Hi, newish member, would these suit OB?

grantnsw · « **on:** 26 Dec 2007, 12:22 pm »

Hi,
I have 4 of these...
http://www.electusdistribution.com.au/productView.asp?ID=244&CATID=15&keywords=&SPECIAL=&form=CAT&SUBCATID=128
and I hope the link works. Would 2 of these per side work ok OB with 27TDFC crossed low at 1400Hz? I have a FR graph but it shows a 12? dB peak at 2kHz. I'll find it and post it if you like. Many thanks, grant

JLM · « **Reply #1 on:** 26 Dec 2007, 12:34 pm »

They look OK, why not cut a couple pieces of plywood and try them out?

Wiring two per channel will result in either a 4 ohm nominal impedance (could be a bit low depending on the amp and how much they vary from nominal) or 16 ohm nominal impedance (if bit more amp friendly, especially for tubes).

grantnsw · « **Reply #2 on:** 27 Dec 2007, 07:19 am »

Thanks JLM,
I was just wondering before I bought the tweeters. Another OB design has Qts < 0.47, so I guess
it would work, but I don't know how loud the bass would be, probably much less than a reflex box.

So 2 woofers in parallel gives nominal 4 ohm and I think that if the woofers are adjacent and floor
coupled, effectively gives + 6dB that is 96dB for the pair? This might just bode well with the tweeter
if I pad it down to about 86-87dB? As you say, there is one way to find out for sure - build it!
thanks, grant

mcgsxr · « **Reply #3 on:** 27 Dec 2007, 06:01 pm »

I am with JLM on this one, the best way to really know, is to buy a 4x4 piece of mdf, and rip it in half. Then you have 2 2x4 foot baffles, ready for some holes to be cut, and some experimentation to begin.

I don't know a lot of people running 8's on OB as woofers, but no reason it could not be done. I would review the designs of our fellow AC member/Circle owner Danny (http://www.audiocircle.com/index.php?board=16.0) to review some of the 2 way OB work that he has done.

Most folks around here are running a full (OK, wide) range driver, augmented with a helper woofer of some kind. I run 8 inch Visaton b200 wide rangers, each with a 12 inch woofer in the baffle. Poke around my gallery for various shots of the baffles, as they evolve over the years.

A two way can certainly be done, but I am not familiar with it, my version of a two way always involves a woofer or two.

I believe conventional wisdom states that an OB woofer is 1/4 the power of a boxed one. So, if you are using 4 OB woofers, you basically net the same as 1 ported or sealed one, in terms of absolute output. It may sound preferable to you, in spite of not being as powerful etc.

Good luck with the experimentation!

grantnsw · « **Reply #4 on:** 29 Dec 2007, 11:12 am »

Hi Mark,
Thanks for your help and the link. I went through 15 pages and found an OB-6? the other night. I'll keep looking for the 2way.

Well, I was just considering what I have already, ie, the 4 woofers. And a very cheap solution to do something OB, with say the 27TDFC's, so your comments are most welcome indeed. The outcome may be cheap and cheerful, err, a rough and ready approach, but it could be fun to play with! thanks again...grant

Dmason · « **Reply #5 on:** 29 Dec 2007, 02:30 pm »

hi Grant

I think it would sound pretty good after some tweaking. In fact, I have yet to hear a driver, cheap or expensive that sounded bad, mounted on an open baffle. This is because the driver, within limits, is operating in an ~optimal situation, with static air masses on both sides of the diaphragm, completely unloaded, less IM cone distortions creeping into the treble band, no backwave bouncing thru the cone as there is with any box speaker alignment, compression artifacts, etc. The key is to find one you like, that has reasonable characteristics. If the mains wideband driver is to be used above 2-400Hz, pretty well ANY driver regardless of Qts spec., will do the trick. In my experience, the key is avoiding crossovers within the presence band of the music. Follow the music. Nothing between, say, 250Hz at the highest, which is Middle C, and 4Khz, and treble implementation becomes easy, depending on the crossover slope you choose, the steeper the better, First Order, a simple cap being best. There is surprisingly little musical information above 4Khz, high harmonics, and what the audiophools like to call, "air." Bass with OB is easy, really, and very cost effective. The Goldwood 1558 15 inch "pro" audio woofer is the new find in this category, well built, well spec'd, and cheap as chalk.

-Richard- · « **Reply #6 on:** 29 Dec 2007, 09:48 pm »

Hi Dan ~

It is wonderful to read your latest insights here, Dan. And the information about the Goldwood GW-1558 is exciting!!!!

Here are the specs for the Goldwood GW-1558 15" Pro Woofer.
Price at Parts Express: $45.50 each. Now that is quite lovely.

They feature accordion paper surround, poly laminated paper cone, and a vented pole piece. * Power handling: 200 watts RMS/380 watts max * Voice coil diameter: 2.5" * Le: .8 mH * Impedance: 8 ohms * Re: 5.27 ohms * Frequency response: 31-2,500 Hz * Magnet weight: 50 oz. * Fs: 31 Hz * SPL: 95.6 dB 2.83W/1m * Vas: 14.19 cu. ft. * Xmax: 3.9mm * Qms: 3.68 * Qes: .76 * Qts: .63 * Net weight: 11 lbs. * Manufacturer model number: GW-1558 * Dimensions: Overall Diameter: 15-3/8", Cutout Diameter: 14", Mounting Depth: 6-1/4", Magnet Diameter: 6-1/8", Magnet Height: 1-1/2".

I like the Fs of 31 Hz... considerably lower than my Alpha 15A's at 41 Hz... and the sensitivity is right up there at 95.6 db.

Alpha-15A:

Impedance 8 ohms / RMS Power Rating 200 Watts / Program Power Rating 400 Watts / Frequency Response 46Hz - 3.5kHz / Sensitivity (1W/1m) 97dB / Voice Coil Diameter 1.5" / 38.1mm / Max. Crossover Frequency 3.5kHz / Resonant Frequency (fs) 41 Hz / Impedance (Re) 5.88 ohms / Coil Inductance (Le) 0.84mH /Electromagnetic Q (Qes) 1.53 / Mechanical Q (Qms) 7.23 / Total Q (Qts) 1.26 / Compliance Equivalent Vol. (Vas) 260 Liters/9.18cu. ft. / Voice Coil Overhang (Xmax) 3.8mm

I have a question, Dan: Do you think the lower Fs of 31 Hz will translate to a 1/2 octave lower bass extension compared to the Alpha-15A's 41 Hz?

I am not certain how the dipole OB wave form (front and back) translates in a woofer in terms of how far lower it can actually go based on the Fs "potential". Any insights would be deeply appreciated.

Warmest Regards ~ Richard

Dmason · « **Reply #7 on:** 30 Dec 2007, 01:07 am »

Hi Richard,

Will the 10Hz lower Fs translate into 1/2 octave lower response? Theoretically, I suppose it should, but again, The Laws of Physics visit the situation. The only real antidote is wider baffles, OR active contouring. I choose the latter; With 15 inch pro audio woofers, people are having great success with 18 inch wide baffles, and contouring, which in my opinon is essential anyway. Again, the cheap and effective fix today is rip those CD's into iTunes and take advantage of their 1-octave DEQ, with free +/-12db Pre amp, which is a really nice addition. I would subtractively EQ the mains, and boost the bass abit, depending on what type of amp one had. If they had 2 watts, they would have to go easy, and eventually perhaps use a BASH plate amp for the woofers. If they had more power available, run the whole thing as a 2 way and EQ away. It works.

With 10Hz lower Fs, the Goldwood clearly ~should~ squeeze out abit more bass, has mo' betta excursion, so it ~~should~~ but I have zero idea as to the veracity of their published specifications, no one really knows until it is tried, and being a man of science, I prefer to believe it when I hear it reported as such. ----> I know someone who is right now working with their pair of new Goldwood 1558's along with the very tasty and no longer Unobtanium Diatone 610PM wideband mains driver, www.orgueclub.com and I should hear back from them in the coming days. There is little need for concern with respect to acceptable bass, and their main concentration will be implementing an inexpensive teensytweet on top of the Diatone to add alittle ...."air." I hope to hear this custom design set up this winter, and if I do, this is a good thing, because it will mean I am on Maui,

where there is some good investigation into this type of OB array, and then on to another archipeligo, where they prefer "front-loaded horns," more commonly referred to as, "conch shells." ...the traditional Tongan War Horn brings up the idea of front-horn loaded, chamberless open baffle speakers. For an glimpse of this, visit the KITS page and look for Long Throw 2 way at www.assistanceaudio.com ..this implementation, I believe, could be the Holy Grail of OB sonics. Not something for the faint of heart, not something where WAF should even walk through the door, but, ... I am going to at some point get a pair as I know exactly what I would like to try with them.

Wind Chaser · « **Reply #8 on:** 30 Dec 2007, 01:49 am »

Quote from: -Richard- on 29 Dec 2007, 09:48 pm

...the information about the Goldwood GW-1558 is exciting!!!!

Here are the specs for the Goldwood GW-1558 15" Pro Woofer.
Price at Parts Express: $45.50 each. Now that is quite lovely.

They feature accordion paper surround, poly laminated paper cone, and a vented pole piece. * Power handling: 200 watts RMS/380 watts max * Voice coil diameter: 2.5" * Le: .8 mH * Impedance: 8 ohms * Re: 5.27 ohms * Frequency response: 31-2,500 Hz * Magnet weight: 50 oz. * Fs: 31 Hz * SPL: 95.6 dB 2.83W/1m * Vas: 14.19 cu. ft. * Xmax: 3.9mm * Qms: 3.68 * Qes: .76 * Qts: .63 * Net weight: 11 lbs. * Manufacturer model number: GW-1558 * Dimensions: Overall Diameter: 15-3/8", Cutout Diameter: 14", Mounting Depth: 6-1/4", Magnet Diameter: 6-1/8", Magnet Height: 1-1/2".

I like the Fs of 31 Hz... considerably lower than my Alpha 15A's at 41 Hz... and the sensitivity is right up there at 95.6 db.

Wow! That's a deal. The 3.9 Xmax, is that total or one way?

stereogeek · « **Reply #9 on:** 30 Dec 2007, 05:04 am »

The Goldwood driver has a Qts of .63 and the Eminence driver has a Qts of 1.26.Wouldn't the Goldwood driver rolloff at twice the rate of the Eminence driver??? You may end up with more bass out of the Eminence.Hmmmm?

Steve

grantnsw · « **Reply #10 on:** 30 Dec 2007, 01:08 pm »

Hi All , Happy New Year!

Dan, thanks!

Some great thoughts there indeed! Awesome stuff for a beginner, I hope I can eventually understand
it all. I've been following a Manzanita thread in another forum, where the TDFC is crossed @ 1500 to
Peerless 830669. This gets good reviews, so I was going to try to emulate it with 2X 8" woofers as
linked above. So your comment.... " I think it would sound pretty good after some tweaking. " is
very encouraging. I'll assume that its Qts of 0.47 is ok then?

But you kinda lost me in crossing over between 250 and middle C. Is middle C, 4kHz? Sorry, I don't know!

A 1500 Hz xo-point is right in our ears most sensitive region? Which begs the question, how do these
published designs get such good reviews? Again, I'm lost, hmm.

The thread is now about 15" drivers, which is great! I thought the Alphas were superior to the Goldwoods,
but again, I'm out of my depth here, and budget, lol.. Stateside prices are way cheaper than here in Oz.

Re: " There is surprisingly little musical information above 4Khz," now thats a revelation! Maybe I'll
save up (for years!) for the SS D3806's, as I can probably only hear to 10kHz anyway! hehe ...55yo ears.

More questions, if ok, please! Do U-frame baffles reinforce more bass than flat OB baffles? If so,
for my 2X 8" woofers per side, how do I 'optimise' the baffle width, while keeping it as narrow as possible,
wrt WAF? I know there are a lot of issues here, like BSC, and stuff way over my head e.g. at Linkwitz.

Can I just use the Edge or another free sim prog? Thanks again, grant

Dmason · « **Reply #11 on:** 30 Dec 2007, 05:21 pm »

hi Grant

The above mentioned recipe is from Michael Mardis, one of the two Haoles on Maui, of whom I speak, so watch out wit dem krazy buggahz, dey Lo Lo, brah...

That might be an outstanding way to start, and has a real speak geek legacy behind it. Apparently it is a very good example of something being far more than the sum of its parts...

Middle C = 250Hz

All musical accompaniment happens between ~200Hz-1000Hz, if the piano keyboard is to be believed.The keyboard is used for all musical arranging to score, and all core musical harmonics occur between these frequencies. It is the harmonics within the various instruments, occuring at higher frequencies, that identify those instruments, their placement, reverb, etc.

Give yourself a gift today. Free 24 bit digital equalization, and lossless digital sourcing
www.itunes.com This is part of the open baffle toolkit.

scorpion · « **Reply #12 on:** 30 Dec 2007, 10:33 pm »

Seems to be some confusion here about fundamentals and harmonics of different instruments and voices.
Here are two good charts that shall explain this to everyone:

This is good knowledge when dealing with speakerconstruction.

grantnsw,

The Edge will tell you only baffle influence not really how your speakers will behave in a given baffle only what that specific baffle will contribute.
You can say that The Edge assumes perfect linear speakers.

However you should go ahead and try with your speakers. Have a look at the U-part of my 'Volks-OB' http://www.audiocircle.com/index.php?topic=46951.0
When trying a U let the baffle width be greater than the wing depth to avoid resonances. Physics is a bit against us.

/Erling

panomaniac · « **Reply #13 on:** 30 Dec 2007, 11:41 pm »

Hi Dan, Grant and all.

There seem to be a lot of ways to do OB, and it's becoming quite a fad.
Starting with the woofer, mid QTS seems to help, good x-max and efficiency are also important.
The Eminence Alpha 15A is popular because of its High Qts which gives it a nice bump in the lows. As you know, I use the Selenium 15WP3 with a Qts of about 0.6

Below is a graph made in X-Baffle of several woofers on the same baffle. It's a big baffle, modeled on the P19 form Lukas the "Lampiztor" site. Baffle is 47" tall x 22" wide. Woofer center is 19" above the floor. Very much like my "Lounge Lizard" OBs. Side wings are not modeled here, but I find the X-Baffle comes pretty close to what I hear and measure, so it will give you an idea.

You can see that the Selenium has more output overall, and that's good, of course. But they all have a similar curve, exec pt for the Alpha 15. It is a much higher Qts driver, so you see the bump down low. That actually helps to flatten the FR curve on this baffle.

Of course the big Alphard 18" will not need to move as far as the 15" drivers to shift the same amount of air, so it has an advantage there. You have to be careful about x-max on OB, as you really need to move some air to overcome the wrap around losses.

What we don't get from the graph is how the drivers sound. Only swapping them out on the same baffle will really tell. I may be in a postion to do that next year. I don't know anyone who has used the Goldwood driver yet, but most people don't like the brand, even the guys at P.E. will tell you they're junk.

But for the price, they should be worth a try, right? Might be a Golden find.

-Richard- · « **Reply #14 on:** 31 Dec 2007, 03:19 am »

Hi Erling ~

Thanks for posting the 2 instrumental frequency graphs... very important information that gives all of us an instant sense of how Hz measurements actually translate to musical reproduction.

It was interesting looking at your Open Baffles again... thanks for the link... you stated in your (always) helpful description: "The inside of the chassis legs are treated by felt to avoid back cone reflections."

I was not entirely clear what you meant by the "inside of the chassis legs"? do you mean the inside of the wings... which also seem to act as "legs" for the OB panels? Also, do you think the wings add substantially to the bass response?

I am certain they sound as wonderful as they look... you must be in audio heaven... wonderful design!!!!

Hi panomaniac ~

I looked up your moniker in my e-dictionary to see if that is actually a "recognized" word: the closest I got was "pano": a family of South American Indian languages spoken in Peru, Bolivia, and western Brazil. Interesting!!! Also: monomaniac: Affected with monomania, or partial derangement of intellect; caused by, or resulting from, monomania; as, a monomaniacal delusion. Also interesting! Of couse this hobby can bring that state on rather easily.

I cannot thank you enough for posting that wonderful graph showing the results of your software with 4 potential usable OB woofers including my Alpha-15's... the hump that shows up as the frequency levels off must be helping to establish the marvleous sound I am getting combined with the B200's... nice to see it visualized.

Again... thanks for sharing your very important information with us... deeply appreciated.

Warmest Regards ~ Richard

scorpion · « **Reply #15 on:** 31 Dec 2007, 10:08 am »

Hi Richard,

Happy New Year to you and everybody else !

Felt is on the inside of the SP130X/8 steel chassis between the steel and the paper cone. The kind of felt you put under furniture legs.

The wings will help bassresponse considerably and maintain it flat down into the 40ies. It is as Pano says the combination of baffle and speaker that
forms the system. I am onto MKII of this design because my Trends 10.1 class-D amp is easily driven into distortion when going loud into 8 ohms
and this is the kind of speaker you like to go loud with.

/Erling

Rudolf · « **Reply #16 on:** 31 Dec 2007, 12:26 pm »

Quote from: grantnsw on 30 Dec 2007, 01:08 pm

More questions, if ok, please! Do U-frame baffles reinforce more bass than flat OB baffles? If so,
for my 2X 8" woofers per side, how do I 'optimise' the baffle width, while keeping it as narrow as possible,
wrt WAF? I know there are a lot of issues here, like BSC, and stuff way over my head e.g. at Linkwitz.

Grant,
building your OB as a U- or H-baffle will reinforce the bass of your 8" woofer a LOT - which you need urgently, since 8" is VERY small for OB. A U- or H- baffle doesn´t need to be wider than the driver diameter. Depth should optimally be the same as the width resp. heigth of the baffle - resulting in a cubical enclosure. For two drivers the baffle heigth would just be doubled.
In a U-baffle the driver baffle would be in front of the cube, for a H-baffle in the middle of the cube.
You can force even more bass out of a U/H-frame by making it deeper, but then you will need to have a closer look at the cavity resonance.

BTW: forget about those 96 dB! For a qts=0,5 driver sensitivity will be 6 dB down at Fs. And that is on an infinite baffle!

scorpion · « **Reply #17 on:** 31 Dec 2007, 12:51 pm »

grant,

You have perhaps noticed that we are talking of bass-OBs, if we take the U-box OB, that is a open box without a back and the H-OB and also the Linkwitz
W-OB that maximally could be crossed over at 200 Hz. No higher without great difficulties.

My top-less U is much more forgiving.

/Erling

grantnsw · « **Reply #18 on:** 31 Dec 2007, 01:51 pm »

Hi Everyone,
I am stunned by the generosity and helpfulness of your replies! Very sincerely, thank you, indeed.
It seems that 'the Professors' of this OB pursuit have deemed to reply to me. Great stuff! and thanks.

I'll need to carefully re-read your input after NY's-Eve, haha, but for now it seems my 8" woofers, 2 per side,
may be a tad inadequate, and the Goldwoods, etc would be better. Thanks, Pano.

But for now , I truly appreciate your replies, and hope to respond soon. NYE now, ....kaboom! ...grant

mcgsxr · « **Reply #19 on:** 31 Dec 2007, 03:21 pm »

Indeed, you have found a very helpful place for OB enthusiasts, I used to surf all kinds of forums for ideas, now I find that most of the good minds have migrated to reviewing these pages, and I can simplify my surfing.

I have looked at the Goldwoods many times, but never pulled the trigger on them. My concerns were the limited XMAX, and stamped steel basket construction - I have a preference for cast aluminum baskets for making bass, I find them far more robust, and less likely to ring. I have never held one of the Goldwoods in my hand (leave the Goldmember jokes please!) but did review their 15 and 18 inch options with much interest for a period of time.

I later found these, and bought the 12's. In hindsight, I should have bought the 15's, mostly just because I love big woofers...

Have a look here, decent chinese built cast basket 12's with good specs with one voice coil left open - that doubles the effective QTS to a pretty good spec of 0.5 or so.

http://www.mach5audio.com/product_info.php?cPath=48&products_id=41&osCsid=a46a9a2e6c54d15d937171c76d02db5d

Mind you, these were 1/2 this price when I bought them more than a year ago...

I think the thing to keep in mind with OB bass (and simply my opinion) is that swept area is very useful - so more woofers is always better, so if considering the Goldwoods, you might consider buying 2 to experiment with, with the plan of adding 2 more later, to add efficiency, and limit the required excursion for more sound etc.

All the best,