Multi-amp thought experiment

[Moondog55]

There has been no interest in my old Rotel 8 channel amp but it is too good to give away. What can I do with a small cheap DSP and 8 * 40 watts? At my first thought that isn't much for bass but that 40 * 4 is equal to most 150watt power amps I've ever owned and those never seemed shy of bass power. 3-Way or 4-Way? I haven't opened up the box for the DSP yet as too much going on at the moment but I need to get my mind organised.

Whatever is going to happen will be in the context of the drivers I have in the shed and on the shelves but that selection is pretty broad and most of the better, smaller drivers will cope with 40 watts. Let's brainstorm even if nothing gets built for a while, I am a terrible ditherer and prevaricator and I think I prefer to tinker than do straight builds but I have the need to build something big soon

[Bon]

Originally Posted by Moondog55

40 * 4 is equal to most 150watt power amps I've ever owned and those never seemed shy of bass power.
3-Way or 4-Way?

I have been running active 3-way speakers for over a decade. I have found that the 2x10" woofers per side, take much more power than you might expect. In my 6.4x6.7x2.4 listening room, 200 watts rms is the minimum for adequate headroom. I tried a 6x Hypex UCD400 amp which clipped with ease on the 4 ohm woofers. I recall that Rotel uses ICE modules, which are more robust when abused, so they might be more tolerant but don't expect too much from 40 watts/channel. Otherwise, I am firmly in the active + digital crossover camp. The flexibility of DSP is a game changer in loudspeaker design. It will never be plug-and-play though. Expect a steep learning curve.

[Moondog55]

Rotel 1048
So 40 into 8R and 65 into 4R so maybe 10" woofers would be too much

[Moondog55]

I've been playing with the Dayton DSP. Nice toy and you can do some crazy stuff using it. Like passing one woofer at 300 but passing a parallel woofer at 80/120 etc

[Lojzek]

I'd first select the sound worthy drivers by measuring these in an "infinite baffle".

[wintermute]

Well, I guess you could do a TMMWW (or a WMTMW) You could use one channel for each W and each M and that would use up your 8 channels. You'd need a separate tweeter amp.

Or a TMWW and just use the one amp. or lots of other combinations

Tony.

[Bon]

Originally Posted by wintermute

Or a TMWW and just use the one amp.

Tony.

This would be my preferred option. Better to drive each woofer separately rather than in parallel. This gives your woofer amps an easier ride. One thing I experienced is that clipping the woofers is easy to do in active mode but the sound stage does not collapse in a steaming pile as it would if a passive is clipped. With 2 woofers you could also try opposed side mounting with coupling rods. This really does effectively cancel the reaction forces into the cabinet.

[Moondog55]

The alternative would be to use a mid/tweeter combination with a proven XO and well know performance and drive them with one channel. Nobody has claimed those Jaycar 50mm domes after all.
As for measuring on a baffle I thought the whole rationale for DSP was to mount according to good practice and then play?

[abstract]

Something big, you say? Can the channels be bridged? If so, that could give you some more power for bass. Failing that, don't forget that larger speakers tend to have higher efficiency anyway. And stereo bass output tends to be mono anyway, so that's amplitude summing at low frequencies, not power summing. IMO it makes a mono subwoofer problematic with most source material, and 2x 10" just sounds better than 1x 12".



In fact, you could probably go up to 2x15", or 4x10", have room-shaking bass for under 10W (OK, ymmv), and still cross over at 100Hz to any 7" mid of your choosing. Although at that point I'd probably start thinking about multiplying the mids for better efficiency in a line array, and then support that with a big tweeter.

[Ugg10]

Originally Posted by Moondog55

I've been playing with the Dayton DSP. Nice toy and you can do some crazy stuff using it. Like passing one woofer at 300 but passing a parallel woofer at 80/120 etc

Is this the Dayton DSP408 ? If so I'd be interested in your thoughts as to how this compares to the Minidsp models (4x10 or two 2x4)?


A shame you haven't go the RMB1066 which can be bridged to make 3x150w (need two) rather than 6x60w.


I have been looking at a similar system using either the rmb1066 or three Quad amps (2x306 plus 1x606). My preferred option, when the drivers come back in stock, is for a TMWW using a SB26CDC (or ADC), Morel EM1308 (or mdm55) and a pair of Anarchy 7" (708 in parallel for 4 ohms) which will fit in 40l box nicely and drop into the low 30hz at f3. This is my choice as I need something fairly small (thin floor stander) for a smallish room (9ft x 9ft) so don't need stadium level of loudness or 20hz sub levels.


You may be able to get away with in stock 704 and run an channel per driver and as you suggest use the dsp to stagger the tow 7" to spread out the bass hump these have at around 200hz. As said it will not shake the earth but would get pretty loud even with 65w per driver as they should result in around 87-89db sensitivity for the bass depending on whether you use the 8 or 4 ohm versions. These drivers sim up fairly well with 24db slopes at 700hz and 4000hz with a notch/parametric filter in the mid bass around 200hz to drop the level down plus another couple to fully flatten the mid and tweeter plus sensitivities are not far out (2-3 db only).


For info the new version of Boxsim (v2.0) allows you to sim active filters and crossovers which is a really nice feature.