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The Mivoc 30Hz Tapped Horn

Volker, a sound engineer and good friend on mine was interested to get some subs to support his monitors in his private recording studio. After some discussions, we decided for a 30Hz lower cut-off while the net volume was supposed to be below 100 liters.

IMG_3883

 

 

As a driver, the budget 10″ Mivoc AWM104 seemed to be a good candidate: It’s free air resonance is specified to be 31Hz while it offers 9mm Xmax.

 

Mivoc AWM104

Here is the complete datasheet.

 

Hornresp input parameters:

Mivoc AWM104_para

 

The simulation of this 4 Ohm diver @ 1W looks like this:

Mivoc AWM104_ap

 

Theoretical max. SPL:

Mivoc AWM104_max-spl

 

Some pictures taken while building them This is when I roughly put it together to get a 1st impression. The clamp holds the access panel in it’s initial design but later I decided to extend it so that it covers the entire mouth opening (refer to the first picture above).

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The throat as well as the internal parts were rounded down to avoid noise of flowing air. A ring was introduced to provide enough free space for the cone:

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The speaker baffle from the back with the glued drive in nuts for the speaker:
IMG_2545

 

The boards of the duct are also rounded down:
IMG_2513

 

here as well:

IMG_2512

 

Just before the sidewall is being glued:

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…and screwed:
IMG_2572

 

For the paint job I used Warnex, which I had left over:

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Wit the speaker connector in access panel the installation is very easy:

IMG_3886

 

The driver just fits inside the width of the horn:

IMG_3884

 

Finally I took some measurements behind the house in the garden. The first one was done with the mic at a distance of 5m (close to the ground) @ approx. 30W:

IMG_3889

 

The second one was done with the mic at a distance of 1m @ 1W:

IMG_3891

 

And these are the results (no smoothing applied) ±3dB from 30 to 100Hz:

REW-SPL-graph

 

The simulation again for reference (which is a good fit):

Mivoc AWM104_ap

 

Considering the frequencies where the peaks and dips are: It becomes obvious that the horn behaves a little bit “shorter” then the simulation. The the actual response is shifted a couple of Hz to the right (peaks and dips are at higher frequencies). Reason might be that I usually determined the length of the folded horn by using a center-line approach.

The sketch below (Image credit to diyaudio member soho54) shows a bend made up of three 25cm squares and the estimated path lengths for the most popular methods:

folding methods by soho54

 

Until now I used the left approach which here proofs to be (too) optimistic – longer than the simulation predicts – when comparing the actual results to the the simulation.

Therefore I suggest to use the method in the middle which is the more accurate “advanced centerline method” by soho54. Highly recommended: Read more on that matter here (posts 206, 207, 209). Soho54 is a very knowledgeable guy, make sure to check out his tutorial: Hornresp for Dum… hmm… Everyone 😉.

I found one more interesting link on that: Horn Folding – a brief study of the centerline vs advanced centerline method

Plans can be found in the download section.