[opnord]

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. The main focus is however on stereo sound.

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 60 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


Does this make sense?

If so I am looking for a good value mid-bass driver for the bass array. I am planning to run this from 400 Hz'ish down to 50-60 Hz. 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 at 400Hz. I understand that both H and U baffle does not work well above 200Hz. So I am thinking of using a flat baffle.
 I have looked at some cheaper drivers like 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)

[scorpion]

May be I can help a little. I think both options are possible to realize even if your room is a bit small. I think it would be possible to have the woofers close to he side walls, perhaps someone more experienced with this placement - like perhaps Rudolf and JohanR - can comment more on this. If you try the IB version I think you should have at least some 10 cubic meters of air behind the speakers and the screen to get intended response.

The following figure is from a Martin King Mathcad model and is illustrating an 8 unit speaker panel of Dayton 225-8 woofers arranged as 4 units in parallel in two groups which are serially connected about a 4 ohm speaker. The panel is 40 cm wide (16") and 200 cm high (80"). A 12 dB/oct lowpass L-R crossover is applied at 200 Hz, this woofer speaker will easily put out 100 dB SPL with under 1.5 mm cone movement at 60 Hz. The average OB sensitivity with 2.83 volt input is 92 dB, then you can also calculate the IB sensitivity.

The figure is also illustrating the IB performance. That's the upper dashed line, not affected by the crossover. The solid line represents the OB response which is an amalgam of IB, baffle and crossover performance. With the chosen crossover hardly any EQ would be required in your proposed frequency band.



/Erling

[AJinFLA]

Welcome aboard.
My opinion -
Option #1. 3' min distance to front wall.
8 x 10" (series-parallel). For 60-400hz passband, consider the Dayton DA270-8 http://www.parts-express.com/pe/showdetl.cfm?partnumber=295-334 for excellent value/performance ratio. The BG will be the limiting factor in terms of SPL, distortion, etc., so no need for the slightly superior motor of the RS. Not with 8 per side in the specified passband.

This IB sub is installed in the back wall which might not be an ideal placement

Actually, that's fine. The LP (sofa?) will most likely be only a few feet away, which means very little if any modal effects. I have a similar setup with IBs directly behind sofa in rear wall (about 1' distance). DSP makes it easy to add any delay necessary.

cheers,

AJ