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Multi-Way Conventional loudspeakers with crossovers

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Old 1st May 2017, 09:35 PM   #341
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sphykik, I've seen 'spikes' like that in my projects when the midrange taps were too small

It might be worthwhile to insure that the midranges are 100% airtight where they attach to the horn, and that the taps are sufficiently large
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Old 2nd May 2017, 09:35 PM   #342
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~65L gives a box ~630mm (2') tall

ss4.jpg
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Old 27th May 2017, 05:59 AM   #343
bwaslo is offline bwaslo  United States
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sphykik,

Did you ever get this resolved? Figurure out where the strange peak was coming from?

Bill

Quote:
Originally Posted by sphykik View Post
I did only take one speaker with me, although in retrospect it would have been wise to bring both. The measurements were done without EQ - just audio directly out of REW through a USB interface into the amp. I am at a conference through Friday, but will do some more testing this weekend. I'll try the other speaker first, and then go from there.

I'm using a decent "chunk" of rockwool material (maybe 8"x8"x3") behind each woofer, but the box is by no means full. I was waiting until final finishing to add more.

Mark - my brother has a 12ft ladder, so I might have to go over to his place and get creative. Thanks for the tips!

Will return with more measurements!
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Old 30th May 2017, 05:44 PM   #344
sphykik is offline sphykik  United States
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Ugh, unfortunately no. I'm currently helping my brother tear out plumbing under a concrete slab in the "fixer-upper" he just bought. Talk about DIY

He and his girlfriend have been staying in my living room for the past month.

Hoping to get back to it soon!
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Old 30th May 2017, 07:19 PM   #345
bwaslo is offline bwaslo  United States
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Ah, sorry.

Guess that'll teach you no to go over and ask to borrow his ladder!
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Old 9th June 2017, 02:40 PM   #346
sphykik is offline sphykik  United States
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I had some free time and got a chance to take some indoor measurements at a lower volume, from a distance of ~3ft.

I did 4 measurements - L/R with no FIR filters and no EQ engaged, and L/R with FIR filters and the Linkwitz Transform + EQ.

I've included the phase plots as well - it's my understanding that they show that the FIR filters are getting me very close to a flat phase, but it seems I need to make some adjustments?

Left - 3ft - No FIR - No EQ
Click the image to open in full size.

Left - 3ft -FIR - LT + EQ
Click the image to open in full size.

Right - 3ft - No FIR - No EQ
Click the image to open in full size.

Right - 3ft -FIR - LT + EQ
Click the image to open in full size.

Oddly enough, the giant spike at ~720hz does not appear as present in these measurements. It still exists in the Left speaker (same one I measured outdoors), but it more of a broad hump and is not nearly as severe.

My room has a 12' sloped ceiling and is quite irregularly shaped, so the differences between L/R measurements are not surprising.

There's a major spike at 100hz, and I'm wondering if that can be attributed to overstuffing.

The null at 175-180hz seems like it might be the room, though the same dip can be observed in the outdoor measurement on Page 34.

A few notes about the outdoor measurements:

The prior outdoor measurements were taken at a much higher volume, quite a bit further away from the speaker. I did my best to position the speaker on grass, and point away from any surrounding buildings into the woods, but it seems I may still have gotten reflections off of the pavement or metal storage units. There was an embankment ~20' behind the speaker as well, and this could have also caused some problems.

Next Steps

I think I need to move the Right speaker into the Left position in the room and take another measurements to see if the 720hz peak is a product of the L speaker or its position in the room.

The plumber's putty "waveguide" under the midrange driver could also be an issue.

Depending on your feedback Bill, I may also try removing some of the stuffing to see what happens to the 100hz peak.

I will have the place to my self again this Saturday and will be able to take some more measurements.

Thanks for taking a look!
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Old 9th June 2017, 07:48 PM   #347
bwaslo is offline bwaslo  United States
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Hi sphykik,

It's a little hard to read your plots' scales. Are those 2dB/division (that's what I'm guessing anyway).

Phase: keep in mind that phase is also a function of distance from the source (or delay, which is the same thing, given the speed of sound). That's why people often talk about "group delay" rather than phase, since group delay is the same shape no matter how much the signal is delayed. Your viewing or measuring software should have a way to adjust the overall delay, remove about 9msec of overall delay from the plots (or adjust for flattest overall phase curve).

The 100Hz peak is in the design not from your stuffing, its an interaction between the driver and the crossover components. Different drivers might do better, but hard to find with good sensitivity and output SPL capability. The peak is in the range where room effects will be dominant, so since you're using MiniDSP for FIR anyway, add a PEQ null there to flatten it out, along with other peaks that the room will contribute.

The null at around 200Hz is ground bounce (also called "Allison Effect"), caused by having two strong paths from the woofers to he mic (one is direct, the other is bounced off the floor or the ground). If you move the speaker up or down from the floor you'll see it move around. You can EQ it a little, but don't try to add more than about 6dB to avoid overdriving woofers or clipping amps. You might not like the sound with that EQ'd out even if you could do it practically, since we are used to hearing nulls in that frequency range and things can sound a little odd without a dip there (most studio recordings are done with the mic close to the instruments so the null is weak in the recordings).

You do seem to have a small bump at around 700Hz on both speakers, not sure what that is from. I played a little with the crossover model, couldn't get that peak by messing with any of the components. Make sure the big midrange inductor isn't close to any of the woofer inductors, and make sure the midrange drivers seal well to the walls of the horn. You could try increasing the value of the larger capacitor in the midrange crossover to bring the bump down a little, but probably it would be easier to just do it in the EQ since you have it (assuming the bump bothers you at all, that is).

Also -- make some measurements a little off-axis (maybe 20 degrees or so off). Directly on-axis overemphasizes any cabinet or horn mouth reflection effects.
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