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Old 31st October 2008, 01:35 PM   #11
MaVo is offline MaVo  Germany
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It could be rewarding to find the optimum compression factor for a driver for pro sound use, since a higher compression leads to more max spl and smaller sized systems. The limiting factor would probably be the potential of cone damage at too high compression, which again seems to be related to the frequency range and excursion, since the same excursion at higher frequency equals more force on the cone. Strong motors like a higher compression value, for example the Beyma 12P1000ND seems to simulate the best for a value around 4-6, again depending on the frequency range while the BMS 18N860 favours one of around 2.

Another thing to think about in order to optimize output per box size is the ratio of cone area to mouth size. Making several small mouthed boxes with the same volume as one big mouth box with only one driver often gives more maximum spl. A good ratio seems to be around mouth size = 1 to 3 times the cone area.
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Old 31st October 2008, 02:42 PM   #12
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Mavo:

How did you figure out which drivers work well for higher compression ratios? Was this just trial and error in Hornresp, or is there a way to figure this out from the T/S parameters?

Craig
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Old 31st October 2008, 04:06 PM   #13
jbell is offline jbell  United States
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quote/
Oh yeah, TH's couple very well
/quote


yes they do... I'm interested in the 'smaller version of jbells box' I know for my install, size was of no consideration. However that does not apply to most, and what you've done is probably more applicable to the audience here.

Don Snyder was kind enough to draw up in cad my quick design, and double check my hornresp params.. If Don has time, I'm sure everyone would appreciate cad drawings of your efforts as well.

Also, I'll 2nd your observation of a 3015lf in a TH. If you don't have a dcx2496, or some other piece of equipment that can do a STEEP high pass at 40hz... don't build it, period.
I used a 48db/oct 40hz High Pass, and the 3015lf was happy with that.
Thanks for sharing
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Old 31st October 2008, 05:25 PM   #14
JLH is offline JLH  United States
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Quote:
Originally posted by craigwalsh


Samuel:

How about this configuration...

That is a variation of a TH that I built. The only problem I see is the woofers are not configured in push-pull. This means that the non-linear suspension components will not get canceled. However, due to Sd being 2X I would say excursion should be greatly reduced anyway. I'm just saying if you are going to the trouble to build a double woofer TH you might as well go all the way and cancel non-linear distortion while you are at it. As an added benefit, I find that the chamber volume can be useful to flatten the response sometimes.

Click the image to open in full size.

My double TH --> http://www.diyaudio.com/forums/showt...97#post1627597

Rgs, JLH
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Old 31st October 2008, 05:50 PM   #15
MaVo is offline MaVo  Germany
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My comments on compression ratio were to illustrate that some drivers model better with higher ratios, not to indicate that they can survive such a horn in reality. One can generally say, that the smaller the driver (for example use two 12 inch instead of one 18) the more punishment it will be able to take, since the membranes are relatively more heavy compared to bigger drivers.

I dont know how real driver failing under heavy hornloading is, but i somehow it seems to be strange that the compression ratio should have something to do when the driver fails, since a closed box for example has an infinite compression ratio on one side of the driver and isnt really known as the most evil driver killer alignment or take a bandpass, which also has a very high ratio of port area to driver area and here this argument also doesnt apply. Maybe this cone failure under high compression is some kind of artefact, which is rather related to generally driving a driver out of its safe range?
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Old 31st October 2008, 06:01 PM   #16
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Quote:
Originally posted by JLH



That is a variation of a TH that I built. The only problem I see is the woofers are not configured in push-pull. This means that the non-linear suspension components will not get canceled. However, due to Sd being 2X I would say excursion should be greatly reduced anyway. I'm just saying if you are going to the trouble to build a double woofer TH you might as well go all the way and cancel non-linear distortion while you are at it. As an added benefit, I find that the chamber volume can be useful to flatten the response sometimes.

Click the image to open in full size.

My double TH --> http://www.diyaudio.com/forums/showt...97#post1627597

Rgs, JLH
From my perspective, this is pretty similar to the LabSub in that it's feeding a small volume throat, with roughly a 3 or 4 to 1 compression ratio. But, using push-pull might help to reduce distortion. The problem is in fitting that into a small TH. I still need to work on modeling this to find the right drivers.
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Old 31st October 2008, 06:07 PM   #17
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Quote:
Originally posted by MaVo
My comments on compression ratio were to illustrate that some drivers model better with higher ratios, not to indicate that they can survive such a horn in reality. One can generally say, that the smaller the driver (for example use two 12 inch instead of one 18) the more punishment it will be able to take, since the membranes are relatively more heavy compared to bigger drivers.

I dont know how real driver failing under heavy hornloading is, but i somehow it seems to be strange that the compression ratio should have something to do when the driver fails, since a closed box for example has an infinite compression ratio on one side of the driver and isnt really known as the most evil driver killer alignment or take a bandpass, which also has a very high ratio of port area to driver area and here this argument also doesnt apply. Maybe this cone failure under high compression is some kind of artefact, which is rather related to generally driving a driver out of its safe range?

I wonder about that too. I seem to recall reading somewhere that the Lab12's have had trouble with this in the past, but that it's been fixed in the commercially available version. It does seem strange to me too that a driver would fail because it's firing into a small space in one direction, but it's certainly possible. Because of the compressibility of air, a closed box does not present itself as an infinite compression load. Indeed, you need to have a reasonable amount of air in a closed box alignment to control cone motion. I agree that smaller drivers like 12s are probably better for high compression alignments.

I wonder if others will chime in here with their experiences using high compression ratios in bass horns. Anyone had cone failures that were not due to exceeding the mechanical limits of the voice coil gap?
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Old 31st October 2008, 06:43 PM   #18
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I'm still splitting hairs between the actual build and the original horn resp data. Amazing how a few CM make a difference.

CraigW, I was thinking about that too. I figured the box would get too big. For a moderately loud band that type of arrangement might work but I'd separate the two drivers from each other at least in the first stage. My thinking is: instead of having two drivers pounding away at each other directly, isolating the first stage or two and combining the two at a later point in the horn might take destructive pressure off both drivers. I'm thinking that high pressure at the driver and first stages will prevent damage.
Think like headers on a car, the idea is to time the exaust ports such that they are all about the same length resulting in smooth flow down the exaust pipe. I could be wrong.

While it's a pain to carry more boxes, it's safer for rental work.
If a driver fails out of 4 you disconnect it in seconds and keep going (Captain, weeve only gut thrree qwarters impulse but I think she'll hold).
With double cabs, if one driver fails in show, the whole cab is down. (Damnit Jim ,I'm an engineer not a Magician!).

A funny thing happens to horn loaded speakers as they age, the cones explode. The same pressures that help the box get louder also rip the cones apart if they get wet or dry rot. Too much compression is a bad thing.

On the 3015, try an opening 310sq cm to 600.
I think the definimax looks better but I can't afford any at the moment. I bought 3015 for another project because the 4015 would not fit....Damn!
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Old 31st October 2008, 06:48 PM   #19
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Quote:
Originally posted by screamersusa
I'm still splitting hairs between the actual build and the original horn resp data. Amazing how a few CM make a difference.

CraigW, I was thinking about that too. I figured the box would get too big. For a moderately loud band that type of arrangement might work but I'd separate the two drivers from each other at least in the first stage. My thinking is: instead of having two drivers pounding away at each other directly, isolating the first stage or two and combining the two at a later point in the horn might take destructive pressure off both drivers. I'm thinking that high pressure at the driver and first stages will prevent damage.
Think like headers on a car, the idea is to time the exaust ports such that they are all about the same length resulting in smooth flow down the exaust pipe. I could be wrong.

While it's a pain to carry more boxes, it's safer for rental work.
If driver fails out of 4 you disconnect it in seconds and keep going (Captain, weeve only gut thrree qwarters impulse but I think she'll hold).
With double cabs, if one driver fails in show, the whole cab is down. (Damnit Jim ,I'm an engineer not a Magician!).

A funny thing happens to horn loaded speakers as they age, the cones explode. The same pressures that help the box get louder also rip the cones apart if they get wet or dry rot. Too much compression is a bad thing.

On the 3015, try an opening 310sq cm to 600.
I think the definimax looks better but I can't afford any at the moment. I bought 3015 for another project because the 4015 would not fit....Damn!

Actually, if wired in parallel, the dual driver box will still perform if one driver dies. But, then it will be way out of alignment! I agree with your sentiment. The other advantage, at least with typical bass horns, is that you get constructive coupling at the mouth area. I'm not sure if that works with TH's though.
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Old 31st October 2008, 07:21 PM   #20
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Quote:
Originally posted by JLH



That is a variation of a TH that I built. The only problem I see is the woofers are not configured in push-pull. This means that the non-linear suspension components will not get canceled. However, due to Sd being 2X I would say excursion should be greatly reduced anyway. I'm just saying if you are going to the trouble to build a double woofer TH you might as well go all the way and cancel non-linear distortion while you are at it. As an added benefit, I find that the chamber volume can be useful to flatten the response sometimes.

Click the image to open in full size.

My double TH --> http://www.diyaudio.com/forums/showt...97#post1627597

Rgs, JLH
JLH:

Yes, your TH looks very nice. I bet it must sound pretty good! I'm trying to get this one into a line length of somewhere between 3 and 4m to get reasonable extension to the mid-30's. As a bass player, I'd like to get some of my 5 string's B string fundamental (about 31 Hz). But, I'd also like high output and a relatively small box size. I know, this is too much to ask. One of those 3 criteria must be thrown out.
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