Would anyone like to comment on the tweeter position?
Should it be vertically centred over the mid driver or closer to the edge to minimise diffraction issues? At present it's sort of somewhere between the two.
Any thoughts about my idea for chipboard and veneered MDF?
I'll go and check out prices next.
Simon
Should it be vertically centred over the mid driver or closer to the edge to minimise diffraction issues? At present it's sort of somewhere between the two.
Any thoughts about my idea for chipboard and veneered MDF?
I'll go and check out prices next.
Simon
Some ideas:
If you screw some heavy slabs (concrete, cobble stone, bricks or whatever you want) to the underside of the horizontal U frame braces you will have some real mass loading to the construction. You wouldn´t need the plinth to reach forward either because the baffle would NEVER topple to the front.
Don´t care too much about decreasing the back opening cross section. 10 % less will do no harm. You could even take a 30x20 cm slab and use it as the bracing instead of wooden ones.
There are mirror tiles of different sizes on the market. If you find them 20 cm wide, you could clad the U frame sides with them. It will make the U frame disappear visually.
Why don´t you want to build the top part of the baffle symmetrically with mid driver and tweeter in line with the woofers? The baffle would look like a pyramid with the peak cut off.
If you prefer the asymmetric look you could still line up midrange and tweeter with the woofers. You still would have a short and a wide baffle side to the drivers.
If you screw some heavy slabs (concrete, cobble stone, bricks or whatever you want) to the underside of the horizontal U frame braces you will have some real mass loading to the construction. You wouldn´t need the plinth to reach forward either because the baffle would NEVER topple to the front.
Don´t care too much about decreasing the back opening cross section. 10 % less will do no harm. You could even take a 30x20 cm slab and use it as the bracing instead of wooden ones.
There are mirror tiles of different sizes on the market. If you find them 20 cm wide, you could clad the U frame sides with them. It will make the U frame disappear visually.
Why don´t you want to build the top part of the baffle symmetrically with mid driver and tweeter in line with the woofers? The baffle would look like a pyramid with the peak cut off.
If you prefer the asymmetric look you could still line up midrange and tweeter with the woofers. You still would have a short and a wide baffle side to the drivers.
Lots to think about there, I've got to work on some ballast... See attached - 500VA tx is good ballast for the bottom, and I've drawn a paving slab on the mid section brace. The bottom will also have a brace so the bottom is two or three layers of wood/material thick. I do need to check for clearance behind the woofers.
The mirror idea is interesting, but probably not for me. I have no need to make them look small, I simply don't have much space.
I hear what you say about a cut-off pryamid, I'll have a go at drawing it. I've avoided it because of the extra work but if it looks much better....
On the sketch, the green and pink panels are coloured to remind me that they'll be the same size as each other.
The mirror idea is interesting, but probably not for me. I have no need to make them look small, I simply don't have much space.
I hear what you say about a cut-off pryamid, I'll have a go at drawing it. I've avoided it because of the extra work but if it looks much better....
On the sketch, the green and pink panels are coloured to remind me that they'll be the same size as each other.
Attachments
Hi Simon,
The mid/tweeter baffling looks fine to me. Breaks symmetry and keeps drivers more out from the walls.
However, you have a sided channel bebeath the mid which will develop its own sound.
If mine I would cut diagonally between about one inch back from the baffle at the top of your existing side wing to about one inch above floor level at the back.
This is something you can try before you make it. Try holding different sides up to your old speakers whilst they are making music.
Cheers ......... graham.
The mid/tweeter baffling looks fine to me. Breaks symmetry and keeps drivers more out from the walls.
However, you have a sided channel bebeath the mid which will develop its own sound.
If mine I would cut diagonally between about one inch back from the baffle at the top of your existing side wing to about one inch above floor level at the back.
This is something you can try before you make it. Try holding different sides up to your old speakers whilst they are making music.
Cheers ......... graham.
Looks like an interesting design, should make some good sounds!
If you can't use 15" drivers due to space but want a higher Qts perhaps consider using the Alpha 12 driver. Fairly high fs mind:
http://www.bkelec.com/Pro/Drive_Units/Eminence/Alpha12.htm
If you can't use 15" drivers due to space but want a higher Qts perhaps consider using the Alpha 12 driver. Fairly high fs mind:
http://www.bkelec.com/Pro/Drive_Units/Eminence/Alpha12.htm
Hi Graham,
Can you clarify what you mean by cutting at a diagonal?
I had thought about the reflection from the mid driver onto the top brace, and I'd thought about cutting a shallow semicircle out of the brace and chamfering the edge to minimise nasty reflections. I don't know if it's needed or if it will help though!
I've attached the latest sketch including the cut-off pyramid shape - it does look better. I also added some more details to clarify what's what. I modelled this mid placement in Edge and we have a similar peak to before: 3dB, and roll-off is -3dB down from the flattest part @ 200hz. I'm worried about integrating that mess with the woofers.
Simon
Can you clarify what you mean by cutting at a diagonal?
I had thought about the reflection from the mid driver onto the top brace, and I'd thought about cutting a shallow semicircle out of the brace and chamfering the edge to minimise nasty reflections. I don't know if it's needed or if it will help though!
I've attached the latest sketch including the cut-off pyramid shape - it does look better. I also added some more details to clarify what's what. I modelled this mid placement in Edge and we have a similar peak to before: 3dB, and roll-off is -3dB down from the flattest part @ 200hz. I'm worried about integrating that mess with the woofers.
Simon
Attachments
Hmm, assumed it was an honest 6mm each way but your probaby right actually. You could model the power handling in WinISD Alpha; enter the driver then simulate it in a 10,000l (ie, infinite) sealed to find out how much power it can handle wrt excursion limits. You can then calculate the max SPL response based on your original OB response graphs. Alternatively you can pay for a liscence for the Basta! software, this will do full modelling of this type of speaker 
It seems unlikely in reality but WINISD Pro Alpha thinks 2 902.222s will take the full 180W of my amps right down to 30hz in a 10 000L box. 115dB @ 50hz. Clearly the numbers will be down, waaaay down when using a 2nd order filter @ <100hz and open baffle loading, but it can only be louder and more dynamic than the mk1 speakers.
Don't ask how I worked this out (it's partly guesswork and partly from external help) but I calculate the speakers will be able to push about 98dB @ 1m @ >50hz with full power from the amps, after open baffle and crossover losses have been factored in.
I know that doesn't sound a lot but in-room should be higher and is already a lot louder than I need in my tiny bedroom. I think I will have good headroom with the Skytronics.
As an aside, the Skytronic 902.222 gives a good sealed box response, e.g. 80L Qtc=0.78 F3=44hz. It might make a great budget 3-way woofer. I also may try a couple on my car's parcel shelf, with T-bass, all in good time!!
Don't ask how I worked this out (it's partly guesswork and partly from external help) but I calculate the speakers will be able to push about 98dB @ 1m @ >50hz with full power from the amps, after open baffle and crossover losses have been factored in.
I know that doesn't sound a lot but in-room should be higher and is already a lot louder than I need in my tiny bedroom. I think I will have good headroom with the Skytronics.
As an aside, the Skytronic 902.222 gives a good sealed box response, e.g. 80L Qtc=0.78 F3=44hz. It might make a great budget 3-way woofer. I also may try a couple on my car's parcel shelf, with T-bass, all in good time!!
Oh no Graham, don't say that! A gradual slant outward to the floor sounds good on paper, it's just massively harder to build, as Arnold Laver (et al) won't cut at an angle, and I can't match their cutting quality so want as many straight right-angled lines in the design as possible.
I personally prefer the pyramid style look and am pleased that it keeps the acoustic centres aligned vertically. On the other hand, the single slant arangement keeps the HF and MF drivers further away from the side walls, which is a plus for that layout. It's also slightly less complex to cut.
Overall I'm very pleased with how this design's shaping up, even if I sacrificed a lot of work today to get there lol
Simon
I personally prefer the pyramid style look and am pleased that it keeps the acoustic centres aligned vertically. On the other hand, the single slant arangement keeps the HF and MF drivers further away from the side walls, which is a plus for that layout. It's also slightly less complex to cut.
Overall I'm very pleased with how this design's shaping up, even if I sacrificed a lot of work today to get there lol
Simon
SimintY,
I like your speaker configuration, however the choice of drivers is debatable. I think Brett thinks you may like to consider a pro mid range driver, for eg. B&C 8" ($92) or PHY 1120($120). Alternative tweeter which is preferable you may like to consider are, Aurum Cantus CS2i or Neo3. All these are not so expensive when compared to the drivers you are using now.
Cheers
I like your speaker configuration, however the choice of drivers is debatable. I think Brett thinks you may like to consider a pro mid range driver, for eg. B&C 8" ($92) or PHY 1120($120). Alternative tweeter which is preferable you may like to consider are, Aurum Cantus CS2i or Neo3. All these are not so expensive when compared to the drivers you are using now.
Cheers
ttan, I think the drivers have been bought already...
Simon, great start to the project. I'm impressed; you're obviously a lot smarter than me!
I piked out and bought some Silver Irises as I just want to get some decent speakers up and running and have a few projects on the go at the moment that I need to finish. I still intend to play with an original OB design one day.
I'll be following this thread!
Cheers
Stuey
Simon, great start to the project. I'm impressed; you're obviously a lot smarter than me!
I piked out and bought some Silver Irises as I just want to get some decent speakers up and running and have a few projects on the go at the moment that I need to finish. I still intend to play with an original OB design one day.
I'll be following this thread!
Cheers
Stuey
Simon,Graham Maynard said:
you need the complete U frame structure urgently. Please refrain from cutting off anything. Taking off the top baffle (or cutting holes in it) alone would cost you around 3 dB throughout the bass area. Slanting the side wings as described by Graham would cost you another 3 dB - at least.
Look at the first diagram here to get the message. In this regard your U frame would be equivalent to my H frame.
Rudolf
SPL responses tell us little about the *sound*.
A constantly dimensioned channel generates an audible signature due to differential pressure modification of the LF driver's response, also when excited by a mid or corner reflection. Sloping (support) wings reduce the channellised wing sound.
I think one driver having almost no wings (start of slope) wired directly in parallel with one having shallow wings (end of slope) will reproduce much more cleanly than a baffle with full woofer height parallel wings. This was why I suggested to Simon that he try holding different shape/size wings up to his baffles whilst music was playing.
On the OB Speakers forum Chakija has just reported that he prefered reproduction with the wings removed from his baffle, so I'll repeat here what I wrote in that thread -
More bass does not equal *better* bass !
Rudolph; the transformer-bass circuit is an electrical circuit capable of increasing low LF response as if the driver is mounted in a U frame, though without imparting the same differential pressure induced transduction distortion that a U frame imposes upon reproduction.
Cheers .......... Graham.
A constantly dimensioned channel generates an audible signature due to differential pressure modification of the LF driver's response, also when excited by a mid or corner reflection. Sloping (support) wings reduce the channellised wing sound.
I think one driver having almost no wings (start of slope) wired directly in parallel with one having shallow wings (end of slope) will reproduce much more cleanly than a baffle with full woofer height parallel wings. This was why I suggested to Simon that he try holding different shape/size wings up to his baffles whilst music was playing.
On the OB Speakers forum Chakija has just reported that he prefered reproduction with the wings removed from his baffle, so I'll repeat here what I wrote in that thread -
More bass does not equal *better* bass !
Rudolph; the transformer-bass circuit is an electrical circuit capable of increasing low LF response as if the driver is mounted in a U frame, though without imparting the same differential pressure induced transduction distortion that a U frame imposes upon reproduction.
Cheers .......... Graham.
ttan98 said:
Hi ttan,
I've already bought the drivers, and I chose them carefully. If I don't like the tweeter I'll have to buy another later. The mid is a safe bet, it's made from paper and has a cloth edge and a large magnet. It has a great response and high efficiency. These are surely ingredients for good sound. Because it's cheap I won't mind cutting off the dustcap and installing a wooden phase plug, damping the basket and even dabbling with the EnABL treatment. FWIW I think it's intended as a low price pro driver. The woofers were chosen purely due to their low price and suitability for open baffle loading. It's too late to say I did it wrong now
Stuey said:
Hi Stuey, thanks for your interest. The road ahead is long...
Rudolf said:
Hi Rudolf,
If I disobey you it's not because I didn't listen first. I'm contemplating a slant, but I'd not remove the top of the U, and to compensate I'd make the bottom of the wings wider. This might be the best of both arguments - each woofer bringing slightly different sounds to the table.
Graham Maynard said:
My experience of this was concreted when playing with crossover slopes and values previously. What looked good on my screen didn't always sound good - BOTH listening AND measurements are vital IMO.
I really appreciate all the comments and advice so far, thanks everyone.
Simon
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