Help me choose a configuration

[oublie]

Hi folks,

I've been working on the design of my home cinema speakers. 7.2 with wall mounted boxes.

The specs for the lcr and surr are as follows.

9 4" drivers in line config
9 tweeters also in line config.

i have them on hand and will finally get around to doing something now.

I've been modelling the design with basta using accurate driver measurements taken using wt2.

The following is what ive come up with for the design but i have a problem deciding between ported and closed alignment.

The box will be 120liters either way 15cm deep 2m high 60cm wide - this seems to give me the best measurements and low end response to the 80hz cutoff.

you will see from the measurements that ported has the following plus points

flatter response in the higher frequencies.
Less cone excursion
Since the cutoff without a high pass is 50hz more room to manouver when integrating the subs.

the negative aspects are

Alightly more complex build but not by much
Dealing with port noise however, with an 80hz crossover and 100+ db at the listening position port speed is only 3m/s - i think this is probably accepable.
Group delay although the difference in delay at 80hz is only about 4m/s

Closed box plus points

Less group delay
Slightly easier build
80hz rolloff so no extra equalisation just the 2nd order xover from the av processor

negative points

less room for manouver with crossover as 120 litres gives a 80hz rolloff
higher cone excursion speaker xmax is approx 3mm so this with probably lead to higher distortion near crossover.

in the pic, green and pale blue is the closed box on axis and 45 degrees off axis

red and dark blue are from the ported box - notice the flatter frequency response at high frequency.

the tweeter is fairly obvious as is excursion and the dotted line is port speed with an 80hz crossover.


So. Which would you choose ported or closed? please bear in mid I will be listening on axis from all 7 speakers at equal distances the sub will come later.

Thank for any help or suggestions.

[whgeiger]

Originally Posted by oublie

Hi folks,

I've been working on the design of my home cinema speakers. 7.2 with wall mounted boxes.

The specs for the lcr and surr are as follows.

9 4" drivers in line config
9 tweeters also in line config.

i have them on hand and will finally get around to doing something now.

I've been modelling the design with basta using accurate driver measurements taken using wt2.

The following is what ive come up with for the design but i have a problem deciding between ported and closed alignment.

The box will be 120liters either way 15cm deep 2m high 60cm wide - this seems to give me the best measurements and low end response to the 80hz cutoff.

you will see from the measurements that ported has the following plus points

flatter response in the higher frequencies.
Less cone excursion
Since the cutoff without a high pass is 50hz more room to manouver when integrating the subs.

the negative aspects are

Alightly more complex build but not by much
Dealing with port noise however, with an 80hz crossover and 100+ db at the listening position port speed is only 3m/s - i think this is probably accepable.
Group delay although the difference in delay at 80hz is only about 4m/s

Closed box plus points

Less group delay
Slightly easier build
80hz rolloff so no extra equalisation just the 2nd order xover from the av processor

negative points

less room for manouver with crossover as 120 litres gives a 80hz rolloff
higher cone excursion speaker xmax is approx 3mm so this with probably lead to higher distortion near crossover.

in the pic, green and pale blue is the closed box on axis and 45 degrees off axis

red and dark blue are from the ported box - notice the flatter frequency response at high frequency.

the tweeter is fairly obvious as is excursion and the dotted line is port speed with an 80hz crossover.


So. Which would you choose ported or closed? please bear in mid I will be listening on axis from all 7 speakers at equal distances the sub will come later.

Thank for any help or suggestions.

Use a sealed enclosure and equalize with a "Linkwitz Transform" section.
You will not like what happens below Fb when drivers become unloaded.
Regards,
WHG

[oublie]

Thanks,

Since your the only one that can suggest a valid reason not to go ported i think i'll try a closed baffle at least to start with. Building work will start soon.

[whgeiger]

Originally Posted by oublie

Thanks,

Since your the only one that can suggest a valid reason not to go ported i think i'll try a closed baffle at least to start with. Building work will start soon.

I like your closure. I had some fun with it.

There are 11 types of people in the world: Those who understand binary, those who misunderstand binary, and those that don't care how you count it.

Regards,

WHG

[oublie]

yeah its an old one but i always liked it. Goes back to when i used to acutally code for a living (computer nerd jokes).