Active speakerset

[Piersma]

Hi all,

I have build some Vifa en Dynaudio speakers in the past but am not a highly experienced speaker builder.
I am also not an experienced speaker designer but I want to take a shot because I got some really nice Scanspeak drivers waiting on the shelf.
Here the drivers I am talking about:

High : ScanSpeak D2905/970000 a 1” soft dome tweeter
Midwoofer: 18W/8531G00 a 6,5” paper cone woofer (revalator series)
I have got one pair D2905 and two pairs of 18W8531.

Here’s the plan:
Build a 2.5 or 3 way activ speaker system with the Scanspeak drivers.

High: the D2905/970000 crossed at 1.7 kHz - 2 kHz
Mid: 18W/8531G00 bandpass in het closed box of 20 litres, -3dB at 55Hz and Qtc 0,71
Woofer: 18W/8531G00 low end bass in a vented box 40 litres, tuned at 31,5 Hz
Bass en mid crossed at 70 Hz

18W/8531G00: Qts 0.36 Vas 59 litres sensitivity 87dB

What do you as experts think of this arrangement?
Comments are very welcome

Regards,
Piersma

[vadi]

I'm not very experienced but I'd cross the woofer jigher to limit the excursion of the midwoofer as much as possible.
Also I'd use a waveguide like describen on Zaph's site.
The drivers should behave similar in terms of distortion so the blend nicely too.

[chris661]

I'd agree about the mid cross-over. Raising it to around 100Hz would be better. The enclosure for it could be made smaller, because you don't need it to go that low.

How does the bass response look for the woofer in the cabinet you've suggested?

[Piersma]

Hi Vadi and Cris,

I will take a look on Zaph's page, i am not to familiar with waveguides.

Here the gainplot for the vented 40 litres cabinet with the 18W8531.

What about 2.5 way or a 3 way configuration?

Thanks !

regards,
Piersma

[s3tup]

Bring the 12m and make an Ekta Grande. The 18w revelators ain't good to my ears on the upper midrange (starting 1.4k). I've been there myself, and didn't liked what i've heared from such pricey drivers in 2way... So i went the 12m route.

Active xover is fine too, but i think you'll need a dedicated midrange driver.

[Piersma]

hi S3TUP,

If i have to i will bring in a dedicated midrange, but only if i have to because the proposed Scanspeak 12M is really expensive.

Another question: the curve of the 18W8531 SPL curve isn't smooth between 20Hz and 50Hz and rapidly decreasing. Will it cause tranfer problems??

Thanks

[vadi]

I found one 6,5" Exodus Audio woofer with 12mm Xmax is about OK for supporting a 6,5" midwoofer in a closed box. Also I'll build only one because of space and I want to try a tapped horn, which might cause less room modes - I'll see. I read you don't get increase in bass SPL next to walls after all.

So I'd build two subwoofers with these you have and probably get much more even bass response, if you have the space.

The response of the horn is similar to you pic, I hope it's OK. You need much more displacement to get it better and loud. Some say stay below 30ms group delay.

[s3tup]

40L box is a a bit small for a pair of these midbasses, they like to be placed in 28-33L/each.
See Troels web site for their "application notes". Project names: Ekta, Ekta Grande, SPXX where XX is some number.

DIY Loudspeaker Projects

He tried different enclosures, and ended up with 28-33L boxes.


The decrease of SPL curve is ok, all the speakers do that. In addition, sometime it's better for the curve to start rolling off slowly at 50-40hz, so it blends well with room gain (SPL increase due to closed room at low frequencies, the larger the room - less gain, lower frequencies). Instead of ruller flat response to 30HZ, and then quick fall off.