[ttan98]

Hi,

I have been visiting this forum for some time now and have learnt a great deal from fellow contributors. Now it is my turn to contribute.

Background

Ever since the Emerald Physics CS1/2 was released I was hooked, I have built a number of models and tested them. I had no experience when I started designing and testing them and I  learned along the way. My technical background helps me a lot. The models included were:

1. TWW, T- Horn and compression driver and WW - twin 12" woofers
2. TMWW, T - Ribbon, M- 7" Mid woofer and WW - twin 12" woofers

both sounded good and none of designs were presented in this forum. Finally I  decided to change the speaker configuration to a True Dipole configuration of TMMWW.

Design

This True Dipole design is inspired by John K's NaO Note. The config. is TMMWW, tweeter, mid-range, mid-woofer, woofer and woofer. All the top drivers are from GR Research, they sounded good at the same time keeping the cost down. The twin 12" woofers were from Eminence, I chose 12" because I wanted to keep the width of the baffle to within a certain size so that it would not look "too big" in the lounge room.

a. Baffle

I have included a few images, a few notes to the baffle design:

a. The woofer baffle is separated from the main baffle that holds the TMM.
b. The main baffle is held in place in the rear to maintain rigidity and keep
     drivers vibrations  to a minimal
c. The rear to the midrange and mid-woofer are chamfered.
d. The top baffle can be removed when there is another new design.
e. The twin woofers is of U-frame design, they are held rigidly in place on the
    enclosure via a cross frame.

b. Crossover

The x-over on the TMM are all passive, 2nd order electrically. The x-over is a function of baffle design and there is no point showing the design here. The image showing the freq. response(far field, woofers disconnected) is for left and right channels, both closely tracked. The dip around 15Khz is due to the tweeter not the design. The lower curve is the response when I placed the microphone in between both speakers about 2.5m away. There is a slight rolling off at high freq. is due to horizontal directivity(the speakers were not toed in) and can be corrected when I use the Behringer 24/96 crossover unit(BehXover) or toed the speakers inwards. The tweeter and midrange is crossed over around 2500Hz.

The top/main baffle, TMM is crossed over to the twin woofers via the BehXover below 300Hz. This arrange adds flexibility to the system config.:

1. Using Bi-amping, top baffle can be driven by low powered tube or  SS amp, the TMM   has about 89dB sensitivity. The woofer section can be driven by high powered SS  amp.

2. I can contour the bass response to suit the room manually or using Room Acoustics wizard software, I have yet to use it.

Design Short Comings and Future Improvements

1. Improves the passive x-over
2. The quality and directivity of the tweeter can be improved
3. Use of Room acoustics software
4. Can change Top Baffle  to a new design.

In conclusion, I like to thank those who have contributed here and there are too many to mention here. Anyone who wishes to give any  improvement suggestions please do not hesitate to do so. Thanks for looking.

[JohnR]

Nice work! The TMM is in effect a 2.5 way?

I was wondering about the response plots you mentioned?

[ttan98]

Nice work! The TMM is in effect a 2.5 way?

I was wondering about the response plots you mentioned?

TMM is actually 2.5 you are right, sorry the missing FR curve is attached.

[Gothover]

Looks fantastic, nice work.

Dave

[ttan98]

Looks fantastic, nice work.

Dave

Thanks...Lots of friendly people here..incl. JohnR, Scorpion, etc. Enjoy visiting here.

More photos here for those interested.
http://www.flickr.com/photos/54808408@N04/?uploaded=12&magic_cookie=db9c0419c74fc347ba0368932b320751

[jimdgoulding]

Damn, sam.  What a piece of work!  The Emerald Physics got my attention, too.  No experience with OB but having OB bass seems right, theoretically, to my imagination.  Congrats.  I presume that a rear firing tweet is to keep things in scale with the other drivers cause they beem.

[ttan98]

Damn, sam.  What a piece of work!  The Emerald Physics got my attention, too.  No experience with OB but having OB bass seems right, theoretically, to my imagination.  Congrats.  I presume that a rear firing tweet is to keep things in scale with the other drivers cause they beem.

Thanks for the kind comments.

The FR curve was taken with the rear tweeter installed, I not sure about beaming of the rear tweeter, what I found is  notice there is a few saw tooth peaks on the curve, it is caused by interactions from rear tweeter. They disappear at some distance away, say 2m

This design is by no means perfect, the FR curve from rear is not as flat as I would have like, this is due to
1. rear tweeter is out of alignment with the midrange and mid woofer,
2. The rear mid and mid woofer is heavily chamfered and FR is quite different, with that from the front response.

[Poultrygeist]

Great job. Your 12's ended up larger than my 15's.

[ttan98]

Great job. Your 12's ended up larger than my 15's.

Maybe I have 2*12" and you have only 1*15" 

[Poultrygeist]

I just build a second set of H-frames that I'm stacking and the frames are 16 inches wide. Yours look wider but maybe not?

[jimbones]

Are you happy with the driver selection? If not what would you change. I am considering my first OB project but I am thinking of building a bass reflex cabinet with an OB top.

[ttan98]

Are you happy with the driver selection? If not what would you change. I am considering my first OB project but I am thinking of building a bass reflex cabinet with an OB top.

The money outlay I paid for the M130, M165 and T3, they quite cheap in comparison with the drivers such as Scanspeaks, high end Seas, Accuton, etc, these drivers are excellent drivers but you have to pay for them. One advantage of  M130 is that it very efficient, you can drive them with tube amps or any low powered amps between 12-25W quite easily. In summary GR drivers are very good drivers, if you want something better  and don't want to spend too much then drivers such as full range Tangband 1611, 5", and SB acoustics(4 ohm 5" version) are also very good drivers selling at slightly higher prices. If I were to do a redesign of the top half I will use either Tangband or SB acoustics drivers, BTW they are fairly efficient too.

Bass reflex bass can be a good match because you can get  low freq. response down to perhaps 30-35Hz, then again they are no longer a dipole config. The decision is yours, you will find the dipole bass is very different from normal bass reflex, they sound different.