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Old 21st November 2012, 03:35 AM   #1
michiu is offline michiu  Canada
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Default Overnight Sensations Slot Port

Hi all,

I'm in the midst of planning my first forray into speaker DIY (I've done some other audio DIY before). I want to keep it relatively cheap so I thought I'd try starting with a Overnight Sensation. However, these speakers will mainly be used at my desk, which mean they need to have acceptable near-field bass response, something my current Paradigm Atoms are lacking (i'm not near a wall and my room is not small). Therefore, I want to make the speakers front ported; however, I don't like the aesthetics of a round port in the front, so I want to alter the design a bit to allow for a slot vent.

My current train of thought is that I'll need to make sure the size of the slot has the same area as the round port while adjusting the length of the port to keep the tuning frequency the same. I'll also need to check the air velocity at the mouth to make sure its below the audible threshold.

I'm not sure whether the volume of the cabinet includes the volume of the vent, however. Also, if I change the dimensions of the cabinet too much, will I need to adjust the BSC?

Can anyone offer me advice/feedback on my plans?
Thanks
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Old 23rd November 2012, 03:58 PM   #2
michiu is offline michiu  Canada
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Anyone have any tips? I'm sourcing my parts soon but if I need to change the crossovers...
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Old 23rd November 2012, 04:34 PM   #3
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If the port is the same cross sectional area, then the length should stay the same. I wouldn't worry about vent velocity in the near field.

Is your computer your source? Can I suggest a different route. Use a 3" or 4" full range driver, like a Mark Audio Alpair7. No cross over. Choose one of the smaller Planet 10 boxes. Use the eq on your computer to compensate for baffle step (if you even need to) and bass boosting (if you even need to). I use the CSS EL70 in a 7L sealed box and do this. And it's embarrasing to admit it, but other than the "large" sound of my home setup, my desk setup is about the best I've heard.

I only suggest this because there are some limitations to using a high cross over wide spacing 2-way like the Overnight Sensations on a desk.
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Old 23rd November 2012, 06:25 PM   #4
michiu is offline michiu  Canada
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Quote:
Originally Posted by tuxedocivic View Post
If the port is the same cross sectional area, then the length should stay the same. I wouldn't worry about vent velocity in the near field.

Is your computer your source? Can I suggest a different route. Use a 3" or 4" full range driver, like a Mark Audio Alpair7. No cross over. Choose one of the smaller Planet 10 boxes. Use the eq on your computer to compensate for baffle step (if you even need to) and bass boosting (if you even need to). I use the CSS EL70 in a 7L sealed box and do this. And it's embarrasing to admit it, but other than the "large" sound of my home setup, my desk setup is about the best I've heard.

I only suggest this because there are some limitations to using a high cross over wide spacing 2-way like the Overnight Sensations on a desk.
Ah I see. But would I include the volume of the vent in the "box volume"?

Your suggestion sounds very nice and simple. I might just do it! Aside from the Alpair7, are there any other full range drivers that you suggest?
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Old 23rd November 2012, 06:59 PM   #5
chrisb is offline chrisb  Canada
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Originally Posted by michiu View Post
Ah I see. But would I include the volume of the vent in the "box volume"?

Your suggestion sounds very nice and simple. I might just do it! Aside from the Alpair7, are there any other full range drivers that you suggest?

Might I step in? The A7 is quite wonderful, and works very well in 10-11 liters & up vented boxes. I've built, but not yet heard them in a smaller (5-6 liter) "milli" sized box. Depending on the quality of music files / streamed source and electronics, they could be more analytical than you'd like.

Then there's the EL70 of which Ryan speaks - it's hard to make this driver sound bad - it's very well suited to the rather unforgiving application of very near-field computer monitor.

If physical size of enclosure is an issue, the smaller frame size Alpair 6 (both metal and paper cones) are also worth considering - Mark engineered these particularly for nearfield application.

Don't overlook Fostex FFxxxWK series, my current computer monitors are FF85WK in solid walnut uFonken enclosures, driven by Topping TP30 - a little amp that sounds much better than its price would suggest, and the DAC is certainly superior to that built into my 4 year old iMac.


There are enclosures designed for all of the the above drivers that are suited for desk-toip use - the ones that I've built/heard (except the small sealed for EL70) incorporate high aspect ratio front exit slot ports
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Last edited by chrisb; 23rd November 2012 at 07:03 PM.
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Old 23rd November 2012, 07:13 PM   #6
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Quote:
Originally Posted by chrisb View Post
The A7 is quite wonderful, and works very well in 10-11 liters & up vented boxes.
Might i suggest 9 litre & less...

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Old 23rd November 2012, 07:17 PM   #7
chrisb is offline chrisb  Canada
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Might i suggest 9 litre & less...

dave

something between the "m" and "d", then? - there are way too many plan drawings to remember them all, and I think none recently have noted the nominal volumes, so I'm just WAG-ing anyway
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Old 23rd November 2012, 07:42 PM   #8
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d=deci is based on 9 litre and the largest Mar-Ken for A7.3

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Old 23rd November 2012, 07:46 PM   #9
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Originally Posted by michiu View Post
Ah I see. But would I include the volume of the vent in the "box volume"?
You need to subtract the volume of the vent, which Paul has likely already done with the specs for the OS. But if you do a slot port, there will be more volume consumed by the material. So account for that.

Quote:
Originally Posted by michiu View Post

Your suggestion sounds very nice and simple. I might just do it! Aside from the Alpair7, are there any other full range drivers that you suggest?
Yes, the EL70 if you can get it. Anything small and Mark Audio, except the CHR70. I've heard these in a desktop system: Creative Sound - Product Details They're ok, and a good price. I personally don't care for the Fostex stuff that much, but others love it, so give it consideration as well.

I know Full Range doesn't have that same appeal as a woofer and tweeter. I've been there. Learned the right way a little while ago. I use multi ways often at home, but a full range has very few draw backs on a desk. With all due respect to Paul, the OS has many draw backs. It's "full" baffle step compensation, high tune, wide driver spacing, high cross over, and driver layout are all a "big deal" in the nearfield, imo. And I'll add that I've listened to and measured this speaker.

If you must have a 2-way on a desk, you'll need to spend more than the OS. You'll need an expensive and small tweeter like the $40 Vifa NE25, $100 CSS LD25x, or $70 SB Acoustic SB29RDCN to get the drivers close and cross over around 1500hz or lower. Only 1 design I know of exists that I would recommend, and the cross over is very complex and expensive. Not worth it.

Last edited by tuxedocivic; 23rd November 2012 at 07:52 PM.
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Old 23rd November 2012, 10:35 PM   #10
michiu is offline michiu  Canada
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The offerings from Fostex and the Alpair6 seem agreeable. The EL70 and Alpair7 would be pushing how much I'd like to pay for a first project though.

After going through a few designs for the above drivers, the mMar-Ken6 seems work fairly well for my needs. I'm also considering a dFonken Slim GR with the FF125WK.

At least, with size in consideration. I don't know much about the specific sonic qualities of these drivers/enclosures. I'll be powering these with an old NAD3020, so I don't think my source will be an issue.
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