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ROAR with Helmholtz front resonator
ROAR with Helmholtz front resonator
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Old 30th September 2018, 08:49 AM   #1
Circlomanen is offline Circlomanen  Sweden
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Location: Göteborg
Default ROAR with Helmholtz front resonator

Click the image to open in full size.

Some quality time with the 6th order bandpass function in Hornresp gave results.

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Almost done building. A last picture of the interior of the box.


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A measurement with my Umik 30 cm outside the mouth.

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Group Delay.

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A more explanatory drawing showing where the port is located.
When I get some more pictures I will show the finished box with its port.

This is a Helmholtz version of the ROAR, inspired by Tom Danleys BC415 (but much smaller and only a single driver).

I hate Helmholtz like I hate root canal work, but when comparing a 8th order bandpass design with my ROAR i got this idea of how to properly drive a Helmholtz resonator. The 8th order bandpass did play loud with continuous tones but the driver will bottom out very easily with transient signals. It takes several cycles before the Helmholtz resonance reaches full amplitude and starts resisting cone motion, which allows the driver to bottom out in a normal Helmholtz based speaker enclosure. A quarter wave resonator resists transient cone motion immediately and will transfer the energy much more efficiently to the Helmholtz resonator in this case. A simple tapped pipe driven with an 8 inch Alpine type-r can have a 30 cm air column amplitude at resonance, while the driver only have 10 mm xmax. The quarter wave resonator will be much better suited to drive the Helmholtz front resonator.

This is some of the thought behind this design.

It is a fun and capable loudspeaker. I will try to get some outdoor measurements once we have some calm whether outside.

Cheers,
Johannes
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Old 30th September 2018, 09:23 AM   #2
epa is offline epa  Netherlands
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i see no pics
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Old 30th September 2018, 07:12 PM   #3
Circlomanen is offline Circlomanen  Sweden
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porten1.jpg

Here it stands close to the wall. The port is a 19 mm deep 200 mm diameter hole in the front piece.

HOAR10snartklar.jpg

Here is a shot of the interior. It is a very simple design. Easy to build. I built this first prototype in 3 hours.

Helmholtz_ROARbygge.jpg

Simulation in Hornresp.

HOAR10filtereq.jpg

Here is a new measurement as it is used. The microphone is 1 cm outside the port. There is a 48 dB/octave LP filter at 100 Hz and a 1,5 dB Q = 1,0 EQ point at 45 Hz.

I hope you can see these pictures. I can see the pictures in my previous post from several different computers and even my cell phone.

My son heard it today when he got home from a friend and his reaction was "WOW!!! It is amazing, very powerful and clean!!!" He was immediately impressed.

Cheers,
Johannes
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Old 30th September 2018, 10:56 PM   #4
Brian Steele is offline Brian Steele  Grenada
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How do you remove the driver from the completed box? I don't see an access panel.

GD looks a bit high, but the response looks pretty smooth after EQ. What does the GD look like after the EQ is applied?

Does the response vary at different SPL levels? I'm wondering how linear that vent is going to be...
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Old 1st October 2018, 03:58 AM   #5
GM is offline GM  United States
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[QUOTE=Circlomanen;5561031]I hope you can see these pictures. [\QUOTE]

Can see them all just fine; my kind of little project!

GM
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Old 1st October 2018, 06:32 AM   #6
Circlomanen is offline Circlomanen  Sweden
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Quote:
How do you remove the driver from the completed box? I don't see an access panel.
With a tigersaw. This is a cheap and fast prototype in 19 mm particle board. I just wanted to test my idea and see if there is any benefit to drive a Helmholtz frontchamber with a tapped pipe. Now that I have verified the design I will probably build two of these properly out of plywood (with access panels).

Quote:
Does the response vary at different SPL levels? I'm wondering how linear that vent is going to be...
The port has the same radiating surface as the driver. I have not had the chance to test it at high power levels yet. With 10 watts indoors everything rattles. It does have a very physically powerful and tactile character.

Tom Danleys BC415 does not seem to have a much larger port compared to the total cone area of the four 15 inch drivers.

The behavior of the vent at high power levels is very fundamental to this design, and is something I will experiment with. Since it is an inherently non linear function, it is something I need to play with in real life. I guess Tom Danley uses something like COMSOL to model and optimize this kind of design.

I hope I can post more measurements soon. The wind has died down considerably today, so I will try to do some outdoor measurements.
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Old 1st October 2018, 07:06 AM   #7
Circlomanen is offline Circlomanen  Sweden
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GD-EQXO.jpg

GD with EQ and xover.
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Old 1st October 2018, 10:20 AM   #8
Circlomanen is offline Circlomanen  Sweden
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With 500 watts from a T-Amp E800, HP 48 dB/octave at 25 Hz and LP 48 dB/octave at 100 Hz we hear no port chuffing or noise. My whole house is buzzing violently, with paintings rattling hard against the walls etc.... We have to redo the tiles in our kitchen. They did not like the vibrations.
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Old 1st October 2018, 10:22 AM   #9
Circlomanen is offline Circlomanen  Sweden
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YouTube

A short video of some music clipping the microphone.
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Old 1st October 2018, 04:50 PM   #10
Circlomanen is offline Circlomanen  Sweden
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outside2meter.jpg

GDoutside2meter.jpg

Here is spl and GD outdoors with the microphone 2 meters from the mouth.

It is obvious that the QW-BP is optimized for indoor (1,0 Pi) use.
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