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2-Way MTM Loudspeaker with Scanspeak 21W8554 and D2904-7100
http://diyaudioprojects.com/Forum/viewtopic.php?f=11&t=2235
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Author:  kkkittehz [ 30 Jul 2010, 05:11 ]
Post subject:  Re: Suitable 8'' Mid/woofer for use in an MTM 2 way speaker.

Do you plan on sitting your house ontop of that speaker?! That is some damn thick MDF, should give for very low resonance and hopefully no rattle at the low end of the spectrum. Nice looking enclosure by the way, any ideas for a colour scheme?

Lewis

Author:  dtsup1 [ 30 Jul 2010, 09:01 ]
Post subject:  Re: Suitable 8'' Mid/woofer for use in an MTM 2 way speaker.

Hi Lewis,

I'm sure I can stand on top of the completed enclosure without fear :D
The panels alone weight about 55kg per enclosure. With the 2 8inchers it will be 65kg! I decided on 25mm thick panels as they are less resonant than my older 18mm designs. I also chose 2 separate enclosures for each woofer. Something like a dual mono amp vs a stereo one in a single chassis.
Centre spacing from woofer to tweeter is 17cm. Thus, I need a low crossover point of about 1500Hz and steep filtering. Fingers crossed, hoping the speakers will sound great.

For the finish I am inclined to use black. They match very nicely with the yellow kevlar drivers. The tweeter has a silver alu faceplate which should blend well with black.
Do you have an alternate suggestion for a colour ? How about maroon ?

The pics are below. I spent 2 hours today cutting up the front baffles with a small Makita Jigsaw. Tough without a clamp.

Author:  Gio [ 30 Jul 2010, 20:07 ]
Post subject:  Re: Suitable 8'' Mid/woofer for use in an MTM 2 way speaker.

That is what I don;t like about MDF - the weight really adds up.

MDF is not as strong in bending as plywood so you do have to brace is more often. But it is much denser, and much stronger in compression.

Can't wait to hear how you make out with the project.

Cheers

Author:  dtsup1 [ 31 Jul 2010, 09:00 ]
Post subject:  Re: Suitable 8'' Mid/woofer for use in an MTM 2 way speaker.

More machining done....8 braces and 2 port holes cut. The latter being cut by a circular saw of 55mm diamater. Total time spent : 4 hours. The only thing left to complete is to purchase some large binding posts (150mm X 70mm) and make the rectangular cutout on the back panel.

Port tuning : 33Hz
Port Diameter : 55mm
Length : 150mm

After modelling the enclosure in bass box pro, the maximum power before port chuffing becomes audible is at 75 watts. Bass F3 is 50Hz anechoic with a -12dB point at 27Hz. In an actual room, this should result in a very tight and detailed bass response totally free of any boom. Estimated actual F3 in room is about 33Hz.

The graphs shown below apply to a single 8'' woofer in a 30L enclosure.

Author:  dtsup1 [ 01 Aug 2010, 02:29 ]
Post subject:  Re: Suitable 8'' Mid/woofer for use in an MTM 2 way speaker.

45 Degree underside chamfer cut to improve air flow for the midwoofer. Since this is an 8'' midwoofer, I doubt I even need the chamfer as usually it is more critical in small drivers like 4''.
Nevertheless I decided it wouldn't hurt to do so.

Author:  dtsup1 [ 03 Aug 2010, 07:35 ]
Post subject:  Re: Suitable 8'' Mid/woofer for use in an MTM 2 way speaker.

1. Woofer's underside cutout enlarged slightly with a circular rasp.

2. Enclosure being glued and fitted with 5mm bitumen-alu foil pads.

3. Old school clamp method by using rafia string. Heavy Varta battery provides additional clamping from above !

Damn boxes are too heavy...the bitumen pads add 5kg extra per enclosure...

Author:  dtsup1 [ 04 Aug 2010, 03:30 ]
Post subject:  Re: Suitable 8'' Mid/woofer for use in an MTM 2 way speaker.

SOme pics of the installed and glued enclosure. I fired them up with a stock 1500Hz crossover 4th order L-R without any L-Pad on tweeter. Some subjective results :

1. Ultra dry bass, plumbs the depths to 25Hz.
2. Sounstage as deep as a bowling alley.
3. Forward sounding as a 3dB L-Pad is necessary on tweeter.
4. Sounds the same when playing at whisper volumes as well as 97dB ++ volumes.
5. Amazing midrange clarity even though an 8'' was used.
6. Serious "live" sound.

I really did not expect it to turn out this well . Perhaps it is due to the incredible ability of the tweeter to be crossed over so low and still sound clean.

IF you close your eyes and listen, it is not hard to imagine a 3 way with a 4.5inch midrange and a 12'' woofer playing !

Author:  kkkittehz [ 04 Aug 2010, 03:59 ]
Post subject:  Re: Suitable 8'' Mid/woofer for use in an MTM 2 way speaker.

I see that you have your television supported by what appear to be two green vase type column thingymabobs, looks like they could be taken out and you could use your speakers to support it. :P Now are you going to paint them or just leave them in their 'raw' format? If the enclosure panels weighed 55kg and then you added 5kg of foil along with speakers I dare say your speakers must weigh around 10 stone. Thats the weight of a large child :P Though it sounds like they make a better noise than if you were to put electricity into a child :D

P.S. Putting electricity into a child is wrong, I dont condone this and if you do do this then eventually they will grow up and 'sort you out' good and proper

Lewis

Author:  dtsup1 [ 04 Aug 2010, 05:26 ]
Post subject:  Re: Suitable 8'' Mid/woofer for use in an MTM 2 way speaker.

kkkittehz wrote:
Thats the weight of a large child

LOL!
The hernia inducing weight makes it a pain to set up but this is a temporary set up to see how they sound. If my other TMM was rated 7/10, this would be a 9/10. The completed weight with stuffing tops the scale at 70kg. Crossover each weight abt 2kg !! Stuffing is 5kg per box.

This 8'' is such a darling to work with. With a 4th order slope to hammer it's aggressiveness in place, they sing. The tweeter goes so low that it blends like the smoothest swiss chocolate ever made.

I cranked up the music and headed over to touch the side panels and felt......nothing ! No vibration, inaudible panel resonance. Dead as a carcass !!

Upcoming tasks: Adding a 3-4dB L-Pad to the tweeter
Measuring SPL vs Freq
Crossover tweaking etc and finally they will be painted !!

Author:  Geek [ 04 Aug 2010, 06:17 ]
Post subject:  Re: Suitable 8'' Mid/woofer for use in an MTM 2 way speaker.

Booyeah! SAW-DUST makin' time! :thumbsup:

Looking good!

Cheers!

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