Defaktum: Scanspeak Three-way - diyAudio
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Old 6th January 2012, 11:12 AM   #1
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Location: Cheshire
Default Defaktum: Scanspeak Three-way

I am about to embark on a 3-way floorstanding speaker project to replace my AOS Studio 12XL, that I had to get rid of due to a crawling baby that has appeared at home. Scan-Speak

I am very keen to do a version of the Hobby Hifi Faktum: Hobby HiFi Loudspeaker Kits: Faktum
Crossover points, 150Hz, and 2.2kHz.

I do have some physical limitations however, and for aesthetic reasons, I want my speakers to be only circa 60cm high. I have designed a pyramid style enclosure that maintains the baffle shape, and spacing of the drivers, however it will only have a bass cabinet of 30-40 litres instead of the 60 litres of the original design.

Click the image to open in full size.

I have seen the HazAudio.co.nz website, and they recommend using the 22W8851 in a 1.2 cubic foot enclosure with a 2.5" vent by 8" long for F3 of 38Hz. This is about 33 litres, which I can accomodate. Extreme low bass is not essential.

Two questions to start with:

Will the reduced bass cabinet volume and different tuning affect the blending with the midrange driver, or just change the bottom end?

What affect will there be due to the bass driver being only 10cm from the floor?

I am aware that the tweeter should be at ear height, but I have tried the AOS Sudio 12s (nearly identical tweeter and mid drivers) on the floor, and their dispersion characteristics were fine.

I have a copy of the original Hobby Hifi Faktum article. Here is a copy of the cabinet drawing and the crossover design:

P.S. I already have the tweeter and midrange units.

P.P.S. My listening room is 6m x 4m x 2.2m. My gear is Twisted Pear BuffaloII into Hypex UCD180HG Hxr.

Click the image to open in full size.

Click the image to open in full size.
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Michael

Last edited by dublin78; 6th January 2012 at 11:29 AM.
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Old 6th January 2012, 11:56 AM   #2
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by dublin78 View Post
I have designed a pyramid style enclosure that maintains the baffle shape, and spacing of the drivers,
Good thinking. They are similar, may be OK without changes.

The various benefits of pyramidal cabinets are debatable. If you have the skills, you might consider rounding the front edges.

Quote:
Extreme low bass is not essential.
If you can't get your reflex to play the way you want to you could always block or partially block the port.

Quote:
Will the reduced bass cabinet volume and different tuning affect the blending with the midrange driver, or just change the bottom end?
To a degree, both. The concern is that your bass crossover is low, ie. not too far from the impedance peaks caused by the cabinet loading. You may be able to proceed regardless and deal with it only if you feel the need.

Quote:
What affect will there be due to the bass driver being only 10cm from the floor?
Less floor reflections. These reflections are sometimes considered for both the bass driver and the mid, and this information used in deciding the crossover frequency between them. Was it mentioned in the article?

Quote:
I am aware that the tweeter should be at ear height, but I have tried the AOS Sudio 12s (nearly identical tweeter and mid drivers) on the floor, and their dispersion characteristics were fine.
Speakers aren't always intended to be listened to on-axis. Consider building them at around ear height, and toeing them in to take the beam off you.
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Old 6th January 2012, 12:11 PM   #3
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Hi Allen: You have given some confidence to progress.

Quote:
If you have the skills, you might consider rounding the front edges.
Actually, I was going to add 20mm to each side, and round it over with a 20mm bit. The verticle lines on my diagram show where the roundover will begin. I think that this should match the effect of the bevelled original.

Quote:
Was it mentioned in the article?
The article is in German, so I couldn't say. Anyone up for some serious German to English translating?
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Michael
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Old 6th January 2012, 12:30 PM   #4
AllenB is offline AllenB  Australia
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There shouldn't be anything in the article that can't be worked out separately. Still, most people ignore this anyway. There are worse things than some floor bounce. Unfortunately though, one of the down sides to a three-way baffle mounted driver complement will be the wide dispersion.
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Old 10th January 2012, 11:35 AM   #5
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Hobby Hifi article:

http://www.vegalab.ru/forum/attachme...5&d=1299273567
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Michael

Last edited by dublin78; 10th January 2012 at 11:51 AM.
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Old 10th January 2012, 05:35 PM   #6
gk7 is offline gk7
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Quote:
Originally Posted by dublin78 View Post
..., however it will only have a bass cabinet of 30-40 litres instead of the 60 litres of the original design.
...
The article mentions slight variations of the enclosure volume between 50 and 70l. With 50l the bass reflex port should be 2cm longer, with 70l 2cm shorter.
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