Giving New meaning to the term "Bookshelf" Speaker (Another Natalie P Thread) - Page 4 - Home Theater Forum and Systems - HomeTheaterShack.com

Old 04-01-09, 11:46 AM Thread Starter
Senior Shackster

Kyle

Join Date: Dec 2008
Location: Gilbert, AZ
Posts: 145
Re: Giving New meaning to the term "Bookshelf" Speaker (Another Natalie P Thread)

Quote:
fbov wrote: View Post
Exactly, but moreso the baffle than the drivers, per se.

Think of a tweeter in free space. The diaphram oscillates in and out, producing a roughly hemispherical wavefront. The only thing that affects the wavefront radiating from the driven element is the edge of the tweeter face.

Now, flush mount it on a large baffle.The edge of the tweeter face is now flush with the baffle, and has no effect. It's the edge of the baffle that can affect the wavefront. An in-wall design, this edge is many wavelengths away, and looks more like a room boundary than a baffle boundary.

Finally, make the baffle smaller, say 9" wide. Now the baffle edges are fractions of an audible wavelength away, and have a marked affect on the wavefront at audible frequencies. The desire to make the transition gradual, over a range of frequencies, and thus less severe, explains the use of large radius roundover or bevel edges around a tweeter.

In your case, there's a low wall at the edge, and one would expect a peak/null in frequency response at frequencies that are 1/4, 3/4, 5/4, etc. wave distance from tweeter to edge. You get a little more linear distortion. It's not a huge effect, but its one of the things that a perfectionist might address, and the proven designs are intended to be as good as humanly possible. Some go so far as to surround the tweeters with wool felt to further modify this transistion.

In your case, it's a choice between the low wall at 9" and a sharp edge 1.5" farther out on each side. You're too far along to change the edge profile without major surgery, and with recessed shelves, it'll look a bit odd if the baffle were flush with the vertical edges, but not the horizontal edges. You have a very elegant installation as it sits, I should probably have kept my mouth shut... sorry!

Frank
Thanks for the clarification. I do appreciate you're input. I have been aware of the possibility of diffraction effects due to the square edges of white bookcase edges. I'm glad you mentioned it. Too often I see threads with finished designs where people for reasons of being polite don't raise significant design issues. Very often its because the design is finished and most posters have a general sense that the builder would like to come away feeling praised for their work and rewarded for sharing. I guess I've been an engineer long enough to get used to a "peer review" process where every piece of works goes through an honest critique by other engineers. So I say lay it on me. I'd like to learn from this experience.

In my case I think you ended up getting right to one of the trade offs most of us married folk have to make is that the wife has to be happy with it. The baffle is recessed so that I have room to place a grill over the speakers. The Grill is going to be ever so slightly recessed as well. I'm going to have to live with the trade off for now.

I would love to design a home theater room where every element starts from a performance design constraint first and then an aesthetics second. I get the sense that many of us DIYer would lean heavily that way. Not that all aesthetic decisions have a negative effect on performance. That is part of the fun of DIY is finding those positive aesthetic decisions that also have a positive affect on performance. That is the sweet spot!

In my case I agree that the recessed baffles with square edges that does have some negative performance consequences. That one I'll have to wonder about. I will probably at some point try taping up some felt to do some temporary testing to assess the diffraction affects.
keelay is offline

Old 04-01-09, 01:59 PM
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fbov

Join Date: Aug 2008
Location: Pittsford, NY
Posts: 302
Re: Giving New meaning to the term "Bookshelf" Speaker (Another Natalie P Thread)

If you're making grills, I'd suggest using quarter round stock, with the flat sides toward the lip and the baffle. That would provide a radiused inner edge for smoother diffraction.

And as an engineer, I appreciate you understand the sense of my comments. In that context, I no longer feel bad about telling you that NatPs are designed for the tweeters to be inboard - you have L and R switched...
http://www.htguide.com/forum/showpos...&postcount=462
But I suspect this is a really fine point!

Have fun,
Frank
fbov is offline
Old 04-02-09, 02:17 AM Thread Starter
Senior Shackster

Kyle

Join Date: Dec 2008
Location: Gilbert, AZ
Posts: 145
Re: Giving New meaning to the term "Bookshelf" Speaker (Another Natalie P Thread)

Quote:
fbov wrote: View Post
If you're making grills, I'd suggest using quarter round stock, with the flat sides toward the lip and the baffle. That would provide a radiused inner edge for smoother diffraction.

And as an engineer, I appreciate you understand the sense of my comments. In that context, I no longer feel bad about telling you that NatPs are designed for the tweeters to be inboard - you have L and R switched...
http://www.htguide.com/forum/showpos...&postcount=462
But I suspect this is a really fine point!

Have fun,
Frank
Thanks again for the input. All input is welcome.

I was planning to do pretty much exactly that with the grill covers. I likely will use HDF and do my own rounding on the inside edge. Square outer edge like you said.

Now that you mention it I don't know what gave me the idea that the tweeter should be on the outside. I read the entire Natalie P (HT Guide) thread and saw both setups featured in the various image postings. I guess I just assumed it could go either way.

If I decide to swap them it will take an hour or two to unscrew the bookcases, move and rewire. Probably not hard enough to keep curiosity from getting the best of me.

-------------------------

Update: It looks like the tweeter inward/outward question has been answered.

Kyle

Last edited by keelay; 04-10-09 at 07:25 PM.
keelay is offline
Old 06-18-09, 04:29 PM
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Windforce

Join Date: Feb 2009
Posts: 7
Re: Giving New meaning to the term "Bookshelf" Speaker (Another Natalie P Thread)

I really like your idea of building the speakers into the bookcase. It gives a really nice finished look. Have you considered also building a subwoofer in as well?
windforce2009 is offline
Old 06-18-09, 10:47 PM Thread Starter
Senior Shackster

Kyle

Join Date: Dec 2008
Location: Gilbert, AZ
Posts: 145
Re: Giving New meaning to the term "Bookshelf" Speaker (Another Natalie P Thread)

Quote:
windforce2009 wrote: View Post
I really like your idea of building the speakers into the bookcase. It gives a really nice finished look. Have you considered also building a subwoofer in as well?

Thanks for the compliment. I like your idea. A Subwoofer could be really cool looking as well especially if you left if exposed. One of the Dayton Reference subs would go very nicely. Unfortunately, I know my wife would never go for it. She says the room already screams bachelor pad. I have been planning to building a large (12CF) box into the ceiling with a white cloth grill cover to "blend in" to the ceiling before my wife and I got the itch to move. So we've started looking and I'm not going to put any permanent fixtures in a house until we settle into a new space. But I do really really really want to add a sub.

Kyle

Last edited by keelay; 06-19-09 at 02:42 AM.
keelay is offline
Old 09-18-15, 09:00 PM
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Chuck

Join Date: Sep 2015
Location: United States
Posts: 8
Re: Giving New meaning to the term "Bookshelf" Speaker (Another Natalie P Thread)

I know this thread is super old but I can't figure out how to PM keelay. I have been thinking about building some Nat P's into a new entertainment center and it looks like your avitar shows that maybe you have changed your Nat P's to stand alone instead of flush mount. If that is the case I am wondering if maybe the flush mount didn't sound as well to you? Thank you for any info you may have
cjbrownco is offline
Old 09-19-15, 09:37 AM
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Chuck

Join Date: Sep 2015
Location: United States
Posts: 8
Re: Giving New meaning to the term "Bookshelf" Speaker (Another Natalie P Thread)

Sorry, just realized that the speaker in your avitar is actually a TriuneAnyway, I still would like to know if you are still liking the sound of your Nat P's flush mounted if you are still on this forum. If anybody else has flush mounted Natalie P's please let me know you like the sound.
cjbrownco is offline

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