A7 Active Crossover Choices

[jocelys1]

My SUBs are ported and tuned to a Q of 0.5 (12" driver). The drivers have a Qts of 0.42.

Have to live with HT LOWs I guess, where it works fine with the 'rolling and tumbling' .

[GM]

How does one tune a reflex to a Q = 0.5? It's a 4th order system, so assume you're actually referring to a roll off slope above Fb @ 6 dB/octave.

GM

- - - Updated - - -

First up, frequency and slope choices. I'm presently using second order Butterworth at 800 Hz.

At the time I had A7s I used the new Altec 771 bi-amp modules @ 500 Hz: http://www.lansingheritage.org/image...-mi/page12.jpg

Today I'd use a dbx Driverack and some sort of 'gapped' XO to blend them over a wider BW, though due to the driver's CTC spacing would still limit the woofer to 500 Hz. That said, for smoothest overall 511 horn response, 4 kHz/1st order passive turned them into ~ just a WG with no real need for CD horn EQ and IIRC, was able to bypass the pots [no attenuation req.] at least with the speakers in the corners of a below grade concrete block basement. Can't recall if I switched to a higher woofer XO point though. Anyway, strictly a YMMV suggestion to think beyond Altec's PA apps mandated choices.

BTW, not familiar with the Mini-DSP [or any other current electronics], but the normal Butterworth 2nd order requires that the HF wiring polarity be reversed and when the VCs are aligned, in phase, so curious how it deals with this.

GM

[jocelys1]

Hi GM. You put in words what I was trying to achieve in the simulations. While working the driver /box design I went with a gradual roll-off with good extension, rather than steep drop-off.

[GM]

A good plan and like most of my designs whereas Altec typically tuned relatively high, to the point of a minor 'bump' at Fb [under-damped] to get that 'West Coast [frat party ] Sound'.

GM

[gearfreak]

- - - Updated - - -
...
Today I'd use a dbx Driverack and some sort of 'gapped' XO to blend them over a wider BW, though due to the driver's CTC spacing would still limit the woofer to 500 Hz. That said, for smoothest overall 511 horn response, 4 kHz/1st order passive turned them into ~ just a WG with no real need for CD horn EQ and IIRC, was able to bypass the pots...GM[/QUOTE]


Playing with the dbx PA2 now. 48db Linkwitz @ 2khz really seems to work for the ferrite 604's, initial impression is that I like what steeper slopes can do and surprised that I like it crossed that high.
(*noting that we've observed repeated in many discussions regarding: the horn being is too small to load very well at the intended or lower ~1600hz)
Minimal parametric eq for perceived as needed BSC, slight lift at 16khz and LF delay of .21 millisecond delay are applied at the moment.
but there's so much more tinkering to be done yet.

[GM]

Yeah, back when JM published his loading cap expose' I noticed that 2 kHz looked a better choice for the horn, but no clue what the woofer's response would be like and frankly wasn't that interested as the original's 1 kHz horn/XO had long since indelibly marked my teen brain, though did have a brief 'affair' with a then neighbor's 604E that we tried in his [my ex] built-in corner A7-500 system.

Historically, I don't even like 2nd order that much unless there's proper offset to wire in phase and LR 4th @ 360 deg disconcerts me above ~800 Hz due to HTRF, so pretty sure 720 deg. would do me in except down low where nobody will notice, but can it be 'unwrapped' with DSP? I mean the 0.21 ms delay is just for increased HF offset, right?

Have you done 604 woofer only response plots? I've yet to see one.

GM

[gearfreak]

Thanks GM. HRTF is a new one for me, I am not picking up well on the relationship yet. More to read up on. Feel free to elaborate of course.

Nah, no response plots from anything, but I should have some free air impedance plots not yet posted for the 604s.
If the dbx (with its mic) is an avenue to response plots then perhaps we'll have something down the road here.

To that end, I'm holding off on trying the dbx auto-eq/wizards.
It will be interesting to see if it aligns or not, with what I think I know.

Yup, the .21 is just to account for the driver offset.

[GM]

Greets!

HTRF: head-related transfer function - Google Search

GM

Looks like all it can do is an RTA plot, which you may can only take a photo of it: https://3e7777c294b9bcaa5486-bc95634...B_original.pdf