Pheonix in a box - inspired by Mr Linkwitz

[chlorofille]

Inspired by S.Linkwitz's Phoenix loudspeaker, I decided to build a vented system using the 8'' Scanspeak kevlar drivers found in the Phoenix.

The system uses 2X 8'' kevlar midwoofers per channel with a Scanspeak
D2904 7100 soft dome tweeter. Each woofer is housed in it's own 33L enclosure, tuned to 30Hz.
Crossover is at 2000Hz LR2 acoustic passive filter. Yes, it goes against all the design consideration of a large MTM, but the crossover sounded a whole lot better than a 4th order passive design.

Enclosure is made of 1'' thick MDF panels. Front baffle is 2'' thick.
Cross bracing is used inside, and the overall weight of each enclosure is 75kg.
Walls are damped with an inner panel of 3mm thick lead sheet.
The next layer is 5mm thick bitumen/alu.
No acoustic foam/wool is used to damp the enclosure atm.


Some goals of this design :

- To maintain the purity of a 2 way system, yet still have sick bass!
- Transparent midrange.
- Bass flat to 33Hz with room gain.
- Able to hit 100dB @ 4m with minimal compression.
-Fairly high sensitivity - 94dB/m
-To design something no one else has (i hope )
-Relaxed, not fatiguing sound and perhaps a vintage tone?

More info to come =)

 

[PeteMcK]

interesting, but 'No acoustic foam/wool is used' seems to contradict your goals of 'Transparent midrange' & 'not fatiguing sound ' - it's used not 'to damp the enclosure' but to damp internal standing waves and reflections.

 

[chlorofille]

Indeed. I'll look for some foam a little later on. Here is the schematic for crossover. LR2 acoustic @ 2000Hz.

For woofer's crossover :
Inductor = North Creek 8 AWG 0.7mH (0.02Ohm)
Cap : 14uF Mundorf M-Cap

Tweeter's crossover :
Capacitor : 4.7uF Mundorf Supreme silver in oil, bypassed with Mundorf 0.1uF silver/gold in oil

500 Hz Resonance notch filter : 1mH Jantzen C Coil 14AWG
100uF Solen polypropylene
4.2Ohm Mundorf metal oxide resistor

 

[Andersonix]

I'm pretty sure SL won't be too pleased that he has inspired someone to make a vented box speaker.

 

[J.R.Freeman]

I'm pretty sure SL won't be too pleased that he has inspired someone to make a vented box speaker.

Now now! I'm sure Mr. Linkwitz would be all for someone experimenting and learning.

 

[Davey]

I'm pretty sure SL won't be too pleased that he has inspired someone to make a vented box speaker.

Yeah, I actually think SL might even take exception to using his name as "inspiration" on a project like this. The two main drivers are the same but there isn't anything beyond that has any relation to the Phoenix design.

Cheers,

Dave.

 

[chlorofille]

Apologies to Mr Linkwitz...

Sincerely hope Mr S.L does not get offended

What do you guys think of such a design? Critics are welcome

Some measurements will be done as soon as I can find a suitable microphone
for taking the SPL plots. Software used will be HolmImpulse

Listening impressions - Ultra tight bass
Relaxed midrange
Very detailed highs
Soundstage is huge, but imaging is not too impressive.

-Dee-

 

[J.R.Freeman]

Those Kevlar cones are nice looking!

I noticed you have a separate chamber behind the tweeter - have you removed its built-in rear chamber? It would be interesting to see if that makes a positive difference, if it could be tried without risking damage to the tweeter.

 

[chlorofille]

Hi J.R !

Nuu I wouldn't touch that tweeter.
The middle chamber is to house the crossover for my initial 4th order crossover.
That took a lot of huge components but after going back to the 2nd order one,
I have lots of leftover space in the chamber.

 

[chlorofille]

Here's a simulated pic of the back view.
An alu plate is fixed to the back to hold the binding posts.
A hole cutout of 50mm X 150mm serves as access to the internal crossover.

The reason for doing this, is because I needed each woofer to have it's own chamber. Thus, the middle section would have to be sealed up to form it's own chamber.

 

[chlorofille]

Haven't updated this thread in ages. The speakers were painted with a black gloss paint last December and is currently being used everyday by my dad - for movies and music. The final crossover is in place with a 4.7uF Mundorf Supreme silver in oil for the tweeter.

The upper midrange decay is very good for the 8'' speaker, but there is a resonance at around 400Hz which cannot be removed regardless of stuffing. Alas, this is the problem of using very thick MDF walls due to stored energy issues. However, bass is extremely clean and pitch perfect to 35Hz.

If I were to rebuild this, I would go for 18mm plywood with extensive bracing to try and push the resonances as high up as possible.

I missed those speakers so much that I got my dad to get a good microphone so I could hear those speakers through Skype!

Current system set up back home (Malaysia) :

Preamp : Pavel Macura Dispre 2 Jfet
Amp: Rod Elliot P3A
Source : Cambridge Audio Azur 550C
: Mede8er full HD media player

Some pics...

 

[chlorofille]

Dear Moderators,

Can you please change the thread title to "Scanspeak 8'' Kevlar MTM".
Thanks.

Regards,
Dinesh