Hello, I've read this interesting Troel's Gravesen article about importance of chamfering rear panel hole for mid-range drivers to avoid artifacts in response, just when I'm going to finish a DIY building where I used a cylindric tube to insulate and load mid-range.
The tube's diameter is similar to membrane's diameter (about 7.5 cm) and its lenght is about 25-30 cm: what must I expect from this solution in terms of response..?
Thank you very much.
The tube's diameter is similar to membrane's diameter (about 7.5 cm) and its lenght is about 25-30 cm: what must I expect from this solution in terms of response..?
Thank you very much.
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But a tube is not a good idea for midrange drivers, since you have too short a wavelength for such a small cabinet. You do not want standing waves in a midrange cabinet, so a tube will be bad and when only a little larger than the driver itself, I see trouble with very close reflecting surfaces and room for damping material.
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But a tube is not a good idea for midrange drivers, since you have too short a wavelength for such a small cabinet. You do not want standing waves in a midrange cabinet, so a tube will be bad and when only a little larger than the driver itself, I see trouble with very close reflecting surfaces and room for damping material.
Bad news..!! I'm not expert so I've made a mistake.
Please, just tell me, how do they work mid-ranges that have a built-in rear little plastic chamber, doesn't their response suffer for the same problem of mine?
If problem is the diameter dimension, I've to avoid in every possible way internal reflections, right?
Please, just tell me, how do they work mid-ranges that have a built-in rear little plastic chamber, doesn't their response suffer for the same problem of mine?
If problem is the diameter dimension, I've to avoid in every possible way internal reflections, right?
These midrange chambers are not a cylinder. They shaped the chamber so that there is no parallel walls and they are mostly for dome midranges, that do not play low in frequency - so they can be smaller.
The shape of a good midrange cabinet/chamber, is not the most important, its mostly the volume and the distance to reflecting surfaces.
The problem with the tube, is symmetry. A speaker cabinet is like a small room. If you have ever been in i a sliding tube for a water slide or in a small cubic space - then you will remember the sound of how that shape changes the sound of your voice. This is the same, when designing speaker cabinets.
So in theory you could keep the tube. But then it needs to be larger, so that you can add a lot of damping material to compensate for it's less optimum shape - without getting in the way of the driver.
You want the sound from the rear of the driver to dissapear into the chamber and never come back - no echo.
The shape of a good midrange cabinet/chamber, is not the most important, its mostly the volume and the distance to reflecting surfaces.
The problem with the tube, is symmetry. A speaker cabinet is like a small room. If you have ever been in i a sliding tube for a water slide or in a small cubic space - then you will remember the sound of how that shape changes the sound of your voice. This is the same, when designing speaker cabinets.
So in theory you could keep the tube. But then it needs to be larger, so that you can add a lot of damping material to compensate for it's less optimum shape - without getting in the way of the driver.
You want the sound from the rear of the driver to dissapear into the chamber and never come back - no echo.
Thank you very much for the clear explanation.
So even if this cylindric rear chamber is closed, internal standing waves can be listened out because of their effects on the driver membrane, right?
..and if I would spread all internal surface of the cylinder with all lenght little cylinder (a sort of 'spaghetti' distributed all around internal surface), will they break reflections in your opinion? Will they create a sort of infinite microchambers able to reduce internal reflections?
I could glue some rigid micro-cylinders as just spaghetti onto a tissue and put this all around the internal surface, what do you think about this strange idea?!
So even if this cylindric rear chamber is closed, internal standing waves can be listened out because of their effects on the driver membrane, right?
..and if I would spread all internal surface of the cylinder with all lenght little cylinder (a sort of 'spaghetti' distributed all around internal surface), will they break reflections in your opinion? Will they create a sort of infinite microchambers able to reduce internal reflections?
I could glue some rigid micro-cylinders as just spaghetti onto a tissue and put this all around the internal surface, what do you think about this strange idea?!
Where are the crossover points of your driver?
Above a certain point mid-frequencies are easily dampened with the right material. A clever combination of polyfill and melamine foam (basotect) should do the job.
Take impedance measurements of different variations as well as frequency measurements, and you will have nothing to worry about with the final result.
Above a certain point mid-frequencies are easily dampened with the right material. A clever combination of polyfill and melamine foam (basotect) should do the job.
Take impedance measurements of different variations as well as frequency measurements, and you will have nothing to worry about with the final result.
A tube is an excellent, perhaps the best, loading for a midrange if done well which involves things like:
- a "bulge" to guide and/or reflect the radiation from the cone around the magnet and down the tube.
- a slow, preferably constant, change in impedance down the tube to minimise reflection
- a reduction in area to increase velocity and make the action of the damping material more effective
A number of commercial manufacturers do this type of thing. B&W are perhaps the most well known.
It is debatable whether such efforts are worthwhile particularly if you have the space to give the midrange a large volume in which to absorb effectively all the rear radiation. Damping materials tend to work well at midrange and tweeter frequencies unlike woofer frequencies.
- a "bulge" to guide and/or reflect the radiation from the cone around the magnet and down the tube.
- a slow, preferably constant, change in impedance down the tube to minimise reflection
- a reduction in area to increase velocity and make the action of the damping material more effective
A number of commercial manufacturers do this type of thing. B&W are perhaps the most well known.
It is debatable whether such efforts are worthwhile particularly if you have the space to give the midrange a large volume in which to absorb effectively all the rear radiation. Damping materials tend to work well at midrange and tweeter frequencies unlike woofer frequencies.
Thank you, please, would you explain bit better what do you mean for 'change in impedance down to the tube'? And for the 'bulge', do you mean something like an increasing in tube's diameter near the driver?
All the energy in a travelling sound wave moving through air will keep going forwards so long as the air in front pushes back (impedes) in the same manner as air. If it becomes harder or easier to move some of the energy in the sound wave will continue moving forward but some will be reflected back. Adding damping material will change the impedance experienced by the sound wave as will changing the cross sectional area of tube. Designing a good tube involves taking care that as much sound travels down it as possible to be absorbed with as little as possible reflected back particularly in the early stages near the cone where the sound is most energetic.
Yes to keep the cross section as constant as possible (impedance again) and, in some designs, to arrange the angle of the wall to reflect sound down the tube. B&W (I think) used to have a diagram of one of their designs showing this but I have failed to find it with google. Anyone?
Not so easily damped when the cup or cylinder is the diameter of the diaphragm - just too tight to get sufficient material in place. I just went through this process and found that replacing the tight and reflective plastic pot with a cylinder large enough to allow an inch of fiberglass around the perimeter resulted in upper mid hash reduction. NO PROOF only listening...
But it makes sense. Good that you tried it, so that you get some practical experience wrapped around all the theory
There are no standing waves in that size of a box. They can't happen to form inside the big woofer enclosure, either.
I don't understand why keeping on giving false information.
Ok thanks, so to simplify:
- near the driver, large section, more stuffing;
- far from driver, small section, less stuffing
Right?
A possible solution for the small diameter would be to insert a cone modeled felt into the tube leaving free internal tube surface and occupying the center axis, with the tip of cone near the driver and the base far. Would it work?
So using a small diameter tube for a mid-range driver is not a problem?
Well, I like idea of putting it out of box, and I'd make it work like an open baffle, but I don't want a new surface upon the cabinet, rather I'd like a baffle-less situation.
So how can I eliminate rear emission or delay it putting in phase with the front one? If it's easier to eliminate it, may it be enough to wrap rear part of driver with a thick and closed back cylinder of felt?
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