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Multi-Way Conventional loudspeakers with crossovers

Where do I start? Pmc wafer cloneish!
Where do I start? Pmc wafer cloneish!
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Old 19th August 2018, 10:19 PM   #1
grahamricho is offline grahamricho  United Kingdom
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Default Where do I start? Pmc wafer cloneish!

I have a dedicated AV/hifi room and have previously built a pair of subwoofers and was thinking about another project.

I'm thinking of going from a 5.1 speakers system to a 7.1 speaker system so need two more surround speakers.

My AV room which i treated acoustically with 6 X 1800mm X 600mm acoustic rock wool filled panels to deaden the room a little....this got me thinking?

I saw at a local dealer some PMC wafer speakers (a hang on the wall flatish panel speaker about 4 inch in depth) which seemed expensive at over a 1000 each, so I thought I could build something similar but build them into a acoustic panel, so all you would see is acoustic panels but the rear acoustic panels would have a surround speaker build in.

The PMC are a transmission Line design and apparently have a H frame inside to direct the bass to the port, how would I start to design one and pick drivers etc? Any problems or ideas?
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Old 20th August 2018, 06:12 AM   #2
fatmarley is offline fatmarley  England
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Is your crossover going to be passive or active? Do you have measuring gear and software to model a crossover?

If you don't have measuring gear and knowledge to design a crossover then some component speakers designed for cars would probably be your best bet. You don't have to worry about BSC in a car, so the crossover should work. The only problem I can see is modeling the low frequency response.

Last edited by fatmarley; 20th August 2018 at 06:19 AM.
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Old 20th August 2018, 07:34 AM   #3
grahamricho is offline grahamricho  United Kingdom
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Hi thanks I wanted to build something a bit better than some car drivers in a box. I have REW and UMIK-1 mic. Is there no tried and tested designs which I could adapt to fit the space I have? Keep the same internal volume but change the dimensions to fit into a 1800mm X 600mm acoustic panel thanks
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Old 20th August 2018, 08:05 AM   #4
grahamricho is offline grahamricho  United Kingdom
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The crossover is passive
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Old 20th August 2018, 08:33 AM   #5
fatmarley is offline fatmarley  England
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It can take years to get your first passive crossover any good.

I think a fullrange driver may be a better idea. This thread looks like it could be perfect for your needs - Ever think of building a Cornu Spiral horn? Now you can!
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Old 20th August 2018, 03:12 PM   #6
jReave is offline jReave  Canada
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If you think you are capable of designing the xo, perhaps with some help, I would probably be looking at some of the low profile drivers out there, like:

Peerless GBS135
Dayton LW150

For surround speakers, both will go below 100Hz in a sealed box which simplifies things. Depending on your SPL requirements, you may want to double up and go MTM with the woofers wired in series for an 8ohm load to help minimize cone excursion. The Peerless 5" has a nice advantage in the sensitivity department over the 6" Dayton but it also has a rising response in the low frequencies which will need some attention.
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Old 20th August 2018, 11:24 PM   #7
grahamricho is offline grahamricho  United Kingdom
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nks for all your replies.

I have Kef reference 2 for my main speakers and the Kef reference 200 for a centre.

What would happen if I bought another 2 Kef reference 200 speakers second hand, worked out the internal volume of the cabinet and made another cabinet with same volume but a different shape? a flat box and ported it with same size port? Also use the crossover from the centre?

Is it possible to just get any second hand speaker and change the shape of the cabinet but keep the same internal volume ? Would it work as the original speaker?

In a ported speaker what happens when you change the internal volume?

Could you use Even a pair of Kef reference model 1 s with the single uni q driver?

Last edited by grahamricho; 20th August 2018 at 11:29 PM.
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Old 21st August 2018, 12:04 AM   #8
jReave is offline jReave  Canada
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These 2 links may shed some light on your questions:

Loudspeaker Spacial Loading
Loudspeaker Diffraction Loss (you can probably ignore the compensation part)

Attached are a few more diagrams that may help as well.

Both the port tuning frequency and the SPL from the port are altered by changing the box volume. If the driver will go down to about 80Hz or below in a sealed box, that may be the better option for surround speakers.

Now if you have a decent AVR and are happy with it's eq app, you may (stress the word, may) be happy just using that to compensate for any changes to the FR with a 'normal' speaker.
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Old 21st August 2018, 06:10 AM   #9
fatmarley is offline fatmarley  England
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Another one to look at - Post #6
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Old 21st August 2018, 10:50 PM   #10
hollowboy is offline hollowboy  Australia
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Quote:
Originally Posted by grahamricho View Post
Is it possible to just get any second hand speaker and change the shape of the cabinet but keep the same internal volume ? Would it work as the original speaker?
If you take a freestanding speaker, and move the components to a very wide flat baffle that is nearly flush with a wall, you'll get more midbass response*, so you'd ideally add some eq or tweak the original crossover (or both).

IMO, with the mic you have + a small selection of crossover parts to play with, you can mess about with attenuation and low order crossovers without needing to be a genius.

*look up threads about "baffle step compensation" and The Edge (the simulator).
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