Thought it might be fun to share this.
Intro:
Years ago, I commissioned a pair of cabinets for a Fostex FE126E (which had been treated by Dave at Planet10, including phase plugs) and a Tang Band W6-1139SI per side. Picture in attachments.
I used them for a while, using active crossovers, but eventually gave up. I couldn't get them sounding good enough to keep, so they've been stored in various places over the years.
Recently, however, I decided to have another crack at them. This time, I have a measurement mic, REW, XSim and a lot of power available - a useful by-product of running a live sound business.
Before I go much further, design goals:
- Good in-room low-frequency extension. I don't want to use a subwoofer, so output to 30Hz (preferably below) is important
- Smooth integration between the 4.5" full-range driver, and the 6.5" woofer, of course.
- Must sound good with any amplifier. I don't want to use DSP to fix the response - the rest of my system is all-analogue, so I'd like to avoid a round of ADC/DAC.
I knew from the outset that these goals meant I was going to end up with a low-sensitivity speaker, since we're up against Hoffmans Iron Law in a big way - I want low bass from a small box.
Crossover:
So, I measured both drivers in-situ, loaded the curves into XSim, and came up with a passive crossover, shown in the attachments. It also shows how much of a mess my room makes at low frequencies, although I'm hoping that the second speaker will smooth things out a bit.
In no particular order, we have:
- 2nd order high and low-pass filters
- Zobel on the Tang Band, because there's a serious amount of inductance there - it's a long-throw subwoofer driver with an over-hung voice coil.
- Notch filter on the Fostex, to kill the 6.6kHz peak
- L-pad to get the Fostex driver's level down to match the Tang Band.
The impedance curves re-iterates the bit about sensitivity - this is not a speaker for wimpy amplifiers, unless you're happy with very low levels. For reference, I'll be using a Crown MA5002VZ, which will put out 2KW/ch into the 4ohm nominal impedance.
My previous observations about the Tang Band woofers is that they do need a rocket up them to get going. Their long-term thermal power handling is limited, but they can withstand short-term peaks of many hundreds of watts without any ill effects. The Crown amp is overkill, but that's okay - it's too heavy for portable PA use, but sounds pretty decent so I've decided to put it into use as a HiFi amp.
I wired up a crossover this morning, and have been listening in mono since. The first step was to short the resistor leading into the highpass section - it was only 2ohm to start with, so wasn't doing much.
I used electrolytic capacitors for the big values, which unfortunately means there's one directly in-line with the Fostex driver. I might look into swapping that out for a big poly cap.
First impressions are good.
I set off with this - YouTube
And cranked it. The bass was impressive - even with just one speaker, the notes were tactile, rather than just audible. So, that's one design goal ticked.
Since then, I've been listening to a variety of music to figure out if I can live with this sound on a long-term basis. So far, though, impressions are favourable.
That's all for now. I'll keep listening in mono for a while, and do some measurements, before spending more money on a second crossover.
Chris
PS - the top-end peak and subsequent lack of HF extension does make me wonder about a 3-way...
Intro:
Years ago, I commissioned a pair of cabinets for a Fostex FE126E (which had been treated by Dave at Planet10, including phase plugs) and a Tang Band W6-1139SI per side. Picture in attachments.
I used them for a while, using active crossovers, but eventually gave up. I couldn't get them sounding good enough to keep, so they've been stored in various places over the years.
Recently, however, I decided to have another crack at them. This time, I have a measurement mic, REW, XSim and a lot of power available - a useful by-product of running a live sound business.
Before I go much further, design goals:
- Good in-room low-frequency extension. I don't want to use a subwoofer, so output to 30Hz (preferably below) is important
- Smooth integration between the 4.5" full-range driver, and the 6.5" woofer, of course.
- Must sound good with any amplifier. I don't want to use DSP to fix the response - the rest of my system is all-analogue, so I'd like to avoid a round of ADC/DAC.
I knew from the outset that these goals meant I was going to end up with a low-sensitivity speaker, since we're up against Hoffmans Iron Law in a big way - I want low bass from a small box.
Crossover:
So, I measured both drivers in-situ, loaded the curves into XSim, and came up with a passive crossover, shown in the attachments. It also shows how much of a mess my room makes at low frequencies, although I'm hoping that the second speaker will smooth things out a bit.
In no particular order, we have:
- 2nd order high and low-pass filters
- Zobel on the Tang Band, because there's a serious amount of inductance there - it's a long-throw subwoofer driver with an over-hung voice coil.
- Notch filter on the Fostex, to kill the 6.6kHz peak
- L-pad to get the Fostex driver's level down to match the Tang Band.
The impedance curves re-iterates the bit about sensitivity - this is not a speaker for wimpy amplifiers, unless you're happy with very low levels. For reference, I'll be using a Crown MA5002VZ, which will put out 2KW/ch into the 4ohm nominal impedance.
My previous observations about the Tang Band woofers is that they do need a rocket up them to get going. Their long-term thermal power handling is limited, but they can withstand short-term peaks of many hundreds of watts without any ill effects. The Crown amp is overkill, but that's okay - it's too heavy for portable PA use, but sounds pretty decent so I've decided to put it into use as a HiFi amp.
I wired up a crossover this morning, and have been listening in mono since. The first step was to short the resistor leading into the highpass section - it was only 2ohm to start with, so wasn't doing much.
I used electrolytic capacitors for the big values, which unfortunately means there's one directly in-line with the Fostex driver. I might look into swapping that out for a big poly cap.
First impressions are good.
I set off with this - YouTube
And cranked it. The bass was impressive - even with just one speaker, the notes were tactile, rather than just audible. So, that's one design goal ticked.
Since then, I've been listening to a variety of music to figure out if I can live with this sound on a long-term basis. So far, though, impressions are favourable.
That's all for now. I'll keep listening in mono for a while, and do some measurements, before spending more money on a second crossover.
Chris
PS - the top-end peak and subsequent lack of HF extension does make me wonder about a 3-way...
