[ttan98]

I have constructed a few Open Baffle prototypes in the past with the following configurations:

a. Full Ranger + woofer + woofer
b. MTM + woofer +woofer
c. Horn + woofer + woofer
d. Horn + midrange + woofer + woofer

all the woofers are mounted on a U-frame.

I thought of trying something different. The configuration is shown in the image attached.

The midrange and tweeter are coaxial driver also the 2 woofers which I intend to get them from PE who is having a sale.The woofers are mounted on a H-frame as per image attached.

The detailed spec for the coaxial is:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-450
the x-over freq to compression driver is about 1.8Khz

The detailed spec for the woofer is:
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=290-365
the 2 important parameters are Qts=0.89 and Fs=33hz

I think the coaxial can x-over to woofer at around 150Hz. The x-over can be done via the DCX2496,  when I am happy with the sound I will design a passive x-over.

I invite comments from interested parties particularly Rudolf, and Martin(MJK).

a. I also welcome any simulation of the dual H-frame woofers. With this configuration my guess is I can get the low freq flat to 40Hz.
    I think the low freq response should be quite good.

b. highlight any obstacles I may encounter.

c. comment on the design and choice of drivers.Total cost of the drivers are about US$220  for a pair of speakers, pretty cheap I think. Of course I  can buy better quality coaxial(eg 10" from Hawthorn)  but I like to keep the cost down. I pick 12" instead of 15" drivers because the latter is too large for me, also my room is medium size.


Thanks for looking.

http://www.audiocircle.com/index.php?action=gallerylastup&cat=0&pos=0

[Rudolf]

ttan98,

judging from the specs that driver combination should do a nice job - and should do nothing a DCX can´t get right. I can´t say much about both efficiencies in that combination - surely no problem for the active X-over, but might be critical for a passive X-over. 
The price and quality balance between the drivers looks convincing to me. But the customer reviews for the coax suggest that the coax X-over needs some correction.
This OB design certainly is not in the Magnetar league, but will get pretty loud on its own in a medium sized room.
Reading your image: Do you intend to terminate the front of the H frames with round holes in the main baffle? I don´t consider this a good idea because of possible reflections - but could be wrong.
Positioning the coax just above the woofers will keep the tweeter center quite low. May be you want to tilt the OB back, so that the tweeter axis will point to ear height.

Rudolf

[MJK]

ttan98,

I don't know anything about the coaxial driver so I cannot comment.

The woofer looks like a great choice for an H frame. You should be able to get flat bass down below the driver's fs of 33 Hz, I would expect bass down into the high 20's in an H frame. You will loose some efficiency in the H frame so having the ability to boost the signal with an active crossover will be important.

Martin

[ttan98]

Many thanks to both Rudolf(got your email) and Martin for their inputs.

I believe and proved by both gentlemen that the 12" Goldwood drivers in H frame I can get the freq flat to 30Hz below the freq.  I expected. Those bass fans should take note.

I am in a dilemma because I live in down-under(Australia) a fair distance from the States, transportation costs is going to be much more than I expected, more than the total price of the drivers. I have to think twice.

If proceed with this project, most likely it willl be my final project and I will make it into presentable one(my other projects are just prototypes), and keep those here posted.

Cheers.

[panomaniac]

That would sure make a budget OB system - not including shipping costs!

JBspeakerman bought a pair of those coax - I almost did.  he says that the woofer is very stiff and probably has a strong rising response.

Don't think he has used them yet, nor do I know anyone who has.   Just FYI.

[scorpion]

I agree with Pano, let the americans test the coax. If it is any value, we will hear.

However the H-frame is not unproblematic either (and especially so in combination with a high efficiency coax), as MJK's analysis shows: http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf . Simulating with Martins models an H-frame with two Goldwoods dimensioned 13" (W) x 25" (H) and 16" (D) inner measures and low-passed at 80 Hz/ 12dB/octav Linkwitz-Riley for maximally flat response will yield 75 db average SPL with 1 watt in 4 ohm. - 3 dB will be at 30 Hz and about 240 Hz. This is simulated at 2.4 m (8') distance at sitting ear-height, 90 cm (36"). 5 mm X-max will be reached at 30 Hz with 60 watts input and give an SPL of 90 dB at that frequency, average SPL will be 93 dB.

/Erling