TRT displacement max

[Drey Chennells]

In a single TRT, what would the minimum width requirement be for a 10” with a 50mm stroke?
And would I have to double for 2 drivers?

(1) 10” Vd 790cc (thanks for checking the math Seth)
(2) 10” Vd 1580cc
https://www.parts-express.com/Dayton-Au ... hm-295-290


Same question for (2) of these 10 in a single TRT:

(2) 10” Vd 413.77cc
https://www.parts-express.com/Dayton-Au ... il-295-164

It’s been awhile but I think I recall Bill discuss potential overdriving of the throat? I don’t want to misspeak..It makes sense to me that the minimum width recommended is generally Vd related so in the case of very high levels of displacement such as with these drivers the minimum width may need to shift up a bit?

This will be laying down in the Range Rover’s cargo..

Thanks for your feedback

[Bill Fitzmaurice]

I wouldn't use anything with more than 15mm xmax, at the risk of throat distortion. Keep in mind that direct radiator subs use very long xmax because being of low sensitivity they have to. Horns don't. The cab widths have nothing to do with Vd. It's the range between where the horn is too narrow to load the low frequencies, because the mouth is too small, and too wide to load the high frequencies, because the throat is too large. If you want to use two drivers you have to double the cab width.

[Seth]

...
(1) 10” Vd 6225cu.in.?
(2) 10” Vd 12450cu.in.?
https://www.parts-express.com/Dayton-Au ... hm-295-290

Vd is xMax times Sd (cone area) and is typically stated in cubic centimeters. (cc, cm³)

That driver has xMax of 25mm and Sd of 316 cm². To properly calculate Vd, you have to first convert xMax from millimeters to centimeters. Easy enough... 25mm = 2.5cm

2.5 cm times 316 cm² = Vd of 790 cc/cm³/cubic centimeters

[Drey Chennells]

Thanks for the explanation on that Bill. I wanted to go biggest baddest but youre saying stay under 15mm so I ordered the RSS265HO with 12.3 Xmax going in a 10” wide cab.

https://www.parts-express.com/Dayton-Au ... hm-295-462

[ACUA]

So far as I know, these horn loud speaker designs are not designed with SPL competition in mind, which completely disregard distortion in all aspects. The idea with the BFM equipment is low cost, efficient and acoustical accuracy. The more that you excite an electromechanical transducer loud speaker aka the more excursion induced in the speaker the higher the distortion. this distortion is related to the time required for the cone to preform the dramatic long distance movement out and back in and then back to neutral again. More distortion occurs as excursion increases as a result of the time increase. there is also the resonance as the spring function of the driver works to dissipate the residual energy, the more energy to dissipate the longer the ringing will be. So in the spirit of achieving and keeping high fidelity, we should strive to keep excursion low as a concept or rule of thumb.

I understand that we also want the best bang for our buck and fewer drivers with more excursion saves space and sometimes money but it does or can come at the cost of fidelity.

[Bruce Weldy]

So far as I know, these horn loud speaker designs are not designed with SPL competition in mind, which completely disregard distortion in all aspects. The idea with the BFM equipment is low cost, efficient and acoustical accuracy. The more that you excite an electromechanical transducer loud speaker aka the more excursion induced in the speaker the higher the distortion. this distortion is related to the time required for the cone to preform the dramatic long distance movement out and back in and then back to neutral again. More distortion occurs as excursion increases as a result of the time increase. there is also the resonance as the spring function of the driver works to dissipate the residual energy, the more energy to dissipate the longer the ringing will be. So in the spirit of achieving and keeping high fidelity, we should strive to keep excursion low as a concept or rule of thumb.

I understand that we also want the best bang for our buck and fewer drivers with more excursion saves space and sometimes money but it does or can come at the cost of fidelity.

You probably don't realize, but Drey has been around here a long, long time and is an authorized builder. He just hasn't been on the forum in a while.

[ACUA]

I do apologize, I have been working out that narrative that I posted for a while and was zealous to comment the moment I saw opportunity. Do you perceive that I have the concept correct despite it being an un-merited posting. I liked the content being generated here:

I wouldn't use anything with more than 15mm xmax, at the risk of throat distortion. Keep in mind that direct radiator subs use very long xmax because being of low sensitivity they have to. Horns don't. The cab widths have nothing to do with Vd. It's the range between where the horn is too narrow to load the low frequencies, because the mouth is too small, and too wide to load the high frequencies, because the throat is too large. If you want to use two drivers you have to double the cab width.

This is good stuff.

[Seth]

Since the question is answered, driver ordered, and Drey (OP) hasn't logged in since his last post... I suppose it's fair to stray and expand the bounds of the conversation at this point without it being a blatant threadjack.

I'll bite.

So far as I know, these horn loud speaker designs are not designed with SPL competition in mind, which completely disregard distortion in all aspects. The idea with the BFM equipment is low cost, efficient and acoustical accuracy. The more that you excite an electromechanical transducer loud speaker aka the more excursion induced in the speaker the higher the distortion. this distortion is related to the time required for the cone to preform the dramatic long distance movement out and back in and then back to neutral again. More distortion occurs as excursion increases as a result of the time increase. there is also the resonance as the spring function of the driver works to dissipate the residual energy, the more energy to dissipate the longer the ringing will be. So in the spirit of achieving and keeping high fidelity, we should strive to keep excursion low as a concept or rule of thumb.

I understand that we also want the best bang for our buck and fewer drivers with more excursion saves space and sometimes money but it does or can come at the cost of fidelity.

I'm not sure whether distortion increasing as excursion increases (yet remaining within it's design parameters) is an assumption/theory or absolute fact. Makes sense to me, but I've never come across that statement before. If it is a fact, I'd be curious how much of it is only visible on test equipment and how much is easily recognized by the average non-audiophile listener.

Personally, I want clean sound. But, I also understand the desire to maximize a build's potential. Within reasonable limitations, who doesn't want the most they can achieve? Which is what I assume Drey is after.

That said, if I were into SPL drags, I'd find the resonant frequency of the vehicle, design an enclosure tuned to that frequency, matched to a driver with a very high thermal power rating, xMax, and xLim. The pic below illustrates excursion throughout the frequency range. The low point is the tuning frequency. That's the point that can take the most voltage before experiencing over-excursion. I'd think the guys that are into it just match all that up so it all occurs at the same frequency. But, I don't follow any of the tech surrounding SPL drags, so it's merely an educated guess.




Back to the TruckTuba... I have to admit, when I read the specs for that driver, my mind immediately went to daydreaming about a 4x10 TruckTuba and what it might do with those drivers. I have a guy that wants me to build a tuned port box for his two 15's for his Tahoe. Pretty sure a 4 x 10 TruckTuba may be able to outrun a pair of ported 15's... in SPL, SQ, and extension. Problem is talking the average guy out of "big" speakers. Hmmmm.

[ACUA]

Another thing of consideration is that the BL of a speaker decreases logarithmically relative to excursion or throw. I realize that different driver designs have different BL ratings and characteristics but for the most part or typically, the more excursion the lower the effective BL. Meaning less motor control of the coil which increases the distortion. So even though a high excursion driver is cool it is usually not ideal for high fidelity, this is one of the reasons that I am drawn to these horn loaded designs.

[Seth]

Another thing of consideration is that the BL of a speaker decreases logarithmically relative to excursion or throw. I realize that different driver designs have different BL ratings and characteristics but for the most part or typically, the more excursion the lower the effective BL. Meaning less motor control of the coil which increases the distortion. So even though a high excursion driver is cool it is usually not ideal for high fidelity, this is one of the reasons that I am drawn to these horn loaded designs.

I'm not a Thiele/Small parameter wizard, so I could be way off base. But, my current understanding is that's an issue that arises when the speaker is pushed beyond it's Xmax. Where less and less of the voice coil is in the magnetic flux within the voice coil gap. So, given two speakers with the same magnetic gap height, one speaker designed with 6mm Xmax and the other designed with a 12mm Xmax, the 12mm Xmax driver shouldn't have any reduced BL at it's Xmax even though it's twice the excursion as the 6mm Xmax driver at their peaks. From what I think I know about this stuff, when the excursion is within the Xmax parameter, cone movement is fairly linear and the cone movement increases linearly with voltage. And beyond Xmax is where cone movement becomes non-linear and increases in voltage produce less and less excursion per volt increase.

No? I really could be completely off base.

[Bill Fitzmaurice]

The issue with xmax is clipping. It takes more excursion to produce the lower frequencies than it does the higher frequencies. When you supply enough voltage the cone stops moving in a linear fashion in the lows but continues moving in the highs, giving pretty much the same result as when an amp or anything else in the signal chain is pushed to clipping. Sometimes this is desirable. Guitar drivers have short xmax, so they'll clip at very low power levels. Subs have long xmax, so they can take high power without clipping. However, there's a limit to how much xmax you can use before other problems arise. In the case of a direct radiator the main problem is Doppler and modulation distortion, in a horn the main problem is throat distortion. The advantage to a horn with respect to distortion is that with the same size driver it can produce the same output as a direct radiator with a quarter the excursion, and a quarter the voltage swing, reducing the potential for distortion throughout the system.

[Seth]

...Doppler and modulation distortion...

New-to-me terms. Did a little reading on them. Very interesting.

Here's a little blurb supporting your statements:
AES E-LIBRARY Modulation Distortion in Loudspeakers

[Seth]

...The more that you excite an electromechanical transducer loud speaker aka the more excursion induced in the speaker the higher the distortion...

As I mentioned before, I hadn't heard that before. But, I just came across the same statement in another forum and the posting member occurs to be fairly knowledgeable.

Distortion starts as soon as the driver starts moving. Distortion increases as excursion increases and if you plot it on a curve it will look like a bell curve. The harder you push it the higher the distortion will climb and the worse it will sound. This much should be obvious. The driver runs into the end of it's magnetic force, the suspension tightens, the inductance becomes increasingly non linear. All these add up and distortion rises as excursion rises.

The same member had some interesting information about Xmax as well, in post 4, about how all the manufactures measure/calculate Xmax differently. Good read.


BTW, I sent you a PM last week.