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Old 16th December 2013, 10:44 AM   #1
xrk971 is online now xrk971  United States
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Default The Nautaloss Ref Monitor

Edit - Jan 12, 2014: The bottom line - here is the final in room response and THD of the Nautaloss II Reference Monitor with Subwoofer and DSP crossover. -3 dB points are 42 Hz to 18 kHz, THD is between -30 dB to -40 dB at an average of 96 dB SPL at the listening position:

Click the image to open in full size.

Click the image to open in full size.

I started this speaker in the Foam Core thread (Foam Core Board Speaker Enclosures?) on somewhat of a whim as I was inspired by the namesake speaker and wanted to try a quick and cheap foam core version to see what it may possibly sound like. (Anthonybisset is credited for coining the name)

Usually, I model and simulate a speaker pretty thoroughly before a build, but in this case, the concept was to have a spiral sealed-TL so I thought it would not be as critical as the point was to absorb the back wave and provide bass extension to as close as possible the natural fs of the driver in an open baffle. Eschewing sims, I began directly with a pencil sketch on a piece of foam core and drew an approximate 36 in long spiral that fit in a 12 in tall x 9 in deep envelope (to keep a reasonable size for a bookshelf or desktop speaker).

I then added some internal bracing at 90 deg intervals for the first 360 deg.

Then put in some speaker wire and added pillow stuffing. I glued some open cell foam around the flat areas near the front - the idea being to avoid any flat surface that could produce a back reflection or resonance that might show up on the front side of the cone. I then capped it off with a combination of hot melt and pva glue. Let it dry for 6 hours then installed the Vifa TC9FD driver.

First sound listening impressions: wow! - the clarity, transparency, and overall balance was just amazing. Although it has no bass below 150 Hz really given that the fs is 120 Hz, however this is perfect for use with a helper woofer or subwoofer crossed at about 200 to 300 Hz. The speaker really sounds good.

To confirm my suspicions that the speaker was indeed very even in character, I set out to measure it using a Panasonic WM61A mic capsule wired to my laptop soundcard. This works well below 5kHz but unfortunately cannot get anything above 6kHz due to what appears to be a low-pass filter built in to the mic input as it was designed for web chats.

The initial measurements really shocked me by how flat it was from 300 Hz on up. The measured THD was very low - I would say probably rivaling some of the very best full range drivers out there costing many times more. However, there was this pesky drop off in the response that made a cliff at 300 Hz. After scratching my head and looking at some sims in Akabak, this drop is a room-effect (distance to walls and floor).

Click the image to open in full size.

Here are sims without room reflections:
Click the image to open in full size.

Here is the sim including rear wall at 50 inches and floor at 45 inches high:

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I then repeated the measurement with the same driver in an open baffle at the same location and also saw the same 300 Hz cliff, confirming that it is not the speaker enclosure (nor driver break-in) that caused this effect. The next step was to orient the speaker so that the room walls were 45 deg and I added a sheet of open cell foam and a pillow on the floor below.

Click the image to open in full size.

The new measurements with the room effects, now mitigated, produced a very nice frequency response curve from 150 Hz on up (I will assume that above 6 kHz the speaker performs closely along the manufacturer's published data - which is actually very flat for a full range driver). Note that from 200 Hz on up the variation in SPL is only about +/ 2 dB and the THD is typically below -50dB with a wide loaf shaped bump at about 3kHz but still very respectable. The phase variation over this range is also very linear and relatively flat. I believe, all these things point to a speaker that will sound very coherent and accurate. Finally, looking at the impulse response function, we see that this speaker has an almost ideal response function that is very clean and short with minimal ringing. This might be described as tight, clean, or fast.

Given that this speaker appears to measure very closely to an OB, I would say that the spiral is doing its job of acting like an infinite cavity by absorbing all the back wave without any reflections.

This speaker can be constructed from exactly 1 sheet of $1 foam core stock and the Vifa driver costs $10. These are not the most efficient drivers but at 85 dB for 2.83V input, they are not bad for near field use. The frequency response flatness, the low THD, the linear phase variations, and the near ideal impulse response make them perhaps one of the best values for a near field "monitor" from 200 Hz to 20 kHz.

Finally, here is the measured response with the effect of the room wall/floor bounce cancellation effect mitigated:

Click the image to open in full size.

It is a fun and easy quick build. Give it a try if you are looking for a cheap but accurate speaker. This will make an excellent top for FAST system.

Cheers,
Xrk971


*** Edit (Jan 5, 2014) *** added measurements from dual driver Nautaloss II (including waterfall and spectrogram).

Nautaloss II Measurements are here: The Nautaloss Ref Monitor

Click the image to open in full size.


Here is the pdf plan for the Nautaloss II The Nautaloss Ref Monitor


Freq Response is very flat from 200 hz to 18 kHz:

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THD is -50dB!:

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Spectral Decay:

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Attached Images
File Type: png Cochlear-2.png (406.1 KB, 1692 views)
File Type: png Cochlear-4.png (446.4 KB, 1177 views)
File Type: png Cochlear-3.png (429.7 KB, 4593 views)
File Type: png Nautaloss-FR-meas.png (48.2 KB, 3883 views)

Last edited by xrk971; 22nd January 2014 at 03:01 PM. Reason: Added sims and additional measurements compared to open baffle
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Old 16th December 2013, 03:42 PM   #2
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this is interesting actually as i'm wondering if it would be worth my effort trying to design something like this for a 15" bass driver.

have you ever investigated how much of an effect the 'lossy' nature of foam core can be improved by bracing the hell out of it? the side wall will be braced by the spiral, would it make an difference adding some lateral bracing to the spiral structure horizontallu?

i do like reading your experiments, some of the results are much better then i would have ever expected!
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Old 16th December 2013, 03:50 PM   #3
xrk971 is online now xrk971  United States
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Gaffhenderson,
Thanks! If you do this for a 15 in bass driver, you get the B&W Nautilus bass unit I think it will provide very clean bass - perhaps as clean as you can hope to achieve impulse response wise and flat freq response wise. I actually braced in both directions (radially and laterally) - can't see it since stuffing covers it. Since I am using a high Qts driver, the lossy structure actually helps to smooth out the peakyness that would otherwise show up with a stiff structure. Get me your driver params and I can run a sim for you if you tell me how long of a spiral you want to make.
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Old 16th December 2013, 04:00 PM   #4
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Originally Posted by xrk971 View Post
Gaffhenderson,
Thanks! If you do this for a 15 in bass driver, you get the B&W Nautilus bass unit I think it will provide very clean bass - perhaps as clean as you can hope to achieve impulse response wise and flat freq response wise. I actually braced in both directions (radially and laterally) - can't see it since stuffing covers it. Since I am using a high Qts driver, the lossy structure actually helps to smooth out the peakyness that would otherwise show up with a stiff structure. Get me your driver params and I can run a sim for you if you tell me how long of a spiral you want to make.
AE TD15M.

sealed volume is around 86-87ltr for 0.7q
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Old 16th December 2013, 04:41 PM   #5
IG81 is offline IG81  Canada
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Quote:
Originally Posted by gafhenderson View Post
AE TD15M.

sealed volume is around 86-87ltr for 0.7q
Considering it would have f3=80Hz doing so, it might be quite the decent system with subwoofers or even by itself corner-loaded depending on one's tastes. I'm using a pair in vented enclosures, almost overdamped alignments, but would go for sealed were I to use actual subwoofers. I'd like to see how sealed compares to a lossy spiral.

BTW, stick a ~60Hz high-pass on the sealed TD15M and power handling will be close to thermally-limited and we're past 120dB by then.

IG

Last edited by IG81; 16th December 2013 at 04:59 PM.
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Old 16th December 2013, 05:18 PM   #6
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Originally Posted by IG81 View Post
Considering it would have f3=80Hz doing so, it might be quite the decent system with subwoofers or even by itself corner-loaded depending on one's tastes. I'm using a pair in vented enclosures, almost overdamped alignments, but would go for sealed were I to use actual subwoofers. I'd like to see how sealed compares to a lossy spiral.

BTW, stick a ~60Hz high-pass on the sealed TD15M and power handling will be close to thermally-limited and we're past 120dB by then.

IG
Using mjks sheets, using a port with zero output Via heavy dampening and minimal actual volume, corner placement shows a pretty flat response down in the 40s.

This is a few feet away from walls but the low end boosts quite considerably when tucked in. The time delay is what draws me to this. The more I can remove unwanted rear waves with a spiral the better!

Click the image to open in full size.
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Old 16th December 2013, 06:39 PM   #7
IG81 is offline IG81  Canada
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Quote:
Originally Posted by gafhenderson View Post
Using mjks sheets, using a port with zero output Via heavy dampening and minimal actual volume, corner placement shows a pretty flat response down in the 40s.

This is a few feet away from walls but the low end boosts quite considerably when tucked in. The time delay is what draws me to this. The more I can remove unwanted rear waves with a spiral the better!
Yeah, ~80Hz is the standard half-space response used by WinISD. Getting into the 40ies with a corner would be nice indeed.

IG
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Old 16th December 2013, 07:27 PM   #8
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by gafhenderson View Post
AE TD15M.

sealed volume is around 86-87ltr for 0.7q
I am having a hard time getting a low Qts driver like this to work well. This enclosure "feels" like an OB to the driver so you want a higher Qts driver if you want deeper flat bass extension. Are you opposed to something like the Eminence Beta 15A? Similar efficiency, 11.6mm xmax, probably costs less. Works much better in a sealed TL Nautaloss.
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Old 16th December 2013, 07:51 PM   #9
IG81 is offline IG81  Canada
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I tend to think a low Fs is the prime parameter for a sealed enclosure. Qt and Vas will then dictate how large the box will need to be. I can't say how this translates to the world of lossy pipes though.

IG
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Old 16th December 2013, 07:53 PM   #10
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Originally Posted by xrk971 View Post
I am having a hard time getting a low Qts driver like this to work well. This enclosure "feels" like an OB to the driver so you want a higher Qts driver if you want deeper flat bass extension. Are you opposed to something like the Eminence Beta 15A? Similar efficiency, 11.6mm xmax, probably costs less. Works much better in a sealed TL Nautaloss.
Main concern is the sound quality. Sealed + linkwitz transform looks to be the way to go for me. It's what to do with the backwave now. The spiral tl effectively dissipates it.

What's your best effort with AE TD15M and the eminence?
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