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Thoughts/ideas on a 21" ported horn sub
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<blockquote data-quote="Kevin McDonough" data-source="post: 212422" data-attributes="member: 10402"><p>Thank you all for your responses <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f600.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":D" title="Big grin :D" data-smilie="8"data-shortname=":D" /></p><p></p><p>Art, the paper I refer to about the different shapes of ports was one by Scott/DIYRM that was put on the 'speaker freakers' group on Facebook. I think this link should work.....</p><p></p><p><a href="https://drive.google.com/file/d/1SU56ScKuPIr7SftWRHB7eeKdjmnnMh3b/view?fbclid=IwAR3K9JrRh-trmRJqXFMWy2NNZchaQ9VuNpPZ88MaV8OS7qhzQpgCteVB_Tk" target="_blank">https://drive.google.com/file/d/1SU56ScKuPIr7SftWRHB7eeKdjmnnMh3b/view?fbclid=IwAR3K9JrRh-trmRJqXFMWy2NNZchaQ9VuNpPZ88MaV8OS7qhzQpgCteVB_Tk</a></p><p></p><p>Though I didn't have time to sit down and go over it in the most amount of detail ever, what I took from it was that a round port with a fairly specific flange/rounding at the end gives the best possible results, but short of that a basic round port is the best option, and everything else outside of that starts to increase problems, for a given size.</p><p></p><p>Now I realise that my own design idea doesn't really follow that, as I'm comparing much smaller overall area of round ports to a bigger rectangular ports. But the round ports provide me with the potential advantage of a much bigger internal volume and better response overall, as long as they can be made to work within the design.</p><p></p><p>I agree with all of the rest of the comments that I would always err on the side of using much bigger ports than this, but then I wonder how commercial designs do it. All of Martin Audio's ported horn designs for example, seem to have relatively small ports for a given size.</p><p></p><p>Their newest big horn sub for use with MLA/Wavefront, the MLX, only has 2 rectangular ports for each of the 18" drivers....</p><p></p><p>[ATTACH=full]208875[/ATTACH]</p><p>And their previous generation ported horn subs similarly only 2 fairly small round ports, very similar looking to the 4" pipes I plan to use, for each 18" driver....</p><p>[ATTACH=full]208876[/ATTACH]</p><p>[ATTACH=full]208877[/ATTACH]</p><p></p><p></p><p></p><p>Similarly with Void Acoustics for example, they have various subs that use round ports, a double 18" example with 4 round ports of a similar size to mine, and a very similar 21" that, while a little more cube like than mine, has a very similar overall volume and only uses 3 round ports of a similar size for the design....</p><p></p><p>[ATTACH=full]208878[/ATTACH]</p><p>[ATTACH=full]208879[/ATTACH]</p><p>And even a DIY option that people seem to regard as sounding great, by Marc O, only has a pretty small/thin slot port who's area seems much smaller than expected for a high power 18"</p><p></p><p>[ATTACH=full]208880[/ATTACH]</p><p></p><p></p><p>All of these designs seem to get good reviews and by all accounts sound good, despite having ports smaller than what I would certainly expect was ideal.</p><p></p><p>Plugging the numbers into BassBox Pro, my usual go to for reflex designs, to check the port velocities etc, it says that in both of my designs, at the rated 1700 RMS power the drivers only reach about 10mm of xmax until way below their pass band, and they need to be pushed to nearly 4000w before they start to approach their xmax of 15mm.</p><p></p><p>Obviously the rectangular port fairs a bit better with the much bigger area, but even the smaller set of 4 round ports (which incidentally BBP says should be longer than what Hornresp says to get the correct tuning, but still just about short enough that they can be a straight port and not have to bend within the cab) only JUST begins to reach what BBP considers the danger zone for port velocity when pushed to that 3000-4000w.</p><p></p><p>Also Art, as per your suggestion I tried modifying the design to show an offset horn. the response isn't quite as good as when a normal horn is used, but it's still possible to get a decent response with the cab being a similar overall volume, and the rear chamber and porting etc all being fairly similar.</p><p></p><p></p><p>(I've not had a chance to grab screen grabs of Hornresp and BBP while making this post, but will add some in later today.)</p></blockquote><p></p>
[QUOTE="Kevin McDonough, post: 212422, member: 10402"] Thank you all for your responses :D Art, the paper I refer to about the different shapes of ports was one by Scott/DIYRM that was put on the 'speaker freakers' group on Facebook. I think this link should work..... [URL]https://drive.google.com/file/d/1SU56ScKuPIr7SftWRHB7eeKdjmnnMh3b/view?fbclid=IwAR3K9JrRh-trmRJqXFMWy2NNZchaQ9VuNpPZ88MaV8OS7qhzQpgCteVB_Tk[/URL] Though I didn't have time to sit down and go over it in the most amount of detail ever, what I took from it was that a round port with a fairly specific flange/rounding at the end gives the best possible results, but short of that a basic round port is the best option, and everything else outside of that starts to increase problems, for a given size. Now I realise that my own design idea doesn't really follow that, as I'm comparing much smaller overall area of round ports to a bigger rectangular ports. But the round ports provide me with the potential advantage of a much bigger internal volume and better response overall, as long as they can be made to work within the design. I agree with all of the rest of the comments that I would always err on the side of using much bigger ports than this, but then I wonder how commercial designs do it. All of Martin Audio's ported horn designs for example, seem to have relatively small ports for a given size. Their newest big horn sub for use with MLA/Wavefront, the MLX, only has 2 rectangular ports for each of the 18" drivers.... [ATTACH type="full" alt="208875"]208875[/ATTACH] And their previous generation ported horn subs similarly only 2 fairly small round ports, very similar looking to the 4" pipes I plan to use, for each 18" driver.... [ATTACH type="full" alt="208876"]208876[/ATTACH] [ATTACH type="full" alt="208877"]208877[/ATTACH] Similarly with Void Acoustics for example, they have various subs that use round ports, a double 18" example with 4 round ports of a similar size to mine, and a very similar 21" that, while a little more cube like than mine, has a very similar overall volume and only uses 3 round ports of a similar size for the design.... [ATTACH type="full" alt="208878"]208878[/ATTACH] [ATTACH type="full" width="500px" alt="208879"]208879[/ATTACH] And even a DIY option that people seem to regard as sounding great, by Marc O, only has a pretty small/thin slot port who's area seems much smaller than expected for a high power 18" [ATTACH type="full" alt="208880"]208880[/ATTACH] All of these designs seem to get good reviews and by all accounts sound good, despite having ports smaller than what I would certainly expect was ideal. Plugging the numbers into BassBox Pro, my usual go to for reflex designs, to check the port velocities etc, it says that in both of my designs, at the rated 1700 RMS power the drivers only reach about 10mm of xmax until way below their pass band, and they need to be pushed to nearly 4000w before they start to approach their xmax of 15mm. Obviously the rectangular port fairs a bit better with the much bigger area, but even the smaller set of 4 round ports (which incidentally BBP says should be longer than what Hornresp says to get the correct tuning, but still just about short enough that they can be a straight port and not have to bend within the cab) only JUST begins to reach what BBP considers the danger zone for port velocity when pushed to that 3000-4000w. Also Art, as per your suggestion I tried modifying the design to show an offset horn. the response isn't quite as good as when a normal horn is used, but it's still possible to get a decent response with the cab being a similar overall volume, and the rear chamber and porting etc all being fairly similar. (I've not had a chance to grab screen grabs of Hornresp and BBP while making this post, but will add some in later today.) [/QUOTE]
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