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Old 7th March 2004, 09:26 AM   #1
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Default box dimention calculators

Help,
am currently building a pair of pa speakers. Can find lots of calculators for box volume but very little on customizing dimentions. The sites I have found have a preset ratio of width, height and depth that is more suitable to home hifi.
any suggested sites that contain information or calculators for customizing dimentions would be of great assistance.
thanks heaps
don c
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Old 11th March 2004, 06:25 AM   #2
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if any one has any info on the importace of box dimentions compared to volume that would be great. I keep seeing a ratio of 1:1.618:0.618 quoted on sites but there must be a way of calculating other suitable dimentions.
thanks
don c
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Old 11th March 2004, 10:05 AM   #3
Vikash is offline Vikash  United Kingdom
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Quote:
ratio of width, height and depth that is more suitable to home hifi
I don't excatly know what you consider more suitable for hifi/PA, but assuming you want to minimise colouration from the enclosure by reducing overlapping standing waves, you will want to use ratios of the irregular nature.

Quote:
I keep seeing a ratio of 1:1.618:0.618 quoted on sites but there must be a way of calculating other suitable dimentions
There are many irregular ratios that you can use to spread out the standing waves. A glance at the standing waves for an enclosure based on the above ratio shows that there are no similar frequencies being excited in more than one dimension. This is typically what you're looking for.
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Old 11th March 2004, 12:57 PM   #4
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vikash
thanks that standing wave calculator was perfect. I imagine that the aim is to make sure that there are no matching frequencies(standing waves) from any cabinet side that could cause frequency cancelation.
I dont think its too far off the thread to get feed back on a box design for the following speaker-

paudio
hp-12w

12 inch
100 watt
Fs 48hz
Re 5.5Ohm
Qms 4.99
Qes 0.65
Qts 0.57
vas 99.77 litres
Xmas 2mm
No (1.67)
Im not sure what it is about this speaker's specifications but several different calculators have come up with recommended vented box sizes around 260 litres. Thats huge. I think I'm going to break my back carrying them.
The recommended vent sizes were also large at around 15cm diameter. I tried using a 6.5 cm vent diameter(I have a couple spare) but the length came up as a negative number.

Thanks
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Old 11th March 2004, 03:20 PM   #5
Vikash is offline Vikash  United Kingdom
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Quote:
...cause frequency cancelation
I think the standing waves sum together causing humps in the FR.

I did a quick model of this driver and it does appear to require a large enclosure. Unibox shows an optimum vented enclosure of 321 Litres for an F3 of 29Hz. However, you're also looking at a max of 97db and <90db at ~2W input before you've run out of xmax at f3.

Halving the enclosure volume results in only a slighly higher f3 (40Hz) with a 0.12 ripple. It seems the larger cabinet is not worth its weight.

I would reccomend using Unibox above all other (free) modellers.
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Old 11th March 2004, 04:01 PM   #6
GM is offline GM  United States
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Assuming the published specs are ~accurate, I believe you will find this golden ratio alignment better suited to PA apps.:

Vb = ~56.689L

Fb = ~31.5Hz

L = ~62.23cm

w = ~38.46cm

d = ~23.75cm

vent = 7.62cm dia. x 15.25cm long.

GM
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Old 12th March 2004, 11:28 AM   #7
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Vikash unibox is great. Much more powerful than the other calculators that i was using. Still working out some parameters such as absorption Qa, Leakage Ql and port Qp. If you know of any sources or further discussions on the net with more detail on port air speed, cone excursion, speaker impedance and the other unibox graphs and what effect they have on design it would be great. I have played with Unibox for a while and got down to a 96 litre box with a f3 of 44hz(using Fb of 40). Thats a much lighter box than I started with.
GM thanks for your comments. I ran your figures on unibox and came up with an F3 of 58.61hz. This box would be ideal for a vocal PA and easy to lift. I will need the PA to go lower than this for backing music. This design might best match with a sub with a 60hz crossover for the kick drum and bass in the backing.

Im starting to warm to the golden ratio but Im use to PA speakers with a greater depth to side ratio than 0.6:1. I wonder if it affects the sound if the speakers are mounted on the narrow side(assuming there is enough room).
Thanks again
don c
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Old 12th March 2004, 02:06 PM   #8
GM is offline GM  United States
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>GM thanks for your comments. I ran your figures on unibox and came up with an F3 of 58.61hz. This box would be ideal for a vocal PA and easy to lift. I will need the PA to go lower than this for backing music. This design might best match with a sub with a 60hz crossover for the kick drum and bass in the backing.

====

You're welcome! This driver can't handle much SPL down low (let the excursion plot be your guide as to how low you can go), so yeah, a high power/excursion sub will be required if you need a lower F3.

====

>Im starting to warm to the golden ratio but Im use to PA speakers with a greater depth to side ratio than 0.6:1. I wonder if it affects the sound if the speakers are mounted on the narrow side(assuming there is enough room).

====

It raises the baffle step, but I assume you EQ the system with at least a 1/6 octave selectivity for each venue, so it's moot. FYI, there are many other suitable acoustic ratios. Design your cab, then use a room mode calculator to see how it fares, and adjust as required.

GM
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Old 15th March 2004, 11:36 AM   #9
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Well I built one box 96L as a compomise with an 11cm diameter port and it sounds good in the middle but is completely lacking in any bottom end. It cuts of much higher than expected in the bottom end(above 100hz perhaps). Will be getting a graphic to check this latter on. It could be the speaker, my box or as you suggested GM, the published parameters that I did the calculations from.
I think I will put them into that smaller box you suggested GM and build a sub. Hey Ive got another speaker from the same company that I have been looking at E12-200s. Check out the specs below-
fs 59.7
Re 5.7
Qms 9.43
Qes 0.5
Qts 0.48
Vas 49.06
Xmax 3.5
all in metric
These seem much more suited to a small enclosure.
Any comments?
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Old 17th March 2004, 01:15 AM   #10
GM is offline GM  United States
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>Well I built one box 96L as a compomise with an 11cm diameter port and it sounds good in the middle but is completely lacking in any bottom end. It cuts of much higher than expected in the bottom end(above 100hz perhaps). Will be getting a graphic to check this latter on. It could be the speaker, my box or as you suggested GM, the published parameters that I did the calculations from.

====

Hmm, it should have a ~40Hz F3 depending on how long the vent is. You are aware that the sim is half space and that any speaker will need 3-6dB of baffle step compensation, right? Of course make sure there's no leaks, it doesn't take much to kill the vent action.

====

>I think I will put them into that smaller box you suggested GM and build a sub.

====

I would if relatively low distortion is required.

====

>Hey Ive got another speaker from the same company that I have been looking at E12-200s.

>These seem much more suited to a small enclosure.
Any comments?

====

Yes, the cab's much smaller, but the tradeoff is less output below ~125Hz in a Pi Alignment. The E12 is marginally more efficient above this point though.

GM
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