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Multi-Way Conventional loudspeakers with crossovers

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Old 26th January 2013, 08:55 AM   #1
DrBoar is offline DrBoar  Sweden
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Default One BC, homage to a classic vintage design

Here are the building blocks for my homage to a classical design
Can you guess the classiscal vintage design that was the inspiration?
Click the image to open in full size.

Some clues
1. In this prototype I use 11mm OSB. Original= 10 and 12mm Plywood
2. OSB sizes are 300x300mm and 300 x 600 mm
3. In the back is soft board coated with asphalt,
4. The softwood is part of the original design the felt is not
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Old 28th January 2013, 01:53 PM   #2
DrBoar is offline DrBoar  Sweden
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More Clues

Assembled side look like this

Click the image to open in full size..

The soft bitumen loaded board is glued to the OSB using a thin layer of latex sealer. The same method is used to glue the felt layer to the fibre board.
Click the image to open in full size.

A dry assembly of the box looks like this. There are no braces in the box and felt was glued to the back after this picture was taken.
Click the image to open in full size.

There are still one or two companies that build boxes according to these principles, but this was the start.

Last edited by DrBoar; 28th January 2013 at 01:54 PM. Reason: wrong image
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Old 28th January 2013, 01:56 PM   #3
oshifis is offline oshifis  Hungary
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Spendor BC1
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Old 28th January 2013, 07:21 PM   #4
DrBoar is offline DrBoar  Sweden
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And the winner is oshifis

Mine are a bit stockier with 35x35 cm instead of 30x30. The only bextrene driver I have for my "Dorspen oneBC", is a early KEF B200. I will use a closed box alignment with a Q of 1.0 and then use a serial cap of 800- 1200 F to lower the Q and the -3dB frequency as descrbed in an issue of Hobby HiFi. The B200 has a ugly metal color frame so I will rear mount it to hide that and also give that BC1 look. I had a pair of Audax bextrene drivers that had amazing bass but very low sensitivity but one driver broke.If that does not work out I can try an accoustic vent to lower the Q.

As a tweeter I intend to use a KEF T27. They claim that their aB crossover both reduce the hump at 10 kHz and reduce the drop above this frequency.
Otherwise I have loads of other tweeeters to use in the top octave in a BC1 style 3 way system.

I got a early primitive crossover with the B200/T27 combo and the later aB crossover was used with later quite different B200 so getting the crossover sorted out will be a challange.

I do have more modern Peerless 8" and 1" but that would not be as fun.

This one is horribly compressed for some reason the BC1 is slender not like depicted here!
Click the image to open in full size.

This look OK
Click the image to open in full size.

Last edited by DrBoar; 28th January 2013 at 07:24 PM. Reason: distorted image note
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Old 29th January 2013, 10:07 AM   #5
oshifis is offline oshifis  Hungary
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Some interesting info:

The Spendor SP-1 Speaker System

Please share your progress with the project!
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Old 30th January 2013, 12:00 PM   #6
DrBoar is offline DrBoar  Sweden
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This is how the box currently stand
The box on the left hold the drivers I intend to use KEF B200 and KEF T27, the frame that you see in front of the box is the reason to use a rear mount.
Click the image to open in full size.

The plan is to use the KEF 104aB crossover, it boost the treble above 10 kHz. I will have to work with lowpass filter to mate it with the high pass as the KEF B200 I am using is different from the one used in the original design.

I will not use electrolytic caps but proper polypropylene ones, at least in the high pass filter.
Click the image to open in full size.
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Old 16th February 2013, 09:25 AM   #7
DrBoar is offline DrBoar  Sweden
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I have been working with M J Kings A compact back loaded horn for a while but now I am back on track.
Click the image to open in full size.
The red caps are NOS 100F caps from West Germany! So I can try out 0.5 1.0 and 1.5 mF, the hardest component to find was the 0.6F.
The SP1039 has a 33 mm VC and 0.25 mH inductance while the SP1014 that I have has a 25mm VC and 0.42mH inductance, Cone and TS parameters are very similar despite that the 1039 has a much bigger magnet.

If the toprange does not work out to my satisfaction I can add a small 12mm dome or a ribbon tweeter above 8-10 kHz
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Old 16th February 2013, 12:45 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

The T27 should be good for up to 30KHz. The BC1 alike Rogers
Studio 1 used a version of the T27 as the supertweeter along
with the Celestion HF1300 tweeter, said to be critical to the
core of the BC1 sound, as a driver it does lack top-end.

rgds, sreten.
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When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
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Old 16th February 2013, 02:12 PM   #9
DrBoar is offline DrBoar  Sweden
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Celestion and Coles not KEF Spendor BC1
The studio 1 do use the T27
Rogers Speakers - Other Models


The T27 was good up to 30 kHz but that was 30-40 years ago, and at least the B200 woofer has aged and changed its TS properties, I have to make some careful measurements on the T27 as it stand today.

I do not intend to clone the BC1 rather build a cabinet and use a driver similar to the Spendor one below 3 kHz above 3 kHz and the very bass range will be different.

Last edited by DrBoar; 16th February 2013 at 02:15 PM. Reason: error
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Old 27th February 2013, 09:28 PM   #10
DrBoar is offline DrBoar  Sweden
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One trick for taming high Q drivers or drivers in to small boxes having to high system Q, is to add a large capacitor. The cap will increase the impedance just above the resonance, this lower the speaker output in this range. It also lowers the impedance below resonance increasing the output of the driver, further down range increasing impedance protect the driver compared to a closed box.

All according to an article in Hobby HiFI, what is there not to like with that! They even have equations. I short of it is that the driver Q in box should be close to 1.0 (0.9-1.1) and then you add hundreds of microfarads in series

Closed box and 100F caps 22 of them for a total of 2200F
Click the image to open in full size.

Q darn close to 1.0
Click the image to open in full size.

Then the caps in many combinations
Click the image to open in full size.
Details
Click the image to open in full size.

So far so good the impedance curves shift according to theory.
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