A driver's Qts and Fs determine what the optimum cabinet tuning frequency should be but once that is accomplished in a design, the bass reach is then determined by the cabinet/line volume. The larger that volume the lower the bass reach but limits will be imposed by the driver's excursion capability, distortion, and port/terminus air velocity.
Paul
..not exactly, various speakers have always been in the same position, the only difference I can suppose is the port position: on the front at 40 cm from the floor and on the bottom bad, rear as you said good, but I can't understand why a 30-40 cm of difference in port position between front and rear makes such an important effect, if in this region waves are spherical.
Waves in real rooms are all but spherical and the position of a sound source close to a boundary influences tuning, efficiency and the exact excitation of standing waves in your room (these are what you actually hear, instead of the response of the speaker). 30cm can make a big difference here. Just move your speakers around in 3D and notice the differences.
What exactly is your design target? For a serious main home system I‘d pick a 4th or higher order setup that reaches 30Hz or lower (for music). A 2nd order system might end somewhat higher, but I would not go far above 40Hz.
And nowadays active correction is so cheap, as is clean amp power, that purely passive tuning almost becomes archaic. The only requirement being a LF driver that has enough Vd within chosen distortion limits to produce the desired SPL. And that mixes somewhat badly with your idea of a 2-way, most long stroke drivers just won’t do clear midrange.
Having said that, there are numerous designs that fit the bill, like my first suggestion. Or setups with the Dayton RSS225, they have been around here for ages, it seems. Two way designs with 8” aren’t that easy to get right.
Anyway, don’t focus on details as LF setup, only the bass-mid or system choices like WTW, but observe the whole picture. As for WTW, for the same und money you likely are better off with a true 3 way system, midrange quality more often than not improves when you can use a dedicated driver while dealing effectively with the undesired port output at mid frequencies.
What exactly is your design target? For a serious main home system I‘d pick a 4th or higher order setup that reaches 30Hz or lower (for music). A 2nd order system might end somewhat higher, but I would not go far above 40Hz.
And nowadays active correction is so cheap, as is clean amp power, that purely passive tuning almost becomes archaic. The only requirement being a LF driver that has enough Vd within chosen distortion limits to produce the desired SPL. And that mixes somewhat badly with your idea of a 2-way, most long stroke drivers just won’t do clear midrange.
Having said that, there are numerous designs that fit the bill, like my first suggestion. Or setups with the Dayton RSS225, they have been around here for ages, it seems. Two way designs with 8” aren’t that easy to get right.
Anyway, don’t focus on details as LF setup, only the bass-mid or system choices like WTW, but observe the whole picture. As for WTW, for the same und money you likely are better off with a true 3 way system, midrange quality more often than not improves when you can use a dedicated driver while dealing effectively with the undesired port output at mid frequencies.
In fact, what you say would explain why by moving the speakers away from the wall I only get a worsening of the low range. Indeed the position of the reflex port, with the same height from the ground of about 40 cm, it is okay if it is 30 cm away, it is bad if it is 60 cm.
Thank you for the advice but my idea of working with an MTM in TL is for educational and fun purposes, because it will allow me to deepen my knowledge on crossover and the problems of crossing point (only one is certainly better) and understand why the TL seems to have that magic in the bass range emission. And the more down in frequency I'll go, the happier I'll be!
So if I actually widen the load volume compared to the optimal one for a maximally flat response, do I get an increase in extension without worsening the timbre and overall quality of the sound message (putting excursion limits aside)?
Does this happen regardless of the driver QTS?
Given that the group delay increases, what are the values to be considered admissible in this 'enlargement' process?
For sure I think I understand that the tone worsens if I use smaller than optimal load volumes, the higher QTS is and the worse it gets with the same cabinet shrinkage. In any case, which are the drivers, in terms of VAS and QTS and FS, best suited to work in TL?
Finally, from the various simulations done in these days with WinISD for simple bass reflex loading it seems that the drivers' FS has little influence on the extension, the VAS and QTS have more role.. where am I wrong?
Thank you.
I don't really think I can answer your question but I can tell you what my experience has been and my preferences for TL design. I prefer drivers with a Qts in the 0.35-0.45 range although I've had success with a Qts down to 0.30 and up to 0.50. I always determine the optimum tuning frequency which is determined by fs and Qts, then I adjust the line volume while maintaining that optimum tuning frequency until I achieve whatever f3 I'm shooting for with the proviso that I don't end up pushing the driver too far or having a too high air velocity in the terminus or port. Keep in mind I am not a bass freak and usually shoot for an f3 in the 30-40 Hz range and quite satisfied if it ends up in the 35-40 Hz range.
Paul
Thank you for this suggestion. Please be patient, what formula do you use to determine the optimal system tuning frequency? If I use Fb = 0.39 * (FS/QTS), using your Marcato as example and Usher 8945P T/S parameters measured by Zaph , Fb = 0.39 * (38 / 0.41) = 36 Hz while system tuning of your system is around 32 Hz, did you push down Fb too it or do you use another formula?
I don't recall exactly what I did on the Marcato, but what I have been doing for a number of years is this: If Qts is equal or close to 0.40, the optimum tuning frequency will be Fs or very close to it. If Qts is above 0.40, the optimum tuning frequency will be lower than Fs, and if Qts is below 0.4, the optimum tuning frequency will be higher than Fs. So, I decide what tuning frequency I will shoot for and start the modeling. If my expectations are wrong, it's very easy to increase or decrease the tuning frequency to find what is optimum using Martin King's modeling software. I've modeled many, many TLs for many, many people and this comes quite easily for me. Keep in mind that resistance added in series with the driver(s), like from a series crossover inductor, will increase Qts. I just looked at my file for the Marcato and saw that I included a series resistance of 0.45 ohms which increased Qts to 0.46 and required the lower tuning frequency I used.
Paul
One more thing to follow-up for the Marcato. I didn't use the published specs for the Usher drivers. I used those that "Zaph" measured and published on his website Zaph Audio in 2008, where the primary differences were a much higher Qes and Qts, and lower Vas.
Paul
Paul
Many thanks again Paul, for your suggestions and for your patience too.
I think for sure I'll give up idea of WTW with 8'' and I'll go to an MTM using 6.5'' midwoofer, chosen as able to reach the lowest frequencies as possible but with a smaller cabinet than one required by 8''. From some speedy sims made in these days I've found the corresponding Monacor SPH-175HQ or Peerless HDS 830883, the last requiring an even smaller load volume than the first at the expense of a bit of sensitivity: let's say that with a 65-80 liters I should be able to reach 30-32 Hz of F3. Soon I'll be more accurate with some graph.
I think for sure I'll give up idea of WTW with 8'' and I'll go to an MTM using 6.5'' midwoofer, chosen as able to reach the lowest frequencies as possible but with a smaller cabinet than one required by 8''. From some speedy sims made in these days I've found the corresponding Monacor SPH-175HQ or Peerless HDS 830883, the last requiring an even smaller load volume than the first at the expense of a bit of sensitivity: let's say that with a 65-80 liters I should be able to reach 30-32 Hz of F3. Soon I'll be more accurate with some graph.
Do you have access to the Dayton Audio RS180P-4 drivers and are they within your price range? If so, let me know and I will do some modeling to see how they work out in an WTW ML-TL if you want.
Paul
Nice driver, good response and good price, I didn't know there's a paper versione in the RS series. Unfortunately that has a FS/QTS ratio too high for my target and I suppose wont't be able to push it down to 30 Hz unless damaging its sounding quality.
FWIW, I've attached some modeling graphs for a pair of RS180P-4 drivers in an ML-TL. I used their published specs for the modeling inputs. Don't know how this may or may not address your Fs/Qts target but the results look pretty good to me and I wouldn't hesitate building it based on these results.
Paul
Paul
Indeed, the pioneer's way based on Fs, VC diameter yields a ~298 Hz and/or 939 Hz XO points, so either a whopping big horn or pretty big tweeter due to its relatively large VC.
FYI/FWIW, IME and proved to my satisfaction when 'proofing' MJK's MathCad design programs against some of my own Tower/Column alignments from 'way back when', the vented TL [closed pipe] alignment [aka MLTL] range from ~0.312 - 0.624 Qts' seems technically good enough, i.e. from Keele's 6th order assisted bass reflex to his Extended Bass Shelf [EBS] alignment.
While the 'sweet spot' [mean] is a ~0.4412 Qts', a 'close enough' simple guideline is:
~0.403, Vb = Vas, Fb = Fs [MLTL]
< ~0.403, Vb = < Vas, Fb = > Fs [inverse tapered MLTQWT]
Qts' = Qts + any added series resistance [Rs]: http://www.mh-audio.nl/Calculators/newqts.html
GM
Where is this from? I thought I'd seen every published/DIY alignment formula in my off n' on ~66 yrs of speaker design, though assumed there was plenty published around the world I didn't know about. 🙁
FWIW, the Margolis-Small Personal Calculator program is the one I settled on where Vb = 20*Vas*Qts'^3.3, Fb = 0.42*Fs*Qts'^-0.96, so yields a slightly higher Fb.
Re determining pipe length tuning Vs tapered tuning, there's lots of insight in MJK's Classic TL Alignments doc.
+1. Assuming small room & power-handling isn't the priority, you'd probably get away with about 1.35KHz, LR4 to a suitable dome. Otherwise, a high quality wideband works for me as a mid-tweet. Assuming the crossover is at speaker level, the components will cost a bit though. 😉 I'll have to get a reminder from you on on that 939Hz frequency BTW -I know where the lower comes from of course, but mental block is kicking in -spent too much of the morning writing up a paper on the Powerful class cruisers & it turns your mind to mud after a while. 😱
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Thank you Paul, only a doubt, if it's a dual driver design, wouldn't it be a too low impedance module being 4 ohm woofers? Another question: is it a complete design with tweeters? If yes, what drivers were there used?
Thank you for your suggestions, I've found that formula in a post of a famous loudspeaker designer on another platform's forum as a method for a first and quick orientation about a woofer loading requirements, however my congratulations for your long experience.
Very useful clarification! Just to clarify, is 'expanding' a tapering in which terminus is placed on the largest part of pipe, right?
At this point, it makes me ask: is the tapering ratio depending by the difference between QTS and 0.403 value?
Thank you again for reporting.
I too would be curios about how did you calculate 939 Hz of cross point staring from woofer diameter (VC?).
Thank you too, but as said some post ago, I gave up idea of using 8'' drivers for a WTW, too large cabinets and too low cross point, returning to 6.5 drivers instead.
Now I fault in love with the younger brother of the topic's woofer, the SPH-175HQ, measured by DiBirama:
or, more, with the Peerless HDS 830883, measured by Zaph, requiring this last a bit, more less volume than the first one, having a beautiful phase plug, an advanced motor and a minor cost, despite a bit worse response around 2-5 Khz, but it seems to me nothing incurable:
In both cases it will probably be however necessary to use a low cross point.
What do you think about these drivers?
For the Monacor, not bad, bit of energy storage (cone edge resonance) around 1.2KHz give or take based on the measurements. Fairly standard motor but it's well designed (I'd take a well-designed 'standard' motor over a badly implemented design with 'advanced' features any day). HD isn't bad. Given the general response curves, I doubt I'd cross it much higher than the 220HQ, but that's just me -I tend to cross low.
I didn't realise the 830883 was still available after the havoc Tymphany have caused, but I see it's in stock in a couple of suppliers. Motor is definitely good; like the Monacor it's got a cone-edge resonance around 1.2KHz give or take. Par for the course for most 'soft' cones. Easy enough to work with, you could cross it a bit higher than the 175HQ, although I wouldn't myself. 😉 Either should yield a good speaker of their type.
I didn't realise the 830883 was still available after the havoc Tymphany have caused, but I see it's in stock in a couple of suppliers. Motor is definitely good; like the Monacor it's got a cone-edge resonance around 1.2KHz give or take. Par for the course for most 'soft' cones. Easy enough to work with, you could cross it a bit higher than the 175HQ, although I wouldn't myself. 😉 Either should yield a good speaker of their type.
Andrea, the two woofers are wired in series as I stated on my attachment in the heading. The actual modeled impedance, with 0.5 ohms added in series with the series-wired woofers to simulate the resistance of an inductor in series with the woofers, creates a nominal 7-ohm impedance. No, I did not choose a specific tweeter as that has nothing to do with the TL modeling (and I don't "do" crossovers). I just assumed you'd likely be using a tweeter with nominal 104 mm diameter mounting flange. Edit: The tweeter's center is the design center for a WTW TL, BTW.
Paul
Paul
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