It's nice to see that you've managed to make some progress in figuring this out. Of course other parameters will shift besides fs through break in, but often some of the relationships between parameters shift together. I'd definitely break in the driver fully and then see how the measured and simmed results compare.
Reducing the port CSA, but keeping the length the same, will lower the tuning and do pretty much what you measured it doing. As to which is better depends on the loudspeaker in question and its interaction with the room, so listening would be required before any decisions can be made. You might find however that with the higher port tuning, that you can get away with less BSC than with the lower. Of course if you're using a PLLXO for BSC, there's less incentive to go this route than if the solution was entirely passive.
Reducing the port CSA, but keeping the length the same, will lower the tuning and do pretty much what you measured it doing. As to which is better depends on the loudspeaker in question and its interaction with the room, so listening would be required before any decisions can be made. You might find however that with the higher port tuning, that you can get away with less BSC than with the lower. Of course if you're using a PLLXO for BSC, there's less incentive to go this route than if the solution was entirely passive.
yeah it really bugs me when things don't turn out like I expected 
I did about 30 minutes of 30Hz this evening and then did the nearfield measurement again (with the 70Hz tuning). It flattened out the response somewhat. Still not going as far as the sim, but definitely better I might leave it running over night with some lowish level 20Hz.
Note that the upper frequencies are more likely affected by a change in the foam, as I kinda ruined the first bit when I stuffed it in the port to try sealed this measurement is with what is left of that foam sitting in the top of the box with none on the rear. It did only affect after about 1K before so I don't think it will be changing anything down low.
Tony.
I did about 30 minutes of 30Hz this evening and then did the nearfield measurement again (with the 70Hz tuning). It flattened out the response somewhat. Still not going as far as the sim, but definitely better I might leave it running over night with some lowish level 20Hz. Note that the upper frequencies are more likely affected by a change in the foam, as I kinda ruined the first bit when I stuffed it in the port to try sealed
this measurement is with what is left of that foam sitting in the top of the box with none on the rear. It did only affect after about 1K before so I don't think it will be changing anything down low. Tony.
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Yes I have to do some more testing with foam (and maybe some of my good stuff as well, but it is rather thick and may not be suitable).
After running for 12 hours there is a slight improvement in low end response compared to last night. Blue trace is this mornings measurement. Apart from below 100Hz it is matching the sim pretty well now. I might leave it running 20Hz for a bit longer.
note I also change the sweep to start at 20Hz this morning. Last nights measurement had the sweep starting at 40Hz.
Second pic shows THD of the NF woofer and port measurements. I find it interesting that the THD on the driver is very flat above the box tuning frequency, but the port shows big variations... all have 1/16 octave smoothing.
Tony.
After running for 12 hours there is a slight improvement in low end response compared to last night. Blue trace is this mornings measurement. Apart from below 100Hz it is matching the sim pretty well now. I might leave it running 20Hz for a bit longer.
note I also change the sweep to start at 20Hz this morning. Last nights measurement had the sweep starting at 40Hz.
Second pic shows THD of the NF woofer and port measurements. I find it interesting that the THD on the driver is very flat above the box tuning frequency, but the port shows big variations... all have 1/16 octave smoothing.
Tony.
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Although I haven't really progressed on this, I thought I would upload a measurement I did of the (still clamped together) box, on Easter Monday.
The measurement was taken outside off my Verandah pointing into the yard, giving quite a bit more usable distance before reflections.
Attached is a 1/8th octave smoothed response curve. All in all it looks pretty good to me. I decided on 1/8th smoothing because gated I can only get down to about 200Hz. It is interesting comparing it to the measurements above.
I think that with a broad notch (assuming I can develop one) between 5 and 10K it should smooth out quite nicely.
All I have to do now is get off my backside, glue in the braces, and glue on the back panel. Oh and make the second one It's looking like this is going to hit the one year mark soon if I don't get moving.....
One thing that looks like it has worked as planned is the baffle geometry, The baffle step sim had a lump where there was a natural dip in the drivers (factory) response between 1 and 2Khz. I was hoping that the Baffle step might fill it in, which it appears to have done nicely.
Tony.
The measurement was taken outside off my Verandah pointing into the yard, giving quite a bit more usable distance before reflections.
Attached is a 1/8th octave smoothed response curve. All in all it looks pretty good to me. I decided on 1/8th smoothing because gated I can only get down to about 200Hz. It is interesting comparing it to the measurements above.
I think that with a broad notch (assuming I can develop one) between 5 and 10K it should smooth out quite nicely.
All I have to do now is get off my backside, glue in the braces, and glue on the back panel. Oh and make the second one
It's looking like this is going to hit the one year mark soon if I don't get moving.....One thing that looks like it has worked as planned is the baffle geometry, The baffle step sim had a lump where there was a natural dip in the drivers (factory) response between 1 and 2Khz. I was hoping that the Baffle step might fill it in, which it appears to have done nicely.
Tony.
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Hi Bret, I've been horridly slack, I see the box sitting on my desk every time I come into the room, and think I really should glue in those braces and glue on the back. I still need to cut the mdf for the second box as well.
It's coming up on a year now so I really should get off my behind and finish these off! In reality there is probably another 1 or two days work to do the cabinets. I also now have a USB sound card so can do measurements much more easily than before. Fitting it in with other stuff that needs doing is the challenge. Weekends tend to be busy, and power tools in the evening after work aren't really an option (not that they are needed to finish one box).
Watch this space, thanks for the prod
Tony.
It's coming up on a year now
so I really should get off my behind and finish these off! In reality there is probably another 1 or two days work to do the cabinets. I also now have a USB sound card so can do measurements much more easily than before. Fitting it in with other stuff that needs doing is the challenge. Weekends tend to be busy, and power tools in the evening after work aren't really an option (not that they are needed to finish one box). Watch this space, thanks for the prod
Tony.
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it's all good
I think I'll be ordering up some 12 or 15mm ply online to get this done quickly and simply (it's a pain to deal with the local ply suppliers now and get stuff cut)... but I don't see any XO here? No XO, it "just works"?
My 11-year-old is helping to paint her 2" peerless 830970 boxes, they're 0.6l or so... they're yellow and will get black stripes....she's supposed to be soldering her AmpCamp Amp to power them, too. Should be done before Christmas
- Bret
I think I'll be ordering up some 12 or 15mm ply online to get this done quickly and simply (it's a pain to deal with the local ply suppliers now and get stuff cut)... but I don't see any XO here? No XO, it "just works"?
My 11-year-old is helping to paint her 2" peerless 830970 boxes, they're 0.6l or so... they're yellow and will get black stripes....she's supposed to be soldering her AmpCamp Amp to power them, too. Should be done before Christmas
- Bret
The plan is to have some passive line level baffle step compensation, and probably a notch filter for the bump in repsonse up high. It peters out after 10K and really should probably have a tweeter, but for this project the object was to run it full range.
Crossed to a tweeter around 4K would probably be good.
Crossed to a tweeter around 4K would probably be good.
Just a small update. I've glued in the bracing and glued on the rear baffle. Sanded the box and it has been primed. I have a very excited 5 1/2 yo who chose pink, yellow and blue spray paint. It will be interesting to see how the box turns out
There won't be any measurements of the completed box till the painting has been completed, the priming is pretty rough, and I now see why people have so much trouble painting MDF, but since it is a 5 1/2 YO that will be doing the final spray job, I'm not to concerned with getting perfection
I suspect it probably won't be till next weekend that I could do any more measurements, as this coming weekend is looking pretty busy.
I had a bit of a play in speaker workshop with the outside measurement (that I posted above) and didn't make much progress with respect to getting a broad notch. I don't think I'll waste too much time until I have a proper measurement with no clamps attached to the baffle
Tony.
There won't be any measurements of the completed box till the painting has been completed, the priming is pretty rough, and I now see why people have so much trouble painting MDF, but since it is a 5 1/2 YO that will be doing the final spray job, I'm not to concerned with getting perfection
I suspect it probably won't be till next weekend that I could do any more measurements, as this coming weekend is looking pretty busy.
I had a bit of a play in speaker workshop with the outside measurement (that I posted above) and didn't make much progress with respect to getting a broad notch. I don't think I'll waste too much time until I have a proper measurement with no clamps attached to the baffle
Tony.
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For completeness some progress photos
Note the extremely wonky installation of braces. I'm sure being slightly staggered improves things I was quite surprised at how effective they are actually.
Also note the extremely dodgy sanding of the primer. Superb finish these will not have
Tony.
Note the extremely wonky installation of braces. I'm sure being slightly staggered improves things
I was quite surprised at how effective they are actually. Also note the extremely dodgy sanding of the primer. Superb finish these will not have
Tony.
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just another photo update I came home early yesterday and my 5 1/2 YO and I set up the speaker in the back yard and she sprayed it to her satisfaction
There is a large run on one side where she got a bit over zealous with the yellow, but it adds texture
Overall I think it looks pretty funky.
Tony.
I came home early yesterday and my 5 1/2 YO and I set up the speaker in the back yard and she sprayed it to her satisfaction There is a large run on one side where she got a bit over zealous with the yellow, but it adds texture
Overall I think it looks pretty funky.
Tony.
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interesting paint job there
I'd be very, very interested to hear someone's comments on using a simple XO for either an SB tweet or - for example - the Vifa XT25. I'm currently thinking about something small and effective for "monitoring" use on my desk at work - I have space for a sub, but the SB12s seem like a great way to keep box size down and still have decent sound. I've seen the XO in the SBTL from one of the German DIY magazines, and figure that might also work, but that's already crossing at 1.8kHz.
- Bret
I'd be very, very interested to hear someone's comments on using a simple XO for either an SB tweet or - for example - the Vifa XT25. I'm currently thinking about something small and effective for "monitoring" use on my desk at work - I have space for a sub, but the SB12s seem like a great way to keep box size down and still have decent sound. I've seen the XO in the SBTL from one of the German DIY magazines, and figure that might also work, but that's already crossing at 1.8kHz.
- Bret
OK here is a measurement taken outdoors with REW showing SPL and distortion. Measurememt taken at 2.83V however not properly calibrated to give accurate spl level. It should be around 88db I think.
It wasn't ideal for measurements today as it is a bit windy, but not too bad just the same. edit: just added some pics of the test setup. The speaker is on a table on the verhandah, I think that the minor reflections in the impulse are probably from the roof above, I'll have to try some experiments out in the yard as well, but it is rather narrow with another house's wall down one side so I tried to position at an angle to any major reflective surfaces.
Tony.
It wasn't ideal for measurements today as it is a bit windy, but not too bad just the same. edit: just added some pics of the test setup. The speaker is on a table on the verhandah, I think that the minor reflections in the impulse are probably from the roof above, I'll have to try some experiments out in the yard as well, but it is rather narrow with another house's wall down one side so I tried to position at an angle to any major reflective surfaces.
Tony.
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Well things move rather slowly around the wintermute household when it comes to projects
Today however there were no pressing issues to be dealt with and no other plans so I spent some time with the jigsaw and router this afternoon, and managed to cut to size the top, bottom and front and rear baffles for the second unit.
Man I wish I had a router table. I could probably have had the entire job done and the box glued together in the same time if I did!
I'm terrible at cutting straight so have to cut everything with a 3mm margin and then use the router (with an old MTM prototype's cabinet as a fence) to get the final clean cut side.
This means basically tripple the measurements, and a lot of stuffing around clamping the workpiece in place for each cut. But I don't have room for a router table so have to work with what I can
Hopefully it won't be another six months till the next status update
Tony.
Today however there were no pressing issues to be dealt with and no other plans so I spent some time with the jigsaw and router this afternoon, and managed to cut to size the top, bottom and front and rear baffles for the second unit.
Man I wish I had a router table. I could probably have had the entire job done and the box glued together in the same time if I did!
I'm terrible at cutting straight so have to cut everything with a 3mm margin and then use the router (with an old MTM prototype's cabinet as a fence) to get the final clean cut side.
This means basically tripple the measurements, and a lot of stuffing around clamping the workpiece in place for each cut. But I don't have room for a router table so have to work with what I can
Hopefully it won't be another six months till the next status update
Tony.
Hi Tuxedocivic, yes I do intend to do line level BSC. Something simple using the ESP passive line level cap and pot (and perhaps a buffer).
Thanks for the offer Henry! I think that eventually these will end up with a tweeter (though perhaps not in the current box, I may not have left enough room )
The top end is a little harsh (no doubt breakup), I tried a couple of sims with the measurement above to put a wide notch around the 7 - 10K mark but wasn't really successful, perhaps just concentrating on the 10K peak might work better. I can have another look at it. I think it should be possible to tame the top end a bit, but the reality is that this isn't really a full range speaker, it was just me trying an experiment, which has I think generally been a success.
As far as computer speakers go though they will I think hold there own But a tweeter would make them very sweet indeed.
I think that the tonal balance is very good, because I put the finished one on top of one of my MTM's disconnected the MTM and ran with the SB instead and the sound was still very natural, and I didn't get any feeling of imbalance. More surprising was that the imaging wasn't impacted. This surprised me quite a bit. I suspect that as a pair they should image very nicely.
Tony.
Thanks for the offer Henry! I think that eventually these will end up with a tweeter (though perhaps not in the current box, I may not have left enough room
) The top end is a little harsh (no doubt breakup), I tried a couple of sims with the measurement above to put a wide notch around the 7 - 10K mark but wasn't really successful, perhaps just concentrating on the 10K peak might work better. I can have another look at it. I think it should be possible to tame the top end a bit, but the reality is that this isn't really a full range speaker, it was just me trying an experiment, which has I think generally been a success.
As far as computer speakers go though they will I think hold there own
But a tweeter would make them very sweet indeed. I think that the tonal balance is very good, because I put the finished one on top of one of my MTM's disconnected the MTM and ran with the SB instead and the sound was still very natural, and I didn't get any feeling of imbalance. More surprising was that the imaging wasn't impacted. This surprised me quite a bit. I suspect that as a pair they should image very nicely.
Tony.
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