Why Aperiodic Bass Loading?

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dodgealum

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Why Aperiodic Bass Loading?
« on: 4 Nov 2010, 08:17 pm »
Lou:

I've been meaning to ask you this for a while and even more so since I've gotten the AP crossovers and heard what they have done to the bass performance of my DA-1.1's. What is aperiodic bass loading and why did you choose this design for your loudspeaker systems?

Daedalus Audio

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Re: Why Aperiodic Bass Loading?
« Reply #1 on: 5 Nov 2010, 08:50 pm »
Lou:

I've been meaning to ask you this for a while and even more so since I've gotten the AP crossovers and heard what they have done to the bass performance of my DA-1.1's. What is aperiodic bass loading and why did you choose this design for your loudspeaker systems?

Mark,  I first started using this years ago with my pro cabinets. essentially there is a restriction in the port (fabric/ dacron etc.) which makes the cabinet behave differently at different frequencies. ie: more like a sealed cabinet above the tuning frequency and then open like a full port at & below the tuning frequency.  this works very well with the short throw drivers which I have made to my spec, and is one of the reasons people usually have little problem with 'boominess' from the speakers. also I find it keeps everything cleaner and more controlled.  it is one approach that works particularly well with certain types of drivers.
hope this answers the question
thanks,
lou

dB Cooper

Re: Why Aperiodic Bass Loading?
« Reply #2 on: 5 Nov 2010, 09:28 pm »
Speakers that are in cabinets loaded this way also (can) have  flatter impedance curves, making them easy to drive. It is not unusual to see impedance peaks to 64 ohms at the bass resonance freq, whereas the Dynacos peak at just above 16Ω IIRC, about a quarter of the  spread seen in many systems. The best known example, the Dynaco A-25, was tuned by adjusting the amount of fiberglass in a slot loaded port while feeding a low frequency square wave through the system, and was renowned for its tight, well-controlled bass. This may have been just as much due to the easy load it presented to the driving amp as acoustic factors.

Mark Korda

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Re: Why Aperiodic Bass Loading?
« Reply #3 on: 5 Nov 2010, 09:39 pm »
Dodgealum,check out Madisound or Parts Express for Scan Speak.They sell  an aperiodic vent for less than 10 bucks.I've used them and there great.You install them in a sealed box instead of a port which the bass reflex uses.It works by reducing the maximum impedance at the box resonance by at least 50%.This results in clearer,better defined bass with more amp power and control in the lower frequencies.It also allows the use of a driver in a smaller than optimum sealed enclosure.I copied this right out of the ad in Parts Express....hope it helps....Mark Korda

Daedalus Audio

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Re: Why Aperiodic Bass Loading?
« Reply #4 on: 5 Nov 2010, 10:05 pm »
our systems do have very flat impedance curves. about 6 ohms +- 1 ohm above 100hz and a smooth rise below 100hz to about 10oms. much of this is due to very careful crossover design as well as the porting.  btw I long ago ditched "tubes" for vents. all my ports are made with 3/4" baltic birch ply so there is no energy loss etc.

thanks,
lou


dodgealum

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Re: Why Aperiodic Bass Loading?
« Reply #5 on: 9 Nov 2010, 03:56 am »
Thanks, Lou. I've always wondered how this design differs from a sealed or ported box. One of the many things that distinguishes your loudspeakers is how natural the bass sounds.  Now I understand a little bit better how you achieve this--thank you!