Ricci's Skram Subwoofer & Files

[jay michael]

Ok, 4 Skrams complete.  Did some measurements today using REW and a minidsp umik 1.  These are loaded with 21sw152 4ohm drivers.  I'm still pretty noob to REW so my testing may not be up standards.  If there is something else you would like to see measured, or measured in a different way please let me know, wont take me long to set it up again.  Measurements were taken in my back yard which is quite large, but there are fences surrounding my back yard.  I placed the mic 1 meter from the mouth with the measurement tip about 2 inches off the ground. I ran the tone generator with pink noise and set the output of the sub to about 90 db.  In the measurement page I tested the output gain and slightly adjusted it louder until REW told me the gain was ok.

Picture 1 shows the settings I have set in the measurement panel. 

Picture 2 shows a single freq sweep measurement all spl raw no smoothing.

 

[jay michael]

SPL and Phase

 

[jay michael]

Distortion

 

[jay michael]

5 measurements averaged

[jay michael]

test area

[Revolt Sound]

4 minutes ago, jay michael said:

SPL and Phase

 

Looks very close to my SK horn measurement. I would be very interested to see the same measurement with all 4 cabs. One with the ports in the center and one with the ports on the outsides.

[jay michael]

Played around a bit with some frequency sweeps at high volumes, the boxes sound really solid, no rattles or vibrations from the caster wheels. They sound clean and powerful, cant say I think the low end sounds any better or worse than the othorns and the measurements seem to show that they are clean much higher.  All 4 playing together are damn loud, I don't hear any real reduction in volume intensity until they drop below 27hz or so, but still have pretty solid output down to the low 20's before they really start to fall off.  I've sold off my old rcf tops but my danley sh46's are supposed to be here monday or tuesday, ill get them playing together shortly after that and give you guys some impressions with some music played through them.

[jay michael]

26 minutes ago, Revolt Sound said:

Looks very close to my SK horn measurement. I would be very interested to see the same measurement with all 4 cabs. One with the ports in the center and one with the ports on the outsides.

Sorry having trouble with picture uploads, seems I've used up my allowable data.  Here is a link to a picture showing phase with all 4 subs, still measured at 1 meter away ground plane with the mic in the middle of the 4 subs https://imgur.com/rtHJQ1n

[jay michael]

Finally a couple build pics of the finished product.

https://imgur.com/4n7h9Un

https://imgur.com/8cYT8Um

[jay michael]

I saved my session in REW,  so if there are any other shots of my measurements you would like to see just ask and ill upload them.

[radulescu_paul_mircea]

Try and limit your graph axis to 10-300 Hz and 45-115 dB. It will show us better details. 

Do you have a way of measuring the Impedance?

Maybe create a Google drive folder to share the measurement data from REW. When you save the data, you can find it in your computer and you can upload it to a shareable folder in your account

[jay michael]

11 minutes ago, radulescu_paul_mircea said:

Try and limit your graph axis to 10-300 Hz and 45-115 dB. It will show us better details. 

Do you have a way of measuring the Impedance?

Maybe create a Google drive folder to share the measurement data from REW. When you save the data, you can find it in your computer and you can upload it to a shareable folder in your account

Ill look into that Paul.  Here is the graph with the axis like you suggested. https://imgur.com/sn1F5We

How can I measure impedance? Can it be done in REW?

[SME]

Impedance can be measured using REW using a custom electrical jig, but I believe that can be a pain to get to work well.  I use a "Woofer Tester 2" to measure impedance.  There may be other methods or products, but I don't know enough about them to recommend any of them.

It's hard to say for sure without seeing impedance measurements, but the frequency response measurements suggest the tune came in a bit lower than 30 Hz.  I also expected to see more output above ~60 Hz, but maybe that has to do with the SW152 vs. DS115?  Or maybe it has to do with measuring at 1 meter instead of farther away.  I'm curious as to @Ricci 's thoughts on these things.

Anyway, those looks like amazing cabs, and tuning a tad lower than 30 Hz is probably not bad for psy-trance which can sometimes have a lot going on at 30 Hz and below.  By chance, do you have a multimeter to use to measure AC voltage?  If you can measure the voltage from the amp, then your measurements will be more meaningful in an absolute sense.  For your cabs using one 4 ohm (nominal) driver each, a good "standard" voltage to measure with is 2 V @ 2 meter or 1 V at 1 meter.

[jay michael]

15 minutes ago, SME said:

Impedance can be measured using REW using a custom electrical jig, but I believe that can be a pain to get to work well.  I use a "Woofer Tester 2" to measure impedance.  There may be other methods or products, but I don't know enough about them to recommend any of them.

It's hard to say for sure without seeing impedance measurements, but the frequency response measurements suggest the tune came in a bit lower than 30 Hz.  I also expected to see more output above ~60 Hz, but maybe that has to do with the SW152 vs. DS115?  Or maybe it has to do with measuring at 1 meter instead of farther away.  I'm curious as to @Ricci 's thoughts on these things.

Anyway, those looks like amazing cabs, and tuning a tad lower than 30 Hz is probably not bad for psy-trance which can sometimes have a lot going on at 30 Hz and below.  By chance, do you have a multimeter to use to measure AC voltage?  If you can measure the voltage from the amp, then your measurements will be more meaningful in an absolute sense.  For your cabs using one 4 ohm (nominal) driver each, a good "standard" voltage to measure with is 2 V @ 2 meter or 1 V at 1 meter.

Hey man, I’ll have to do some research on the impedance thing. I did play with the mic distance a bit, and it seemed the response was flatter the closer I was to the mouth. With the mic further away from the mount the response had more of a rising profile to it.  I stuck with 1 meter as that was what josh mentioned in his testing article, but I could easily redo it if he suggests otherwise when he gets a chance to chime in.

i do have a quality multimeter. Are you suggesting running pink or white noise through the amp and literally measuring across pos and neg at the Speakon?  

[SME]

6 hours ago, jay michael said:

Hey man, I’ll have to do some research on the impedance thing. I did play with the mic distance a bit, and it seemed the response was flatter the closer I was to the mouth. With the mic further away from the mount the response had more of a rising profile to it.  I stuck with 1 meter as that was what josh mentioned in his testing article, but I could easily redo it if he suggests otherwise when he gets a chance to chime in.

i do have a quality multimeter. Are you suggesting running pink or white noise through the amp and literally measuring across pos and neg at the Speakon?  

Does your multimeter have "True RMS" capability or something similar?  The best test signal may be a 50-60 Hz sine wave as that's likely what the meter handles best.  Play it at the same level that you use for a sine sweep measurement and measure the voltage.  You might want to do this while the amp is connected to a load, as I've heard rumors that even some solid state amps don't like running disconnected.  Most are probably fine though.

Whatever voltage you read, you can either adjust the test signal level until you get to 1.0 V (if measuring at 1 meter) or adjust the data afterwards based on the actual voltage and distance used.  Assuming the measurements are accurate, this tells us how the sub(s) respond in an absolute sense.  If you also know the max voltage your amplifier can output, then you have an optimistic estimate of max output using that amp.  The estimate is very optimistic though because the driver and/or other aspects of the system may overload or sound bad before you max out the amp.  The amp itself may not be able to maintain the max voltage if the current/power demand is too high.  Still the information is very useful to be able to understand the performance and capability.

Edit: I have cable with SpeakOn on one end and bare wires on the other.  I also have a paralleling SpeakOns Y-adapter.  This let's me measure voltage even when connected to a sub.

[jay michael]

20 minutes ago, SME said:

Does your multimeter have "True RMS" capability or something similar?  The best test signal may be a 50-60 Hz sine wave as that's likely what the meter handles best.  Play it at the same level that you use for a sine sweep measurement and measure the voltage.  You might want to do this while the amp is connected to a load, as I've heard rumors that even some solid state amps don't like running disconnected.  Most are probably fine though.

Whatever voltage you read, you can either adjust the test signal level until you get to 1.0 V (if measuring at 1 meter) or adjust the data afterwards based on the actual voltage and distance used.  Assuming the measurements are accurate, this tells us how the sub(s) respond in an absolute sense.  If you also know the max voltage your amplifier can output, then you have an optimistic estimate of max output using that amp.  The estimate is very optimistic though because the driver and/or other aspects of the system may overload or sound bad before you max out the amp.  The amp itself may not be able to maintain the max voltage if the current/power demand is too high.  Still the information is very useful to be able to understand the performance and capability.

Edit: I have cable with SpeakOn on one end and bare wires on the other.  I also have a paralleling SpeakOns Y-adapter.  This let's me measure voltage even when connected to a sub.

Ah cool thanks that’s super helpful. I’m using a powersoft k10. I’ve got some spare Speakon connectors so I’ll prob just make a test cable like you did. I’ll gave to take a look at my meter, it should have something similar, it’s a professional grade automotive multimeter. I’ll try to get another measurement soon. 

[jay michael]

I did do some more frequency sweeps today, testing some new cables I made up with my k10.  One thing that really surprised me is the directionality of these things. I didn’t use a db meter to measure but these things have a substaintial reduction in energy behind them, which I’m pretty excited about. My rcf’s were basically as loud behind and they were in front.  Going to be handy on our festival site as we have had some noise issues in the past with a neighboring property.  

[chrapladm]

Ok so I am sure someone knows by now how may sheets of 18mm do I need for a pair of Skrams?

 

I am going to start building my pair very slowly. I am going to be out of town a lot for work over the next coming weeks but would like to get started on building these. I have had my pair of SW152's for quite some time sitting on a shelf. Got a lot of other issues going on to make my,  already extremely slow, progress on builds even slower but this build will definitely get my spirits up.(Life has been rough for a few years now)  Hopefully will finish them in 2 months or less. Will also be looking at designing or build an existing design for my single 15HST. 

[jay michael]

1 hour ago, chrapladm said:

Ok so I am sure someone knows by now how may sheets of 18mm do I need for a pair of Skrams?

 

I am going to start building my pair very slowly. I am going to be out of town a lot for work over the next coming weeks but would like to get started on building these. I have had my pair of SW152's for quite some time sitting on a shelf. Got a lot of other issues going on to make my,  already extremely slow, progress on builds even slower but this build will definitely get my spirits up.(Life has been rough for a few years now)  Hopefully will finish them in 2 months or less. Will also be looking at designing or build an existing design for my single 15HST. 

I made a post earlier on page 3 with cut sheet plans. A pair will take 6 sheets of 5x5 18mm and 1 sheet of 5x5 12mm.

 

[Jedi940]

On 7/13/2019 at 4:59 PM, jay michael said:

Ok, 4 Skrams complete.  Did some measurements today using REW and a minidsp umik 1.  These are loaded with 21sw152 4ohm drivers.  I'm still pretty noob to REW so my testing may not be up standards.  If there is something else you would like to see measured, or measured in a different way please let me know, wont take me long to set it up again.  Measurements were taken in my back yard which is quite large, but there are fences surrounding my back yard.  I placed the mic 1 meter from the mouth with the measurement tip about 2 inches off the ground. I ran the tone generator with pink noise and set the output of the sub to about 90 db.  In the measurement page I tested the output gain and slightly adjusted it louder until REW told me the gain was ok.

Picture 1 shows the settings I have set in the measurement panel. 

Picture 2 shows a single freq sweep measurement all spl raw no smoothing.

 

Did you happen to do any testing with some of the vents closed?  That response looks pretty good.  I would be curious how it performs at some of the lower tunings as well. 

[jay michael]

I didn’t, And probably won’t. The tuning is low enough for my my needs, wouldn’t make sense to me to trade efficiency for a lower tune 

[Ricci]

14 hours ago, jay michael said:

I did do some more frequency sweeps today, testing some new cables I made up with my k10.  One thing that really surprised me is the directionality of these things. I didn’t use a db meter to measure but these things have a substaintial reduction in energy behind them, which I’m pretty excited about. My rcf’s were basically as loud behind and they were in front.  Going to be handy on our festival site as we have had some noise issues in the past with a neighboring property.  

Hey Jay. Thanks for posting graphs and feedback on yours.

Try to limit your graphs to 10Hz-300Hz or something like that and about a 60dB total range of SPL. Anything below about 50 or 60dB is going to be getting into noise floor anyway. You want to focus in on the data of interest on the screen.

SME mentioned measuring voltage. That's easy and useful to do. Whenever you setup to measure next time. Run a 60Hz sine wave from REW's generator through the system and measure with a DMM at the speaker terminals. If you are using speakon it's easy as pie just measure at the screws on the connector with the collar pulled back. Mark down your gain setting in REW and save it with the voltage in the measurement notes. You can calculate the voltage based on the gain as long as the gain setting is tracked.

The response shape looks good to me. Looks a little bit different above 130Hz than I expected. More rolled off above 130Hz. Do you have a low pass filter engaged? Low frequency corner seems a little lower than expected too. That could be closer proximity to the port than the horn section.

Anyway good effort. Can you tell me what frequency the notch is on the top end? 150Hz? Doesn't matter too much but it gives me some data on how the vent resonance behaves. Doesn't really matter since these are subs and look flattish to at least 130Hz or so but I was curious how it would turn out. Vents are using the back wall and have effective length much longer than the physical length. The vent resonance I was hoping would behave closer to the strict physical length than the apparent length but it doesn't seem to have worked quite as well as I'd hoped. Oh well...That's all behavior above 140Hz anyway.

I've been very busy so I haven't had too much time to check in around here lately.

 

[jay michael]

Yup, rookie mistake!  I had my prolite 7.5 amp set with the sub crossover setting engaged on the back! Sorry guys.   I have run the test over again using my k10, mic measured at 1 meter from the mouth and 2 inches off the ground with a voltage of 1 volt measured at the speaker terminals.   It still has the notch that starts at about 149hz.... but it doesn't roll off drastically after 100 hz like it did on the previous measurement. I was in a hurry and forgot to check what my amp gain settings were, ill take a look tomorrow.  Anyways, here are pictures of the measured 1 volt at the terminals and the new freq response.  

https://imgur.com/kWPYnU3

https://imgur.com/GK5D7zt

[Alexlel]

Hello !

@jay michael Your last measurements has been done with 1 cab ?

@Ricci How close is it to the simulation (21SW152-4) ?

I expect to build 2 Othorns next month but the Skram looks like a real contender, what sensitivity should I expect for 1 Skram, 21DS115-4 loaded ?
My aim is to get the highest output between 25hz and 70hz , can't make up my mind between Othorn or Skram...

[SME]

13 hours ago, Ricci said:

The response shape looks good to me. Looks a little bit different above 130Hz than I expected. More rolled off above 130Hz. Do you have a low pass filter engaged? Low frequency corner seems a little lower than expected too. That could be closer proximity to the port than the horn section.

I think proximity of measurement to the port would affect the balance between upper and lower frequencies, not the low frequency corner.  It looks like the rear wall may be effectively lengthening the port more than anticipated.  The tuning looks to be around 26 or 27 Hz maybe?  I'm curious what the simulation looks like.  How much extra length do you add to the port in the sim to account for the rear wall?