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Multi-Way Conventional loudspeakers with crossovers

Open Source "Tower XL"
Open Source "Tower XL"
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Old 3rd July 2019, 10:51 PM   #871
LineSource is offline LineSource  United States
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I found a baffle edge treatment picture of a 1" quarter round on a 12" midrange MTM plywood cabinet.
Note the hand sanding block.
Note no blood stains.

? Any early builder using DSP with tri-amps?
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File Type: jpg one inch quarter round on Plywood.jpg (117.4 KB, 421 views)
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Old 4th July 2019, 08:19 AM   #872
KaffiMann is offline KaffiMann  Norway
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Quote:
Originally Posted by tmuikku View Post
It is just a concept that seems to hold true with my prototype box. Use Hornresp MLTL wizard, tune parameters for your box, adjust L12 con (driver position) and see the lowest resonance come and go. Driver at ~halfway the resonance goes away, seems to be at the half wavelength on the longest dimension (attached, ~106cm height, ~160Hz lowest standing wave).
This is as good as you can expect with these dimensions, really, since the driver is ~midway, and the resonance port of the enclosure will be lifted a bit up from the bottom, the only wiggles you have to care about would be the stuff over 300hz.
It is the distance driver-to-port both directly and via reflecting surfaces that is most important.

If the driver is closer to the bottom in this sim, it will be much worse. Top-to-bottom reflections are important, but not quite as important as driver-to-surfaces-and-port. IMO + some variations pending on other design decisions and tons of salt etc.

Around 108cm would be about 280hz or so, distance drives-top-bottom where the port is. But the port is a bit up from the bottom, and the top will have a tilt that effectively breaks the path between parallel surfaces. So a bit of damping material and some other careful considerations should make it good to 4-500hz or so methinks.

So if this is in the right kind of ballpark, IHA = waste of time.

Edit:
LineSource, Love those edges, gets out the beautiful layers soooo nicely, just a touch of lintseed oil and it's done.

Last edited by KaffiMann; 4th July 2019 at 08:28 AM.
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Old 4th July 2019, 03:00 PM   #873
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by KaffiMann View Post
...the only wiggles you have to care about would be the stuff over 300hz.
Really? I am not sure but I believe the x-over point would be close to or lower than 300 Hz, so these resonances would not be excited anyway. Also, damping a > 300 Hz resonance with a bit of wool or melamine works better than at the lower frequencies.
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Old 4th July 2019, 05:13 PM   #874
diyuser2010 is offline diyuser2010
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Quote:
Originally Posted by LineSource View Post
I found a baffle edge treatment picture of a 1" quarter round on a 12" midrange MTM plywood cabinet.
Note the hand sanding block.
Note no blood stains.

? Any early builder using DSP with tri-amps?



1.25 radius, 15" MTM cabinet. Hand sanding was used after router, several passes were used.



Large plywood square base screwed to stock router base.
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Old 11th July 2019, 12:38 PM   #875
KaffiMann is offline KaffiMann  Norway
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Originally Posted by mbrennwa View Post
Really? I am not sure but I believe the x-over point would be close to or lower than 300 Hz, so these resonances would not be excited anyway. Also, damping a > 300 Hz resonance with a bit of wool or melamine works better than at the lower frequencies.
Exactly.

/On a mobile in Bali far awsy from my computer.
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Old 26th July 2019, 05:38 PM   #876
Aatto is offline Aatto  United States
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Sorry for long absent, got busy with real world stuff.
So it looks like we have a very solid starting point. Hoping to start cutting very soon, in next few weeks, I ll be on and off again, since this is a busy month but will not abandon this project.
any other ideas or consideration before prototyping ?
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Old 4th August 2019, 03:10 PM   #877
Paul Vancluysen is offline Paul Vancluysen  Belgium
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To give the project a startup again, I did some study on the smaller Tower XL, the last proposal done by Aatto.

Cabinet:
For the dimensions I used Aatto's drawing of post #858. I did adapt my own drawings also to calculate new volumes and driver positions, see in attachement.
The netto volume for the woofer now is about 180 litres and for the midrange 13 litres.

Woofer basreflex system:
I used the TSP of the AE TD15X-8 as measured by Aatto a time ago, see Leap driver model in attach. To avoid SPL boost around 100 Hz, fB has to be chosen at 22 Hz or lower.
The port is realized with two tubes of 10 cm diameter each and 40 cm long. Calculating the minimum required port area Sv for this 15 inch driver with Sd = 855 cm2 and xmax = 14 mm conform R. Small (Sv larger than 0.8 x fB x Vd), Sv has to be larger than 211 cm2. That are 2 tubes of 12 cm diameter each. I have chosen 10 cm tubes to reduce the tube length to 40 cm, that means a port area sufficient up to 10 mm excursion peak.

This is the result of the system simulation:
AE TD 15X-8 in VB = 180 L, fB = 22 Hz, F3 = 33.8 Hz, F6 = 25.9 Hz, F10 = 20.2 Hz.
This is a basreflex system more damped than a B4 alignment at the same system frequency. See the comparison of the low frequency SPL (green) versus a B4 (red) in the plot. In attach also the SPL of the woofer system on infinite baffle (pink) and in full space (blue).

The speaker that can be designed will have a sensitivity of 88 dB @ 2.83 Vrms, 1m and -3 dB at 34 Hz, full space.

So far the first input for the design from my side.

Last edited by Paul Vancluysen; 4th August 2019 at 03:13 PM.
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Old 4th August 2019, 03:36 PM   #878
mbrennwa is offline mbrennwa  Switzerland
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Thanks Paul!

40 cm is pretty long for a bass reflex port. The tube resonance would be at about 430 Hz (fundamental). I don't remember where the mid/woofer x-over frequency is, but it should be well below 430 Hz to avoid issues with the tube resonance.
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Old 4th August 2019, 03:53 PM   #879
Paul Vancluysen is offline Paul Vancluysen  Belgium
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Hi Matthias,

Thanks for feedback, I didn't look yet to the port resonance.
We can chose fB a little higher for a more short port, but I don't prefer because some SPL boost will appear around 100 Hz. Or making the tube diameter lower, but in that case there will be more port noise.

With the 8 inch midrange the X-over frequency can be lower than 300 Hz... And probably also steep filtering will be applied.

Edit:
Simulating in Leap with 2 x 10 cm tubes of 40 cm long, fB = 22 Hz, the port resonance is 375 Hz.
With 2 x 10 cm tubes of 25 cm long, fB = 26.5 Hz, the port resonance is 570 Hz.
With fB = 26.5 Hz for this woofer in 180 L volume, the SPL boost becomes 0.12 dB around 100 Hz. That is acceptable.
So I think it is better to decrease the port length to 25 cm and use 2 x 10 cm tubes.

Last edited by Paul Vancluysen; 4th August 2019 at 04:21 PM.
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Old 9th August 2019, 05:28 PM   #880
Aatto is offline Aatto  United States
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Hi pal and thanks for well detailed work.
88db is a little shy of the 90db goal but compromises... but i m happy with the low frequencies respond, looking good.
sorry for my late replies, I m very busy with real world stuff, but still getting ready to start cutting, I bought a table saw and a router, should be good enough to start building, I still need a good table saw blade and some router bits to start working hopefully very soon.

Stay Tuned..
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