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Sub-Woofer Question - AudioPhool Experts (which I am not - an expert, that is).




 
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Author Topic: Sub-Woofer Question - AudioPhool Experts (which I am not - an expert, that is).  (Read 23567 times)
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W1RKW
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« Reply #50 on: December 26, 2009, 07:55:37 PM »

Don't forget the input end.... Source material and the input device.
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Bob
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« Reply #51 on: December 27, 2009, 09:15:22 PM »



Yet another qwazy sub woofer company:

http://www.rythmikaudio.com/products2.html

...submitted for your approval... - Rod Serling

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_-_- bear WB2GCR                   http://www.bearlabs.com
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« Reply #52 on: December 27, 2009, 09:18:44 PM »



The mother lode:

http://www.diyaudio.com/forums/subwoofers/

of course you'll have to browse back in time to find projects and ideas that correspond to what we've been discussing...

               _-_-bear
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ke7trp
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« Reply #53 on: January 14, 2010, 05:36:31 PM »

Steve. I got this in today. If you want it, you can have it real cheap. I have two sets.  I just tested it. Its real heavy and has real solid Low end. Very compact. Plenty of punch.

http://www.anthonygallo.co.uk/pages/products-subwoofers-mps150.php
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flintstone mop
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« Reply #54 on: January 15, 2010, 09:47:34 AM »

Very intersting thread and the many flavors of music reproduction.
I may have missed something, though, has Steve ever mentioned his taste in music? I do know that he is lover of the very low end of audio. I don't know if this is just some criteria picked out like a "spec sheet" or if he listens to classical music and wants to feel the lower notes of a pipe organ or would this be for a home theater app and the effects of a dinasour tromping through the forest?Huh dunno
And this has not been "audiophoolery" coz we are basically looking for a design of a speaker to reproduce a certain effect in the listening environement.

Fred
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Fred KC4MOP
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« Reply #55 on: January 15, 2010, 04:57:11 PM »

Long Post Warning!!!!!!   Long Post Warning!!!!!!   Long Post Warning!!!!!!   Long Post Warning!!!!!!   Long Post Warning!!!!!!
Hi All,

Have to jump in on this one. I noticed a few of you saying "bigger is better". That's an old notion based on old technology. I will elaborate...

Drivers years ago had many limitations, low power handling, limited excursion due to materials available, poor heat dissipation, low efficiency (electrical), etc. Large boxes with huge mass and diameter drivers where the solution with the available driver choices.

The compromises made were, large diameter (and high mass as a result) moved alot of air ... but very very slowly. High damping factors are required for the amplifiers to control the loads and to overcome momentum of the mass of the drivers. This was difficult to achieve due to amplifier designs and the gauge of speaker wire at a given length; not to mention the associated costs. Older designs were "slow" or "tubby" when examined in the time domain.

Another compromise was large boxes were required, due to the fact that the larger the box the lower the resonance. Older driver designs which had small excursion ratings (Xmax) will self destruct over time if driven below the resonance of the box design; whether it is a closed box or ported. So to achieve low frequency response you needed a large box. Another problem associated with large boxes is in the external cabinet stiffness. External resonance (vibration) of the boxes is radiated and at various phase angles from the cabinet. This causes unpredictable acoustic additions and cancellations within the listening space. Think of it like a longer span on a truss or i-beam. The longer the length the less stiff it is. These factors are difficult to control without massive and extensive internal bracing or extremely stiff cabinet materials (like concrete for example). Additionally internal bracing lowers the internal volume of the box, forcing the box to be even larger.

Another factor is in sound pressure levels and the ability to compensate for Fletcher-Munson curves (equal loudness contours). At lower frequencies human perception (whether aural or tactile) is much lower than at higher frequencies. Below 100Hz most of this perception is tactile in nature (felt rather than heard). Furthermore the lower you go the more tactile it becomes. To overcome this, large diameter drivers were employed to "move more air"; to increase the SPL (sound pressure level) output of the loudspeaker system (this also forced even larger cabinets as a result, BTW). Power and driver efficiency now also become a limiting factor.

Power was limited back in the day. Finding an amplifier over 200w for instance was difficult and expensive. So loudspeakers were made to be acoustically efficient. Porting or even horns were employed to boast efficiency, but efficiency is a compromise that limits other factors, such as speed, frequency response flatness, phase coherency, and a host of other factors. Additionally, even if the power was available, the drivers electrical efficiency (the ability for the motor to covert the electrical energy into kinetic work) was very low.

Another response to this was that users of these systems, in order to get more perceived output, placed their speakers in the corners of the room. Now while this did increase the perceived levels, it would caused sever instability in the frequency response of the system due to phase incoherency. The coupling effects of a loudspeaker to a surface is such that while certain frequencies (particularly low frequency) are boosted while others are cut. The response curve becomes very non-linear the closer you come to a surface with a loudspeaker. This effect is doubled or tripled when we are talking about a corner in an enclosed space. So while the perceived loudness is increased, it is only happening at certain frequencies, and in fact lowered at others. Furthermore, since these issues are related to phase incoherency they are not easily correctable by room equalization in terms of amplitude response manipulation.

Many other compromise solutions have been employed over the years to overcome or side step these limitations in technology. Some worked better than others, but all had shortcomings and side effects. The need was there to improve the basic technology. Over the years drivers and cabinets have improved due to advances in materials. This allowed the important parameters to be improved and better uncompromised performance levels could be  achieved. Some of these are improved magnetic materials & structures, more durable and flexible surround materials, higher power handling techniques (in drivers), stiffer cabinet materials, higher power levels and efficiency in amplifiers, smaller amplifiers at these higher levels, etc.

One early attempt at overcoming the prevailing limitations in the motor structures of drivers was tried, with some success, by ServoDrive in the Contrabass model. It utilized an industrial servo motor to move the cones of two opposing drivers. It was used primarily for live sound application and scientific purposes. (note: Pink Floyd used these for a while in its live shows). Here's some images:




While this system was able to produce significant low frequency information down to 16Hz (-3dB at 22Hz) it was prone to mechanical failure due to the belts and rods used to move the cones. But when it worked ... IT WORKED WELL!!!

Damping factor is an often overlooked issue in low frequency reproduction. Three factors effect this parameter: the amplifiers own rating (output impedance), the various impedance loads of the loudspeaker system (whether it is reactive or more resistive) and the gauge and length of the speaker wire (resistance). Assuming one has an amplifier with a high damping factor ability, locating the loudspeaker any distance from the amplifier would force an increase in wire gauge proportional to the length. It is important to use loudspeaker cables with sufficient gauge (thickness) for the length being used. The resistance introduced by inadequate cables reduces both the output power and the motion control of the loudspeakers. The latter occurs because the damping factor decreases as the cable resistance increases. This is very important because the amplifier’s excellent damping factor can easily be negated by insufficient loudspeaker cables.

Incidentally, larger drivers tend to be more reactive than purely resistive, complicating the damping factor curves at various low frequencies. In most situations, damping factor is high enough so as to not introduce significant distortions. This does become problematic when thin speaker wire is used over long distances to feed a loudspeaker. The resistances added to the system are significant enough to swamp the effects of a low impedance output amplifier. So while damping factor is an issue it is not as critical as other parameter discussed here. I only mention it since the impedance at lower frequencies vary quite significantly in most loudspeaker systems especially near and below cabinet resonance. Additionally, older larger drivers tend to be more reactive in their impedance than resistive.

Ummm ... and take notice: no mention of OFC speaker cable here!!!  Grin

With the advent of small very efficient amplifier designs this whole thing becomes a moot point since one can now place the amplifier inside the loudspeaker. This is a common practice these days.

Also, smaller diameter lower mass drivers with high Xmax (excursion) have been developed. It is not uncommon to find subwoofers with 12" drivers operating well below the cabinet resonance these days. The limiting factors forcing large cabinet sizes have been mostly overcome due to advances in driver design. These include longer excursion, high power handling, more efficient magnet/motor structures, lower mass. With the addition of very high power amplifiers built into the cabinets other limiting factors have been overcome. Additionally, the active electronics inside cabinet can be designed to operate specifically for the subwoofer system. For instance some manufacturers have added analysis systems right into the subwoofers to adjust parameters like phase alignment, room correction, ELF control and limiting design specifically for the subwoofer. One good example of this is some products by JL Audio in its Fathom series. I have some experience with the 12" version (F112) of this sub. Here's an image:


This particular system measure 18.5" x 15" x 17.6" and has a measured frequency response of 21-119Hz ±1.5dB with the -3dB point being 19Hz. The internal amplifier can deliver 1200w RMS of power, short term.

It is now possible to build small subwoofers that have extended low frequency ability; as low as 15Hz. And do so with high output and very flat phase and amplitude response. One caveat: This is all based on anechoic conditions ... read on ...

Bear in mind, all of this is modified by the room, which is really the dominant limiting factor. No room in the average home is anechoic in nature. Real world issues take precedence. Room effects on low frequency are almost impossible to overcome or even predict, which is why anechoic measurement is important (as well as the previously mentioned active electronics). The anechoic measurement gives a starting point and a reference of performance, which is used by the active electronics. Internal volume, physical dimensions and and shape of the room effect low frequency performance. Most homes do not have ideal rooms for this type of audio performance. Since there is a point of reference, in the form of an anechoic measurement, the active electronics applied here helps modify the performance of the sub to bring the sound closer to the known anechoic ideal within a real world room.

BTW, in the sound reinforcement world it is not uncommon for most subwoofer systems to be based on small drivers with large excursion, usually 12". This is becoming much more prevalent these days at the top pro level, especially in line array systems. Most subs are self powered and "flown" usually at the top of the Mid/H line array. This is an example of a line array with 12" based subs.


Of course, extreme low frequency information (40-35Hz and lower) are usually avoided in this application due to masking effects in large spaces. This is not the case in home systems where open microphones are not in play, so low frequency extension, as low as possible, is preferred.

All of the above is not audiophoolery. It's basic simple physics ... or not so simple physics as it were.  Smiley

John
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« Reply #56 on: January 22, 2010, 06:56:52 PM »



The Servo drive is not dead - Tom Danley still makes subs...

Here's a driver for Steve:

http://www.diyaudio.com/forums/swap-meet/156894-maelstrom-x-18-subwoofer-drivers-w-warranty.html

                   _-_-bear
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