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need to design a small midrange box!

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Mosaic

Well-Known Member
Hi all:
I have a requirement for a midrange, 300 - 4000Hz drive at around 50W RMS max. Tenor Steel pan amplification.

The flat diagonal of the box rear panel should not exceed 12" as it must fit inside a 12" cylinder. I am hoping for perhaps something in the 8 x8 x8" range as the max dimensions.

The spkr 'box' can be a cylinder as well.

I am looking for a guide to design such a box. Sealed seems the most forgiving.
I guess the driver might be around 4 - 5" but I am open to suggestions.

I still have to get the driver.

Scrapped an Aiwa mini stereo today, but got a 6.5" woofer and a 2" Mid and a tiny tweeter out of a reflex enclosure. Thought I could reuse the woofer and midrange in a smaller sealed box enclosure as I don't need the low end of the bass. Not sure how to size the box volume though...as I am NOT trying for bass here.

this calculator:

https://www.diyaudioandvideo.com/Calculator/Box/

Needs data I don't understand, if someone can explain those parameters (and where to find em) I would appreciate it.

Interestingly there is a sample for a 4" spkr on this page:
https://www.diyaudioandvideo.com/Tutorial/SpeakerBox/
that comes up with a .77 litre volume. If that's a decent ballpark I can work with that.

Also, I am wondering if 4" PVC waste pipe (true dia. = 4.5" ) could be made into a housing by endcapping one end and mounting the spkr in the other. The waste pipe can be made malleable with a heat gun to 'suit' the speaker fit.

thx much
Ancel
 
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For those frequencies and power I would use a single mid-range or full-range speaker, perhaps one of these.

The speaker parameters for calculating the box volume are normally included in the speaker specs.

A piece of PVC or ABS pipe should work fine as a enclosure. Some high end speakers have used round enclosures because they tend to minimize the resonances that a square box has.
 
Thanks for that crut.
Since a lot of mid ranges have sealed backs, do I really need to create a particular air volume in the housing or just go for a minor convenient volume as would occur when leaving room for the magnet and then end capping?
 
An ordinary full-range speaker in a small enclosure will have a high and very pronounced resonant frequency. A bongo drum.
An ordinary 4" speaker will have a maximum power rating of 5W to 10W.

A mid-range speaker with a sealed back is designed to have a sealed back.
A half-decent mid-range speaker will have a power rating that you need. Buy one.
 
The general problem of loudspeaker box design is due to the frequency range required at the bass end.
For bass speakers, the audio frequency range required generally extends down to below the normal cone resonant frequency. However, in your case the low frequency range is probably above the cone resonant frequency, or at least, you choose a cone resonant frequency of less than 300 Hz.
the figure of 50 watt worries me a little. This requirement suggests a larger diameter cone than 3 or 4 inch; more like 12 inch. Some of the posts are canvassing this aspect.
The paper you refer to is based on the Thiele/Small parameters. This stuff comes from a paper by Neville Thiele who was the Technical director of the Australian Broadcasting Commision in the 1960's/70's. The paper is a hallmark work on loudspeakers and considers the box, loud speaker parameters including cone equivalent compliance and damping due to the magnet system and the amplifier output impedance and low frequency response and accoustic efficiency.
The reference is essentially considering the low frequency response only.
For completeness, the actual paper is;
"Loudspeakers in Vented Boxes", by A.N. Thiele and was presented at the IRE Convention (australian IRE) in March 1961. At the time,Neville worked at EMI Australia; this company being part of EMI of the UK.

So if you go for a wide range loudspeaker, then you will not be bothered by such design parameters. But I would be using a larger box rather than a smaller box and to me 0.7 cubic feet sounds adequate. Your 0.77 litre is very small and will most likely lead to too much accoustic damping on the cone, which will lead to a higher electrical power input.
hope this helps.
 
But I would be using a larger box rather than a smaller box and to me 0.7 cubic feet sounds adequate. Your 0.77 litre is very small and will most likely lead to too much accoustic damping on the cone, which will lead to a higher electrical power input.
Instead of re-inventing the wheel, the OP should simply purchase a mid-range speaker with a sealed back that was designed to have a sealed back. I saw some 4" mid-range speakers rated at 90W or more and they produce very high sound levels, almost as high as the sound level from a tenor steel pan. It is amazing that they can make and tune those percussion instruments.
 
I wonder who makes it and why they do not publish a frequency response curve for the inexpensive speaker?
 
Mosaic,
Re your post 7;
The data values they give are the Thiele/Small parameters.
Re and Le is the voice coil resistance and inductance and because the resistance dominates the impedance, it can be taken as 8 ohm. thats where the 8 ohm comes from.
Fs is the cone resonant frequency, and is 100 Hz, and is below your cut off frequency of 300 Hz.
Qts and Qes are damping parameters related to the electromagnetic damping of the loudspeaker. They relate to the accoustic efficiency of the loud speaker in a box. The data sheet says that the accoustic efficiency is 91 dB per watt. Qes is from memory, the sharpness of the resonance curve of the cone at the resonant frequency of 100 Hz measured in the open air.
Qts is calculated from Qes and Qms.
Vas is the equivalent air volume of the speaker and this value relates to the air volume of the particular enclosure.
Xmax is the maximum cone displacement allowed for the speaker.
Generally, a high quality loudspeaker has a Qes of lower than around 0.4.

Because you want to operate your speaker at more than 2 octaves above the cone resonant frequency, the box characteristics are not greatly important.
From what you say you want, you could go with this speaker and not worry too much about the Theile/Small parameters because you are not concerned with the low frequency response at 100 Hz.
Hope this helps you.
 
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