MTH30 Questions : Complete Noob!

[tb46]

Hi Djim,

That's the way I see it, but I don't have the measurement facilities to investigate these fine points. You certainly got the ball rolling in the SS15 thread. :-)

Regards,

[turbodawg]

Originally Posted by tb46

Hi,

Attached is a SPL comparison between a Dayton RSS390HO-4 in a bass reflex enclosure (V_net=2.5ft^3) 1W/4Ohm, and a B&C 12PS100 in the MTH30 @ 1W/6Ohm.

I would go with the MTH30 between those two. The MTH30 should be good to at least 160Hz.

Regards,

That is a very peaky response on the mth30, if it had a flat response it might be around 100 db in 2pi.

Also, i said output not sensitivity, the 15" dayton has over 50% more cone area and twice the xmax. I would like to see a comparison with the drivers at xmax, please.

Btw, when simming for the actual 35hz tune of my built subs, it sims to 94db with a f3 of 35hz. Figure 34-100 hz 92 db/w/m/pi +/-2db. I get actual strong in room response at 30hz.

[tb46]

Hi turbodawg,

Post #52: "... my built subs, it sims to 94db with a f3 of 35hz..."

I just went by your previous volume and SPL remarks, it doesn't matter much one way or the other, the big difference is in the enclosure technologies. Anyway, I'll attach another 'quick and dirty' SPL comparison, and the Hornresp export files if you want to do any more work with this. As you will see, it is not even easy to say "at Xmax" or "at rated Pmax(?)".

Regards,

[weltersys]

Originally Posted by ghettosynth

I specifically need something "one man" portable."
Well, I'm still debating on what exactly that I'm going to do here, I'm fairly certain that I'm going to build at least one pair of small 12" TH subs.

1) Connector plates, I want to use speakons.
2) Finish, I'm leaning towards some sort of paint, but I want to know what people like and use, and what's cost effective.
3) Handles and pole mounts.

I have no sense of how the quality of the horn fold impacts real results, but, given what I've read elsewhere on this forum, performance is relatively insensitive to small deviations holding all else constant.

Consequently, it appears that I can trade off some SPL for LF extension in the THAM12 by just making the cabinet about 3 to 4 inches taller.

Finally, I haven't sim-ed it yet, but, I'm leaning towards the B&C 12NDL76 for weight reasons. Any thoughts on this, are there any other good choices of driver in the 10 pound range that I should consider? In particular, is there anything less expensive that would work almost as well?

tnx,
gs

You can find handles, connector plates and pole mounts at Parts Express.
I like Duratex paint, but it is not cheap. I usually use Behr paint ("Beluga" is the blackest black) for the first coat to save $, but for a pair of subs a gallon of Duratex will be more than enough for 2 coats and lifetime of touch up.

To make a TH go low, the path length must be about 1/4 as long as the low frequency desired. In a small TH, cramming in a long path length adds weight and reduces net volume, a BR alignment using high Xmax low FS drivers actually works better for LF extension and output in a small box.

The B&C 12NDL76 has only 6.5 MM Xmax, and a lightweight cone at only 53g Mms. It is targeted at lightweight speaker on a stick applications.
As I have mentioned before, lightweight cones distort badly when driven to Xmax in a tapped horn.
The BC 12TBX100 with 11mm Xvar and 119g Mms would be capable of at least 6 dB more clean real world output for an additional 17.4 pounds weight penalty.

Neo prices have gone up, there really are no "light and cheap" speakers any more.

Art

[weltersys]

Originally Posted by sebDIY

Did you ever worked professionally in real conditions? I doubt !

How can you compared a dedicaced bass cabinet to fullrange?
And level is what I need, I don't need to goes under 50Hz.

Trying to compare fullrange to bass cabinet is like comparing apples and oranges.

Any 15" fullrange I have tried (and I've tried a lot) can't outperform my system 2 MTH-30 + 2 ZX1 EV. This is for me, the best combination I have found in term of SPL, size, sound, weight.

Pearhaps for your use, you will need better than 50Hz cutoff, but for me it's perfect. My usage is professional not home, it makes big difference.

I have worked professionally in sound and light production since 1972, designing and building speaker enclosures and mixing live sound at events ranging from 50 to 250,000 people.

If you rent the old Prince movie "Purple Rain" you can watch the little guy humping one of my 1979 era low mid cabinets in the Minneapolis nightclub First Avenue.
I refurbished the First Avenue house sound system used for DJ music prior to that movie. It could do a solid 40 Hz, fairly good for that time last century.

Over the course of the last 41 years, I have encountered literally thousands of designs, and designed dozens of different enclosures ranging from small monitors to large subwoofers.

As far as comparing a full range cabinet to a sub, if the sub has a lot more low frequency extension and output, yes, the difference is like apples to oranges.
And yes, one should elevate a full range cabinet, the FR response of the Mackie HD1502 in post #38 the 15" was about 5 feet above the ground, outdoors.

Compared to the "full range" EV ZX1-100, which can only put out around 114 dB to around 100Hz, the MTH30 provides almost another octave of extension and a lot more output.

However, compared to a Mackie HD1502 full range cabinet which can put out a real 125 dB at one meter down to 60 Hz, we see the MTH30 only goes 1/6th octave lower, and perhaps 2 dB louder when driven to Xmax, not much of a sub.

If you are satisfied with LF dropping off at 24 dB per octave from 55 Hz, that is completely OK, it seems many are.

The OP largely plays classic house music, a genre that has quite a bit of program material in the octave below 55Hz.

Now that there are high Xmax drivers that can take loads of power and go low and loud (35 Hz 125 dB) in small boxes, one does not have to sacrifice LF extension for size.
Yet people still do, which I find interesting.

Art Welter

[sebDIY]

If you are satisfied with LF dropping off at 24 dB per octave from 55 Hz, that is completely OK, it seems many are.

Sorry, but most hits of house I have to play have nothing below 50Hz. Here is an exemple with spectral content frequency of Black Eye Peas I've got a feeling :



As you can see, there's nothing to reproduce below 50Hz. Even you have a 30Hz PA system, it's change nothing!!! So a 50Hz -3dB is perfect for this type of music

If I worked in a club, I would prefer a 40 or 30Hz PA system, because acoustic is supposed to be good, and music isn't just over compressed commercial tracks with nothing below 50Hz. But mobile DJ is another work, and in this way, I repeat again, MTH-30 does the perfect job for this, and I don't think it's a coincidence if the MTH-30 is one or if not the most used DIY bass cabinet by mobile DJ in europe.

However, compared to a Mackie HD1502 full range cabinet which can put out a real 125 dB at one meter down to 60 Hz, we see the MTH30 only goes 1/6th octave lower, and perhaps 2 dB louder when driven to Xmax, not much of a sub.

125 dB is theorical, but you truncate the truth: If you crossover a sub, the RMS level of signal is reduce by 3 or 4dB, so there's 3 or 4 dB of gain available for the sub, and the same append with the top: it hasn't to reproduce bass frequencies. The bass filtering reduce also peaks, so the MTH-30 will play at least 6dB more level than the mackie at clip limit.

Another point: you can not reproduce music at high levels with a flat response curve. It's common to push sub level for 12 dB or higher. So it is useless to have a top level that makes same level of a sub. In this way, the ZX1 and MTH are perfectly appropriate. OK the mackie will play louder in the high, but if you listen the mackie flat, it will be unlistenable due to the lack of bass. So you will probably want to push bass on eq, add distorsion to bass, but finally, you will reach clip limit of the amp very quickly, and the level will never as loud as a 2 way active system. That's the truth !

[ghettosynth]

Originally Posted by tb46

Hi ghettosynth,

Post #40: "...trade off some SPL for LF extension in the THAM12 by just making the cabinet about 3 to 4 inches taller."

In Hornresp adding 10cm to the L23 dimensions makes very little difference.

Regards,

I'm new at this, but as I understand it, that would only increase the height by about an inch and one half. I increase the L23 length by about 20cm, give or take, and maintain the mouth opening by adding some additional wood. If I go even further, I get diminishing returns.

That said, I want to make sure that I understand what "very little difference" means. Moreover, at the same time I want to develop intuition for how these parameters interact to affect the result.

[Brian Steele]

Originally Posted by sebDIY

Another point: you can not reproduce music at high levels with a flat response curve. It's common to push sub level for 12 dB or higher.

Is this true? I don't really do PA, but that sounds a bit "bass-heavy" IMO, particularly considering that our sensitivity to bass is higher at louder levels (according to the old FM curves).

[ghettosynth]

Originally Posted by weltersys

You can find handles, connector plates and pole mounts at Parts Express.
I like Duratex paint, but it is not cheap. I usually use Behr paint ("Beluga" is the blackest black) for the first coat to save $, but for a pair of subs a gallon of Duratex will be more than enough for 2 coats and lifetime of touch up.

Thanks, with respect to hardware etc, I should have been more clear. I know that parts express carries products, I want to know if there are kinds of products here that I should avoid with a TH cabinet, and why.

To make a TH go low, the path length must be about 1/4 as long as the low frequency desired.

Thanks, that helps.

In a small TH, cramming in a long path length adds weight and reduces net volume,

Do you mean holding external dimensions constant? What I find interesting is that hornresp designs are indifferent to cabinet dimensions and I'm trying to get a good feel for how varying the handful of parameters, holding a driver constant, affects performance.

The B&C 12NDL76 has only 6.5 MM Xmax, and a lightweight cone at only 53g Mms. It is targeted at lightweight speaker on a stick applications.
As I have mentioned before, lightweight cones distort badly when driven to Xmax in a tapped horn.
The BC 12TBX100 with 11mm Xvar and 119g Mms would be capable of at least 6 dB more clean real world output for an additional 17.4 pounds weight penalty.

Neo prices have gone up, there really are no "light and cheap" speakers any more.

Art

Great, thanks. I was concerned that might be the case.

[Djim]

Originally Posted by sebDIY

Sorry, but most hits of house I have to play have nothing below 50Hz. Here is an exemple with spectral content frequency of Black Eye Peas I've got a feeling :

Hi sebDIY,
The lowest musical note in Black Eye Peas - I've got a feeling, are a E1 notes (plays for 8 bars) that comes back each time at the end of the melody.