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PostPosted: 27 Jul 2010, 06:50 
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Joined: 24 Jun 2010, 00:48
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Location: Christchurch, NZ
A slightly older project which I always procrastinated painting. Enclosures now have 1 thick paint coat awaiting more sanding. I used some generic primer which was recommended by the hardware store owner which made sanding a living hell. The primer stuck so easily to the sandpaper after drying, which had a rubber like feeling.

TMM 2.5way - 2X Scanspeak 18W8546 and Wavecor TWA05 silk dome non ferrofluid tweeter
Enclosure type : Bass reflex tuned to 33Hz; both woofers sharing 30 litre internal volume. (15L per woofer)
Crossover - LR2 @ 2000Hz and 150Hz.
Lower woofer starts roll off at 150Hz onwards
Basically a 2 way + subwoofer but both woofers play through the bass region.
6.8mH coil on lower bass is a Jantzen C-Coil 12AWG with 0.05Ohm dcr. (extremely critical)

External DImensions : 1000 X 200 X 300mm
25mm Thick MDF with 5 internal braces
Weight : 30kg per enclosure
Stuffing : 10 old cotton clothes per enclosure
Crossover tuned by ear took 3 weeks to perfect, 3 hours spent each day.

Sound : Crystal clear, out-of-wall imaging, warm midbass and pitch perfect deep bass (30-60Hz)
Instruments sound lifelike. Fairly small footprint, excellent for medium sized rooms with good WAF.

More updated pics to come...


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PostPosted: 27 Jul 2010, 14:03 
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Location: Christchurch, NZ
Drivers installed...bumble bee scheme !


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PostPosted: 27 Jul 2010, 23:57 
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Joined: 07 Feb 2010, 15:42
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Location: England
Forget just having them painted black, you should add actual yellow stripes to it and some small wings :D

Other than the missing stripework, they look really good!

lewis

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PostPosted: 28 Jul 2010, 00:44 
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You're right. The stripes would have been nice.

Quick update...the 5.6mH Jantzen C-Coils came in today from US, after 5 days of shipping. I replaced my old Mundorf 5.6mH Iron Core with the Jantzen. Mundorf inductor has 0,4Ohm DCR while the Jantzen has 0.078 Ohms.

Ironically the biggest audible difference was in the midrange. Oddly, although the lower woofer needed to play from 150Hz and below, it had a direct effect on the midrange. Electric guitar notes have a sharper bite and attack. Very thrilling !!

Here we run into some disadvantages of going TMM. Firstly, in a TMM, the lower woofer acts as a baffle step compensator. This means that the crossover point for it depends on the width of your baffle. With my 8 inch baffle, this frequency is 570Hz. With a simple 6dB filter through the use of a single 3.3mH inductor, I found too much intereference in the frequencies. The midrange got slightly hazy and singers in th soundstage were sized too large. Voices were not hanging precisely in space.
The 3.3mH air core inductor also increase resistance which ultimately caused the lower woofer to lose more efficiency and play softer. I decided to lower the freq to 150-200Hz and sharpen the rolloff with a 12dB/oct filter. The 150Hz freq demanded the use of a much larger inductor - 5.6mH. This had to be an iron core as the resistance would be low enough to not cause much power losses. The bass seemed to have lost some punch and was softer. In order to make up for it, I was forced to use a very good quality inductor and that meant spending much more $$.

In an MTM, only one inductor would apply to both midwoofers. Even if a baffle step compensation was used, the inductor value would be small and of low DCR since the paralleling of woofers create a lower impedance. Thus if a 1mH was needed on 8Ohm speakers, a 0,5mH would be needed for an 4 Ohm crossover. In conclusion, an MTM would be more efficient and sound louder, while most importantly, cost lower. On the other hand, an TMM can provide a richer and more powerful lower midrange at the cost of slightly lost efficiency. If time permits, I would build up a test cabinet in an MTM style and compare.


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PostPosted: 28 Jul 2010, 04:47 
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Here's a shot of the C-Coil tag.


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PostPosted: 02 Aug 2010, 22:47 
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Loving the sound !! Speakers were cranked up to 92dB @ 3m and showed no sign of giving up.
Behringer EP1500 fed the speakers with about 250 watts into 4Ohms. Bass pounded in the chest - no sub on at all. Even on the loudest bass passages, the amp delivered power and refused to muffle up the tiniest stroke of the hi-hat. Moral of the story : One amp is simply not enough. We need variety to suit moods !

This speaker has the most articulate bass of anything I've ever built. Truly shocking 40-120Hz region. Every freq change is heard. Smoother and more detailed with more guttural slam than my 3 way with Peerless HDS + Scanspeak 12M + Peerless HDS 8'' Exclusive. If I turn on the sub, a 33Hz room node will be introduced, thus muddying up the bass.

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PostPosted: 03 Aug 2010, 03:03 
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Joined: 02 Aug 2010, 08:36
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Location: Australia
It's quite unusual to see a SS project with the kevlar drivers!

I've used the EP2500 to drive my mains and the bass impact you can get, even with relatively small bass drivers can knock you off your seat! I did literally jump off one time in panic.

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PostPosted: 03 Aug 2010, 04:16 
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Hi Paul,

I had a look at your blog. Very interesting stuff !
Btw what main speakers are you using ?

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PostPosted: 18 Aug 2010, 14:21 
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Hi Dinesh,
I'm "in-between mains!" but temporarily using some thrown together active open baffles, shown here:

http://redspade-audio.blogspot.com/2010 ... ve-ob.html

Only just saw this response.

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PostPosted: 18 Aug 2010, 14:24 
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It looks pretty good. I can't imagine what your serious speakers will be like. :mrgreen:

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