MJ Reference I Sub

Hi Guys!

Thinking of getting the above to replace my KEF TDM45B. Has anyone got any experience of the MJ in a HT set up? does it really go down to 10Hz? Is it better than a Rel Storm III, is it capable of driving a decent size room? I normally watch film at about -15db. I also don’t want something to obtrusive and the MJ looks quite nice.

Looked at the SVS subs but as my KEF has gone faulty 3 times and has blown countless safety fuses, I really want a warranty I can use! Rel doesn’t seem to be to popular around here and MK seem hard to find and a bit steep!

Cheers for the info in advance.

PS anybody want to buy a KEF sub!

 

I have the MJ Ref 1 sub. I can highly recommend it. I'm now looking at buying a second one at some point, not because it's not powerful enough but it will help to flatten out my rooms response. Get yourself down to your local dealer and book a demo of various subs at the price point and make your own mind up.

 

MJ Acoustics make really good subs but their marketing department should be working for the Government as they are prone to some shocking exaggerations and "going down to 10Hz" is the worst one.

 

It is true that REL make some pretty poor subs: That the Quake and Q150 are rubbish, is true as is the Q201. I have a Q400, though and think it a very good sub. But I certainly didn't pay full price.
So here is the rub, REL do make good kit, but most are over priced. If you can find some ex-dem deals, then you can get some good REL badged kit (like the Strata/Storm III).
MJ acoustics make some good kit. The REF 1 is a good'un, but not if you first priority is movies. On a home dem, I found it a "musical" sub, that is to say refined and subtle rather than up front, meaning impact was lost on OTT movies (like Underworld).
I would say that the REF 1 is mainly as good as a Storm III, which is saying a lot considering the price difference.

Russell

 

It does actually produce a 10Hz tone, albeit at about -50dB.

I tested this theory with a Meridian 568.2 processor which has built in test tones down to 9Hz.

 

QUOTE:
"MJ Acoustics make really good subs but their marketing department should be working for the Government as they are prone to some shocking exaggerations and "going down to 10Hz" is the worst one.

Ian J


Almost any unit/box can be made to produce 10Hz at some level.
The question is whether there is any discernible/usable output at that level. It really comes down to everybody agreeing at what point (-dB) one can discount any manufacturers claims for 10Hz output? Do you have a particular figure in mind Ian?

NIMBY

 

I think that +/- 3db is fairly widely used in the hifi world and is much more meaningful. Some manufacturers use -6db which is a little wide of the mark but there again there is the question of whether the figures should be taken in room or anechoic.

I couldn't care less if they all used a similar basis though

 

Quote:
"It does actually produce a 10Hz tone, albeit at about -50dB".

"I tested this theory with a Meridian 568.2 processor which has built in test tones down to 9Hz."

Crustyloafer


Are you absolutely sure that your test tones were flat down to 9Hz?

Are you sure there were no roll off filters in your test system?

What meter did you use? Did you make "known error" corrections?

Did you measure close to the unit/port or "in room"?

Could the Ref1 have a high pass filter at subsonic frequencies to protect the cone from 'mad' excursions?

-50dB just seems way, way too low a level. There has to be an explanation. What were the figures at 30, 25, 20 & 15Hz?

NIMBY

 

Cheers for your insight guys!

That SVS web site is still calling to me!

Have also found a KEF PSW4000 for £850, herd one of these at the manchester show last october and was quite impressed, anyone got any opinions on this box?


Cheers Guys!

 

I didn't mention SVS as you specifically requested something unobtrusive but I spent many months furtively sneaking a look at the SVS website trying to convince myself that it would look good in the corner of my loving room.

I pressed the "buy" button some months ago and the Tower of Power has held pride of place in my living room ever since.

 

Ian,
What's the "Tower of Power" like on music?

NIMBY

 

Ian i'am starting to talk myself into a 20-39 PC-Plus, it just seems to good to be true, and much better value than most of the subs available over here. can you tell me are the tuning ports on the top of the tube? and is the sub very position sensitive? if I can re locate it I may be able to talk the wife round!

Cheers for the info!

 

I find that the 20-39 PC Plus works very well with music which I would guess is to do with the fact that the design isn't compromised by trying to make the sub too small.

I have stuck mine in a corner which is not supposedly the ideal place but it performs well where it is.

A Servo 15 owner who came round for a demo said that I would have had difficulty if it were a Servo 15 shoved in the corner like that as it wouldn't perform properly.

 

I was just making my point that their figures are totally unrealistic. When I ran the test tone from the Meridian processor I didn't take any measurements I just listened and observed. There was definitley a noticeable output at 9-10Hz, but at what level I couldn't tell you. It's still a good sub anyway and I'm glad I got it, may get a second one soon to cancel out the troughs and peaks in my rooms response. This thread is getting a little bit too anal for my liking. If it sounds good to me then that's all that matters.

 

Thanks for your honesty crustyloafer.

It was great joke but a manufacturer's image and products are at stake here.

10Hz is completely inaudible at <any level> if your sub isn't producing harmonics = distortion.

Download the signal generator programme and use a Tandy/Radio Shack meter (with the correction figures included: +20dB at 10Hz!!) and see what you come up with.

I'd be prepared to bet 10Hz is reachable with the Ref1.

My 10" (single unit) bandpass passive subs are only -7dB at 10Hz (if you correct for the Tandy meter). That's 93dB relative to 100dB output across the rest of the band with a 30 Watt wimpy amp only cruising.
Still think 10Hz can't be reached with a 10" unit?

Best regards

Nimby

 

You have to be *very* carefull with frequency response numbers.

They can be measured in different circumstances.

A) They *should* be acurately measured in a anechoic chamber (or at least semi-anechonic) and be accurate to a decibel right across the frequency range.

b) Some manufactures give *in room* measured responces which are skewed as they are taking into account room gain.

C) You should examine a the +/- level.

REL over the years have changes their specs to hide lower perfomance for they smaller subwoofers.

They used to give +/- 3 db ranges, then used +/- 6 db, this looks like the subwoofer drops lower by using a lower frequency number but infact misleding and incorrect as the actual level is now worse than before.

Now even on their website they dont even give +/- ratings at all!!! very poor IMO.

NIMBY:
-7 db at 10 hz on a ten inch bandpass unit, I don't thing so.

You are most likley picking up higher up harmonics on the meter, you are not actually getting real output at 10 hz.

In general Bandpass subwoofers are often notoriously bad performers in the home.

Bandpass enclosures do not play very wide range of freqencies, they tend perform best in there very limited passband and roll of sharply above and below.

The only subwoofers that hit solid infrasonics are IB (Infinite baffle) and huge very low tuned ported/passive radator systems (approx 16 hz).

E.G.

Mutiple SVS tuned very low, DIY Adireaudio Tempests/Tumults, and Strike AV 15's ect.

 

Hi E.G.

Interesting post.

The problem manufacturers have with subwoofer measurement figures is the enormous variety of rooms in which they will be used.

A reservation I have heard from the manufacturers is that it would not be fair to their own products to quote figures. Because the next (competing) manufacturer would simply employ a more flattering measuring environment.

The wavelength of the frequencies they are dealing with would demand an enormous anechoic chamber to avoid room reinforcement. Probably much larger than a conventional floorstander speakers would need.

The small size of these subwoofer companies would suggest that building such a facility for their own use would be be financially crippling.

Until a suitable completely independant testing facility is available to all they would prefer to maintain a "level playing field" by not providing any figures at all.

My stand on this would be to suggest a test tower set above a conifer plantation. In still conditions it would be as close to anechoic as really matters. It has the advantage of cheapness.

Another problem is that should they provide any figures at all. It would only provide fodder to every cynical Tandy meter wielding enthusiast to "disprove" in his own (telephone kiosk sized) listening room.

There is also the question of the life of the drive unit in the box. Unless steep active filtering manages the subsonics. Then cone excursions on the increasingly fierce DVD recordings available would be pushed (and pulled) beyond sensible limits. Particularly with ported boxes which have very low resistance below roll-off.

Really the manufacturers have a nightmare scenario. They must provide a nicely finished box no larger than a house-brick to satisfy WAF requirements. Particularly in the ever smaller modern rooms. Yet modern DVDs provide tracks that would destroy their units if driven at anything like full power. All this has to be set against an acceptable price for the box. If the manufacturer provides close to perfect performance he is governed by the laws of physics and real life costs. That means (as you say yourself) BIG!


Regarding the bandpass speaker I would humbly suggest that such harmonics would be audible. As harmonics would have to be up in the audible range. The narrowness of the frequency response band is desirable (-3dB @ 20 & 120Hz) as they were deliberately matched to particular satellite speakers. (From David Purton's: "The Coupled Cavity Handbook")

Purton does indeed show a steep roll-off. My original measurement figures were -27dB @ 10Hz. However it seems to be freely accepted that the Tandy SPL meter reads -20dB at 10Hz. Hence my new and surprisingly flattering figure of -7dB.

NIMBY

 

You may be surprised to know how few UK Subwoofers are actually made by the company who's name appears on the front anyway with REL, B&W and Vibe being the only three that I am aware of who's subs aren't made by someone else (and I am guessing at B&W and Vibe)

 

Ian,

I read somewhere (ages ago now) that B&W's speakers were made in Denmark. Perhaps it was only the drive units?

NIMBY

 

I contacted MJacoustics about the Pro 50 and the Reference 100. These subs according to the specs goes as deep as 15hz and 13hz respectively but no mention of the SPL. MJacoustics emailed me back and said, and I quote, that

"Both units produce their low frequencies @ somewhere between -6 to -10 dB depending of course on input content."

The question is, how low can it go at -3dB? I think 20hz is the absolute low that the human ear can sense.

 

Contact them again and ask them this question and I wouldn't mind betting that Alistair Campbell would be proud of the evasiveness of their answer

 

An avforums member "Dan Gleebles" did some measurements of the Pro50 using as near to anechoic conditions as he could - the results were: 33Hz @-3dB, 27Hz @-6dB - pretty much what one would reasonably expect from a small enclosure with an 8" driver and a 50 watt amp.

Here's the thread: http://www.avforums.com/forums/showthread.php?s=&threadid=71969&perpage=15&pagenumber=3

Matt.

 

The plot thickens!

Going back to the REF1: "Home Cinema" refers to the room filling with the same 15Hz as provided by more costly subwoofers. (Or words to that effect).

No mention is made as to whether the 15Hz was sensed or measured. This frequency being inaudible though it can certainly be felt.

Since this frequency is specifically mentioned in their review of the REF1 I wonder if anybody has anything to say about this?

NIMBY

 

I'll make up a test tones disc and give it a go.

 

I tried to measure it with Avia but gave up as the needle was swinging about all over the place and i needed 2 sets of hands and 4 eyes to try to record it all!

 

gazzerr,

Did you have your meter set to 'slow' and 'C' weighting?

I downloaded the free trial NCH tone generator from Swift software. Your browser will find it. Run a cable from your computer's "speaker out" socket to the sub low level input. You may need a miniature stereo jack to phono adaptor. Just set the meter on the carpet close beside the sub but not touching it.

Don't overload your sub at very low frequencies. It is expected to get quieter as the ear quickly loses sensitivity below 30 Hz. The tempation is to crank it to be able to hear what's happening. Keep at the same level and just record the readings. 80-85 dB is probably a safe level to record the entire frequency response as you step down in frequency using this software.

BTW: You can't drive a passive sub from the computer without an amp if anyone reading this thread is tempted to try. Active subs have their own built in amp of course.

My DIY passives are each able to produce 98dB at 20Hz using a low volume setting on a 30 watt amp. 87dB at 15Hz and 75dB @ 10Hz <all uncorrected Tandy meter readings relative to 100dB continuous output at 30-120Hz>. Just don't tell micb3rd.

NIMBY

 

If those are real numbers then it sound like you have a decent set of woofers there.

You got me very intereted in your design now, what subwoofer driver and size enclosure do you use?

What are the tuning frequency(s) for the bandpass enclosure?.

Did you model it in any software? Bass Box Pro or WinIsd etc?

If so what is the sumulated F3 and F10 points?

 

Hi micb3rd,
I hoped you'd bite.

6th order Series Bandpass: Seas 10" 25F-EWRX 8 Ohm on an internal baffle in a 55/25 litre box. Internal port 75mm dia x 550mm. Exit port 100mm dia. x 393mm. Poles at 20 & 45 Hz. Eff. 82dB for 1 watt. Continuous 100 Watt power handling. Maximum output about 102dB. Though I've seen a competely silent 105dB with only a 30 watt amp. I've lost my original driver parameters but found these in an old Wilmslow brochure:

vc 39mm
Qts .23
Qes .24
Qms 3.8
Vas 175l
fs 26Hz
1w1m 91dB
imp 8 ohms
-3dB @ 16 &120hz

Design by David Purton. One example from the "The Coupled Cavity Handbook" a £5 booklet available from Falcon, Wilmslow etc. Designed to compliment LS3/5a satellites.

I have been looking for free software since I built a stereo pair about 8 years ago. I have only recently discovered the errors in the TANDY SPL meter. So don't know where I stand now. I would have prefered the meter was error free as it closely matches the claimed parameters of the boxes after repeated testing.
If you have software that can look at the 6th order series design I woud be very interested in hearing your results.
This might be better discussed on the DIY forum. I only offered my results for a comparison with the interest being shown in testing the MJ REF 1 & smaller Pro 50.

Best regards
NIMBY

 

RadioShack SPL meters are inacurrate at lower frequencies, only much more expencive microphones are accurate.

Check out these two links for the correction values.

http://www.svsubwoofers.com/faq_rscomp.htm

http://www.danmarx.org/audioinnovation/rsmeter.html


The Seas 10" 25F-EWRX driver is actually programmed into WINISD so you can play around with it in software and model up some enclosures.

What surprised me is that, it looks to be surprisingly flexable, providing faily decent responses from sealed, Vented and 4th order bandpass, the 4th order bandpass results were a shock to me, it actually looks ok (very unusual as most drivers don't model that well in them).

Strangly enough the standerd 6th order bandpass looked very unconventional.

As I don't have the The Coupled Cavity Handbook I can't really model your exact enclosure.

Thanks for the extra information Nimby.

 

David Purton expressed his delight with this particular driver and how well it fitted into the various enclosure designs.

I already had the meter error figures thanks but I still don't like them. It means I am only a couple of dB down at 10Hz! It's not supposed to be that easy and it wasn't predicted.

Subwoofers DIY has a project to change the capacitors on the meter circuit board to correct the bass roll-off. But I don't think my blowlamp is big enough for the job.

A drawback with my boxes is a lack of maximum SPL for HT.

I'll have another go with WINISD and see what happens.

Thanks
NIMBY