Hello, looking in this data sheet
http://www.scan-speak.dk/datasheet/pdf/21w-8555-00.pdf
i see for the first time a parameter ... ratio fs/Qts
What does it tell ?
I am quite curious being obsessed by both ... fs and Qts i mean.
Thanks and regards,
gino
http://www.scan-speak.dk/datasheet/pdf/21w-8555-00.pdf
i see for the first time a parameter ... ratio fs/Qts
What does it tell ?
I am quite curious being obsessed by both ... fs and Qts i mean.
Thanks and regards,
gino
This rough ratio is taken for the choice of enclosure.
<40 TML
40<80 closed
50<100 Bandpass
80<120 BR
>120 is good for hornsystems
It's only for a first look which enclosure is good working with the chassis.
The only way I know for what you have to take this ratio
Thanks a lot for your kind reply.
I was thinking that the Qts was enough for this choice.
In the sense that low Qts > bass reflex
Medium-high Qts > closed
I was clearly wrong.
Kind regards,
gino
Oh, it seems to have several theorys about choosing an enclosure
There are lists by using only Qts, another one is this fs/Qts ratio.
A better one should be the Efficiency-Bandwidth-Product EBP.
It's a ratio of fs/Qes...
I work with a simulation-program called LASIP.
The results had been very good and worked very well for me.
Doing the calculation by hand is so annoying that I gave it up
I think everyone on this forum will have it's own theory about choosing an enclosure.
If you have time, play a little with the values and different chassis and look at the results, how much they will differ.
Have fun!
Kind regards from rainy Germany
There are lists by using only Qts, another one is this fs/Qts ratio.
A better one should be the Efficiency-Bandwidth-Product EBP.
It's a ratio of fs/Qes...
I work with a simulation-program called LASIP.
The results had been very good and worked very well for me.
Doing the calculation by hand is so annoying that I gave it up
I think everyone on this forum will have it's own theory about choosing an enclosure.
If you have time, play a little with the values and different chassis and look at the results, how much they will differ.
Have fun!
Kind regards from rainy Germany
Your table for fs/Qts ratios is also valid, it determines which ratio is the best for a particular enclosure. Ratio fs/Qts alone determines a range how deep loudspeaker will go.Oh, it seems to have several theorys about choosing an enclosure
There are lists by using only Qts, another one is this fs/Qts ratio.
A better one should be the Efficiency-Bandwidth-Product EBP.
It's a ratio of fs/Qes...
I agree with you, software simulations are absolute necessity.
Kind regards from sunny Macedonia
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Thanks again. Now i understand perfectly.
Actually it is in the datasheet of a woofer and this makes perfect sense.
Kind regards,
gino
This ratio also tells you something about a driver's likely performance even if your particular driver has different values for fs and Qts as compared to the manufacturer's published specifications. Over a production of drivers there will be variations in individual values for the T/S parameters, but as long as the ratio is pretty consistent, as well as the value of Vas x fs2, all of those drivers will perform very much the same in the same enclosure.
Paul
Paul
Thanks very much for your explanation
In very basic terms, am i wrong if i say that i cannot expect significant emission from a driver below its fs ?
Moreover that the lower the Qts the higher the quality of the driver ?
For me the Qts is a little like the ratio weight/power in a car ... the lower the better
I know that i am trivializing a bit the all issues but ...
In this way the higher the ratio fs/Qts the better the woofer ?
With 65 being a good ratio and let's say 100 an excellent ratio (it would mean for example 20 Hz for fs and 0,2 for Qts. Excellent values indeed)
Thanks a lot and kind regards,
gino
You can get significant emission from a driver below its fs but at some point it may not be quality emission. Personally I prefer to use drivers with a Qts range of 0.35 to 0.50 because they almost always work well in some sort of TL, the only the of bass enclosure I care to design and build. If I would be forced to use a driver out of that Qts range, I'd much rather use one with a higher value than a lower value. I don't particularly care what the fs/Qts ratio is, however, other than what I expressed about consistency in a production run (I left out "run" in my previous post). In end, though, there's no single thing that makes or breaks a driver or a design because there are so many compromises to deal with.
Paul
Paul
Is in not that simple..
I recommend you to read "Loudspeaker Design Cookbook" by Vance Dickason.
For closed box the lowest possible f3 (frequency at which SPL is 3 dB down, i.e. the beginning of low end rollof) is 0.707fs/Qts.
For vented box f3 is about 0.4fs/Qts (with bigger box), but it depends on Qts.
With high fs/Qts you can expect very high f3 (no low bass).
Lower Qts in vented box has "tighter" sound.
From my experience in designing and building TLs, a high-Qts driver will not necessarily have a high f3. Once you determine the optimum system tuning frequency for a specific driver, which means for me an overall flat response, f3 is determined by how much volume is in the box (the line). I definitely don't prefer to use high-Qts drivers, not because they can't produce low bass, but because it's often impossible to achieve a response shape I find acceptable and the box needs to be larger than I want.
Paul
Paul
True... in fact, with high Qts very low f3 is possible, but, as you said:
High fs/Qts ratio has no low bass. High ratio comes from low Qts, or high fs, or both.
WRONG. You cannot expect significant emission from a driver below ~0.4 * Fs/Qts (in a BR box, higher if closed). Fs on its own does not mean much. (Neither does VAS, by the way - a previous post is right in quoting VAS*fs^2 as the relevant number).
WRONG. Low Qts just mainly means more motor strength (in itself often a good thing, but sometimes you can have too much of a good thing...), and in some cases (often to a lesser extent) high mechanical damping due to friction/stiction (NOT a good thing).
WRONG. If you look at the physics and do the proper maths, a better analogy to the power/weight ratio that you imply is the efficiency: eta0 = (ρ0/c) * (Sd^2/Mms) * (Fs/Qes)
NO. To put it bluntly, the higher the Fs/Qts ratio, the LESS it is a real Woofer and the MORE it is a MID-range driver.
As always, it is not a question of aiming for the maximum possible value of any given parameter, but for the best possible compromise for the intended application.
Marco
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Hi and thank you very much for your valuable reply.
If i understand well what i said is valid only for Qts=0.4.
Very good ! thanks !
I have to explain. I like very much Scanspeak woofers and lots of them have low Qts ... so i was thinking that this is a good thing.
They are also very expensive.
I understand now that this is not a general rule. Thanks !
this is too difficult i am afraid. I am just able to read figures.
I do not know what is behind that.
But anyway i think i have got the message.
Yes and thanks. I am using now this calculation software and i see that if fs is high to get bass is really difficult. I have just put some values to try.
So a low fs is important for a woofer.
For me the most important thing is low distortion. I believe in accuracy and distortion is the exact contrary.
I prefer a limited bass response, for instance, but a clean and controlled bass.
I have also posted a question in the lounge because there is a school saying that only closed speakers can give an accurate bass.
I would like to understand if this is true because it is a basic criteria for selecting speakers.
It could be a urban legend ... i really do not know.
I have only understood that low Qts is for bass reflex and medium for closed speakers. High is more critical i suppose.
But the comment on the fs this is important.
For instance i have never seen a fs < 50 Hz for 6.5" woofers (i am looking at these currently).
So when i see 2 ways with woofer of this size and reviewers mentioning how good the bass is i now wonder ... of what bass they are talking about ?
At least 8 and better 10" would be a good point to start of some real bass i think.
Thanks a lot again for the very kind and valuable advice.
Kind regards,
gino
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Most people may not think or agree with me on my interpretation of TL's,
yet I do agree with Paul here (et al) that higher Qts does not prevent low bass. Example is a MLTL I'm currently testing (an experiment) where the drivers Fs/Qts ratio is 86, Fs is 40 (run in, 41.5 static. Spec 42Hz ±15%) and the Qts is ~0.49 and a Vas of 29.5 liters, quite high for it's size. Plays a well from 26Hz up with a 6.5"woofer Xmax of 6mm at rated power in a ~76" line with a vb of ~27liters and a cross sectional area roughly equal to the Sd.Wife was impressed with the 113dB @2.5m (tangential) 30Hz sine wave test at listening position. At these positions there is an equilibrium in the room modes at this frequency, so no boost via room or EQ was used to achieve result. Below 26 is not usable as distortion is quite audible, yet low end is very well damped to 16Hz virtually eliminating the need for a high pass filter on the bottom end for music use (not HT)
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In the broad sense of a distortion being anything added or subtracted vrs the input yes. As it is most commonly measured Geddes has scientifically shown to be meaningless unless very high (>25).
dave
Another example.
Fs/Qts ratio is 172, Fs is 91 and the Qts is 0.53 and a Vas of 2.3 liters.
With room-gain, in a Woden designed ML-TL into the high 30s, low 40s. Anechoic sim attached. I am very pleased with the performance of these little 4" Peerless.
To evaluate a woofer, i don't pay attention tothe numbers, but look at the sims... i have been surprised more than once.
dave
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It is quite surprising, astonishing at times, roving through a zillion sims of potential candidates. It's that, now wipe that grin of your face and cut some wood already, kind of feeling
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