For Full Range With Subs -- Sealed Box Vs Open Baffle ?

[DrDeville]

Hi All,

I'm currently building a 300B SET amp and (nearly) full range speakers, to experience some of that SET - Fullrange magic I hear about. I want to be able to play complex, bass-heavy music without congestion, so my strategy is to use the 300B/fullrange system from 120hz or 180hz up, and relatively inexpensive (PartsExpress) dual powered subwoofers below that.

My understanding is that by relieving the fullrange speakers of base excursions, I will be able to play louder without congestion.

My bogie system is the S.E.X.y speaker on the Bottlehead site-- Fostex FE166E speakers in 1/4 cubic foot sealed boxes. As I understand it, the sealed boxes will create an acoustic 2nd order highpass filter with rolloff at around 120Hz, and prevent large drive excursions -- cleaning up the sound, and protecting the drivers.

This sounds great to me but, always having been a fan of planar speakers, I'm wondering if I can apply the same principle to open baffle mounted full ranges, and get a more airy, holographic sound?

I'm thinking a Fostex FE166E or FE167E in an approximately 3' open baffle (no WAF here) driven directly by my SET amp, with a 2nd order passive 120Hz or 180Hz passive highpass filter between the preamp and SET amp.

I invite all comments, concerns, suggestions, experiences on sealed versus open baffle in my situation, and whether to use the FE166E or FE167E in an open baffle with an SET amp with a low damping factor (output impedance).

Questions like--

Which speaker would provide better performance in this OB configuration?

What will the sonic tradeoffs be between OB and SB in this setup?

Will the OB with electronic 2nd order highpass be as uncongested and excursion limited (protected) as the sealed box with its mechanical/acoustic 2nd order highpass?

What have I overlooked?

I'm hoping that the OB configuration would let me get a more airy, electrostatic sound, yet the highpass filter will allow it to play loud and complex music without congestion. And that the large baffle will eliminate the need for a Baffle Step Correction filter ( BSC ).

Thoughts?

[Rudolf]

Originally posted by DrDeville
I'm thinking a Fostex FE166E or FE167E in an approximately 3' open baffle (no WAF here) driven directly by my SET amp, with a 2nd order passive 120Hz or 180Hz passive highpass filter between the preamp and SET amp.

You are just asking whether you should choose your Porsche 911 or your Corvette for taking part in the Paris-Dakar trans-sahara-race.
If you insist on those Fostex drivers for OB, I would recommend the FE167E because of its slightly higher Qts. But there are a lot of drivers of same size which are much better suited for OB use. If you ever want to try something different with the FE166/167 - let it be some kind of horn.

[johninCR]

I don't mind the low Q drivers on OB, but forget the big baffle, it won't help. Your XO point needs to be more like 300hz and go OB with the bottom end too.

[serenechaos]

I played around with FE166 (ES-R actually) and FE167 in OBs for a while, different sizes & wings.
They just never did sound that good to me, probably for reason suggested, wrong application. The best I can say that came from the experiment was the drivers are now well broken in.

I'm just finishing a pair of Ron's Austins for the 166s.
Awesome.
The best I've ever heard, period, down to 40Hz.
Much better with a SET than SS to me.

Also tried a FE108, totally different (to my ears).
This little guy is really great OB, almost as goon as in super swans, but "differentn."

My next step is like your question, integrating a sub...
Robert

[Rudolf]

John,
you are certainly right with that.
Just to illustrate which baffle size would be sufficient for 300 Hz:

This open baffle with 122 x 35 cm area and the Ciare HX 132 will allow a frequency response +/-2,5 dB from 300Hz to 11 kHz. "ohne Sperrkreis" means without notch filter and "Hochpass" obviously means highpass.
Measurement was done 15° off axis to the short side of the baffle.