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and customers usually specify low cost, either by competitive bidding or because they have other things to spend their money on, such as speakers 😀
True story ... in my younger days (earky '80's), worked in Chicago as a carpenter building a special room for teleconferencing. Was only 2 other rooms like this in the world at the time.
The insurance company paying the freight neede to house a complete computer room as well as the conference room needed to talk to their associates in NYC and LA. The room had to be soundproof and electronically impenetrable. We used high density FG and lead lined sheetrock in the perimeter walls below (2) additional sheets of 5/8".... as well as a vapor seal to prevent the halon gas (fire extinguishing) form leaving the room ... as specified by the architects/engineers.
The room passed all tests .. sound absorption .. electronic defeat .. room held pressure longer than spec'ed. We we're very proud. ... but it was because we used what was spec'ed and installed it correctly. As far as I know ... FG is still the best @ doing this. I know there are new things on the horizon because FG is a real PITA to manufacture ... but so far, I don't believe anything matches it.
I picked up a couple 15" drivers recently .. some older pioneers .. and put them into a couple makeshift "U" frames. Might be my room (16x30) but man .. there was a (3-6?) db increase in LFR right off the bat. The bass is overpowering when the gains are matched. I had to cut the LF level 3-4bd to get it to match the other drivers output ... one of which is an ESS Heil.
hehehe ... don't know what Stig listens to over there but he must do it with earmuffs on 😛 I think you're OK using a couple 15's for starters.
your overpowering bass can be at a much higher frequency than you expect
(because of the rising response)
u frame resonance might also be playing into it.
i agree that a couple of 15"ers can produce good dipole bass.
provided one or more of the following:
their total efficiency is higher than rest of the system
you crossover or use equalization to fight the rising response
big/wide baffle
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Talking about box colourations ...and what about the driver ? 😡
If you know about conventional cone break-ups and mathematical models for the loudspeakers , when they are considered in their 'pistonic range' the formula of F = 344 / ( 3.14 * D ) D is the Diameter in meters .
But a real rigid piston behavior doesn't happen in reality , due to resonance modes of the material and also geometry ( exp. , semi-exp , flat , etc . ) and they affect linearity , as the cone has to 'flex' to respond to the frequencies at the limit operating range , but this is quite 'normal' .
Indeed , for a 15 " the formula gives 333 Hz as the limit to be reproduced , but it can be tripled to 999 Hz .
But this might not be the case of the AN drivers as they exhibit low cone mass and big magnets , and probably a lowish Le to prevent high reactance to high frequencies 🙄
This will help with the excursion, but if you use a mid driver of the same efficiency you can simply waste the same power in the mids/highs using resistance. You could correct the dipole roll off with a passive network before the amp and avoid this.
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I agree, a baffle-step correction circuit before the power amp will avoid wasting limited power from my tube amp for starter. Of course, passive line level filters have to be tailored to the input impedance of the amplifier and that makes it less flexible for experiments with different amplifiers. A buffered (active) filter may be more flexible, perhaps a simple CF.
But I'm still 'stuck' without any measurement set up for in-room FR data and I'm reluctant to spend big bucks - it could end up being a toy that distracts me from listening for the next many months 😱
When I wrote that I was just referring to LF production ... the 15's I'm using are crossed over @125hz. I should have been more clear on that.
They're just in a low buck frame right now. I wanted to test them out in that type of enclosure first. As I said above .. they're xo'ed pretty low. They have a LR4 order commercial xo (lowpass) strapped to them right now. No EQ so they roll off naturally. All in the spirit of experimentation.
Just was trying to illustrate my initial impressions of a couple 15" drivers (for bass) with Bigun ... for what it was worth. I need to work with mine to get it just as I'd like ... but initially, they seem like they will be able to do the job just fine for me.
Don't know anything more about the drivers than what they came out of ... and their response in that (old) enclosure. I need to muddle through with them as a result.
Actually, I like to listen at quite soft levels. The reason I have sixteen 21" woofers is to get clean 20 Hz from a dipole. You simply can't do that with a couple of 15".
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But you do things that mortals don't, I mean, who the heck uses sixteen 21" woofers other than a speaker-dealer! 😱🙂 At 20Hz the wavelength is the size of a house.
last time I looked at the data sheet I didn't see a spec for Le.
Great links - these sound diffusors look really good. I'll keep reading!
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I know that feeling 😉, but apart from a mic, what is there to spend? My biggest issues are disrupting other's lives, rearranging living areas and hauling my speakers onto pseudo stands, such as coffee tables 😉
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Probably the biggest issue is my lack of time - it's not difficult to find a few minutes here and there to read on the forum, but when it comes to building and testing I enjoy it all the more when I have several hours of free time...
I do like the diffusor ideas still - I found another person who has implemented it.... first time I saw smoothed wooden surfaces instead of sharp angles
http://www.htforum.nl/yabbse/index.php?PHPSESSID=ahumoi0fmhm1gu74f2sq0apc81&topic=41295.0
I do like the diffusor ideas still - I found another person who has implemented it.... first time I saw smoothed wooden surfaces instead of sharp angles
http://www.htforum.nl/yabbse/index.php?PHPSESSID=ahumoi0fmhm1gu74f2sq0apc81&topic=41295.0
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I'm not seeing how that is a diffuser, it's far too regular. Is there any empirical evidence that these sorts of structures inside an enclosure make the slightest difference beyond reducing enclosure volume?
Can assure you the real Cremonas don't look anything like that inside (I have looked in mine) but the idea is quite interesting all the same.
Again, if you use absorption material that works then you will loose 99% (literally) of the energy trying to go through and bounce off the surface beyond.
If the material is inadequate then it will be so at the lower frequencies and the 1/2 wavelength resonance will be the least fixed by the damping material. The diffusor shown hasn't got enough depth to deal with any longer wavelengths. It would only provide scattering at frequencies where any absorber would do a great job.
These are cures advocated by those that neither understand the theory nor have done the measurements.
David S.
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Reflex Loaded Open Back ?
hmmm, so maybe diffusors are a crock, unless the box is big enough that it is more like applying a room treatment !
I'd like to revisit the ideas Cal presented - open box for mids, and which I thought might be a 'hidden-genius' feature of the Miles (post 62) where an opening behind the driver allows the mids to 'escape' (see diagram in post 95).
The difference between what Cal did and what we have in the InConcert Miles is that Cal wasn't aiming for a reflex loading. But in both cases there is an unimpeded path for the mids to escape from the box right behind the driver so that they are less likely to bounce around. It's the opposite of an Onken port which can make for a difficult escape route for sound.
So what are the pitfalls in designing a bass reflex cabinet where a large vent is located directly behind and in-line with the mid driver ???
hmmm, so maybe diffusors are a crock, unless the box is big enough that it is more like applying a room treatment !
I'd like to revisit the ideas Cal presented - open box for mids, and which I thought might be a 'hidden-genius' feature of the Miles (post 62) where an opening behind the driver allows the mids to 'escape' (see diagram in post 95).
The difference between what Cal did and what we have in the InConcert Miles is that Cal wasn't aiming for a reflex loading. But in both cases there is an unimpeded path for the mids to escape from the box right behind the driver so that they are less likely to bounce around. It's the opposite of an Onken port which can make for a difficult escape route for sound.
So what are the pitfalls in designing a bass reflex cabinet where a large vent is located directly behind and in-line with the mid driver ???
Not sure if it's a pitfall but I'm curious about a drivers magnet structure and how it affects the rear wave. In section, the whole affair reminds me of a poppet valve (magnet being the valve head).
I know that in an engine a valves shape can have a pretty big impact on cylinder filling due to more/less optimum valve head shape and bore throat shape/taper. Do the same vortices play a part in waveform development ... good/bad ... or is this a non issue due to velocity differences in the analogy?
I've never seen any air flow issues as long as the openings are big enough. The only time I've seen that the chassis openings were an issue was with some stamped chassis mids with very steep angle walls. This would put the opening close to the through hole and further restrict the air flow. Extra routering or a 45 degree back opening usually fixed that.
I do suspect that the magnet structure causes a significant reflective surface and that some of a woofer's upper frequency response wiggles could be traced to that.
David S.
I do suspect that the magnet structure causes a significant reflective surface and that some of a woofer's upper frequency response wiggles could be traced to that.
David S.
John Krutke/Zaph reports airflow issues leading to audible distortion on his site with some Tang Band woofers. I don't remember the model numbers but it was the ones with the underhung motor ie huge magnets relative to driver size.