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post #91 of 218 Old 04-08-2013, 02:48 PM
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Quote:
Originally Posted by tuxedocivic View Post

For a completed speaker I measure in full space, because if not, the lower frequencies will look tilted up if some baffle step compensation is employed. Also, the method you use seems to be a full space method... You measure shooting up from the ground, and 2m ground plane, then splice above the baffle transition frequency. Correct? That would be a 4pi measurement.

I think when I said this I confused you by what I meant because I did not say this well. I realize a ground plane measurement is half space, but by moving the mic back 2m you're reducing the SPL by 6db to get the pseudo-full space result. That's what I mean.
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I use a ladder and can get reflections out to 10msec which gets me close enough to free space beyond the baffle step.

See what I'm saying here. No baffle, no boundaries, omni radiation. Free space. That's what I do. Sometimes I don't even use a gate and the results are quite reflection free.

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Look at a set of typical polar response charts and you'll see a circular pattern at the low end of the bandwidth. That's a free space measurement. Going up in frequency at some point the pattern will shift to only 180 degrees wide. That's a half space measurement. Nothing in the measurement protocol has changed; the speaker, its placement, the mic and its placement, are all the same. The only thing that has changed is the frequency being measured.

Ya, like this example of a speaker I designed last fall.



You can see that I took polars of the baffle step region without issue using my method. And that was a short ladder.

Here's another example of how I measure free space, this one one was a taller ladder wink.gif



Do you still disagree that I'm measuring free space? Would you like to see some more of my measurements? I'm not claiming to measure anechoic down to 30hz. Yes, you would need a crane for that. I use ground plane for that. But to get me results down to 80hz where I cross over to a sub, and most others do as well, putting the speaker on a ladder works quite well IMO. I think your method is quite clever and great. But I prefer using the ladder for cross over design and confirmation, because you have to splice in an akward place. rolleyes.gif
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post #92 of 218 Old 04-08-2013, 03:01 PM
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Quote:
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Do you still disagree that I'm measuring free space?
Not as far as you took it. One octave higher and it wouldn't be.

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post #93 of 218 Old 04-08-2013, 03:17 PM
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rolleyes.gif

Right from your website: http://www.billfitzmaurice.com/TLAH.html

"Here's a 1m/1W SPL chart, measured outdoors, full-space" Seems you don't understand yourself ?
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post #94 of 218 Old 04-08-2013, 04:08 PM
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Looking forward to the black piano finish on these that we will eventually talk you into smile.gif

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post #95 of 218 Old 04-08-2013, 08:16 PM
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Yeah come on Nick Piano Black SEOS's are the best!

 

 

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post #96 of 218 Old 04-09-2013, 03:37 AM - Thread Starter
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Looking forward to the black piano finish on these that we will eventually talk you into smile.gif

^Haha thats funny! Must resist peer presssssssssssssssssshure..........!
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Yeah come on Nick Piano Black SEOS's are the best!





I fear i might let you guys down.... Im pretty sure im doing the duratex.

However, never fear, im thinning it waaaay down and hope to do it with a very smooth finish. I am going to do some testing and see how much i can thin without interfering with curing.

Im also going to experiment with spraying this thinned mixture with a cheap Harbor Freight HVLP gun and see if i could do a final light sprayed texture coat.
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post #97 of 218 Old 04-09-2013, 04:27 AM
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Question for Bill, how do you figure out what frequency the baffle step is? You posted that on a 2 foot by 2 foot baffle the baffle step will be 565hz. How did you arrive at that frequency?

Also, once the baffle step frequency is known, what do you do with it in regards to the crossover? I know very little about crossovers and am trying to learn as much as I can.
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post #98 of 218 Old 04-09-2013, 04:58 AM - Thread Starter
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OK guys at the risk of being offensive, im gonna ask that the discussion be re-focused on the SEOS build.

I appreciate the contributions thus far on the technicalities of measurement, however i see this getting appreciably OT for my build thread.

Thanks.
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post #99 of 218 Old 04-21-2013, 10:23 AM - Thread Starter
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Well plenty of progress but nothing you guys havent already seen..... Double baffle installed on 2nd cab and third has all bracing installed.

Just been chugging through the machine work and assembly of it all :S

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post #100 of 218 Old 04-21-2013, 03:45 PM
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Nick,

Lookin good!
Nice workmanship - even on the bracing

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post #101 of 218 Old 04-21-2013, 03:52 PM
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Quote:
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Nick,

Lookin good!
Nice workmanship - even on the bracing

+100 smile.gif

When I read you were using Duratex I was like eek.gif (and I like me some Duratex, but with the time and effort into the curved build I was thinking something a little different from a finish perspective)....

Then I read that you are putting these behind a false wall.
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post #102 of 218 Old 04-21-2013, 04:16 PM - Thread Starter
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Originally Posted by cuzed2 View Post

Nick,

Lookin good!
Nice workmanship - even on the bracing

+100 smile.gif

When I read you were using Duratex I was like eek.gif (and I like me some Duratex, but with the time and effort into the curved build I was thinking something a little different from a finish perspective)....

Then I read that you are putting these behind a false wall.

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Nick,

Lookin good!
Nice workmanship - even on the bracing

Thanks guys. It really was a personal challenge to myself. Ive made gobs of mistakes most were easily hidden though biggrin.gif

Additionally curved back cabinets do offer some performance benefits over rectangular cabinets which was an additional drive. One thing i havent done is look at the waterfalls of the measurements and see if i can see any obvious cabinet resonances. How is this done? Just look at waterfall?

I will say these things are very inert. Even without all the bracing i can hear the resonant freq of the curved back being higher with the imcredibly scientific knuckle rap......
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post #103 of 218 Old 04-21-2013, 05:15 PM
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i think they are going to look great with any finish choice

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post #104 of 218 Old 04-22-2013, 07:59 AM - Thread Starter
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i think they are going to look great with any finish choice

Thanks B!

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One thing i havent done is look at the waterfalls of the measurements and see if i can see any obvious cabinet resonances. How is this done? Just look at waterfall?

Anyone have any thoughts on this?^ How does one measure/interpret the resonant behavior of the enclosure?

I looked at the waterfall for the measurements I took and didn't see any ringing when interpreted in the same way I would interpret room measurements. The amplitude dropped on the waterfall like a rock all the way down to where ambient sustain began to be seen(ambient noise). If this is how to do it, the cabs are pretty non resonant.....IDK.
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post #105 of 218 Old 04-22-2013, 09:33 AM
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Hey Nick. They probably are incredibly non-resonant, but that's not how to do it. You use accelerometers physically attached to the cab. Not many DIYers do this. Not really worth it. Just build overkill like you. An impedance plot can sometimes help.

What you're seeing in your waterfall is good, although you'll have to make sure the time scale is very short compared to a room measurement. You should probably add a gate as well. And you need to be sure it was very very quite when you took the measurement. Indoors is best, but then that's a whole other problem.
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post #106 of 218 Old 04-22-2013, 10:09 AM
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Hey Tux, can you use WT3 or DATS to measure the driver in-box without crossover? If you found Qts in box (Qtc), aren't Fb and Fs constants when the resonant frequency changes (enclosure volume change)? From there an impedance plot would show the spike at the resonant frequency.

Don't wanna muck up your thread Nick, was just thinking you might be able to use DATS to find out Fb and then interpret the data.

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post #107 of 218 Old 04-22-2013, 10:15 AM
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Hey RB. Absolutely you can do that. But I think nick is wondering about panel resonance. If he did an impedance sweep he might see some blips on the sweep that could indicate a panel resonance, but I'm not to knowledgable on deciphering that and its not a very accurate way to do it. I think it just shows very obvious problems.
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post #108 of 218 Old 04-22-2013, 11:06 AM
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Hey RB. Absolutely you can do that. But I think nick is wondering about panel resonance. If he did an impedance sweep he might see some blips on the sweep that could indicate a panel resonance, but I'm not to knowledgable on deciphering that and its not a very accurate way to do it. I think it just shows very obvious problems.
If a panel resonance isn't obvious enough to show up on an impedance sweep it won't be audible. Inadequate damping will also show up on a sweep.

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post #109 of 218 Old 04-23-2013, 05:08 AM - Thread Starter
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OK thanks, after looking up how to perform the impedance sweep, IDK if its worth the time in this situation.


I def would want to take a look at an impedance sweep if this were ported to get actual tuning but, I'm pretty sure the panel resonances are under good control.

Back to making dust.......
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post #110 of 218 Old 05-06-2013, 05:53 AM - Thread Starter
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Slowly cranking on these. There is a lot of machine work that goes into these. I have emptied my shop vac twice now and its already about half full again!

Anyways the second cab is complete and the third is about 80% done.

Here's a shot of the second just before chopping off the round backs and roundovers were done.

Note: This time I got smart and integrated the brace for the front baffle into the window bracing. biggrin.gif


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post #111 of 218 Old 05-06-2013, 01:12 PM
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Nice! And +1 on the bracing comment, those braces look fantastic.

Chris

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post #112 of 218 Old 05-07-2013, 04:21 AM - Thread Starter
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Nice! And +1 on the bracing comment, those braces look fantastic.

Thanks Man.

Your username is awesome BTW, makes me wanna swill a couple every time I see it...... biggrin.gif
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post #113 of 218 Old 05-26-2013, 05:26 AM - Thread Starter
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Three soldiers needing uniforms.....



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post #114 of 218 Old 05-26-2013, 05:40 AM
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They look very cool. Not too much longer now!

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post #115 of 218 Old 05-26-2013, 07:10 AM
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Those are going to be some really pretty speakers! Although as I said, I am disappointed in the fact that you are going with Duratex, as imho that is going to kill the looks! If it were me, I would
go with something unique like a gloss white, or apply real wood veneer and stain them a deep expresso! As unique as these beauties are, I just think you should do something equally unique on the finish. I wish that I
had the skills and knowledge to make some curved cabinets like these! How did you figure out how to do this? I have all the necessary tools, but very little knowledge on how to do something like this. Congrats on this build,
I am sure you will love them!
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post #116 of 218 Old 05-26-2013, 10:14 AM
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Those are going to be some really pretty speakers! Although as I said, I am disappointed in the fact that you are going with Duratex, as imho that is going to kill the looks! If it were me, I would
go with something unique like a gloss white, or apply real wood veneer and stain them a deep expresso! As unique as these beauties are, I just think you should do something equally unique on the finish. I wish that I
had the skills and knowledge to make some curved cabinets like these! How did you figure out how to do this? I have all the necessary tools, but very little knowledge on how to do something like this. Congrats on this build,
I am sure you will love them!

Nick put this link on how to kerf in post #1 smile.gif

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post #117 of 218 Old 05-26-2013, 10:39 AM
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Keep in mind MDF doesnt kerf like that in all places...
Up here in western Canada you can't get MDF to do that, different recipe.
The material used on these is much more like our particle board.
Would imagine its not just here that there would be a difference.
My advice would be to test cut a small piece before purchasing all the material.

Beautiful job on the cabinets, those are gonna be gorgeous....smile.gif
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post #118 of 218 Old 05-26-2013, 07:48 PM - Thread Starter
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@Marty

I hear ya man. These are going behind a screen so gloss white is a no go. I rounded all corners so veneer is kinda out the question without a sharp edge to terminate it. I did have a veneer thought which i may use on surrounds but im keeping that idear to myself wink.gif

I will do back lighting to show them off and i "pop" my screen for interested folks when theyre over so they will get some showtime but not out in the room.

Thank you Mr Perry.
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post #119 of 218 Old 06-01-2013, 07:09 PM - Thread Starter
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Started puttin tuxedos on the three amigos.....



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post #120 of 218 Old 06-01-2013, 08:07 PM
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So Nick;

How do you like working w/Duratex?
Did you thin it?

I found it very forgiving, without thinning. For my final rolled coat ; I misted the speakers directly with water while simultaneously rolling it out.

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