hey i'm a bit new to SQ but looking at woofer response graphs i have an
idea to add $50 tweeters to a pair of Hertz ("Hi Energy - HV165") woofers
(off the popular HSK165 splits)

Since the roll off on many woofers occurs at 1khz i have considered adding
a cap to the pair of tweeters (first order, 6db) to protect them against
low frequencies at approx 2khz. this should allow them to operate over 2khz
while the woofer will naturally roll off at around 1khz ... if this is
successful will the result be similar to that of a crossover ? obviously
not. i believe this is the method coax speakers use however. so if i use a
resonable woofer (hv165) and a reasonable tweeter (eg. pioneer) with a cap
to limit the tweeter to >2khz will i achieve the result of a good coax
speaker ?

to put it another way ..
if you buy a new set of splits with crossover, and u throw away the
crossover and just use the capacitor for the tweeters ... how will the SQ
change ?

* what's the $#$%#@ address for the HERTZ website ? can't find it anywhere, response graphs for Boston RALLY NEO 3RD tweeters and Hertz woofers would be wicked

the SQ will change considerably IMO.
the crossover is tuned to suit the speakers, and will often have appropriate slopes for the speakers.

if you run a 6db HP on teh tweeter, but nothing on the midbass, then the tweeter will be 90 degrees out of phase with the woofer.
it's not terribly hard to add a coil to the midwoofer too, how confident are you that the natural rolloff is at 1khz?
and what slope does it roll off at?
if you goto www.audison.it, click on elettromedia, it'll have a link to hertz in there.

Benny so the crossovers (12db) that I am building for Pete (Ultim8DTM5), another customer and myself for the ambient tweeters will be **** house? ahahahaha

9k up 12db down slope what you think?

oh just to add that these will be almost the size of a standard x-over and will handle over 100wrms

depends,
do they contain impedance correction circuitry, as well as attentuation circuits, and crossover points and slopes that suit the driver, and keep them in phase for proper integration?

if you can answer yes to all of that, then i expect they'll be great.
if not... then you might still get lucky

dont use a single series cap for these tweeters

there are very very very few tweeters that sound good with a 6db/oct x-over plus then you have power handling issues and x-over point problems. Look at the fs of the tweeter it really requires a very low fs to work well, from 700hz to 800hz is definitely preferred.

one of the very very few tweeters that work extremely well on a 6db/oct x-over is the dyn audio esotar. However even with this very high power tweeter (with very very low fs around 750hz) to make it work effectively and handle a lot of power the x-over point is from 4khz to 5khz...yes that high...and then the issue comes with what mid will be flat to that point..not many and you would require no more than a 5 1/4 mid but better would be a dome midrange unit to blend the stage together.

to make the tweeter go lower you require steep x-overs...not as you have tried to point out shallow 6db/oct x-overs. This will help with power handling and frequency response. For a 2khz point you would have to look at either an acitve 24db/oct on both 6.5mid and tweeter or a passive. This would give you similar power handling as a x-over point at 4khz with 12db/oct (which is an extremely popular setting for car tweeters & mids). Now here comes another problem. With such a big roll-off you require very careful aiming positioning of both mid and tweeter. It is important to position both mid and tweeter very close to one another to get a seemless front stage. 2inches basket to basket would be a limit with a 24db/oct setting.

in the end the stock 12db/oct standared x-over is a lot more forgiving compared to a 24db/oct setup. I think designing a new x-over is a lot more complex and could achieve better results after lots of listening and tuning the setup. Go for the almost plug & play 12db/oct standard x-over it will make life a lot easier.

The phase "issue" occurs only around the xover point too (although it's much worse for 6dB because the phasal anomolies extend further around the xover point)

damn that's a pretty full-on reply ! thing is i can't even tell much difference between focal splits on the GL Pro demo board .. anyway mmm .. sorta lost for words there .. ok it will sound **** but

1) will it sound heaps better than not having a tweeter at all ?
2) isn't this exactly how tweeters are setup on a set of coax speakers ?

yes in coaxial setups most cheap sets use the tweeter to extend the top end response of the speaker. they use the roll off the the mid and add a tweeter with a 6db/oct to extend the treble. These cheap ass "super tweeters" help but the result isnt all that great. I love the sound of well designed high quality spilt speakers..why would you want to down grade to that cheap coaxial setup level???

good coaxials use high grade tweeters and external x-overs with at least 12db/oct on the tweeter. Look at kef uni-qs, boston z, polk momo and lots more.

why would you want something thats well built to sound bad....just why????