Hi everyone.
First, sorry for my probably poor english.
I'm currently designing a portable backpack speaker that has to be powerful enough for small outdoor parties. I already have the drivers and the mids and highs are already pre-calculated, i'll just have to adapt them to the design i choose.
I want to be able to have a strong output to the low 40 hz (F1 note above -3db is the way i design all my speakers, it sounds well for the type of electronic music i like to listen to) in the best db/size ratio.
I've already made some small portable BR boxes and a 12"TH (modified THAM design) trolley battery (<- low cost aliexpress) powered transportable speaker. I just wanted to simply design on software to get the solution for my new project, but there's something that i still don't know/understand.
When i tested the TH indoor, the output was obviously impressive compared to other designs i've listened to, but when testing outdoor, the difference seemed WAY bigger. The TH even sounded louder than indoor (?). And further from the speakers i went, bigger the difference between the BR and the TH was. It weirdly seemed to contradict the simple "-6db/2*distance" theory. I don't have the stuff to measure it (despite i'm designing speakers) so i don't have any number to show you (and it may even be just my ears making mistakes).
I've been looking for the explaination on various forums and few different explainations came.
1- "The size of the horn's mouth makes it different than a "point", so the 6db/2*distance rule doesn't apply until we get far enough"
- I doubt it applies for only a THAM12 sized mouth
2- "the horn makes the bass go "on the front of the speaker" without spreading everywhere so the sound power isn't wasted"
- I wonder why the difference isn't as big when i'm closer to the speaker then
3- "the sound 1m far from the speaker is 1m far from the sound source for the direct radiator and 1m+ the length of the horn for the sound source of the TH (sound source = driver for the TH). So if you measure 100db at 1m for both, you would measure 88db at 4m for the direct radiator and 94db for the TH if its horn is 2m long (100db was at 3m for its sound source, if you add 3m it doubles the distance so -6db)"
- This one is interesting and would make me build a second, smaller horn for my next project.
4- (do you know any other ?)
I also read about a 18"TH not making sound before a certain distance (15-20fts), which is what we would call "throw" (?), which means the sound just doesn't react the same way to the distance. I'd like to understand this one if it's true.
So in conclusion, do you know if there is a difference in the way the sound reacts to the distance depending on the design ? (i don't know if this question seems so english, sorry).
And more precisely, do you know what would sound the loudest oudtoor (between 3 and 8m far), a 93db/w/m BP6 or a 90db/w/m small TH ?
I already thank you if you took the time to read it.
First, sorry for my probably poor english.
I'm currently designing a portable backpack speaker that has to be powerful enough for small outdoor parties. I already have the drivers and the mids and highs are already pre-calculated, i'll just have to adapt them to the design i choose.
I want to be able to have a strong output to the low 40 hz (F1 note above -3db is the way i design all my speakers, it sounds well for the type of electronic music i like to listen to) in the best db/size ratio.
I've already made some small portable BR boxes and a 12"TH (modified THAM design) trolley battery (<- low cost aliexpress) powered transportable speaker. I just wanted to simply design on software to get the solution for my new project, but there's something that i still don't know/understand.
When i tested the TH indoor, the output was obviously impressive compared to other designs i've listened to, but when testing outdoor, the difference seemed WAY bigger. The TH even sounded louder than indoor (?). And further from the speakers i went, bigger the difference between the BR and the TH was. It weirdly seemed to contradict the simple "-6db/2*distance" theory. I don't have the stuff to measure it (despite i'm designing speakers) so i don't have any number to show you (and it may even be just my ears making mistakes).
I've been looking for the explaination on various forums and few different explainations came.
1- "The size of the horn's mouth makes it different than a "point", so the 6db/2*distance rule doesn't apply until we get far enough"
- I doubt it applies for only a THAM12 sized mouth
2- "the horn makes the bass go "on the front of the speaker" without spreading everywhere so the sound power isn't wasted"
- I wonder why the difference isn't as big when i'm closer to the speaker then
3- "the sound 1m far from the speaker is 1m far from the sound source for the direct radiator and 1m+ the length of the horn for the sound source of the TH (sound source = driver for the TH). So if you measure 100db at 1m for both, you would measure 88db at 4m for the direct radiator and 94db for the TH if its horn is 2m long (100db was at 3m for its sound source, if you add 3m it doubles the distance so -6db)"
- This one is interesting and would make me build a second, smaller horn for my next project.
4- (do you know any other ?)
I also read about a 18"TH not making sound before a certain distance (15-20fts), which is what we would call "throw" (?), which means the sound just doesn't react the same way to the distance. I'd like to understand this one if it's true.
So in conclusion, do you know if there is a difference in the way the sound reacts to the distance depending on the design ? (i don't know if this question seems so english, sorry).
And more precisely, do you know what would sound the loudest oudtoor (between 3 and 8m far), a 93db/w/m BP6 or a 90db/w/m small TH ?
I already thank you if you took the time to read it.
There are various bass speaker cabinet designs -Which vary in size and bandwidth. The loudest - given a comparable driver & power level, will be the largest and /or have less bass extension, while the less efficient designs will be smaller and / or have more bass extension.
Individual bass cabinets have almost no directional properties, as the wavelengths are bigger than the cabinets. To introduce directionality the bass cabinets need to be used in multiple arrays where positioning and phase can be used to direct the bass - or more typically to make a total mess of the bass distribution.
'Throw' relates to loudness at distance, so either is due to greater output from the cabinet, or by directional gains from the bass array.
Individual bass cabinets have almost no directional properties, as the wavelengths are bigger than the cabinets. To introduce directionality the bass cabinets need to be used in multiple arrays where positioning and phase can be used to direct the bass - or more typically to make a total mess of the bass distribution.
'Throw' relates to loudness at distance, so either is due to greater output from the cabinet, or by directional gains from the bass array.
I've heard about that type of experience (horns being more "long throw"), but I'm not sure there's much technical data to back the experience up. I think some of it might be subjective and some of it objective, and on the latter, I've got a suspicion that it might have to do with two things - group delay across the subwoofer's passband and changes in radiating area with frequency. With tapped horns, the GD across the passband can be fairly low (compared to a vented box with the same passband) and the radiating area remains constant - the area of the TH's mouth. With a vented box, the GD is different and the effective radiating area changes as frequency drops and the vent takes over from the driver, and with most vented boxes the radiating area of the vent is a LOT smaller than the radiating area of the driver. It's in fact one of the things I'm investigating with my latest POC build, an offset-driver TL, where the vent area is almost the same as the driver's Sd (510 cm^2 vs 530 cm^2). If it has the same "effortless" sound that I experience with my TH build, then I might be on to something...
In your case though, I think it might be difficult to come up with something that's back-pack size and can do 40 Hz at an appreciable level. Might want to look into some sort of passive-radiator alignment to try to achieve that.
In your case though, I think it might be difficult to come up with something that's back-pack size and can do 40 Hz at an appreciable level. Might want to look into some sort of passive-radiator alignment to try to achieve that.
Thanks you for your replies.
Well, my case is still a kind of mystery. I'll see If my horn is buildable with light materials (inside), or i'll build the bandpass.
The speakers are already designed, give both around a little less than 114 db at their maximum, 43,6hz a very little higher than 111db (Horn a little less sensitive, but i can put 350w while in the bp only 250 before reaching xmax). I don't have the hornresp record right now, but If i Remember correctly, the horn is around 28liters, BP around 25. I have to add the mid-high speakers (If i Remember correctly, less than 8l combined), the battery, the Amps, dsp etc...
The problem is not the backpack volume, but it's weight. With the BP, there would be less internal structure and i can put easily the subwoofer magnet closer to the back so it's easier to carry.
But if the advantages of a horn are important enough, i'll try to make something backpackly carriable with it.
(If you want to know, thesubwoofer driver is a Ciare HSG-44 wired with 2 amp channels (one Coil right channel, the other coil left channel), so if my knowledge is not too bad, Re should be 3ohms in that case... correct ?)
Well, my case is still a kind of mystery. I'll see If my horn is buildable with light materials (inside), or i'll build the bandpass.
The speakers are already designed, give both around a little less than 114 db at their maximum, 43,6hz a very little higher than 111db (Horn a little less sensitive, but i can put 350w while in the bp only 250 before reaching xmax). I don't have the hornresp record right now, but If i Remember correctly, the horn is around 28liters, BP around 25. I have to add the mid-high speakers (If i Remember correctly, less than 8l combined), the battery, the Amps, dsp etc...
The problem is not the backpack volume, but it's weight. With the BP, there would be less internal structure and i can put easily the subwoofer magnet closer to the back so it's easier to carry.
But if the advantages of a horn are important enough, i'll try to make something backpackly carriable with it.
(If you want to know, thesubwoofer driver is a Ciare HSG-44 wired with 2 amp channels (one Coil right channel, the other coil left channel), so if my knowledge is not too bad, Re should be 3ohms in that case... correct ?)
It will be 3 ohms per amp channel. How many amp channels are you planning to use?
I was comparing that Ciare driver to the Dayton Audio DCS205. The DCS205 is an 8" driver that has almost 9mm Xmax, but it's a single-coil 4 ohm driver with a much smaller voice coil. It does cost a little less however. I used it in my "Boom Unit" design, which has a net volume of 26 L. I can't see my "Boom Unit" fitting into a backpack, unless it was a pretty big backpack, LOL.
I was comparing that Ciare driver to the Dayton Audio DCS205. The DCS205 is an 8" driver that has almost 9mm Xmax, but it's a single-coil 4 ohm driver with a much smaller voice coil. It does cost a little less however. I used it in my "Boom Unit" design, which has a net volume of 26 L. I can't see my "Boom Unit" fitting into a backpack, unless it was a pretty big backpack, LOL.
Having tested I do know the inverse distance law applies to all types of sub designs, but it caused a big stink when last "discussed", ending up with Wayne and I receiving infractions and sitting in the "sin bin" :^)
Wayne disagreed with most of us that did inverse distance testing, but did not do the tests himself.
https://www.diyaudio.com/community/threads/waynes-12pi-sub.187387/page-18#post-2650776
Tom Danley weighed in on post #313.
Post #350 references Rog Mogale of Void Acoustics, who did the same basic inverse distance law test as Phil Lewendowski and I did, using a small 4th order bandpass sub that contained a single 12" woofer compared to an 18” horn loaded design, and found it only 1 dB louder from 8 meters and beyond.
Post #356 references Josh Ricci, who agreed with me and Pat Brown, whom I agree with.
Post #356 Moderator (wintermute) wrote "Art and Wayne I think it is clear that there is no resolution here. It is time to agree to disagree."
Anyway, for the size of cabinet the OP is considering, the inverse distance law will apply for any type of sub design.
Art
Wayne disagreed with most of us that did inverse distance testing, but did not do the tests himself.
https://www.diyaudio.com/community/threads/waynes-12pi-sub.187387/page-18#post-2650776
Tom Danley weighed in on post #313.
Post #350 references Rog Mogale of Void Acoustics, who did the same basic inverse distance law test as Phil Lewendowski and I did, using a small 4th order bandpass sub that contained a single 12" woofer compared to an 18” horn loaded design, and found it only 1 dB louder from 8 meters and beyond.
Post #356 references Josh Ricci, who agreed with me and Pat Brown, whom I agree with.
Post #356 Moderator (wintermute) wrote "Art and Wayne I think it is clear that there is no resolution here. It is time to agree to disagree."
Anyway, for the size of cabinet the OP is considering, the inverse distance law will apply for any type of sub design.
Art
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2 amps channels for this driver. But 6 or 3 ohms change the result a lot on hornresp, and i don't have enough amp knowledge to know If this setup will give something else and If the amp (tpa3255) adds some ohms at the output (can't find the information, but i read some amps do). So before designing the final enclosure, i have to take it in count.
(I was lucky for my horn to sound that good without knowing all this)
The speaker itself would be the backpack. I just have to build a good detachable trail backpack-like strap system. I just want it to be light enough with the heavy elements Well placed close to the back.
This is what i also understood before testing my Systems. But my non measured observations are weird and i haven't found any other measurment than the ones you gave about this topic.
Btw, there is also something weird.
Big thanks to you all for your help
Oops, i forgot to finish my post (and i don't know how to edit). What seemed weird is that the th shakes everything quickly in the room (even when set not much louder than the BR), but i imagine the different directivity makes the sound react differently in the room (could the BR sound be amplified by the small room resonance ?).
What's the frequency? Mine shook once during a movie scene at ~14 Hz and the ceiling along with its miscellaneous storage came raining down on us due to one of the concrete block constructed floor pillars cracked up ('floating' floor construction not a good plan for action movie HTs).
Sorry, "shaking" was too strong, i should have used "vibrating strong enough to make screws in a box make some noise".
That said, when putting what i think was close to full power (it was before i put the dsp so i was a little shy with the power) it made a plastic bag filled with Small tools fall from their disorganized storage (was close to fall anyway) when putting a work in progress sound with a lot of sub-50hz Bass (almost nothing below 40hz, and the th wouldn't give it If there was some anyway, tuned to give ~-2db at ~44hz).
As such this part of your sentence makes total sense. The efficiency of the TH exceeds a BR by a large margin. The efficiency gains from a TH are very significant. 😉
As far as the efficiency difference goes, my answer would be... it depends. Noticeable, yes, but I'm not sure I'd say it's MUCH more if designing for the same Fb with the same driver.
Here's the results of some recent measurements I took, same driver driven by the same voltage, used in my POC3 TH and my new POC7 ODTL design. Fb for both designs is pretty close (within 1 Hz). The TH is 1~2dB more efficient over part of the passband. However, the POC7 has a much wider useful passband (the TH is pretty much unusable above 100 Hz), and the ODTL box is smaller, and the rolloff to Fb is shallower. Output is pretty much the same at Fb.
Here's the results of some recent measurements I took, same driver driven by the same voltage, used in my POC3 TH and my new POC7 ODTL design. Fb for both designs is pretty close (within 1 Hz). The TH is 1~2dB more efficient over part of the passband. However, the POC7 has a much wider useful passband (the TH is pretty much unusable above 100 Hz), and the ODTL box is smaller, and the rolloff to Fb is shallower. Output is pretty much the same at Fb.
An interesting thing to consider here is that, if I made the ODTL larger, the efficiency around Fb would be increased, which means output at that around that frequency would be better than a TH of the same volume. In-band efficiency however is set primarily by the driver, so in-band efficiency would still be less than the TH, but not much less. The TH should have better power handling within the passband however.
I'm thinking you need to measure the output and not just rely on anecdotal evidence - could the items in the room be shaking from the 100Hz+ peak of a TH?
Even if you don't have a mic on hand, try playing around with HPF and LPF combinations in your comparison (ie, 50-70Hz only), to get an idea of what "sounds" louder compared to what is measurably louder.
Even if you don't have a mic on hand, try playing around with HPF and LPF combinations in your comparison (ie, 50-70Hz only), to get an idea of what "sounds" louder compared to what is measurably louder.