help with compression driver/sensitivity matching issue

[bikehorn]

I am in the midst of building a pair of Karlson K15s. I am using a 15" woofer with a 96 dB sensitivity which places it in a somewhat awkward place when it comes to tweeters since domes all seem to have lower sensitivity and compression drivers are all 100+ dB. I have two options and i need to decide quickly:

one option would be to use the Dayton PT2 planar tweeter. i like planars but this one has a sensitivity of 94 dB. that's still 2 dB below the woofer. i don't want to pad the woofer. i did want to put a zobel on it though, and as a side effect they apparently lower efficiency a bit...i actually want this. if i can knock off a dB or two "accidentally" with the zobel while smoothing impedance then i think i will go this way.

on the other hand i could use a compression driver and a horn lens or karlson tube, however, it seems like matching the sensitivities will be a nightmare since the compression driver i wanted, the Selenium DH200 is rated at 105 dB. how can i go about this? what kind of issues am i going to face with this kind of padding?

[infinia]

Hi
Please post your crossover target and the circuit proposed. Maybe you can add baffle step compensation for the woofer? This would bring down the woofer eff at the crossover point. Or think Biamp for the most tweekablity.

[bikehorn]

with the planar tweeter(which would be hung directly in front of the woofer for a coaxial effect), i would be crossing it over at 2500 at 18 db/oct. this means the woofer has to work all the way up to 2500 at which point i plan to put a second order LP on it. however, i will at least try it without any network on the woofer to see if it naturally rolls off well enough or if i can get away with a first order. the high crossover frequency for the woofer is in my mind the weakness of this approach, however, i have a few restrictions(budget, trying to approximate a point source, not wanting a 3-way). in this case the woofer would be the more sensitive of the two, whereas with the compression driver, the woofer would be less sensitive than the HF unit.

I don't have the drivers yet, i have only just begun the cabinet construction.

on the other hand, with the compression driver mounted in a karlson tube, i could cross it over lower, second order at 2000 although i might move it up to third order if the overlap is excessive. i would prefer to do this, since although i wouldn't get a "coax" effect it allows a lower crossover frequency and i can remove the compression driver from the tube later on as i plan to build and try out a pair of Smith horns with my Karlsons at some point, with which i could reuse the existing driver and crossover. plus, higher sensitivity! i wouldn't mind that.

essentially i am looking for a way to bring the compression driver in line with the woofer but i'm just worried that padding it by 8 or 9 dB is going to cause issues. is it?

Biamping is very appealing but beyond the scope of my equipment and budget right now...these are going to be my everyday listening speakers during the week and keg party speakers by weekend. because of the high efficiency i will only be driving them with 35 watts per side of my Technics SA-300 receiver. i have plans to build a Krell KSA50 clone and a minimalist preamp but at present, i have to design my speakers around what i've got.

[bear]

As the previous poster noted, biamping is likely the best solution for you.

Regardless, if you use a compression driver you can benefit from a nicely matched relatively low power tube amp to run the top end, which ought to be of subjective benefit if you go with an ordinary compression driver.

A 5-10 watt or so Parafeed style amplifier would be just peachy!

Padding the compression driver is not much of a problem. They don't rely upon amplifier DF like large cones do.

But you do want a *real* horn of some sort if you use a compression driver. The diaphragm likes to be loaded appropriately.

The KSA50 clone and the Karlsen design are at opposite ends of the audio spectrum - I wouldn't want to run them together.

IF this is the Karlsen design that has a slot that looks like the profile of an exponential horn, be advised that you need to be able to get direct radiation from the woofer (don't shadow it or fill the slot), and that it performs like a "bad horn" when measured. A "bad horn" is one that has too small of a mouth to support the frequency of interest - the result is that you get a comb filter effect. That being large dips and peaks across the response, as opposed to a relatively flat response.

Of course, real LF horns are large, larger than the Karlsen enclosure.

There are other way to go for high sensitivity though.

The Karlsen might be an interesting project, but before you go and put a lot of time and energy into making a super clean highly finished set of speakers, you might want to do a quick and dirty proto, and/or read some more on them.

But, imho, if you want to go for a high sensitivity speaker system, you should be looking at smaller amps be they tube or solid state class A in the main - and build them urself!

There is a school of thought that says, high sensitivity from low midbass up and high power/high DF amps on the bottom...

As always, Ymmv.

_-_-bear

[noah katz]

You could try the Eighteensound XT1086 horn/waveguide with the compression driver.

Not only is it apparently free of horn colorations (search on the High Efficiency Asylum on "XT1086"), but the mouth of the waveguide might get clear of the Karlson box, eliminating all kinds of diffraction problems.

Not sure how it would effect the Karlson operation though.

[bikehorn]

like i said earlier, biamping is completely beyond my budget right now. maybe someday but it's just not an option at present. forget the amps themselves, just a decent set of tubes for a parafeed style amp(or a pair of monoblocks, because that's probably what they would be) would cost more than my entire collection of audio gear and my stack of LPs too. i'm 19 and i just finished my first year of university...i don't and won't have reference quality equipment and in the house i'm sharing with my friends, i won't have a particularly special listening room either. not to mention that aside from one of my friends, i'm the only audiophile i know.

the Karlson i'm talking about is definitely the one with the flared front...the one everyone loves to hate for some reason or another. i know it has its weaknesses like any other enclosure desgn...i will deal with resonances when i find them. regardless, i've started construction already and i've been reading about them for upwards of a year. i know i won't be able to get 30 hz out of them, but that's okay. what i wanted was tight, punchy bass response with lots of slam...i don't mind if it doesn't go ultra low. i also did not want a typical boring sealed or ported floorstander and this being my first DIY, i didn't want to try a horn or long folded t-line just yet. high efficiency is also not a primary priority, however i'd like to stay above 93 dB. more is better but it's not a deal breaker.

so, there is nothing really to be worried about when attaching a 9 db pad to the compression driver?

thanks for all the help so far. i am looking into various horn lenses and waveguides.

[noah katz]

"so, there is nothing really to be worried about when attaching a 9 db pad to the compression driver? "

Nope; check the XO schematics in the two 2-way kits here

http://www.eighteensound.com/index.aspx?mainMenu=kits

[bikehorn]

great! thanks. i'll post the completed speakers in a week or so.

[jerishi]

I'd encourage you to finish the Karlson enclosures... using best high sensitivity drivers available. I grew up with a pair in my (fathers) house... and have yet to find anything quite like it. F.W.I.W.- I'm 54 yrs. now... I remember the amp was a low power tube amp. I've often wondered( over the years) ... why they 'measured' so horribly...(when I had time to read such things)... and sounded SO good to me as a kid. I've... over time tried to duplicate same... BUT... in smaller environs... (and enclosures). Best of luck to you... and I'll follow this forum w/interest.

[Josephjcole]

What about a fifteen inch coaxial driver? It seems like that might be what you are aiming for anyways.... just a thought.
Joe