Modyfying the parameters of a 15" woofer

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#21
noviygera said:
After a long search I could not find a 15" or 18" woofer with parameters am I looking for:

High Qms (over 20)
High BL
High Vas
Low Mms
Low Fs (under 30hz)
Low inductance

This is going to be a multiple driver 8-12 vented or T/L subwoofer for impactful, dynamic bass at very low listening levels.
Click to expand...

Qms doesn't matter at all. Frequency and time response depend on Qts.
Relax that restriction and you have lots of options. Look to short coil pro drivers.
 
#22
Ron E,

very interesting thank you for replying. Let me clarify please. I will be crossing over the subs at about 100Hz. And I have read that high Qms (or low mech damping) is very important for getting a "lively" sound from a speaker. Was this a referral to the "midrange" range and therefore it is not as important for bass?
I am trying to figure this out: Is it not true that the more mechanically damped a transducer is, the more "dead" it sounds because the mechanical damping is like puttting an absorber on the cone?
It will measure well but not make any music. Your thoughts?

Thanks,
Herman
 
#24
noviygera said:
Ron E,

very interesting thank you for replying. Let me clarify please. I will be crossing over the subs at about 100Hz. And I have read that high Qms (or low mech damping) is very important for getting a "lively" sound from a speaker. Was this a referral to the "midrange" range and therefore it is not as important for bass?
I am trying to figure this out: Is it not true that the more mechanically damped a transducer is, the more "dead" it sounds because the mechanical damping is like puttting an absorber on the cone?
It will measure well but not make any music. Your thoughts?

Thanks,
Herman
Click to expand...

You can have mine.
A high Qms driver will (when it's not connected to anything) ring. A low Qms driver won't.
Introduce an amplifier with a low output impedance (almost anything solid state), and the damping from the effective short circuit across the voice coil will mean it won't ring much at all. Notice how Qes is always very close to Qts: the electrical damping is (I've not seen a modern driver that's contradicted this) the dominant one.

What's your source regarding Qms - it seems like you're taking it to heart, so it must've been somewhere reputable...

A lively bass sound will probably come from one or more peaks in the frequency response, probably in the 60-100Hz range, giving visceral, chest thumping bass. See this thread for more.

Chris
 
#26
noviygera said:
Let me clarify please. I will be crossing over the subs at about 100Hz. And I have read that high Qms
Click to expand...

Qms=2*pi*Fs*Mt/Rms

Qms as a parameter is strictly defined only at the fundamental resonance, where in most drivers electrical damping dominates. The parameter Rms actually changes with frequency, so any attempt to use Qms to assign a "sound" to a driver is pure folly.

A myth. I know of a designer who talks about this - his preference for stiff cones and low loss surrounds is not a "bad" one, but it doesn't really translate to Qms as a T/S parameter. Certainly one can go too far with damping in curvilinear thin poly cones with thick, lossy surrounds and end up with "tupperware" midrange, but the opposite paradigm in terms of a straight metal cone with a low loss surround is just as bad. Most "real" designs are a compromise. The surround termination changes the breakup region...not the bass.
 
#28
chris,

>>What's your source regarding Qms,

The Audio Physics Speakers designer stated that in an interview. You can probably find that online. To me, it seems reasonable that the less damping of the cone, the more of signal is reproduced, I am talking about my personal theory here.

Jernejc, thanks for the Beyma recommendation, they are very interesting.

I have an idea. I will make an experiment by using two 12" woofers that have very similar response modeling in a box. WinISD, they model almost identically as far as bass rolloff, but Qms of one is double of the other. I will burn them in and A/B test them in an identical box and report my findings.
I am talking about these drivers:
Pioneer A30IR50-51F 12" Butyl Surround Woofer
Dayton Audio ST305-8 12" Series II Woofer

Herman
 
#35
For your reference: http://www.diyaudio.com/forums/mult...me-user-tell-best-bass-i-have-ever-heard.html

I remember John (or Nick?) has mentioned that there're both aluminum or non-metal materials for thier VC formers. Among them, the materials might be the only difference of the drivers' construction. The one with aluminum VC former has a feature as Eddie current shorting ring, thus providing brake force. And this reflects in the Qms (because of the passive nature). According to John (or Nick?), there's no difference in performance (sound quality) between the 2 materials. (The difference is the heat conduction... )

So that leads to a conclusion that Qms is irrelevant to sound quality.

I'd say it's pretty much in sync with what I've heard in many other cases. I can't find any certain relations between the bass sounds I like and the Qms of the woofers.

Again, for the bass sound quality, there're so many other factors to be considered, so many other problems to be solved. So, drop the Qms, step back, see a larger picture.
 
#36
Hi,

The best "box bass" i have heard for low level listening is the Onken and even better Onken W with Altec 416 drivers. If you want to go all the way, I would say LARGE horn or IB with low mass and large cones. I run a large horn integrated into a room corner in my basement and an IB with 4x15" in my living room and I would say both meets your (and mine) requirements. For the IB i would go for low mass and a Qt of around 0.5, not higher. I would also not stare at Fs to much, an IB can have alot of output below that and it is easy enough to electrically compensate for that.

BR,
Anders
 
#38
CLS said:
How do you compare that to your IB and horn ?

🙂
Click to expand...

Well...at low levels i must say that i would be happy with any of them. The Altec 416 in a good enclosure is very tuneful and really dynamic sounding. For higher levels i would pick the horn or the IB as i have it. In my set up i do have good response to around 16Hz, both in the horn and the IB and that can not be matched by the Onkens.

BR,
Anders
 
#39
tinitus said:
the cone 'rings' less with power amp ON ?

heck, I tried it just now
HUGE difference
with power amp ON, its almost like the box is filled with water

with power amp OFF, more like drumskin
Click to expand...

Amp off, Qms.
Amp on, Qts.

Since we listen to music with the power amp on, Qts is what matters.

Rms changes with frequency, it could be high at low frequencies and low at high frequencies. Again, despite the changes with frequency in Rms, the published parameter Qms is defined at just one point - driver resonance out of a box. Even putting a driver in a box changes Qms in ways that cannot be predicted by simple T/S theory.

Qms changes the electrical impedance at resonance, not the frequency or time response, unless you have a high output impedance amp - where you would get peaks at resonances - "added warmth", or even "punch".

Qms as a predictor of bass quality is junk science.
 
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