Might as well post a system i built

[noodle_snacks]

Here is the PA System i built:

http://img155.imageshack.us/img155/9910/p1030833croppedresizedlh5.jpg

The bottom, horn loaded subwoofers are not my own design, however the tops are, i used computer based measurement equipment (including a microphone) to design the crossover. I drive the tops with about 150wrms a side, and the bottoms with 450wrms a side and they can be heard from a kilometer away with surprising clarity (they are 98db efficient). Ask me if you want more details on the design of the tops, The sub design can be found at http://diy.cowanaudio.com/. (http://diy.cowanaudio.com/) I carpeted all the boxes (big job!) and but the aluminium edging on the bass boxes to protect them a bit. To give some sense of scale, those subs stand about a meter high (900mm + 100mm castors). The rear chamber volume was scaled up, and simulated with horn resp to accomodate the 15in woofers i used.

[Cliff Rogers]

Hey NS, what is the screwed up bit of paper on the table next to the..... nah, only joking, nice job. :2tsup:

[Harry72]

Nice computer speakers mate!

[soundman]

the bottoms look like "S" bins.
Next time you build send me a PM & Ill point you toward some hardware to meke things easier.
Good job for someone who dosn't do it every day.:2tsup:

Carpeting boxes is hard work even when you do know the tricks.
A horn loaded mid high pack would be a better match for the "S" bins... but hell its good enough for party speakers:D :D

An associate of mine likes freaking out the young lads form his church.
So he invited a group of blokes over for a doom party.
Borrowed a projector
and set up
a pair of altec A7 ( voice of the theatre) cabinets (15 & horn, horn loaded) for left and right and a pair of 604 (15" concentric) studio monitors for rears
a couple of 500watt per channel amps.
Dave is about 60 and likes his computer games:D :D

cheers

[noodle_snacks]

Bottoms aren't S bits as such, they are actually horn loaded, designed to be placed together as one unit, firing into the wall, what sort of hardware are you talking about? Why would you say horn loaded tops would be a better match? Is it a directivity issue primarily? They are already about 98db efficient. They are peerless horn tweeters, power response is a bit dodgy (big dip at 2khz), but for playing drum and bass etc at parties it don't matter. I have my hifi rig for home.

That doom party sounds pretty fun, some of the sound effects are nice in that game.

[soundman]

The "S" bun is a horn loaded design originaly from JBL.Called such because of the (sort of) "S" shaped path inside the box.
Or they could be a turbo knock off... (I havn't chased the tread) the turbo design is much simpler... the driver loads from the side / bottom.

I've had systems with mixed horn and front loaded boxes and it always ends up a bit.... not right.
Yep its a directivity thing.
I come to think keeping the whole system as similar in technology as possible is the go.
I prefer to see the same brand or at least type of speaker thry the whole system.... it makes it much easier to ballance and tune the system.

As far as hardware..... there are whole catalogues of catches, latches handles, corners, extrusions........ for this stuff.
Then you start on the speaker components themselves.

One of the important areas is the aluminium extrusions..... the worst thing in the world is handling boxes that have been fitted with standard aluminium angle. When its been on the road a while it gets dinged & daged which raises nasty sharp burs which will open you up like a jam tin & rip big holes in your clothes.

The entertainmen industry extrusions are made of a harder compound and are shaped with rounded edges and don't seem to get anywhere near as hasardous.
combine them with sone good steel corners and its a much better thing.

Most people don't use extrusion on speaker these days. If you use good carpet and make your joins well off the edges there don't seem to be any problems.
Carpet has also gone out of favour in the last few years, heavy duty texture paint is now the finish of choice. Many of the brand name boxes are now comming with a thermoplastic coating, which is tough as.

Oh you need to spray up the open horn of the bass box... GMH flat black is the item of choice.

cheers

cheers

[soundman]

If the design is his horn sub jnr yep thats an "S" bin.

He's been having a good time knoicking off a couple of other designs too.:D :D

cheers

[noodle_snacks]

Heh, epic bump but, your only right about the horn subs, they were a design that suited what i wanted, I did play around with a few hornresp things and folded some stuff myself though, didn't building anything. I did state this in the OP. Where are you are quite mistaken is with the tops, as well as any other designs i have "ripped off". They are all completely of my own design :cool:. I have sound and impedance measuring gear, and use speaker workshop + other design type programs to design and testing things (plus my own ears!). Next time, read my post a tad more thoroughly and give credit where it is due.

I also hate to break it to you, but nope, its not a directivity thing. Thanks to the laws of physics surrounding waves, unless the mouth of the horn(s) or the distance the speakers are placed apart is large compared to the wavelength of reproduction, (or you have built a cardiod or dipole sub, which wouldn't have the output for pro audio, so unlikely to be the basis of your comparisons) then no, directivity and bass should not be applied in the same sentence. Unless of course you love high distortion or have things crossed too high for it to be considered a subwoofer, in which case the horn mouth or the distance apart could become significant.

Haven't had any troubles with the extrusions, but i probably only move them once a month or so. My biggest problerm in the design is the fact that i have used steel screws and aluminum haha , i reckon add a bit of salt water and i could get them to corrode away (can you say electrochemical cell!). Whilst I understand your point regarding jagged edges etc, there is also a large cost difference for the consumer when buying hardware built for a neiche market, such as speaker boxes.

[kiwigeo]

Nice speakers but I think you need to get a bigger lounge :D

[munruben]

Looks ok to me.:wink::2tsup:

[soundman]

Don't give me that old wavelength and directivity chestnut.
that one has been sprouted for years and has been proven to be only party ..... a small part true.
All horn loaded boxes exhibit similar directivity bahaviour to some degree or another and at frequencies far lower than the mouth/wavelength theory would sugest.

there is a lot more and less to horn theory than many would believe.
the turbosound bass device is proof of that fact.
orthodox horn and bass theory will tell you that it can not meet its spec's...... but it does.


as far as the knock off comment it was directed at the source of the "s" bin design.........I looked at the web site... long long ago..... and many of his "designs" I could have pulled straight out of books I have and are
recognisable as a previous named design.....with minor variations.

afterall, truly NEW speaker designs are a rare thing these days.

I still stand by my similar technology comment
you have a small "horn loaded" tweeter, a large front loaded bass driver on top of a folded horn loaded low bass cabinet...... of course there will be mis-matches.

dont get me started about so called subwoofers....... a true subwoofer also is a rare thing..........there is a whole range of failure to understand, BS, hocus pocus and superstition about bass and bass reproduction.

cheers

cheers

[noodle_snacks]

Don't give me that old wavelength and directivity chestnut.
that one has been sprouted for years and has been proven to be only party ..... a small part true.
All horn loaded boxes exhibit similar directivity bahaviour to some degree or another and at frequencies far lower than the mouth/wavelength theory would sugest.

there is a lot more and less to horn theory than many would believe.
the turbosound bass device is proof of that fact.
orthodox horn and bass theory will tell you that it can not meet its spec's...... but it does.


You quite obviously have a limited understanding of simple physics, and you are making it sound like others have tried to talk sense into you before. Believe it or not, horn theory doesn't actually have that much to do with the polar response of a bass horn. I suggest you do some reading about the Huygens-Fresnel Principle. As far as the room is concerned, you can treat the horn mouth as the source of the sound. Directivity is the result of the superposition of multiple waves with a fixed phase relationship. The phase difference determines whether the waves constructively or destructively interfere. Unless you are suggesting that for the frequencies of interest there are significant phase differences across the mouth of the horn, then for all frequencies of interest there will only be a few degrees phase difference from any two points at the horn mouth, so regardless of measurement angle you would get a very similar amplitude. Where the directivity of a bass horn may actually differ is with harmonic distortion, or any higher frequency stuff being erroneously sent to the speaker.






as far as the knock off comment it was directed at the source of the "s" bin design.........I looked at the web site... long long ago..... and many of his "designs" I could have pulled straight out of books I have and are
recognisable as a previous named design.....with minor variations.

afterall, truly NEW speaker designs are a rare thing these days.

You might pull your designs directly out of books, however it seems to me the designer of the bass horns had the sense to simulate his driver choices and fold the horn himself in order to get things right, it wasn't quite the copy & paste job you seem to make it out to be.


I still stand by my similar technology comment
you have a small "horn loaded" tweeter, a large front loaded bass driver on top of a folded horn loaded low bass cabinet...... of course there will be mis-matches.




Your "technology" comment doesn't make much sense to me. By your logic a PA speaker should have a tweeter with no horn assembly and a woofer, following this approach you would actually end up with a big directivity mismatch between the woofer and tweeter around the crossover frequency. The woofer would be beaming, whilst the tweeter would act like a point source. It is the defacto standard for PA speakers to use compression drivers and horns to control the directivity (and/or boost efficiency). Well designed hi-fi speakers use smaller woofers, and cross over low enough so that there is a minimal directivity mismatch again. A mismatch will result from poor system design, and isn't applicable to subwoofers anyway, unless they are crossed over high, in which case they are glorified woofers. If i were to follow your advice, I'd start using cone tweeters just to get a really good technology match with my woofers!

That said, there are most definately directivity mismatches between the tweeter and the woofer at the top end of the woofers response (For the top bins), I realised that this would be the case before construction, however the top speakers are principally for outdoor/boom box use, so off axis response to about 30 degrees is all that is important, I was not willing to spend the money on compression drivers and matching horns for the matched directivity with the woofers, as i use other speakers at home anyway.




dont get me started about so called subwoofers....... a true subwoofer also is a rare thing..........there is a whole range of failure to understand, BS, hocus pocus and superstition about bass and bass reproduction.


It seems to me that you seem to be full of BS, hocus pocus and superstition about bass and bass reproduction. I presume that "so called subwoofers" are those that don't reach 20hz (or below). I have both built and listened to a number of subwoofers, which have extension to at least 20hz, and are often equalised flat with a BFD or similar. The reality remains that the amount of material below 40hz is limited, especially for music. My own defintion of a subwoofer would be a speaker designed to augment main speakers at low frequencies, if it only goes as low as it's playback material requires, then it is still a "true subwoofer".

[soundman]

I see no sence in continuing any discussion with someone as disrespectfull as youself. regardless of the subject matter or the validity of the information.
I have no interest in anything you have to say.

Oh by the way I read no further than your insulting first sentence.

:Q:Q:Q:Q:Q

[Cliff Rogers]

Ring side seats on this one. :rolleyes: :D

Damn Soundman, I was just getting interested. :D

[Harry72]

NS dont believe 90% of the crap online about sound physics, most is just a bunch pedantic procrastinating antisocial loosers babbling on about something they've read somewhere online thats not actually true...

BTW, soundman isnt called soundman for no reason... its what he does, he's probably been doing it longer than you've been on the earth!

[noodle_snacks]

What i have been reading is actually quite sound physics, have a look for yourself:

http://en.wikipedia.org/wiki/Huygens'_principle (http://en.wikipedia.org/wiki/Huygens%27_principle)
http://en.wikipedia.org/wiki/Interference

Not stuff made up by as you so aptly put it "bunch pedantic procrastinating antisocial loosers babbling on about something they've read somewhere online thats not actually true..."

Profession or not, the physics is just plain wrong, otherwise there is no disrespect intended.

[Harry72]

Building speakers for home and pro sound reinforcement is like comparing a Porsche to a tractor.
One use's fineness to achieve nice sound the other use's brute power to go the distance.
Go along to a concert while setting up and chat with the sound guys and see how things are done in the real world(not the online one), you can use all the physic theory you want soon as a few people walk into the area... the physics change and keep changing and changing.

Yes physic's have a major roll to play but when the properties keep changing there's no controlling them(computer aid goes a long way now tho), thats why home speakers can be set up to sound so sweet using nearfield and diffraction/absorption techniques.

Have you used these speakers for sound reinforcement yet?
If Christiaan Huygens was around today you may well have a wave theory on variable sound fields, his mathematical genius was what 300+yrs ago... there was no speakers his theorems were based on naturally produced sounds. No speaker can produce real true life sounds yet, single driver designs are the closest so far.

[noodle_snacks]

Don't be so quick to assume I don't have any live sound experiance. I have been behind the mixing desk for a large theatrical production, and a number of rock concerts. I have been involved in the setup of many more. Just so you know i also have quite a few stereo and multi-track recordings under my belt as well (But i don't see that comming up). I have used my subs (and some better EV tops), in a live sound environment before, the set has recieved a lot of use at parties and the like.

You are correct in that the number of sabins in a room will change when people walk in and move around (i have textbooks with figures for this, but it really depends on what people are wearing). However I am principally disputing soundman's incorrect statement about the directivity of horn subwoofers. Because both front loaded and horn loaded subwoofers will have extremely similar anechoic directivity, the way their responses are effected in a room with all these changing variables would be identical, given identical placement. So whilst it is true room acoustics can get pretty complex pretty quickly, the point is moot as far as the directivity of the speaker is concerned.

[Harry72]

Playing with horn loaded sub placement in a large area/room, I've found that sub bass can directional depending on placement... try this in open air, face you bass bins forwards step back at least 20m, play some heavy bass dance music... then face them backward and listen from the same spot, guess what... no bass!
Now do the same set up with a conventional sub (sealed/ported/bandpass), it'll make very little difference as they are more omnidirectional.(no horn to guide the waves, hence soundmans comment)

[noodle_snacks]

Playing with horn loaded sub placement in a large area/room, I've found that sub bass can directional depending on placement... try this in open air, face you bass bins forwards step back at least 20m, play some heavy bass dance music... then face them backward and listen from the same spot, guess what... no bass!
Now do the same set up with a conventional sub (sealed/ported/bandpass), it'll make very little difference as they are more omnidirectional.(no horn to guide the waves, hence soundmans comment)

I will one up you on that, do it, measure the things and show you it is the harmonic distortion that is directional, not the fundemental. When i have them out of their hole again (won't be for a few weeks). I will have to find a car park or similar for a groundplane measurement.

[Harry72]

Cool, keep us posted on your results!

[noodle_snacks]

Checkmate :cool:

Had a party sooner than i thought, Here is the polar response measured every 30 degrees, outdoors using a swept sine groundplane measurement. The noise floor was approximately 50db below the the level of the measurement. The repeat count was set to 8 for maximum noise immunity. The center of the subwoofers was kept a constant distance from the microphone. As you can see for your self the subs are only beginning to show signs of directivity around 150hz. With the crossover in place this neglible amount would amount to zero.

Here are the measurements:


http://img245.imageshack.us/img245/2272/wcowanhornpolarresponsere2.jpg


And the same thing with traces seperated:
http://img297.imageshack.us/img297/310/wcowanhornpolarresponsemo3.jpg

[Harry72]

Just some questions on your findings :)

Distance was the mic set at?
What was surrounding the cabs?
Were there any walls or reflective surfaces?

Seems to be a steep roll off after 40Hz no matter what orientation.
How much equalisation do you use to flatten out the response(normally), between 75~85Hz you have a 4db drop after that it gets somewhat raggedy, the response from 40~75Hz is nice tho!
Do they exhibit these characteristics indoors?

[noodle_snacks]

Just some questions on your findings :)

Distance was the mic set at?

I basically followed Dr Joe D'Appolito's recommendations, The mic was placed around 2m, Further than he recommended, but i wanted to make sure i was in the far field. The mic was about 1cm from the ground. Using the formula in his book, this measurement would be accurate up until around 800Hz, more than enough for our purposes.



What was surrounding the cabs?

Grass, But the nearest thing was a tree at around 10m. Making the total path length difference around 20m, making any reflection from the tree down at least 20dB, when compared to the main wave.I made sure the subwoofer was rotated not the microphone, so the acoustics were not effected.


Were there any walls or reflective surfaces?

Well the ground, but that had no effect on the results, and the tree, which would have had neglible effect.


Seems to be a steep roll off after 40Hz no matter what orientation.

Yep, this does improve a bit with corner placement, (30-35hz is possible). With only one sub the response drops off a bit at 50Hz (like a shelf filter), then rolls off at 40hz, corner placement can fix this. The original design (see the link in the first post), states that its a 40hz horn.




How much equalisation do you use to flatten out the response(normally),

I have a BFD, and use that with my mic to equalise them to within 1-2db of flat. This frequency response measurement will be useful to set some default EQ for parties etc.



between 75~85Hz you have a 4db drop after that it gets somewhat raggedy, the response from 40~75Hz is nice tho!

Yep, it'd be interesting to figure out the cause, raggedy or not its still pretty insigificant when compared to room effects, and the humps aren't too nasty (+/- 3dB)


Do they exhibit these characteristics indoors?
Lower extension is possible, but you are at the mercy of room modes, but for the most part yes. Listening tests indoors of directionality indoors is not a good idea, there are too many reflections (at high frequencies), and standing waves to deal with (low frequencies)