HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

having had pretty good success with wiring in my AV sub for stereo use to flesh out the lower registers I've been contemplating building a couple of dedicated subs to supplement each of the front speakers

The easy way would be to use a dedicated plate amp on each sub, its designed for the job and has all of the connectivity and crossovers built in.

However I can't help thinking a dedicated high quality power amp would do a better job. That brings us to the issue of what to use for a crossover. Again in my head I'm thinking an adjustable low pass line level crossover is what I need.

However I can't seem to find any. Building one is a bit more DIY than I had in mind. So any suggestions gratefully received

Never use a sub with nva amplifiers.

Line level crossovers have a bad effect on the music (see discussion of music v sound), they are too complicated and they mask musical information. The only good crossover is no crossover. The nva way is just a capacitor protecting the tweeter and a padding resistor to put it in level balance with the bass / mid or bass and mid. Bass and mid are doped to create the frequency curve required.

Read Karatestu's DIY speaker threads.

thanks Doc, so youd' run a 12" driver with just doping?

Ask Karatestu, that is what he has done, I doped and sold them to him. I hate all electronic filters - passive or active though active are worse, they are the work of the devil in musical terms. So that answers any question about them.

I should probably add that the tweeters and mid bass are running on a dedicated amp channel each so any crossover would only be yet another dedicated amp channel affecting the sub bass

Do as you want but look for music not sound.

well if doped 12" works so much the better as I agree if you don't have to use a filter better not to.

I had for some reason assumed that at that size doping was insufficient. Though now I think about it I have no idea why. I'll have a chat with Stu

I actually made a pair of passive subs for a laugh using a pair of Richard doped qtx 12" drivers a couple of weeks ago.
All i did was to get 2 big cardboard boxes 18"x18"x16", seal them very well with tape and run them open with no crossover in parallel with my metronomes.
They were actually quite good, the speakers are an 8r load, the subs in parallel made it 4r but the f5 power amp doesnt seem to care about the load dropping.
There was box colouration obviously, but you could tell what was the box and what was the driver.
The wife then said no to 2 large boxes so fun stopped.

There wasn't a need for a crossover, maybe an inductor to cut the top off the driver as its response seemed abit spiky past 1k ish, but just for a laugh it showed potential.

I dont know what Richards amps are like in terms of what sort of load they will take, it probably dropped lower than 4r, but maybe a carboard box lash up could show if there is any need, or benefit to running subs.

It was done for a laugh, but was good to see if there was any benefit.

interesting though surely using an inductor is effectively a crossover?

Yes, its a single component to keep higher frequencies out of the driver. Wether its needed or not is another matter. A pair of lugholes would tell you that.
When i built the mets I ran just a cap on the tweeter and the main driver open, the very top of that driver was not very nice so i ended up with an inductor to slope the response off until I was happy with it.
Those speakers have a cap and a resistor to pad down the tweeter, and an inductor on the main driver and thats it. No doping on the main driver though, so as simple as poss without doping the driver