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Old 31st January 2013, 12:41 PM   #61
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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.
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Old 1st February 2013, 11:18 AM   #62
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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.



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Old 1st February 2013, 11:36 AM   #63
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That foam certainly smooths something or other around 1kHz that's for sure.
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Old 2nd February 2013, 12:17 AM   #64
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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.

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Old 8th May 2013, 12:41 PM   #65
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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.

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Old 18th July 2013, 07:08 AM   #66
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hi,

I have a pair of these drivers in the garage and was thinking about what to do with them - whether I end up chopping up part of the car's dashboard or maybe something cute 'n' fluffy and functional for the office.

How's it looking?

- Bret
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Old 18th July 2013, 09:21 AM   #67
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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.
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Last edited by wintermute; 18th July 2013 at 09:23 AM. Reason: typos.
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Old 18th July 2013, 06:42 PM   #68
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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
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Old 18th July 2013, 10:38 PM   #69
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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.
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Old 7th August 2013, 11:35 AM   #70
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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.
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