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Old 19th October 2006, 07:27 PM   #1
just a guy is offline just a guy  Canada
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Default 5 - 25 Hz

This idea has been discussed in this forum before but didn't really go anywhere. The Graham Holliman Infrabass Speaker uses a new loading method to lower the natural resonance of a sub to the 5 - 25 hz range, allowing very efficient output in that range.

When I say this is a new loading method, I only mean that it is relatively unexplored, as the idea has been around for at least twenty years. Usually I like to do a fair bit of research before I build but it is hard to find any info on this design.

Below are links to the patent and the old thread from this forum. Also, the text and some pictures of an article/ad by a company selling drive units and crossovers for this design, including notes from a guy that made one. Some of the details are sketchy and sometimes contradictory between these sources but it's all I can find. Most of this stuff is quite old.

http://v3.espacenet.com/textdes?IDX=...&QPN=GB2037534

http://www.hi-fi.ro/fhifi/download.p...c3b3fff7bd6562

http://www.diyaudio.com/forums/showt...238&highlight=

I am requesting more information, if anyone has any idea where to get some. I have been contemplating this design for weeks now and have some ideas but I don't want to get into it unless there is sufficient interest for a decent conversation. In my opinion this is a much better approach than using multiple 18 inch drivers in huge boxes tuned well out of their comfort zone trying to get below 10 hz.

Comments, opinions, ideas? Wanna talk about it?
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Old 19th October 2006, 08:58 PM   #2
moray james is offline moray james  Canada
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Default have you considered...

a dual driver "W" frame dipole? This is a velocity device and as far as I know it is the smallest volume sub box that you can make. If you reduce the vent area of the two drivers to between 1/4 to 1/3 the driver area then this increases the radiation resistance that the drivers will see and will decrease your driver Fs typically by 7 to 10 hertz (sometimes more). So if you were to start out with a driver (15 - 18 inch) with an Fs of say 18 Hz. (not all that uncommon these days for car subs) and the driver had lots of xmax and did not generate much rear noise (turbulence) that would get you right where you want to be. The key factors are driver noise and xmax. With dipoles you will need plenty of travel to make up your dipole roll off and you will probably require multiple units no matter what cabinet style you choose to make such low bass have impact.
You might try to see if you could get Tom Danley to comment as he is as far as I know the King of infrasonic bass reproduction.
You can take a look at this thread to see what kind of driver values you will want. The two options are to go with a driver Qts of about 0.35 and actively EQ the system or to use a driver with a Qts of about 0.5 to obtain more output at roll off without the need for EQ. Most of the really big hi xmax car drivers today would be about right to get the job done without EQ I should think.
Good luck and watch that you don't hurt yourself as such frequencies at level can do physical structural damage to your skeleton not to mention rearranging your intestines (seriously) and there is the house and neighbours to be concerned with. Tom has some great stories of this kind of bass. Best regards Moray James.
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Old 19th October 2006, 09:15 PM   #3
moray james is offline moray james  Canada
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Default have a look at djk's assesment of the acoustic cannon...

Looking at the cross section drawing there are stricking similarities between the infra bass unit and the discription Dennis gives for a "half square antenna" even though the infra bass unit uses some horn loading of the initial section of the line. I hope that this is of some interest".

Quote of djk below.


I use a spacing of 1/4 the total tube length -- as does the Bose Acoustic Wave Music System"

The patent says:

"The separation between openings 28 and 31 is of the order of half the length of the shorter tube between the front of driver 22 and opening 31."

which is 1/8th the total tube length. In the SUMMARY OF THE INVENTION they claim:

"A preferred separation is within the range of one-eighth to one times the length of the path for pressure waves "

This is simply being expedient on their part in making the claim as broad as possible. It covers the Acoustic Wave at 1/8 exit spacing and the Sound Cannon at 1W exit spacing.

The optimum spacing for the smoothest fequency response and the highest broadband gain is 1/2W exit spacing.

"For those of us too dumb to know what the hell you're talking about, could you elaborate?;-)"

I ran a Yahoo search on 'half square antenna' (what a radical idea!) and came up with:

http://www.qsl.net/ka1ddb/20meterhalfsquaredwg.jpg

http://www.cebik.com/hs.html

http://kc5jk.tripod.com//sitebuilde...half-sq-ant.gif

"To get DX angle radiation and gain without the tower and the Yagi, use a HalfSquare. What's a HalfSquare? A HalfSquare is a simple, light, unobtrusive and inexpensive DX gain antenna that you can hang almost anywhere you can put a dipole.
How is it made? Start with a wavelength of wire supported from its ends, and feed it at a point one quarter wavelength from an end. In this form the antenna is called a long wire. It has a decibel or so of gain off its ends and its radiation angle is a little lower than a dipole or Yagi at the same height, but it's no killer DX antenna yet.
Move the support insulators in a quarter wave from each end and let the tails hang down. Bingo! What you have now is a HalfSquare-two quarter wave verticals separated by a half wave horizontal phasing section. By this simple trick you have pushed the takeoff angle down into the serious DX range and you suddenly have nearly an S-unit of broadside gain to boot. As a bonus the feed-point impedance drops to 50 +."

Notice the author mentions that the performance really increases when you have the exits 1/2W apart?

As noted in the Bose patent virtually any spacing from 1/8W (boom box) to 1W (straight cannon) will work, it will just require more equalization to smooth out, and be less efficent.

Assuming a loss-less tube: "providing a nominal 6 db increase in sensitivity compared to the same driver in the infinite baffle. "
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Old 19th October 2006, 09:32 PM   #4
BAM is offline BAM
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Could someone give the patent number?

I'd like to experiment with this design and smaller drivers. I could probably load the whole thing into Akabak and simulate it that way. I wonder how the design would work with woofers smaller than 8". I suspect there's quite a bit of mass loading going on that pushes the driver's Fs lower. But what I really would like to explore is if adding a serious taper to the long vent (like 1:3) could introduce enough mechanical damping to make one of these things listenable. To the naked eye, it looks like the driver is simply loaded along the length of the tuned port, but thinking from an acoustic network perspective, it looks like the driver is actually connected to two separate air masses. Then the tube behaves as a single air mass for the infrasonic effect where the whole mass is just bouncing on the volume of air stored in the large chamber.
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Old 19th October 2006, 09:38 PM   #5
just a guy is offline just a guy  Canada
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Regarding your first post, I am familiar with W dipoles, but only through research. They are a good idea but in the range of 5 - 25 hz high output is key. W dipoles are not known for sensitivity.

Also there are some claimed advantages to the Holliman box. In addition to great sensitivity, it claims low distortion and no practical lower limit. The design the inventor had the most success with only went down to about 7 hz but he claims it can be tuned as low as you like.

I like the idea of using a cheap 10 inch driver in a reasonable sized box to cover the lows, although I am considering the 15 inch version. I think there is lots of potential here.

About the second post - sorry, I didn't understand any of that.

BAM - the patent number is GB2037534, from the first link I provided. Someone in the old thread tried to model it in Akabak before. Also linked to in my first post. Anyway, I think there are reasons other than mass loading why the fs is lowered. I think that decoupling the driver from the resonant chamber is what accomplishes that.
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Old 19th October 2006, 10:10 PM   #6
RobWells is offline RobWells  United Kingdom
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I'm into the idea of tying the speakers roll off into the rooms gain.

My tempests were pretty flat 10 - 30Hz without any EQ. If I was aiming for the 5Hz - 20Hz range right now, and had the space, I'd be looking at probably 24 tempest drivers in an IB or in Linkwitz Transformed boxes. They'd basically take up both front corners in the listening room, 12 per side. I'd build the manifold / box out of the corner so I could load them ' push push' .

Naturally you need the right room to do this, but it doesn't work out too expensive.

I used tempests as an example, but any decent 15" / 18" would do.

btw, I'd still cross them to my labhorns at around 25Hz - The labs kill my tempests for sound quality.

Cheers.

Rob.
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Old 19th October 2006, 10:16 PM   #7
just a guy is offline just a guy  Canada
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Anyway, since there is interest already, I'll get it started with some observations. I don't think any program (although I am not familiar with Akabak) can model this, as it is an unused loading method. It uses the "blowing across the mouth of a bottle" resonance and the driver is decoupled from the resonant enclosure.

There seem to be 3 main factors in this design.

1. The driver. I have no info at all about what type of driver is best, although lots of xmax seems preferable.

2. The resonant enclosure. This is the box at the heart of this plan, just a helmholtz resonator, a sealed box with a hole in it. Modelling each of the versions with a helmholtz resonator calculator shows tuning ranges from about 40 hz (15 inch version) to about 70 hz (10 inch version). So it would seem that the exact tuning of the helmholtz resonator is not incredibly important. On the other hand, the length of the port makes huge differences in the resonator's bandwidth and q, if changed.

3. The tapered ports. These start at the hole (X in the plans, the hole in the resonator) and extend to the sides, and then downward to the bottom. At first glance I thought these were two separate parts, but they form a steadily increasing port almost 4 feet long (15 inch version). The patent info says these ports should be as long as possible with a minimum of taper. I don't necessarily think that is sound advice.

More on all this later...
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Old 19th October 2006, 11:36 PM   #8
ScottG is offline ScottG  United States
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Quote:
Originally posted by just a guy
Anyway, since there is interest already, I'll get it started with some observations. I don't think any program (although I am not familiar with Akabak) can model this, as it is an unused loading method. It uses the "blowing across the mouth of a bottle" resonance and the driver is decoupled from the resonant enclosure.

There seem to be 3 main factors in this design.

1. The driver. I have no info at all about what type of driver is best, although lots of xmax seems preferable.

2. The resonant enclosure. This is the box at the heart of this plan, just a helmholtz resonator, a sealed box with a hole in it. Modelling each of the versions with a helmholtz resonator calculator shows tuning ranges from about 40 hz (15 inch version) to about 70 hz (10 inch version). So it would seem that the exact tuning of the helmholtz resonator is not incredibly important. On the other hand, the length of the port makes huge differences in the resonator's bandwidth and q, if changed.

3. The tapered ports. These start at the hole (X in the plans, the hole in the resonator) and extend to the sides, and then downward to the bottom. At first glance I thought these were two separate parts, but they form a steadily increasing port almost 4 feet long (15 inch version). The patent info says these ports should be as long as possible with a minimum of taper. I don't necessarily think that is sound advice.

More on all this later...

Yes.. Akabak can model this.. in fact it WAS modeled with this already in the other DIYAudio thread..
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Old 20th October 2006, 12:10 AM   #9
just a guy is offline just a guy  Canada
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The model that was done, if I remember correctly, showed very poor performance below 50 hz, strong above that. In reality, if one is built and measured, it should be exactly the opposite. I don't think these simulations are taking into account this type of loading method and I don't think they can possibly be accurate. Again, I am not familiar with the software but I don't trust the previous results. They go against everything else that has been published about this box.
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Old 20th October 2006, 04:07 AM   #10
paulspencer is offline paulspencer  Australia
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I've had a look through the links, the patent and the word file, other thread and its comments. It seems hard to believe that this could work well as a part of an accurate hifi system.

I note that its seems unlikely that the driver excursion is damped, hence excursion will be out of control. Be careful. I recall hearing of guys with the AE speakers AV12 having excursions so high when operating undamped that the cone hit the back of the terminals and dented itself! That would mean an excursion of more than 60mm!

Still, I'm curious to see this sub. I doubt it would work in my room since I have no real gain to speak of. I suspect that the rooms that are suitable are those with very solid boundaries with major room mode issues, hence boomy bass is also a problem, not necessarily due to the alignment itself.

I can see how this could be frustrating. The output you will get down that low will most often be very little, and usually unintended. My system runs flat down to the low 20s and I have an RTA in my system all the time. I find there is nearly always response down that low that is worth reproducing. Below 20 Hz there isn't much. Watching TV I sometimes find that the recording of some commercials have quite loud and unintended boomy sounds that come from the person's breath going into the mic.
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