Questions about measurements and bi-amping for new project?

[aj01]

Hi,

I'm thinking about starting a new project and have a few questions. This is all kind of at the extreme edge of the budget for me (and I'm planning on using some gear I already have), so I'd like to make sure I don't make a major mistake along the way. Thanks again to the people who have answered questions for me in the past, I'm really getting started this time.

System - 3-way, jbl tweeter, 2" 500hz horn, dbb bass bin (may experiment with some horn-loaded midbass)

1. I'd like to be able drive the mid/high with the same amp and may change the drivers on the bass bin, so I'd really like to do a passive crossover at ~5800 and use an active at 500Hz. Is there any problem in using a 2-way active crossover into a tube for the mid/high and a ss amp to handle the bass?

2. My first idea of equipment is a Blueberry preamp into an Ashly xr1001. The two things that make me a little nervous are that the output impedance of the Blueberry is 3.5k and the input impedance of the Ashly is 20k. Most places I've read that you want this ratio to be around 20, so would the matching be made worse by trying to go from an rca to an XLR over this same interface?

3. Do I need to do some calculations on the output of the bass bin when choosing crossover settings and amps? This may be a stupid question, but if I have a small tube amp driving the mid and a large ss driving the bass - could I wind up outside the range of a crossover?

4. Would it be better to wire up two woofers in parallel or series?

5. Can someone recommend a usb microphone and software for testing?

Thanks again.

[Mike Dubay]

Aj,

Some well thought out questions, since I am working toward the same goal I will put my 2c in.

1) No problem using a passive cross over for the mid/tweeter and active between them and the bass, it's a common thing to do. I currently have an SE tube amp powering my tweeter and squawker and a solid state amp running the woofer. I'm currently doing my crossover passively, using an attenuation switch to balance the woofer and the squawker/tweeter along with a passive preamplifier. Saving for an Ashley myself.

2) Yes, I doubt if this would be a problem, but out of my area of expertise.

3) Most of the bass bins using ported boxes come in around 100 db/watt, 103/105/watt for some of the folded horns. Horn loaded squawkers provide around 105 to 108 db/watt. So the 3 to 8 db attenuation would fall with in the abilities of the Ashly xr1001.

4) For the best efficiency gain you can run the two woofers in parallel, you gain about 3 to 4 db/watt that way. Your amplifier has to built to handle the low impedance generated by doing this. If you start with 4 ohm woofers, and your amp is not rated for 2 ohm loads then wire them in series.

5) No software recommendations here. I use test tones recorded on the CD player and a Radio Shack SPL meter.

[Don Richard]

1. I'd like to be able drive the mid/high with the same amp and may change the drivers on the bass bin, so I'd really like to do a passive crossover at ~5800 and use an active at 500Hz. Is there any problem in using a 2-way active crossover into a tube for the mid/high and a ss amp to handle the bass?

Make sure that your 500 Hz horn and driver has response below 500 Hz, because even a steep slope active xover will allow energy below 500, possibly causing driver damage. When a driver is rated to 500 Hz it is normal practice to cross @ 800-1000 Hz. You should be able to use SS and tubes together, but you might have level/impedance issues that can be dealt with sucsessfully.

2. My first idea of equipment is a Blueberry preamp into an Ashly xr1001. The two things that make me a little nervous are that the output impedance of the Blueberry is 3.5k and the input impedance of the Ashly is 20k. Most places I've read that you want this ratio to be around 20, so would the matching be made worse by trying to go from an rca to an XLR over this same interface?

This could be an issue. Transformers or impedance matching boxes, or an SS preamp with a lower output impedance will probably be needed.

3. Do I need to do some calculations on the output of the bass bin when choosing crossover settings and amps? This may be a stupid question, but if I have a small tube amp driving the mid and a large ss driving the bass - could I wind up outside the range of a crossover?

I suggest using power amps with input level controls so that amp gains can be matched, and gain structuring can be better controlled.

4. Would it be better to wire up two woofers in parallel or series?

If the woofers are paralleled your SS amp will output more power. Ensure that the amp is rated for the resulting impedance.

[aj01]

Thanks for the advice. I bought an Ashly xr1001 off of ebay and have to save up a little bit for the ALK extreme slopes.