[Captainhemo]

They do take up twice as much floor space.

They do but it's kind of irrelevant...  the  subs need to sit out from the  wall  say  a min of  3'  ... the  amps typically sit right behind the   sub  tower so you're already     using up  that  space........sort of   

Yeah, the  HX 800's were  nice but n reality, the   dual  A370's  probably offer more   configuration options.
I do know where there is  a pair of  HX800's  and    stack of 4   per  amp  tha t might  be available if  someone o was intersted

[emailtim]

got these wired up yesterday,  now up and  playing .  Wow
Need to  slice up  some  no rez  now


If we get things a  bit more organized  this aft, will  get  a  couple  more pics

jay

Has anyone measured the OB subs with and without the alternating driver installations to determine what the deltas are between the 2 configurations ? 

Would be nice to have a definitive answer on performance and distortion in addition to just weight distribution and aesthetics.

TIA

[Early B.]

Has anyone measured the OB subs with and without the alternating driver installations to determine what the deltas are between the 2 configurations ? 

Would be nice to have a definitive answer on performance and distortion in addition to just weight distribution and aesthetics.

I'm interested in hearing more about this, too. I'm guessing there would be a subtle sonic difference between the two configurations, as well, due perhaps to how the subs load the room.

[emailtim]

I'm interested in hearing more about this, too. I'm guessing there would be a subtle sonic difference between the two configurations, as well, due perhaps to how the subs load the room.

FWIW, here are a couple of THD plots of my mono-triple (from 40Hz down) playing at 100dB.  The mains are playing at 95dB +/-5dB from 40Hz upwards in this plot.  From about 107Hz up, the complete system is under 1% THD and most of the system from 418Hz up is under 0.3% THD or @ 50dB down from the fundamental.  Most of the sub is at 2.7% THD and under with three peaks, each peak is caused by the 5th, 3rd and 2nd harmonics in that order.

Most of the THD is comprised of 2nd, 3rd and 5th harmonic distortions (which have been disabled to more easily see the black THD plot), but a reduction in 2nd order should make a difference (at least to the plot).  Reducing volume, reduces the THD levels below 40Hz to that of bass driver, so more sub drivers could help lower distortion.  Davey mentioned in another thread that there would be a -15dB reduction in even order harmonic distortions by alternating driver directions (see second plot scaled in dB), but I don't think I can achieve that figure due to having an odd number of drivers (only 2 of the 3 would cancel).

Between the 2 plots, you can see the majority of the system's THD ranges from [2.7% to 0.3%]  or @ [-30dB to -50dB] below the fundamental at this specific SPL.

Left scale is in % THD:



Left scale in dB for comparison:

[Danny Richie]

FWIW, here are a couple of THD plots of my mono-triple (from 40Hz down) playing at 100dB.  The mains are playing at 95dB +/-5dB from 40Hz upwards in this plot.  From about 107Hz up, the complete system is under 1% THD and most of the system from 418Hz up is under 0.3% THD or @ 50dB down from the fundamental.  Most of the sub is at 2.7% THD and under with three peaks, each peak is caused by the 5th, 3rd and 2nd harmonics in that order.

Most of the THD is comprised of 2nd, 3rd and 5th harmonic distortions (which have been disabled to more easily see the black THD plot), but a reduction in 2nd order should make a difference (at least to the plot).  Reducing volume, reduces the THD levels below 40Hz to that of bass driver, so more sub drivers could help lower distortion.  Davey mentioned in another thread that there would be a -15dB reduction in even order harmonic distortions by alternating driver directions (see second plot scaled in dB), but I don't think I can achieve that figure due to having an odd number of drivers (only 2 of the 3 would cancel).

Between the 2 plots, you can see the majority of the system's THD ranges from [2.7% to 0.3%]  or @ [-30dB to -50dB] below the fundamental at this specific SPL.

I'm not sure if you realize this but the level of average room noise will be typical about 45 to 50db down as well. So the room noise will be as loud as the distortion levels that you are trying to measure and impossible to separate from the room noise. Outside of an anechoic chamber you are not likely to get any meaningful or consistent data.

And whether the distortion numbers are 1% or 3% isn't going to tell you anything about the way it sounds. You're looking at figures that are well down in output.

Distortion numbers also vary with output levels, and there is no industry standard for taking them. So there is no way of making meaningful comparisons to measurements made by someone else in another place.

What really tells the tale is to look at the spectral decay. This will show you the settling time. Audible differences here are quite significant especially when looking at servo controlled drivers.

But this also is difficult or impossible to measure in a room as you'll just be looking at how long it takes the signal to quite bouncing back and forth in the room rather than how long it takes the woofer to stop.

And like distortion numbers it will vary with output levels. So to make any meaningful comparisons you'll have to match output levels.

[emailtim]

Well, I may be the first to post actual measurements for the question, "Does alternating drivers help", but here goes. 

Note, I am measuring a mono-triple in a 1.5" thick MDF H-Frame with normal cavity sizes of 13" x 13" x 6.5" crossed over @ 40Hz with a 48dB/octave slope.  No mass loading membranes or open cell foam has been applied to the cavity walls.  All measurements were taken without moving the mic located at the listening position and at the same volume and XO settings.  At least 9 measurements were taken with all drivers facing forward and at least 9 were taken with the center driver of the triple reversed in a quiet room with no lights, HVAC, fans, etc. running.

For those that are concerned the measurements are being lost in the noise floor, here is a plot (all 3 drivers facing forward) showing THD, the Noise Floor and the first 1-9 harmonics.  The noise floor is 15.7dB below the THD plot @ 25Hz and what I have been told from audio engineers, humans are suppose to be able to hear down into the noise floor, but by how much, I don't know.  Since there is 15.7dB difference (THD versus Noise Floor) for this experiment, we won't have to go there.  Also, harmonics below the noise floor have been greyed out in the plot.



I think there has been 2 lingering questions about alternating drivers, 1) output levels and 2) sound quality (subjective and/or qualitative).  Since my hearing is different from everyone else's, I can only share my measured plots and my perceptions of sound preferences.

Reminder: These tests are based on an odd number of drivers so I don't get equal cancellations like folks would who have even number of drivers.

As for #1, output levels, The calibrated mic only sees at most @ a 0.3 dB drop by reversing the center driver.  I can get more boost by narrowing the cavity opening or increasing the plate amp's volume level to compensate.  From my experiment, with the plate amp's volume level set to 11 O'Clock, I am not concerned with this in-room 0.3dB SPL drop which maybe different elsewhere in the room.



As for #2, sound quality, there is a 2.3dB THD drop @ the 23.3Hz plateau and 4dB THD drop in the peak @ 38.3Hz (40 Hz crossover point, Purple is all facing forward, Blue has center reversed).  Can this be heard, I don't know, but I am more than willing to accept this free lowering of the THD.  FWIW, the peak at 38.3Hz is primarily comprised of the 2nd order harmonic distortion.  The first two relatively unaffected peaks are comprised of odd order harmonics.

CORRECTION:  Plot title is incorrect.  Should read: "All Forward THD vs Center Reversed THD"


Comparing the multiple measurements, the preceding observations are pretty much consistent throughout.  I would expect slightly better improvements using an even number of drivers. 

Since we are DIYer's, we should all be interested in how to build/assemble our projects to get the best/cleanest sound possible.  Hope this helps giving a quantitative data point on the original question of whether or not to alternate drivers.

Update:

For those concerned about reflections, here is an impulse response of the room and system.  GIK Acoustics suggests all early reflections should be down at least 15-20dB within 20ms-40ms.

https://www.gikacoustics.com/unpacking-etc-time-domain-measurements-early-reflections/

[Danny Richie]

You have spent some time on this producing some interesting information.

As for distortion numbers telling us how it will sound? I'd have to say that it is not going to be something that we can distinguish real well if at all by knocking something up or down several db in level on something that far down as the music is playing. It is perceived as part of the input signal too easily.

And if you are getting readings 15db above the noise floor then you have an exceptionally low noise floor.  Typically there are close to par.

What is really impressive is the flat response to well below 20Hz. 

In the comparison of all facing forward verses on flipped it is not clear which is which.

And the most telling of all was the decay rate of the impulse response within the room. That is a huge amount of time that those long wavelengths are bounced around in the room before setting. Killing that and making it as fast as possible will have a much greater audible effect than anything.

Even when I measure and test a speaker, I see the impulse response and apply gating to do away with room reflections in the measurement. And by 2 to 4ms the speaker output has ended (with a 1 watt signal), but the wall, floor, and ceiling  reflections carry on for a really long time comparably.

[emailtim]

And if you are getting readings 15db above the noise floor then you have an exceptionally low noise floor.

The plots are straight out of REW and a Cross Spectrum Calibrated MiniDSP UMIK-1 mic.  Nothing has been altered.  It is, what it is.

Typically there are close to par.

I could appreciate that.   

What is really impressive is the flat response to well below 20Hz. 

Actually, I am very happy with the flat response from 40Hz on down.

In the comparison of all facing forward verses on flipped it is not clear which is which.

Sorry that the description of the THD drops were not clear.  Summary:  Alternating the center driver resulted in at most a 0.3dB drop in SPL and a 2.3dB and 4dB drop in THD compared to all drivers facing forward.  Purple is all facing forward.  Blue is center driver reversed.

And the most telling of all was the decay rate of the impulse response within the room. That is a huge amount of time that those long wavelengths are bounced around in the room before setting. Killing that and making it as fast as possible will have a much greater audible effect than anything.

Actually, the early first reflections are down considerably within 20-40ms, but true, the waterfall plot can be improved in the sub frequencies.  Part of that may be due to the open floor plan in the back of the room.  Here is a plot out to 300ms.  Mid-bass, mids and high frequencies are down @ 50dB in 300ms.

[Danny Richie]

While we are talking about spectral decays....

For comparison, when I am measuring a speaker only (no room reflections) and show some woofer break up or ringing that carries on for an extra 2 to 3ms that is something that is often pretty easy to hear with music information within that area.

So just imagine how much the room reflections are affecting what we hear.

Fortunately anything arriving 6ms in time away from the fundamental is enough time for our ear to perceive it as a second event or later arrival.

Another biggie is how much cabinet wall resonances can add to what we hear. It can also be a large order of magnitude greater than measured THD from the drivers themselves.

[Richard U]

Very early in this thread a few people wanted a single instead of the double in a flat pack. Has there been any more thought about offering one? For me, space is the concern and mounting my main speaker on top of it would be ideal using two singles for left and right.

[Danny Richie]

Very early in this thread a few people wanted a single instead of the double in a flat pack. Has there been any more thought about offering one? For me, space is the concern and mounting my main speaker on top of it would be ideal using two singles for left and right.

We don't offer a amp and woofer combination designed for a single 12" woofer. To reach nominal SPL levels in open baffle a pair is also recommended.

They also don't have to be vertically stacked. They can be horizontally stacked.

[Richard U]

What is the difference in using two in separate boxes vs two in one box? I was planning on using the A370 mounted in a separate box that you offer,

[Danny Richie]

What is the difference in using two in separate boxes vs two in one box? I was planning on using the A370 mounted in a separate box that you offer,

Adding longer cables to the servo control system causes some delays in the control. It is recommend not to add any more cabling length than what is already connected to the amp. That's why we keep the amps located right behind each woofer cabinet.

[Richard U]

I did not think 4' to 5' to each driver would have such an impact. Thanks.

[Ngoliath]

This is my first project. I realize it’s a bit ambitious to start with the NX-Oticas and the dual subs, but I figured I might as well jump in with both feet. So far, so good. I’m going to try and do the paint job myself. I’m testing out the results on the amp boxes now with some oil based gloss black.

Funny thing is, I cleared a small space in my garage to work and have spent half my time assembling workbenches and equipment. I didn’t realize that you already have to have handyman skills to become a handyman.

[Ngoliath]

That I clearly not my garage. This is my new space. I’m looking forward to a few more projects, if I can get this one right.

[riverdinaudio]

How do I place order for pair of triples for my Servo Sub 5 kits.  Still $870?

[Captainhemo]

How do I place order for pair of triples for my Servo Sub 5 kits.  Still $870?

Email me  @ captainhemo at  shaw.ca

Prices are  at the top of the  first post  on page  1.


jay

[birkbott]

I have a kind of basic question on these.

Let's say you're doing a double (2 driver) configuration. How are these wired to the amp? I see a lot of wiring with both sets of binding posts on each driver being used, but as a noob when it comes to subwoofer wiring I don't know why.

Is there a wiring diagram available anywhere?

[Early B.]

Is there a wiring diagram available anywhere?

Here it is...