Advice needed: Semi-open or infinite baffle project?

[harryharry]

I am thinking of a new speaker project in my bat cave. I use this room mainly as a listening room for stereo sound but do also have a home theatre system installed with a projector, a 110 inch screen, a center channel speaker and surround speakers.

I am now considering setting up a new speaker in this room. The idea is to use the Bohlender Graebener RD-75 as tweeter/mid-range driver and then use an array of 8", 10" or 12" mid bass drivers.



I am currently using an infinite baffle sub consisting of two 18" Fi IB3 drivers under 50 Hz. This IB sub is installed in the back wall which might not be an ideal placement however my experience is that under 60Hz it is impossible to hear the directivity of the bass driver.

The room is rather small: 3 x 5,5 m (10' x 16') which makes it too small for a normal open baffle speaker. I therefore have two options:

Option 1: Semi open baffle speaker


Option 2: Infinite baffle speaker


What do you think?

I am also looking for a good value mid-bass driver. I am planning to run this from 200-300 Hz down to 50-60 Hz. 12" is the maximum I have room for.
One driver I have found that might work is the AE Dipole12 driver. I have also looked at other cheaper drivers like Peerless SLS 10” or 12”, Dayton RS225 or RS270 and Eminence Deltalite II 12” driver. I do not have a lot of experience with open baffle/ infinite baffle speakers and would therefore appreciate some advice.


The whole system is going to be driven fully active by computer DSP. (Today I use Twisted Pear Buffalo DAC, Lynx Two B and FIR filters in my current setup)

[JonMarsh]

I'm going to swim against the stream here and recommend the IB setup, perhaps with more angle on the panel and cross fire. You'll get more output level in the lower frequencies and the drivers will have to work less. Flush mounted systems are a hangover of my recording studio days, and properly done work well- that's what my GF essentially has for her HT in her family room. This is the best way to get the boundaries to work for you.

[harryharry]

For an IB setup (option 2) do I need to worry about the bass driver impact on the ribbon (RD75)?

If so I need to build the ribbon into its own separate box/room?

[Juhazi]

In IB setup you should buil a non-resonant wall behind the screen or make boxes for the speakers anyway. The boundary effects, dispersion, phase etc. can be handled yes, but only with some expertise. A nice subject to be studied...

I think that many people are a bit afraid of in-wall (IB) setup, we are so accustomed to free-standing speakers and the principals of positioning them.

IB setup with multiple subs for HT and some separate speakers for hifi stereo "playing"

[harryharry]

Any recommendation for the drivers for the bass array? 6x12", 8x10" or 10x8" drivers per side is the maximum I have room for. I do not know if it is realistic to find a 8", 10" or 12" driver that will play loud enough at 60Hz and clean enough above 200Hz. I understand that both H and U baffle does not work well above 200Hz. So I am thinking of using a flat baffle. Some people have the XO point at 200Hz for the RD75 while others recommend a much higher XO point (600Hz). I think it therefore be smart to choose a driver that are clean above 200Hz so I can experiment with the XO point.

[Face]

http://www.aespeakers.com/products.php

https://sites.google.com/site/drivervault/driver-measurements/15

I'd presume their 12" models measure similarly.

Be aware, there can be a waiting period...

[harryharry]

The Dipole12 is expensive to use in a large array. I was hoping to find a cheaper driver.

[gregw]

I have set up a similar system using the RD75 in an open baffle. I currently am using eight 15" TC Sounds aluminum cone drivers, 4 per side, crossed over at 280Hz. I plan to put the eight 15" woofers in an infinite baffle for subwoofer duty and use 8 RS225 drivers per side between about 60 and 600 Hz.

In an infinite baffle, Linkwitz's SPL_Max1 spreadsheet shows excursion limited output of 127dB into half space at 60Hz with 16 RS225 drivers. I believe you can add another 6dB to that output since 60Hz will be the crossover point to your subwoofers. The RS225 has been used crossed over much higher than 600Hz.

http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-356

Do you have the RD75s? I think you will be very pleased with the results. It would be interesting to hear them in a monopole as a comparison to my setup.

http://www.htguide.com/forum/showthread.php4?t=40538

[harryharry]

Why do you prefer the RS225 over RS270? The cost is an obvious difference however I believe the RS270 should play clean up to 600Hz and have more cone area. For 8 x RS225 the cone area is 1688 cm2 while 8 x RS270 will have 2768 cm2 cone area.

[gregw]

With the RS270, I could only use 6 per side because I only have about 80" of headroom in my basement. If you can use 8 per side then they could well be a better option. Others here have recommended the RS180, so you ultimately have to pick your own poison. The 4 15s I am using right now per side sound excellent. I am hoping that the RS225s are an improvement which will also allow using the 15s for sub duty.

The RS225 has a smoother response well beyond where the RS270 starts to have issues so there is less likely to be any audible effects at a 600 Hz crossover though both may do fine. Others can comment more authoritatively on this aspect. It seems to me I have seen recommendations to use a driver with a clean response to at least one octave beyond the crossover frequency. The RS270 looks to have a significant dip in response at about 1200 Hz.

The added cone area and displacement would make more of a difference if you were planning a dipole. With a monopole, the RS225s seem more than adequate.