20 Hz to 20 kHz Dipole Speaker System

oldgears · « **Reply #160 on:** 11 Mar 2009, 06:15 am »

Martin,

Nice project, thank you. I want to try something like what jkelly did (reply#70 http://www.audiocircle.com/index.php?topic=59619.60 ) for his speakers and use just one baffle for both drivers; though instead of seal the top end like he did and made it permanent, i want to be able to remove the middle baffle and use different baffle with different drivers like hemptone 4.5, 8, etc.....

My question is this - does the H frame need to be airtight (meaning no air leak out to the top or elsewhere) in order for it to work right or that does not matter since this is "open baffle"

Thanks.

MJK · « **Reply #161 on:** 11 Mar 2009, 09:27 pm »

Quote from: oldgears on 11 Mar 2009, 06:15 am

I want to try something like what jkelly did (reply#70 http://www.audiocircle.com/index.php?topic=59619.60 ) for his speakers and use just one baffle for both drivers; though instead of seal the top end like he did and made it permanent, i want to be able to remove the middle baffle and use different baffle with different drivers like hemptone 4.5, 8, etc.....

My question is this - does the H frame need to be airtight (meaning no air leak out to the top or elsewhere) in order for it to work right or that does not matter since this is "open baffle"

I think that you should have a tight seal all around the H frame. I am not sure it has to be glued but it should be very tight or have a gasket.

If you plan to swap out full range drivers, why do you want a one piece construction. As of this moment I have built two pairs of OBs that sit on the H frame, one has the Jordan JX92S driver and the other the Fostex F120A driver, which can be switched out in a matter of a couple of minutes by loosening some screws and disconnecting two wires per side. If you know you were going to build for only one full range driver I can understand the single baffle, but for flexibility to use multiple drivers it seems kind of limiting/complex.

oldgears · « **Reply #162 on:** 11 Mar 2009, 09:47 pm »

Quote from: MJK on 11 Mar 2009, 09:27 pm

[I think that you should have a tight seal all around the H frame. I am not sure it has to be glued but it should be very tight or have a gasket.

If you plan to swap out full range drivers, why do you want a one piece construction. A

Thanks Martin for the replied. The reason why one piece was just to please the wife as she only approved the one piece (i showed her both options.) I will try to have a gasket in there somehow. Thanks again.

oldgears · « **Reply #163 on:** 12 Mar 2009, 06:54 am »

Martin,

If I am to use the Alpha 15 for the H frame. What is the smallest dimension I can use - 21" is a little too wide for my home - do you think i can get away with 14" deep by 18" wide. Thank you.

MJK · « **Reply #164 on:** 12 Mar 2009, 10:27 am »

Quote from: oldgears on 12 Mar 2009, 06:54 am

If I am to use the Alpha 15 for the H frame. What is the smallest dimension I can use - 21" is a little too wide for my home - do you think i can get away with 14" deep by 18" wide.

You can shrink the H frame size a little. I would leave the depth the same and decrease the width and height to be just big enough to fit the driver on the baffle. So a 16" or 17" square that is 16" deep, with the same low pass crossover frequency, should work fine.

If you change the bass driver you may need to adjust the passive crossover components and double check to make sure the final efficiency matches the full range driver. If you are going active with a pair of amps then the gain settings on the crossover solves the efficiency matching problem.

oldgears · « **Reply #165 on:** 12 Mar 2009, 09:39 pm »

Great. Thank you so very much Martin. 17" square and 16" deep it is. I will go active so efficiency matching is not a problem. Thanks again.

Telstar · « **Reply #166 on:** 15 Mar 2009, 06:21 pm »

Quote from: mor2bz on 9 Nov 2008, 01:48 am

I recently received a form letter sent to those on his mailing list describing the
situation. Unfortunately many people made commercial designs without cutting
Martin in for the pittance he asked. And very few DIY types were buying his
program. Those who had bought in remain allowed, but no new subscribers
will be able to buy.

I now join the ranks of those who enjoyed the benefit of his programs and posts
in this forum, and even built one of the projects he gave for anyone to build
(the eminence alpha15/fostex 103 openbaffle), but never became a paid subscriber
for his work.

Lucky you.
I started thinking about OB projects in the end of november (see the date of the post in this very forum), right after the datasheet were removed. And I hate to have to ask people to run a sim for me.

jkelly · « **Reply #167 on:** 20 Mar 2009, 12:41 am »

I have been enjoying the use of a rear firing GR Research (Danny)
GR-T6(s) with a 5.7 Solen and 4 ohm resister. This give the sparkle
to the highs that I sometimes missed from the Jordon and really fills in the
stage nicely.

EDIT: After using the GR-T6 tweeter with caps/resistor (needed), I have to
say that I really love this speaker system. Adding the tweeter in the rear
brought life to the sound and life to the soundstage. It has transformed
the speaker for me. I am now sitting about 6 feet from the speakers almost
in the near field because I want to get closer to the music. The entire wall
is full of music now. The 18" woofer bass is addicting.
Please give this a try - I hope you will have similar results.
I have the speakers about a foot and a half from the outside walls, toed in,
and ~6 feet from the back wall.

This is with the passive crossover and Bolder maxed out SB3/PS and Rawson amp.
And of course the rear firing tweeter is wired out of phase.

Jeff