Passive means for bass extension ?? - diyAudio
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Old 13th October 2012, 12:02 AM   #1
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Default Passive means for bass extension ??

Hello all,
I am looking for some ways to extend the low end of a sealed bass unit, at the cost of efficiency. I know of the large capacitor trick, but that is not enough extension.

On the Manzanita thread in diyaudio, a large inductor giving a 1st order low pass filter well below 100Hz has worked wonders for a dipole. This not only sounds great but on simulating with Martin's passive U-frame sheets looks absolutely flat. I tried to simulate the same idea with a sealed cabinet, as the low end rolloff is similar though not the same as a dipole. Used Martin's sealed passive TL sheets but not even close to a flat low end response. Tried Jeff Bagby's Passive Crossover Designer...no luck.

Is there any other passive contouring trick to extend the LF end of a sealed cabinet.

Thanks.
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Old 13th October 2012, 12:29 AM   #2
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One classic technique used to extend bass response (at expense of eff.) is to add mass to the cone. This was elegantly done on a commercial scale years ago by Peter Snell in his infamous Model A and others. He poured resin around the dust cap which solidified. It lowers Fs in proportion to the amount of weight added up to a point.

Look at the picture on the last page of the download at this link. http://www.classicspeakerpages.net/I...showtopic=4762
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Last edited by speakerdoctor; 13th October 2012 at 12:32 AM.
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Old 13th October 2012, 12:44 AM   #3
sreten is offline sreten  United Kingdom
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Hi,

For a sealed cabinet your best bet is a passive 1st order step filter at line
level, which usually interacts with other high pass sections so +12dB
might end up being only +6dB, or an active peaking 2nd order high
pass, can be build around the line amplifier or power amplifier.

There is no passive EQ at speaker level that works well for bass other
than proper baffle step compensation AFAIK. Sealed and vented boxes
impedance peaks prevent any form of passive low bass manipulation.

rgds, sreten.
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Old 13th October 2012, 12:49 AM   #4
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Quote:
Originally Posted by sreten View Post
Hi,

For a sealed cabinet your best bet is a passive 1st order step filter at line
level, which usually interacts with other high pass sections so +12dB
might end up being only +6dB, or an active peaking 2nd order high
pass, can be build around the line amplifier or power amplifier.

There is no passive EQ at speaker level that works well for bass other
than proper baffle step compensation AFAIK. Sealed and vented boxes
impedance peaks prevent any form of passive low bass manipulation.

rgds, sreten.
Are you referring to an upstream, line level BSC filter? Here's a link to one designed for a vintage Advent speaker (closed box). What it does basically, is eq the mid to high range, bringing it down so the bass is in better balance with the rest of the response.
http://www.classicspeakerpages.net/I...showtopic=2692
Check out post #133 and #135 (schematic of the LL BSC circuit)
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Last edited by speakerdoctor; 13th October 2012 at 12:52 AM.
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Old 13th October 2012, 12:58 AM   #5
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by speakerdoctor View Post
Are you referring to an upstream, line level BSC filter?
Hi,

Very leading question, and of course I'm not, though its a valid approach.
It misses the point completely that BSC can easily be implemented passively.

rgds, sreten.
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Last edited by sreten; 13th October 2012 at 01:07 AM.
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Old 13th October 2012, 02:51 AM   #6
Bare is offline Bare  Canada
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Add a 2 to ~3 ohm resistor (experiment :-) in series with the speaker wire.
This will increase bass .. some.
Beyond that you either need new drivers or a better 'fit' enclosure
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Old 13th October 2012, 03:11 AM   #7
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Is the box properly stuffed?
Perhaps using an appropriate density of fill would give you a few Hz
In the long run using the box programs and buying a better driver is cheaper and easier and so much is room dependent that i would be guessing if I offered any more advice without knowing all of the parameters
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Old 13th October 2012, 10:30 AM   #8
tvrgeek is offline tvrgeek  United States
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Do you think the OEM just did not want deeper flat bass? You are trying to cheat physics. In my experience, physics always wins.

Mass does lower Fs at the expense of HF extension and efficiency.
Stuffing will help a tiny bit with Q, but nothing dramatic. ( may have other positive effects on reflections)
Knocking down the top end shifts the overall balance to give the sound some weight at the expense of efficiency.
Putting the speakers against the wall, or in a corner gives reinforcement to the bass that is there, not deeper.
Building a new box with different alignment ( ported that means) will give a lot more LF extension, if the driver is suitable.

Why must this be passive? Just a little active eq can give a good 5 to 10 Hz real extension without risking the limits of the driver. Look at the circuit for sub eq on ESP. Not the LT, the more flexible bass eq circuit.

There is only one really good method that works every time. That is a terminus replacement. Replace the thing at the end of the speaker wires with one that goes deeper. There ain't no free lunch!
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Old 13th October 2012, 01:24 PM   #9
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Thanks everybody for the input.
I have tried the series resistor to increase driver Qes, large cap to cause resonance at the knee and lead to bass boost at the low end.
My purpose is to have the smallest possible bookshelf size speaker with bass extended down to at least 30Hz flat. I am not cheating Hoffman Law and so sacrificing efficiency to get bass extension and small size.

The easiest way I can think of is Linkwitz transform, but that is an active method. Going active is cheap now but as this speaker is not to be used by me but my father who prefers a plug and play solution, the prime consideration is convenience.

My best guess to do this, was a passive BSC filter after the amplifier, starting at about 60Hz, which is the cabinet resonance frequency and start of the cutoff in the simulations. Using Martins BSC designer on the closed TL sheet, if I try a frequency this low, although there is desired attenuation at the mid-high frequencies but there is minimal attenuation at the system resonant frequency which becomes even more peaky after inserting the BSC filter. Wonder if it is causing a superimposed electrical resonance at the cabinet resonance, increasing the resonant peak.

Last edited by soundaatma; 13th October 2012 at 01:26 PM.
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Old 13th October 2012, 01:31 PM   #10
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No one has suggested the obvious.
Make sure the speaker is on the floor and near the wall(s) or best in a corner.
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