[jschwenker]

Hi all,

Here's one of those deep questions, real specific to a particular application but yet one where a number of folks might learn some things by the exchanges it could trigger, among those interested.

I'm wondering whether to block my main speaker's passive radiators (PR)  (effectively much like a speaker port) in order to arrive at even better blending to subwoofers.

Current situation:  Thiel 3.7 mains and Thiel SS1 subs.  Behringer DCX2496 crossover controller.  Crossover point 80Hz (hoping to stay comfortably above the mains resonant frequency for that PR but comfortably below the upper limit for good SS1 operations)  Using a second order filter slope and retaining normal phase but delaying the mains to align well with the subs.  (peak of combined 80 Hz response does come in at just about the delay place where one would expect it to, given the second order filter delay and the SS1s being located maybe 2.5 feet behind the mains)

System sounds very good on well recorded drums etc but not one to shy away from considering other major tweaks, am thinking I might machine up some beefy disks to install between the PR and cabinet to blank them off, returning the design to a sealed box system with potentially cleaner mid bass allowing better yet sub integration.

In this special case I would need to worry less than some do about impacts on main woofer excursions of operating a woofer unit that was not designed for sealed box use, since I am not sending much of the lower 2 octave's energy to the main speakers. Understand also that blocking off the PR may lead to a cabinet volume that might be not so appropriate for the woofer.

Main question:  Do folks know of a web site that does a pretty good job of discussing the rules of thumb I might want to employ, when considering this - say in particular, calculating if I'd like to place some sort of dead object of some kind in there to reduce the sealed cabinet volume??  (probably some things in the stickies for this circle, just haven't yet dug in there...)

Other comments welcome too...

Thanks!!  John

[Russell Dawkins]

Have you tried the same, but with fourth order crossover slopes to both the subs and the mains, i.e., both high pass and low pass at 24dB/octave?
I don't think second order would be steep enough not to cause the passive radiator to still be involved. Alternately, if you prefer second order for some reason, you might try 100-110Hz or thereabouts, since the subs are in line with the mains but behind. At least I would try fourth order to the mains, if not the subs; you don't have to have the same slope on both.

[jschwenker]

Thanks for the suggestions Richard. 

Yes a 4th order setup would be one of the most straightforward things to do.  I claim that some folks end up concentrating their listening a bit on slightly on slightly different things and I happen to be one of those oddballs that enjoys the transient details - perhaps to excess.  As such I really love what the well implemented Thiel 1st order crossovers can do at higher frequencies.  So though I've not tried it I am assuming the 4th order, while it would do excellently with say lower notes of a bowed bass might not do quite as well with carefully recorded bass drum hits.  (as does my time shifted 2nd order)

Good call on trying one or both of going higher in frequency and/or differing the filter slopes on each side.  I have some rudimentary spreadsheet ways of exploring those kinds of waveform and filter slope additive results set up and maybe I'll play a little there too.  (of course should be allowed that the room space may be participating a fair amount in the folding and "de-phasing"/re-phasing at these low Hz)

Cheers,  John

[jschwenker]

Oops, sorry, Russell that is...  haha

[SoCalWJS]

OOC

Have you taken any in room measurements (REW, OmniMic, or similar) to see if you have some acoustic issues to address? Room treatments can be especially effective in the mid bass/bass region.

[jschwenker]

Hi WJS,

I do have a DSPeaker 2.0 anti mode that I have used as both a response smoothing and just as a measurement system.  The room does have some difficulties, some of which are solved by the anti mode when hooked in.  However, again as a card carrying phase nut it is my judgment that such augmentation dulls up the clarity of LF transient response a bit.  I have some good treatment absorbers that largely solve a ceiling reflection that I was getting from a wrong way sloped ceiling but little else is practical in this room.  Thanks for contributing!

Cheers,  John

[fredgarvin]

Perhaps you could try mass loading the pr, as Brian Cheney did, in your case to dampen the reponse.

[Russell Dawkins]

Have you considered moving the subs closer to you than the mains, so you could delay them instead of the mains? I have always preferred this idea, as it preserves sub headroom and I would rather suffer whatever degradation delay introduces in the sub frequencies rather than the mids/highs.
It also can contribute to a lower general level of bass as heard throughout the rest of the house, which can be a benefit.

[jschwenker]

Thanks Fred & Russell, 

Mass loading might be more difficult to do without permanently altering the original speaker parts, which I'd rather avoid - but I'll acknowledge it for consideration.

Just due to the second order filter 1/2 wave shift, at 80 Hz the mains must be delayed about 6 mS or about 7 feet equivalent.  So I would need to locate them about 7 feet closer to the listening position and then could operate with no delays.  Quite interesting for an experiment maybe but pretty impractical for this particular room.

Yours,  John

[jschwenker]

Sorry, friend pointed out, that would of course be locating the subs 7 feet closer to the listening position than the mains.  BTW I do like the other reasons stated too, sub headroom and lower bass energy well away from that listener location...