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Old 28th August 2012, 08:05 AM   #491
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Since there will be some air loading effect, Fs might be lowered somewhat, but I would not expect a gross effect.

Nelson claims an SPL increase, but I have not seen any evidence. It is still a clever design for an OB subwoofer, though, since in this setup, the acoustic path between front and back side of the driver is optimized given a certain baffle size.

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Old 28th August 2012, 10:05 AM   #492
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Default Tight slot lowering Fs in NPs slot loaded baffle?

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Originally Posted by Octavia View Post
Maybe this was already covered but ... does having the drivers facing each other in Nelson's push push configuration lower the Fs of the drivers? If so any estimates on how much? 10Hz? Does it affect the Spl? How much? 3dB?
Having followed this thread from the start, I have ended up reading all that I could find on PPSL and Ripole as they also utilizes slots.

The Ripole discussion contains a lot of info on how a tight enough slot (1/3 to 1/4 of SD) will lower Fs because of air-loading. This is a part of the Ripoles design objectives. I can not see why this effect would not affect NPs slotloaded open baffles as well?

Another effect is the quarterwave resonance in the slot/plenum. As far as I can see, this has not been addressed much in the slotloaded open baffle discussion. An interesting comment on this mecanism comes from Rudolf who has a lot of hands on experience with slots i Ripoles:

Rudolfs comments was also a wake up call for my aspirations on trying to make a PPSL with 12" or 15" and to try to extend the response >400Hz to meet my JBL 2360/2446 combo. Having read only PPSL threads I was under the impression that it could be possible to extend the response beyond 400Hz if I made the slot as narrow as possible and if I did fill the back corners of the slot. + a few other minor tweaks. Now I have realised that it is the deepness of the plenum that sets the frequency of the resonance and that a PPSL with a 12" or 15" is best used as a <100-120Hz for high quality home playback purposes.
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Old 28th August 2012, 03:18 PM   #493
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Default Some measurements

A friend ran some measurements in order to help with beaming issues and room interaction. There are 5 graphes that may or may not be helpful to others. After some placement adjustment, we were able get a good respsonse that was well balance. In the end, the beaming was fixed and the imagine was improved.

Tests were done around normal listening levels. We did not run max SPL tests, and I didn't think to ask at the time. Like I said, we were just trying to adjust for overall balance. My friend left sound absorption panels to test around the room. He'll be back at some point. Might ask for max SPL readings then.

Vince

ps, inserted a photo of speaker for reference. It's built as described in the original article.
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Old 28th August 2012, 03:48 PM   #494
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Quote:
Originally Posted by Naturlyd View Post
Having followed this thread from the start, I have ended up reading all that I could find on PPSL and Ripole as they also utilizes slots.

The Ripole discussion contains a lot of info on how a tight enough slot (1/3 to 1/4 of SD) will lower Fs because of air-loading. This is a part of the Ripoles design objectives. I can not see why this effect would not affect NPs slotloaded open baffles as well?

Another effect is the quarterwave resonance in the slot/plenum. As far as I can see, this has not been addressed much in the slotloaded open baffle discussion. An interesting comment on this mecanism comes from Rudolf who has a lot of hands on experience with slots i Ripoles:

Rudolfs comments was also a wake up call for my aspirations on trying to make a PPSL with 12" or 15" and to try to extend the response >400Hz to meet my JBL 2360/2446 combo. Having read only PPSL threads I was under the impression that it could be possible to extend the response beyond 400Hz if I made the slot as narrow as possible and if I did fill the back corners of the slot. + a few other minor tweaks. Now I have realised that it is the deepness of the plenum that sets the frequency of the resonance and that a PPSL with a 12" or 15" is best used as a <100-120Hz for high quality home playback purposes.
I posted this link to some scale model results I measured back when the thread started. It addresses SPL gains which do not materialize.

As for the lowering of Fs, that is highly dependent on the effective air mass load in relationship to the driver moving mass. There would not be much of a change in Fs (or Qts) for a heavy cone driver. For a lighter cone there could be a decrease in Fs and an increase in Qts yielding slightly higher SPL around Fs. But the higher frequencies would basically remain unchanged except for the 1/4 wave resonance. I would recommend rolling the response off well before the 1/4 wave resonance for obvious reasons.
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Old 29th August 2012, 05:10 AM   #495
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Thanks all thats helpful. I guess the point is that drivers with lower mms will fare better in this application, which from what I have been reading is just the opposite of what a tapped horn prefers.
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Old 31st August 2012, 11:47 PM   #496
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Old 1st September 2012, 12:03 AM   #497
Octavia is offline Octavia  United States
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Just a quick thanks to Naturlyd for the comments and the comparison with Ripoles. For my purposes I wouldn't be going above 150Hz and can tweek things a bit to fine whatever turns out to be the sweet spot. More fun awaits!
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Old 1st September 2012, 06:02 PM   #498
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Old 3rd September 2012, 04:47 PM   #499
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Old 3rd September 2012, 04:54 PM   #500
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Default Lookin' Good !!!!!

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Looking nice!!!! What size speakers ? Look like 12's maybe ,How's the response?
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