Zobsky ponders the Aura NS6-255-8A

[zobsky]

I bought a set of 4 drivers

Aura NS6-255-8A 6" Paper Cone Neodymium Magnet Woofer


Specifications: *Power handling: 50 watts RMS/100 watts max *VCdia: 1" *Impedance: 8 ohms *Re: 6.0 ohms *Frequency response: 55-5,500 Hz *Fs: 55 Hz *SPL: 91 dB 1W/1m *Vas: 0.58 cu. ft. *Qms: 10.8 *Qes: 0.58 *Qts: 0.55 *Xmax: 3.9 mm *Dimensions: Outside diameter: 6-1/8", Cutout diameter: 5-3/8", Depth: 3-3/8".

Response attached.

• The basic idea is to build a pair of 2.5 way speakers for music (not home theater) using the 0.5 driver to remove the need for BSC. The listening room will probably be small to medium depending on where they end up living.
  
• Without considering crossover design and choice of tweeter at this point, what I'd like advice on are the possible bass alignments. Iv'e got plenty of sub drivers lying around if absolutely needed, but I'd like to extract the most from the aura's. A solid in room 40 or lower Hz IF POSSIBLE.
  
• Enclosure size is not an issue, as my spouse doesn't mind larger speakers.
  
• Ampllfier - can be built depending on the speaker requirements, but I'd like to use my 7 watt push pull 2A3 amp if possible.
  
• Impedance - 4 or 8 ohm nominal is accaptable.

That said, I've considered.

1. Sealed - not in favour of this due to the high crossover point.
2. Aperiodic - considering MAPD ( North Creek Music's new MAPD driver loading ) but haven't ever tried it before so can't comment
3. Reflex - preliminary . WinISD sims indicate I can get to 40 Hz easily with a bass reflex, though I can't say what this translates to in reality.
4. negative taper TL
5. MLTL
6. BVR

For what its' worth,

1. I have a licensed version of MJK's mathcad models that I will use but before starting down that track, I'd like to solicit some opinions on the best alignment / combination of alignments. I'm leaning towards TL, MLTL or Aperiodic
2. I'm considering developing a 2 way series crossover in parallel with the augmenting 0.5 driver - but that's something to be tackled at a later time

Thanks in advance

[zobsky]

Response document (too large to attach) is downloadable from Download ns6-255-8a.pdf

[zobsky]

Here's a first sim at an open ended tapered TL. Sorry about the ad-based hosting service, since I can't upload pdfs that large to diyaudio. I designed it for a shallow rolloff below 70 Hz that will (hopefully) be augumented by room gain and the 0.5 woofer

Comments ?

aura1.pdf

[18Hurts]

I looked at the pdf and noted it showed a single woofer,

Knowing little about TLs, won't the 0.5 woofer demand a change to the dimensions or is it an issue?

Good to see a design for the Aurasound closeout woofers, I use their 5.25" NRT woofers in my center channel and they timber match to my Infinity Overtures very well. It is a 2.5 way design with four 5.25" woofers and a 30mm dome tweeter XO'd third order at ~1750Hz.

Looking forward to seeing the results of your 2.5 way TL, those 6" woofers have great efficiency and hope they have great sound to match.

[zobsky]

Originally Posted by 18Hurts

I looked at the pdf and noted it showed a single woofer,

Knowing little about TLs, won't the 0.5 woofer demand a change to the dimensions or is it an issue?

Yes, I intend to build a separate cabinet for the 0.5 woofer.

Here too, there are a couple of possibilities

1. An identical cabinet alignment to the main woofer
2. A complementary response to acoustically even out the peaks and dips in the main woofer response, within the 0.5 woofer's passband. Here's an example (though for an MTM dual T-Line) Nike Transmission Line Loudspeakers

[18Hurts]

[QUOTE=zobsky;2670246]Yes, I intend to build a separate cabinet for the 0.5 woofer.

Now it comes together,

After reading way too much in the full-range section of DIY, the 4 ohm version reminds me of a "full-range with helper tweeter". The charts indicate it can go out to 7 KHz then roll off quickly and smoothly. A candidate for running "full-range" with a single cap to a Vifa "horn" soft dome at 7 KHz? $9 a woofer and $10.80 for a tweeter would make a very inexpensive speaker for basic use. The thing that also attracts me is the very efficient nature of the drivers for home theater purposes. Two of the 4 ohm versions in series with a 1st order crossover to take care of the bass and power handling then another 4 ohm for the 500 to 7K region naturally rolling off to a shallow 6dB cap for the tweeter. A simple padding resistor to adjust the tweeter output and finished.

It is not a design for me, but for a buddy that needs a center channel and two Bipole/Dipole surrounds for his home theater. His receiver is not very good at driving 4 ohm loads so the 8 ohm under 500 Hz dual-woofer in series would protect that. The Bipole/Dipole is just two sets wired in series with a switch. Getting all three speakers well over 91dB at one watt is a requirement and so is keeping the cost down. All three speakers would require $55 in tweeters, $63 in woofers, 6 capacitors and one coil. His main speakers are 92dB at a watt and his beloved receiver provides 50 watts so that is what I'm working with. He is not an audiophile in any sense but would like an output that matches the mains with "adjustable" surrounds so the Aurasound comes to mind.

I gain by playing around with 1st order crossovers, get some experience with "full-range with helper tweeter" designs and I might actually like the sound. The Auras have 4 and 8 ohm versions so making a 4 ohm version of the dual-woofer to single woofer 1st order version with a capped tweeter. Always sniffing around for a computer desk speaker that is efficient enough for great output from a T-Amp.

[zobsky]

[QUOTE=18Hurts;2670579]

Originally Posted by zobsky

Yes, I intend to build a separate cabinet for the 0.5 woofer.

Now it comes together,

After reading way too much in the full-range section of DIY, the 4 ohm version reminds me of a "full-range with helper tweeter". The charts indicate it can go out to 7 KHz then roll off quickly and smoothly. A candidate for running "full-range" with a single cap to a Vifa "horn" soft dome at 7 KHz? $9 a woofer and $10.80 for a tweeter would make a very inexpensive speaker for basic use. The thing that also attracts me is the very efficient nature of the drivers for home theater purposes. Two of the 4 ohm versions in series with a 1st order crossover to take care of the bass and power handling then another 4 ohm for the 500 to 7K region naturally rolling off to a shallow 6dB cap for the tweeter. A simple padding resistor to adjust the tweeter output and finished.

It is not a design for me, but for a buddy that needs a center channel and two Bipole/Dipole surrounds for his home theater. His receiver is not very good at driving 4 ohm loads so the 8 ohm under 500 Hz dual-woofer in series would protect that. The Bipole/Dipole is just two sets wired in series with a switch. Getting all three speakers well over 91dB at one watt is a requirement and so is keeping the cost down. All three speakers would require $55 in tweeters, $63 in woofers, 6 capacitors and one coil. His main speakers are 92dB at a watt and his beloved receiver provides 50 watts so that is what I'm working with. He is not an audiophile in any sense but would like an output that matches the mains with "adjustable" surrounds so the Aurasound comes to mind.

I gain by playing around with 1st order crossovers, get some experience with "full-range with helper tweeter" designs and I might actually like the sound. The Auras have 4 and 8 ohm versions so making a 4 ohm version of the dual-woofer to single woofer 1st order version with a capped tweeter. Always sniffing around for a computer desk speaker that is efficient enough for great output from a T-Amp.

To the first question, don't bipole / dipole surround speakers employ a pair of tweeters per channel, as opposed to one?

To the first and second question, one way to cheat using a first order crossover on a helper tweeter would be to start off with a sensitive tweeter with a fairly low Fs and underlap the crossover point i.e. cross it over higher than the expected crossover point thereby padding the tweeter down and also protecting it from bass signals. I know of folks using first crossovers on efficient tweeters at , 15 KHz, in order to blend with woofers rolling off at 7 Khz

[sreten]

Hi,

Some quick modelling in Win ISD indicates 50L for two drivers vented at
40Hz gives - 3dB at 45Hz, -4dB at 40Hz, -6dB at 35Hz and -10dB at 30Hz.

Roll off is quite shallow down to the knee at 35Hz, it an alignment suited
to low power, as it has much high efficiency in the lower bass compared
to sealed. How big ~ in box volume in the TL ?

rgds, sreten.

[18Hurts]

[QUOTE=zobsky;2670684]

Originally Posted by 18Hurts

To the first question, don't bipole / dipole surround speakers employ a pair of tweeters per channel, as opposed to one?

To the first and second question, one way to cheat using a first order crossover on a helper tweeter would be to start off with a sensitive tweeter with a fairly low Fs and underlap the crossover point i.e. cross it over higher than the expected crossover point thereby padding the tweeter down and also protecting it from bass signals. I know of folks using first crossovers on efficient tweeters at , 15 KHz, in order to blend with woofers rolling off at 7 Khz

You are correct, the bipole/dipole use two tweeters and two woofers facing 180 degrees from each other. The dipole is out of phase. The reason for this is I have no idea what he wants or likes so the switch option is a must. The surrounds will be two boxes hinged together so he also has the option to run bipole at different angles if he wants. He can run "monopole" if he so chooses (I am not the audiophile police) The Aura 6" woofer coupled with a
Vifa BC25SC06-04 1" soft dome (93dB 1w/1m or 96dB 2.83V) would give the output he requires.

I do like your idea of underlapping so the louder tweeter blends into the less efficient woofer. The Vifa has an Fs of 1350Hz so no power/distortion issues crossing at 9 KHz with a first order cap. Since he might be running bipole at angles, the additional treble would be beneficial. Thanks for the thought!

[zobsky]

Here are a couple more simulations. The first is a tapered TL, somewhat better than the last one I posted. My concern is that despite my best efforts, it doesn't seem significantly better than the infinite baffle response trace).

The second one is an MLTL . . This curve seems more promising but the size seems unreasonable, in view of the fact that I'm considering adding another aura as a 0.5 woofer (though it may not be needed if a single driver can really dig this low with authority - though I have my doubts). This sim becomes impractical if I have to double up on the size to accommodate a 2nd 0.5 driver.

Comments / optimizations on my simulations ?