Can someone explain the theory behind "sound reinforcement drivers"?

[mrfeedback]

"Unfortunately thats also what guitar-players, drummers, soundmen etc prefer our instruments to sound like !"
.......But not all soundmen.
The sound I do on Friday nights has all the LOW bass you could ever want, but not that sternum rattling emphasis.

Shirts, trousers, soles of the shoes rattle, but none of that peaking around 60-80 Hz that Grey mentioned.
Moving 20, 25 or 30 Hz graphic faders by 1 dB or less is clearly aparrent.
Fine tuning eq's can deliberately add slight emphasis to any particur area of the body from the chest all the way down to the shoes, and getting audience buzzing around the groin area gets the whole room bopping everytime.

Eric.

[phase_accurate]

Hi Eric

I didn't want to insult anyone. Not all soundmen have bad taste of course, but still too many unfortunately.

BTW: The first live-gig where I heard REAL bass was twenty years ago with the British band Shakatak, playing over a Meyersound P.A.


Regards

Charles

[mrfeedback]

No insult taken.

Eric.

A Dire Straits show I saw 20 years ago had serious low bass too.
And a AC/DC show that I worked too - that rig was all Meyersound and one of the best sounding systems that I have heard - lows, mids and highs were all great.

[kelticwizard]

Synergy:

Thanks for the tip on the Precision Devices-I had heard of them but never checked them out.

Just saw one model-the PD152. Once you get past a little discrepancy in their stats-resonsnce frequency is listed as 45 Hz in one place and 40 Hz in another, it looks pretty good Thiele-Small wise.

The response gets kind of ragged over 800 Hz, or so, but this is meant for bass guitar anyway. BK electronic sells them for the equivalent of $160, once you eliminate the VAT.

Put into an 3 ft³, (85 liter) box, it should yield an F3 of 45 Hz-significantly closer to my goal of 42 Hz than other drivers come.

The hitch is the Qts of 0.269. Too low to give a smooth response. That is the problem with the McKenzie as well.

There is a possible solution. This is the Augmented Passive Radiator enclosure invented by Thomas Clarke in the 1970's. Been meaning to build one for some time, haven't gotten around to it. He write two articles, complete with index, equations, etc for the Journal Of The Audio Engineering Society in the seventies.
Here are some posts on the Augmented Passive Radiator System:http://www.diyaudio.com/forums/showt...2564#post82564

Although the illustration would seem to show diffuculty in using this for a bass cabinet, I believe it can be constructed. The Large external PR would be on the back of the enclosure.

This is supposed to match most any speaker to any size box with a 3 dB advantage. The 3 dB advantage can take the form of ¼ octave lower F3 or the same F3 as a ported box of similar size but with a 12 dB instead of a 24 dB rolloff.

Stephen D:

Thanks for the update on the bass situation. Still, considering that most 3 Ft³ cabs have an F3 of 60 Hz, (albeit with a lower Fb), I still think that a cab with an F3 of 42 Hz or so is a step in the right direction. 30 Hz F3 in a cab of 97 dB@1W/1M would appear to be out of reach with an unequalized 3 Ft³ cab, at least for now.


Grey:

Are you saying the simulations are not correct-yes, I know the room throws everything off anyway-or that there is more to this than looking up the free air resonance of the driver, sticking it in any size box and expecting response down to the Fs?

All I am asking is that if we simulate a speaker/box combo and it shows the F3 at a certain frequency, do we have a fighting chance of it actually going down and acheiving that F3 in a real world situation, understanding the enormous variations room-to-room?

[GM]

>Low Fs looks good in simulations, but does not equate to flat response in the real world, witness the Shiva/Titanic/et. al. Fs for these drivers is typically in the teens to twenties, depending on driver and version, yet not one of them can reproduce anything like flat bass without eq.

====

True, but it has absolutely nothing to do with their low Fs, only their high inductance. Cancel it out and they will perform as predicted.

GM

[Stephen D]

"Yes, it's quite possible to rip a cone loose from the basket. But that's not necessarily saying that it was playing a deep note at the time--just a loud one."

True, but most often it is the result of notes that are far enough below the port tuning where the port & spkr are out of phase & the spkr moves wildly from the unloading with little to no effective SPL output. I've seen it to many times to count. Even just last week a kid brought his Bass combo amp to me thinking there was something wrong with his amp because it made this loud clicking
sound every time he played the bottom few notes on his low B string (5 string bass). Well. he was just hearing the speaker slapping against the back plate. He wasn't playing loud. It was just a cheap combo bass rig with a 15" in a ported cab with a
port tuning to high (About 50 Hz I'd guestimate).

Originally posted by kelticwizard
Stephen D:

Thanks for the update on the bass situation. Still, considering that most 3 Ft³ cabs have an F3 of 60 Hz, (albeit with a lower Fb), I still think that a cab with an F3 of 42 Hz or so is a step in the right direction. 30 Hz F3 in a cab of 97 dB@1W/1M would appear to be out of reach with an unequalized 3 Ft³ cab, at least for now.
[/B]

Agreed.
I didn't mean to imply that the goal should be to achieve an F3 down to that lowest B on a 5/6 string bass. Just think it needs to be taken into consideration when choosing ported spkr/cab alignments & at least shoot for alignments that allow low enough port tuning to offer some protection against over excursion from sub port tuning frequencies. I try to keep port tuning less than a half octave above the lowest rational frequency expected.
I think F3 of 42 Hz is an amiable goal as long as the Fb is well enough below that (as I said at most around 36 Hz). The ported subs I'm currently building for my bands small club gigging PA have an Fb of 36 Hz & a calculated F3 of 39.4 Hz. I think it's a fair enough compromise.

PS. That PR looks interesting.

[GRollins]

Wizard,
Sad, but true. The Thiele-Small parameters are way, way too simplistic to give a good estimate of real response once the driver is bolted into the cabinet. Then the room complicates things even further. But the T-S calculations barely get you out of the starting gate.
Any more, I build a test chamber of the same volume and configuration as the final cabinet I intended to build when I started, then test the response. It's enough to drive a man to drink. I don't blame the T-S model, per se, it's just that it doesn't cover enough factors.
This is why speaker companies have test equipment. If it were as simple as a few equations in an Excel speadsheet, no one would buy commercial product. Yes, yes, I know...not everyone owns a table saw, etc. but out in the real world T-S is only half, if that, of what you need to get flat response.
Beg, borrow, or steal some test equipment.
Then be prepared to cry real tears.
Eric,
Yeah, I vote for the groin effect.

Grey

[mrfeedback]

Originally posted by GRollins
Eric,
Yeah, I vote for the groin effect.

Yeah, when I get this happening right, I get very friendly babes coming up to the desk and telling me how much they are liking the sound. .

Eric.

[phase_accurate]

I think F3 of 42 Hz is an amiable goal as long as the Fb is well enough below that (as I said at most around 36 Hz). The ported subs I'm currently building for my bands small club gigging PA have an Fb of 36 Hz & a calculated F3 of 39.4 Hz. I think it's a fair enough compromise.

I assume that you are using 15 or 18 inch drivers for you P.A. subs. So your 36 Hz tuning is O.K. to me. But I don't think a 36 Hz tuning would be good for a 4x10" bass-box since you won't have enough excursion control between 40 and 60 Hz. In this case a tuning over 40 Hz and the use of a highpass filter would give better results IMO.

Regards

Charles

[Stephen D]

Originally posted by phase_accurate


I assume that you are using 15 or 18 inch drivers for you P.A. subs. So your 36 Hz tuning is O.K. to me. But I don't think a 36 Hz tuning would be good for a 4x10" bass-box since you won't have enough excursion control between 40 and 60 Hz.

Enough port air support for excursion limiting of the more used 40 - 60 Hz range was also a concern to me & is why I also chose 36 Hz as the lowest freq I was willing to tune to for this project. I'm actually using a pair of 300 watt 12" Pioneer car subs for one cab since I had them & they are a little higher efficiency than typical of comparable 12" car subs with a pair hitting about 94dB 1w/1m & they have 8.4 mm linear Xmax so they should do OK for this small club venue application though not really a candidate for pro sound reinforcement like being discussed here. We have some
JBL 4530 scoop cabs & some 18" ported cabs for our outside
& large venue gigs but needed something smaller for some of the smoky little bars we do. I still have to come up with one more small to medium size cab for this small venue rig. One candidate
is a 4x10" using the Dayton Quatro 10's. They have an 8 mm Xmax & model pretty well with a 36 Hz tuning in roughly 3.5 cub ft.

For this small venue application I can get by with medium efficiency long excursion drivers but moving to high efficiency drivers for large venue applications it becomes difficult as you
suggest to utilize that lower port tuning as the excursion on
the smaller high efficiency drivers is generally to low except for
the most expensive drivers.