Ace bass guide?

[Boscoe]

I'm interested in this so does anyone know of a guide that includes all formula and such?

Thanks
Boscoe

[bjorno]

Originally Posted by Boscoe

I'm interested in this so does anyone know of a guide that includes all formula and such?

Thanks
Boscoe

Hi, Scroll down on this thread and click on the suggested 'similar threads'
or do a search:

ACE-bass amplifier design

Enclosure for high Q driver

A student report (Sorry in Swedish!! ) I found to be very good:

http://users.student.lth.se/et06ps2/..._Soderberg.pdf

One more:

Use Linkwitz Transform to reduce size of Enclosure?


b

[Trevor White]

Originally Posted by Boscoe

I'm interested in this so does anyone know of a guide that includes all formula and such?

Thanks
Boscoe

The original AES paper was a good guide. Also there was a subsequent AES paper which described a design using it.

[CharlieLaub]

Not a design guide per se, but Stahl's patent,
US Patent # 4118600 Loudspeaker Lower Bass Response Using Negative Impedance and Resistance Loading, can be downloaded here:
PAT2PDF - Free PDF copies of patents: Download and print!

Enter the patent number and click on "fetch patent".

-Charlie

[CharlieLaub]

I have done a lot of modeling and thinking about ACE BASS over the years, although I have not actually built a sub using this circuit. I have no doubt that it works as advertised, more or less. There are some details to be considered, however...

Keep in mind that ACE BASS is essentially a fancy boost circuit! As Svante will tell you, the passband efficiency of the driver is unchanged. This does not mean that you can model the driver with the "modified" TC parameters in a box modeling program and assume that the entire response is at the raw driver's passband SPL. It is not. This is because the low frequency SPL of the driver is essentially "equalized" up to the passband level by ACE BASS by applying additional power to the driver. That's it! No magic.

ACE BASS "changes" the driver parameters by providing a power lift with some phase shift as well - these are the only things that can change in the electrical circuit after all! This is all implemented using a feedback network, which allows the parameter modification of the ACE BASS to be possible, but also brings some problems if/when the real driver Rdc (voice coil resistance) changes, e.g. when you deliver a lot of power to the driver and the voice coil heats up. Because the entire feedback scheme is based on near full cancellation of the driver's Rdc, when Rdc increases with V.C. heating all of the modified parameters change as well. This causes drift in the performance of the system away from the target, and is one of the main "problems" with the ACE BASS system, in my opinion. There have been many reports of people successfully building and using the circuit, however many of these just use it for a closed box system, for which the Linkwitz Transform would be simpler. The LT does not suffer from the performance drift of the ACE BASS but can only be used for CB systems. The ACE BASS is the only circuit that I am aware of that can be used with vented or passive radiator systems, so it definitely has a niche there. You can just use an amplifier with negative output resistance to "reduce" driver Qes, but this does not extend the response like ACE BASS or the LT.

The other main "problem" with ACE BASS is that in theory it requires that Rdc is completely canceled by the amplifier's negative output resistance. This can often result in an unstable system that goes in to run away feedback, so often only some partial cancellation can be achieved. I believe that this is due to the inductance of the voice coil creating a high-Q circuit within the feedback loop of ACE BASS, so using a low inductance driver (or multiple drivers in parallel to reduce inductance) may make this a non-issue. But when only partial cancellation of Rdc is used to increase stability, ACE BASS may not work well, although exactly how much cancellation and stability are achieved, and the resulting performance of the ACE BASS circuit, are not crystal clear to me. Maybe Svante can comment on this here?

If you use the modeling program Basta!, which has built in modeling of the ACE BASS circuit, you can see some of these issues that I have described above.

I am always curious to follow the latest ACE BASS news, so if you do build the circuit and can do some measurements and give your impressions, please post about it!

-Charlie

[Aucosticraft]

Originally Posted by bjorno

Hi, Scroll down on this thread and click on the suggested 'similar threads'
or do a search:

ACE-bass amplifier design

Enclosure for high Q driver

A student report (Sorry in Swedish!! ) I found to be very good:

http://users.student.lth.se/et06ps2/..._Soderberg.pdf

One more:

Use Linkwitz Transform to reduce size of Enclosure?


b

When I saw the title , I was sure Bjorno must be here would like to hear more from you.

[bjorno]

Originally Posted by Aucosticraft

..would like to hear more from you.

Hi Acousticraft,

You will!

FYI adding links to a Swedish forum where the ACE-Bass principles are discussed. Use Google Translate!

http://www.faktiskt.se/modules.php?n...wtopic&p=61803

http://www.faktiskt.se/modules.php?n...er=asc&start=0


http://www.faktiskt.se/modules.php?n...208&highlight=



A Quote:

From the last URL using Google Translate:

Svante:

If we start with the closed box, there are usually two suspensions involved. It is the box spring (= air suspension) and the suspension springs. The box springs a bit more ((stiffer))when the cone moves inward than when it moves outward, it is therefore nonlinear and so in a very predictable way. Cone's suspension is also nonlinear, but in ways that vary between elements.

Distortion of these nonlinearities give rise to the greatest at low frequencies, partly because the excursion is greatest when, partly to the mechanical impedance (which is the steering angle with the applied force) is dominated by the suspension at low frequencies. At higher frequencies the impedance is of course mass-controlled and which allows suspension only weak influence of impedance and movement.

With ACE (still sealed box) adds further suspension, and the suspension is as linear as the element's power factor. If the suspension is allowed to dominate over lådfjädring((the air-spring)) and suspension springs, you get typically lower distortion than without ACE. Givertvis can be compared with a larger box without ACE, but I think that the comparison is unfair. The only reasonable approach is well to compare equal-sized boxes with each other.

In the case of bass reflex, it is difficult to see the connections, but ACE linearized by at least konupphängningens((the cone)) suspension. Box springs are not affected as directly by ACE, but the box springs affect on the other hand, no more than without ACE.

... but of course, makes((if you make)) one little box, you get problems, both with and without ACE. It is also com((mon) (even more when using) LT.

One problem that ACE brings is increased propensity for distortion due to nonlinear talspoleinduktans((Voice-coil inductance)). In the early models (eg, A4-14, B2-50 and B4-200) ((,therefore one of the driver was turned back to front))so turned to be an element back to front.

((= added by b))

b

[CharlieLaub]

Originally Posted by bjorno

A quote from:
http://www.faktiskt.se/modules.php?n...208&highlight=

In the case of bass reflex, it is difficult to see the connections, but ACE linearized by at least konupphängningens((the cone)) suspension. Box springs are not affected as directly by ACE, but the box springs affect on the other hand, no more than without ACE.

b

This is the main advantage of ACE over other circuits, like the LT, that boost power to equalize the response.

Because the driver is in the feedback loop, it is part of the system including all of the driver's electrical and electrical-equivalent-of-mechanical "components". As the quoted post mentioned, and I am now re-iterating, if the ACE BASS circuit is configured to drastically reduce the effective Vas of the driver (increasing the effective compliance of the driver suspension), it puts a large linear capacitance (from the capacitor in the circuit) in parallel with a smaller non-linear capacitance (from the driver's suspension compliance). Because the driver suspension's non-linearities are a large contributor to the distortion of the driver, these are reduced because the ACE BASS's capacitance is much larger than the capacitance from the driver suspension, and so the non-linearity of the latter is made smaller relative to the total capacitance representing the suspension compliance.

But this does not reduce the non-linearity of the air-spring inside the box, however the larger you make the box, the more linear the air-spring becomes, because the ratio of cone displacement (excursion times cone area) to the volume of the box goes down. This idea can be turned in to a mantra for all subwoofer designs: if you want lower distortion, make the box bigger. If a circuit could differentiate when the cone is compressing the air in the box and when the cone is expanding it, and could apply different signals to compensate for the different behavior of the air-spring during the in and out parts of the motion, the effect could be compensated for. Otherwise, you cannot remove this effect, only minimize it with a larger box.

-Charlie

P.S. I forgot to mention that the ratio of driver cone displacement to box volume can also be modified by using a smaller driver! Since you can use a smaller driver when you switch from a closed box system to a vented one, this is another route to lowering distortion arising from air-spring non-linearity: switch from large driver in a closed box to a smaller driver in same size or larger vented box. The other approach is to stuff a closed box wiht fine fibrous material (e.g. fine polyester stuffing), which results in an "apparent" increase in box volume.