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djverne
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Piccalo build

Mon May 04, 2015 4:18 pm

I’m working on building the Piccolo kit which I purchased off of Meniscus audio. I have the boxes glued together and I’m getting ready to cut the holes for the tweeters, woofers, and ports after I am done veneering. My question is how important to the build and overall sound quality is the offset tweeter. Is it possible to center it or will it change the sound noticeably? I am not sure If when setting up the speakers is the tweeter offset to the inside or outside too ……..(new to this hobby).

Initally this was suppose to be a private message for Jeff B, but since I am a new member that feature is disabled for me. Any feedback from Jeff or board members would be greatly appreciated.

-Daniel
 
Jeff S.
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Re: Piccalo build

Fri May 08, 2015 2:45 am

I would build them the way they were designed. Here's a link that has a discussion about offset tweeters. Also you might want to post this on PE's tech talk.
http://techtalk.parts-express.com/showthread.php?246753-Offset-tweeters-inside-or-outside&highlight=offset+tweeter
 
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mattsk8
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Re: Piccalo build

Fri May 08, 2015 10:03 am

I'm pretty sure I posted in that linked thread, and you could call Meniscus and ask them as well. If I'm understanding this correctly, the reason for offsetting a tweeter has to do with baffle step compensation or BSC. Where I'm a tad foggy on the subject is the difference between BSC, and baffle diffraction. BSC is mainly only an issue with the high frequencies (the tweeter). Here's a thread that goes into a bit more discussion on the subject of BSC and exactly what that is (though it doesn't discuss tweeter offset)... http://www.rjbaudio.com/Audiofiles/flus ... nting.html

So the theory is, if you offset the tweeter, this helps alleviate some of the issue with diffraction. But, I've honestly never heard the difference. Not saying you should do this, but I would actually bet that if you built one with the tweeter offset, and another with it centered, you couldn't tell me which was playing if you were blindfolded. My ER18s have offset tweeters, and I can't hear one iota of difference if that tweeter is on the inside, or if I swap sides and the tweeter is on the outside. I'm pretty sure (not positive though) that we played with this when the Blues MTM was designed, and they measured almost identically with the tweeter centered verses offset.

As mentioned in that link above, flush mounting the tweeter does make a substantially measurable difference with regards to BSC though.

Food for thought, YMMV ;)
 
Jeff B.
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Re: Piccalo build

Fri May 08, 2015 10:22 am

Daniel,

This is strange - I replied to your PM on the Parts Express forum regarding this question, and then I replied to this thread with an answer as well (or at least I thought I did). However, now I do not see my answer, so I will give it a third try.

The tweeter is offset in the Piccolo to smooth the on-axis response due to edge diffraction by making the distance from the tweeter to to the edge as random as possible. If you center the tweeter there will be a measurable change in the response at some frequencies, but I do not believe it will be audible in any way. Most of my designs since the time of the Piccolo have simply kept the tweeter centered. If you want to center your tweeter it will be fine.

Jeff B.
Jeff's Excel Loudspeaker Design Software
http://audio.claub.net/software/jbabgy/jbagby.html
 
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mattsk8
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Re: Piccalo build

Fri May 08, 2015 10:57 am

Thanks Jeff 8-) . Not my thread, but I did benefit from your answer :D .

To the OP, if you'd like to go a bit deeper, I found a good explanation of the difference between BSC and diffraction. http://www.salksound.com/wp/?p=160
 
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Wolf
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Re: Piccalo build

Fri May 08, 2015 11:43 am

Matt- Offset tweeters are to randomize the distances of the edges to the tweeter and reduce the diffraction ripple in the response. BSC is a compensation of the baffle-step loss below the point where the wavelength equals the width of the baffle of the speaker. Baffle step loss is mainly a low frequency issue loss due to the cancellation of waves wrapping the perimeter of the cabinet. There is a peak before rolloff as well that sometimes has to be dealt with.

Later,
Wolf
 
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mattsk8
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Re: Piccalo build

Fri May 08, 2015 12:13 pm

Wolf wrote:
Matt- Offset tweeters are to randomize the distances of the edges to the tweeter and reduce the diffraction ripple in the response. BSC is a compensation of the baffle-step loss below the point where the wavelength equals the width of the baffle of the speaker. Baffle step loss is mainly a low frequency issue loss due to the cancellation of waves wrapping the perimeter of the cabinet. There is a peak before rolloff as well that sometimes has to be dealt with.

Later,
Wolf


Thanks Ben. I definitely need to read more on BSC and just exactly what that is and how it's corrected. After I posted my original response, I started reading. Signals below 750 Hz will move around the cabinet's baffle, while signals above that will play forward (the higher you go in the FR, the more forward they play I'm guessing?). So if you have no BSC to compensate in the loss of frequency from the waves moving around the baffle, you'll have a bright or thin sounding speaker. Correct?

Most of this^^ was taken from here... http://www.salksound.com/wp/?p=42
I actually read Salk's explanation a while ago, and I've had Jeff's blog printed about this for a long time now. It's funny how the further you go in speaker design, the more this stuff starts to make sense :)

I do understand diffraction as it relates to flush vs top mounting a tweeter or centered vs offset, I've actually played with it and can't hear the difference between offset vs centered tweeters in a standard baffle. I had BSC and diffraction confused with each other :oops: .
 
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Wolf
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Re: Piccalo build

Sat May 09, 2015 2:08 pm

Signals below 750 Hz will move around the cabinet's baffle, while signals above that will play forward (the higher you go in the FR, the more forward they play I'm guessing?). So if you have no BSC to compensate in the loss of frequency from the waves moving around the baffle, you'll have a bright or thin sounding speaker. Correct?


It has to do with the 2pi to 4pi radiation transitioning of frequencies as they decrease. You know- bass is Omni, and upper treble is directional. The width of the baffle sets the frequency, and the wider, the lower it starts the peak and loss combo. The point can very from ~600 to ~2k.

Infinite baffle or in-wall speakers do not have the width since the wall is a room boundary, and the wall is the width, and there is no distance from the front baffle to the front wall; and therefore, the effect is not there.

Omni speakers also do not need BSC, and this is because the radiation is equal in all directions horizontally.

Later,
Wolf
 
djverne
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Re: Piccalo build

Thu May 14, 2015 5:18 am

Stepped away from the net for a few days and I am surprised to see some activity on this thread. Jeff thanks for taking the time to reply 3 times. I had sent you a personal message on the parts express forum but I got locked out and have not been able to changed my password to read it : ( anyways...

Being able to center the tweeter is a big plus for me. It coincides better with my veneer plan.

Originally my plan with the Piccalo build was to have a few variations:
1. Center the tweeter if possible, +1
2. Install magnets into the front baffle for grills (have to have them with a two year old), done
3. Keep the front baffle edge 90 deg to make it easier to veneer and than line up grills, -1

So I gather that it is correct to assume that rounding off the corners is the most important step in minimizing the diffraction ripple. If not rounded off can the speaker grills be designed in such a way (using felt) that they will negate not having the rounded corners on the front baffle? I only ask because I have not tried to Veneer onto something that is round. I'm sure I could do it with a little practice, but I am pretty new to this.
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djverne
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Re: Piccalo build

Tue Jun 02, 2015 1:48 am

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