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Old 12th March 2014, 04:12 PM   #1
Podders is offline Podders  United Kingdom
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Default first speaker build, a little bit of help please

Hope I'm not going over old ground here- I've searched the forum but can't find the info I'm looking for. Finally got round to my first speaker build and have gone for the (supposedly) full range Monacor SPH- 30/8. Very briefly where I'm struggling to find and answer is on the port and it's dimensions and location, and how critical these might be. I'm thinking of setting the driver in the middle- halfway between top and bottom.The internal volume is currently 4.7 litres and as the pic hopefully shows is based on a flat fronted cylindrical enclosure.(diameter 162mm, height 215mm). I might add a tweeter later. Thanks.
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Old 12th March 2014, 05:20 PM   #2
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We don't get many Monacors on this side of the pond so have no experience. I can say that placing the driver in the middle of the baffle is not a good idea.

In a box that size vent placement is likely uncritical.

dave
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Old 12th March 2014, 06:39 PM   #3
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I think the port needs to be calculated by the cabinet and driver parameters combined, what kind of drivers are you using?
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Old 12th March 2014, 07:44 PM   #4
Podders is offline Podders  United Kingdom
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Thanks Dave. I'll re-adjust the drivers away from the middle.
The drivers are 3 inch Monacor.
Would you advise using some sort of damping material?
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Old 12th March 2014, 09:24 PM   #5
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Quote:
Originally Posted by Podders View Post
Would you advise using some sort of damping material?
Yes. In a BR walls are lined.

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Old 12th March 2014, 09:27 PM   #6
chrisb is offline chrisb  Canada
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I generally like to line all exposed interior panels with at least a light layer of "felt" of some description . The 1/2" bonded Ultratouch recycle denim gives great results in small enclosures, often requiring no additional fill, but it's not widely available.

Except if to be mounted on a bookshelf or otherwise close to a rear wall, location of port / vent is probably not important, but as said above, it wouldn't hurt to adjust placement of driver off dead center of the panel. We could argue for days about the "optimal" offset, but you could probably pick any value you like - as long they're identical on all enclosures in the set. I happen to like the .618 / 1 / 1.618 ratios when driver location isn't critical, as is the case in some designs.
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Old 13th March 2014, 07:46 AM   #7
Podders is offline Podders  United Kingdom
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Thank you all for your advice. From my basic research, using the formula Fs/Qes (105/0.49) giving EBP of 214, it would indicate a port is needed. But as Dave suggests above given the enclosure size vis a vis the small driver size then maybe I don't need to port. Thanks again.
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Old 13th March 2014, 07:59 AM   #8
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Model the driver. It will give a good estimation of the bass response sealed ornot.

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Old 13th March 2014, 10:52 AM   #9
sreten is offline sreten  United Kingdom
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Hi,

Qts = ~ 0.4, Fs = ~ 100Hz, Vas = ~ 1L.

In those cabinets it will need venting but don't expect
miracles with +/- 2mm of excursion with the high Fs
and low Vas. in fact its hard to tune in 5L without
getting serous one note bass, or no bass at all if
you go sealed. 50Hz tuning is the best of a bad job.

If you want bass out of those cabinets you need a
different driver, with a much lower Fs and Vas ~10L.

rgds, sreten.
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Old 13th March 2014, 12:35 PM   #10
Podders is offline Podders  United Kingdom
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Thanks again Dave, I'm a complete novice so I don't know what to model the driver entails.
Thanks also to Sreten. Again novice that I am I don't expect miracles with this. For the port I was thinking of adapting some small-ish diameter plastic pipe (25mm?) and inserting at the back. Looking at other speakers the port appears to be quite long relative to the depth (front to back) of the enclosure. Cheers.
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