![Rolling Eyes :roll:](./images/smilies/icon/rolleyes.gif)
B&W P4 speakers I bought new in 1997 with my long suffering (and highly modified) Naim CD3.5 and a Nait3. Nait 3 is long gone. I auditioned half a dozen speakers in the £700 (1997) region and the B&W's won me over.
![Image](https://i.imgur.com/vwJPUHj.jpg)
These are a two way with 6.5" kevlar mid bass and 1" metal dome tweeter. They are a quarter wave tapered line (kind of transmission line). Due to the distance the 6'5" is from the end of the line (Zd is a key parameter of the design) the mid bass can't be moved so this will have to stay a point and squirt but looking on the bright side it stops me messing about too much and taking forever to complete
![Very Happy :grin:](./images/smilies/icon/biggrin.gif)
These were my main speakers for 20 years until I found this forum and started dabbling in the dark side of doping and drivers pointing in unnatural directions. They served me well and I was satisfied with them for 15 years. But as my sources and amps got better they started to annoy me a little.
I don't have a problem with TL bass like some do so it makes sense to keep that part of these speakers. TL design is not easy and they were designed with that particular mid bass in mind so the only option is to keep the 6.5 MB as well. With it only being a two way then certain compromises had to be made. The crossover is at 3.5 kHz as the 1" dome has to be crossed over that high to avoid distortion.
The MB only has a single inductor in series (1st order) so only attenuates at 6dB per octave above the xover frequency (3.5 kHz). Being kevlar doesn't help with it's nasty break up. This is the main problem with this speaker - it lets too much of the MB's nasties through.
The tweeter has an electrical 3rd order high pass filter which is required to roll it off enough before it's resonant frequency is reached. I would like to avoid anything over first order filters in this speaker.
So the tweeter has to go.
![Shocked :shock:](./images/smilies/icon/eek.gif)
Doping of the MB is not going to happen with this. It has a smaller than needed magnet and a much too relaxed suspension and spider. Plus I don't believe doping and no filter works for a point and squirt as the MB beams too much at higher frequencies.
So what am I going to do then ? Well the MB driver will have it's first order low pass filter knee brought right down from 3.5 kHz to 500 Hz which is the -3dB point in the baffle step loss. This should keep out more of the kevlar cones break up resonances higher up. It also lets me use different sensitivities for the drivers and so do some baffle step compensation for free (as it were). I hope that is low enough not to mess too much with phase in the all important mid frequencies where the ear is much more sensitive to such things. If I want to lower the xover frequency below 500 Hz then I will have to make the baffle wider and I don't really want to get into that.
But what about above 500 Hz ? The traditional thing to do would be to go to a three way design with mid and tweeter. I have considered that but there are other alternatives. A compression driver - no thanks. That leaves the option of using a single full range driver. That would make what is known as a FAST or WAW speaker.
I think I like the sound of that the most out of the three options and it gives me flexibility to add a tweeter later on if I can't get on with the FR's top end. It's not like adding tweeters though as a FR needs an enclosure and is not closed back. Plus although enclosure volume for a TL design is not that important (within reason) the FR will be taking away the MB's enclosure volume. So that led me to look at very small FR drivers, the smaller the better in fact.
I came across on my travels a small 2.5" FR which is very well thought of and doesn't break the bank. It has a very flat frequency response and won't mind a 1st order roll off at 500Hz. It also fits right in the tweeter cut out without any modification
![Dance :dance:](./images/smilies/eusa/dance.gif)
![Dance :dance:](./images/smilies/eusa/dance.gif)
I have cut a section of pipe to fit between the front baffle and back panel which will comprise the mid tweeters enclosure. This takes away a little of the TL's volume but more importantly it does not change the distance from the centre of the 6.5" mid bass to the end of the line (top panel). Pipe will need stuffing
![Talk to the hand :hand:](./images/smilies/eusa/hand.gif)
There won't be any speaker level xover with this speaker
![Naughty :naughty:](./images/smilies/eusa/naughty.gif)
![Naughty :naughty:](./images/smilies/eusa/naughty.gif)
![Naughty :naughty:](./images/smilies/eusa/naughty.gif)
![Drink :guiness;](./images/smilies/banana/food-smiley-005.gif)
![Drink :guiness;](./images/smilies/banana/food-smiley-005.gif)
![Drink :guiness;](./images/smilies/banana/food-smiley-005.gif)
More later .........