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Enclosure Design & Construction
Twin 18" PA-Sub 6th-Order Blowthrough in Trunk... Sanity Check.
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<blockquote data-quote="recon440" data-source="post: 8724608" data-attributes="member: 636364"><p>Hi Buck,</p><p></p><p>Thanks for all the examples you posted and I really appreciate the insight. Your designs look really impressive.</p><p></p><p>Eyeballing it it's almost like the front chamber in your designs is generally 200-100% the size of the front chamber. I don't saying that as I think it's a funny that most people refer to a "ratio" when designing 4ths and 6ths but it does give an rough idea of the Q of the box (amongst a myriad of the factors). With such a generalization am I correct in thinking you are typically designing for a flat free-air response to ~30Hz? Regardless, it looks like a realistic ratio I'm using here (~7CF:3.5CF) but I usually like to simulate it to get a better idea. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /></p><p></p><p>To be frank, taking into account Hoffman's Iron Law, in my case I am quite aware that total box size might be overall undersized to leverage the full low end sensitivity of two 18's (let alone PA ones) but it's pretty much the largest I believe I can feasible slot into my trunk. Yes, I can do the XLs but weight and the top end response of these B&Cs is really attractive. It's also compelling that if I want to mess around at a car meet, I can pull out the rear section out of the front section and play it as a simple vented enclosure @ 130+ @ >60+Hz which is kind of a sweet spot of bass thats audible in PA applications.</p><p></p><p>I'm not exactly targeting to get loud at 30Hz and am looking to get loud in the sweet spot ~40Hz and up. In my experience a true car subwoofer will probably be 3dB louder down low (or at least tuning peak base on QTS of a given driver) but give up a lot on the top end (~6-10dB if were talking 70Hz+). As I understand it, you need at least 4 times the power or 4 times the box to get as loud 1/2 octave lower which get unfeasible when were talking about already pretty much maxing up the trunk volume of a large sedan... LOL. I think that's a feasible trade-off I can live with for perceived loudness.</p><p></p><p>Ultimately, I am hoping to get much louder than the two Type Rs broad-band. Is there anything that concerns you in the sim here? It seems that it's picking up at least 5dB in the sweet spott in this regard watt-for-watt. Even on the low-end (<35Hz) it should be similar and should pick up at least another 3-5dB when I dump 2-3 times more power on the B&Cs. I think that the inductance of the B&C is quite low and well controlled so that should be quite accurate in regards to simming it.</p><p></p><p>As for tuning in the future, it seems like there is a lot of flexibility with the front and rear port adjustments. Despite the smaller chamber, based on port lengths it does not appear as though they are mutually exclusive in regards to having a large chamber to let the woofers "breathe". If I make the front port quite long, we can get the xmax extremely high at low frequencies. Is that something you noticed too?</p></blockquote><p></p>
[QUOTE="recon440, post: 8724608, member: 636364"] Hi Buck, Thanks for all the examples you posted and I really appreciate the insight. Your designs look really impressive. Eyeballing it it's almost like the front chamber in your designs is generally 200-100% the size of the front chamber. I don't saying that as I think it's a funny that most people refer to a "ratio" when designing 4ths and 6ths but it does give an rough idea of the Q of the box (amongst a myriad of the factors). With such a generalization am I correct in thinking you are typically designing for a flat free-air response to ~30Hz? Regardless, it looks like a realistic ratio I'm using here (~7CF:3.5CF) but I usually like to simulate it to get a better idea. :) To be frank, taking into account Hoffman's Iron Law, in my case I am quite aware that total box size might be overall undersized to leverage the full low end sensitivity of two 18's (let alone PA ones) but it's pretty much the largest I believe I can feasible slot into my trunk. Yes, I can do the XLs but weight and the top end response of these B&Cs is really attractive. It's also compelling that if I want to mess around at a car meet, I can pull out the rear section out of the front section and play it as a simple vented enclosure @ 130+ @ >60+Hz which is kind of a sweet spot of bass thats audible in PA applications. I'm not exactly targeting to get loud at 30Hz and am looking to get loud in the sweet spot ~40Hz and up. In my experience a true car subwoofer will probably be 3dB louder down low (or at least tuning peak base on QTS of a given driver) but give up a lot on the top end (~6-10dB if were talking 70Hz+). As I understand it, you need at least 4 times the power or 4 times the box to get as loud 1/2 octave lower which get unfeasible when were talking about already pretty much maxing up the trunk volume of a large sedan... LOL. I think that's a feasible trade-off I can live with for perceived loudness. Ultimately, I am hoping to get much louder than the two Type Rs broad-band. Is there anything that concerns you in the sim here? It seems that it's picking up at least 5dB in the sweet spott in this regard watt-for-watt. Even on the low-end (<35Hz) it should be similar and should pick up at least another 3-5dB when I dump 2-3 times more power on the B&Cs. I think that the inductance of the B&C is quite low and well controlled so that should be quite accurate in regards to simming it. As for tuning in the future, it seems like there is a lot of flexibility with the front and rear port adjustments. Despite the smaller chamber, based on port lengths it does not appear as though they are mutually exclusive in regards to having a large chamber to let the woofers "breathe". If I make the front port quite long, we can get the xmax extremely high at low frequencies. Is that something you noticed too? [/QUOTE]
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