first speaker build, a little bit of help please

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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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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.
 
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.
 
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.
 
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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Thanx for the numbers sreten. Based on my criteria, a 1 litre box tuned to 110 Hz (with a high ratio slot vent) a but lower with a more typical piece of plumbing pipe. F3 near 100, F10 about 80.

5 litres is WAY too big a box for this driver. Best to leave it sealed and add solid fill to reduce volume to about 2 litre net which will raise the Q to about 0.5 (as low as one woild want), F3 of 200 Hz, F10 of 85 Hz.

Or start with a different box. The vented 1 litre net volume box would be more satisfying IMHO.

dave
 
Many thanks for your advice, although I'm afraid some of it's over my head. Back to the drawing board I think, a pity having got as far as I have with the enclosures and baffles (solid American Walnut). I may just adapt and add solid fill as suggested. Thanks again.
 
It's been around my head for some time to use that driver, but to make a two way with a paper tweeter in a waveguide ( 16 cm diam), and using 1st order filter for both, confiding in the good behaviour at the ends of audio spectrum
of the FR, and...a bad efficiency of the tweeter!!!
Maybe the 4Ω version suits better for the purpose ( max 20 W-30 W peak )as it allows small amplifiers to....well, no, forget it :p:eek:

It should work well in a paper/ rolled tube snail TL tapered of about 90cm-1m, no absorber at all ( just at the start of the line )
 
The finished speakers. Sound ok and for my first effort I'm fairly happy. I suspect rear mounting the drivers, even with the rounded flared cut out isn't the best. Would like to add a tweeter and tweek to see if the overall sound can be improved.
 

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It may not be all due to your speaker design and construction. Upgrade to this amp and you will vastly improve the sound quality compared to the Lepai. Just add 19v laptop brick. Look in class D forum for Tpa3116d2 amp. Here is link to latest "best" offering.
http://www.yuan-jing.com/tpa3116-class-d-2-0-stereo-amplifier-board-50w-50w

What driver did you end up going with and is that a bass reflex design? Cool shape!
:cool:
 
Hi xrk971. Yes you're right- I tried the speakers with my Denon amp and they sounded a lot better. Thanks for link, I wonder if the the amp you suggest is available in the UK? The driver is the 3" Monacor SPH 8ohm. I ported the enclosure at the rear so it's not bass reflex, but maybe that would improve the sound if not the appearance. Thanks for the compliment.
 
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