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Multi-Way Conventional loudspeakers with crossovers

A Bookshelf Multi-Way Point-Source Horn
A Bookshelf Multi-Way Point-Source Horn
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Old 10th January 2016, 04:14 AM   #11
Mindsource is offline Mindsource  Canada
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Once this is done it would be great to measure it Geddes style and send the files to him. If you ask him nicely he will likely map it for you.
GedLee LLC

Last edited by Mindsource; 10th January 2016 at 04:43 AM.
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Old 10th January 2016, 09:28 AM   #12
bushmeister is offline bushmeister
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Wow Guys! I go to bed and a whole design starts to come together whilst I am sleep!!

Thank you so much for the input and effort you guys are putting in!

If we can make this work it would be fantastic! I am very excited about this project. So far, I have built multiple full range speakers in various boxes - ikea salad bowls, fish bowls, boom boxes. etc.

I have built a number of straight forward two way designs - mostly using SB acoustics drivers - which I think are fantastic value. One set I built in left over engineered oak floor boards - which created a surprisingly dead cabinet when combined with adequate damping.

I have built those high end three way monitors- which I am still overjoyed with, and as a result of making, I sold my studio monitors which were my previous reference.

I have tried my hand at CLD baffles, decoupling of drivers with sorbothane etc, various bracing techniques - including CLD bracing - which works amazingly well.

But all these techniques have been with direct radiator builds, and whilst I have always attempted to keep a smooth, even power response and carefully manage lobing behavior, I have not done a CD design like this before.

Xrk - love the sketch! However, I was thinking more about trying to keep this as bookshelf as possible (of course all ideas are fluid at present!), so I was thinking about getting the horn itself to play as close to 80hz as possible, then use subs below.

I use four distributed subs with my three-way scan-speak design, and it works incredibly well.

However unfortunately, I am still awaiting these SB65s, which is very frustrating!
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Old 10th January 2016, 09:35 AM   #13
bushmeister is offline bushmeister
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Another thought I have had:

Tapping the horns - they are extremely rigid, light, with a very high pitched 'ring' on the 'tap test'. In my experience, this tells me they will likely have very high stiffness with high resonances. These can often be tamed very successfully with existential damping - of the form used in cars (think dynamat) to dampen resonances in the metal structure. (This form of damping is much less useful for lower resonances you get in heavy thick MDF/Ply constructed cabinets - for which the best technique is CLD.)

So I am thinking, that covering the outer surface of the horn profile with 4mm thick bitumen damping product could help reduce unwanted resonances and lower distortion further.

I hope this, combined with the sorbothane gaskets - which should minimize direct energy transfer and mechanical excitation of the horns - should give us a very clean output.

Last edited by bushmeister; 10th January 2016 at 09:39 AM.
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Old 10th January 2016, 09:44 AM   #14
xrk971 is online now xrk971  United States
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A Bookshelf Multi-Way Point-Source Horn
You are in luck because according to Byrtt's sim of the woofers in a 2liter(ea) rear chamber it goes down to about 80Hz. Now it is much smaller and closer to a "bookshelf" vs a design with built in woofer. XO around 80Hz with your distributed subs is perfect then. I still need to confirm Byrtt's simulation but we are probably at least not completely off. There is always LT to push it up a bit at expense of excursion so max SPL may be affected.

Do you know if the profile of the WG is available anywhere? I would like to model this horn with bass injection holes and we can get close to optimal before cutting injection ports.

It would be useful if you can take the factory PDF drawing and use a ruler to get me at least 5 dimensions of horn height and width at 5 different axial distances. Every 20% of length basically. This would be enough to form a rough model in Akabak.

Also, can you can please use either geometry to estimate the volume of the front cone of the woofer formed if you place it against a flat wall. If you have driver in hand easy to use dry rice or beans and measure volume.

These hard numbers come a long way to getting to a rough model.

Thanks

Last edited by xrk971; 10th January 2016 at 09:59 AM.
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Old 10th January 2016, 09:51 AM   #15
bushmeister is offline bushmeister
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Xrk,

I am on it! Give me an hour or so and I'll have them!
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Old 10th January 2016, 10:02 AM   #16
xrk971 is online now xrk971  United States
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A Bookshelf Multi-Way Point-Source Horn
Quote:
Originally Posted by Mindsource View Post
Once this is done it would be great to measure it Geddes style and send the files to him. If you ask him nicely he will likely map it for you.
GedLee LLC
Good idea - I am sure Bushmeister has capability to measure polar response.

2d color contour plots of SPL vs frequency aren't exactly hard if you have scientific plotting SW that does interpolation from an array. Like Mathcad can do this quite readily. I have not plotted DI maps before but this type of plot is standard fare in Mcad.
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Old 10th January 2016, 10:07 AM   #17
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by bushmeister View Post
Another thought I have had:

Tapping the horns - they are extremely rigid, light, with a very high pitched 'ring' on the 'tap test'. In my experience, this tells me they will likely have very high stiffness with high resonances. These can often be tamed very successfully with existential damping - of the form used in cars (think dynamat) to dampen resonances in the metal structure. (This form of damping is much less useful for lower resonances you get in heavy thick MDF/Ply constructed cabinets - for which the best technique is CLD.)

So I am thinking, that covering the outer surface of the horn profile with 4mm thick bitumen damping product could help reduce unwanted resonances and lower distortion further.

I hope this, combined with the sorbothane gaskets - which should minimize direct energy transfer and mechanical excitation of the horns - should give us a very clean output.
Good idea, but you can take it further by covering the whole exterior side of the hard plastic with sand loaded caulking or other viscous adhesive. Use it to fill gaps between the wooden board and the horn. I have heard of people covering plastic horns with dampening caulking to great success. If you tap it and it rings there may be an issue there. Once the four wooden boards are attached and holes drilled the mode of vibration will probably change (for the better as less "bell like").
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Old 10th January 2016, 10:07 AM   #18
bushmeister is offline bushmeister
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OK Xrk, these are the best plans I could get online - using screenshot etc.
What further measurements specifically would be helpful?
Attached Images
File Type: png Horn 1.png (63.6 KB, 1305 views)
File Type: png horn2.png (34.5 KB, 1291 views)
File Type: png horn3.png (48.0 KB, 1285 views)
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Old 10th January 2016, 10:14 AM   #19
xrk971 is online now xrk971  United States
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Originally Posted by bushmeister View Post
OK Xrk, these are the best plans I could get online - using screenshot etc.
What further measurements specifically would be helpful?
So along 5 points on axis of middle picture measure correspond max and min elliptical diameter (Max is horiz and min is vertical) and label it in a sketch similar to third picture on right. See how it starts as 36mm round (actually now modified by you) then goes egg shape elliptical? I basically need these to calculate the WG cross sectional area as a function of axial distance from the 36 mm throat.

You can sketch the drawing and save as PNG or whatever.

Thanks.

Tip : it is much more precise if you cut cardboard ellipse to fit and measure cardboard. Do this for 4 points since throat is round.
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Old 10th January 2016, 10:55 AM   #20
bushmeister is offline bushmeister
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OK - I hope you can read this OK!

Measurements taken at 5cm intervals as measured vertically on axis from centre of throat. The throat is unchanged at it's narrowest. So 0cm, 5cm, 10cm, 15cm etc....
Attached Files
File Type: pdf scan0001.pdf (435.6 KB, 153 views)
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