I'm surprised the HF above 10k is measuring so well.
Looks like a great design for mini hi-res monitors. Point source, no crossovers, no backwave coloration, small diameter driver with good polars into the HF. Seems exactly right for budget 2.1 or 5.1 or even 7.x editing setups.
Anyone know from memory if B&W specifically patented the spiral chamber absorption technique?
Looks like a great design for mini hi-res monitors. Point source, no crossovers, no backwave coloration, small diameter driver with good polars into the HF. Seems exactly right for budget 2.1 or 5.1 or even 7.x editing setups.
Anyone know from memory if B&W specifically patented the spiral chamber absorption technique?
Unfortunately, Holmimpulse doesn't have cumulative spectral decay (CSD) capability. From how short the impulse response ringing is, I would imagine that it looks like a steep cliff-like feature over the 'spectral mountain range'.
I can do some gated measurements if that helps.
Bass Nautaloss with Dual 6.5in Drivers - build begins #1
I want to see how this really works as a moderate subwoofer that can integrate with the Nautaloss tops to enable extension down to 50 Hz but with the same clean impulse and flat response. I just got some of the PE buyout 6.5 in woofers (4 ohm $4.88 ea). I started with a hand sketch on a full sheet of foam core (20x30 in) and I know I want a 5 ft path based on my previous sims. I made the width exactly 6.67 in to maximize the number of channels from a 20 in wide sheet and this should be a 3-sheet project. You will need some remnants from other project to make the bracing. I only had time to glue up the first strip. It is a pretty easy speaker to make really. 1 hr invested so far.
I want to see how this really works as a moderate subwoofer that can integrate with the Nautaloss tops to enable extension down to 50 Hz but with the same clean impulse and flat response. I just got some of the PE buyout 6.5 in woofers (4 ohm $4.88 ea). I started with a hand sketch on a full sheet of foam core (20x30 in) and I know I want a 5 ft path based on my previous sims. I made the width exactly 6.67 in to maximize the number of channels from a 20 in wide sheet and this should be a 3-sheet project. You will need some remnants from other project to make the bracing. I only had time to glue up the first strip. It is a pretty easy speaker to make really. 1 hr invested so far.
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Bass Nautaloss with Dual 6.5in Drivers - build begins #2
Making some more progress - all the curved channels are now in place. Bracing is the next step. As I was building this, it occurred to me that the round empty center could be a driver chamber and this could be a bass horn, or if the drivers were mounted face out, a BLH. The 1.5 m path at quarter wave would have an approximate tuning of 56 Hz or higher. A horn needs to be designed and simulated prior to construction much more rigorously. Whereas the spiral absorber is much less critical. Made me think though...
Making some more progress - all the curved channels are now in place. Bracing is the next step. As I was building this, it occurred to me that the round empty center could be a driver chamber and this could be a bass horn, or if the drivers were mounted face out, a BLH. The 1.5 m path at quarter wave would have an approximate tuning of 56 Hz or higher. A horn needs to be designed and simulated prior to construction much more rigorously. Whereas the spiral absorber is much less critical. Made me think though...
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Bass Nautaloss with Dual 6.5in Drivers - build #3
Added bracing. This turned out to be pretty time consuming as I made the braces curved and skeletonized to avoid straight edges. it is pretty stiff and very light as a speaker structure goes. We will see how it holds up to bass beats.
Added bracing. This turned out to be pretty time consuming as I made the braces curved and skeletonized to avoid straight edges. it is pretty stiff and very light as a speaker structure goes. We will see how it holds up to bass beats.
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Sippy,
It may be that with the spiral to absorb the back wave, you can get away with a volume smaller than the usual sealed prismatic box. I will run a sim for you when I get some time and see how big the Nautaloss needs to be for a Beta 12lta. We do indeed enjoy some very nice prices on buyout drivers here in the US. I got a box of qnty 8 of the 6.5 in woofers for under $40. From the reviews I have heard they can sound really good almost on the verge of a full range at 3.5k. I am having good luck with high Qts drivers in the foam core as it is lossy and helps to smooth the peakyness that would otherwise show up in a stiff cabinet.
Bass Nautaloss with Dual 6.5in Drivers - build #4
Next step was to make the baffle for mounting the drivers. Since these are larger and heavier drivers than the usual 3.5 in Vifa's that I use, I decided to use a 3-layer foam core baffle, with the outer layer being the very stiff high quality Elmer's brand foam core with thick paper. I also added some braces where the baffle is narrow due to the cutout and a 4th layer where the screws will go. The bottom edge of the baffle is carved with a razor to be angled and flush with the curve of the spiral where it touches. Still need to glue it in place, then add wiring and terminal cup, and then stuffing prior to sealing off with the final side.
Next step was to make the baffle for mounting the drivers. Since these are larger and heavier drivers than the usual 3.5 in Vifa's that I use, I decided to use a 3-layer foam core baffle, with the outer layer being the very stiff high quality Elmer's brand foam core with thick paper. I also added some braces where the baffle is narrow due to the cutout and a 4th layer where the screws will go. The bottom edge of the baffle is carved with a razor to be angled and flush with the curve of the spiral where it touches. Still need to glue it in place, then add wiring and terminal cup, and then stuffing prior to sealing off with the final side.
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The closest thing I could find was B&W's disc-shaped radial spiral back absorber: US7201252 B2 (2007)
https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/US7201252.pdf
Nothing for the 'Nautilus' proper - for the spiral axis to be perpendicular to the driver cone axis. In fact, the claims (1) and (2) are very specific about the spiral is transverse to the speaker axis.
Which leads me to believe that there either exists a patent by someone else or it is obvious to one skilled in the art of speaker building that they could not claim it. But I could not find this other patent, so I am guessing that the Nautilus shaped 'snail' spiral and its orientation to a driver cone is (obvious) and in the public domain.
Please correct me if I am wrong about this...
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Bass Nautaloss with Dual 6.5in Drivers - build #5 - Finished!
After the baffle was glued in place, I installed the terminal cup and wiring, then started to add stuffing. The stuffing is dense at the closed end and progressively gets looser as I go towards the drivers, stopping at about 80% of the way. I heard that the spiral effectively absorbs the back wave with a minimal of stuffing near the drivers - which helps to keep the sound more 'open'. Don't know if that is true or not but if I need to add more it can be done thru driver cutouts. Finally, I capped it off with a sheet of black paper-faced foam core (it was flatter than the white stuff which has waviness to it) and will give it a more interesting look. I used a combination of PVA (95%) and small strategically placed spots of hot melt glue to tack the top in place while it dries. Then I stacked all the heavy objects I could find on top to clamp it and let dry overnight.
I got impatient and installed the drivers and who says you can't listen to speakers at low volume while the glue dries?
It sounds pretty good. I think these are bass/mid bass units rather than a true sub as I don't think that as a sealed cabinet it will go much below 60 Hz. However, I plan to bi-amp and use active XO/EQ in the future so using maybe some EQ to boost the bottom end may work well as there is not an xmax issue down there in a sealed cabinet.
So next will be some measurements and the moment of truth...
So far, I have 5 hrs into this speaker and $15 worth of parts/materials.
After the baffle was glued in place, I installed the terminal cup and wiring, then started to add stuffing. The stuffing is dense at the closed end and progressively gets looser as I go towards the drivers, stopping at about 80% of the way. I heard that the spiral effectively absorbs the back wave with a minimal of stuffing near the drivers - which helps to keep the sound more 'open'. Don't know if that is true or not but if I need to add more it can be done thru driver cutouts. Finally, I capped it off with a sheet of black paper-faced foam core (it was flatter than the white stuff which has waviness to it) and will give it a more interesting look. I used a combination of PVA (95%) and small strategically placed spots of hot melt glue to tack the top in place while it dries. Then I stacked all the heavy objects I could find on top to clamp it and let dry overnight.
I got impatient and installed the drivers and who says you can't listen to speakers at low volume while the glue dries?
It sounds pretty good. I think these are bass/mid bass units rather than a true sub as I don't think that as a sealed cabinet it will go much below 60 Hz. However, I plan to bi-amp and use active XO/EQ in the future so using maybe some EQ to boost the bottom end may work well as there is not an xmax issue down there in a sealed cabinet.
So next will be some measurements and the moment of truth...
So far, I have 5 hrs into this speaker and $15 worth of parts/materials.
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Bass Nautaloss - Measurements and Sound Clip
OK, call me impatient and had to get some measurements while the glue is drying.
Before I installed the driver into the box, I had mounted it on a 24 in x 36 in open baffle and measured its response at about 36 in above the floor.
The drivers were wired series in this box so the nominal impedance is 8 ohms, the sensitivity (with voltage) dropped but the amount of xmax was reduced allowing for the speaker to play overall louder and with reduced distortion.
The measurement was with the mic 12 in away, centered between the two drivers and 4 in off the floor. Obviously there will be some floor enhancement and we do not expect any baffle step loss. Blue is Nautaloss Bass, and red is same driver in an open baffle (OB).
The measurement looks very good - almost identical to the open baffle measurement with the exception of the enhanced bass loading due to the floor (or reduced highs however you want to look at it). The response confirms that the Nautaloss behaves as if it is an open baffle or infinte back chamber as there are no reflections. The measured -3dB point was 52 Hz - same as the driver's fs provided by the manufacturer. This is actually sufficient bass for me to use this as the helper woofer for the Nautaloss tops which will be high passed at about 300 Hz. Sensitivity should be commensurate with the Vifa (85 dB vs 88 dB for woofer).
The THD also looks quite good - and this is playing at typical listening levels with amp volume knob at usual 1030 o'clock position.
My gripe is that this cheap woofer has a terrible suspension damping and flaps all over the place - as exhibited by the ringing in the impulse response. But its decays rather quickly (< 1 ms) so should not be too perceptible. But hey, what do you expect from a $4.88 driver
Overall, I have to say that this performance is quite astonishing for the price and time invested. I think upgrading to a better 6.5 in woofer may be in the works. However, this cabinet design has proven itself to act as if it is a sonic black hole for the back radiation.
In case you are wondering what it sounds like, here is a short clip recorded with the same measurement mic in mono.
OK, call me impatient and had to get some measurements while the glue is drying.
Before I installed the driver into the box, I had mounted it on a 24 in x 36 in open baffle and measured its response at about 36 in above the floor.
The drivers were wired series in this box so the nominal impedance is 8 ohms, the sensitivity (with voltage) dropped but the amount of xmax was reduced allowing for the speaker to play overall louder and with reduced distortion.
The measurement was with the mic 12 in away, centered between the two drivers and 4 in off the floor. Obviously there will be some floor enhancement and we do not expect any baffle step loss. Blue is Nautaloss Bass, and red is same driver in an open baffle (OB).
The measurement looks very good - almost identical to the open baffle measurement with the exception of the enhanced bass loading due to the floor (or reduced highs however you want to look at it). The response confirms that the Nautaloss behaves as if it is an open baffle or infinte back chamber as there are no reflections. The measured -3dB point was 52 Hz - same as the driver's fs provided by the manufacturer. This is actually sufficient bass for me to use this as the helper woofer for the Nautaloss tops which will be high passed at about 300 Hz. Sensitivity should be commensurate with the Vifa (85 dB vs 88 dB for woofer).
The THD also looks quite good - and this is playing at typical listening levels with amp volume knob at usual 1030 o'clock position.
My gripe is that this cheap woofer has a terrible suspension damping and flaps all over the place - as exhibited by the ringing in the impulse response. But its decays rather quickly (< 1 ms) so should not be too perceptible. But hey, what do you expect from a $4.88 driver
Overall, I have to say that this performance is quite astonishing for the price and time invested. I think upgrading to a better 6.5 in woofer may be in the works. However, this cabinet design has proven itself to act as if it is a sonic black hole for the back radiation.
In case you are wondering what it sounds like, here is a short clip recorded with the same measurement mic in mono.
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Bass Nautaloss with Quad Driver Push-Pull
I had a crazy idea to add two more drivers in a face-to-face push-pull configuration in hopes of reducing THD and increasing efficiency. The drivers are now wired in parallel-serial for a nominal 4 ohm load.
I did not expect it to work this well though: I got a 10 dB boost in the bass efficiency (nominal single driver efficiency was 88 dB, I suppose that means it is now 98dB?? ), the THD dropped by 5 dB, and most importantly, the impulse response stopped flapping and is now much, much tighter.
The quad driver P-P config is green, the two driver version is blue, and the OB reference is red.
Just to reduce the cluttered graph, here is the quad driver P-P all by itself:
I am happy with this outcome
I had a crazy idea to add two more drivers in a face-to-face push-pull configuration in hopes of reducing THD and increasing efficiency. The drivers are now wired in parallel-serial for a nominal 4 ohm load.
I did not expect it to work this well though: I got a 10 dB boost in the bass efficiency (nominal single driver efficiency was 88 dB, I suppose that means it is now 98dB??
), the THD dropped by 5 dB, and most importantly, the impulse response stopped flapping and is now much, much tighter.The quad driver P-P config is green, the two driver version is blue, and the OB reference is red.
Just to reduce the cluttered graph, here is the quad driver P-P all by itself:
I am happy with this outcome
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Photos of Completed Nautaloss System
I have the Nautaloss bass speaker running through a mixer to combine left/right channels. The Nautaloss tops are driven by my diy TPA3116D2 amp, the Nautaloss bass is driven by the Yamaha RX360. I still don't have a crossover and running both speakers fullrange - yet it sounds amazingly good. The bass is very clean and fast now. The 50 Hz extension is just the right amount of reach for now.
I have the Nautaloss bass speaker running through a mixer to combine left/right channels. The Nautaloss tops are driven by my diy TPA3116D2 amp, the Nautaloss bass is driven by the Yamaha RX360. I still don't have a crossover and running both speakers fullrange - yet it sounds amazingly good. The bass is very clean and fast now. The 50 Hz extension is just the right amount of reach for now.
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