@jhollander said:
Friday night open unlimited? Hope you have got the interface figured out.
Yes. My anticipation is that they will either 1) give me a stereo pair of power amplifier outputs to make my connections, or 2) give me a stereo pair of line level preamp outputs to make my connections. In the former case, I would simply hook one channel (either right or left) of each power amp output to the power amp input of my respective SPA-250 amplifier. I'll be using two SPA-250's, one for each channel. Each SPA-250 would then send the amplfied bass below 125Hz to each Dual W6-1139 subwoofer box. Each SPA-250 would also send 125Hz and higher output to each ND-90/Neo3 box. The SPA-250 has a built-in 6dB/octave xover at 125Hz to perform this function. The SPA-250 low pass roll off will be 24dB/octave at 125Hz (based on my settings). The SPA-250 high pass going to the ND90/Neo3 box will be 18dB/octave acoustical (6dB + 12dB nature roll off of ND-90's). I have tested this combo and I get a very good summation in the 80-200Hz region when using the SPA-250's normal phase switch position.
If they give me a stereo pair of line level outputs, the SPA-250 can handle that too. Same basic connections, except that the SPA-250 would NOT be using a pair of internal dropping resistors to reduce the voltage down to line levels. Everything else then works the same.
One big question I have, is whether or not they will allow me to adjust the subwoofer gain level, to match the room size, before my speakers play. At home, I know that an SPA-250 gain setting of about one O'Clock will blend in the subwoofer output level just about right (based on RTA measurements and listening tests). However, one O'Clock at home is NOT the same as one'Clock in a much larger venue. I may need to jack the gain on the subs up to as much as two O'Clock to compensate for the larger room. A quick RTA measurement in the room would tell me this. Hopefully, when they run the test to set levels, they will allow me to look at their laptop's RTA screen (with no A,B or C weighting applied) so that I can quickly adjust my subwoofer gain to match the room. If they will not allow this, then I will simply have to take my best guess at the correct gain setting and hope for the best. (sorry for the long winded response).
Thanks for the feedback. That's what I thought. Even though they allow more time for "Open Unlimited" setup, they really seem to push you to set up quickly and go. So you have to be prepared in advance or you will make mistakes. This will be my third time in "Open Unlimited." Plantanic speakers in SDC 2014 and Symmetrical Isobarik MK II speakers in 2016. Both times I set the Sub output way too low, but this was when the event took place in the much larger dance studio. The room they have us in now is somewhat smaller.
@4thtry said:
Thanks for the feedback. That's what I thought. Even though they allow more time for "Open Unlimited" setup, they really seem to push you to set up quickly and go. So you have to be prepared in advance or you will make mistakes. This will be my third time in "Open Unlimited." Plantanic speakers in SDC 2014 and Symmetrical Isobarik MK II speakers in 2016. Both times I set the Sub output way too low, but this was when the event took place in the much larger dance studio. The room they have us in now is somewhat smaller.
I had all the speaker cables made and all the cables labeled. Everything was plug in so all I had to do was plug everything in and turn it on.
I could be wrong but I think Bill's dilemma is that he is only using his own amp for the woofers and using the "house" amp for the MMTMM. Is that correct Bill? It would be quick and easy if you had two amps and only needed a stereo line level input from PE's front end.
Craig, you are correct. The SPA-250 has just one power amp. This amp powers the subwoofers with a fixed 24dB/octave low pass filter. The gain of the subwoofer can be adjusted with a pot. The low pass xover frequency can also be adjusted from 40 to 180Hz with another pot (I have it set at about 125Hz or so). The SPA-250 also has a high pass output to feed the MMTMM that uses a fixed 125Hz 6dB/octave high pass filter. But in order to use this feature you need to use another external power amplifier and connect it to the line level outputs of the SPA-250. Otherwise, the SPA-250 simply "passes through" PE's "house amp" signal to the MMTMM.
But even if I used two power amps and took my input from PE's line level outputs from their front end, I would still have the same problem of trying to guess at the appropriate subwoofer level to match my MMTMM level. I know what this matching level should be at home, but the SPL at low frequencies drops in larger venues (due to lower room pressure). I therefore need to guess at how much to boost the bass to make it sound balanced in the larger space. What I need is a hand-held RTA meter together with some type of very small, portable broadband signal level generator/amplifier. Then, once I get to the venue, I could take a quick RTA spectrum measurement and adjust my subwoofer levels to match the room.
Do you have a friend who works at the local library or a hotel? You might be able to set your rig up in a larger meeting room to get your levels dialed in. It might not be perfect, but better than just wingin' it.
Ah, they are plate amps. So, he only needs a hi-level speaker input from the house amp to run his show.
I can recall a knob twist or 2 for various subwoofer level settings, but not much. Usually, this ends up making the subs sound heavy, IME. I would set them up in your room, dial them in, and then add one or 2 approximate detent(s) more (if there are detents on the pots, or where the next would be if there were detents). This way you won't be boomy, and won't be light. More than this added will likely be too much.
@Tom_S said:
Do you have a friend who works at the local library or a hotel? You might be able to set your rig up in a larger meeting room to get your levels dialed in. It might not be perfect, but better than just wingin' it.
Unfortunately, no. I should have completed and brought these to InDIYana earlier this year.
I like the idea of controlling the match between the TM and woofer with my own amps with a fixed gain. If you start tweaking for the venue it won't match any passive reference speakers they might be using.
@jhollander said:
I like the idea of controlling the match between the TM and woofer with my own amps with a fixed gain. If you start tweaking for the venue it won't match any passive reference speakers they might be using.
My understanding is that when you get into the "open unlimited" category, the judges seem to expect tight, deep bass, flat all the way down to 20Hz. They do not seem to be comparing the bass level to any type of on-site passive reference speaker. What I would like to do with my tweaking attempts is to adjust just the bottom 2 octaves below 100Hz. Everything else would remain the same (see graph below). In my model, I am applying the full BSC from 150Hz to 1kHz. If I were to cross at a much higher frequency, say 400Hz, I would not consider tweaking for the venue, because that would mess up the BSC as well.
In both cases where I crossed to a subwoofer with plate amplifier at 100Hz, the judges sharply critiqued my speakers for insufficient deep bass. For instance, regarding the Plantanic speakers (in SDC 2014), one judge commented ". . . lean bass - but very clear." He then gave me a very low tonal balance score of 3 with an additional comment of "needs more bass." Another judge commented that my speakers had an ". . . odd thin sound." For the Symmetrical Isobarik MK II speakers (SDC 2016), one judge commented that my speaker ". . . needs more bottom end . . . " Another commented ". . . bass OK, not that low . . . " I think the reason this happened is because I failed to compensate properly for the size of the room. I set my sub gain level based on how they sounded in a much smaller room at home.
I forgot to mention, in the above comparison graph, the green 12 O'Clock gain setting sounds "thin" in my room. The black 1 O'Clock setting sound just right. Very balanced sounding. The red 1:30pm setting is starting to sound a little bass heavy. And the blue 2 O'Clock setting is way too much (bloated). Each 30 minutes of gain adjustment boosts (or cuts) the gain by about 2.5dB. I am leaning towards a boost of about 2.5dB (1:30pm) for the SDC event. (Note: The 25, 30, 42, and 60Hz peaks and dips are room modes and should be averaged out with additional smoothing, which I did not do.)
@jhollander said:
Makes sense when comparing in room response. Have you checked what a spliced nearfield looks like with a gain setting?
John, do you mean a spliced nearfield of the ND-90 (ie., NF+FF+Diffraction model)? I did this when setting up the VituixCAD model when I merged NF+Diffraction model with the ND-90 far field spinorama measurements (28 measurements, vertically and horizontally). But I have not performed a "validation" type measurement yet that includes NF spliced data for the ND-90's. I'll give that a try. I'll also check to see if I can merge it with a W6-1139 nearfield measurement as well, but I do not think this is possible, because there is no "workable" splicing overlap between the ND-90's and W6-1139s in the 100Hz region.
I made a couple SPA-250 sub amplifier boxes out of Menard's laminated shelving material. The particular boards I selected have a nice, darkly colored laminate with a cool looking granite type sculptured surface. To make them look nice, I mitered the 4 corners to eliminate any exposed particle board. However, the shelves are 3/4" thick. So when I mount the amp in the opening, the mounting plate does not cover the entire outside raw particle board edge. To fix this, I rounded the outside top edge with a 1/8" roundover bit and filled the exposed area with wood filler. Then I sanding the edge smooth with 220 grit, masked it off, and painted the exposed edge with semi-gloss enamel. Should look pretty good when I get done.
Project is all done and ready to go! Now I need to figure out how to fit all this junk in my car for the long trip.
Here is pic showing the completed plate amp boxes and all connections. I'm using two sets of dual banana plug cables between the plate amps and MMTMM's. Note to self: Be sure to bring all these cables along to the event! The two conductor polarized type IEC power cables are very hard to find (and very stiff for a 16ga cable)!
Here is a pic of the bottom side of the two plate amp boxes. I installed a dual banana jack on a small aluminum angle that accepts dual banana plugs. I used a 5/8" router bit to make a small clearance notch for the cable.
I completed the crossover mods using my new DIY coils and a few other parts. As you can see in the before and after pics, I removed the 9 volt "charge coupled capacitor" battery and caps and used the extra space for the new parts.
Before:
After:
Finally, I silicone glued two 1/4" thick rubber damping material squares to the back side of the Neo3 tweeter plastic back chamber enclosures. @wolf gave me these samples several years ago. Hopefully, the thick, heavy rubber will help to dampen any resonances. I think @wolf did something similar to his pair of Neo3 enclosures.
Yep, I have that rubber sport flooring on the backs of my Neo3, my Usher 9845 domes, and any other driver or chamber I felt needed it. Used to be called Tough Tile originally when Jeff introduced it to me back in 2002, made of shredded tires. Nick used it constrained in his Pnemosynes build too. I still have a partial and a full 24x24 sheet left. Coupled with a good damping material like Ultratouch or Sonic Barrier, I feel it rivals the asphalt mass layers of other layered types. What I have is 3/8" thick, but you can get similar products in rolled 1/16" sheet to about half inch thick at Menards, Amazon, etc. Most of them have targets as weight room or exercise flooring tile.
I have loose-hung it with screws, press fit to size, or glued it with E6000. Good heavy stuff!
@6thplanet said:
Label everything for easy identification.
Unfortunately I won't be there Friday to hear them😒
You're going to miss the Pizza Party! Bringing speakers on Saturday?
Labels would be a good idea. When I look at my cables, the connections seem so simple that I figure it would be almost impossible to screw it up. But that is what has happened so many times to designers in the open unlimited category. You set up at high speed and then Chris hands you the wireless microphone. Then you stumble through your verbal presentation in front of the judges and crowd. Really nerve-racking!
After I put the Dayton SPA250 plate amps in my laminated boxes, one of the plate amps stopped working. It was almost completely dead with no bass output at all. When I cranked up the volume, I could hear a faint crackling noise coming from the woofer cones, but no bass. The woofers also started to randomly motorboat up and down from about 100 to 500Hz at very low output levels.
So I popped the cover. Power supply voltage rails all checked good. Driver and power output transistors all checked good. No signs of burnt resistors, bulging caps, etc. After about 2 hours of debugging, I isolated the problem to somewhere on the preamp/crossover PCB board (see back side pic of this PCB below).
Then I remembered something. When I mounted the amps in the boxes, it was a very tight fit. To get the amps to fit in the boxes, I had to remove the small, rubber side plugs that were used to cover up access holes for the 35Hz bass boost switches.
But when I removed the rubber plug on one of the amps, I also stuck a screw driver in the access hole and fiddled with the 35Hz bass boost switch, just to try it out and see how the switch worked. This on/off switch is very small and is located in the middle of the preamp/crossover PCB board (see pic below).
And a close up pic of the tiny on/off switch:
But when I fiddled around with this, I inadventently created the problem, because the switch got stuck half way between the on and off position. At the time, I did not realize this. I thought the switch was in the off position. When I powered it up, the "half way" switch position created an "open circuit trace" type situation on the preamp/xover PCB. This disconnected the audio signal path and caused the amp to go into a mild form of oscillation. Fully seating the switch in either the "on" or "off" position completely solved the problem. Lots of bass. No more crackling or motorboating.
Moral of the story: If you fiddle with the 35Hz bass boost switch on an SPA250 plate amp, always make sure the switch is fully seated in the on or off position! For a while there, I thought this plate amp was completely cooked.
Comments
Yes. My anticipation is that they will either 1) give me a stereo pair of power amplifier outputs to make my connections, or 2) give me a stereo pair of line level preamp outputs to make my connections. In the former case, I would simply hook one channel (either right or left) of each power amp output to the power amp input of my respective SPA-250 amplifier. I'll be using two SPA-250's, one for each channel. Each SPA-250 would then send the amplfied bass below 125Hz to each Dual W6-1139 subwoofer box. Each SPA-250 would also send 125Hz and higher output to each ND-90/Neo3 box. The SPA-250 has a built-in 6dB/octave xover at 125Hz to perform this function. The SPA-250 low pass roll off will be 24dB/octave at 125Hz (based on my settings). The SPA-250 high pass going to the ND90/Neo3 box will be 18dB/octave acoustical (6dB + 12dB nature roll off of ND-90's). I have tested this combo and I get a very good summation in the 80-200Hz region when using the SPA-250's normal phase switch position.
If they give me a stereo pair of line level outputs, the SPA-250 can handle that too. Same basic connections, except that the SPA-250 would NOT be using a pair of internal dropping resistors to reduce the voltage down to line levels. Everything else then works the same.
One big question I have, is whether or not they will allow me to adjust the subwoofer gain level, to match the room size, before my speakers play. At home, I know that an SPA-250 gain setting of about one O'Clock will blend in the subwoofer output level just about right (based on RTA measurements and listening tests). However, one O'Clock at home is NOT the same as one'Clock in a much larger venue. I may need to jack the gain on the subs up to as much as two O'Clock to compensate for the larger room. A quick RTA measurement in the room would tell me this. Hopefully, when they run the test to set levels, they will allow me to look at their laptop's RTA screen (with no A,B or C weighting applied) so that I can quickly adjust my subwoofer gain to match the room. If they will not allow this, then I will simply have to take my best guess at the correct gain setting and hope for the best. (sorry for the long winded response).
Bill, when I was in that category, it was taken your best guess, but that was years ago
^^ I don't recall letting people set levels.
Me neither
When I brought the Cherry Pi's they had line outs to feed my system and there was no time to make adjustments.
Thanks for the feedback. That's what I thought. Even though they allow more time for "Open Unlimited" setup, they really seem to push you to set up quickly and go. So you have to be prepared in advance or you will make mistakes. This will be my third time in "Open Unlimited." Plantanic speakers in SDC 2014 and Symmetrical Isobarik MK II speakers in 2016. Both times I set the Sub output way too low, but this was when the event took place in the much larger dance studio. The room they have us in now is somewhat smaller.
I had all the speaker cables made and all the cables labeled. Everything was plug in so all I had to do was plug everything in and turn it on.
Ron
I could be wrong but I think Bill's dilemma is that he is only using his own amp for the woofers and using the "house" amp for the MMTMM. Is that correct Bill? It would be quick and easy if you had two amps and only needed a stereo line level input from PE's front end.
Craig, you are correct. The SPA-250 has just one power amp. This amp powers the subwoofers with a fixed 24dB/octave low pass filter. The gain of the subwoofer can be adjusted with a pot. The low pass xover frequency can also be adjusted from 40 to 180Hz with another pot (I have it set at about 125Hz or so). The SPA-250 also has a high pass output to feed the MMTMM that uses a fixed 125Hz 6dB/octave high pass filter. But in order to use this feature you need to use another external power amplifier and connect it to the line level outputs of the SPA-250. Otherwise, the SPA-250 simply "passes through" PE's "house amp" signal to the MMTMM.
But even if I used two power amps and took my input from PE's line level outputs from their front end, I would still have the same problem of trying to guess at the appropriate subwoofer level to match my MMTMM level. I know what this matching level should be at home, but the SPL at low frequencies drops in larger venues (due to lower room pressure). I therefore need to guess at how much to boost the bass to make it sound balanced in the larger space. What I need is a hand-held RTA meter together with some type of very small, portable broadband signal level generator/amplifier. Then, once I get to the venue, I could take a quick RTA spectrum measurement and adjust my subwoofer levels to match the room.
Do you have a friend who works at the local library or a hotel? You might be able to set your rig up in a larger meeting room to get your levels dialed in. It might not be perfect, but better than just wingin' it.
Ah, they are plate amps. So, he only needs a hi-level speaker input from the house amp to run his show.
I can recall a knob twist or 2 for various subwoofer level settings, but not much. Usually, this ends up making the subs sound heavy, IME. I would set them up in your room, dial them in, and then add one or 2 approximate detent(s) more (if there are detents on the pots, or where the next would be if there were detents). This way you won't be boomy, and won't be light. More than this added will likely be too much.
InDIYana Event Website
Ya, they are the Dayton plate amps. I have two of them. No detents, but the knobs are clearly marked. A gain setting of One O'Clock is perfect at home, so I think I will go with Two O'Clock at the SDC. PE still sells them:
https://www.parts-express.com/Dayton-Audio-SPA250-250-Watt-Subwoofer-Amplifier-300-803?quantity=1
Unfortunately, no. I should have completed and brought these to InDIYana earlier this year.
I like the idea of controlling the match between the TM and woofer with my own amps with a fixed gain. If you start tweaking for the venue it won't match any passive reference speakers they might be using.
+1
My understanding is that when you get into the "open unlimited" category, the judges seem to expect tight, deep bass, flat all the way down to 20Hz. They do not seem to be comparing the bass level to any type of on-site passive reference speaker. What I would like to do with my tweaking attempts is to adjust just the bottom 2 octaves below 100Hz. Everything else would remain the same (see graph below). In my model, I am applying the full BSC from 150Hz to 1kHz. If I were to cross at a much higher frequency, say 400Hz, I would not consider tweaking for the venue, because that would mess up the BSC as well.
In both cases where I crossed to a subwoofer with plate amplifier at 100Hz, the judges sharply critiqued my speakers for insufficient deep bass. For instance, regarding the Plantanic speakers (in SDC 2014), one judge commented ". . . lean bass - but very clear." He then gave me a very low tonal balance score of 3 with an additional comment of "needs more bass." Another judge commented that my speakers had an ". . . odd thin sound." For the Symmetrical Isobarik MK II speakers (SDC 2016), one judge commented that my speaker ". . . needs more bottom end . . . " Another commented ". . . bass OK, not that low . . . " I think the reason this happened is because I failed to compensate properly for the size of the room. I set my sub gain level based on how they sounded in a much smaller room at home.
I forgot to mention, in the above comparison graph, the green 12 O'Clock gain setting sounds "thin" in my room. The black 1 O'Clock setting sound just right. Very balanced sounding. The red 1:30pm setting is starting to sound a little bass heavy. And the blue 2 O'Clock setting is way too much (bloated). Each 30 minutes of gain adjustment boosts (or cuts) the gain by about 2.5dB. I am leaning towards a boost of about 2.5dB (1:30pm) for the SDC event. (Note: The 25, 30, 42, and 60Hz peaks and dips are room modes and should be averaged out with additional smoothing, which I did not do.)
Makes sense when comparing in room response. Have you checked what a spliced nearfield looks like with a gain setting?
John, do you mean a spliced nearfield of the ND-90 (ie., NF+FF+Diffraction model)? I did this when setting up the VituixCAD model when I merged NF+Diffraction model with the ND-90 far field spinorama measurements (28 measurements, vertically and horizontally). But I have not performed a "validation" type measurement yet that includes NF spliced data for the ND-90's. I'll give that a try. I'll also check to see if I can merge it with a W6-1139 nearfield measurement as well, but I do not think this is possible, because there is no "workable" splicing overlap between the ND-90's and W6-1139s in the 100Hz region.
Yes, my thought was trying to figure out the level match between the ND90s and the amp plus W6s.
I made a couple SPA-250 sub amplifier boxes out of Menard's laminated shelving material. The particular boards I selected have a nice, darkly colored laminate with a cool looking granite type sculptured surface. To make them look nice, I mitered the 4 corners to eliminate any exposed particle board. However, the shelves are 3/4" thick. So when I mount the amp in the opening, the mounting plate does not cover the entire outside raw particle board edge. To fix this, I rounded the outside top edge with a 1/8" roundover bit and filled the exposed area with wood filler. Then I sanding the edge smooth with 220 grit, masked it off, and painted the exposed edge with semi-gloss enamel. Should look pretty good when I get done.
Masking tape removed to reveal the cool looking laminate:
Project is all done and ready to go! Now I need to figure out how to fit all this junk in my car for the long trip.
Here is pic showing the completed plate amp boxes and all connections. I'm using two sets of dual banana plug cables between the plate amps and MMTMM's. Note to self: Be sure to bring all these cables along to the event! The two conductor polarized type IEC power cables are very hard to find (and very stiff for a 16ga cable)!
Here is a pic of the bottom side of the two plate amp boxes. I installed a dual banana jack on a small aluminum angle that accepts dual banana plugs. I used a 5/8" router bit to make a small clearance notch for the cable.
I completed the crossover mods using my new DIY coils and a few other parts. As you can see in the before and after pics, I removed the 9 volt "charge coupled capacitor" battery and caps and used the extra space for the new parts.
Before:
After:
Finally, I silicone glued two 1/4" thick rubber damping material squares to the back side of the Neo3 tweeter plastic back chamber enclosures. @wolf gave me these samples several years ago. Hopefully, the thick, heavy rubber will help to dampen any resonances. I think @wolf did something similar to his pair of Neo3 enclosures.
Label everything for easy identification.
Unfortunately I won't be there Friday to hear them😒
Yep, I have that rubber sport flooring on the backs of my Neo3, my Usher 9845 domes, and any other driver or chamber I felt needed it. Used to be called Tough Tile originally when Jeff introduced it to me back in 2002, made of shredded tires. Nick used it constrained in his Pnemosynes build too. I still have a partial and a full 24x24 sheet left. Coupled with a good damping material like Ultratouch or Sonic Barrier, I feel it rivals the asphalt mass layers of other layered types. What I have is 3/8" thick, but you can get similar products in rolled 1/16" sheet to about half inch thick at Menards, Amazon, etc. Most of them have targets as weight room or exercise flooring tile.
I have loose-hung it with screws, press fit to size, or glued it with E6000. Good heavy stuff!
InDIYana Event Website
You're going to miss the Pizza Party! Bringing speakers on Saturday?
Labels would be a good idea. When I look at my cables, the connections seem so simple that I figure it would be almost impossible to screw it up. But that is what has happened so many times to designers in the open unlimited category. You set up at high speed and then Chris hands you the wireless microphone. Then you stumble through your verbal presentation in front of the judges and crowd. Really nerve-racking!
No, not competing this year.
After I put the Dayton SPA250 plate amps in my laminated boxes, one of the plate amps stopped working. It was almost completely dead with no bass output at all. When I cranked up the volume, I could hear a faint crackling noise coming from the woofer cones, but no bass. The woofers also started to randomly motorboat up and down from about 100 to 500Hz at very low output levels.
So I popped the cover. Power supply voltage rails all checked good. Driver and power output transistors all checked good. No signs of burnt resistors, bulging caps, etc. After about 2 hours of debugging, I isolated the problem to somewhere on the preamp/crossover PCB board (see back side pic of this PCB below).
Then I remembered something. When I mounted the amps in the boxes, it was a very tight fit. To get the amps to fit in the boxes, I had to remove the small, rubber side plugs that were used to cover up access holes for the 35Hz bass boost switches.
But when I removed the rubber plug on one of the amps, I also stuck a screw driver in the access hole and fiddled with the 35Hz bass boost switch, just to try it out and see how the switch worked. This on/off switch is very small and is located in the middle of the preamp/crossover PCB board (see pic below).
And a close up pic of the tiny on/off switch:
But when I fiddled around with this, I inadventently created the problem, because the switch got stuck half way between the on and off position. At the time, I did not realize this. I thought the switch was in the off position. When I powered it up, the "half way" switch position created an "open circuit trace" type situation on the preamp/xover PCB. This disconnected the audio signal path and caused the amp to go into a mild form of oscillation. Fully seating the switch in either the "on" or "off" position completely solved the problem. Lots of bass. No more crackling or motorboating.
Moral of the story: If you fiddle with the 35Hz bass boost switch on an SPA250 plate amp, always make sure the switch is fully seated in the on or off position! For a while there, I thought this plate amp was completely cooked.
Nice save!
Glad that's all that was wrong with it!