What's The Importance Of 30hz?

[Andy Westcott 0]

Question:

How important is a decent response to 30Hz with modern music?

 

Personally I like hearing these ultra-low bass frequencies on the odd occasions they occur, and believe they add a dimension to the music not often heard from a typical mobile disco setup - I enjoy feeling the floor shake!

 

I pose this question because I am in a bit of a dilema - look at the two graphs of computer-predicted responses below:

 

http://myweb.tiscali.co.uk/andyspatch/hosting/graph140.gif

http://myweb.tiscali.co.uk/andyspatch/hosting/graph280.gif

 

As you can see the first graph's response 'turns' at about 50Hz, but the design exhibits a slightly higher efficiency. However, response at the deeper bass frequencies falls of considerably to the point where at 30Hz the response is almost -12dB.

 

Compare this to the second graph where the resonse is pretty flat to 30Hz throughout the sub-bass region, although is about 3dB down overall as compared to the first design - this is what I currently use.

 

These differences were implemented by changes in cabinet volume and appropriate porting.

 

The plan, should I eventually go for the higher efficiency design, would be to stack a pair of bins each side, giving me a massive power handling capacity - double the present rating, and a 4 ohm load as well.

 

So - if you were designing a new PA system, would you go for efficiency and sheer decibels and sacrifice the true sub-bass, or accept a bit of an efficiency loss and keep the extended response?

[Spear 0]

One way to look at it is simply that if you go for quality then you can always use higher rated drivers to compensate for the efficiency loss.

Then you could have Dido's Here With Me shaking the building to the foundations

[dh140770 0]

So - if you were designing a new PA system, would you go for efficiency and sheer decibels and sacrifice the true sub-bass, or accept a bit of an efficiency loss and keep the extended response?

 

The top design effectively tails off at about 40hz compared to around 31hz for the same levels. It really depends what type of music you are playing but personally I would go for efficiency. I don't play much Drum and Bass so those low frequencies are few and far between and an efficient 40hz would do what I play justice anyhow.

 

Having briefly looked into speaker designs before, i'd reckon the lower of the 2 designs is bigger in terms of size? and i like to keep the units small if I can so they eliminate the need for me to buy a trailer.

 

Personally, I'm starting to become a big fan of the active designs as they really are designed to match amp and speaker perfectly. Put years of research into enclosure design into the equation too and they really become a viable solution. Built in redundency too, as if one side fails, the other carries on. Certainly the ones i've looked at seem to favour size and efficiency over bass extension too.

 

[Andy Westcott 0]

Yes - the lower design is pretty large: 280 litre cabinet, the ones in my photos if you've seen any of them.

There are odd occasions where deep bass notes appear, and I am reluctant to lose this but I do find the extra efficiency and power handling of the smaller - but doubled-up - design appealing.

 

However, it wouldn't be practical to EQ the smaller cabs to reach 30Hz as there is very little loading on the diaphram at those frequencies and damge due to over-excursion would be a possibility at high levels.

 

So - the question remains for all to ponder:

Is a good response to 30Hz a useful thing to have, assuming you have the means to transport the cabs?

Is it better for (appropriate) audiences to be able to feel the thump of the dance music as well as hear it?

[Dukesy 0]

So - the question remains for all to ponder:

Is a good response to 30Hz a useful thing to have, assuming you have the means to transport the cabs?

 

Sure, why not.

Being nosey, what make of drivers do you have?

 

Is it better for (appropriate) audiences to be able to feel the thump of the dance music as well as hear it?

 

Probably unlikely for the local OAP home to 'give it large' on the dance floor...with the exception of course to the Cocoon brigade, but if the 'appropriate' demand is there, then of course! Go for it! smile icon

 

[Andy Westcott 0]

I don't mind anyone being nosey. smile icon

 

Bass drivers are Fane, as are all the drivers in my PA.

The specific drivers currently being used in the bass bins are the Colossus 18XB.

Good quality drivers, good & heavy, seem to be well-built and capable, rated at 600 watts AES and well suited to large volume cabinets.

 

Not sure whether things have changed quality-wise since they were taken over by Precision Devices as my purchases were pre-takeover.

[norty303 0]

Personally i'd go for the smaller more efficient design. Despite what people think, DnB doesn't have that much low content beneath 40hz. The smaller design will sound better to as the group delay will be less (the graphs should bear this out)

 

I'd be looking at some of those other graphs at this point, particularly the excursion one. If you have low excursion at rolloff/port tuning then you can get away with boosting the low end to increase the gain in this area. It's how a lot of bigger manufacturers cheat with their own dedicated processors. Using something like an Ultradrive/Driverack you should be able to accurately dial in a low shelf. I'm not sure if you're using BassBoxPro but you can simulate gain at points across the range to see what effect it has on headroom/xmax.

 

Also critical in this is the use of a steep high pass filter at the correct frequency.

 

 

P.S. oh, and also from experience, we do mainly specialised dance events, we are yet to find a good 40hz box unsuitable. Don't forget that the box doesn't stop at 40hz dead, you will hear quite a bit below this anyway. I suppose you could play a 33hz sine through a neutral box and hear how it sounds, and then decide if you need to hear/feel that content. In listening tests we've found that people think sub notes are lower than they actually are (e.g. 50hz - 'ooh, thats low, ooh get that!' etc

 

Personally, I'm starting to become a big fan of the active designs as they really are designed to match amp and speaker perfectly. Put years of research into enclosure design into the equation too and they really become a viable solution. Built in redundency too, as if one side fails, the other carries on. Certainly the ones i've looked at seem to favour size and efficiency over bass extension too.

 

Perhaps at the top end of the market they are finely matched - elsewhere generally a regular passive box with an amp module put in it (often with the requirements of price and wattage being foremost, over quality/durability)

 

I'm not sure how having an amp break leaving the enclosure useless is redundancy? Having an amp break and being able to connect another still working amp channel to the enclosure is redundancy. Separate components will always be more flexible than all in one units as the options for connection them together are greater.

Edited February 7, 2008 by norty303

[Andy Westcott 0]

It's true what you say about peoples' perceptions of the 'deepness' of bass notes - a 50Hz fundamental is a pretty deep note in itself, although there are occasions where true deep notes occur: I have several tracks with good content at around 35Hz, although as you mentioned, this would be reproduced fairly well by a 40Hz cab.

 

But thanks for your comments - it was remarks like this I was looking for as you have had experience with the smaller cabs and not found them wanting too badly. You see - what I don't want to do is invest a lot of money & time in building a quad of subs only to be disappointed by the performance.

 

Incidentally, the program I used for these simulations was WinLSD Pro alpha. Not a bad little program but it does have an issue with the algorithm used for calculating port lengths, which are shown incorrectly: I discovered in practice you need to look at the impedance graph and tune the actual ports to produce the dip at the same point as the program suggests, then it's correct.

 

Whatever it's a lot easier than pencil and paper, which is what I've used in the past before I entered the computer world. smile icon

 

Anyone else with thoughts on 30Hz and the importance (or otherwise) of being able to reproduce notes this deep?

[norty303 0]

We had a similar thread on speakerplans about going low and loud and the FK1 Infrabass was touted as an example. However it does use a very specific OEM driver to ge the results. Not many companies make an off the shelf driver with the require T/S because there's simply not much desire for it. Also, its a one trick pony, it really needs a bass box above it to provide the definition and punch.

 

The most novel, and probably likely approach to making lots of noise down low without blowing the bank?

 

This came from Rog Mogale, the Void Acoustics designer who said he would build a load of small 12" 6th order bandpass boxes and stack them all together. Apparently size for size, weight for weight, amp power for amp power, this combo would blow away every other type/config of cab and driver you could throw at it.

 

Given the time and money I'd love to try something like that because its both portable and scalable. Get 1 decent amp that will drive 2ohm loads comfortably and you're away. 8 cabs per amp, 2500w per channel. Nice! :)

[dh140770 0]

OK. I know this isn't car audio but this made me think of something i saw once on Pimp My Ride

http://www.mtx.com/caraudio/products/enclo.../jackHammer.cfm

 

I'm sure one of these would be enough for your need, check the power handling, but you might have problems getting it around as the driver alone weighs 369lbs!

 

Enjoy!

[norty303 0]

The jackhammer is a load of rubbish from a pro audio perspective. Whilst it might have massive power handling the sensitivity is waaaay down thus making that power handling figure a requirement.

 

The best drivers are those which make the most noise with the least input. Thats why Tony Andrews has 400w drivers in his bass bins.

[nigelwright7557 0]

I like plenty of bass so use 15 and 18 inch speakers which go down below 30Hz.

I also use a box with 6 tweeters in it to make sure I get a good range of sound spectrum too.

 

I use folded horn speaker boxes to get better efficiency.

 

Folded horn sound good but due to it being a box within a box the woodwork can get a bit heavy.

Useless for stairs so I have a couple of 2*12 cabinets which arent folded horn for gigs which are harder to get into.

 

Havings said that bass bins can be big anyway to get the required volume to work properly.

 

[norty303 0]

I also use a box with 6 tweeters in it to make sure I get a good range of sound spectrum too

 

How does having lots of the same type of speaker make the range of the sound spectrum any greater? Surely it just makes the frequency they play in louder?

 

Also, judging by the numbers involved you're probably referring to piezo tweeters, which are not reknowned for their audio quality, especially when used as most companies implement them (using natural properties of piezo to control frequency response) they can be good for adding 'fizz' but are inadequate when trying to reproduce the upper midrange as they are so frequently asked to do.

[Andy Westcott 0]

Those piezo tweeters are a strange thing really;

Everthing points to them being a fabulous invention, and yet they still don't seem to have managed to squeeze any decent efficiency out of them.

 

And they are so electrically fragile:

I used to use a 50 watt valve amp many years ago, and my first build did incorporate some of these tweeters. Unknown to me at the time, the amp was oscillating at about 25 - 30KHz and this rapidly saw off all the tweeters. The actual output couldn't have been more than a handful of watts at this frequency and it certainly didn't affect the audio at all, but it was enough to cause the tweeters to fail open circuit. I'm assuming this was the reason, anyhow. A dynamic device would (and did) survive this.

 

Anyhow - back to 30Hz:

I suppose the best way to operate this low down would be to have bass cabs designed to maximise efficiency between say 50 and up, and have a seperate large cab tuned low just for reproducing 25 - 45Hz. Trouble is, that's a lot of amps and cabinets for a mobile setup!

 

I'm still toying with the idea...

[norty303 0]

I think you've got 2 choices really if you want to retain any sort of efficiency - which one will depend on how loud you need to go.

 

You can go the wide-bandwidth route with a reflex box tuned to about 35hz, and get something that will play up to 200hz or so if you're lucky and spend a good amount on a decent driver.

 

Or you can go the 2 way bass route with a dedicated low frequency box, either 4th or 6th order bandpass design with a short horn box to play above it. this way you get maximum efficiency in each bandwidth and the capability to go very loud and clean if neccessary.

 

If you go the 18" short horn route a lá FK1 F218 or turbo 218 then you sacrifice some low end for good efficiency in the 45 - 140hz bandwidth. As a good allround box i'd probably build single 18" short horns/bandpass horns for my next system rather than the 2 way bass setup i have currently.

[Andy Westcott 0]

I like the idea of a 6th order bandpass box, but the design and dimensions are so critical that I'm not sure that it is really a DIY job - I certainly haven't designed anything like it before and trial & error are not an option.

 

Judging by the replies to this thread, not many people have any interest in going as low as 30Hz - maybe I shouldn't chase the unnecessary either. I'll have to stick with my current cabs a bit longer anyhow - give myself time to decide; At least there's a fair bit of power handling capacity available for boosting up on the inefficiencies, although the dip in the mid-bass region is there due to a massive rise in impedance, so the amp & speaker aren't really loaded anyhow.

[norty303 0]

BassBoxPro6 does a pretty good job of modelling BP6 and BP4 cabs, so it shouldn't be any great difficulty for you to work one out. After all, its just 2 reflex boxes joined together at the baffle. Standard tuning rules apply. If you don't have BBP6 I might be able to point you in the direction of a copy, although there's a few floating round the place if you know where to look. I modelled my cabs in BBP6 and got a plot pretty similar to the measured output from Beyma so its not far off.

 

TBH though, if you want a well trusted BP6 design that plays flat to 30hz at high level (4 cabs gave 144db at 35hz at a sub shootout 2 years ago) then the X1 on speakerplans is your box. It's been resized into a few different variants so it sits better under a range of cabs, one will probably fit your needs. 1 thing tho, small it ain't and it uses a range of drivers, most of which are £200+