To friendly hornresp guru..

Xmech is probably extremely difficult to achieve anyway. Xmech is the physical distance a speakers moving parts can move before coming into contact with back plates OR when the suspension simply cannot stretch any further(most likely-but would require some serious force to stretch that far). The magnetic assemby probably has minimal strength at this point and it's highly likely you won't EVER be able to make the driver bottom out(hit a solid stop-like a backplate-overexcursion and xmech are different things really)
I had to prove this to a mate(as well as the effects of clipping) by driving a 10watt 4" pioneer driver with 300wrms of bass cd goodness. Sure the cone was being driven as far as it will ever go,but at no time did the voicecoil hit ANYTHING and going from 50wrms to 300wrms yielded little difference. Look at a flux density chart for a driver,outside xmax,flux density drops very rapidly and suspension stiffness increases quickly also. Xmax is also factored by suspension effects too(xsus),xmag is the magnetic side of it
For example,get an 18incher with 35mm xmech and push as hard as you can on the cone(don't break it!)-I can pretty much guarantee the suspension will stop you first!(i've evn seen a demo of a guy who stood on the cone of a car sub and the suspension held him up!)
And a 8" sealed back mid may have an xmech of 5mm,this will simply be the stiff/short suspension running out of travel,these mids have very short voicecoils so i doubt it'll touch the backplate.
In the real world you'll probably just get hideous 'whoomping' more than anything and EVENTUAL driver faliure. There are of course exeptions but I'm fairly sure your average(quality) LF driver these days shouldn't be able to smash kapton into steel.(maybe with massive power on your loungeroom floor and no box!-but I'd bet that the voicecoil would actually have to tear from the cone)
It's sort of like working out the exact rpm your cars crankshaft will shatter,the engine will simply become so inefficient it'll probably never actually reach those revs,even floored in neutral due to losses and out of powerband wheezyness!
And in my not-so-professional opinion,building an enclosure which reaches xmech at rated power is fairly well off the mark!

Stiff-surounds are generally a saving grace for bass-horn speakers, however there are other issues to considder. I know that 18Sound's 18LW1400 has problems long-term with the surround. A speaker with a stiff suspension will just stay where it is and that's the end of things (except if like some manufacturers you don't glue down your spiders properly)

However if you look at what happens, the speaker gives off energy in it's mid-point. Now with a small mouth lots of the energy at the horn mouth will now be reflected back into the horn and will come back to "load" the speaker (however with some time having passed inbetween). However at a touch above fc this loading will catch the speaker in phase and "help" the speaker further mechanically (look at the driver excursion in hornresp and picture the wave. The more complete the transformation from pressure (throat) to velocity (mouth) the less refraction at the mouth (seen in less ripple in frequency response and cone excursion)


Edited by Timber_MG

Methinks JD01 mentioned it failing somehow (tearing iirc). PM him.

Is this the double?

I can take and post some screenshots when i get home! (Still at work and surfing in web again.. )

edit: Here they are..I had forgotten that i had simulated these with assumed TA-2400 power/bin (figuring that it would give me about 800Wrms to 4 ohms/channel) but i think i should be able to play these down to 50Hz with 2 cabs together and then down to 45Hz with all 4 together even though i had that 600W as it is now on these pics..










Edited by hiphei

I use always 2 or 4 cabs together. At the moment they've been played with about 400W/cab 4 cabs total and this is the first time i've paid attention to excursion.. I think that the lowcut has currently been set to 35Hz by not so lucky guess. We've played few gigs with them so i think maybe i'm lucky that the drivers are still OK..! (During the last show beer pints were walking on tables and clip leds flashed briefly on TA every now and then.. ) I think i will modify the back chamber before the next gig and rise the HPF..

Do You think that polyurethane would be suitable material to fill them up?

Edit: Uh.. almost forgot.. There were not enough segments so i did put the final parts as 1 exponential segment.. Hmm.. Is there a way to add them (more segments) in Hornresp..?


Edited by hiphei

Hi mobiele eenheid: I meant the double 18" horn that was being mentioned on J&H a while back.