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post #1 of 8 Old 04-16-12, 12:01 AM Thread Starter
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Example of full range with miniDSP

Since others are asking about this, I thought I would share some of my progress ("fooling around") with using the miniDSP as a replacement for the Bose 901 [series 2] active equalizer. Why go to the trouble? Because with REW I can (among other things) hunt and flatten the worst peaks in the bass.

Most recently, I EQ-ed my Bose 901's "by ear" using 1/3 octave pink noise bands and the plug-in that offers the graphic EQ. For those who don't know, this is one method to subjectively EQ a speaker system so that each band of noise sounds the same loudness. In theory, this makes the system "flat" for your own ears. I've toyed with this set-up for several hours of listening and I'm impressed. Compared to "ruler flat" EQ, the subjective method gives much more bass which is what 901s should do.

Based on sweeps of the Bose 901s with no EQ of any type, I have a good idea of where the room modes are. In my case, I notched out two around 70 and 140 Hz. So far, I cheated: I used the DEQ2496 for that. Ah, but more to come.

Having a satisfactory 1/3 octave EQ for my system, I did a loop-back measurement of the miniDSP using REW. now I have my personal Bose EQ curve that I can analyze. I've done this, inspired by the article "Minimal EQ" (geared towards subwoofers, as is nearly everything about REW).

The filter creator feature in REW can be set to work on a full range curve such as mine. By varying your choice of which hardware it will use, and also limiting the number of filters, you can make the curve fit as accurately as you like. After many runs, I have gotten a pretty close fit with just 8 filters. Note these are all still "on paper", none of them has been tried in the PEQ plug-in.

Is it worth a tutorial? Maybe. It is sort of a waste of time, perhaps, since I am mostly duplicating what I did with the GEQ plug-in. However, remember if I use the PEQ plug-in, depending on how stingy I was with the main curve fit, I still have some extra filters I can use such as for narrow filters in the bass. That would still be just ten filters.

This is not all wasted effort ("yet") -- I plan to use REW to find the best curves to set up a friend's 901's using just the parametric EQs in a Sherwood R-772 Newcastle (HT receiver). This will be a bit of a challenge because there are limited PEQ per channel and each one only covers part of the frequency range. My plan is to analyze friend's curve in sections and find the best single filter for each one. Will it work? I am sure to brag or wail in this forum, stay tuned.

Last edited by StanDingwave; 04-16-12 at 12:07 AM.
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post #2 of 8 Old 04-16-12, 12:53 PM
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Re: Example of full range with miniDSP

I've rarely (if ever) seen a magazine publish the frequency response of Bose speakers in reviews. Out of curiosity, what kind of response are you getting out of the 901s?
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post #3 of 8 Old 04-16-12, 09:50 PM Thread Starter
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Re: Example of full range with miniDSP

I can't run a sweep right now. However, I pulled up an early attempt and I was able to get pretty flat (call it +/- 3 db) between about 2K to 10K (the max of that sweep). In practice it's hard to get much above maybe 12K Hz, which is fine with me since my hearing ends around there

The bass can go down to 20-30 Hz (these are "Series II" -- acoustic suspension, which Bose changed to a ported design starting with Series III -- really a different type of speaker.) In the sweep I'm looking at, it is very erratic, about +/- 8 dB but I blame that on not fine tuning as much. Given a lot of filters (I can do up to 20 per channel with a MiniDSP) the 901 can be beaten into submission. I doubt you'll ever get "ruler flat" out of a 901, but that was not the design intention, nor is that (as academics say) "necessary and sufficient" to get good sound.

I think the 901 makes a good challenge to try to EQ (without using Bose's EQ unit) because of the built-in need for a lot of boost on the low and high frequencies. If I think to, I will post a more recent (and hopefully more worthy of bragging rights) frequency response later.
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post #4 of 8 Old 04-17-12, 06:05 AM
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Re: Example of full range with miniDSP

I am curious.

EQ is not effective in mitigating non-minimum phase speaker room interaction, and that is exactly what the direct-reflecting model attempts to maximize.

So how are you determining the actual spectral content of the speaker?
Is this without the control unit that effectively synthesizes the lower octaves? Or is this with the unit with its extensive EQ already being applied to the system?

And you now want to further EQ the EQ'd system measured (possibly) 'in room' in a maximally non-minimum phase environment????

The fact is the direct reflecting models seeks specifically to create such a well mixed comb filtered environment through speaker room interaction (to the point where it ONLY has one forward directed driver) that the superposition of direct and beau coup indirect signal comb filtering literally dominates over a wider spatial region creating a 'larger but more amorphous' image.

Think of it as a system pre-dating by 20 years exactly the response of which what Toole now advocates (but of which his supporters are loath to admit as apparently they their reflections are 'fancier'...).

Trying to EQ this violates the very concept it uses to create its signature response. And Bose has already EQ'd the direct signal - the ONLY part of the system you can legitimately EQ!

I fear you are fighting the very concept of the speaker as well as the very definition of what EQ can and cannot do.
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post #5 of 8 Old 04-21-12, 09:05 PM Thread Starter
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Re: Example of full range with miniDSP

Here is a 'from the field' report on using REW with not the MiniDSP, but the Sherwood R-722 and its 5 somewhat limited PEQ per channel, to EQ a pair of Bose 901 (w/o the Bose Active EQ). After many sweeps, I have gotten the response reasonably flat (use one octave smoothing, much less scary that way). Essentially flat response (+/- 3 or so) between 50 Hz and 7 or 8 Khz. Even an enormous boost at the high end can't seem to get it up. My victim, er friend, is very pleased with the results. In any case, my decision (aided by HTS i think) in the choice of the Sherwood R-722 has been validated. It's a fantastic deal at about $200. 100 watts per channel and the PEQ were its main points. It'll take my friend years to figure out all the controls. As for using REW, it probably took 40-50 sweeps and tweaks to get the "golden curve" and any further gains seem to be minimal. I'm here two more days so doubtlessly will fiddle some more.
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post #6 of 8 Old 04-22-12, 06:24 AM
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Re: Example of full range with miniDSP

Hey Stan,

Forty or fifty sweeps? If you’re using a generic equalizer (i.e. one not “supported” by REW), it makes more sense to use the RTA feature and tweak response in real time. Much quicker and easier, but you might want some ear plugs because of the pink noise signal.


Last edited by Wayne A. Pflughaupt; 04-27-12 at 04:36 AM. Reason: fix typo
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post #7 of 8 Old 04-23-12, 06:05 PM Thread Starter
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Re: Example of full range with miniDSP

Good point. I have done that with my DEQ2496, of course, but did not know that REW would do pink noise. It might have been faster.

I am pleased to report that, after many hours of fiddling, I have the Bose 901 beaten into submission. Yes, with a third-octave EQ it would be much easier to tailor the response, but still for 5 filters and with restrictions on each channel, I think I did pretty well.

On the HDMI front I admit total defeat and befuddlement.
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post #8 of 8 Old 05-16-12, 06:30 PM Thread Starter
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Field report #2: much easier the 2nd time!

I have set up a 2nd Sherwood Newcastle R-722 for a second friend. This one is driving a pair of restored ("sort of") Bose 901 Series V. Set up was much faster since I had my training a month ago with the first friend and I avoided any HDMI attempts this time. I used REW to run a few sweeps. I have tried the pink noise & RTA but feel more at ease with the sine sweep (probably since I have used that the most.) Like install #1, most of the EQ only needs three filters (lows and highs). I am dialing in the mids by ear (and octave pink noise bands) to fine tune it a bit. It won't shake the walls (only 100 W/ch.) but it sounds quite good.
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