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Author Topic: Bass Box6 Pro Design Accuracy?  (Read 4907 times)

Antone Atmarama Bajor

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Bass Box6 Pro Design Accuracy?
« on: July 29, 2005, 01:40:31 am »

     Hi All,
I've been playing with Bass Box 6 Pro a bit and was wondering if anyone here has any experience with its predictions translated into real world.

    Lately I've been toying with the Idea of building an LF reflex cabinet that has a reasonable amount of low frequency extension.  But I'm trying to confine it to a few semi flexible parameters.

1 the box will be either one 10 cubic foot or 2 5 cubic ft. Cabs (after Porting).  There is a possibility they will be op axial to help reduce Harmonic Distortion.

    The power handling should be around 1200 watts (I have an old Alesis Matica 500 that will put this out bridged at 4 Ohms.

    The Drivers will never exceed Xmax across their entire power bandwidth.

    The output will be as high as possible at 30Hz, and hopefully significantly above the threshold of hearing at 20Hz.

    So far my candidate Drivers are:
Eminace Lab12 X 4
Sonicraft SC12NRT X 4
Aura Sound NRT18NRT8 X 2

In a 10 Cu ft Box
4 X Lab 12 =122.5dB @ 30.03Hz 116.5dB @ 20.16Hz
4 X SC12NRT =121.5dB @ 30.03Hz 114.7dB @ 20.16Hz
2X NRT18NRT8 =120.8dB @ 30.03Hz  111.6dB @ 20.16Hz

For contrast In a 20 Cu ft Box
2 X NRT18NRT8 = 126.2dB @ 30.03Hz 117.6 @ 10.16Hz
4 X Lab 12 = 123.3dB @ 30.03 Hz 120.6dB @ 20.16Hz
4 X SC12NRT = 122.1 dB @ 30.03 Hz 119.3dB @ 20.16Hz

Although The Dual 18" can out umph the 12s in the midbass ranges.  It would seem that the Quad 4 cabs Have almost 3dB on the 18's in the 20's (as predicted by bass box).  Though It also predicts that the Lab 12 will exceed xmax a little around 28Hz and below 20 at 1200 Watts in a 20cu. ft. enclosure.  The SC12NRT will exceed xmax bellow 20Hz also.

    At the end of all of this dinking around with Bass Box software it has led me to the conclusion that it is very hard to get a conventional reflex cabinet/driver combination to produce any significant energy to and bellow 30Hz.  And I'm doing it the cheater way.  

    I've come across a lot of candidates that looked amazing until I checked the Cone displacement and its showing the driver exeeding xmax 5xmax over.

    If anyone has any suggestions (I'm not ready to do the Lab12 Yet) for Driver choices etc. let me know.

Thanks

Sum-
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Wayne Parham

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Helmholtz, tuned pipes and other stuff
« Reply #1 on: July 29, 2005, 03:52:14 pm »


I think your proposed cabinets are good.  Simple and effective, good extension and output and small enough to be easy to place and carry.

Excursion is one of those areas where we all want to have our cake and eat it too.  We want huge excursion limits but also want high flux density around the voice coil and very little suspension motion resistance.  But its hard to get 'em all at the same time.

The deeper and louder you need to go, the more displacement you'll need.  Displacement is the product of surface area and excursion, so for a given woofer size, greater excursion means greater capacity for high output bass.

But that means the woofer cone moves further, unless assisted by some form of acoustic device.  Resonance is a way of increasing bass output while reducing excursion, but only over a limited region.  Horns reduce excursion too, but deep bass requires pretty large horns.

You can use either Helmholtz resonance (bass-reflex, bandpass) or standing wave resonance (tuned pipes, horns) to decrease excursion at the frequencies of interest.  You already mentioned the good-ol' bass-reflex box, and that's one good way to do it.  You might also look at a bandpass box, which essentially puts more Helmholtz resonators around the woofer.  Each of these will decrease excursion requirements and increase output over a certain range.

Tuned pipes used 1/4 wave resonance to do the same thing.  A horn is essentially a flared pipe, one that spreads out the resonances and also acts to point the sound, if large enough and shaped appropriately.  You could use a tuned pipe to reduce excursion, and you might be able to keep the size down if a narrow band is all that is required.

You can combine features too.  Just because a transmission line or horn uses standing waves as its fundamental tuning feature doesn't mean that Helmholtz resonance can't also be used, by design choice or perhaps by accident.  Same goes for a bass-reflex box, which may also have some standing wave phenomenon inside it.

You can make a tuned pipe or horn with an additional Helmholtz resonator, sort of a hybrid bandpass box.  I suggest looking at some of the modeling tools provided by Martin King at www.quarter-wave.com if you're interested in this sort of thing.  Most software tools either model sealed box and Helmholtz (sealed, reflex and bandpass) systems or they model standing wave features (horns and tuned pipes).  Martin King's software does a good job of modeling both phenomenon in an acoustic device.

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Elliot Thompson

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Re: Bass Box6 Pro Design Accuracy?
« Reply #2 on: July 30, 2005, 04:23:05 am »

sumsound wrote on Fri, 29 July 2005 06:40

     Hi All,
I've been playing with Bass Box 6 Pro a bit and was wondering if anyone here has any experience with its predictions translated into real world.




Works as planned.  Cool

Made all my subs with the program, and, have no regrets.

Try to focus on the Normalized Gain. Thats the prediction
of the response. Once you jump into the 1 watt/2.83volt,
or wattage arrived by the manufacter, thats out of Bass Box
Pros hand, and the mechanics of the driver takes over.

Best Regards,

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Elliot

Antone Atmarama Bajor

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Re: Bass Box6 Pro Design Accuracy?
« Reply #3 on: July 30, 2005, 01:28:28 pm »

Ohh for shure.

    with the criteria I've set for myself I will never Exceed RMS ratings as well as Xmax across the drivers power bandwidth.  The goal for me is to attain the highest output possible at and bellow 30Hz.  I think I will try to see how it sounds running the things flat down to 27.5Hz so that means I need to cut everything above it up to 5dB  I don't know if I'll be underwhelmed by the output at around 121 dB.  I'm hoping not.

    I'm kinda tripped out by the fact that my BT7's don't sound as loud at 30Hz if you're sitting right in front of them.  But you really notice it the further you get away from them.  From that article explaining "Long Throw Sub woofers"  I wonder if the same will be true for a 4X12" Direct Radiator?

    I have considered the Bandpass Box but the seem to rob you of sensitivity, so I sorta ruled them out.  I'm not sure about passive radiators.  Group delay and Phase seem all wacky in the models I've done.

    Does anyone here know if the Lab 12 will perform in this box as predicted.

    Any thoughts on loading them op-axial, and how much effect it will have on lowering Distortion especially in the lower extremities?

Thanks Guys

Sum-
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Elliot Thompson

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Re: Bass Box6 Pro Design Accuracy?
« Reply #4 on: July 30, 2005, 09:52:23 pm »

sumsound wrote on Sat, 30 July 2005 18:28

Ohh for shure.

I'm kinda tripped out by the fact that my BT7's don't sound as loud at 30Hz if you're sitting right in front of them.  But you really notice it the further you get away from them.  From that article explaining "Long Throw Sub woofers"  I wonder if the same will be true for a 4X12" Direct Radiator?


Yes, it will. A 30 Hz wave is too long, and, you can't
isolate it in a smaller enviorment.

What you can do is use a lot of 4x12 Direct Radiators
that reads flat in normalized gain in Bass Box Pro.

How much you'll need will depend on how much you want
to excite the room.

But, bare in mind, frequencies that low will always
be per-dominant at a distance. And generally sounds
better.

Quote:


I have considered the Bandpass Box but the seem to rob
you of sensitivity, so I sorta ruled them out.



A Bandpass will give you what you want if the objective
is to get a peaky 30 Hertz. However, it will increase
the excursion, and, tax the driver a lot.

I think you need to get your hands on a Bandpass filter,
tune it to 30 Hertz, and, listen to various tracks.

You'll find that in order to achieve 30 Hertz at a sizable
level, you'll need 40, 50, & 60 Hertz as well.

This is where sinewaves can throw you off. For your sub
will sound fine playing a 30 Hertz sinewave, but, music
offers various sinwaves. And, you need the other frequencies
around 30 Hertz, to enhance 30 Hertz.

Quote:


I'm not sure about passive radiators.  Group delay and Phase seem all wacky in the models I've done.



Then you better go sealed, for all direct radiators offer
Group Delay, and, Phase Issues.

Best Regards,
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Elliot
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