Building a portable speaker

[normspanners]

the diaphragm has to move forward when producing the sound but your idea it would be moving backwards

A speaker at rest is in the mid position, surely, so in a normal two housing set up it doesnt matter if they are both wired up 'backward' they will still work exactly the same. Aspeaker makes noise when it travels in either direction all it is doing is moving air.
Having them out of phase in one housing would be helping each other to get the maximum air moving which should increase the punch IMO.

Quote from speaker phasing
When two woofers are mounted in the same enclosure and one woofer is inverted, you would need to wire it “Out of Phase” in order to make the sub perform correctly. When the woofers are pointing in different directions, and one is out of phase, the cones will then move together and not cancel out.

 

[richie00boy]

No, wiring them out of phase would cancel the sound.

 

[Maker]

Ok, so mono it is then, that simplifies (And cheapens ) things. I know I'm not going to get really low bass outside in a small enclosure but I'm sure I can beat the 4 x 1" full range drivers in the Pill.
Now I'm thinking just one woofer and one tweeter then. How should I design the case? I know that's a huge question but I don't even know where to start. I'd love to use machined aluminium like a Jawbone Jambox but I think it'll have to be MDF, oh well, maybe for V2.

 

[Maker]

Just downloaded WinISP, now, what on earth does one do with it?

 

[richie00boy]

You need to understand what the graphs are all about. Maybe you can find some online guidance, but I recommend you get yourself a copy of the "Loudspeaker Cookbook" by Vance Dickason.

 

[Maker]

You need to understand what the graphs are all about. Maybe you can find some online guidance, but I recommend you get yourself a copy of the "Loudspeaker Cookbook" by Vance Dickason.

I've had a thumb through of that on Google Docs, it's just too much information for me.

 

[Dee J]

Speaker tech seems to have advanced a lot in the last couple of decades. The Bose soundlink mini seems pretty good from what I heard of one recently. I'm still in retroland here with a NAD amp driving a couple of Dynatron crates. Still got a couple of big KEFs around, but we blew the cone on one of those!

 

[Maker]

I know someone with a Bose and it's very nice but so expensive.

 

[the snooper]

A speaker at rest is in the mid position, surely, so in a normal two housing set up it doesnt matter if they are both wired up 'backward' they will still work exactly the same. Aspeaker makes noise when it travels in either direction all it is doing is moving air.
Having them out of phase in one housing would be helping each other to get the maximum air moving which should increase the punch IMO.

Quote from speaker phasing
When two woofers are mounted in the same enclosure and one woofer is inverted, you would need to wire it “Out of Phase” in order to make the sub perform correctly. When the woofers are pointing in different directions, and one is out of phase, the cones will then move together and not cancel out.

Speakers wired the wrong way round can damage easily, when wired correctly and it reaches its maximum excursion the spider will stop the travel and the coil is leaving the magnetic field wired wrongly the coil is pushed backwards on each beat which it is not designed to do and the former gets a bashing when it bottoms out there are plenty of pictures on the net with this type of damage

 

[Dee J]

Speakers wired the wrong way round can damage easily, when wired correctly and it reaches its maximum excursion the spider will stop the travel and the coil is leaving the magnetic field wired wrongly the coil is pushed backwards on each beat which it is not designed to do and the former gets a bashing when it bottoms out there are plenty of pictures on the net with this type of damage

Well I never knew that... What about AC driven speakers... Either tranformer coupled or driven by a push-pull amp - where positive and negative voltage excursions are equal... Are there special speakers for those applications?

 

[richie00boy]

Speakers wired the wrong way round can damage easily, when wired correctly and it reaches its maximum excursion the spider will stop the travel and the coil is leaving the magnetic field wired wrongly the coil is pushed backwards on each beat which it is not designed to do and the former gets a bashing when it bottoms out there are plenty of pictures on the net with this type of damage

Sorry but that is nonsense. Speakers are AC devices, i.e. move forwards and backwards around a central rest point. Each "beat" will make the cone travel out then in (or in then out if wired the other polarity).

 

[richie00boy]

Quote from speaker phasing
When two woofers are mounted in the same enclosure and one woofer is inverted, you would need to wire it “Out of Phase” in order to make the sub perform correctly. When the woofers are pointing in different directions, and one is out of phase, the cones will then move together and not cancel out.

I don't know where you got that quote from, but it is wrong. Especially when talking about bass reinforcement where the wavelengths are very long. Think about the effect on the room pressure, after all the speaker is basically a piston firing into the room.

 

[Maker]

Would a Siemens TCA 2456 be of any use, I happen to have one. AFAIK, it's some kind of amplifier. I also found a crap load of opto-couplers, reed relays and logic gates too, plus loads more I haven't Googled yet.

 

[normspanners]

I don't know where you got that quote from, but it is wrong. Especially when talking about bass reinforcement where the wavelengths are very long. Think about the effect on the room pressure, after all the speaker is basically a piston firing into the room.

Surely if the speakers where in a sealed tube and both facing outward, unless you wanted the speakers to compress the air inbetween to create a 'bounce' effect due to air pressure in the tube, which would require massive wattage they would have to work in harmony ie out of phaze but in mono therefore assisting and complimenting each other.
The combined thrust applied by two pistons has to be greater than one, and therefore with a battery power ie low output set up would increase the drive.
Have the speakers 1/3 ish down the tube to create a slight lag from the sound from the long side??

quote

To answer your question, let's look at some scenarios.
1. A standard rectangular box with both drivers located on the front. Both drivers should be wired to be in the same phase as the other. So, as one moves outward so should the other.
2. A standard rectangular box with one driver on the front and one driver on the back. The drivers should be wired 180 deg. out of phase so that as one moves forward the other moves backward. If you were to look at it from above, both drivers are actually moving in the same direction at the same time.
3. A tubular enclosure with a driver at each end. This works the same as #2.

What it all boils down to is that the drivers mounted to the enclosure should move in the same direction at the same time, regardless of box position.

 

[normspanners]

One of my amps has an inversion switch so that you can alter the phasing of each channel to 'tune' the system if there is a lag for any reason. but that is purely for the improvement in sound quality
therefore normal (ie single driver vented) speaker damage, cannot occur. IMO

Absolute Phase:
A Prerequisite To Optimum Performance

The making of records is a very complex process involving a bewildering quantity of electronic equipment, each possessing the potential to manipulate phase. The microphone, cables, mixing console, tape machines and the myriad of signal processors (delay, echo, reverb, equalizers, limiters etc., etc.) could each be wired out of phase with respect to one another. In addition, smaller phase errors (several degrees here and there) may occur within the electronics of any of these components. Finally, your stereo system may perform tricks of its own to further complicate the issue. Many tube preamps for instance, invert phase. Often this occurs only in the phono section, which puts the turntable out of phase with the line sources. So, after the original signal has traversed its' long and complicated path, it may arrive at your ears out of phase with the original musical event.

How do we know which orientation is correct? A trial and error approach is really the only way that we can determine proper orientation. If a phase reversal switch is not available on the preamp, one must invert phase at the amplifier or speaker terminals. In an LP-only system you might chose to reverse the leads at the rear of the phono cartridge. Remember that inverting phase at the amplifier terminals will change the phase for all sources. This may or may not be correct. For instance, if as described earlier, your preamp inverts phase of the phono section only, then swapping the phase at the speaker terminals corrects the problem for the turntable, but inverts phase for all other sources.

What happens, sonically speaking, when our system is out of phase? Most listeners experience a constricted soundstage with a pinched center-image and reduced lateral spread. In phase, the soundstage will open-up, giving a more rounded feel to the center image, and offer a more correct presentation of depth.

 

[normspanners]

SORRY TO GO ON ----BUT

I don't know where you got that quote from, but it is wrong. Especially when talking about bass reinforcement where the wavelengths are very long. Think about the effect on the room pressure, after all the speaker is basically a piston firing into the room.

http://www.danmarx.org/audioinnovation/theories.html

Compound or Isobaric - Dual Drivers

Basic Theory

​

Two drivers are mounted together in an enclosure with a cavity of air between the two drivers. The drivers must operate in phase with each other. The cavity of air between the drivers should be made as small as possible without compromising the operation of either driver. The modeling for this type of enclosure is done just as you would any other speaker enclosure except you take the Vas of the driver and divide by 2. This will in effect make all your speaker enclosures half as big as they would normally be for any particular driver.
Advantages Improved sonic bass response. Bass is claimed as being tighter, faster, more accurate and more pure. Vas of the driver is cut in half. The volume of enclosure required to obtain a specific frequency response can be achieved in only half the volume. This is where isobaric enclosures have their biggest advantage.
Disadvantages Wasted amplifier power to driver the internal sub. Efficiency of the system is down 3 dB as compared to a single driver due to the added cone mass and the reduced Vas. When you compare isobarics to a system which houses two drivers each in their own enclosure, this system wis actually 6 dB less efficient.
Best Applications Where size is a big issue. When you want the box to be very small. Where more accurate bass is more important than lots of bass. If you have a hefty amplifier with plenty of juice to spare and a driver that can handle a good amount of power. Suited for music, home theater and car. Not used too often these days.

so working on that basis if the second speaker was facing the other way it would have to be out of phase electrically to be in phase mechanically.

Isobaric Subwoofer Design
The flagship of the a-Class subwoofer family, the formidable as-418 installs four custom-engineered, 18-inch drivers into a compact enclosure comparable in size to most dual-18-inch subwoofer designs. Drivers are configured into a pair of front-to-front, isobaric (push-pull) configurations. The direct radiation from each front driver is combined with the output of the companion rear driver in a tuned vented enclosure. This Compound Force design enables more output and less distortion, while at the same time delivering four 18’s in an enclosure no larger than a typical dual 18-inch subwoofer.

This is not a new concept, having been originally introduced by Harry Olson in the early 1950’s. Technically, “isobaric” is not really an enclosure type; it is a loading method. This loading method involves the coupling of two woofers to work together as one unit. This is typically accomplished either by placing two woofers face to face or by coupling two woofers with a small chamber. The result of coupling the two speakers is that the coupled pair (iso-group) can now produce the same frequency response in half the box volume that a single speaker of the same type would require. For example, if a speaker is optimized for performance in a 1 cu.ft. sealed enclosure, one iso-group of the same speakers can achieve the same low frequency extension and overall response characteristics in a 0.5 cu.ft. sealed enclosure.

 

[richie00boy]

Yes, that is correct. The back-to-back (or front-to-front) and out-of-phase scheme also has the advantage over the first one shown in that cancellation of even harmonics takes place.

It is a technique used to double the moving mass of the speaker and therefore get lower response frequency/box size.

It did not appear to me though that this is what you were suggesting, it seemed you were describing a tube where both drivers were exposed to the outside room.

 

[richie00boy]

I've had a thumb through of that on Google Docs, it's just too much information for me.

The problem is that loudpeaker design is a complex subject and the design is always a trade of compromises. You can't expect to produce a stunning design in a couple of weeks.

One book I found useful in my early days was "Designing, Building and Testing Loudspeakers" by David Weems. This is a simpler and smaller book which you may find more accessible. It just covers the basics, there are some gaps but it is a very good start.

 

[normspanners]

It did not appear to me though that this is what you were suggesting, it seemed you were describing a tube where both drivers were exposed to the outside room.

My idea of design using 6inch plastic pipe and car speakers for cheapness and simplicity

bass drivers would be in mono but out of phase electrically in phase mechanically
The thing is all this apart from the amp can be sourced second hand
to stay in with your £20

 

[Maker]

I've seen so called Gainclone amplifiers made from LM3875 or similar chips, to my untrained eye, they seem perfect for me. What do you think?

The problem is that loudpeaker design is a complex subject and the design is always a trade of compromises. You can't expect to produce a stunning design in a couple of weeks.

One book I found useful in my early days was "Designing, Building and Testing Loudspeakers" by David Weems. This is a simpler and smaller book which you may find more accessible. It just covers the basics, there are some gaps but it is a very good start.

I know there's a lot to it but I'm not expecting an absolutely amazing speaker. Would it be that bad if I don't do any anything fancy to the case, just make a box to hold everything with two big holes to poke speakers through?