Unconventional subwoofer design

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BAM:

Just figured I would include a diagram of an eighth order bandpass in case anyone is familiar with the configuration, but not the name.

Also, I was in a thread where someone had simulated a tremendously low F3 for a bandpass box. There was a post by someone who seemed to be a professional who said that bandpass simulations, especially those of configurations with multiple ported chambers, do not conform to real life output.

I could not comment one way or another, having never built a bandpass. But I thought I would pass it on.

Is there any particular advantage of this enclosure style? Does the 8th Order bandpass give a lower F3 than other enclosures, such as the vented box?

I have heard that the more resonators, (ported chambers), involved, the greater the group delay, and possibly worse transient response. But again, I do not speak from experience on this.

Here is the configuration for anyone who has seen this enclosure.

Good luck with your project. Please let us know how it turned out.
 

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Bam,

I'd have to say I'm not in general a fan of bandpass subwoofers, although it does depend on your application. I'd say they are suitable for non critical applications, where you are willing to sacrifice some quality to get more output - say in a PA setup, or for some boom boxes with small drivers that otherwise wouldn't really be up for the task - especially computer speakers if you want to add a little boom to your computer games. A 4th order bandpass, OTOH, is perhaps more feasible as it doesn't compromise sound quality as much. Jamo once had such a sub, with a 10" driver in their flagship speaker - actually they had two of them in isobarik configuration inside a curved speaker.

It really depends on what you want it for. I believe bandpass boxes are very sensitive to the parameters of the driver, so it may prove hit and miss unless you actually measure the parameters to be sure they are what they are supposed to be.

Subwoofer simulator is a good one to use. However, be aware that if the parameters of your driver are a little different to the published specs, it could mess up your design.

Ok, so why use a bandpass? ...

Basically it allows you to trade efficiency and bandwidth. They gain output by narrowing the bandwidth. So, compared to a vented box, a 6th order bandpass will have a higher F3 and higher efficiency. They also tend to have higher power handling due to the increased excursion control. This is particularly useful in PA, where low extension is not really useful, and high output is desired. If you design a bandpass to have a lower F3 than a vented box, you start to loose efficiency. If you want a lower F3, this is probably not the way to go. If you want a lower F3 than you can achieve with a vented box, your options include:

transmission line
horn loaded
sealed box with eq (with high excursion drivers, at the expense of output)

Bose used an 8th order bandpass with small midbass drivers in their older acoustimass modules. They go low enough for most music and roll off rapidly on the upper end, so that they are more flexible placement wise - distortion is less audible as it has to get out through the ports, and the rolloff helps also to prevent being able to localise the sub. If you aren't fussy about sound quality, it's quite clever, and will easily satisfy most people. But it will satisfy very few who are likely to be found browsing this forum!

regards,
Paul
 
Bam,

one more comment - my suggestion is to get hold of some scrap MDF or whatever you have available and have a go at a box - compare vented to bandpass, but don't put in too much effort to a nice box at first - make a quick dirty prototype and be ready to experiment a little.

Another thing that would be interesting to try is to model with two versions of the driver - put in a second version of the driver with slightly different parameters. Also, make sure you break in the driver as the parameters are likely to change as the suspension gets a little looser.

It's best to make a decision after you have experimented yourself, and made a quick prototype. Let your own ears be the judge.

cheers,
Paul
 
Be GENTLE!!!!

BE very kind to your woofers with this type of a setup. These boxes can be woofer eaters. I won't warrantee them if I build them. People tend to turn them up to loud because they have such a small passband. They "want to hear the tunes" and if you over drive the woofers by excess eq or wxcess power the flap around and melt, die , blowup etc. Not for the faint of heart!!!

Mark
 
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Well, I just modeled one of those Peerless 833599s. Subwoofer Simulator will not model two.

The power delivered to the woofer is 96 watts.

The sensitivity seems to go down, but the bandwidth seems to go down very far for a speaker with an Fs of 37. Speaker normal sensitivity is 88dB.

Group delay is a very large 45 ms.

Green line=output without room gain

Red line=group delay

Purple line=cone excursion


Next post is the box dimensions.
 

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diyAudio Moderator Emeritus
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Here are the box dimensions and tunings.

I would certainly make the Av of the vent larger than 1 inch, but I did not have time to calibrate a bigger vent for the same tuning.

But I think everyone gets the idea.

The box seems to have the potential to give smooth tuning for frequencies well below the speaker's resonances-in fact, about a whole octave below.
 

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mwmkravchenko and bull are right - 6.5" drivers don't go far as subs BUT a bandpass box is the best you can do with a smallish box and these drivers as far as output and power handling go.

A bandpass box should not reduce sensitivity at all! Not unless you increase the bandwidth too much. Compare it to a vented box with similar extension and you should be able to get slightly more efficiency.

regards,
Paul
 
The whole deal with this particular thing is that when you try and use larger woofers, like 8" or 10" or 12", you wind up with a refrigerator-sized box. I want to try and fit this at least into the space of a large suitcase. It will be powered with 150 watts. The woofers on their own each have a power handling of 150 watts and an impedance of 8 ohms. Used in parallel, they should suck the entire 150 watts from the amplifier. The woofers also have decent sensitivity, though (88dB 1w/1m). This will all add out to 91dB 1w/1m. I am actually now thinking of building some MTM satellites for it with some 12-ohm 4" things I have laying around.

One question about the readings you got with Isaac's subwoofer simulator. Does that mean that my 6.5" woofers in this box will actually be able to reach down below their Fs to the 20Hz F3 that it is predicting? I might model up one for myself and change it to see that the lowest frequency it tries to do is 35Hz and extend its possible range up to 200Hz.
 
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BAM said:

One question about the readings you got with Isaac's subwoofer simulator. Does that mean that my 6.5" woofers in this box will actually be able to reach down below their Fs to the 20Hz F3 that it is predicting? I might model up one for myself and change it to see that the lowest frequency it tries to do is 35Hz and extend its possible range up to 200Hz.

Well, the 1 Watt curve will be -3 dB down at 19 Hz or so. BUT at 19 Hz, the cone excursion for your 6.5" is 23mm!

Actually, TC Sounds makes a 6.5" that will be linear at 23 mm. Only trouble is, they mostly sell Original Equipment Manufacturers, so you have to locate which manufacturer uses it. I hear Styke sells ome of TC Sounds speakers, so you might look there as well.

Assuming a normal excursion of ±6mm or so, plus a little added for nonlinear travel, you still fall far short. Even if you double it for 2 woofers.



If you don't mind my saying so, I don't think being able to put out 101 dB at 19 Hz is such a great idea. You will need more SPL than that to make going down that low worthwhile, even with room gain. I would definitely move the F3 upward for greater sensitivity, greater output and less cone excursion.
 
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A couple of questions.

First, what would you call the size of a large suitcase-2 or 2.5 cu ft?

Second, are we still on the idea of using two 6.5 inchers? Because two 6.5 inchers will have about the same deal as one 10 incher, and the 10 incher will likely have greater excursion.
 
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Oops! TC sounds no longer makes the 6.5"

They do make an 8" though. Small Vas for it's Fs of 29 Hz. It looks interesting if you are into making a sub that will fit into even a small suitcase.

Check out the woofer:
http://www.tcsounds.com/Images/8tc2_2574.pdf

Check out TC Sounds:
http://www.tcsounds.com/

AS far as getting your hands on one-that might take some doing. You might want to make that a separate thread.


PS: that peerless 6.5" does NOT have a shorting ring or extended pole piece. That means it might hit high distortion as it nears resonance, as non-symmetrical magnetic field speakers do as they near resonance. This might mean trouble, since this box has three resonance points, not just one.
 
The single 10-incher will give me a refrigerator in my room, while the 6.5's will not. Something about the moving mass of the cones or some other characteristic specific to smaller drivers, I think. I am trying to get this to fit under an end table that my parents have. Bose seems to get away well with the most plain-vanilla 5.25" drivers I have yet seen, so I think that the Peerless 6.5" drivers will give me what I am looking for. They seem to model out into reasonable box sizes. I am setting my size limits at about 3 feet (36") deep, 20" high, and 12" wide. If I can realize an enclosure smaller than that, with single 3" ports connecting the chambers, then I will. Lowest frequency I am trying to reach with these drivers is 35 Hz. I am building this for the heck of it, and I am going to build some satellites for it with some drivers that have been sitting under my bed back at home (I am at college) seemingly forever waiting for a use. Into the back of the 8th-order box I will be building in my 150-watt subwoofer plate amp, for a powered apparatus. The third port to the outside will be a flared Precision Port kit. There's my agenda. As far as driver distortion, I am expecting that any of that will be contained within the acoustic chambers, for the kind of distortion-killing effect that Bose touts so highly. You will notice I am not trying to get that low. When I want that kind of low bass, I will listen to my vented 500W AV12-equipped subwoofer, which I am predicting to have a possible F3 of 16 Hz with three 3" flared ports.
 
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BAM:

Two things:

A) I know you are aware of the other thread on this subject.
http://www.diyaudio.com/forums/showthread.php?threadid=24397

I just wanted to reiterate about the symmetrical magnetic field. It is not just a case of high distortion-the voice coil actually displaces from moving back and forth from the centerpoint to going all the way to the end of it's travel. This shears off half the waveform in a ported box. The eighth order bandpass consists of 3 ported chambers. Draw your own conclusions.

B) Your dimensions for this box, (36" X 20" X 12"), with one inch building material, translate into 3.5 Ft³. That is one large enclosure. Are you sure you want to go thru all this trouble with the eighth order bandpass sub?

A vented Shiva or even a sealed one-should give you all you need down to 35 Hz. You can parallel two vented Peerless 10" CSX or CCC and get down to 35 Hz, with an efficiency of 91 dB and major excursion output.

It is your project and if you want it in the form of two 6.5's in an 8th Order Bandpass, that is great. Just thought I would let you know that there are a lot of less complicated alternatives out there.
 
I know there are a lot less complicated ways of getting bass, and probably better bass at that. But I have never seen a DIY-built 8th-order bandpass subwoofer, and I want there to be at least one existing DIY 8-O bandpass design. Just like there is an existing design that uses Wave Cannon theory, I want to build at least one 8th-order bandpass. That is my whole motivation for this project. Otherwise I would have just built some sort of sealed 10" woofer. My whole aim in this, though, is to make sure that my 150-watt plate amplifier dies not sit idle.

I am actually putting this project on hold until the summer, I think. I want to make some money and perhaps use those new Elemental Designs midbasses that they are coming out with. They are 6.5" paper cones with 13mm one-way Xmax. they use foam surrounds, though, so that is bad. Perhaps I will try the Adire Extremis midbasses, if they are in a decent price range.
 
I built an 8th-order box, long before I knew enough for SubSim's conception. It used a cheap chinese-made 8" woofer. This was in the early 90s, so I can't remember the tuning frequencies, and surely the driver unit wasn't a match for the enclosure.

This type of enclosure does require a capable woofer. The one I made had a glass panel so I could see the cone excurssion. The cone movement is so small that the voice-coil vent is almost useless. The driver easily runs into thermal overload rather than mechanical overload.

A 30Hz signal at 100Wrms was just too much that it fried the coils within seconds. I could smell and see the smoke vibrating in and out of the main vent. It was loud while it lasted, kinda cool actually :D

The fun of construction and hearing the unconventional design was all I wanted out of the whole thing :)


Cheers,
Isaac
 
Bam,

There is nothing wrong with foam at all from a performance point of view. In many ways it is ideal, I think it is actually better than rubber. Adire discuss in their whitepaper on the Shiva the reason for using foam surround. The only issue is longeivity in some areas. My parents have a pair of old boom boxes that are 20 years old and now they are starting to fall apart. But I have seen the same thing with rubber surrounds as well. In 20 years time you probably will have passed it on anyway. Most here have a much quicker turnover of their speakers than that!!!

regards,
Paul
 
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f4ier said:
I built an 8th-order box, long before I knew enough for SubSim's conception. It used a cheap chinese-made 8" woofer.

This type of enclosure does require a capable woofer. The one I made had a glass panel so I could see the cone excurssion. The cone movement is so small that the voice-coil vent is almost useless. The driver easily runs into thermal overload rather than mechanical overload.

A 30Hz signal at 100Wrms was just too much that it fried the coils within seconds. I could smell and see the smoke vibrating in and out of the main vent. It was loud while it lasted, kinda cool actually :D

Cheers,
Isaac

In that case, I would point out that the Eminence LAB 12 was designed for horn enclosures, where cone excursion is suppressed as well. Therefore, it would appear to be a good match for this type of enclosure as well.

Although it does not fit the size or price goals for this project, I thought I would just throw this in just in case you decide to build one of these with a bigger budget.
 
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