[chakija]

For past 16 moths i have been playing with several different mid and FR drivers, and i am currently settled with these old alnico oval FR. I installed phase plug and got even better results.
Only problem is i don't have any specs, only that they are 4 Ohm 5 W...dustu pictures 
Sound is quite fine with only one alpha crossed with 6.7mH and  30uF (that values i had in "drawer" ) and oval playing FR, but i feel like i need more bass. I know it is difficult to say if 2xalpha will be sufficient or maybe too much, but i am willing to try anyway.
I wanted to ask if this baffle shape and position of loudspeakers on baffle is adequate?


Cheers !

[Graham Maynard]

Normally elliptical drivers have their longer dimension vertical for broader horizontal radiation.

[chakija]

Hi Graham...
TY for replying. I have modified baffle like u said and i made it leaned for 5 deg angle.
Please excuse me for mu idleness, but how would your T-bass perform in this configuration ?

[Graham Maynard]

I know it will work fine, but it would be better to get going as standard in order to take first footsteps towards the understanding we all need.
That same choke should work fine if you have a transformer you can press into service with say a couple of 1 ohm resistors and a 1,000uF capacitor. 

[chakija]

Is there anyone who has pictures of "new" series of Alpha's ?
Mine has silver sticker on magnet, and i heard that new ones have black sticker and rubber surrounding on magnet. Is there a possibility that T/S parameters are different ?On Eminence site, link for pdf of 15" Alpha is broken   

This may sound kinda stupid, but would u recommend to put 1 of this new ones with old series of Alphas so that i would then have 3 old and 1 new Alpha because my local dealer doesn't have 2 new alphas in stock but only 1 old and 1 new ??!??
I could get 2 new, but i would need to wait for next shipment 

[Graham Maynard]

Hi chakija,

Can you try one new driver, and if better then wait for another ?

Personally I have found running similar sized drivers which have slightly different characteristics on an OB to be better than running two which are identical. 
This would not necessarily apply to drivers sharing cabinet volume.

Cheers ........ Graham.

[chakija]

HI Graham,

I will order 2 new Alphas because i find it at another loudspeaker dealer. Meanwhile i will be working on my baffle ,if you agree that its shape is acceptable...

Thanks again for your reply and advice ! 

And another question...
If i wire 2 alphas in parallel, then 6.7mH would give me 6db slope at ~95Hz . Is it a good starting point for adjusting because my oval FR would go down to ~150 Hz without crossover ?!?
Even now with only one alpha ,this 2 blend fine enough to my ear...

[Graham Maynard]

Hi chakija,

You are making a good start there

The cut introduced by the choke cannot be calculated as with crossover circuitry because it is low pass until the capacitor notch tunes it with series resistor Q reduction.
Stick with that choke value.

Effectively the capacitor introduces a turnover between say 30 and 70Hz depending on value, and the peak depth of cut (at say 120Hz to match corner sited baffle reproduction peaking) is controlled by adjusting the (cheap) resistor values.

The frequency response is not 'king' however - but this cannot be appreciated until the circuit is auditioned and optimised for individual constructions and rooms, whereupon the benefit becomes immediatel recognisable.

A simple series C with damping resistor connected directly across the voice coils might be all your oval will need.

Cheers ........ Graham.

[chakija]

Hi again...
Could u plz comment setup shown on the picture ?
Is this a right way to put 2 Alpha's on H baffle ?
Is 20'' depth enough ?

[Rudolf]

Is this a right way to put 2 Alpha's on H baffle ? Is 20'' depth enough ?

Look at this simulation of scorpion for two Alphas in a H frame. http://www.audiocircle.com/index.php?topic=59619.msg530516#msg530516 Dont miss the explanations up to post #20

[chakija]

Hi Rudolf !

That simulation really looks promising indeed !
It shows just the right sensitivity i am trying to achieve !
Now i only have trouble to decide how to mount drivers on baffle.
I didn't quite understood position of drivers on baffle and baffle shape ?!? Are they mounted like orions, or like shown on picture i posted, without that "middle" partition ???
I did figured that height doesn't have that much influence 
And what about leaning mounting baffle slightly so that it make, say 85deg with floor instead of 90 ???

[Rudolf]

You don´t need a partition between the drivers in the H frame for acoustical reasons, but any horizontal bracing will improve the rigidity, keeping the frame from resonating. You also don´t need to build a step between two baffles - as done in the Orion. One baffle for all drivers could do - if stiff enough. And I don´t think that 85° would make any difference compared to 90°.

[chakija]

Thanks for clarification!

On my local forum we talked about benefits of dual woofers in H baffle comparing to singe (or dual) in flat baffle,U ,or even H baffle with Graham's circuit...
It is clear that T-bass brings new things in bass, but what i am now deciding is whether to buy another par of alphas, or i should try T-network first in order to reach this ~93db spl which are shown in scorpion's simulations.
Expense is almost same...

[Rudolf]

It is clear that T-bass brings new things in bass, but what i am now deciding is whether to buy another par of alphas, or i should try T-network first in order to reach this ~93db spl which are shown in scorpion's simulations.

Two Alphas should give you some bass to start with. And you could always add one more to each baffle later.
I´m not sure about the T-network. Read somewhere that it includes a low pass at 75 Hz, but I´m not sure. In that case you had to Xover to the wideband driver at that frequency. I believe your alnico would better be crossed at ~200 Hz than at 70-80 Hz. Maybe you should ask Graham for the best solution WRT T-bass.

[JoshK]

What do you guys use for simulating passband now that MJK's software is gone?  I was looking to try out the Alpha 15"s (x2 per side).  I'd just go with what Erling and MJK had modeled, but I am looking for a different passband target (shifted higher, say 50-300hz or thereabouts, 400hz might be nice).  I am guessing I can make the H shallower to acheive my goal, but it'd be nice to tinker.

I don't know if the upper end is also limited by the Alpha's or just the H baffle resonance. 

FWIW, I am trying to keep to a 20" width.  I am using a AES Lambda TD12M for mids crossed (passively) to a WG loaded B&C250.  I am intended to use an IB sub below 50hz.  The crossovers at 50hz and from woofers to mid will be active, with active amping. 

P.S.S. because my room has very large openings into the rest of the house (8' tall by 8-12' wide archways), I don't perceive much room gain below 50hz.  There is some modes above that obviously. 

[chakija]

Well, i finally bought those two alphas and i must say they sound different. I hope that my dealer will replace them when new shipment arrive 
The new one, with black sticker has much less shouting in mids and it radiates more lower bass energy comparing to silver sticker alpha.
I hope that there is someone to confirm this...

[Graham Maynard]

Hi Josh,

Wall openings do not make any SPL difference (other than loss of reflections and standing waves) when the LS is an OB dipole.
OBs don't pressurise a room volume in the same way a monopole does.

I have had my excellent test 18" + 15" drivers on a single upright 18" wide Contiboards; the taller - the better !

Cheers .......... Graham.

[JoshK]

Graham,

Thanks for the response.  I know about how dipoles load a room, etc.  What I was trying to ask is regarding the passband due to the H profile creating a resonance.  One must lowpass the dipole woofers below that resonance for good fidelity.

I wanted to know people's experience with making an H less deep, which will lessen the "D" and thus move the dipole loss corner up higher.  I am willing to trade the low end to try to move the higher end upwards.  I wanted to know if lessening the depth of the H would possibly also shift the resonance upwards as well, or whether it was strictly based on the dimensions between the side walls. 

Hopefully my question is clearer now.

Josh

[Rudolf]

I wanted to know people's experience with making an H less deep, which will lessen the "D" and thus move the dipole loss corner up higher.  I am willing to trade the low end to try to move the higher end upwards.  I wanted to know if lessening the depth of the H would possibly also shift the resonance upwards as well, or whether it was strictly based on the dimensions between the side walls. 

Josh,
there is only one source of resonance in a H frame and - yes - those quarter wavelength resonances will shift upwards with lessening the depth of the H. There are no resonances based on the dimensions between the side walls.
Widening or narrowing the H-frame will alter the effective depth "D" of the H frame to some degree, but it will not introduce a separate resonance.

[panomaniac]

...black sticker has much less shouting in mids and it radiates more lower bass energy comparing to silver sticker alpha.

That's strange.  Do they otherwise look the same?