OK, I'm still not clear on reversing attenuation...

[bowbender7]

I have built the RS150 design with the following crossover http://www.htguide.com/forum/attach...tachmentid=9526

Since I built the BSC version (for future placement), I actually have the speakers in a less than ideal location for now. Because of this, the bass and midbass is very warm. I would like to change the tweeter attenuation values to actually brighten up the top end.

I have researched until I am blue in the face and come up with differeing opinions on whether only changing the series resistor value would alter phasing or pass freq. I would like to try changing the 4ohm series to maybe a 3.5 or 3 ohm - Will I need to alter the parallel resister also to keep things just as they should be regarding phase and cutoff??

I would be very appreciative if you have any thoughts to share!

Thanks, Sean

[joecarrow]

That link didn't work out for me- can you try posting again?

As a first thought, I'd ask if it's possible to improve your placement problem somewhat by adding some absorbing material in the vicinity of the speakers. In the past, I've been forced into a lot of non-optimal configurations, and I've done everything from sheets of foam behind/next to the speakers to stuffing a sock in the port.

Also, in my opinion, the state of active components has advanced somewhat from the days when high-fidelity people would tell you "do not use an equalizer!" to the point that the added noise and distortion of a decent equalizer is really the least of your problems if it corrects a more distracting problem. This is definitely more expensive to implement than a crossover change, but who knows- maybe you have an equalizer available?

[ThomasW]

[bowbender7]

Not sure what I did with the link there.... thanks Thomas.

I have researched, thanks to help from Thomas and some other resources which collectively give conflicting info regarding changes made with resistors. Some say that they have no bearing on cutoff freq. or phasing and I have also read what I believe to be respectable info that any changes made in this type of lpad must use a calculation :

((R1 x S1) / (R1 + S1) where S1 is the tweeter’s nominal impedance, and R1 is the value of the resistor hooked across the voice coil - then a series resistor of the differing value is added to regain the original load)

This is suppose to maintain an equivalent total load and not alter the cutoff frequency as changing the value in a single resistor (first order) crossover would do.

So here I am, wanting to play a little and learn a lot - the calculation I show above does not work out in any realistic resistors considering the starting point of 4ohm and 30 ohm ( I know I can series them to obtain value..but it seems this may be overthinking something that should be alittle simpler 8) )

The speakers sound excellent considering their placement (they are on very short stands on top of a TV stand and scooted out to the front as much as possible)

This would be a very minor (albeit arguably unnecessary) tweak, but understanding the relationship will help me along my way to understanding general crossover design a little better. Most info regarding this is given in response to requests to attenuate the high pass section - my request for guidelines to do the opposite seems to lead to a very fruitless journey since I have no modeling software.

Please dont mistake this inquiry as anything other than a compliment to CJD's designs :T - it is also not a request to completely redesign the crossover for some arbitrary cabinet dimensions or driver change. I just want to learn, and fiddle with the knowledge a little bit, hands on.

[cjd]

So I couldn't find my old files, had to rebuild this. I was going to get back to you.

Overly warm in the bass and midbass doesn't sound like what I would expect - this is still "light" on baffle step intended for near-boundary placement. However, as a first-step simple solution to see if changing the padding is the trick, remove the 30 ohm parallel resistor. You can drop to 3ohm after removing the resistor but no more.

All this does is change the general tilt to an upward one (a 4dB rise out in a room, probably a 2-3dB rise near boundaries.)

Instead, I might first inquire how you have these stuffed? It may be too much.

By the way, if you want full baffle step, swap to a 2.2mH inductor (woofer) and up to a 7.5uF cap and a 5ohm series resistor (tweeter).

C

[ThomasW]

Changing the value of the the components in the L-pad effects only the output level of the tweeter.

It has no impact on phase, the crossover point or anything else.

[augerpro]

To add to Thomas's reply and answer one of your questions: When using an Lpad changing the series resistor does not change phase, it just drops the tweeter level, for the most part. If you are just using a series resistor for attenuation however, then the resistance interacts with the rest of the XO and changes response of the tweeter, and thus phase.

[bowbender7]

Thanks for the responses guys. CJD - I have played with stuffing a fair bit and determined that too much stuffing takes away some of the transparency of the midrange. I have about 2 oz of polyfill stuffed behind the tweeter, and a single layer of 1/2" polyfill sheeting running from the bottom of the cabinet to the top of the cabinet. This is in addition to the 1/2" layer of PE sticky-back foam covering all internal walls.

I will try removing the parallel resistor and see what happens.

Thanks ;x(