Sub designers - what do you think

**joecarrow** · 28 September 2007, 10:13 Friday

You really can't trust in-room frequency response in the bass region as an indication of sub performance due to room interaction. You could move the mic, or move the sub, and get a wildly different response.

Bottom line- regardless of the measurements, if you're not happy with the sub then you're not happy with the sub.

A single 10" sub playing 2.5 meters away and hitting 90 db has its work cut out for it. The excursion is probably huge, and that "pop" you hear might be the sub bottoming out. That's really bad for the sub, so try not to turn it up so loud. If it's still not loud enough for you, move the sub closer to where you sit, or get a bigger sub.

**ThomasW** · 28 September 2007, 11:39 Friday

Us "technical guys" use pink noise to make measurements.

A set of measurements taken with the meter 1" from the cone, compared to a set at the listening position provides the best information.

http://home.comcast.net/~thomasw-2/SubwooferSetupandEQpage4.html

**Briz vegas** · 28 September 2007, 23:21 Friday

Thanks tech guys and particularly for that link ThomasW :T .

I thought the tech guy at work was saying nodes. seems the term is modes - my mistake. Unfortunately the meter was only home overnight so I can't really repeat the experiment.

I will make a couple of points in my defense.

1. I know what warble tones and white noise are - I assume pink noise is related to white noise. The sub plays my receivers setup tones and the stereophile warble tones at good volumes. I have no complaints there at all.

2. This problem arose when I was listening to the Ani Difranco track at a modest 70db. This is my preferred volume for most music. although occasionally I may creep up closer to 80db if I am being outrageous. The track is such a benign little number that I could not believe the sub was popping at a modest level - this was the start of my 4 month long quest for an answer - and I mean more than just "she's right mate"

3. To my mind the two most telling points are a) in a side by side test a similar Rel sub showed that this track can be played at much higher levels without breaking a sweat, and b) this track has very low frequency "stop start" content that is likely to be causing the popping.

Unfortunately I cannot easily do the measurement 1/2 inch from the dust cap (unless I can somehow borrow the meter again - tricky) however I do not think it is the room causing the very low frequency reading - if that was the case why was the dance track not giving the same result. Ok, that is obviously lay persons logic at work (the noise guys at work tell me that predicting and managing low frequency noise is a nightmare) but it does put up a hypothesis as to why the sub is popping.

I have pretty much decided that the sub is relegated to HT duties. I did buy it as a music sub two years ago but my preferences have changed in recent months as I now have a new very high quality 2 channel system. I may even exchange the REL for a bigger sub so that it gives more kick for the films - I have heard some Energy subs that kick like a mule, are clean and cost half the price. If I know the REL is not faulty then I can do the exchange - I would not feel right doing it any other way.

One more alternative- I know a guy who likes to build his own subs - I may just talk to him about building my own for fun.

**Dennis H** · 28 September 2007, 23:34 Friday

You haven't really explained what you mean by "popping." I suspect Joe has it right and it's just the driver bottoming with a metal on metal sound. If so, that's a good way to destroy your sub so stop doing that!

By the standards of this forum, a single 10" isn't really adequate for decent SPL for either movies or music so it's no surprise the sub is being overworked. We're multiple 15" kind of guys.

**JonMarsh** · 29 September 2007, 11:21 Saturday

there may also be a problem with the amplifier clipping- and further, some CD's will have "special effects" recorded in the bass, with subharmonic amplification, and may post a special challenge compared to more run of the mill cuts.

A really old example of this is "Dark Side of the Moon". There's a Sarah McLachlan cut that poses issues for some systems due to this. Depends on EQ, too, but your sub system probably doesn't use any boost. Then there's the old dynamic range bugaboo- a simple meter may not accurately show peaks, and they are the real torturous points because subs are quite dependent on Xmax and cone area to deliver, and a short term overload is an immediate mechanical overload.

If you're pushing a 10" sub to where you say it's rattling the house, you're pushing it way out of the comfort zone at low frequencies. Using Sigfreid Linkwitz's simple Excel spread sheet to calculate SPL capabilities as a function of cone area will tell the tale- while a 10" driver probably won't be Xmax limited for SPL above 60 Hz, below 40 or so it definitely will be, especially if sealed.

Guys here that are sub fans are usually looking o

**J-Dub** · 29 September 2007, 14:26 Saturday

I could see one of two things. "both mentioned before"

I listen to both electronic and acoustic tracks and had a similar issue with a computer sub I built. The driver was VERY small but suitable for near field listening. It was 5.25" but has a 9.2mm xmax. With all of that excursion the electronic bass is very smooth and clean but one time i ran across a track where the Bass drum kicked it past its limits and needed to be turned down immediately. The drum was obviously modified electronically but I dont think that was the culprit so much as the suddent jolt of the drum.

If you are planning on building a sub or having one built consider using a 12" at minimum or a 15". I have used the 12" peerless xxls and had similar issues at high volume. The Dayton Titanic 12" is a great driver but for the extra cash I prefer Sound Splinter drivers. You'll go def before you hear any popping out of those! They do require a lot of amp though.... which brings me to the next possibility:

As mentioned before the other may be the amp clipping. 150W for a sub isn't a whole lot but that all depends on the sensitivity of the driver. If you are listening to house shaking levels with a 150W amp it is highly probable the amp is clipping.

Thats my .2c Hope it helps!

**Briz vegas** · 29 September 2007, 21:36 Saturday

Thanks guys, very useful info.

I will stress once again that my experiment was to work out the performance limits only. I do not use my system in this way normally and in the experiment it was turned down as soon as any nasty sounds started.

The problem occurs at 65db. THIS IS NOT LOUD

In my test with the other tracks (and the movie) the sub was rattling windows but was not distorting, popping etc etc - It was working perfectly. I do not watch movies at this level, and I rarely rent action movies - 90% are rubbish. Live music video it about the only time I played the sub at significant volume.

By popping I mean instead of a solid "dud" sound its more like a sort of "plop" sound.

I think J-Dub is close to the mark - the kick/bass drum sound has been played around with on my problem track.

Thanks again for all your comments

**Kevin Haskins** · 29 September 2007, 23:44 Saturday

Its impossible for me to tell you exactly what is happening but my vote would be that your clipping the amp. If they designed it smart, they would design it to clip before it bottomed. If they use a little EQ on the bottom and a fairly cheesy underpowered amp you can get them to clip with the appropriate transient. Your measuring music which is not steady state. A test signal has a nice continuous output and you can get an accurate SPL reading from it. Music isn't like that... you get some frequencies played at higher levels than others. You can have a large transient in the bass that causes the amp to clip, especially since its only a 10" driver in a small sealed box with a relatively low powered amp.

**J-Dub** · 30 September 2007, 00:39 Sunday

I think J-Dub is close to the mark - the kick/bass drum sound has been played around with on my problem track.

I was just translating for Jon

BY JONMARSH: subs are quite dependent on Xmax and cone area to deliver, and a short term overload is an immediate mechanical overload.

sometimes these short drum kicks are pretty tough on a driver.

OK, My reccomendation if you are serious about audio and it sounds like you are, is to purchase a pink noise generator, a beringer calibrated mic and some software. You can get them from www.partsexpress.com

The guys here will tell you exactly which ones to get depending on your budget for measuring equip. You may also want to ask for the appropriate software everyone likes to use. You will be able to use this equipment for a lot more than just your sub.

Next you'll need to measure the frequency response and distortion of your sub. This will point out any problems at any particular frequency and allow you to make decisions based on the info.

BUT, before you do all of that, I will say this: If you aren't happy with the way it is performing, throw it in the guest room or give it to the kids and get you a new one. You'll be happier.

**Scottg** · 30 September 2007, 01:34 Sunday

Originally posted by Kevin Haskins

Its impossible for me to tell you exactly what is happening but my vote would be that your clipping the amp. If they designed it smart, they would design it to clip before it bottomed. If they use a little EQ on the bottom and a fairly cheesy underpowered amp you can get them to clip with the appropriate transient. Your measuring music which is not steady state. A test signal has a nice continuous output and you can get an accurate SPL reading from it. Music isn't like that... you get some frequencies played at higher levels than others. You can have a large transient in the bass that causes the amp to clip, especially since its only a 10" driver in a small sealed box with a relatively low powered amp.

I'm sure thats *exactly* what is happening..

Commercial sealed sub? ='s *boosted* lower freq.s

Boosted lower freq.s ='s *MUCH* higher demands for amplification at even low spl's.

Add in a significant transient (even only a few db more than the low average) and you have quickly exceeded the amplifier's capability. "Pop" goes the amplifier. 8O

**Briz vegas** · 19 October 2007, 03:08 Friday

Finally got some good professional advice

Finally I have a response that I am happy with, but no thanks to REL or the importer. An excellent local dealer was prepared to listen to what I had to say, do a few simple checks and tell me what they had found.

Now that I understand the issues I feel that the Strata 5 is a good product and mine is healthy - it turns out that my problem CD was simply putting huge demands on a relatively small sub by feeding it high levels of extremely low frequency information.

This is my understanding.........

My test with the professional quality SPL meter already gave an indication of the issue. The Ani Difranco track I had problems with was reading almost flat from 63hz down to 12.5hz measured at the seating position. It turns out that this is one of those rare legendary "system killer" recordings. If you have a system that genuinely goes down to 13 hz then this recording will be a huge headache unless you have huge headroom in your subs amp.

The tech guys played the track (why would no one else do this) and straight away the pop started - the amp was clipping. Why? - they fed it test tones and at 13hz the amp ran out of steam and control was lost just as it did with the Ani Difranco track. The little sealed sub had enough in the driver to deliver but the demands were too high on the 150w amp. The same track tripped up the Rels much bigger brother in the same way, and at not much higher volume. To be fair to REL, the track simply had bucket loads of very very deep bass energy that you simply don't normally find on CDs or DVDs.

DVDs, I am told, just don't have content below 34hz and CDs stop at about 28 hz. I am talking about what is actually put on the disk - not what is technically possible to put on the disk. For example the Jurassic Park dinosaur footsteps are up at 38hz (not talking about the harmonics which tend to be less of problem as there is typically less energy).

Unless I play Telarcs 1812 overture I am unlikely to experence this problem with any other source material. With 99.9% of content the Strata 5 is more than capable of producing plenty of quality bass to keep me happy.

**ThomasW** · 19 October 2007, 03:51 Friday

Originally posted by Briz vegas

DVDs, I am told, just don't have content below 34hz and CDs stop at about 28 hz.

This is incorrect.

Many action/adventure DVD soundtracks have very low frequencies, some as low as 5Hz. There are music CDs with 14Hz pipe organ notes and equally low notes from pedal synths. There's a CD recording of a Space Shuttle launch that has a 1/8th Hz sound during liftoff

**Briz vegas** · 19 October 2007, 05:10 Friday

But if one were to do a statistical analysis these examples would be the outliers on the old bell curve like my CD, No ? (honest question)

I have not done the research myself - maybe Dolby Labs can tell me different, but this dealers advice certainly seems to fit with my experience. ie it would explain why it took 2 years of regular use for me to find one track that the Strata 5 could not handle despite some occasional "enthusiasic" use on my part.

You would never sell subs if they sounded like mine did on that track. Commercial stuff may leave something to be desired but a business model for a commercial product will only stand up if the product can handle most of what is typically thrown at it.

DIY and purpose designed stuff provides the opportunity for perfectionists to design for the small percentage that leaves the off the shelf product gasping for breath, or for the true bass addict (which I am not).

I spent a night outside night clubs last year with a sound level meter as part of my work. The bass in those places slams you in the chest far more than ANY movie I have watched anywhere and its all at around 63hz. That was confirmed by guys that do this work every night of the week. I don't see what substantial output at 5 hz actually achieves. I also understand that power requirements basically get astronomical at these sorts of frequencies. On top of that the wave lengths we are talking about start to get pretty long also. Sounds like an audio nightmare to me. We had problems enough managing building design in environments experiencing sound in the 63 hz range.

**Brian Bunge** · 19 October 2007, 07:59 Friday

Having built a sub that would do 10Hz flat in room (in only an 18" cube!) I can tell you that it adds a level of articulation and realism that most commercial subs can't accomplish.

**ThomasW** · 19 October 2007, 10:19 Friday

Originally posted by Briz vegas

I don't see what substantial output at 5 hz actually achieves.

Tell that to the people working on the Foley stages containing 20 large Bagend subs putting these sound effects on DVDs.

On top of that the wave lengths we are talking about start to get pretty long also.

A full wavelength is not needed for 'audibility', this is why we can measure 20Hz, 1" away from a dust cap.

**1Michael** · 19 October 2007, 13:54 Friday

"and CDs stop at about 28 hz"
I don't know who told you this but I have a CD that is a 0-100Hz (thats Zero to 100) sweep that I use to break in my subs with, that works quite nicely.

**Dennis H** · 19 October 2007, 14:44 Friday

Support & Service FAQs | Best Bookshelf Speakers

http://www.svsound.com/questions-faqs.cfm#moviedemos

Get your speaker and subwoofer questions answered here. We'll help you find the best home theater system for your audio sound needs.

**Briz vegas** · 10 December 2007, 09:26 Monday

Thanks for the link Dennis. Well thats interesting.

Of course I am sure that if I asked the question at the dealers again they would clarify by saying that their comments were a generalisation and they were referring to high energy stop start bass at very low frequencies.

I have Das Boot and Contact. Rel passed with flying colours - go figure. In the past I have watched about 1/2 the movies on this list with no sign of problems.

**rc white** · 10 December 2007, 20:01 Monday

subs

The first thing that I noticed is that Briz lives in Australia.
Since most of Australia is semi to tropical houses tend to be open plan, flow through ventilation plasterboard walled creations that are difficult to set up a descent standing wave in, let alone pressurize. An Australian hi fi magazine tested some typical Australian houses some years ago and came to the conclusion that you might as well set your sound system up in the middle of a field, as it is much the same as the average Australian house as far as sound goes.

I know people who have built sub woofers along the room gain standing wave guidelines one normally finds on the net for Northern hemisphere conditions, only to find that gross overload and no real low bass to be the consequence.

I do not know if this is true in this case, however most people find that the frequency response in an open 2pi environment is the one that matters and this means a bigger and more expensive sub woofer for the same performance as your typical Northern hemisphere one.

The 63Hz. measurement is the standard punch peak, (some these days call it slam), you find in live electric music, it is cheaper and more compact to have mobile p.a. systems to do this and if you look at most sound reinforcement woofers they are optimized for qb5II boxes at around 60Hz. this give the most bass from the least space, the holy grail of mobile p.a. systems.
rcw

**Dennis H** · 10 December 2007, 20:48 Monday

I know people who have built sub woofers along the room gain standing wave guidelines one normally finds on the net for Northern hemisphere conditions, only to find that gross overload and no real low bass to be the consequence.

I do not know if this is true in this case, however most people find that the frequency response in an open 2pi environment is the one that matters and this means a bigger and more expensive sub woofer for the same performance as your typical Northern hemisphere one.

Hey now, lighten up on us poor Yanks. Don't blame us for wimpy subs. Remember, we're the ones who made 18x 15"-driver IBs popular.

Sub designers - what do you think

Sub designers - what do you think

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