Converting Magnepan MG10QR's to DSP crossover

[SoundMods]

[/quote]A typical AGC 3 amp fuse has a resistance of 0.045 ohms. Even if the resistance rose to 1 ohm the fuse would blow at 0.3A which represents 1/3W into 4 ohms. Hard to determine the mechanism that could cause an audible change.[/quote]

The I recommend you think about it. The sand-filled fuses besides having silver-wire fuse elements lowering the source impedance even further -- have immunity to acoustic break-through that can modulate the power supply or audio signal in not so nice ways. I've performed many a A/B comparison over the years and the improvement is audible and in some cases not subtle. Even better -- if you can find them -- BUSS makes (or made) a fuse with glass beads.

[tomp]

I never heard the term acoustic break through. What is it? Could not find it on Google. BTW, compare the resistance of the fuse to the DCR of a 4 ohm driver that is typically around 3.5 ohms. Also, even if the silver wire has lower resistance, it may also have a much higher melting point which means more loss across the fuse to get it to blow. Also compare any fuse with an electronic speaker protection circuit that in addition to rated current will trip with very low levels of DC or HF using a relay with silver/nickel contacts that worst case have 0.05 ohm resistance.

[SoundMods]

I never heard the term acoustic break through. What is it? Could not find it on Google.

It's English. Webster's Dictionary will 'splain it.

[tomp]

I've heard of acoustic and breakthrough but never the two used to describe some phenomena.

[SoundMods]

I've heard of acoustic and breakthrough but never the two used to describe some phenomena.

The sound in the room is not stopped by the casework or speaker enclosure -- it travels and "tickles" the fuse element. Those fuses were designed for industrial equipment to suppress vibration passed through to the fuse element. For that purpose it enables reliability -- for my purpose it so happens it helps the sound reproduction. That's one reason I add substantial constrained layer damping to the case work and speaker enclosures.

[HAL]

My hypothesis is that metal fatigue from the heating and cooling of the fuse element that is probably creating the element movement while passing signal is changing it vs time. The amount of element movement was not insignificant.

Will be interesting to see what happens with the new fuses. Need to clean the contacts and make sure they are holding correctly as well.

Having the Class D amps with 2ft of speaker cable is always a good thing. Done that many times and always a big improvement in sound quality.

Until I can get the final room treatments done, time to break out what I have left of RPG foam panels and the styrofoam diffusor panels for the room to help. Pretty much a giant echo chamber at this point. Fun to use it to record at this point, but not great for listening.

[HAL]

Ahhh... the final piece of floor has been installed and the adhesive should be fully cured tomorrow. Now time to put in the temporary room acoustic materials. Hope to have the acoustician estimate for room measurements and 3D model tomorrow.

The MG10/QR's are getting a pair of modular open baffle H-Frame 4x8in servo subs. Have flat packs for the cabinets in work and hope to have them in a few weeks. They will work with the Rythmik Audio HX300 servo amps I already have. These are good down to 30Hz in room, so add about 2.5 octaves below the MG10/QR 80Hz rolloff.

Fun is about to begin!

[HAL]

Have the first step of the room acoustics materials setup to check out. Side walls have some absorption and rear wall has more diffusion. Room needs more absorption, but a lot better than the reverb chamber it was.

Installed the Magna Risers on the Magnepan MG10/QR speakers. The screws on this pair were 1/4-20 x 1-1/4" style where normally they are 10-32's. Just had to remove some of the coating from the screw holes on the stands to fit the original screws.

Next is to wire them up to the Class D amps and start making some acoustic measurements.

Attachments

[HAL]

To go with the MG10/QR DSP Crossover project, worked with folks to develop a modular 8in Servo Sub OB H-Frame 4x8 stack. These are for the GR-Research 8in servo subs from the latest design. These will work below the 80Hz cutoff of the planars down to 30Hz.

These are the flat packs being test fitted before glue-up and then off to be painted.

Attachments

[HAL]

The Magna Risers went back for modification. The bottom position works with the 1/4-20 screws, but the top position does not.

They are going to rework the slot so that the speaker can be installed on the top pair of screw holes as the work better with subs in that configuration from their previous testing.

The box will be delivered Monday for the work and then ship them back.

Also purchased 8 new 1/4-20x 1.25in stainless steel bolts that are replacements for the original soft steel bolts. The finish is corroding from when they were in storage.

The new fuses are already installed and going to set them up with the Class D amps for testing with the original stands until the reworked ones arrive.