Graham Holliman Velocity Coupled Infra Bass Speaker? - Page 12 - diyAudio
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Old 11th November 2006, 05:24 PM   #111
Mikey p is offline Mikey p  Canada
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Hi bjorno,

You said in post #100:
""I spent this weekend a lot of hours testing this Holliman phenomenon with a real setup (40L box and Peerless XLS 10) and came to the conclusion that the high efficiency 5 to 25 Hz bandwidth probably is only a myth for this type of infra speaker.::

I understood that to mean you were attempting to reproduce the Holliman 10 inch subwoofer design. My apologies if that is not what you meant. My statement that the design plans for the Holliman 10 inch version calls for a resonant cavity with an internal volume of 100 litres comes from the plans themselves. As to what spesific drivers the Holliman sub used, there was a reference made to the Richard Allan Atlas 15 woofer was used in the Holliman 15 inch version.. The T/S parameters of the Richard Allan Atlas 10, 12 and 15 inch drivers can be found here:

http://www.diyaudio.com:80/forums/at...amp=1083330126

I am still trying to verify if these were the drivers used in the Holliman design.
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Old 12th November 2006, 09:12 PM   #112
bibster is offline bibster  France
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Quote:
Originally posted by Mikey p


In the design plans for the Holliman sub the 10 inch version calls for a resonant cavity with an internal volume of 100 litres. I'm not sure what was tested with the 40 litre box as stated above. It certainly wasn't a Holliman design.
Sorry, but..... the way I read the .doc on the net, the resonant cavity is about 55 liters in the 10" version (Top: 78cm, bottom: 70.9cm, sides: 27.6 cm long and depth/width: 32cm)

Quote:
Originally posted by just a guy
I would like some details of your build, please. In particular the driver used (specs I am interested in are qts, fs and vas) and the sensitivity of the design. I don't care if you measure with a meter or not, I just want to know if it keeps up with the mains. Also, how much power can it take before it hits xmax?

Maybe you can try a couple of different drivers with radically different qts? You could just hold the driver over the hole (without screwing it on) and test at low power just to get some impression of how different drivers will affect the outcome.
The build: (It's rebuild today!) made of 15mm MDF, thin top doubling: 3.2mm isorel/hardboard, battens: 20x30mm pine (30up).
Hole 'B' (Coupling thinggy) is 50mm, Hole 'B' (the chamfered one) is 100mm (smaller side measured), chamfer is 45 deg. by jigsaw...
One of the sides is now glued to the rest, the other is screws only.
Couldn't cut, or have cut, the edged of panels 'F' (Sides of the cavity) under the right angle, so I just fit it, and caulked... (Yes, I should get a decent tablesaw....)
Didn't make pieces 'L' (Curved fillet) (yet?)
The pieces 'K' are yet to be fitted.... They don't seem needed to me... a 30Hz. wave wouldn't fit in the cavity ANYHOW... Please correct me if I'm wrong.

Now, the driver is the only 10" I have availible now... I said scrap, but should've said CRAP instead!! ah ah ah .... ahum.. anyhow: The T/S param's AS ADVERTISED by the constructor:
Qts: 0.45
Fs: 34
Vas: 145 (!!!!!)

Now, listening, very softly in my shop/garage, next to the childrens bedroom (11PM here)...
Crap!!!
Okay.... setup: iBook (iTunes), Edirol UA-25, Yamaha integrated amp --> G/H box
No tone control whatsoever.
Listening to Watermark (Enya) in mp3 (Has to be said!) and I can't hear any low, that is only mid. coming out of there...

Now, signalsuite please (os X tone gen.)... 30 sec. sweep form 0 to 100 Hz.
I can't give any graphs, so I'll just express myself... :-)
Nothing, then ' WOW!!' then shortly back to 'nothing' then 'less impressive' the end
I guess the 'WOW' is 'round 25/30 hz... (Near Fs??)

Let's check...sinuses:
27 (naaah), 28 (hmm), 29 (getting there), 30 (almost), 31 (BANG!), 32 (BANG!), 33 less, 34 less etc..

REMEMBER THIS IS IN MY GARAGE, NOT A SUITABLE ENV.!!!!
Could be a room-mode or so.... (approx 10m long the garage...)

So far, not convinced... But neither was I with the scrap-build, sohoooo.... We'll see tomorrow! With my el-cheapo sub-amp @ 50Hz cut off (12dB I guess)

Anyhow, It doesn't keep up if I'll put it // to my mains (so far!) but hey, I've a really shitty driver in there!!

good luck, Paul
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Old 12th November 2006, 09:54 PM   #113
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Thanks for the details. I think the problem is the driver. It should perform a bit better with all pieces screwed and glued, but for the most part I think the driver qts is too high. A lower q driver will exhibit more control during these resonances. Unfortunately lower q drivers are usually at least a bit more expensive.

I've tried putting the Atlas 15 specs into WinISD (if the Atlas is truely the driver this box was meant for) and it seems to be a high sensitivity pro-type driver meant for an incredibly small box. This type of driver's cone really doesn't want to move much and it's hard to get bass out of them without a horn.

I was worried about this from the beginning, because the driver I intended to use has a qts of .4. You can raise qts (and lower fs) by adding weight to the cone, but unfortunately I don't think there is anything you can do to lower q (without replacing parts of the driver).

I don't think there is any tweak you can do to the box to fix this issue (unless you want to add some type of chamber for back pressure on the other side of the driver, which is probably a bad idea). I think you need a lower q driver. But remember, I'm just guessing here, I'm no expert.
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Old 13th November 2006, 06:38 AM   #114
bibster is offline bibster  France
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It MUST be the driver....

I'll see what I can get over here, for not too many pennies....

This driver I use(d) is some 10" 'pro'-driver, rigid accordeen surround, kaplan membrane. Cheap belgian brand or so (Sphynx audiosystems). As I said, I didn't spend a lot on it. At the time, I wanted to make a wicked one, and put 2 of those in there. YEs that's where the wood for the first scrap build came from :-)

Any hint on easiely availible sub-drivers are welcome. The speakershop 'round here in Toulouse (Maison du hautparleur) carries some proper stuff?
I'm ready to spend no more than 100 on it.
Please advise anyone (Something I could RE-use maybe?)

I'll keep you informed, Paul
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Old 13th November 2006, 09:58 PM   #115
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Before spending a single penny on another driver which also may turn out to be unsuitable, I'd try a different approach. I may find myself in this situation soon, so I'll tell you what I'll do if it happens to me. To make absolutely sure you are getting the best performance out of the current driver, I would check on a couple of things first.

The first thing that comes to mind is the chamfer. I think the point of the chamfer is to make the length of the chamfered port essentially zero. If it is not chamfered enough, I think the port length is at least the thickness of the wood used; instead of zero, it's closer to an inch. That may not seem like a lot, but putting those numbers into a helmholtz resonator calculator shows that a difference in port length of fractions of an inch dramatically change the bandwidth and q of the resonator. Zero length port = wide bandwidth and low q, 1 inch port length = narrow bandwidth and high q. You mentioned that some of your work may be a bit rough, that's the only reason I bring this up, but I think the correct chamfer is essential to the operation of this box. I'd check my chamfer just to make sure it's as close to perfect as possible and if in doubt I'd chamfer it even more than 45 degrees.

Next I would be a bit worried about air leaks. You mentioned one side of your box is still loose. The best way to deal with that would be to screw and glue that side on of course, but if you don't want to do that I would line all of the touching edges with foam weatherstipping and then screw the side on. I don't trust an unsealed fit, a small air leak can ruin even the most perfect of designs.

After I had checked on these things and made absolutely sure that changing the driver is the only way to make things better, I would audition any driver I could get my hands on. It should be a quick and easy process, you don't even have to screw the driver in, just place it over the hole and run a low level sweep, then swap in the next driver. I would even make adapters to accept 8 and 12 inch drivers as well. I would want to try to audition as many drivers as possible before making a purchase. And not just different drivers, but drivers with considerably different parameters as well.
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Old 15th November 2006, 06:58 PM   #116
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When looking for info on the Helmholtz Resonator I found this sitewww.phys.unsw.edu.au/~jw/Helmholtz.html , in the part about a guitar being a resonator they talk about a port without length and this seemed to fit what this sub design was going for. Your port length should be Radius X 1.7. The design I was working on came out to 37.5Hz to 6.78Hz with a .57499 cubic meter resonator and X1 length of 4.826 meters.

I don't think I will have any time to build it until summer, Holidays and 4 grand children birthdays, busy time of year for me.
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Old 16th November 2006, 05:16 AM   #117
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TwisterZ thanks for the great link. This is certainly very interesting information and surprised me a great deal. If I am understanding this correctly, a port with no length actually has a length of radius x 1.7. So if the hole is 6 inches and has no physical length, the port length is actually 5.1 inches. Am I missing something here or is that right? Anyway, this is the helmholtz resonator calculator I was using, it's the second calculator on the page. http://www.mhsoft.nl/Helmholtzabsorber.asp

If you have the time, I'd love to know what went into your calculations for the design you were working on. Just wondering how you came to your dimensions and how you know what the final tuning will be. Looks like your resonant chamber is considerably larger than the plans, the ports x1 are considerably longer and the frequency range is considerably larger than the original. So if you know exactly how to design for a particular frequency range, I'm really interested. I have some ideas about tuning but I'm nowhere near designing for performance as exact as you expect.

Also, I'd like your opinion on a suitable driver and maybe which driver you intend to use if you have picked one already.

Actually any information AT ALL would be greatly appreciated. I won't be able to build for at least a couple of weeks yet but I'd love to have enough information to design as precisely as you have.
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Old 16th November 2006, 10:03 AM   #118
bibster is offline bibster  France
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JaG,

I've been paying a bit with the formulas offerd at that site: Pumped them into an Excel sheet.

Quite interesting results!!! Why didn't G.H. made the top of the resonator more like the vel. couping thing: Just a rather large (smoothed) hole, with a 'doubling' of thin material (==> no port length) over it.

I deduct that the 45deg. chamfer could be way 'smoother', in order to achive a null port length.

Have a look at my numbers (all in cm/m...)

Paul
Attached Files
File Type: zip gh-hh-resonator.zip (12.5 KB, 108 views)
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Old 16th November 2006, 11:01 PM   #119
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I'm not 100% sure that the purpose of the chamfer is to simulate zero port length, it's just my best guess.

Good work on the chart, there's a lot of work there and it illustrates how much small differences in port length affects output. Hopefully the calculator I linked to takes the "end correction" that is referred to in the link from TwisterZ is accounted for in the calculator parameters.

I had already considered using the same hardboard used for the velocity coupler for the "baffle" of the resonator as well but it all depends how much the hardboard costs. I may not use it at all.
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Old 17th November 2006, 01:33 AM   #120
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This is the Resonator calculator I was using.
www.vk2zay.net/calculators/helmholtz.php

X=Radius X 1.7
X1=Length of second horn

Add these 2 together for the resonator calculator to get your low frequency cut off.

My notes are quite the mess so I will try to get this right.
The woofer will be infinant baffle on the rear, firing into a resonator 3.5" away from the restrictor plate that has a 6" hole (1/3rd the speaker). The port for the resonator is 9" with the back angled away inside the chamber. The X1 horn will start in the 3.5" gap on each side of the 9" port expanding out to the side then turning and expanding along side the resonator as it tappers to a point at the horn mouth.

[IMG]\\Roseville\general\Steve P\Referance\Subwoofer\Holliman Sub.JPG[/IMG]
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