reggae, dub, electronica etc there is more and better bass than I have heard before. Fast, detailed, delicate and warm.
I can't understand what I did wrong to get this result. I think the NOS tubes I am using must take some responsibility along with the 80kg of sand I managed to squeeze in.
I should have been more skeptical of statements that OBs do not make good bass.
That is not always true.
Hi Sreten!! I have another little question if you don't mind.
You say that sound coming behind the speaker interferes with the sound from the front of the speaker and as they are of opposite phase, they can cancel each other.
I was thinking about this then I though , in a sealed box for example, I am thinking, is the energy from the rear of the speaker really(totally) absorbed by MDF for example ?? or it is absorbed and blocked partially ?? I have read that low frequencies are hard to block, and that MDF didn't have a great coefficient of absorption with regards to low frequencies.
Another question, if the box itself vibrates, it's radiating sound-waves right ?? and this in turn can mess with room acoustics and mess with the waves coming from the front of the speaker right ??
I have read also that Aluminum is a very neutral material and quite ideal for baffles and enclosures, may I know why ?? I have noticed some pro monitor speakers having Aluminum cabinets. What are the advantages of those ?
Sorry for those annoying questions but I am really eager to learn
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Stuff the box.
It is my experience that both a sealed box and a bass reflex box is best fully stuffed with with something that absorbs the sound.
I find the that waves reflected from the back and other surfaces come back through the speaker cone, and mess with the sound. It may dampen the bass response a little bit, but that is a price well worth paying for improved clarity of sound.
I would not depend on any hard material that makes up the wall of any enclosure to absorb the sound. Any hard material will reflect most of the sound waves.
It is a simple law known to physics that an impedance change in the medium through which a wave travels will reflect a wave. The greater the difference of impedance, the greater the reflection.
It is my experience that both a sealed box and a bass reflex box is best fully stuffed with with something that absorbs the sound.
I find the that waves reflected from the back and other surfaces come back through the speaker cone, and mess with the sound. It may dampen the bass response a little bit, but that is a price well worth paying for improved clarity of sound.
I would not depend on any hard material that makes up the wall of any enclosure to absorb the sound. Any hard material will reflect most of the sound waves.
It is a simple law known to physics that an impedance change in the medium through which a wave travels will reflect a wave. The greater the difference of impedance, the greater the reflection.
The following site has some good ideas an how to get good bass from a sealed box.
Elliott Sound Products - The Audio Pages (Main Index)
Elliott Sound Products - The Audio Pages (Main Index)
Boxes are not lined/stuffed to absorb the back wave. The back wave in the box is pressure wave, not the traveling wave the comes off of the front. BR's are lined to absorb standing waves inside the box due to reflections between the walls. Closed boxes are stuffed to increase the apparent volume by changing adiabatic heating into isothermal heating.
Bob
Bob
Hi,
In sealed box bass cone movement pressurises the air in the box,
effectively adding to the suspension stiffness. That is why the
suspension stiffness is usually give as Vas (in L or cuft).
e.g. a driver of 60L Vas, Fs 30Hz and Qts 0.35 placed in a box
of 1/3 Vas, in this case 20L, gives a Qbox of 0.7 and Fbox 60Hz.
Theoretically the suspension and the air spring of the box should
act like a capacitor, only storing energy not dissipating it. In real
life there are some losses but not a great deal, the air is a spring.
You can't talk about absorbing the back wave until you go to big
and very long lines, most TL's utilise the back wave, not absorb it.
An infinitely stiff box would produce no sound due to the pressure.
Real boxes do flex under the bass pressure, but more importantly
resonate in the midrange depending on damping and the mass
to stiffness ratio of the panels, ribbing and bracing can help.
Aluminium has no particular properties making it ideal for cabinets,
though presumably an alloy of it is is good for small die cast cabinets.
An added similar mass of internal surface damping is a good idea.
Bigger injection moulded pro speakers use a plastic mix that
includes decent damping in the bulk properties of the material.
Stuffing does add some internal volume and also like lining vented
boxes damps the standing wave air space resonances in the box.
rgds, sreten.
In sealed box bass cone movement pressurises the air in the box,
effectively adding to the suspension stiffness. That is why the
suspension stiffness is usually give as Vas (in L or cuft).
e.g. a driver of 60L Vas, Fs 30Hz and Qts 0.35 placed in a box
of 1/3 Vas, in this case 20L, gives a Qbox of 0.7 and Fbox 60Hz.
Theoretically the suspension and the air spring of the box should
act like a capacitor, only storing energy not dissipating it. In real
life there are some losses but not a great deal, the air is a spring.
You can't talk about absorbing the back wave until you go to big
and very long lines, most TL's utilise the back wave, not absorb it.
An infinitely stiff box would produce no sound due to the pressure.
Real boxes do flex under the bass pressure, but more importantly
resonate in the midrange depending on damping and the mass
to stiffness ratio of the panels, ribbing and bracing can help.
Aluminium has no particular properties making it ideal for cabinets,
though presumably an alloy of it is is good for small die cast cabinets.
An added similar mass of internal surface damping is a good idea.
Bigger injection moulded pro speakers use a plastic mix that
includes decent damping in the bulk properties of the material.
Stuffing does add some internal volume and also like lining vented
boxes damps the standing wave air space resonances in the box.
rgds, sreten.
Hi!
I am a bit confused. I found different explanations about the wavelenght:
The bass begin to roll off at 6dB/octave, when the baffle width is equal to 1/4 wave leght of the low frequency.
Some says it is measured from the middle point of the driver, some says it is measured from the edge of the driver.
In the "Open baffle study, August-2003" from Troels Gravesen He calculate it very strange. He used a 24 cm width baffle (driver in the centre), but calculating with 45 cm!?
How can I calculate the 6dB/octave bass roll off?
Greets:
Tyimo
It is common to calculate the rolloff by measuring from the midpoint of the front of the driver, around the baffle, to the midpoint of the back. See here:
Electro-acoustic models
Electro-acoustic models
Why is the K1 o.17 and not o.25 when we are seeking the 1/4 wave length of the low frequency for rolloff onset?
Fe = .17 X 343 / D
Fe in Hertz
343 speed of sound at room temp.
D in metres, can be measured as baffle width or from centre of driver on the front to centre of driver on the back, shortest distance.
If as above then a 1 metre wide baffle would be:
Fe = .17 X 343 / 1 = 58.31 for 6/db per octave roll off.
Correct or is it 116 or other?
Fe = .17 X 343 / D
Fe in Hertz
343 speed of sound at room temp.
D in metres, can be measured as baffle width or from centre of driver on the front to centre of driver on the back, shortest distance.
If as above then a 1 metre wide baffle would be:
Fe = .17 X 343 / 1 = 58.31 for 6/db per octave roll off.
Correct or is it 116 or other?
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