I, GROMAN, who agree on most of your points,Austin said:
here Quote your Final Summary:
Final Analysis:
The trend seems to be constant for all criterions in designing a loudspeaker. There is not a single
technique that will produce the best results, but by a combination of many techniques and materials, a
reproduction of sound quite close to the original recording is possible. While this study only focused
on the aspects of the cabinet that can improve loudspeaker performance, there are other considerations,
such as the integration of quality drivers and electrical components, which will have a profound impact
on the speaker's overall performance as well. Though when considering only the cabinet, it is
important to keep in mind the effects of diffraction, internal resonance, cabinet wall transmission,
and time alignment. Successful designs are judged purely on subjective listening tests. That said,
the subjective test results favor a cabinet that tapers in the rear and has some damping material
inside the enclosure, to help eliminate internal resonance. The cabinet eliminates diffraction by
removing 90-degree angles from the front baffle and using a damping material like felt to absorb most
of the waves before they reach the edges of the baffle. Slanting the front baffle, or staggering
separate enclosures the proper distances compensates for time alignment. A combination of MDF, and
hardwood is used and is possibly layered. Using quality drivers, quality construction techniques,
and satisfying the recommended criterion still leaves the designer with infinite possibilities. The
perfect theoretical design is rarely the best in practice, so tweaking is always required to get the
best out of a design. Unfortunately, there is not a recipe for the best loudspeaker, but there are
CLEAR ADVANTAGES to using shapes other than the standard rectangle.
for further studies:
read Vance Dickason
Loudspeaker Design Cookbook.
It is already there for those who want
to read it once more.
gro
fotenote.
worst case BOX is for me.
cubic - baffle and all sides equal in size
no internal stuff - no braces, in corners or
to divide surface in sub surfaces.
thin walls by a resonant material,
like wood with long fibres=strings
The material is of low density, balsa-tree
can come up with more WORST case points,
but have to go out into my city
and meet some of my friends
see you later
gro
Damn! there goes Groman again! He brought up balsa wood and I started thinkin'
I hate that!!!
We might have to give him a medal
IF you are making a bass only box such as a subwoofer, wouldn't it be best to use a lightweight but very rigid material such as balsa core or honey comb material?
So, what is the purpose of bracing? To raise the resonant frquency of the panels higher than the frequency that the speaker is reproducing right? If the woofer only goes to 100 hz and the panels have a resonant frequency at 150hz then they won't resonate.
So...... if we make the panels heavier, then we are lowering their resonant frequency so they are MORE likely to vibrate!
So wouldn't the best bass cabinet be heavily braced & lightweight material?
I'm making a bass box so need to know soon!!!
I hate that!!!
We might have to give him a medalIF you are making a bass only box such as a subwoofer, wouldn't it be best to use a lightweight but very rigid material such as balsa core or honey comb material?
So, what is the purpose of bracing? To raise the resonant frquency of the panels higher than the frequency that the speaker is reproducing right? If the woofer only goes to 100 hz and the panels have a resonant frequency at 150hz then they won't resonate.
So...... if we make the panels heavier, then we are lowering their resonant frequency so they are MORE likely to vibrate!
So wouldn't the best bass cabinet be heavily braced & lightweight material?
I'm making a bass box so need to know soon!!!
Variac said:
As long as the cabinet doesn't balloon.
A commonly used sub box material that fits this criteria is sonotube. And it works well.
Tightly coupled push-push drivers helps too. Most of the movement of one driver is cancelled by the other leaving very little left over to transmit into the enclosure.
dave
I can not say I agree with this, Ive had greatly differnet responces form woofers in different shape boxes, Id imagine it would be due to resonance and or diffraction.
Resonance: "sounds below 100HZ the cabinent shape is unimportant in respect to resonance"
Diffraction: "Since all shapes are more or less the same for low frequencies"
What exactly is the difference between standing waves and resonance, Is resonance only the fundimantal freq where as standinwaves is a 1/2 of that, what about harmonics, they contribuet to a resonance but harmonics need to be addressed?
His bracing section did not address how it cuts up the box into smaller chambers making the natural tone of the box higher, this is desired for a sub box. you want the natural tone to be much higher then the speakers frequency range. ALso non symetrical internal bracing will help cancel out internal resonance.
is poly fill the answer and it all doesnt matter?
Ported and non-ported boxes react differently to the box used, a sealed box you can just ploy fill it but a ported box needs the airflow and the boxes tonal properties are more important.
what do you guys think...
Time alignment: angle the front, ok
He should have addressed a more important issue, like the distance between speakers, for example in a 3/2 speaker geometry the D'Appolito speaker geometry and how it is effects the dispersion and or lobing errors. Acoustic radiation patterns are more noticable then time alignment, but thats just my opinion...
Resonance: "sounds below 100HZ the cabinent shape is unimportant in respect to resonance"
Diffraction: "Since all shapes are more or less the same for low frequencies"
What exactly is the difference between standing waves and resonance, Is resonance only the fundimantal freq where as standinwaves is a 1/2 of that, what about harmonics, they contribuet to a resonance but harmonics need to be addressed?
His bracing section did not address how it cuts up the box into smaller chambers making the natural tone of the box higher, this is desired for a sub box. you want the natural tone to be much higher then the speakers frequency range. ALso non symetrical internal bracing will help cancel out internal resonance.
is poly fill the answer and it all doesnt matter?
Ported and non-ported boxes react differently to the box used, a sealed box you can just ploy fill it but a ported box needs the airflow and the boxes tonal properties are more important.
what do you guys think...
Time alignment: angle the front, ok
He should have addressed a more important issue, like the distance between speakers, for example in a 3/2 speaker geometry the D'Appolito speaker geometry and how it is effects the dispersion and or lobing errors. Acoustic radiation patterns are more noticable then time alignment, but thats just my opinion...
Hi electricashman, where to start...
Say you are looking at a system running at 30Hz - the wavelength of sound at that frequency is roughly 11.5m.
For a box to affect response due to resonance at this frequency it would need to have one dimension of at least a quarter of a wavelength, i.e. 3m long.
I can't give you specific details for edge diffraction, but in general, it only becomes a problem over about 2kHz, and in general is swamped by room effects anyway.
If you want, I will post more details later, but my bed is calling at the moment!
Say you are looking at a system running at 30Hz - the wavelength of sound at that frequency is roughly 11.5m.
For a box to affect response due to resonance at this frequency it would need to have one dimension of at least a quarter of a wavelength, i.e. 3m long.
I can't give you specific details for edge diffraction, but in general, it only becomes a problem over about 2kHz, and in general is swamped by room effects anyway.
If you want, I will post more details later, but my bed is calling at the moment!
now this has got me a bit confused....
1. can one use hardwood instead of MDF?
2. How much baffle edge difraction does one expect in s simple 6" floor stander. What if the 6" is above the tweeter so it sees 3 edges instead of 2?
3. from what I know baffle edge distortion is depedant of bafle width (f = c/W) where c = 343 m/s f = freq. at which is starts and W is width in meters.
for W=0.25m and c = 343 f = 343*4 = 1372Hz. at about 137Hz (F/10) baffle edge difration level out (about 6db below the level at say 1500 Hz). So baffle edge difraction is mostly between 137 and 1370Hz for a 10" baffle. Am I right?
rounding of the edges does not help too much; adding a sub at 100-150 Hz not much either; but room gain adds about 2db so in the real world if one had a 6" 2 way floow standing system suplemented with a sub one would need 3db of compensation only. right?
help!
1. can one use hardwood instead of MDF?
2. How much baffle edge difraction does one expect in s simple 6" floor stander. What if the 6" is above the tweeter so it sees 3 edges instead of 2?
3. from what I know baffle edge distortion is depedant of bafle width (f = c/W) where c = 343 m/s f = freq. at which is starts and W is width in meters.
for W=0.25m and c = 343 f = 343*4 = 1372Hz. at about 137Hz (F/10) baffle edge difration level out (about 6db below the level at say 1500 Hz). So baffle edge difraction is mostly between 137 and 1370Hz for a 10" baffle. Am I right?
rounding of the edges does not help too much; adding a sub at 100-150 Hz not much either; but room gain adds about 2db so in the real world if one had a 6" 2 way floow standing system suplemented with a sub one would need 3db of compensation only. right?
help!
navin said:
There is one phenomemnom with two distinct characters depending on frequency (and blended in between.
What you refer to is usually termed baffle-step diffraction as the speaker transitions from a 2 pi to 4 pi stereradian radiation. Rounding is aimed at baffle-edge diffraction where a waveform traveling along the cabinet baffle is reradiated when it encounters a discontinuity (includes the edge of the cabinet). This happens in the freq range where 2 pi radiation is dominant.
There is a good bit in the Wiki on the former.
dave
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