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Multi-Way Conventional loudspeakers with crossovers

Open Source "Tower XL"
Open Source "Tower XL"
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Old 21st June 2019, 05:03 PM   #841
mbrennwa is offline mbrennwa  Switzerland
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This would still have the top and bottom of the bass enclosure at the same positions, still parallel to each other. I don't think this would help with the standing waves, with the first mode at approximately 140 Hz.

I attached a drawing of my earlier suggestion of a slanting separator between the mid and bass chambers. Without the parallel top / bottom, the standing waves in the bass chamber would be less pronounced. Also, they are not focused to discrete frequencies, which is maybe even more important. The first mode would be "smeared" across a frequency range of about 140 to 200 Hz (from eyeballing the dimensions in my drawing). Spreading the resonances will be much less audible than focusing the whole mode at one single frequency.

The only option I see that might work to deal with the internal resonance would be to use an internal Helmholtz absorber (IHA). An IHA is a small box inside the bass chamber, with a bass-reflex port coupling this small volume to the main bass chamber. The IHA volume/port is tuned to the resonance frequency of the bass box, and the IHA volume is strongly stuffed with a lot of damping material. The IHA volume then couples to the resonance in question and converts its sound energy to heat. IHAs are often used in several designs of the German DIY magazine Hobby HiFi, and they seem to work ok.
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Old 23rd June 2019, 04:57 AM   #842
mbrennwa is offline mbrennwa  Switzerland
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Oups! I meant to write "The only OTHER option I see ... would be an internal Helmholtz absorber (IHA)."
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Old 23rd June 2019, 07:58 PM   #843
Aatto is offline Aatto  United States
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I added the mid range section to the new drawing (the red part) it is around 11 liters, and it is possible to add an opening to the back wall to try open or closed option as Paul suggested ( good to hear from you Paul)

as for unparalleled top and bottom, we can cut some boards with different height and attach them in order to make an angled surface (the yellow part), it will take about 10 liters but compromises..

please see the attachments and let me know what you think.

Open Source "Tower XL"-txl-v3-ii-drawing-jpg
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File Type: jpg TXL V3 II Drawing.jpg (168.1 KB, 287 views)
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Old 24th June 2019, 06:21 AM   #844
KaffiMann is offline KaffiMann  Norway
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Quote:
Originally Posted by mbrennwa View Post
But I might be too obsessed with the golden ratio thing.
Yes. Golden Ratio is just an approximate hypothesis from way before any proper simulation software existed, a nifty idea, but not very helpful.
It can actually work against the most optimal compromise for a specific solution, since you'd most likely focus more on the not-so-important Golden Ratio vs actually making a proper box and put drivers in more optimal locations relative to internal modes.

But that's just my opinion.

I really wish you could hear a proper front firing slot port design someday.

/taunt off
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Old 24th June 2019, 08:08 AM   #845
mbrennwa is offline mbrennwa  Switzerland
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Originally Posted by Aatto View Post
I added the mid range section to the new drawing (the red part) it is around 11 liters, and it is possible to add an opening to the back wall to try open or closed option as Paul suggested ( good to hear from you Paul)

as for unparalleled top and bottom, we can cut some boards with different height and attach them in order to make an angled surface (the yellow part), it will take about 10 liters but compromises..

please see the attachments and let me know what you think.
Your version of the "unparalleled" top and bottom is the right idea, but not enough if you ask me. The difference between the internal box height at the front and at the height is about 10cm, which is about 8% of the total height. This means the modes / standing waves along the height of the box will be focused within a relatively narrow frequency range of 8% compared to the version with parallel top / bottom: fundamental mode of the parallel version is about 140 Hz, so your "unparalleled" version would spread this to about 140 Hz to 150 Hz, which is still a rather narrow frequency band.

I would suggest to try to spread the modes as much as possible. Take another look at my earlier drawing, where the difference between the internal heights at the front and the rear is much larger. My version also takes care of the midrange chamber, so it would be easier to make. Or am I missing something that is not to like about it?

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Originally Posted by KaffiMann View Post
Yes. Golden Ratio is just an approximate hypothesis from way before any proper simulation software existed, a nifty idea, but not very helpful.
It can actually work against the most optimal compromise for a specific solution, since you'd most likely focus more on the not-so-important Golden Ratio vs actually making a proper box and put drivers in more optimal locations relative to internal modes.
I agree 100% !
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Old 24th June 2019, 10:03 AM   #846
Paul Vancluysen is offline Paul Vancluysen  Belgium
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I prefer the proposal of Matthias with the non-parallel separation between woofer and midrange. It is applied in many commercial speakers. But it occupies a lot of volume for the midrange for this speaker enclosure, around 30 L. With a large mlidrange enclosure, the internal resonances become lower too and are more difficult to damp.
Maybe making a smaller midrange cabinet in some way, around 10 L volume.
I have done a trial in the attached drawing with the green separations. And maybe the extra volume for the woofer at the top can be filled with some dampening material.
Just an idea...
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File Type: jpg 20190624 Drawing cabinet.JPG (83.3 KB, 194 views)

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Old 24th June 2019, 10:27 AM   #847
tmuikku is offline tmuikku  Finland
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Yep it is a compromise land Not sure the slanted panel is worth the trouble for the woofer standing waves. Mid box like #840 or #843 and put polyfill for the whole top part from woofer up might have more effect than a slanted top panel. Anyone with extra ply/mdf and time for a prototype box?
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Old 24th June 2019, 12:14 PM   #848
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by Paul Vancluysen View Post
I prefer the proposal of Matthias with the non-parallel separation between woofer and midrange. It is applied in many commercial speakers. But it occupies a lot of volume for the midrange for this speaker enclosure, around 30 L. With a large mlidrange enclosure, the internal resonances become lower too and are more difficult to damp.
Maybe making a smaller midrange cabinet in some way, around 10 L volume.
I have done a trial in the attached drawing with the green separations. And maybe the extra volume for the woofer at the top can be filled with some dampening material.
Just an idea...
Welll, actually, looking at your drawing, I just ha another idea... the part where your green lines do not cover my red line could be the opening of the internal Helmholtz absorber (IHA). This would allow combining the non-parallel walls (to smear out the resonances / modes) with the Helmholtz absorber; best of both worlds! In addition, the volume of the Helmholtz absorber becomes part of the main woofer box at frequencies that are lower than the Helmholtz tuning frequency, because the port is transparent for those frequencies. This means the IHA does not "waste" the box volume for the woofer chamber.

Let me know if I need to make a new drawing to explain this idea a bit better.
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Old 24th June 2019, 12:31 PM   #849
Paul Vancluysen is offline Paul Vancluysen  Belgium
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Well, it seems to me a good idea to add an Helmholtz absorber on that place in the enclosure. From my side I have no experience with it, but it cannot be that difficult to calculate it. If Attoo and even other builders are prepared to implement it, for me it is ok.
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Old 24th June 2019, 01:03 PM   #850
KaffiMann is offline KaffiMann  Norway
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Quote:
Originally Posted by mbrennwa View Post
Oups! I meant to write "The only OTHER option I see ... would be an internal Helmholtz absorber (IHA)."
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Well, it seems to me a good idea to add an Helmholtz absorber on that place in the enclosure.
Now we're firmly back in Yamaha NS5000 territory.
I am a bit uncertain how that would work in a BR, I know it works in sealed boxes because the modes are more pressurized, no alternate path to choose. But in a BR I think the math for taking into account port behaviour at varying SPL might be a bit more complicated.
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