Visaton FRS 8 M Parallel Notch Filer Design

[swin1]

Hi there, first of all I'd like to say thanks for this forum, I read it regularly and get a lot of help from other people's questions and opinions.

I am designing a small inexpensive home theatre setup, using the Visaton FRS 8 M each for front, centre and surround. I can get the HiVi B3n at a similar price, but am not convinced by the sensitivity and my already constucted boxes are small in volume - 2.3L for front and 1.7L for surround, which seem to be small for this driver. I like the look of the FRS 8 M with it's high sensitivity and modeled frequency response (from the visaton website.)

http://www.visaton.de/bilder/frequen...frs8m_8_fs.gif

Given the apparent spike @ 10khz, it seems a parallel notch filter would be appropriate. My question is, am I right in assuming -3db at 9khz and 11khz, and attenuating by 7db to correct this spike?

Your comments would be much appreciated and any input or further about this driver would also be great for discussion, as I am still deciding on it.

Cheers
Andrew

[pacificblue]

That peak is very narrow, so filtering it out with a passive notch filter will be difficult. Being so narrow it also has little potential to be utterly disturbing. If you are listening slightly off axis, it might even vanish by itself.

It might be a good idea to wait till you have the speakers, listen to them, and find out, if that peak really bothers you in real life.

[hm]

i agree with pacificblue,

i tested the FRS8M in my TROMBONE,
over 1 W the driver gets a bit crisp,
but OK.

[swin1]

Hm, what's your opinion on the higher frequency output of this driver, balance and distortion?

I intend to actively crossover to a sub around 125-150khz, so I am hoping for output in the upper region, the room in which they will be used is roughly 4m x 4m in size.

[hm]

"over 1 W the driver gets a bit crisp,"

try a sub modul with active satellit crossover, 150 Hz ,
12 or better 18 db.

for the money a very good driver,
with the Trombone you need no sub.

[pacificblue]

To get the FRS8 down into the region of 125-150 Hz with the boxes you mentioned in the first post will be a demanding task. You should rather expect something above 200 Hz, if you don't listen too loud. For serious listening levels, the crossover should be above 300 Hz. If you add two subwoofers placed very near to the front speakers you avoid that they are perceived as separate sources.
Or use the FRS8 at least for the front speakers in bigger boxes, like hm's Trombone or Cyburg's Needle.

[pacificblue]

Oops! I just notice that you are talking about the FRS8M. That's even worse for the lower regions, because that driver is made for higher efficiency. Crossover to sub above 300 Hz for neighbor-compatible listening and above 400 Hz for serious SPL. The Needle uses the FRS8. Maybe an alternative for you?

[swin1]

pacificblue,

Modelling these in a 1-2L sealed enclosure results in an f3 of ~180hz, surely a filter around this region would suffice at low listening levels?

a subwoofer will be placed midpoint between these drivers. I intend to listen to them at low volume levels, they are being driven by a 10w opamp per channel.

Certainly I would filter them much higher, with a midbass if they were to be used at high volume levels.

[pacificblue]

Originally posted by swin1
Modelling these in a 1-2L sealed enclosure results in an f3 of ~180hz, surely a filter around this region would suffice at low listening levels?

Did you check that with Visaton's Boxsim? That software includes baffle response and the measured response of the FRS8M.

The FRS8 without M looks more promising for your set-up. If you help it in the lower regions with a big baffle, a crossover to your sub between 150 and 200 Hz is possible. The FRS8M would just so reach down to 200 Hz with a big baffle.

1,7 and 2,3 l enclosures don't look as if you were after a big baffle though. So you should rather expect 300 Hz or higher for the FRS8M.

[swin1]

The baffles are 200mm x 200mm and 250mm x 170mm respectively, so they are quite reasonable for 80mm drive units I think. Assume they will be wall mounted, so baffle step should be less of an issue.

I think the problem here is box size for output levels at lower frequencies, is the general conclusion that the Visaton drivers are not useful in small boxes? We are talking about enclosures 3L and smaller.