porous absorbers plus BBC A 10 membrane absorbers

[charles sabbah]

Hello,
I have an 18 m2 listening room.In order to adress a 20 db pic at 60 hz (vertical mode) i have used successfully 12 BBC A10 membrane absorbers.They are covering two third of my ceiling.I have a 6 m2 cloud which is 34 cm far from the ceiling with 4 panels of rockwool (10 cm thick ) of 48kg per cubic meter density covering the early reflection points.Since the 60 hz pic is not yet fully controlled ,although dramatically reduced, and i still have an uneven frequency response from 45 to 300 hz i was wondering if i could achieve better results in the bass frequencies by using the 13 cm left between the front of the BBC A10 and the bottom of the wooden frame of my cloud.I thought of having as many rockwool 7.5 cm /48 density panels as possible between the front of the BBC panels and the wooden frame leaving an about 6.5cm plenum behind the porous panels.Do you think it will impact negatively the efficacy of the BBC traps or bring additionnal absorption at 60 hz and above .If the principle works i cxould even consider lowerig my wwooden frame by 10 cm to create extra space for thicker rocwool panels.Hope my question is clear,not too stupid and i look forward to reading your answers.Many thanks.Charly.

[Bilou]

Up !

I'm interested in this subject to. I'm using BBC A10 traps for 50-100hz, but it could be interesting to know if it's possible to make some treatment in front of these type of bass trap to adress the 100-500hz zone with mineral wool and plenum (and plastic coverage to keep some 'lively' highs)

Ethan, Glenn, S.A.C, DanDan... What do you think about it ?

[Bilou]

Charles -> maybe you could post some photos ???

[johndykstra]

where is SAC lately? weird...

[audiothings]

Bilow and Charles - PLEASE tell us more about your BBC traps... pics, measurements (pre and post)... whatever ya got... VERY interested...

I have been trying to find out for months, if putting a velocity trap in front of a pressure trap will hinder the absorption potential of the pressure trap, and I have not been able to get a definitive answer...

where is SAC lately? weird...

Yeah, I'm missing him too... Where are you SAC, please come back!

[charles sabbah]

Hi audiothings,
The BBC A 120 is a membrane absorbers developped by the BBC to adress low frequencies.You will find its characteristics in the BBC companion report 1992/10 .They also describe the way to build it.It is an easy to build ,inexpensive and very powerful device to absorb frequencies betwen 50 and 100 hz with a pic absorption of 63 hz .
The way you formulate your question is exactly the one i should have used.By the way i just found out that you already asked this question sometimes ago and that it was cleary answered by few experts (among them Dan Dan and Ethan)
Apparently the answer is clear:Yes one can use a porous absorber(velocity absorber)in front of a pressure absorber provided that your porous absorber is far enough from the membrane not to prevent it to vibrate.Ethan is also recommending,if i read him properly, that the selected porous absorber should absorb at higher frequencies that the membrane absorber.Please Ethan,correct me if i am wrong .Thank you guys for having already answered my question and sorry for having asked an already answered question.
Charly 1944