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Old 17th February 2011, 05:09 PM   #11
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Quote:
Originally Posted by jrenkin View Post
Being only one and a half sets of speakers from being a newbie myself, I suggest you go with an established design out of plywood.

If you do something complex, immovable and not at all adjustable out of concrete, you have to get everything just right the first time and re-dos are a PITA.

Besides, the first time(s), it won't be perfect, so give yourself a break and start simple, established and enjoy the process of learning enough so that you can safely pour concrete in the future.

A good simple start could be a BIB. you could pick your driver based on the space available. I did a BIB with the Fostex 208EZ and it is big and sounds great. Easy first build with excellent results and with the right driver, enough bass, which is important, a room the shape of yours may eat some lower frequencies.
Thanks - I've just had a look at the BIB stuff. Your point about starting with something relatively easy is a perfectly valid one of course, although I'm wanting to be a bit ambitious with this because I won't necessarily have the time or opportunity to repeat the process in the near future!

I plugged the Lowther PM6C specs into the calculator on the BIB site by the way... assuming I got the specs right (different sources seem to disagree on them) it suggested a 2.4m high cabinet which is pretty big! (see below)


Can anyone comment on the advantages of building a more complex design (for example the Spawn double horns linked to earlier) compared to something like the BIB design (assuming I build both competently of course)?
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Old 17th February 2011, 05:10 PM   #12
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Originally Posted by Ty_Bower View Post
How curious. Version 1v0 (dated 23-03-07?) of the drawings had a note near the bottom of page two. The current package 1v01 (dated 22-03-09?) has some changes, and the mention of Lowthers is no longer there. I think that part of the drawing got snipped because it contained some response plots that tended to cause more confusion than clarity. Regardless, I suspect the design is still valid for the Lowthers. Perhaps Scott Lindgren can chime in.

If you are to build them, definitely use the newer drawing package. I seem to recall there are some important corrections in it, especially with regards to the wedge deflector.



It's been done here before. Search long and hard, and you should find the thread. The builder used some kind of styrofoam for the casting, poured the cement, then used a solvent to remove the foam. I'm sure it was messy and most likely bad for the environment. He managed to build one but never completed a pair. I'd stick with wood. If you pour a solid block of concrete to the dimensions you've described earlier, you're dealing with over 2.2 tons per cabinet. Even recognizing that some fraction is going to be empty space (60%?) it's still going to be incredibly heavy.

edit: Here's the thread with the concrete horn -
TQWT Concrete cabinet attempt, building thread.
Quote:
Originally Posted by hm View Post
Here you get feedback, plan, measurement, may be take goo.. translate if you need:
tuba
tubamess
tubaFB
tubaplan
basstuba
basstubamess
basstubaFB
basstubaplan
Quote:
Originally Posted by Scottmoose View Post
To an extent, yes, providing it's correctly designed, bigger is better. However, as horn length increases, so does group delay, thus the acoustic XO frequency from horn to direct radiation will need to drop to render it ~inaudible and / or you will need some form of digital delay on everything above that point. If this XO occurs significantly below the driver's mass corner, you will then need a short front-horn to 'fill in' the resultant dip in the response.



The room dominates low down, so unless it's of ideal acoustic proportions & you've lots of treatment, then yes, you want to think about it. A lot of it is common sense though; if you want to fill a concert hall, you don't pick an LS3/5a.




It's been done, but it's not especially easy. I wouldn't discourage you from it, but I'd probably consider something in wood initially, as it's quicker & simpler to ascertain whether you like the results or not. If you do, & you're feeling ambitious, you could always consider the cast concrete at a later date.
Thanks all for your comments.
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Old 17th February 2011, 05:25 PM   #13
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One thing to consider is that with horns built in, you have zero options for tweaking the position or toe-in to get the best response. Special consideration is also needed for the 2 pi loading.

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Old 17th February 2011, 07:02 PM   #14
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One thing to consider is that with horns built in, you have zero options for tweaking the position or toe-in to get the best response. Special consideration is also needed for the 2 pi loading.

dave
Sure. I will probably construct them in such a way that I can rotate them to some degree, possibly even build them before finishing off the surrounding cupboards etc so I can tweak the position a bit before fixing it.

What is the 2 pi loading?
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Old 17th February 2011, 07:44 PM   #15
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2 pi is radiating into a 1/2 sphere (2pi steriradians).

But actually with the floor (and ceiling) playing a roll 1pi steriradians might be closer.

Sachiko for instance is designed to be out from a wall, so you might find excessive bass gain (not a bad thing as long as you have a way to turn it down)

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Old 17th February 2011, 10:14 PM   #16
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Originally Posted by planet10 View Post
2 pi is radiating into a 1/2 sphere (2pi steriradians).

But actually with the floor (and ceiling) playing a roll 1pi steriradians might be closer.

Sachiko for instance is designed to be out from a wall, so you might find excessive bass gain (not a bad thing as long as you have a way to turn it down)

dave
Ok, I think I sort of understand what you are talking about...

When you say it needs to be taken into consideration, do you mean choice of speaker design, or alterations to a chosen design... or something else?
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Old 17th February 2011, 10:55 PM   #17
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In a 2pi case you will not have baffle step to deal with. In a design with acoustic BSCompensation built in, you will instead have to deal with a rise on LF response, you may need an anti-BSC filter.

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Old 9th August 2012, 11:16 AM   #18
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So, a year and a bit on, I am resurrecting this thread because I am getting closer to the point where I can start building these.

A question though - I had been thinking of building the "Sachiko" from the Frugelhorn website (part of the "Spawn" family), however, I've just had a look now, and there no longer seems to be a "Sachiko" design there.

I'm guessing these are updated designs? Is anyone able to help me with the question of whether Lowther PM6Cs would work with any of the current designs? Or would I be better to use one of the older ones? As per the post below, from earlier in the thread, it seemed to be the case that an earlier iteration of the design had been tested with Lowthers.


Quote:
Originally Posted by Ty_Bower View Post
How curious. Version 1v0 (dated 23-03-07?) of the drawings had a note near the bottom of page two. The current package 1v01 (dated 22-03-09?) has some changes, and the mention of Lowthers is no longer there. I think that part of the drawing got snipped because it contained some response plots that tended to cause more confusion than clarity. Regardless, I suspect the design is still valid for the Lowthers. Perhaps Scott Lindgren can chime in.
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Old 9th August 2012, 01:41 PM   #19
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Happened to notice this thread...

Imo, with the Lowther drivers you have to deal with the inherent aspects of that driver. Generalized solutions are not going to work well.

The basic response of the driver is more or less a response that gently droops from a mid point in the frequency range down to either end.

Many people have tried to augment the lower frequency section, and to produce "real bass".

It's problematic, the solutions vary in effectiveness.

I think that MJK's solution is to use his TQWT design but with an electrical network to flatten the response, at the expense of sensitivity.

The various front horn designs seek to augment the lower freq range via the horn. The back horn seeks to augment the lowest freq response.

Oh, while thinking of it, looking at ur earlier sketch it seems that corner placement facing down the long way in the room might be a good option to consider.

Depending on how much effort and time you want to put into the speakers, I'd suggest that you might want to start with the following:

- a basic FFT (freeware or low cost ware) speaker measurement set up for your laptop or PC, with a low cost, or home made (Linkwitz site) WM-61 Panasonic capsule.

- a very very basic and simple enclosure to get familiar with the driver and it's characteristics. probably a large face (bigger is better) not too deep, internally absorptive box.

- the box can be sized according to the T/S parameters and the results from a basic freeware or shareware box simulation program. you can decide sealed or ported to start.

This is just to get you measuring and listening to the drivers in short order... maybe even a used commercial enclosure of the right size with a bit of MDF cut to fit over a 15" or 12" dia speaker hole will suffice.

First listen, then measure, then you will have a basis for knowing what you want or need to do.

that's my advice...

_-_-bear

PS. if ur not using the Lowther, then your project has no limitations, anything is possible !
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Old 9th August 2012, 01:43 PM   #20
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Btw, most of the designs you see are with narrow baffles.

This is done for cosmetic and WAF reasons in the main.
The best sound will be with a WIDE baffle.
If you have no constraints, then look beyond the typical compromises that most designs of necessity embody.



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