BillFitzmaurice.info

Wait...

I found a function in Hornresp I didn't know existed. If I Sample from the "Accoustical Power" window, it indicates "Horn throat peak sound pressure"

Sampling from 40Hz to 125Hz at 41.8 volts indicates the highest peak pressure of 2014Pa occurs at 40Hz and also again at 100Hz. Yet, at 60Hz (point of maximum excursion in the band pass) throat pressure is only 184Pa. So, now I'm a little confused. I had a sneaky suspicion it would be more complicated than just diaphragm excursion.

The absolute maximum pressure occurs at 24Hz and if we adjust the voltage to 26.2 volts at 24Hz the throat pressure is 2014Pa and SPL is 108dB. BUT, diaphragm displacement is 11mm, 62% over the drivers Xmax. And there's no Xlim spec on the datasheet. It is not advisable to try this. Might be okay. Might not. Impedance is 19.2Ω at that frequency, so it's only 35 watts. And the air circulation around the voice coil with that much excursion would certainly be sufficient. So, I'm not particularly worried about the voice coil melting. More concerned that the voice coil former could possibly bottom out on the backing plate and cause damage that way.

Anyway, that's all I got at the moment. Hope it helps.

Oh!.. and 2014Pa is equivalent to about 0.29psi. Doesn't seem like much until you consider the diaphragm area. There's about 37 ponds of pressure (positive and negative, 74lb of pressure swing) acting on the horn side of the cone on every single oscillation at those frequencies and corresponding voltages. Interesting factoid.

Where physical air movement is concerned that's seen on the Particle Velocity chart, which mirrors the excursion chart. In any event I wouldn't be concerned about throat pressure. When it's too high it results in harmonic distortion, not driver destruction. That comes with over excursion that reaches xlim.

Hmm. Not sure where I got the notion that the cones of some HiFi, Car Audio, and budget drivers not being able to withstand the pressures of horn loading. I thought for sure I read it in the plans. But, that's not what it says. Oh well. Good to know. Thanks for straightening me out on that.

@joblow88... Just put the 40Hz high pass on it, limit at 40v, and let'r rip. It'll probably do just fine for years and years.

joblow88 wrote: ↑Fri Sep 23, 2022 3:42 pm So i took one for the team and i bought a GRS 15PT-8 https://www.parts-express.com/GRS-15PT- ... hm-292-808 and i plan to test it in my soon to be finished t48. I was wondering if there was a way to stress test the cone strenght once in the cab without angrying the whole neighborhood. I was thinking maybe a lower frequency at the right voltage would create the same throat pressure... I'm also planing to run at rms power out of the cab for an extended period of time to look at the thermals.

Hey, no one has quite said it yet as such, it's there, but throughout multiple posts, kinda.

You should already have the T48 plans, and in those plans is "protecting your drivers". Read that.
You can play the T48's lower under 1 condition; if you have 4 or more cabs.
It's not just Xmax, point of maximum excursion, or throat pressure per se, it's about the combined mouth area and mutual coupling that allow the lower HP.
Sure it's your money, and DIY, and you can do what you want, but if you really want to take one for the team, find out how well this driver compares to a recommended driver in regular useage, to the point of voltage limit.

You have another option, if you want lower. Build the right cab. The T60...

joblow88 wrote: ↑Fri Sep 23, 2022 3:42 pm ...I'm also planing to run at rms power out of the cab for an extended period of time to look at the thermals.

It's also worth mentioning, this is a really bad idea and could potentially damage the driver from over excursion, bottoming out the voice coil on the backing plate or the coil exiting the gap outward and not making it back in the gap on it's return.

I really appreciate you wanting to beat the piss outta this driver for us. However, I'm convinced it's best to just put it in the enclosure and test it under typical use conditions.

Seth wrote: ↑Sun Oct 02, 2022 4:47 pm Hmm. Not sure where I got the notion that the cones of some HiFi, Car Audio, and budget drivers not being able to withstand the pressures of horn loading. I thought for sure I read it in the plans. But, that's not what it says. Oh well. Good to know. Thanks for straightening me out on that.

@joblow88... Just put the 40Hz high pass on it, limit at 40v, and let'r rip. It'll probably do just fine for years and years.

I read something about the pressure in the FAQ on 18'' drivers. That where i started to get worried.

I think the question is settled. 40v limiter and 40Hz HP it is.

Thanks every one

I'll make sure to do some follow up.

I just went back and read through some of the conversations we had earlier this year. Don't you also have a 3015LF you can put in the T48? Running both drivers in Hornresp indicates a maximum SPL at 40HZ with the GRS 15PT-8 will be approximately 112dB. Max SPL at 40Hz with the 3015LF would come in at about 117dB. About 5dB more with the 3015LF. Making one 3015LF loaded cab almost equivalent to two 15PT-8 loaded cabs. Although, two 15PT-8 loaded cabs could then be v-plated for another 3dB... which would trump a single 3015LF loaded cab by a good margin.

Food for thought.

Have fun. And, yes, please do keep us posted on how it goes.

Seth wrote: ↑Mon Oct 03, 2022 11:25 am I just went back and read through some of the conversations we had earlier this year. Don't you also have a 3015LF you can put in the T48? Running both drivers in Hornresp indicates a maximum SPL at 40HZ with the GRS 15PT-8 will be approximately 112dB. Max SPL at 40Hz with the 3015LF would come in at about 117dB. About 5dB more with the 3015LF. Making one 3015LF loaded cab almost equivalent to two 15PT-8 loaded cabs. Although, two 15PT-8 loaded cabs could then be v-plated for another 3dB... which would trump a single 3015LF loaded cab by a good margin.

Food for thought.

Have fun. And, yes, please do keep us posted on how it goes.

Yes i plan to put my 3015 in it after i just wanted to test the grs cheep driver fist. Now im making a small setup that i can trow in the back of my civic with 2 OTop12 JArray.

I have to say that even with a cheep ass driver and shitty placement (I dont have the wires yet), it sounds amazing! Cant wait to put it in a corner with the 3015. Thanks bill for the great plans

It’s a thread revival but….did the grs driver survive?

Fastskiguy wrote: ↑Sun Jan 29, 2023 10:55 pm It’s a thread revival but….did the grs driver survive?

Sure did with the limiter on. But i swapted it for my 3015 and it definitly give more punch. So i cant say on the long run... Ill make 7 more t48 in the fall and i plan to put GRS in 6 of them. We will see from there.

Sorry for the late respose i've been in the studies over my head... But i just got a grant of 5000 cad to upgrade my system So you should hear from me more in the upcoming month