It's misleading to talk in terms of watts. A dynamic loudspeaker is all over the place impedance wise. Best to refer to Spl at a given voltage input. The usual reference being 2.83V RMS. It's sort of irrelevant that this happens to be 1W into an 8 Ohm resistive load.
And almost all audio amplifiers are voltage sources, so the voltage does not vary with load impedance. Current drawn will vary inversely with impedance.
Last edited:
AES Papers -- Official website of D.B.Keele
"35 "Comparison of Direct-Radiator Loudspeaker System Nominal Power Efficiency vs. True Efficiency with High-Bl Drivers," presented at the 115th Convention of the Audio Engineering Society, New York (Oct. 2003)."
I wish B&C could start to manufacture a 12 inch driver with short xmax (4 mm), extreme Bl, low mms, 50 - 60 Hz Fs and a Qes below 0,05 based on the 18IPAL motor.
Last edited:
It is possible to EQ this flat with a "normal" voltage amp and some DSP or analog EQ, or by using a current drive amp with an appropriate output impedance. For highly reactive loads i prefer current drive amps for DIY and class D for professional applications. PowerSoft and B&C has developed the IPAL technology based on this, so it is not only some strange guy from Sweden using Hornresp arguing about this.
This is what i have shown with my Hornresp sims. Hornresp is not flawed. My simulations are not wrong. It is basic physics.
Cheers,
Johannes
The distortion added by EQ to extend the FR of low Q driver will be far less than the distortion of a high Q driver playing without EQ at the same SPL. Active line level EQ can add inaudible distortion to the amp signal, while the distortion added by speaker level EQ will vary with the quality of the coil used, but it can be very low if you use (expensive) large wire gage, air core inductors. Even with cheap iron core coils I think the clarity will be better than a high Q driver with no EQ.
A high Q driver has a weak motor and surround that can't control or damp the cone. The lack of control allows exaggerated motion which makes high dynamic and harmonic distortion. This cone slop is what allows it to play low and loud without EQ. The price is poor transient response. While sloppy sine waves might be OK at 40Hz, up at 300Hz where you want to blend with your detailed mid driver you still have the slop and lack of detail, so the high Q woofer becomes a liability. It sounds too warm, all the time.
Servo drivers are a good way to go for OB because they have high Q driver which reduces power requirements when playing loud and low, but the servo system electronically lowers the Q so you still have detailed tone and punch.
Again, an efficient driver alone does not mean it is efficient where you need to use it. A compression driver can be 115dB 1W but will not be useful below it's intended bandwidth. The same goes for woofers. I agree that DSP does not add large amounts of distortion. This is another misconception. EQ is typically always a better option than passively padding a system to high levels. However, you simply cannot add EQ without increasing the applied power.
As an example, in this case here the the Dipole15 has a lower 1w/1m efficiency. However, it is far more efficient down low where it needs to be. At 30hz the difference is 6dB. You can EQ the response and boost it by 6dB. This then means the B&C still needs 4x the input power to get to that new EQ'd level. This is not as significant at 1W vs 4W but becomes very significant at 50W vs 200W or more. The higher the input power, the more the thermal distortion and the more flux modulation there is.
Regarding the higher Q driver, there is a point where the Q is too high and the woofer lacks damping altogether. I would agree that as you get to the point of Qts of 1.2 or higher that point has already been reached. The ideal Q is going to be .707 so staying within the range of .5 to 1.0 will still be quite well damped. Ask those who have stated that the Lotus Group Granada, Kyron Gaia or Kronos, or Soulsonic Impulse put out the best bass they have ever heard. Those drivers have a Qts of .68, which is nearly perfect for this alignment.
There are 2 issues which make this higher Q much more problematic, one which i discussed before. The first issue with MOST drivers that have a Q in that range is that the Q does not stay in that range. They have short Xmax which is easily reached and suspension that limits the travel too soon. At Xmax the Bl has dropped by 30% and suspension is often 2x as stiff as at rest. This pushes a Qts 1.0 driver up to Qts of 2.3 or more as soon as it is travelling to the short Xmax. Yes, this driver will greatly lack control. The same happens in vented boxes. A woofer can model decently with the small signal parameters but everything changes as the driver moves. This is when they become one-note, boomy, loose, etc.
Secondly is the low flux density in the top plate and pole. The lower the flux density, the more it modulates as the coil moves through the gap. It is an inductor for all practical purposes. Putting an inductor around the steel pole makes it become a strong electromagnet. The more current in the coil, the stronger the magnet. As this new magnet moves through the gap, it modulates, or pushes around, the permanent magnetic field. The lower the flux density, the worse this effect. The higher the input power, the worse this gets. This is why it is important to have a driver that is efficient in the range you need to use it.
This flux modulation is the BIGGEST issue with the motor having control over the woofer. This is why motors with more flux density tend to be lower distortion. The permanent field is stronger and less prone to modulation. Less power needs to be input to move the coil meaning the moving electromagnet is weaker. Flux modulation,Le(i), and non linear inductance, Le(x), are the only distortion elements that actually affect the current applied to the woofer. They create a reactive load for the amplifier which is very problematic.
The coil needs a stationary permanent magnetic field to "push off" of in order to position itself in time and space. When the supposed permanent field is in motion due to the coil modulating it, the coil can no longer be positioned when and where it should be. This leads to that loose, sloppy, uncontrolled bass that many associate with weak motors.
That all said, there is an even better way to eliminate both the Le(x) and Le(i). That is to force the coil to act as an air core inductor instead of an iron core. This is what we have done in all of our woofers. Adding the full copper Faraday sleeve to the pole instantly shorts all eddy currents that modulate the flux field essentially fixing it in place. While all shorting rings have benefit, most are limited in what they can do because of their position. The coil needs to be next to the shorting ring for it to have much effect. The sleeve on the entire pole is always next to the coil no matter where it goes in its travel.
You can see how the Le(x) is "flawless" in all of our woofers here. If you go through the site:
https://sites.google.com/site/drivervault/driver-measurements/15/ae-speakers-lo15/le-x
Once the inductance doesn't change with excursion and the permanent flux field don't move, the motor strength can simply be dialed in to the optimum Q for a specific application. For open baffles that is between .5 and 1.0 to get the best balance of damping factor and low F3 point. We then used an underhung motor which keeps the Bl very flat throughout the intended excursion. Add in a suspension that can travel nearly 2x as far as the electrical Xmax and the compliance doesn't change much either. As Bl doesn't drop wildly and Cms stays close to the same, the Q does not change. Add in the elimination of flux modulation, flatten the inductance curve, and you finally have a woofer that sounds the same at low levels as it does at high levels.
Servo woofers do have some good things about them. The main drawback is that there is some lag associated with the correction. If attention is not put into addressing the flux modulation first, you are now attempting to correct something that is a highly reactive load. The end result often is not very natural sounding.
I understand why you keep repeating this lie. You are making a living on Dipole 15 drivers (among others). Can you please be a little more up-front about this in your posts. I had no idea, and i kept wondering why you so stubbornly kept repeating this lie/misunderstanding...
If we accept the idea that David McBean (Hornresp), Don Keele, the engineers at PowerSoft and B&C is not trying to lie to us all (they have no vested interest, defending the Dipole15), then a simple simulation with Hornresp will clearly show the superiority of the B&C 15NW100 over Dipole15 (efficiency - spl/w/m @ 30 Hz and above). Please lie all you want. You only hurt your own reputation... But it will not change that fact.
I hope everyone who reads this fires up Hornresp for some quality-time comparing high Qes, low Bl drivers like Dipole15 against high Bl, low Qes drivers like B&C15NW100, 15TBX100, Beyma 15P80Nd/Fe etc...
I don´t care much about keeping this discussion going. The facts are out there. Hornresp is a short download away, and most manufacturers of pro drivers publish TS parameters online.
In my world is 88 dB @ 30 Hz from 0,6993watts not more efficient then 88 dB @ 30 Hz from 0,4328 watts - both drivers simulated in a 10000 cm2 baffle (simulation from earlier in this thread).
Cheers,
Johannes
Last edited:
I would appreciate not being called a liar simply because you have no understanding of basic loudspeaker models. As others have pointed out as well, you are not applying power into a resistor, you are applying power into a loudspeaker. It is only a shame that you are trying to misguide others with your clear ignorance. We are talking the most basic modelling of enclosures here and I have provided models with many pieces of software that are being properly used. End of story.
If you wish to provide a B&C 15NW100 we can simply build the baffle and measure. This will verify the results.
Last edited:
Do you have any data/references supporting this bold statement ?
This is a typical "intuitive explanation". AFAIK, there is no data to support it (apart from the rising Q phenomenon at high excursion John mentioned upper in this thread).
Did you check the shape of the impulse response Martin J. King published here : http://www.quarter-wave.com/OBs/OB_Design.pdf ? There is no trace of transient response degradation for the Alpha 15A driver with Q>1.0
300Hz is several octaves away from the driver's Fs, so Q becomes rather irrelevant.
For test, just a plain baffle. Maybe double the with and hight of the woofer diameter.
1 meter x 1 meter baffle would be fine. After first test you could add some wings to eliminate some cancelation.
A fairly small plain baffle will do good quite high in frequency, and a large baffle or some kind of open baffle will have better low freq efficiency but will not extend that high in frequency as a small plain baffle.
1 meter x 1 meter baffle would be fine. After first test you could add some wings to eliminate some cancelation.
A fairly small plain baffle will do good quite high in frequency, and a large baffle or some kind of open baffle will have better low freq efficiency but will not extend that high in frequency as a small plain baffle.
I'm not sure what you say here. A 1x1 meter baffle will work below 340 Hz, not above. You can use as small a baffle you wish for bass, its just a matter of max SPL and eq.
And the drivers mentioned are 18", but less can do it. I have heard good results with 12" and 15" on very small plain baffles. They didn't work below 40 Hz, but it's ok for normal pop and rock and most other music. Personally it's not enough for me, since I also love deep organ.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.