[evozero]

Hello all, My first post so please be gentle.
I stumbled across this forum while looking up EP cs range and GR research open baffles. I have built some simple OB's to try out this type of speaker system. I have no technical knowledge, and copied someone else's design. Here is the recipe.

My room is only 14ft X 12ft 9ft ceiling, with speakers against the rear wall and 3ft from side walls.
The baffles are Two panels cut to 38"x10" & the front panel 26"x38",Drivers are mounted at centres of 6" and 22" when measured from the top of the 38x16 panel.
2 x Audio Nirvana super 8 & 2 x Eminence Beta 15. Both with Dynamat on the cages, a very worth while tweak!
I have a 150uF Mundorf capacitor in line with the full ranger, along with a crappy 4.6ohm 7watt wire wound resistor.
Passive 8 Ohms subwoofer filters Crossover frequency 120Hz,12dB/oct.
The AN8's are powered by a DIY Tubelab Simple SE, single ended, and the Beta 15's by an old 20WPC Sony integrated and adjusted the output to bring up the bass.
Looking at the EP and GR systems, they have much narrower front baffles. This makes me think i should be doing the same?
I am thinking about buying some parts express plate amps to replace the Sony amp and remove the passive filter,
http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=300-804&scqty=2
These will give about 170 watts RMS @ 8 ohms output.

But this has me thinking, save the money and start acquiring the parts for a Super V or similar?
Would this be too large a system for my room, and if so could i reconfigure my current drivers on to a better baffle design?
Many Thanks
Ian

[gvimhoof]

Hello Ian,

I run an FE103E open baffle over an Eminence Alpha 15 in an H-frame passively.  I got the design from Martin King's website www.quarter-wave.com and I have been very happy with the results.  I'm no expert, but he is and I recommend spending some time on that website and subscribing to his worksheets.  I run my speakers ~4ft from the back wall, in order to let the sound stay open.  Too close and they really suffer.  This leaves me with ~8.5ft throw to my listening position.  I like the looks of that cloth on your baffles!

[evozero]

Hi Gvimhoof,
I am aware of Martin Kings website, i think that is where my baffle design originates.
After reading this article below, i have tried to position the speakers as suggested and remove the sound absorbing panels behind to allow the Di-pole reflections to bounce off the wall.
http://enjoythemusic.com/diy/0709/open_baffle.htm
It did make a huge difference, but my baffle being so wide might be blocking some of these reflections.
This is why I was asking for suggestions on baffle design, for these drivers if possible.
Or even change the speakers for something like GR research, either way I am not going back to a box design, love open baffle!
Cheers
Ian

[Rudolf]

... but my baffle being so wide might be blocking some of these reflections.

Ian,
without knowing the precise specs of your ANs and the crossover, I would suggest the following:



Cut the baffles to the width you need for the Eminence (red). Recuperate the lost bass by installing a sort of H frame to the Eminence - 10 cm deep to the front and 10 cm to the back of the baffle, as indicated in blue.

The AN will loose 2 dB in the 100-250 Hz range and will peak 1-2 dB around 500 Hz, but I can hardly suggest any suitable change to the crossover without seeing measurements. It is a quick and dirty proposal, but if nobody else is suggesting a more educated guess ...

Rudolf

[gvimhoof]

I agree with Rudolf.  Open baffle over H-frame gave me excellent results.  If you have pulled your speakers away from the wall and decided that you can live with them in that placement, then I would encourage this approach.  The speakers I built (in my earlier pic) only have a footprint of 16in X 17in.  The baffle itself is 16in X 38in X 1in.  They really don't take up a lot of real estate and they have a wonderful open sound out there on their own.

PS-  you can see the "full review" on my thread "Question about Open Baffle project," as far as how they sound.  I don't think cutting it down to 16in wide will compromise your AN's performance.  Those seam to get really good write-ups here, as well as other forums.

[evozero]

Hi Guys,
Thanks Rudolf for the diagram, this is exactly the sort of input i am looking for.
I will try and fill in some  details, the AN has a 150uF Mundorf capacitor, crappy 4.6ohm 7watt wire wound resistor. AN spec sheet;
Although I have heard the spec is not accurate, but have no measurement equipment or software.
The Beta 15 has a Passive 8 Ohms subwoofer filters Crossover frequency 120Hz,12dB/oct.
Crossover

Barebaffle
Baffle details, panels cut to 38"x10" and frony baffle cut to 38"x16"
As you can see the side panels are 10” deep and only one side, so I have more wood available to make the H frame deeper if need be.
In the OB article above it discusses “The distance to the top of the baffle and also the shape of the baffle top, does seem to have a greater potential for effecting the final sound. This is a bit more involved with the soundstage illusion and will be covered more in the next section. For now I would say that it is generally considered prudent for this distance to not be our shortest. If the shortest distance to an edge is this top dimension, some suggest that the sound will interact in this area first and have ill effects on soundstage. We also have seen good results from making these top sections domed or sloped. “

What do you think to this suggestion, also putting felt on the rear of the panels?
Many thanks for now, I am really grateful and learning a lot.
Cheers
Ian

[evozero]

Hi Again,
Looking at your suggestion again, i could remove the rear 10" baffle and cut the marked vertical line on the front baffle, this would give me another 10" baffle to use. cut them at 24.5" height and glue them on the sides. Then cut four pieces for the top & bottom of the H frame, two for the front, two for the back.
Do this sound ok?
I have been trying to understand Martin J Kings document about U & H frames, so i get why you are suggesting this idea and it makes sense.
What about the cross over, will i need to change it?
Many Thanks
Ian

[Rudolf]

Ian,

I just got aware that you have an additional panel at 90° to the loudspeaker baffle. I can't simulate that with any precision, so the following will be some wild guess:



Above is a simulation for the AN S8 in your baffle with the cap and resistor: dotted line for the baffle as of now (old baffle) and continuous for the baffle as proposed (new baffle). You see how the wide baffle sims fairly flat from 250 Hz on. The red line is the nominal SPL level for the AN in this situation. The AN would be 6 dB down at 120 Hz (left vertical pink line). This indicates that the sim is not thaat shabby. 

The new baffle shows a broad 3 dB peak from 400-1300 Hz. This should be EQed with a notch filter. We can calculate that filter somewhere in the future. The crossover to the Beta15 should move up from 120 Hz to 160 Hz (right vertical pink line), which should be no problem either.

I would suggest that you remove the rear 10" baffle and cut the marked vertical line on the front baffle to get a baffle width of somewhere near 16''.

If you can follow my suggestions and want to proceed, just let me know. We can look into the notch filter and the crssover than.

Regarding that OB article: IMHO you should work with the existing baffle first and watch, how it turns out. You can always change to another baffle with another driver position later, but such change can't certainly not be 'under my control'. 

Rudolf

[evozero]

Rudolf, this is brilliant, thank you for helping me.
The current incarnation is my first speaker build, I just copied someone else. The Beta just uses a cheap off the shelf sub woofer filter, so I was anticipating optimising this and maybe using better quality parts, maybe you could advise me?
I have some spare wood, so if it ever stops raining in London I will get the saw out!
Should I go strait to adding the H frame around the Beta, and cutting the front baffle to 16"?
Cheers
Ian

[Rudolf]

Ok Ian,

let us take the next step. Yes, you can cut the front baffle now to 16". In a room as small as yours you really need to take the "narrow" baffle route to get the dipole effect working. For the H frame I would like to do another sim to see how deep it needs to be. Can you tell me the values on the subwoofer filter parts and how they are connected? This would help in understanding the original design better.

Cheers
Rudolf

BTW: Do you have any means to make your computer your audio source? It is not about measurements in any way - it's only listening to some sinus tone sweeps later when we fix that notch filter.

[evozero]

hi again Rudolf,
I can use the wife's laptop to connect to the hifi no problem.
The sub woofer filter is ready made, Crossover frequency 120Hz,12dB/oct is the listed spec on the manufacturers website.
http://avslgroup.com/product/900.584UK So I don't know the capacitor and inductor values, sorry.
I use valves to power the AN8, and a Sony integrated amp for the Beta 15". So far I have just used the volume on the Sony to adjust the bass levels.
Do I need the H frame with this configuration? or just turn up the Sony and to compensate for the narrower baffle?
Another option is to but the parts express plate amps, they have a built in Adjustable crossover from 40 Hz to 180 Hz, and has a slope of 24dB per octave. They are on sale until this Sunday, so should i go for it?
My uneducated guess is the sound stage is being partly blocked by the wide front baffle, sat in the sweet spot there is huge depth, then sound appears to radiate front the front baffles forward.
Many thanks
Ian

[Rudolf]

Hi Ian,
I've finally got a grip on what you have at home.
If that is really a usual 120 Hz/12 dB filter, the response of the Beta 15 in your wide baffle will look like this (left):



This means very prominent kick bass (can be fun), but not much deep growl. Is that what you experience at home? Under dipole conditions you need a nominal 40 Hz filter to achieve an acoustic 120 Hz slope (right). A passive 40 Hz dipole filter needs a 30 mH inductor - ouuch . Last time I looked they were 50 Euro.

You would be way better off with one (or two) of those plate amps.

To get the same bass response in the 40 cm wide baffle compared to what would be possible in your big baffles you would need a H frame with 40 cm depth front-to-back. I was a bit too optimistic when talking about 20 cm. 

If you would want a pure plain baffle of 40 cm width, you could achieve the response shown by the light red line. You loose about 6 dB of loudspeaker volume. Note that it is not your amplifier which might run out of gas, but the Beta 15. Whether that is a problem depends very much on the levels you are listening at. If you need a higher level than the pure baffle will allow, you can still add the H frame later.

This is the filter you need for the AN:



I have omitted the 150µF cap. You can do that if your valve amp is not DC coupled at the output. Otherwise you need the cap to block off any DC, but you should triple up to at least 470µF.

This has been much info pressed into a short place. Feel free to ask any questions, if I was not clear enough.

Rudolf

[evozero]

Hi Rudolf,
I don't really have a comparison for the bass sound, I think the kick drum is pronounced as you suggest.
I never could get much bass running all drivers from my valve amp, only adding the Sony fixed this.
If the H frame needs to be 40cm deep, i will build it from scratch and get some extra wood.
This I think is better, as i can leave these baffles as they are and try out a new design, then if it's an improvement transfer the cloth etc.
So starting with a clean sheet, What would you suggest? I don't mind a completely different design.
would I use the same H frame dimensions. Then add a baffle on top, maybe a rounded top to help imaging?
I am going to order two of the plate amps from Parts express and will get the passive components at the same time.
As i remember it, the 150uF cap was to stop the lower frequencies for the AN8, the resister 4.6Ohm i came to attenuation the output of the AN8.  So both components could be wrong and can be replaced.
Many Thanks
Ian

[evozero]

Ok, I had some free time. Popped down to my local wood yard to collect some oak veneered MDF. I asked them could i have a look at some off cuts, found two pieces of 18mm birch ply about 100cm x 53cm. How much governor? Take em, he said!

So now the possibilities have really opened up.
I realise this might be taking too much of your time, so please say if I am asking too much.
I can ask for help on DIY Audio if that is the case.
I am really excited now!
Cheers
Ian

[Rudolf]

Ok, I had some free time.

Free time is bad. It mostly ends in spending money. 

How much governor? Take em, he said!

You have been lucky. 

So now the possibilities have really opened up.

We will try to use that to your advantage.

I realise this might be taking too much of your time ...

Too late, it already has taken too much of my free time. But it has kept me from spending money instead. So I have to be thankful to you, mate. 

Hi Ian,

let's jump into business immediately. You want the baffle for the AN to be 40 cm wide, not much wider or smaller. The centre of the AN should be 15 cm below the upper baffle edge. The total height of the baffle would depend on the driver height, which you can choose freely. Rounding the top of the baffle concentric to the AN would be counterproductive. It should be straight. You may do an inclined cut if you want so. There is absolutely no need to round off the edges of the baffle in any way, but it does not hurt either. Same for placing the AN off center on the baffle. It really does not help with the acoustics, but you could choose it for aesthetical reasons.

The H frame needs to be at least 40 x 40 cm inside - otherwise you will have difficulties to later mount the Beta 15 on its baffle. When placing the mounting holes for the driver, avoid to have them nearest to the baffle edges.

Depth of the complete H frame is 40 cm too - including the mounting baffle for the Beta 15. You are free to construct the frame any way you want. If you want to have the baffle for the AN exactly as wide as the outside of the H frame, it obviously needs to be almost 44 cm wide. That would be no problem WRT acoustics.

The depth of the H frame is not to be carved in stone. It can be reduced down to 20 cm, but you will lose bass efficiency below 80 Hz on that way.

There is no rule that the baffle for the AN and the H frame must be in one piece. It is convenient (and will provide slightly more bass), but you can make them separate items, if you want. They have to be placed side by side however when in use.

You will need the three parts for the notch filter and you should retain the 150µF cap and the resistor. In connection with the plate amp they will be part of the different choices you have to get the best crossover between both drivers. More about that later.

Now we want to see some sawdust ...

Rudolf

[gvimhoof]

Obviously, that wood shop is in on a conspiracy to get you hooked on OB DIY!   

Sawdust!  Sawdust!  Sawdust!

[evozero]

Hi Rudolf,
I can waste as much time as you have, thanks 
I have been learning Sketchup to help design this quickly, my friend is a auto cad / 3DSmax guy and offered to model it properly next week.
But just to give you an idea.

The H frame box is 40x40 and 40 deep with the beta in the middle.
Front baffle sits on top and is 57cm high, with the AN centred at 32" with 15cm to the top of the baffle. This sets the AN centre the same as the current baffle, around ear height when sitting down.
I will make some side panels to add rigidity and blend the H frame and  front baffle, with a cut out meeting near the bottom of the AN.
Any suggestions, or changes to the components?
The parts express sale ends Sunday for the amps.
Many, many thanks
Ian

[jhm731]

Rudolf-

What's your thoughts on this OB plan for use with the AN Super 8 Alnico?

Thanks,

Dan

[Rudolf]

Hi Ian,

Sketchup is good enough for me anytime.
Your design is approved. The crossover between the drivers will be 200 Hz max, so pushing the baffle to the front of the H frame will be no problem.
I am a little bit concerned that the side panels might get to high up. I would not let them extend beyond the straight red line in any direction. Something like the curved line would be very ok.



If you are thinking of side panels like on Linkwitz' Orions - they are only second best for stability and will make the baffle wider. Then we would have to calculate a notch filter for a U frame geometry -which I can't simulate with sufficient precision.
If you are concerned about the rigidity of the forward baffle, you should think about a central spine behind the AN. It is always better to stop unwanted motion, where it it generated, instead of 20-30 cm away.

I thought the PE amps had been ordered already. There are really no caveats about them from my side. If you need side panels as deep (or deeper) as those on the Orions you better wait with the filter components until a final decision and source them locally. There should be some electronics component shop even in London. The component values already given will be fine for the baffle as shown.

This starts to make fun. I'm just getting MJKs worksheet for the H frame and OB combination. So i am pretty shure this will become a quite decent system.

Rudolf 

[Rudolf]

What's your thoughts on this OB plan for use with the AN Super 8 Alnico?

Hi Dan,
If you offset your driver horizontally on that baffle, it will beam to the "short" side:



For everybody sitting outside the sweet spot this will mean different frequency response from both drivers.

I prefer centered drivers, even when on-axis response is less linear, and listen about 15° off axis:



I took the parameters for the AN super 8 without Alnico (as above). Don't care for anything above 1500 Hz in the simulation. It is for the pistonic driver only and does not know about brake up mode or whizzer cone.

Rudolf