M6N in MTM, lacking bass

[mintos]

I put together a set of HiVi M6N MTM to use as mains, but I found them lacking in bass. The bass seem to tapper/fade very fast. Not punchy or distorted, just fades. The enclosure is 23.39 Liters with a .5x7.5x5" slot in front. Bassbox says the F3 should be 68 hz. However, I find the bass is less than the pair of B4N MTMs I built for surround duty. (This is just by ear)

I've included the crossover. Is my box too big? Or two small?

Swan suggests

Recommended Box Volume(Vb)(L) : 14
Tuning Frequency(Fb)(Hz) : 46
-3dB Cut-Off Frequency(F3)(Hz) : 46

[ThomasW]

And your measurements of this design show what in terms of a real world frequency response?

[mintos]

Just by ear

[ThomasW]

Are the woofers wired in phase?

[mintos]

yes and in series

[cjd]

they'll have pretty low SPL compared to the tweeter... doesn't seem to be any baffle step compensation?

[mintos]

they are rated 88, in series they are 91 is. the TB tweeter is rated 90. No BSC, these will be placed pretty much right against the wall. I'm listening pretty close as well. < 1m

[kevinp.]

why does the graph look like it wants the woofers in parallel? There shouldn't be any db gain with 2 woofers in series, right?

[mintos]

There is a 3db gain for more surface area

[kevinp.]

but you lose that by doubling resistance, correct?

thats why you gain 6 when going parallel - 3 for halving resistance and 3 for doubling SD - as far as I know

[mintos]

Still same power going through both. I = V/R where I is constant and R doubles, so V is halved.

[kevinp.]

every reference I've ever read showed adding drivers in series adds nothing - can anyone else confirm this is false? I'm confused now.

[JonMarsh]

Unibox never lies.... :W

[kevinp.]

Unibox never lies.... :W

ugh - and here I was hoping you'd step in and answer


still doesn't make sense to me. If Voltage is halved isn't that the -3 db that wipes out the +3?

[mintos]

voltage doesn't matter, if enough to push through resistance. I matters becauce P = IR

[kevinp.]

but with resistance doubling then I is halved...

[kevinp.]

I dont know - I'm too tired to think about the formulas right now. I'll trust my Speaker Building 201 and Speaker Workshop for now...

[HareBrained]

What is the area of the port? Is it 0.5" x 7.5" = 3.75 sq. in.?

If this is correct, your port area is too small, the length equates to 42Hz (assuming some stuffing), the aspect ratio is too large, 1:15, and the volume is too small. In Unibox, it show the response rolling off beginning at 80Hz.

The port area should be closer to 6 sq. in. (even that is below recommended for full power). The length would depend on the final volume and tuning. The aspect ratio of a slot port should be no greater than 1:8. 1"x6" would have been better. The a volume closer to 30L would be better.

If you have any stuffing or wall lining, make certain nothing is blocking the port and it's an clear and easy path from the driver. If you've got heavy fill, it will have a very high F3. You could try removing some of the stuffing.

[mintos]

I was concerned with the group delay graph using a larger slot area. With 1" the GD graph shows +/- 3ms GD at 600 hz. I'll try a bigger box.

[Johnloudb]

voltage doesn't matter, if enough to push through resistance. I matters becauce P = IR

V = I*R

Power (P) = I*I*R = (V*V)/R

So, you if double the Impedance (R) by wiring two drivers in series you get half the current for a given voltage. This means you put 1/2 the power into the drivers, but double the surface area.

What does this say about sensitivity? Here's some info Jed posted in answer my question about wiring his W4 mids in series in his new Lineup Maxx design:

https://www.htguide.com/forum/showpost.php?p=455515&postcount=764

[Undefinition]

I put together a set of HiVi M6N MTM to use as mains, but I found them lacking in bass. The bass seem to tapper/fade very fast. Not punchy or distorded, just fades. The encloser is 23.39 Liters with a .5x7.5x5" slot in front. Bassbox says the F3 should be 68 hz. However, I find the bass is less than the pair of B4N MTMs I built for surround duty. (This is just by ear)

I have a pair of M6N waiting for a design. I only measured their T/S specs. According to Unibox, they want a pretty big vented box... like optimally, about 30 liters for one driver. On the other hand, HiVi's spec sheets say you can do one driver in a 14 liter enclosure; however, I could never get this to model reasonably. It gets a massive "bass boost" around 90 Hz, and the F3 is around 50 Hz at best.

So you're using a box that's--essentially--even smaller than HiVi's recommendation (remember, 2 drivers equals twice the needed enclosure volume). Ideally, your 23 Liter box should really only have one driver in it; THEN you'd get some excellent bass, probably an F3 in the upper 30's. Honestly, with two M6N in a box that size, you should really only be running it sealed. It's just too small.

[mintos]

yeah I figured... but damn I only have a 10" table saw.

[JonMarsh]

yeah I figured... but damn I only have a 10" table saw.

? Why is that a problem? That's all I've got, too.

I built these with a 10" table saw, an inexpensive Ryobi model, BT3100. No Delta Unisaw here. :W




You've gotten some very "sound" advice for solving your problem with bass extension above- why not go for it? This is something where an ounce of analysis before cutting wood saves grief later. I've never used WIN ISD, so I can't comment on it's capabilities; but Unibox is very good, and easy to do "what ifs" and solve for specific Q's and alignments in the box design.

[kevinp.]

Jed's explanation echoes what I've been trying to point out. In layman's terms (the only way I know how to show this)...

1 8 ohm driver = 88 db spl @ 1watt (2.83 v)

2 above drivers in parallel = 4 ohm (+3 db) x2 SD (+3 db) = +6 db (2.83V = 2 watts)

2 above drivers in series = 16 ohms (-3 db) x2 SD (+3db) = +-0 db (2.83V = 1/2 watt)

[JonMarsh]

ugh - and here I was hoping you'd step in and answer


still doesn't make sense to me. If Voltage is halved isn't that the -3 db that wipes out the +3?

Yes. People will believe Unibox before me, and justly so.

[ThomasW]

People will believe Unibox before me, and justly so.

When the number of drivers is doubled, Unibox defaults to double the power whether the drivers are wired in series or parallel. The only thing changed in these 3 sims is the 'Drive Unit Configuration' in the drop down box

[mintos]

current dimensions are 22"x11.5"x9". If i need to make the box larger, which dimension should I enlarge? And what's the best way of doing it?

Thanks

[ThomasW]

Usually the depth is increased that way the crossover doesn't need to be changed

[mintos]

oh because of the baffle face area? Interesting...

[Undefinition]

current dimensions are 22"x11.5"x9". If i need to make the box larger, which dimension should I enlarge? And what's the best way of doing it?

I say cut a new baffle, for only one woofer (a TM arrangement), and call it a day. Either that or seal what you made.

There's no practical use in "extending" your box. If you're dead-set on an MTM, then you need a redesigned cabinet, something between 45-60 Liters (eg: floorstanding)

By the way, despite HiVi/Swans recommendations, BassBox was correct. This is Unibox's graph of a 22 Liter box, tuned to 46 Hz. Two woofers.



Here is what I'm suggesting. Same box size, same tuning. Just one driver:

[Jed]

every reference I've ever read showed adding drivers in series adds nothing - can anyone else confirm this is false? I'm confused now.

Typically... when you wire 2 woofers in series you get 0 gain. When parallel you get 6dbs.

Read Linkwitz.

Jed

[mintos]

I'm going to seal both up, call them centers and be done with it. I'll try again with bigger boxes next time, but I'll probally use different tweeters. That TB ceremic one sounds very harsh.

[kevinp.]

You could also try padding them down to match the woofers... 2db hot if manufacturers claims are correct may make bass seem weak or tweeters harsh imo

[mintos]

Yeah, I used 3.5 since I've some 7 around. They are better, but still too bright for my taste. I might as well adjust the XO while I fix the box. I think PE got the specs wrong for Tang Band 25-1719S. It says FS of 800 and it plays down to 800. it doesn't sound like it can play that low.