@hollowboy , not the smoothness but the steepness of the slope. I'm not seeing anything that for sure doesn't look like a resonance, and not room gain.
In fact what causes the Helmholz resonance, the venting of the room, as a loss of pressure would work against potential room gain.. QED.
In fact what causes the Helmholz resonance, the venting of the room, as a loss of pressure would work against potential room gain.. QED.
Related : https://www.diyaudio.com/community/threads/room-gain-complementary-rgc-tuning.133398/ .
Question is when one starts a sealed box diy project, how does one decide if a low Q driver is the way to go. The room modes are not known. I presume, one completes a box, measures. modifies till you get your desired result or restart with another alignment or go the multiple sub route or DSP. Note this is only for bass response. Seems like a lot of variables. Multi sub is what I would pick with my limited knowledge.
SMathews
Question is when one starts a sealed box diy project, how does one decide if a low Q driver is the way to go. The room modes are not known. I presume, one completes a box, measures. modifies till you get your desired result or restart with another alignment or go the multiple sub route or DSP. Note this is only for bass response. Seems like a lot of variables. Multi sub is what I would pick with my limited knowledge.
SMathews
I am contemplating this very thing. My inclination is to go moderate Q and then tune with box size and perhaps crossover design and series cap if needed. If you go super low Q it is hard to raise the lower end. In any case one is unlikely to miss the mark by too much as long as fs is low.
Being 'old school', due to severely limited power available one designed the speaker to be whatever performance we wanted based on half (2pi) space and fine tuned the speaker's response 'in situ' (room/listening positions) with tone controls/whatever, so exceeding the woofer's low distortion point basically only happened when the amp began clipping from over zealous volume control settings.
The trade-off was box size that we basically had no choice but to accept for wide/full-range performance, but nowadays it's become depressingly obvious that most folks (me too not too many years away I fear) must try to find a balance point between desired size Vs cost Vs speaker optimal performance with full-range frequency response shaping (EQ) setting final in room response.
All that said, fairly recently high SQ DSP, high power driver prices have plummeted to the point where it's rendered speaker design pretty much moot for most DIY HIFI/HT apps in that one can stick (multiple) inexpensive drivers in acoustically tiny sealed cabs, so while I'd have normally designed/recommended a transient perfect 0.5 Qtc, which tends to be relatively huge/IB, now wouldn't think twice if the desired box size was a 5.0 Qtc as long as it had the desired flat BW efficiency once DSPed 'in situ'.
The trade-off was box size that we basically had no choice but to accept for wide/full-range performance, but nowadays it's become depressingly obvious that most folks (me too not too many years away I fear) must try to find a balance point between desired size Vs cost Vs speaker optimal performance with full-range frequency response shaping (EQ) setting final in room response.
All that said, fairly recently high SQ DSP, high power driver prices have plummeted to the point where it's rendered speaker design pretty much moot for most DIY HIFI/HT apps in that one can stick (multiple) inexpensive drivers in acoustically tiny sealed cabs, so while I'd have normally designed/recommended a transient perfect 0.5 Qtc, which tends to be relatively huge/IB, now wouldn't think twice if the desired box size was a 5.0 Qtc as long as it had the desired flat BW efficiency once DSPed 'in situ'.
I've had luck with just designing for a Q of .5 -.57 and adjusting the lower octave response with DSP. I find that pretty flexible for me.
I am building a sealed 5 cu ft box with TD15X (Qts = 0.28, Fs=23, Xmax =14mm), Box Sim gives: F3 = 64Hz, F10 = ~30 Hz, Qtc = 0.55. Planning to use multiple subs to smooth the response in the room down to 30Hz. Low pass at 300Hz (2nd order), to Unity horn.
Listening/Living room (1/2 of A frame) is 22' wide, 22' long, 7' high at low end, 17' high at high end. The A is split down the middle by a wall with 4' wide openings on either side of the wall. All stick and Drywall.
SMathews
Well, call it something else if you like, but the results are the results 🙂
They got an average of +3dB 50-190Hz (and more lower down) when they took the speaker from outside to inside.
Maybe the causative mechanism is more accurately called "insert whatever phrase here", but I see gain, and I see a room.
There are plenty of nice 15" drivers that are > 95dB and not crazy expensive.
Assuming you want no processing / low parts count for the mains, look for benign (non spiky) HF, to keep the crossover easy.
Some Faital drivers seem good for this, and the specs seem pretty honest. I have a 12" pair, and the FR plot I measure matches the spec sheets very well (the differences are within the margin of error of my tests), so I assume that any of their drivers that looks good, is good.
This also looks great, and is a well regarded brand:
https://usspeaker.com/beyma 15MI100-1.htm
As a reality check:
Efficiency of the Beyma calculates as 97.4dB http://www.mh-audio.nl/Calculators/DriverReferenceEfficiency.html
It only 4.5mm X-max, but (a) that's often the case for very efficient drivers and (b) is probably more than enough if you are driving it with a small valve amp.
"A sub can handle the last 8va when needed."
Or subs. I'd rather run 4x12" than 1x18". Using a swarm gives you the ability to put them in multiple locations to smooth out room modes.
Ugh, series capacitor? Long ago at an AES conference outside Detroit (Novi I think) David Clark was presenting about that, boosting the low end with a passive network (at the price IIRC of a lowered impedance near the peak? Below the peak?). I once had to redesign a passive subwoofer crossover, the interaction with the resonance frequency impedance peaks was awful for both highpass and lowpass. I suspect you could also end up with some amp-nasty total impedance. I have seen some people talking about sophisticated simulation of this so it is possible to get it to work if you put in the time. But I wouldn't want to just simulate, I'd want to measure actual impedance sweeps to be sure there weren't nasty dips.
I think it's better to err on the side of low Q...someone once posted tone burst simulations for me showing the 0.8 0.9 1.0 were not really so awful from a transient point of view. Actually better than a very low Q. HOWEVER that is a kind of illusion-picking real woofers to fit in realy boxes, you can't divorce the Q from the resonance frequency. Low Q = low resonance. I'm still wishing for a tone burst simulator, to see say what does 80 Hz look like with higher and lower Q/resonance.
IS there such a thing? Last year I was looking at a lot of woofer curves with exactly that in mind. They were ALL spiky, it was depressing.
did you look at the Beyma 15MI that I linked to?
Some of the faital drivers too. I have the 12FH520 which are pretty easy to like. Some of their other models seem to have even gentler HF rolloff.
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FWIW, since willing to go with a relatively big sealed box, then from a purely technical POV using the pioneer's optimal 'universal' box loading constants where 'a' = 1.44* (rounded up) can be reduced to:
Vb = 467/1.44 = 324.31 L
F3, Fc = 23*1.56 = 35.88 Hz
Qtc = 1.56*0.31 Qts' = ~0.48424
[Qts']: [Qts] + any added series resistance [Rs]: http://www.mh-audio.nl/Calculators/newqts.html
[Rs] = 0.5 ohm minimum for wiring, so may be higher if a super small gauge is used as a series resistor and/or there's other series resistance.
* https://www.ajdesigner.com/phpsubwooferclosed/constant_equation.php#ajscroll
Thanks. Some history ......
I was actually backed into this configuration. I bought the TAD Unity kit from Nick Mckinney (may he RIP) 20 yrs back, with 2 TDX 15's and 2 PR's per bass box. Sold one set of TD15X's (big mistake) in the process of trying to sell everything. Then member "thylantyr" convinced me to keep a pair (bless him). Well being a novice I decided to then pursue another tried and tested design, Nicks "God Of Thunder" (GOT... 1 TD15X with 2 PR's). Started building the box a while back , then just started completing the box, only to find out the PR surrounds were shot (most probably in a house move). There are no replacement surrounds for the Lambda PR's. Checked with John at Acoustic Elegance. So the easiest way out is a sealing the 5 cu ft GOT box.
If I understand you correctly, I should increase to 324 L, right?
SMathews
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Oh really?! I originally had a 'gentleman's agreement' with him for just horns to market a system that included a dual driver/PR using Avatar/Adire drivers I dubbed the mini-Contrabass when I mentioned it on the Basslist, but then one day without warning or explanation I didn't 🙁, though did do a few of the subs for locals. 🙁 Wasn't aware Nick offered one.
I also sent him my Altec 515B measured specs to make me some ferrite versions, but Lambda folded, so it too never happened. 🙁 Never gotten around to seeing if John STRYKE/AE ever offered it, though seen some from more recent manufacturers that are targeted at GPA's version at significantly lower prices, which is a clone of Altec's version that has a higher Fs, Qts, lower Vas, though are drop-ins for any of the B's various horn, vented cab alignments.
Regardless, not 'should' per se as I've already posted about box size + DSP and historically using/recommending 0.5 Qtc', which as your vintage spec driver implies, all hovered around 0.5 way back when, hence my choice; just your post offered me the option to post some more pioneer tech trivia I've never seen published, which BTW is a cornerstone of T/S theory to refute all those folks that claim they were pretty much clueless till it was invented.
I also sent him my Altec 515B measured specs to make me some ferrite versions, but Lambda folded, so it too never happened. 🙁 Never gotten around to seeing if John STRYKE/AE ever offered it, though seen some from more recent manufacturers that are targeted at GPA's version at significantly lower prices, which is a clone of Altec's version that has a higher Fs, Qts, lower Vas, though are drop-ins for any of the B's various horn, vented cab alignments.
Regardless, not 'should' per se as I've already posted about box size + DSP and historically using/recommending 0.5 Qtc', which as your vintage spec driver implies, all hovered around 0.5 way back when, hence my choice; just your post offered me the option to post some more pioneer tech trivia I've never seen published, which BTW is a cornerstone of T/S theory to refute all those folks that claim they were pretty much clueless till it was invented.
GM thanks for your feedback. Appreciate it. If my current plan does not work out for some reason, I now have another path forward. Reading one of your posts on the progression of speaker design, from waveguide/horn + woofer to Danley's Synergy Horn + woofer, reassured me that I am on the right track.
SMathews
I'm taking post 44 and 45 to heart!
My idea is in an active 4way with an analogue crossover, connect the sub output from the crossover to DSP unit for the sole purpose of raising the low end and correcting for high Qtc.
"fairly recently high SQ DSP" - Any suggestion for DSP unit - Mini DSP seems to dominate. Maybe other choices I'm not aware of?
My idea is in an active 4way with an analogue crossover, connect the sub output from the crossover to DSP unit for the sole purpose of raising the low end and correcting for high Qtc.
"fairly recently high SQ DSP" - Any suggestion for DSP unit - Mini DSP seems to dominate. Maybe other choices I'm not aware of?
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Long story short, I started with a now long gone circa early '80s original dbx system and only other (very limited) 'hands on' experience is with a then new dbx system used here and was impressed enough to probably not bother to research further regardless of speaker system design/room acoustics, though a local DIYer that made a two way Unity concept went with whatever brand DSL uses and IIRC mentioned it was a step up from others, so might want to check with him.
I used to run a pair of 0.5Q sealed 18s on my 'pub sized' PA and the LF response was sufficient to cause feedback on turntables such that it was necessary to set an HPF on the LMS.
Hi GM,
Are the formula's you used in your post shown above, documented some where. I am trying to wrap my head around it. I have been using BassBox Pro to model/design the cabinet. A closed box with Vb = 324.31 L gives an F3 of 73.75 using BassBox Pro, whereas you shown an F3 of 35.88. Could you shed some light on this. Thanks.
Regards
Simmonds