Help: Expertise in Speaker Cab Design?

Subject: Expertise in Speaker Cab Design?
From: JedMarum
Date: 16 Mar 01 - 09:04 AM

I am really tempted to design and build a pair of subs to compliment the PA cabs I use for the band. I am using 2 pair of JBL 925s (two way cross with 2 15s and 1 1/2 inch compression horn). These have been great cabs, versatile and protable - but the occasions we play outdoors, the occasions we play with laregr band sonfigurations, and the occasions we play begger clubs (although most have PAs) we could use the added bottom, and push.

I would like to recreate something like the JBL SR4718X which is single 18" in a fairly compact cab (you can see a picture here here). Does anyone have expertise in this area? I'd like to find the formula for determining the correct volume of air, and port size/s, in order to maimize freq, output and efficiency. Any other pointers would be helpful, too. Anyone?

Subject: RE: Help: Expertise in Speaker Cab Design?
From: Bert
Date: 16 Mar 01 - 02:38 PM

Jed, is this site what you're looking for?

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 16 Mar 01 - 03:55 PM

this is a good site, bert. Thanks.

Actually I was hoping to find a Mudcatter or two who may have tried it, and get some feedback about their experience. It seems a simple enough project, especially the bass cabinets, but then there must be a reason so many people buy them, instead of making them!

Subject: RE: Help: Expertise in Speaker Cab Design?
From: Bernard
Date: 16 Mar 01 - 04:45 PM

The reason why people buy 'em instead of making 'em is simply resources for research and development.

Why re-invent the wheel?

If it was that easy to design and build a speaker cab, why can JBL, Bose, Hughes and Kettner (et al) still make loadsa money out of it?

I'm a P.A. engineer, and I've seen small-time loudspeaker manufacturers come and go, and often get telephone enquiries like 'I've got this (great lengthy explanation) loudspeaker chassis, what cabinet do I need to build?'

In short, don't waste the effort unless you've nothing better to spend your time and money on.

Ask yourself - 'Why did he write the book?'...

Answer - 'Because it makes more money than building speaker cabinets!'

Sorry - I'm not being cynical, even though it probably comes across that way!

Subject: RE: Help: Expertise in Speaker Cab Design?
From: Bernard
Date: 16 Mar 01 - 04:50 PM

However, if you insist, I've got an old MSDOS based program to assist you to calculate the optimum cabinet volume.

PM me with your email address if you want it. Very small, being DOS!

You also need to find the resonant frequency of the chassis you intend to use - the sand trick with a frequency generator is still as effective as many more complicated methods.

Subject: RE: Help: Expertise in Speaker Cab Design?
From: John J at home
Date: 16 Mar 01 - 05:31 PM

Bernard, you beat me to it! I saw the thread and was going to suggest you were the man for the job! Anyway it's 22.30 Altrincham time; I'm knackered and I'm going to bed. JJ

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 17 Mar 01 - 09:52 AM

Brenard - I guess mt gut was telling me all along, what you said. I will still PM you, becasue I want to know, but JBL makes fine stuff, and the more thought I put into design, the more I relaized, you probaby get a pretty bargain, for all of the engineering that goes into a well designed enclosure. Strength of frame, weight, road warrior finish, handles/wheels, wiring - not to mention air volume, ports, materials. I couldmake two or three pairs of cabs before I got it all right, maybe more - even if I'm careful about the engineering.

Maybe a better question for you would be, what subs might match well my two pair of JBL 925s? I wrote to JBL and they thought the SR4718X (a single 18" in a ~2' ported cube) would work. Do you have any thoughts?

Subject: RE: Help: Expertise in Speaker Cab Design?
From: Bernard
Date: 17 Mar 01 - 10:10 AM

Yes, the SR47 18x could work, but may be somewhat bulky. Added to which, ported cabs can sound a little 'indistinct'.

We use the Hughes and Kettner HL118 in a variety of configurations - 'horn loaded' 18" capable of handling around 600 watts.

'Horn Loaded' means the design of the cab is a bit like a horn - not to be confused with a 'full-range' unit with horn and crossover. As a result, the cab is more compact, but very 'punchy'.

If you can afford it, bi-amp your system with an active crossover. That way you have full control over the subs, and mid/tops.

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 17 Mar 01 - 10:42 AM

Yes, I presumed I would bi-amp, (not that I can afford it - but that's never stopped me before)! I am not sure I mind the bulk, but I'm intrigued about the Hughes and Kettner option you mention.

The horn loading? I presume the enclosure uses a design that extends the front (or back) of the speaker to create a horn? Something along the idea of the old Altec Lansing VTs? How much smaller is the enclosure? How much do they cost? Where can I get 'em? And 600 Watts sounds fairly efficient, if they are acoustically in the range of the JBLs. Is that true? I could drive them with a single Crown 1000 CE. Correct? And who should I look to for a cross over?

Subject: RE: Help: Expertise in Speaker Cab Design?
From: Bernard
Date: 17 Mar 01 - 11:20 AM

I'll be back in work on Monday afternoon, and I'll dig out the spec sheets then.

The 'horn' is 'folded' inside a conventional rectangular box...

We prefer them to the JBL's, and use them with JBL 4726's and 4851's. We've even used them with Bose 802's!

For crossovers, we use the Audio Logic X324, or Brook-Siren Systems (BSS) - here's their website: BSS

BSS do a unit called the 'Omnidrive' which can be computer controlled, but is much more complex than you need - although they have now brought out a compact version called the 'Minidrive'.

You can get some interesting software from their site - not all of it is any use unless you have the products, but you can still play with it!

Subject: RE: Help: Expertise in Speaker Cab Design?
From: GUEST,thumbwax
Date: 18 Mar 01 - 06:24 AM

.6:1.0:1.6...these are the ideal ratios of thickness:width:height. The Golden Mean.

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 18 Mar 01 - 11:02 AM

Bernard, I couldn't find the 4851s you mention, but the 4726s are comparable to the 925 I am running. I use two pair of 925s, which gives me four 1" compression horns. The 4726s each have a 1 and 1/2" compression horn. I may be a bit heavy in low mid, with two sets of 925s and a sub, but I think that could be handled by where/how we cross over, and EQ. No? I chose the 925s for the versality; one pair=one good small system, two pair=one good mid sized system, I can use one or more 925s for a stage monitor if there is a good house system. I have used the four speaker setup outdoors for small applications, with great success.

There is one added advantage to using the 925s, and that is the directional diversity I can acheive with them. When they are splayed, I get an good wide throw - with enhanced high end efficiency because the horns are placed side by side and angled for maximum width. When they are faced square, and side by side - or piggy backed with horns placed together at the center of the stack (that is, bottom cab right side up, top cab upside down) - I get a similar efficency for a longer, narrower throw.

The 925s have been a good design for our needs.

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 18 Mar 01 - 11:03 AM

thumbwax, I don't understand?

Subject: RE: Help: Expertise in Speaker Cab Design?
From: Bernard
Date: 18 Mar 01 - 08:33 PM

We do the inverting cabs trick, too.

Can I have a pint of whatever Thumbwax is drinking, please?!

The 4851's and 4852's are a large-ish trapezioid enclosure with 2x12" 4726-type drivers, and an exponential horn. The 4851's also have a pair of 'baby's bum' UHF horns similar to the 4726, but smaller.

Sounds like you are well sorted with your 925's - I hope I remember to dig out the H&K info in the morning!!

The crossover point is important, but having the system bi/tri-amped is the crucial bit - you can balance it up so much more easily. Passive crossovers are okay for low powered rigs, but you need an active system for what you want to achieve.

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 19 Mar 01 - 09:27 AM

Bernard - I found the H&K website and have spent a bit of time looking around (it's a good site, and their equip looks great). I also discovered that their stuff is sold at my favorite "toy" store (Guitar Center), very near my house - so I'm sure I'll be visting today!

Two good things about the Guitar Center; price, and, their credit card option - you can buy stuff on their card, not pay anything for a year and then pay it all off before they charge you interest. I've done this a few times, now. Of course they hope you'll go into the next year and have to pay monthly installments that include an outrageous interest fee, but if you pay it off, there's no fee. I use this plan or large purchases, even when I have the cash available. I just make sure I pay it off before the year is up.

I don't think I'm ready to buy 'em yet, though. I'd need more amp power, a rack, a cross over, cables. It adds up quickly. Still, it's tempting ....

Subject: RE: Help: Expertise in Speaker Cab Design?
From: Bernard
Date: 19 Mar 01 - 01:03 PM

Just when I was about to apologise for not having had time today to dig out the 'bumph'!!

I've been at an airport modifying the 'crash phone' so that the dialogue goes out on the Fire Station public address.

So I got to press the Big Red Button that set off all the alarms, and opened all the doors!!

Never a dull moment...

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 19 Mar 01 - 01:05 PM

LOL - sounds like a fun job!

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 12 Aug 01 - 02:10 PM

OK - I'm back to this subject, if I can get any help ... I am in a position of having to make do with what I have plus the absolute minimum budget. How can I design a quick, simple cube for a single 15" JBL to maximize its low freq capabilies. That is, the low end of the spectrum is all I'm after here. How do I find the formula for determining the optimum cabinet volume, and port features? Does anyone know of a good speaker enclosure design book?

Subject: RE: Help: Expertise in Speaker Cab Design?
From: Richard Bridge
Date: 13 Aug 01 - 06:08 AM

Don't use a cube. Standing waves.

Do calculate the volume and port size. I haven't got the URL at the moment but "the subwoofer page" tells you exactly how to do it. FOr simplicity go for a simple reflex cab. You could try a fourth order or sixth order bandpass but it gets trickier. TO find the subwoofer page do a dogpile search for subwoofer.

Also Eminence do a book of cab designs, and I think the old fane book is still available. EMinence also do a computer program.

It ain't hard.

I built two subs for my daughter's band using EMinence Kappa 15s (I should have used Kappapro 15LF's but you learn from exeprience). I also should ahve built them a little bigger, but I ahd come by some high density fibreboard for nothing (too thin, but since it was free I could laminate two sheets together with PVA glue and a few screws)and the size of that was the limiting factor. I also used a discarded kitchen worktop for the baffles and backs. I had some speaker carpet and corners and aluminium edging left over from a former project. Add in 4mm internal cable, socket plates, handles, poprivets etc, and I built the pair for under GBP 200.

They aren't as pretty as the tops I made out of mahogany laminate, but they go pretty well. They ar ehowever quite heavy.

One local blues band said "One of the best small PA's I've ever used". A local performing arts college to whom I hired them when theirs were stolen said "the best homebrews I've ever used".

They are too polite, but the cabs do look reasonably workmanlike, and when I worked with another local skatepunk band (sort of halfway between scratching and rap with a bit of added melody)and used thier Peavey 2000 to drive the subs and my Yamaha to drive the tops, I was seeing cone excursions of about half an inch and a fairly solid thump.

Try the subwoofer page and see what you think.

If you are in UK (North Kent) PM me and you could see them.

My latest theory involves a 6th order bandpass with two drive units front-to-front on teh middle baffle (a bit like a contorted Isobaric), but I don't suppose I'll ever try it 'cos the drive units would cost about GBP 600, and daughter's band split, so there would be no point.

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 13 Aug 01 - 10:06 AM

Richard - sounds like what I'm looking for. I found several links to "the subwoofer page" but all were dead ends. Apparently it is no longer hosted anywhere. I'll keep looking, though.

Years ago I ran across a text book that had enclosure design theory including formulae for making the volume and port calculations. I suspect that by spending a few hours at the Dallas library and I could find another book. I had hoped there'd be available a modern version of it, and something on the web.

Thanks for the comments.

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JohnInKansas
Date: 13 Aug 01 - 11:20 PM

Many years ago, I found a "handbook" on how to design speaker enclosures at a local "Radio Shack." My recollection was that it had some useful formulas, although the "projects" were typically trivial.

Since most of the stuff they offer for sale now is about 40 years behind the times, they might still have something along the line of what you want. Advantage - it should be relatively cheap!

The "Yamaha Sound Reinforcement Handbook" published by Hal Leonard has some good "general theory" about how to tell if you did a good job - and how much you can expect to get out of various types of drivers/enclosures, but unfortunately no useful formulas or equations in this area. - This book is more about how to hook up what you've got.

John

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 14 Aug 01 - 09:22 AM

In the 70's the focus for hi fidelity and efficiency in sound reinforcment meant large carefully designed enclosures for the best speakers available ... then along came Bose and others saying the physics didn't exclude smaller cabinets, and that higher tech electronics and massive amps could reproduce quality sound too. The new school of thought won the day, and now we think nothing of thousands of Watts for each channel - driving large numbers of speakers in small, inefficient cabinets. I remember driver my band's PA with 70 Watts per channel and having plenty of power for our pair of Altec Lansing VTs. Now I use 1000 Watts for each pair of small cabs (JBL 925s)! But - we've come a long way in sound reinforcement in 30 years. There's lots and lots of pretty good quality sound equip out there in the market place, and in use on stages - and people know pretty well, how to use it.

If I still had a day job, I could afford to go out and buy a good, well matched pair of subs for those few times each year I'll need them. JBL makes a fairly compact cube with a single 18" that would match well with two pair of the 925s - that is one pair of subs for two pair of 925s.

I just can't help thinking I could make something that would help ...

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 14 Aug 01 - 09:25 AM

I guess I'm a bit of a sound equip junkie!

Subject: RE: Help: Expertise in Speaker Cab Design?
From: Richard Bridge
Date: 14 Aug 01 - 11:26 AM

I might still have a hard copy of the subwoofer page, but I'm not sure I have the 4th and 6th order calculations.

I'll have a look.

I guess North Kent is a bit of a long way for you then!

Subject: RE: Help: Expertise in Speaker Cab Design?
From: Richard Bridge
Date: 14 Aug 01 - 11:34 AM

Found the site Jed

http://www.diysubwoofers.org/

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JedMarum
Date: 14 Aug 01 - 11:48 AM

Marvelous site, Richard. Thanks very much!

Subject: RE: Help: Expertise in Speaker Cab Design?
From: Richard Bridge
Date: 14 Aug 01 - 06:43 PM

The penny has just dropped that you may be talking about what is sold in the UK as JBL TR225s (from the description) - 4 ohm, very high efficiency (104 DBm/1w/1m), just a fraction unrefined, 450 watts per cab.

If so you are going to need a LOT of power to sub them. Active crossovers start about GBP 115. YOu are going to need a good amp of about 1k per side if you crossover at about 120 hertz to give the real "dead rat smack" to kick drum. I don't think the JBL drivers will take it, nor even black widows. Try EMinence kilomax, or Fane Collossus, RCF if you've won the lottery, or perhaps Ciare who do a 1k woofer with a fundamental frequency of 20 Hertz from about GBP 250 each, butthe efficiencies of most of them are quite a bit lower than the 225 cab.

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JohnInKansas
Date: 13 Oct 01 - 11:56 AM

As usual, day late and dollar short... but this may still be of interest to some.

June 12, 2001 PC Magazine "Opinion" column by Bill Machrone, Computer-Aided Rock n Roll describes an experience "tuning" an existing CAB. The page was active 10/11/01, but I'm not sure whether site login is needed to find it, and although the site provides good info, it's not exactly navigator friendly.

To keep this post short, I can post a slightly edited text separately, if anyone is interested. The article briefly describes shareware used to calculate cabinet parameters, some design details, and use of shareware (Cool Edit and other) for testing cabinet performance. The notes on testing might be most useful.

(Bill Machrone bio) gives some info on the author.

The author's website documents the process, from first simulation to final tuning, along with screen shots of the before-and-after spectral analysis, at www.billsbest.com/thmarshall.html

The WinISD site given for the analysis shareware in the magazine article was unable to connect 10/11/01, but a link to http://www.linearteam.dk/ given in the "billsbest" page does connect.

The Spectrogram site given in the original article has moved to http://www.visualizationsoftware.com/gram.html.

Cool Edit site is given in the "billsbest" article as http://www.syntrillium.com/

The "billsbest" article also cites a "history" page at http://www.enjoythemusic.com/magazine/viewpoint/soulofsound/ch1pt1.htm. This may be the most interesting information linked.

The speaker used was from Carvin at http://www.carvin.com/

John

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JohnInKansas
Date: 13 Oct 01 - 12:29 PM

Ah - the joys of html

First couple of paragraphs above, rewritten slightly:

June 12, 2001 PC Magazine "Opinion" column by Bill Machrone, describes an experience "tuning" an existing CAB.
The page was active 10/11/01, but apparently main site login is needed to find it, and although the site provides good info, it's not exactly navigator friendly.

url for the article is http://www.pcmag.com/article/0,2997,s%253D1498%2526a%253D2156,00.asp titled Computer-Aided Rock n Roll, but it appears that you must go to PCMagazinefirst, and navigate from there to get into it.

To keep this post short, I can post a slightly edited text separately, if anyone is interested. The article briefly describes shareware used to calculate cabinet parameters, some design details, and use of shareware (Cool Edit and other) for testing cabinet performance.

The author's website documents the process, from first simulation to final tuning, along with screen shots of the before-and-after spectral analysis, at www.billsbest.com/thmarshall.html. This site apparently is also accessible only from within the pcmag site. (?)
I'm not sure why, but if I clicky into pcmag.com, then hit back, I can come back here and clicky into the "subsites."

PCMagazine go here, then come back?

Bill Machrone bio gives some info on the author.

Machrone homepage should give details.

Remaining sites should work without going thru pcmag.

The WinISD site given in the magazine article cited above was unable to connect 10/11/01, but a link to http://www.linearteam.dk/ given in the "billsbest" page does connect.

The Spectrogram site given in the original article has moved to http://www.visualizationsoftware.com/gram.html.

Cool Edit site is given in the "billsbest" article as http://www.syntrillium.com/

The "billsbest" article also cites a "history" page at http://www.enjoythemusic.com/magazine/viewpoint/soulofsound/ch1pt1.htm. This may be the most interesting information linked.

The speaker used was from Carvin at http://www.carvin.com/

John (holding breath to post)

Subject: RE: Help: Expertise in Speaker Cab Design?
From: JohnInKansas
Date: 13 Oct 01 - 12:38 PM


Apologies to all. I can't seem to make the links inside pcmag site work from here.

Those interested can possibly find the original articles from either zdnet, the ziff-davis publishing net site, or pcmag the pcmag site.

The edited (slightly shortened) text of the article is:

June 12, 2001 Computer-Aided Rock 'N' Roll By Bill Machorne: (Bill Machrone bio)
...
PCs allow us to model just about anything, from a flower garden to an addition on a house, a new wardrobe, or an electronic circuit. I love simulation and modeling applications, but I also love being able to complete the circle by using a PC to confirm the quality of the effort. It might be as simple as a digital picture of the end result, or, as you'll see here, an audio spectrum analysis of a speaker design.
Analyzing the Variables
My son's electric bass teacher recently acquired one of those huge Marshall half-stacks ("This one goes to eleven!") that have looked so impressive behind bands since the late 1960s. It had all the retro vibe you could ask for, but it sounded terrible. Since I had previously built an electric bass and a good-sounding speaker cabinet for it, he asked me to help improve the Marshall's tone. It had a single 18-inch Celestion speaker inside–typical of the British Invasion sound–but the speaker wouldn't put out the low frequencies required by the bass, and the cabinet was not tuned to the speaker.
In 1963, Australian engineer Neville Theile analyzed all the variables that determine how a speaker interacts with its enclosure and how the size of the box and the tuning port could be adjusted to get the greatest tonal range out of the speaker while also increasing its accuracy. A decade later, Richard Small extended and simplified Theile's work in his doctoral thesis, reducing it to straightforward equations and a dozen or so electrical and mechanical specifications. Today, every reputable speaker driver manufacturer publishes what are known as the Theile-Small parameters so users can calculate the optimal size and tuning of the cabinet. You can find at least a dozen commercial, shareware, and freeware PC programs that utilize them.
Although it's buggy, one of my favorite speaker-modeling programs is WinISD (www.lineartcam.org/winisd.html). It includes a huge database of drivers and their T/S parameters, so you can shop for the driver that works best for you. We combed the database for 18-inch speakers that would outperform the Celestion–and found surprisingly few. The answer finally came from Carvin, a company that builds and direct-markets guitars, amplifiers, and components. Carvin's 18-inch speaker looked like a winner, according to the WinISD graphs.
Although the speaker was the same size, a fair amount of woodworking was needed to create a proper tuning port in the Marshall cabinet. After we reassembled the cabinet with the new speaker, I powered it with my 350-watt Ampeg B2 amplifier. It rocked. It was deeper and fuller, and it sounded the way a bass speaker is supposed to sound. We knew it was loud enough when it set off a long-disused mousetrap about 15 feet away.
Conclusive Spectral Analysis
Still, ears are easily deceived. Simply making one speaker a bit louder than another makes it sound much better. To verify the actual improvement in audio quality, I made WAV recordings of the cabinet before and after the modifications, using sweep tones that spanned the useful frequency range. I used two computers; one generated the sweep tones and fed them into the amplifier, while the other recorded the sound, from the usual o1-meter distance.
Again, off-the-shelf PC software did the job. I used Cool Edit 2000 to combine the two waveforms into left/right stereo tracks so I could easily compare them side by side. Cool Edit also provided a spectral analysis, but I found another shareware program, Spectrogram (www.monumental.com/rshorne/gram.html), that provided a different, dramatic graphical representation of the power produced at each frequency. The spectral analysis was conclusive: The Carvin speaker in a tuned cabinet easily outperformed the original configuration at those critical low frequencies.
I documented the process, from first simulation to final tuning, on my Web site. You can see it, along with screen shots of the before-and-after spectral analysis, at www.billsbest.com/thmarshall.html.

John