Legis' Horny Tales

I have been playing with the idea of making lower tuned tapped family members for my 4-way synergy horn system for quite some time. They will add the bottom octave to the system's repertoire. The TH's that are visible in the picture are tuned to ~32-33Hz and they do not go that low to give the "air vibration" effects near 20Hz, that only very low THD bass systems, that go low enough, can create. The new horn family members will take over where the higher tuned TH's start to roll off.

Given I had already these 4x18" BMS woofers and was at least subconsciously limited to the following size, here's what I came up with. After many hours of trying to squeeze a 10-13Hz horn/TQWT etc. into the same "small" size while keeping good efficiency, I gave up and returned to the original path, ie. maximize the efficiency and settle for adequate extension of ~16Hz that does not have air turbulence and other problems.

Tapped TL seemes to work very well with the BMS woofers and TL's notch after the pass band is good for me since I want to maximize the acoustic low pass. The woofer configuration will be push-pull.

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16Hz tapped transmission line (T-TL) vs. 750 litre sealed box with same woofers. Two of these things corner/boundary loaded are ought to make some kind of noise.

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SPL vs. frequency at 1000w/10mm limit (in comparison to 750l sealed again):

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One fold scheme. The picture does not show bracing etc...

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Today is the day I will go and get the wood and start building these things. Some pictures are bound to follow at some point, I keep you posted. :)
 
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Looks like fun and way over the top as your projects usually are. You will paint it Ferrari red as well?

Will be following this. Good luck !

Thanks X! I have not decided on the color yet, propably not fully red though. Maybe white with some red/black/?? details. I'll also have to see how the baltic birch plywood looks like when they are ready, staining could also be an option. The plywood is 21mm "Class B" baltic birch (some surface damages), but looked to be quite OK quality.
 
Random progress pictures.

21mm thick 15-ply plywood close-up:

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Upper modules:

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Threaded inserts for attaching the side panels:

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Nice progress! You have pillow covers on the foam blocks at the mouth of the TH's - nice touch. I see you have acoustical treatments on wall - is that new?

I have to ask what those 6 long aluminum tubes are? 1/4-wave Helmholtz stub mid-bass traps? Do they have a measurable effect?

I see you are doing woodwork in your super clean listening room. Where is the sawdust? :D
 
Nice progress! You have pillow covers on the foam blocks at the mouth of the TH's - nice touch. I see you have acoustical treatments on wall - is that new?

I have to ask what those 6 long aluminum tubes are? 1/4-wave Helmholtz stub mid-bass traps? Do they have a measurable effect?

I see you are doing woodwork in your super clean listening room. Where is the sawdust? :D

Yes, I also think that cloth on the foam blocks was a nice addition visually :). I will also dampen the new TH's mouths the same way.

We have moved to a new apartment a month ago. The new room was pretty ugly acoustically, so I had to give it a little treatment. Acoutic panels (~8,5m2 total area) on the walls and white "tube bass traps" to the corners and other strategic spots. I have 6 tubes tuned to ~40hz and 6 tubes tuned to ~160Hz, together they cover the modal region 20-280Hz pretty well and kill the bass echoes quite good. Each tube trap in 80 litres, 120cm x 30cm dia, filled with rockwool, both ends sealed.

The aluminum pipes are Argent Room Lense imitations. Each pipe is open on both sides and each pipe in the groups of three have different amount of polyfill stuffing inside. I have got the impression this is how original Room Lenses are also done. Argent advertises they act as a wide band Helmholtz resonators but I have not measured any effects. I'ts propably quite small. I mainly use them as diffusers, to shatter some of the side wall's first reflection. They also make the stereo image somewhat more airy.

I do the more dust heavy work in a separate study room that I have temporarily emptied for this purpose. Some small drilling etc. goes well in the living room, like putting in the threaded inserts, nothing a quick vacuum cleaning cannot handle. :) But routing the woofer's holes was quite something inside the study room, without a breathing filter. :D
 
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Somewhat quick & dirty setup as I did not seal any non-permanent joints with a sealing gasget tape. Impedance plots show that the horns leak, which is not a suprise. Because of this the tuning of the horns are 20Hz and 21Hz, not 17,5Hz like simmed.

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Simulated impedance:

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The response does not go as low as simmed, though my amp, uncalibrated mic, mic pre and dac might all have some attenuation at 20Hz also. I believe the leaking also decreases it somewhat because the tuning is higher.

Measured from the mouth while horn was not close any walls. Other plot is with the horn that has 2 x BMS 18s430v2 (better plot), and other that has 2 x BMS 18N850 woofers. (I have a 33Hz room mode which affects these measurements)

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2pi sim:

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How do they sound? FUNtastic :D! Absolutely massive authority and utterly easy sounding. Very pure low notes and the low rumble. The sound signature is the same as with my other THs, in short it's precise but still mellow and has some quality to it which I would best describe as musical and natural. The two TH bands integrate semalessly together.
 
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Just readed some beyond the ariel thread, hate it so much and started to feel nauseous cause all the talking and no measurements.

So did you hit those 100db sweeps late at night?

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and you should change your couch to leather one, otherwise it will be ripped like naulakissa´s own chair
 
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Can you show what HD plot looks like for 100dB at 1m from mouth?

HD plots don't do justice since they are without damping in the line, quite leaky and the side panels rattle a bit at those levels. Sealing tape and smart line damping would do wonders.

Also my mic distorts itself quite heavily, the H2 plot always follows the transfer function's shape for this reason when the SPL is past ~90-95dB. If I move the mic further away from the sound source, the distortion percent decreases while it should not. Actually I think it should behave somewhat other way around, ie. if there is a strong room resonance at 33Hz, then the H2 at~16,5Hz and H3 at 11Hz etc. should be boosted since the room's transfer fuction gives more gain to mentioned harmonics at that specific measuring spot.And vice versa at 33hz the THD should decrease since the signal gains the room mode's gain compared to the 66Hz/99Hz etc. harmonics.

Here's three measurements taken from the mouth, at 1m and at 2m. Drive level is way below 2,83V, something like 7-10dB lower :D. See how the "imaginary THD %" drops and H2 shape also stops/reduces following the signal at 2m (because the mic's distortion stops being the main contributor?). It stops following the transfer function completely after the level is reduced 10dB and measured at 2m.

SPL is the same in all three measurements. This is also the leakier box out of the two.

Mouth:
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1m:
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2m:
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Also here is another 2m measurement that's level is decreased -10dB compared to previous measurements. The imaginary H2 % now starts to rise when level is decreased. The distortion cannot go any lower after some point since the inherent noise and hum of the phantom power supply/mic, which rises toward LF. At mid and high freqs the phantom and mic noise is less harmful.

2m -10dB:
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It's very hard to tell, with suboptimal measuring equipment, when one is actually measuring truely speaker's own distortion and when something else. I don't even know if modal region thd can be measured in room accurately. My other white TH's measure quite differently in this new apartment than the last.

THD measurements would at least require some low THD mic and low noise phantom supply. Or a dynamic microphone, I understand they are linear, but the bass response is usually quite a downward slope.
 
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Just like with the smaller TH's, also these react VERY well to flow resistance/damping at the mouth. Even better than the last. The piece leaves approx. 4cm tall area open from the bottom.

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Sweeps are 1M long so the infra levels are accurate. Blue line is with the flow resistance/damping.

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I haven't been able to accurately simulate this effect with the HR (with neither of my THs), it predicts more sensitivity loss above tuning and less sensitivity gain below tuning with both a) restricting the mouth area and/or b) filling the last section of the horn (which, in the sim, does not give extra sensitivity below tuning but quite the contrary!).


If you have a TH, try adding flow resistance to the mouth that covers the it partially and see what happens!
 
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