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 Post subject: naked OB speaker
PostPosted: May 29th, 2019, 11:29 am 
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Joined: January 14th, 2015, 11:15 pm
Posts: 236
I posted recently about the curious naked speakers with the PRV 5MR450-NDY along with 18" woofers. Scroll down to the end of the following.

https://www.trans-fi.com/ob-speakers

More about the PRV here
https://www.parts-express.com/prv-audio-5mr450-ndy-5-midrange-neodymium-woofer-8-ohm--294-2705

I'm thinking of doing something like this but without the very heavy 18" woofers. 44 pounds per woofer is way too much for me these days. And I don't play music that loud and mostly I listen to classical. I would just use one PRV per channel.

Instead, I am thinking of two options. I already have a couple of the Goldwood 18" woofers that Roscoe also used. I could get a couple more.
https://www.parts-express.com/goldwood-gw-1858-18-pro-woofer--290-386

Or I could try the GRS 15" units with 4 for about $100.

https://www.parts-express.com/grs-15pf-8-15-paper-cone-foam-surround-woofer--292-415

Both Goldwood and GRS speakers have a high QTS suitable for open baffle and they are relatively lightweight. I suspect that mounting the woofers facing each other creates some sort of SLOB effect which I seem to remember is supposed to lower the fs.

Suspending the speakers should not be too difficult. Certainly, I would not be doing all the steel pipe stuff. The speakers would be visually interesting and different.

In a small room it would not require too much power to run the PRVs and the woofers could be handled by a separate more powerful amp. Crossover with a Minidsp or similar.

Any comments or ideas.

ray


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 Post subject: Re: naked OB speaker
PostPosted: May 29th, 2019, 12:02 pm 
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S.L.O.B. would require that they be wired anti-phase.


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 Post subject: Re: naked OB speaker
PostPosted: May 29th, 2019, 1:27 pm 
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Stuart Polansky wrote:
S.L.O.B. would require that they be wired anti-phase.


Not if they're mounted facing each other...

Roscoe


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 Post subject: Re: naked OB speaker
PostPosted: May 29th, 2019, 2:13 pm 
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Roscoe Primrose wrote:
Stuart Polansky wrote:
S.L.O.B. would require that they be wired anti-phase.


Not if they're mounted facing each other...

Roscoe


That wasn't my image of what was suggested. My bad!

Remedial reading comprehension for me! Ray did write that in plain English!


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 Post subject: Re: naked OB speaker
PostPosted: May 29th, 2019, 2:39 pm 
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Joined: June 22nd, 2013, 11:00 am
Posts: 517
Could you use tweeter and midrange instead of a full-range driver?


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 Post subject: Re: naked OB speaker
PostPosted: May 29th, 2019, 3:04 pm 
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mix4fix wrote:
Could you use tweeter and midrange instead of a full-range driver?


Yes, but:

1: Most midrange drivers don't go down low enough to meet the large woofers needed for this type of design. A "midbass" driver would probably be a better choice.
2: Most tweeters have sealed backs, to you won't get the dipole radiation pattern you'd get with a full-range driver unless you mount a second tweeter pointed backwards and wired out of phase. You may want to pad the second tweeter down a bit as well.

Roscoe


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 Post subject: Re: naked OB speaker
PostPosted: May 29th, 2019, 3:18 pm 
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Joined: June 22nd, 2013, 11:00 am
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Just asking. I want to use those drivers I got from Tom.


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 Post subject: Re: naked OB speaker
PostPosted: May 29th, 2019, 3:43 pm 
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Joined: January 14th, 2015, 11:15 pm
Posts: 236
I am thinking that using two woofers per side makes exceeding xmax less likely than just having one. It may also make suspending the woofers easier. I was wondering if there was a special distance needed between the woofers, but since there is no SLOB effect, then I presume it doesn't matter.

Possibly I could use pvc pipe for the frame and possibly fill it with sand. A triangular shape comes to mind. Any other ideas? I would use some sort of dowel or long bolts to separate the woofers and then suspend the set of two woofers by a piece of one of those exercise bands. The yellow would be quite fetching.

Each PRVs could be suspended by a heavy-duty rubber band.

This might be worth playing with.

ray


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 Post subject: Re: naked OB speaker
PostPosted: May 29th, 2019, 4:06 pm 
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Roscoe Primrose wrote:
mix4fix wrote:
Could you use tweeter and midrange instead of a full-range driver?

2: Most tweeters have sealed backs, to you won't get the dipole radiation pattern you'd get with a full-range driver unless you mount a second tweeter pointed backwards and wired out of phase. You may want to pad the second tweeter down a bit as well.

Roscoe


Or

Attachment:
Opposing-Tweeters.PNG
Opposing-Tweeters.PNG [ 52.43 KiB | Viewed 911 times ]


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 Post subject: Re: naked OB speaker
PostPosted: May 29th, 2019, 4:10 pm 
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Joined: June 22nd, 2013, 11:00 am
Posts: 517
That's not going to work.


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