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Old 28th May 2011, 08:52 AM   #11
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Quote:
Originally Posted by Josh Ricci View Post
Anyway here is a rough HornResponse approximation of the Akabak script.
Hi Josh,

The 4-segment Hornresp approximation doesn't appear to be too rough, when compared to the 48-segment AkAbak result :-).

See attached comparison.

Kind regards,

David
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Old 28th May 2011, 10:51 AM   #12
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Wow! that's great response down to 15hz. I bet they go very very loud. Someone on the hometheatershack did a horn with a 18" malx driver and that was very impressive.

Its the first time Ive ever heard anyone doing a horn with a LMS driver.
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Old 28th May 2011, 01:08 PM   #13
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Quote:
Originally Posted by David McBean View Post
Hi Josh,

The 4-segment Hornresp approximation doesn't appear to be too rough, when compared to the 48-segment AkAbak result :-).

See attached comparison.

Kind regards,

David
Ha! Yes not too rough. Amazingly close actually all things considered.
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Old 28th May 2011, 01:38 PM   #14
DrDyna is offline DrDyna  United States
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That thing looks beast. I've been oogling at the TC Sounds 18s for a few months now. What are you driving them with? (apologies if I missed it)
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Old 28th May 2011, 04:18 PM   #15
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I just got them together with the drivers in thursday night. Haven't really had a chance to mess with then much yet. Power will be a bridged Crest 8002 on each until I get a new amp.
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Old 28th May 2011, 09:51 PM   #16
Zero D is offline Zero D  United Kingdom
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Default Hi

@ Josh Ricci

Hi

First off, congrats on attempting this, the AkaBak work, & the nice looking photos of the build

I wonder what made you choose a driver, mainly designed for vehicles ? I know there is no law etc that says you can't, thank goodness. I expect for one you were attracted to the quoted Xmax: 38.1 & Power handling: 2,000 watts RMS & Fs: 20.5 Hz apart from anything else. As impressive as they are though, one of the things that most of the vehicle drivers i've looked at, fall down on is Sensitivity, = SPL: 89.7 dB in this case.

Choosing a non vehicle driver opens up the field Considerably, with quite a number of candidates. For eg, a large driver with less power capabilities, but higher sensitivity, would easily match or exceed the SPL of most vehicle drivers. Did you model any such drivers, if so which ones & what did you discover ?

Also i would be concerned about the "rubberised" etc surround for sustained periods of time at high power, & also in the long term. My experience with drivers with similar surrounds on Commercial cabinets, is they don't last very long as they tear apart. This "might" not be the case with the LMS Ultra 5400, or some others, and i only mention it as a precaution, as they are not cheap ! And neither is the recone kit = replacement basket !

I see no mention of Xmax on TC's www ? only Xmech = Mechanical displacement limit (one way) Xmax is listed on PE as above. So i'm curious to know what Actual the Pk - PK Xmax "Official" specs are.

I find it strange that TC Sounds don't "appear" to list the T/S parameters for it ? TC Sounds Inc. I did find them on TC Sounds LMS Ultra 5400 18" DVC Subwoofer But no mention of Pk or Pk - Pk ?

Re - damping

My experience in designing/build bass/sub cabs is not to use any. Unless whatever material/s are used, are VERY firmly secured, they can cause more trouble than not. This is because high air pressures move the damping, in some cases quite considerably, which affects & interacts with the T/S parameters in real time, and/or some lag. This obviously affects the response in all sorts of unpredicatable ways. Also any damping is only really effective at higher frequencies than bass.

I think trying to run those/similar cabs higher than 80Hz will not achieve what you desire.

Quote:
I am not sure what the cause of the 100hz null is. 100hz is a roughly 11.25 ft long wavelength. This is a 22 ft long horn.
22 divided by 11 = 2 = I believe = destructive interference.

I sincerely hope you take my observations/advice in the way they are intended, & wish you All the best with it
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Old 29th May 2011, 10:43 PM   #17
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Zero D no offense taken.

First thing is that I do not look at drivers based on the field they are generally used in. That is pretty much pointless to me other than to get perhaps a guess as to the componentry in its design. I look for drivers that fit the intended application. I also look at manufacturer specs with a grain on salt. I have seen far too many that do not live up to the billing. This driver is used for a diy HT driver far more than car audio. Also it has been thoroughly tested by quite a few different 3rd party sources including Klippel testing. I have used this driver long before the horns. However skeptical you may be of the performance claims I assure this driver has been thoroughly vetted and backs them up. There are tons of builds and data available on it.

I have some "different" views on some things than most people. I don't want to get too far into that. I do have a good amount of experience with many highly considered pro drivers. None of them will do what this one should in this cab. These are for low bass and regardless of using a horn or not you still need a lot of displacement to make low bass. Most pro drivers will have some 6-8 db less displacement limited headroom. Efficiency is great but in bass it is dominated by the cabinet volume, the corner chosen, and the motor strength( I mean bl^2/RE). In these days of cheap watts power is not an issue. Efficiency is great but doesn't mean a whole lot if the displacement isn't enough to handle some power. I doubt that you would be able to achieve the same corner and total cab size and get much more efficiency than a db or 2 regardless of the rating of the driver. I find the sensitivity spec one of the most useless for subwoofers. These usually have little bearing on the performance below 100hz given the way they are gathered.

A half wave cancellation makes sense since the horn is 22 ft and 100hz is roughly half of that. However if this is a typical type of resonance due to the total length shouldn't it have shown up in the simulation?
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Old 29th May 2011, 11:16 PM   #18
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Quote:
Originally Posted by Josh Ricci View Post

A half wave cancellation makes sense since the horn is 22 ft and 100hz is roughly half of that. However if this is a typical type of resonance due to the total length shouldn't it have shown up in the simulation?
nope, construction matters.

The only place in your design where you have parallel opposing faces is the last segment before the mouth. I suspect that is where the back reflection is occurring.
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Old 30th May 2011, 02:19 AM   #19
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What was your train of thought as far as construction? At 24" wide I would have gone with dual braces in every section. Is it your experience that this is overkill? It is obvious you did your homework on this, so your thoughts will be revealing.
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Old 30th May 2011, 07:15 AM   #20
Bluto is offline Bluto  United States
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I like it but it's a bit too small.
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