ONS MMTMM Crossover Design - is something off?

[Jeremy White]

Hello,

I just finished building Paul Carmody's ONS MMTMM center channel.

When I selected the kit from a competitor to this site, I chose the HiVi T-20 option.

When I received the parts, I had an 8.2 Ohm resistor across the tweeter which seemed as if it was for the Dayton ND20FA (which was an option.)

I purchased a 5.6 Ohm resistor locally and installed it in the place of the 6Ohm resistor in the schematic.

When listening to the speakers, which sound fantastic for music, seem a bit warmer then I would expect for dialog. I'm seeing a few other comments about the HiVi that also echo this. The people who used the Dayton seem much happier. I disconnected the other speakers (on accident) and only listened to the tweeter and it seemed to be quieter than I would have expected in comparison to at the same amplifier volume.

I'm wondering -

1) Was the crossover modelled to the HiVi 4 Ohm or the 8 Ohm? Perhaps PaulC used the 4Ohm in his calculations and I used the 8 Ohm?
2) Could my choice of 5.6 instead of 6 ohms make such an impact?
3) Is there anyway I can model the components myself with the schematic to see if something is off? Is this easy as I'm very new to crossovers?

Thoughts? Comments?

Cheers!
-Jeremy White

[Steve Lee]

Try the 8.2 Ohm across the tweeter and it should be louder/more present.

[djg]

Ask the vendor, they are very nice people and will correct any errors they might have made.

[Jeremy White]

Ask the vendor, they are very nice people and will correct any errors they might have made.

Unfortunately, the vendor hasn't been very responsive. Friendly - but not replying to emails.

[djg]

I call them.

[Jeremy White]

Try the 8.2 Ohm across the tweeter and it should be louder/more present.

Shouldn't that divide the voltage by 8 instead of 6? Making it quieter?

-Jeremy

[Steve Lee]

Shouldn't that divide the voltage by 8 instead of 6? Making it quieter?

-Jeremy

The resistor and tweeter are in parallel so they both see the same voltage.

The parallel resistor is a shunt/shorter circuit to ground bypassing CURRENT away from the tweeter - The lower the resistance the higher the current therefore a higher resistance is needed to reduce the current in the shunt so the tweeter gets more of it available to play louder.

[billfitzmaurice]

The resistor and tweeter are in parallel so they both see the same voltage.

I'm not familiar with the design, but that being the case the resistor won't affect the volume of the tweeter. It will affect the load seen by the high pass filter, which will alter the filter transfer function and the tweeter response. The resistor would only affect the volume of the tweeter, and the transfer function of the filter as well, if it was series wired with the tweeter. This is why we use LPads to lower the volume of tweeters. They do so without altering the load seen by, and therefore the transfer function of, the high pass filter.

[Steve Lee]

Thanks for the clarification, Bill.

[rpb]

I'm not familiar with the design, but that being the case the resistor won't affect the volume of the tweeter. It will affect the load seen by the high pass filter, which will alter the filter transfer function and the tweeter response. The resistor would only affect the volume of the tweeter, and the transfer function of the filter as well, if it was series wired with the tweeter. This is why we use LPads to lower the volume of tweeters. They do so without altering the load seen by, and therefore the transfer function of, the high pass filter.

Changing the resistor will change the spl. The combined impedance of the tweeter, and resistor change, thereby causing a change in current flow through the series resistor, and that will cause a change in the voltage drop across the series resistor. That change in voltage drop changes the tweeter output. It may also change the roll-off, but the spl does change as well. A sim can show this to be true.

[Steve Lee]

I am watching this discussion closely and thanks - OP --> Standby, this may get interesting but much learning can be obtained as this progresses.



RPB - keep going.

Bill - does current NOT play a roll here?

[rpb]

I am watching this discussion closely and thanks - OP --> Standby, this may get interesting but much learning can be obtained as this progresses.



RPB - keep going.

Bill - does current NOT play a roll here?

I feel like I had this argument before, and lost, but I change the parallel resistor sometimes to make small changes. I can't run a sim right now, because I don't have a computer with the software available. Try any 8 ohm tweeter with a 4 ohm, and 8 ohm pad, and then change the 8 ohm to 4 ohms, and see if I'm correct. Use a big cap, or no xo to see if the effects are strictly from the resistors. Maybe the effect is very small. Sometimes a small change is what's needed.

[billfitzmaurice]

Changing the resistor will change the spl.

Only if wired in series. As I understand it the OP has it wired parallel. Please read my post again.I don't believe you understood what I said.

Bill - does current NOT play a roll here?

It only plays a part in so far as the current demand on the amp goes up with a parallel wired resistor. It doesn't affect the tweeter output, which is voltage sourced, not current sourced. The voltage to the tweeter is unaffected by the presence of a parallel wired resistor.

[Steve Lee]

Only if wired in series. As I understand it the OP has it wired parallel. Please read my post again.I don't believe you understood what I said.


It only plays a part in so far as the current demand on the amp goes up with a parallel wired resistor. It doesn't affect the tweeter output, which is voltage sourced, not current sourced. The voltage to the tweeter is unaffected by the presence of a parallel wired resistor.

OK - so the parallel resistor is for the amp's benefit and has no effect upon the tweeter since it (tweeter) sees the same voltage as the parallel resistor?

[DeZZar]

It just changes the load the amplifier sees but a parallel resistor all by itself, per OP's question, has no effect on the "volume" of the tweeter - it only has an effect in combination with series resistance like an lpad. You can reduce output without a specific series resistor if there are other series components providing a level of resistance already - then a parallel resistor can reduce the output without a specific series resistor.

[billfitzmaurice]

I wouldn't say the parallel resistor benefits the amp, but yes, both it and the tweeter see the same voltage, just as two tweeters parallel wired will see the same voltage. In that case the higher current draw would serve some purpose, as two identical tweeters driven with the same voltage will have 6dB higher output than one.

[rpb]

There is also a series resistor. Any current through the tweeter, and through the parallel resistor goes through this series resistor. If more current goes through the parallel resistor due to changing its value, then more goes through the series resistor as well. Voltage drop across the series resistor is dependent on the current through it. If more current flows, there is more of a voltage drop across the series resistor. This reduces the voltage seen by the tweeter, and changes its spl.