Another Arvo Pärt MKII.V Build

[JonMarsh]

For surrounds, I'm presuming you want to get down to 80 Hz, and HP filter in the processor at that frequency. at the least, you'd need something like a pair of RS265 on the bottom end, in addtion to your midwoofers. A larger panel and 4 M8a per side might do it, but you'd still need some LF EQ, or the equivalent of baffle step in the crossover. Could go with a single 12" on each side, a single midwoofer. That's an interesting idea...

[Eric S]

Sorry, yes - I intend to HP them at 80Hz in the processor. Using a single 12" driver along with one mid-woof sounds like an interesting alternative...

[Dennis H]

A pair of the 12" Peerless SLS looks interesting for the midbasses on a small flat baffle with an 80 Hz crossover. They are similar to pro drivers in some ways. Things that appeal: $72 price, reported good sound from guys using them in Europe, first (very minor) breakup at 700 Hz, 91dB sensitivity, 8 mm Xmax, light Mms for minimal baffle vibration, pretty high impedance so two in parallel is no problem. They look like a good match for a Peerless Exclusive midrange.

http://www.madisound.com/cgi-bin/index.cgi?cart_id=3937043.9925&pid=1946

[JonMarsh]

Interesting suggestion, Dennis! Two in parallel would get you a four ohm load for some further improved senstivity and power handling; then you could throw away a little of that in the diopole step passive EQ. Might be fairly clean up to 250, which would be the acid test. QTS is nice, too. Wonder how linear it is when you push it a bit?

Looks pretty lightweight with that small magnet, which eases fabrication. Hmmm, do I smell another attempt at a low buck Gradient Klone? Too bad I'm not really all that fond of the Seas Coaxial. Maybe just a waveguide, 27TDFC, and 883 midbass?

[Dennis H]

Sounds like a plan, Jon! The smaller 18sound waveguide might work well with the 27TDFC. It has a flat bolt-on mount so you could probably use it without modification -- just a thick felt gasket to absorb reflections/diffraction from the waveguide's opening being slightly smaller than the tweeter's.

http://www.eighteensound.com/index.aspx?mainMenu=view_product&pid=179

[Eric S]

:E :E Whoa! That quickly went over my head!! :E :E

I thought one of the important aspects was to retain (as closely as possible) the same set of drivers all the way around. Doesn't using Peerless and Seas drivers kill this?

[JonMarsh]

:E :E Whoa! That quickly went over my head!! :E :E

I thought one of the important aspects was to retain (as closely as possible) the same set of drivers all the way around. Doesn't using Peerless and Seas drivers kill this?

I'd say it would be a good idea to use the same size and directivity of drivers. My own preference would be nearly identical systems, but unfortunately folks don't seem to be wiling to make that kind of investment in surrounds.

Using a design which has very similar power response (i.e., frequency response versus axes) is critical for perception of equivalent voicing. Yet "conventional" HT wisdom often uses rears with very different dispersion vs frequency than the main speakers. IME, not a great idea. A T-M-W diople will have a fairly similar reponse to a properly designed MTMW diople, and will have less room interaction and be more faithful to what's on the disk. OTOH, it may be more necessary to do THX type equalization for some disks, rolling the highs somewhat with a tilt-down equalizer for an accurate tonal balance, as many film tracks are EQ'd based on the assumption of direct radiator monopole speakers that are flat on axis but with a falling room power response, due to restricted off axis performance in the upper range, but full off axis dispersion in the bass and lower midrange; also due to presumed HF fall-off with distance, which doesn't occur in most home environments.

[Eric S]

Thanks for the explanation, Jon. That makes more sense to me!

[Dennis H]

I was actually thinking of an all new inexpensive Arvo that would be crossed at 80 all around and could keep the front baffle width down to 13-14". Seems like, with most HT receivers, you need to either run the mains full range or cross them at 80 or above. Their mixer blends all the "small" channels plus the LFE channel and then applies the lowpass to the whole works before sending it to the sub. So, if you cross at 40 Hz, you end up throwing away all the LFE channel above 40 and the 40-80 stuff is prime LFE content according to Roger Dressler of Dolby.

[JonMarsh]

A 13-14" dipole panel would push up the dipole hump to ~350 Hz or so. Panel on the Arvo tends to compensate a bit for the roll off of the midwoofer and allows it to work down to
~200 without much EQ, IF you put it asymmetrically as the Arvo does. If it's mounted symmetrically, there will be a hump in the response before the panel roll off, requiring a more complex crossover/equalizer. Doc Emmet Brown always says do something acoustically instead of electrically when ever you can....

[Dennis H]

A 13-14" dipole panel would push up the dipole hump to ~350 Hz or so.

That seems okay to me if the woofers will handle it. Offset the mid and center the woofers; their wide cones should reduce the hump. Crossing a bit higher takes the strain off the small single mid and would give the woofers and the mid a bit over 2 octaves each. No idea if the 12" Peerless will cross that high or not though.

Edit: I've tried modelling dipoles in The Edge and it really seems to exaggerate the dipole hump. SL's measurements of the Phoenix don't look nearly as bad as the software predicts. It looks like a nominal 3-400 Hz crossover with the poles spread a bit would pretty well take care of it.