As I survey the many build threads over the last dozen years, I notice some people design complicated shapes for the midrange cavity: non-parallel walls, multifaceted shapes, tapered transmission lines, etc... while others use a simple box shape with good proportions.
I am searching for information on how midrange enclosure internal shape affects measured performance. There does not seem to be a lot of published literature out there, so I am interested in any measurements that anyone has done which show any effects.
Full disclosure: I am skeptical that a complicated internal shape has any benefit... but this is not a firm belief. I am open to any evidence, or even a convincing argument that a complex internal cavity has benefits.
j.
I am searching for information on how midrange enclosure internal shape affects measured performance. There does not seem to be a lot of published literature out there, so I am interested in any measurements that anyone has done which show any effects.
Full disclosure: I am skeptical that a complicated internal shape has any benefit... but this is not a firm belief. I am open to any evidence, or even a convincing argument that a complex internal cavity has benefits.
j.
Maybe there is a reason why don't have so many literature about this subject.
I think, if you fill the midrange enclosure with adequate sound absorbing material, then the virtual internal shape becomes irregular.
For midrange, I always use internal dimension ratios of 1:1,618, or 1:1,26 or 1:1,2 if possible. Because why not?
Internal Standing Wave Calculator for Loudspeaker Enclosures and Rooms
I think, if you fill the midrange enclosure with adequate sound absorbing material, then the virtual internal shape becomes irregular.
For midrange, I always use internal dimension ratios of 1:1,618, or 1:1,26 or 1:1,2 if possible. Because why not?
Internal Standing Wave Calculator for Loudspeaker Enclosures and Rooms
Well, start with the hypothesis that it doesn’t... but as for your question, there is little ‘research’ on this freely available. Members of ou local (Dutch) DIY community had some things researched years ago, but no clear conclusions other than that the use of sufficient internal damping had a lot more effect on the measurements than the shape. Which makes perfect sense I think.
Well we are in agreement.
My opinion is that an ordinary box shape, if well stuffed, will perform as good as any exotic shape. At low frequencies, the enclosure is uniformly pressurized and rarefied by the driver. As the frequency rises to the point where the enclosure dimension is 1/2 wavelength, the effectiveness of the stuffing becomes dominant.
But I would love to see any evidence to the contrary.
My opinion is that an ordinary box shape, if well stuffed, will perform as good as any exotic shape. At low frequencies, the enclosure is uniformly pressurized and rarefied by the driver. As the frequency rises to the point where the enclosure dimension is 1/2 wavelength, the effectiveness of the stuffing becomes dominant.
But I would love to see any evidence to the contrary.
Here's a 2nd repeat of one of my prior posts on midrange enclosure shapes:
"Jim Moriyasu authored an article in the 7 & 8 2000 issues of Speaker Builder Magazine, "A Study of Midrange Enclosures". He tested 18 different midrange enclosures mounted on an IEC baffle, 1.65m x 1.35m. He measured frequency response and Cumulative Spectrum Decay (CSD) or waterfall plots at a near field 2". He used a Focal 5NV4212 Neoglass midrange with a phase plug, flush mounted on the baffle. Enclosures were tested with and without damping material, Acousta-Stuf at 1 lb/cu. ft."
Cube (2), small (Qtc = 0.7) & large (Qtc = 0.5)
Rectangle, golden ratio (2), small & large
Tube w/ flat end (2), small & larger
Vifa tube with hemispherical end
Pyramid, three sided
Pyramid, four sided (2), small & large
Transmission line, tubular (2), small & large
Transmission line, square
Transmission line, triangular
Anechoic Enclosure, with rigid foam insulation wedges
8" x 8" x 6" Enclosure
Egg
Spherical
So much information is shown in the plots of the articles, with so much for personal interpretation, that paying for the article e:files is worthwhile....
" Summarizing the articles results, hopefully doing the article justice :
Appropriate use of damping material and a sufficient internal volume for a Qtc of 0.5 or less is more important than shape. In general (not always), the larger enclosures performed better than the small enclosures. The damped transmission lines performed well. The undamped and damped cubic enclosures were not as resonant as expected. The undamped flat-backed tube and the undamped Vifa tapered tube were very resonant. While performing well, the justification of using a spherical or egg shaped enclosure for actual improved performance is very questionable. Beveling the rear edge of the baffle midrange opening is important."
"Jim Moriyasu authored an article in the 7 & 8 2000 issues of Speaker Builder Magazine, "A Study of Midrange Enclosures". He tested 18 different midrange enclosures mounted on an IEC baffle, 1.65m x 1.35m. He measured frequency response and Cumulative Spectrum Decay (CSD) or waterfall plots at a near field 2". He used a Focal 5NV4212 Neoglass midrange with a phase plug, flush mounted on the baffle. Enclosures were tested with and without damping material, Acousta-Stuf at 1 lb/cu. ft."
Cube (2), small (Qtc = 0.7) & large (Qtc = 0.5)
Rectangle, golden ratio (2), small & large
Tube w/ flat end (2), small & larger
Vifa tube with hemispherical end
Pyramid, three sided
Pyramid, four sided (2), small & large
Transmission line, tubular (2), small & large
Transmission line, square
Transmission line, triangular
Anechoic Enclosure, with rigid foam insulation wedges
8" x 8" x 6" Enclosure
Egg
Spherical
So much information is shown in the plots of the articles, with so much for personal interpretation, that paying for the article e:files is worthwhile....
" Summarizing the articles results, hopefully doing the article justice :
Appropriate use of damping material and a sufficient internal volume for a Qtc of 0.5 or less is more important than shape. In general (not always), the larger enclosures performed better than the small enclosures. The damped transmission lines performed well. The undamped and damped cubic enclosures were not as resonant as expected. The undamped flat-backed tube and the undamped Vifa tapered tube were very resonant. While performing well, the justification of using a spherical or egg shaped enclosure for actual improved performance is very questionable. Beveling the rear edge of the baffle midrange opening is important."
resonance ratio according the load dimension and shape.
Think the load as a room, angles and wall intersections, echo floater, and so on.
You can calculate the ratio with dimension.
As far I believe to understand you don't want a big resonance, so irregular internal shapes break the energy into a multiple resonance of less energy.
I use a tube as many for the mid and I break the diameter to length ratio with some nozzle plastic can from food industry sourced in local supermarket. And of course + the stuffing that helps at higher frequencies. Some do it with bracing.
though I have no idea how much it's important in real life ? It must be important for some to prefer open design.I do believe than a sealed one is as good if not better once it's properly made and it lands about your question as one of the parameter (my feeling).
I used golden ratio like Lojzek but more for the visual looking of the external enclosure... golden ratio works fine with aethetic (Vitruve, pyramids, and so on)
Think the load as a room, angles and wall intersections, echo floater, and so on.
You can calculate the ratio with dimension.
As far I believe to understand you don't want a big resonance, so irregular internal shapes break the energy into a multiple resonance of less energy.
I use a tube as many for the mid and I break the diameter to length ratio with some nozzle plastic can from food industry sourced in local supermarket. And of course + the stuffing that helps at higher frequencies. Some do it with bracing.
though I have no idea how much it's important in real life ? It must be important for some to prefer open design.I do believe than a sealed one is as good if not better once it's properly made and it lands about your question as one of the parameter (my feeling).
I used golden ratio like Lojzek but more for the visual looking of the external enclosure... golden ratio works fine with aethetic (Vitruve, pyramids, and so on)
I have used 4 sided 5 sided pyramid and round conical “sports cone”. When covered with mass loaded butyl and stuffed progressively denser at e vertex, they all sound transparent and measure as if the back was in an infinite baffle. That is, no audible or measurable back reflection coloration. An 11in tall soccer sports cone works very well for this application. It has high convenience, low cost, and high performance. Although, smaller 7.5in ones could work very well too depending on the volume you want.
REEHUT 7.5“ Plastic Traffic Cones - 12 Pack Thick Soccer Training Cones for Outdoor Activity & Festive Events (Set of 12 or 24)- 4 Colors https://www.amazon.com/dp/B01N5H02RC/ref=cm_sw_r_cp_api_glt_fabc_NAJT2XPZAPPJJP1TKHT6
Like this:
REEHUT 7.5“ Plastic Traffic Cones - 12 Pack Thick Soccer Training Cones for Outdoor Activity & Festive Events (Set of 12 or 24)- 4 Colors https://www.amazon.com/dp/B01N5H02RC/ref=cm_sw_r_cp_api_glt_fabc_NAJT2XPZAPPJJP1TKHT6
Like this:
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Think it's the easiest/best way for diy : sort of a la Nautilus B&W method.
However, it's even better if you mirror this shape as a nozzle (that's theory, does it matter, I dunno)
far better than the whisky card box I use (that I like because it's around 2.5 liter and gives t the SS 10F we bot likes a 0.55 Qtc
: not saying I use the main bottle overture as the back of the load to change when I want the internal stuffing.
Maybe also a problem with foam is maybe a part of the energy is going outside the pyramid foam (perhaps, who knows ?) . Now it could be seconded with an outside tube
Sport cone is a clever idea, you can feel it to reduce the volume if you need...
However, it's even better if you mirror this shape as a nozzle (that's theory, does it matter, I dunno)
far better than the whisky card box I use (that I like because it's around 2.5 liter and gives t the SS 10F we bot likes a 0.55 Qtc
: not saying I use the main bottle overture as the back of the load to change when I want the internal stuffing.Maybe also a problem with foam is maybe a part of the energy is going outside the pyramid foam (perhaps, who knows ?) . Now it could be seconded with an outside tube
Sport cone is a clever idea, you can feel it to reduce the volume if you need...
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Yes, DIY Nautilus, aka foam core Nautiloss is another excellent rear chamber. Perhaps the best.
The Nautaloss Ref Monitor
The Nautaloss Ref Monitor
xrk971 wrote:
Do you have any measurements showing a back reflection from a standard box shape? perhaps some "before & after" data where you employed a cone or a foam nautiloss...
If this is based on subjective evaluations, I am fine with that. I do believe there are some aspects of sound perception which we do not yet fully understand, and do not yet know how to measure....
... but hopefully you have some data ?
Do you have any measurements showing a back reflection from a standard box shape? perhaps some "before & after" data where you employed a cone or a foam nautiloss...
If this is based on subjective evaluations, I am fine with that. I do believe there are some aspects of sound perception which we do not yet fully understand, and do not yet know how to measure....
... but hopefully you have some data ?
I more and more want to go with digital FIR EQ
....but what to measure and where ?
-outside the mid enclosure ?
- just behind the rear cone ? .. with some delay ? How much and for what frequencies.
- in the midle of the rear chamber ? In its corners ?
- on the enclosure ?
And how it's related to a subejective enhancement ?
That's the problem, not easy to deal with.
Think people like augerPro and some have certainly empiric conclusions that can helps, sometimes // with factual datasheet and/or measurements.
Have you seen at Diyaudio the long thread about enclosures and damping ? Certainly good things can be read and applied on the midrange.
I like myself loudspeakers where the mid is cuted-off very low : around 100 to 150 Hz . They have classical mid load cabinet en sounded pretty good. Despite a low end which is strong in those low frequencies.
I believe on eof the secret but the shape, volume of the enclosure, is the possibility to correct the damping with a long enhancement process with try & error in the listening room where the mid is planned (of course after having made the main process of filter that you already master).
Thatm eans a mid load that is not sealed like Troels G. is doing for illustration and like most of the companies of course that sell on shelves loudspeakers, but in our diy world, a mid where you can remove the back wall : a la Arbeth for instance : sealed but screwed for removing purposes.
Some testimonied that a close rear back wall but larger width chamber than the mid driver front wall baffle, sounds good, like the UK Audio Note speakers... But I don't know, some here had made inputs in that direction. So at the opposite of a long load to absorb the rear wave ! Go figure !
AugerPro lurking ?
....but what to measure and where ?
-outside the mid enclosure ?
- just behind the rear cone ? .. with some delay ? How much and for what frequencies.
- in the midle of the rear chamber ? In its corners ?
- on the enclosure ?
And how it's related to a subejective enhancement ?
That's the problem, not easy to deal with.
Think people like augerPro and some have certainly empiric conclusions that can helps, sometimes // with factual datasheet and/or measurements.
Have you seen at Diyaudio the long thread about enclosures and damping ? Certainly good things can be read and applied on the midrange.
I like myself loudspeakers where the mid is cuted-off very low : around 100 to 150 Hz . They have classical mid load cabinet en sounded pretty good. Despite a low end which is strong in those low frequencies.
I believe on eof the secret but the shape, volume of the enclosure, is the possibility to correct the damping with a long enhancement process with try & error in the listening room where the mid is planned (of course after having made the main process of filter that you already master).
Thatm eans a mid load that is not sealed like Troels G. is doing for illustration and like most of the companies of course that sell on shelves loudspeakers, but in our diy world, a mid where you can remove the back wall : a la Arbeth for instance : sealed but screwed for removing purposes.
Some testimonied that a close rear back wall but larger width chamber than the mid driver front wall baffle, sounds good, like the UK Audio Note speakers... But I don't know, some here had made inputs in that direction. So at the opposite of a long load to absorb the rear wave ! Go figure !
AugerPro lurking ?
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I have closely followed the threads by Augerpro and Remlab, as well as DonVK's ongoing investigations.
I am not being selective; I would like to discuss any data available. With that said, the most straight-forward data would be frequency response.
If internal box reflections come back through the cone, I would expect them to either (1) in phase, which would show up as a peak, or (2) out of phase, which would show up as a null, or (3) some random phase which would be somewhere between the out-of-phase null and the in-phase peak.
I have never seen this on any near field measurement I have made of a woofer or cone midrange driver. The near field response is typically very smooth, much smoother than the far field response. The attached is typical of what I would expect of a 6-inch driver. The NF response seems representative until about 1800 Hz, where the wavelength becomes too small relative to the cone. My NF responses of my SB17CAC35 and SB17MFC35 are similar.
All of my builds so far have been simple box shapes, because that is what I know how to build. Now perhaps I am just extraordinarily lucky and all of my three recent cabinets have optimum internal shape. But perhaps it is the stuffing?
Maybe there is something else I should be measuring?
I am not being selective; I would like to discuss any data available. With that said, the most straight-forward data would be frequency response.
If internal box reflections come back through the cone, I would expect them to either (1) in phase, which would show up as a peak, or (2) out of phase, which would show up as a null, or (3) some random phase which would be somewhere between the out-of-phase null and the in-phase peak.
I have never seen this on any near field measurement I have made of a woofer or cone midrange driver. The near field response is typically very smooth, much smoother than the far field response. The attached is typical of what I would expect of a 6-inch driver. The NF response seems representative until about 1800 Hz, where the wavelength becomes too small relative to the cone. My NF responses of my SB17CAC35 and SB17MFC35 are similar.
All of my builds so far have been simple box shapes, because that is what I know how to build. Now perhaps I am just extraordinarily lucky and all of my three recent cabinets have optimum internal shape. But perhaps it is the stuffing?
Maybe there is something else I should be measuring?
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