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Discussion Starter #1
Hi, I'm new here and have looked around a bit, but could not find a thread that really addresses my topic in the way I was hoping.

I built a sonosub for a 15" driver. Though it's large enough to qualify as an LLT (approx. 11.5 cubes, two 6" ports), I currently have it tuned to 20 Hz and am high-pass filtering it below 19.7 Hz in an effort to get the most 20 Hz output possible as opposed to trying to dig as deep as I can. I had been using a Cerwin Vega 15D4 driver, which seems to have a sensitivity of 93 dB SPL 1W/1M. Vas is 9.91 ft^3, fs is 21 Hz, and Qts is .332. Xmax is given as +/- 0.8", although that is almost certainly the mechanical limit. This driver, though having a somewhat low Qts, was intended as an automotive subwoofer, not pro sound. Unfortunately that driver has suffered damage due to displacement overload. The first time the spider came off the basket and I easily repaired it with liquid nails. More recently the spider is separating from the voice coil former, and that looks much more difficult to repair, so I may be in the market for a new driver.

As I understand the situation, ported drivers with a relatively low Qts tend to be limited to not much lower than their Fs in their output response. This is not a problem in my current application, but I would like to be able to dig deeper when desired. (I built the cabinet with two 6" ports that plug into sockets in the baffle, and most of the port lentgh sticks out from the enclosure by however much is needed for the desired tuning. The resulting design appearance/shape does not bother me in the least.)

I am also interested in maximum reasonable efficiency. So my question is: Will my 93 SPL driver deliver the same output for less power than a typical modern 88 SPL hi-fi/HT sub driver? I would like more Xmax, but I cannot afford 2000 watts of amplifier power to get only marginally more excursion than I was getting with the Vega on 240 total watts. Also I don't care if there is a moderate peak at 20 Hz.

Given my not minding a slight 20 Hz peak, combined with my efficiency needs, would a modern high-excursion driver in the range of 88 dB SPL 1W/1M still be my best bet? Or should I look once more for a somewhat lower-Qts higher-sensitivity unit (if such a beast can be found)?

Thank you very much!! :bigsmile:
 

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Not much sense in using a 20hz tuning if there is a 19.7hz highpass - you're throwing a ton of good output down the toilet. Either up the tune to around 25hz or drop the highpass to around 15hz.

As for a better replacement driver, I'd take a look at the Exodus Tempest X, CSS SDX15, Fi Q15, or SS RL-p15.

Also, not to be a party pooper, but the subwoofer you described does not meet LLT criteria by a pretty fair margin.
 

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Discussion Starter #4
Unfortunately, I'm stuck with the 19.7 Hz because that's the lowest setting available until I purchase new crossover equipment. I just want to have the option to go lower when that becomes financially feasible.

Yes, it's true, the Vega driver does not meet LLT requirements. I was just talking about the cabinet volume compared with the size of driver.

Basically I want to have a ton of output around 20 Hz, as well as the ability to go lower if I want, but I would like to avoid making the output very much worse at 20 Hz than it is now for the same power. If anything I want it to be greater!! I agree the 93 dB spec does seem a bit suspect, but that driver in that cab could reach its mechanical limits over pretty much the entire range of interest (with the possible exception of right at cabinet resonance) on just 240W cont. of amplifier power, so that's why I was asking. I'm not at all against purchasing a new driver up to $0.4 K, possibly even kluging an 18 to fit in there, maybe a Maelstrom? (although it wouldn't be an LLT cab anymore at that point!) I just don't want to have to buy a bigger amplifier to reach the same excursion I was getting with the old driver.

Cerwin Vega actually published 96 dB SPL 1W/1M for this driver in their applications manual, but elsewhere they said the 96 dB was at 2.83V/1M without saying how the coils were wired, so it would be 90 dB SPL it they used both 4 Ohm coils in parallel. A 2 dB difference would seem to be trivial compared to the probable significant improvements in driver technology that have taken place since the Vega drivers were made, even at the same price point.
 

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Discussion Starter #6
Hi, Mike, it's an old 240W Audiovox car amp powered by an RV 12V converter with extra filtering. Kind of kluged together. I am dropping below the recommended minimum impedance of the amp at some frequencies, but not near tuning, where I use it most. And since that's a cheap amp brand, I doubt I'm really going much over 240W even with the underimpedance load. It hasn't failed yet and I've used it extensively, so that doesn't seem to be a problem for the amp. I have a larger QSC pro amp but I acquired it broken and haven't had the time to fix it yet.

I would like to not make the cab any smaller as this would negatively impact efficiency as well as my ability to get lower frequencies out of it when finances permit. Are you saying that size of cabinet doesn't offer enough control over the driver at that frequency and that's contributing to the overexcursion?

Thank you everyone!
 

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Are you saying that size of cabinet doesn't offer enough control over the driver at that frequency and that's contributing to the overexcursion?
No, I just curious if a smaller cabinet was an option. If you're going to replace the Cerwin Vega with some other sub, either you find a sub that works in the cabinet volume you have or adjust the cabinet volume to suit the new sub. As for an over excursion issue with the Cerwin Vega, I can't say since I can't find the parameters to model the sub.

I reread your initial post and this got by me:

I built the cabinet with two 6" ports that plug into sockets in the baffle, and most of the port lentgh sticks out from the enclosure by however much is needed for the desired tuning.
That is incorrect. There is only one tuning frequency and it is determined by the length of both ports. How far they stick in the cabinet or stick out of the cabinet has no effect on the tuning. The tuning frequency can only be adjusted by a different length of the ports, or by blocking one port and using only one.
 

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Given my not minding a slight 20 Hz peak, combined with my efficiency needs, would a modern high-excursion driver in the range of 88 dB SPL 1W/1M still be my best bet? Or should I look once more for a somewhat lower-Qts higher-sensitivity unit (if such a beast can be found)?
Down low it's all about moving air, i.e. acoustic efficiency, so radiator, box size and low distortion excursion rules and since you can't have 'your cake and eat it too', you'll have to decide what design trade-offs you're willing to make to meet your performance goals, or not. Don't forget to factor in spacial loading.

A simple single driver solution is an extreme driver such as the RE XXX18 in a 4th order band-pass alignment with enough 'clean' power to make it happen:

GM
 

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Discussion Starter #10 (Edited)
That is incorrect. There is only one tuning frequency and it is determined by the length of both ports. How far they stick in the cabinet or stick out of the cabinet has no effect on the tuning. The tuning frequency can only be adjusted by a different length of the ports, or by blocking one port and using only one.
I guess I wasn't very clear in my description. :rolleyesno: I meant that I simply 'unplug' the ports and replace them with longer ones for lower tuning, not just push further into the enclosure the existing ports, which would in fact slightly raise the tuning. The new, longer ports aren't in the way in my room, even for a 14 Hz tune, so that's what I mean about desiring upgradability to LLT when this becomes possible.

GM, thanks for the CV pdf link- I had lost the URL over the years and hadn't had a chance to re-look it up!

Considering the tradeoffs, I guess I should define my needs better: I want the ability to dig down below 20 Hz, possibly to LLT frequencies, by re-porting this sub, unless this ability results in a significant reduction (more than 2 dB) in the output I can get at 20 Hz with the Vega 15D4 sub (or the best potential modern replacement) on the same power. How significant are the tradoffs? Would an LLT-ish driver that will respond well at 13 Hz have significantly reduced output even at 20 Hz compared to other, non-LLT optimized drivers? Or am I just worrying for nothing? (I do realize that tuning the enclosure well below 20Hz will result in reduced efficiency at 20 Hz. I'm concerned about the inherent limitations of choosing one driver over another, possibly with slightly differently-optimized parameters; not the tradoffs resulting only from tuning differences.)

I just got started with Linux and don't have a modeling program yet. What would be a good LF modeling program that will run under Wine or in Linux directly?
 

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OK, gotcha on the ports, understood.

Everything is a trade off. We'll use the 15D4 as an example. Pink is what you have, 240 watts with a HPF at 19.7 hz, Xmax is reached. Green is with 160 watts and a HPF at 16 hz, Xmax is reached. As you ca see the lower the tuning the more low end extension you get at the expense of overall SPL.

15D4.JPG
 

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You're welcome, though not a link, it's a copy off my computer. I do happen to have a link though: http://english.gttrading.it/utilita/default.asp?sect=&opt=Manuali Cerwin-Vega

Hmm, let's see, a driver with ~93 dB eff./20 Hz and infra-bass BW capability requires a ~20 Hz Fs, 0.7 Qts, 40 ft^3 Vas or some variation thereof that = the same box alignment, so a mass loaded (to lower Fs, raise Qts) '50s era Altec 416A would get you in the 'ballpark', but with only a ~3.8 mm Xsus, won't handle but a few watts down this low, so would be excursion limited to ~100 Hz peaks. Hardly worth the expense/effort and a waste of a great mid-bass woofer.

Anyway, as me and Mike have pointed out by example, you trade BW for efficiency and vise versa and as I referenced in a previous link you can't have 'your cake and eat it too'. Physics, it's the LAW.

Sorry, not aware of any Linux, Wine speaker design programs.

GM
 

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Discussion Starter #13
OK, thanks for the replies! It sounds like the Vega is optimized for slightly higher frequencies than I'm trying to reproduce, (like typical car audio boxes), and also isn't as efficient as they'd have us believe by failing to specify how the voice coils were wired. I'll start looking at the various drivers available and see which seem most suitable. I think I'll stick with 15 inch and save myself the trouble of trying to convert the box to use an 18 inch driver, which would take it out of the running for LLT anyway!
 

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I have a solution for you if you want to use the cabinet that you have.

Green is what you have, The CV in 11.5 cu.ft tuned to 20 hz with 240 watts and a HPF at 19.7 hz.

Pink is a Titanic 15 in exactly the same setup. It will match the CV on 20 hz output.

Orange is the Titanic 15 in the same cabinet only tuned to 16 hz with 500 watts input and a HPF at 14 hz. You get the low end extension and exceed the 20 hz output that you have now. All you need is a bigger amp and the proper HPF to do it. It's called upgraditis. :yes:


Titanic 15.JPG
 

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Not much sense in using a 20hz tuning if there is a 19.7hz highpass - you're throwing a ton of good output down the toilet. Either up the tune to around 25hz or drop the highpass to around 15hz.
Is he wasting output because his 19.7Hz filter takes out too much output up past his 20Hz tune, or, because it is taking away to much output he would get below tuning?
 

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Both. 19.7hz is the center frequency, meaning some output starts to drop off above 19.7hz as well as below it, though mostly below it. Also, in the deep bass range, excursion is at its lowest at tuning, so it's not like everything falls apart 0.1hz just below tuning - you have some freedom in allowing the driver to play lower.
 

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Discussion Starter #17 (Edited)
Mike, the Titanic does sound like a viable possibility, thanks for the suggestion, and thanks for running the numbers! I'm really liking the improvement that only a doubling of power would produce! At 20 Hz I would get the 3dB increase, and it looks like 12 dB more at about 16 Hz!

Though I would like to upgrade to an 18" driver, I don't have the space for a larger enclosure. But I do have room for the longer 16 Hz ports. When I fix my QSC amp, I will have plenty of power (about 1000W bridged into 4 Ohms), so it looks like I'll be doing that soon, and I'll have to invest in an appropriate crossover.

For a 15" driver I would be willing to go up to about $300, or maybe a bit more, in order to get the most I can out of that one cabinet that I have space for. Are there other models I should consider?

Yes, I can feel the upgraditis coming on! :bigsmile:
Thanks again!
 

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Discussion Starter #19 (Edited)
Now that CSS really does sound like a huge improvement! It looks like I would get about 7 dB more output at 20 Hz than what I can get now (after fixing my amp, of course!) and lower extension as well! That's worth it in my book. Now I need to research crossovers!

Thanks again!:bigsmile:
 

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Discussion Starter #20
:T I just ordered an SDX15 and a Reckhorn B2 for my SSF so I'm covered for all possible tunings I might be using! I'll get myself going with the existing amp, then upgrade when I get a chance. Thanks Mike for the suggestions and running the numbers, it's greatly appreciated!
 
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