Subwoofer comparison SRX728 vs Vertec 4883

[TJ Cornish]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Was that graph with or without processing applied?

After further thought, I don't see any harm in posting the graph from JBL, so here it is. As far as I can tell it is unprocessed. It looks very different than the processed graph in the 4883 spec sheet.

If you only see the processed graph-then you have no idea what the raw response of the cabinet is-especially down low. It is VERY common these days for manufacturers to put a boost down low to make the cabinet appear to go lower.

yes it can do that-at the lower levels-HOWEVER-if you turn the cabinet up, whatever boost you have applied (often 6dB or more) HAS to be subtracted from the max output (at the freq it is applied)-because the driver simply can't handle it.

And then the whole "1 watt thing" goes out the window-as they are no longer appling 1 watt to the cabinet for the graph.

I have no idea which way is which-but the previous graph say 'processed"-so that really doesn't say a whole lot.

I like the way EAW does on a lot of cabinets (sadly not all). They show you the unprocessed response-the processors response (where you can easily see the bossts that may be applied) and the final result.

With the unprocessed graph-you gan get a better idea of the cabinet is actually capable of doing-especially when turned up.

This gives way more information than a simple processed response. I would HOPE that a processed response is pretty flat-if not-something is wrong.

Of course HF boosts are also common-but most people don't seem to care about that as much. But that can also add additional heating to the voice coil-and additional distortion because you are asking the driver to do something it can't-at least easily. And the HF boosts aren't as likely to cause damage (at least as much as the low freq boosts) from overexcursion or overheating.

Agreed on all counts. The measured graph from JBL says that 2.83v are applied to both 8ohm drivers in parallel, so this is a 2 watt measurement at 4 meters, meaning we need to add 6dB to the graph to get a 1w/1m equivalent.

 

[TJ Cornish]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Phil said lots of great stuff.

Thanks for your response Phil. The 4883 spec sheet claims it's a bandpass box, which I believe has some differences compared to a reflex box. There's a significant impedance maximum at 68Hz, and the impedance minimum is about 40Hz. Does this indicate a box tuning of about 40Hz?

The fishiness in comparing the 4883 and the SRX728 is they have the same power handling. The 4883 driver has a 25mm xmax. The SRX728 driver has a 23mm xmax. Definitely not a 1.8X difference.

 

[Ivan Beaver]

Re: Subwoofer comparison SRX728 vs Vertec 4883

View attachment 4495
After further thought, I don't see any harm in posting the graph from JBL, so here it is. As far as I can tell it is unprocessed. It looks very different than the processed graph in the 4883 spec sheet.
Agreed on all counts. The measured graph from JBL says that 2.83v are applied to both 8ohm drivers in parallel, so this is a 2 watt measurement at 4 meters, meaning we need to add 6dB to the graph to get a 1w/1m equivalent.

NO.

Double the power gives you a 3dB gain-not 6. And a 4M distance is a 12 dB loss. So the last time I checked- 12 loss +3 dB gain is a net gain of 9dB Not 6.

Is the measurement ground plane or whole space? That can make for another 6dB difference at some freq.

I still have the question of any processing boost.

You have to look at ALL of the parameters involved

 

[Art Welter]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Thanks for your response Phil. The 4883 spec sheet claims it's a bandpass box, which I believe has some differences compared to a reflex box. There's a significant impedance maximum at 68Hz, and the impedance minimum is about 40Hz. Does this indicate a box tuning of about 40Hz?

The fishiness in comparing the 4883 and the SRX728 is they have the same power handling. The 4883 driver has a 25mm xmax. The SRX728 driver has a 23mm xmax. Definitely not a 1.8X difference.

TJ,

The Fb is likely to be the same as the impedance minima, but as you can see the sensitivity falls rapidly below 50 Hz.
The chart would indicate a 1 watt one meter sensitivity of about 101 dB in the 50 to 100 range, not out of line for a box rolling off so high.

DJK’s post #75 and a recent post by FE3T:
JBL 2268HPL as opossed to JBL2242H - diyAudio

explain how the 23 mm figure is Xmech, not Xmax, as FE3T says in post # 93
“The most usually speced Xmax for the 2268 from reputable resellers are 8mm.”

Phil Lewandowski tested the JBL SRX 718 which also uses the 2268 in his thread "Basic Distortion Testing"
ProSoundWeb Community - Index

His tests confirm that the 2268 Xmax is indeed only around 8mm, he had to reduce the drive level on the 718 to 49 v at 35Hz, and 23 V at 30 Hz to keep the excursion and distortion down to the 10 % level.

I have tested a JBL SRX 728 and can confirm JBL’s frequency response and sensitivity specs are accurate for half space.

The 4883 uses the 2263H-1 which also mistakenly reports the Xmech of 23 mm as Xmax.

Both transducers use the 75 mm (3 in) Dual Coil Dual Magnet , neodymium Differential Drive®.
The 2268 Sd is 1269, the 4883 only 552, therefore it would take 2.3 of the 12” to equal the displacement of the 18”.
However with an Fs of 41.2 for the 12” and 33 for the 18” the 18 can support a lower box tuning and put out more LF.

At any rate, there are many drivers with far more Xmax than either of these JBL drivers.

The B&C 18SW115 has 15 mm Xmax (30mm Xmech), almost double the X max of the JBL 2268 or 2263.

Doubling Xmax results in 6 dB more output.
The far cheaper Eminence Lab 12 has a real 13 mm Xmax, a pair of those can blow away an old school 18” in the 30-40 Hz range.

In tests using the B&C 18SW115-4 I found that a tapped horn of only slightly larger dimensions (still smaller than a JBL SRX 728) than a bass reflex had 6 dB more output with the same drive level.
Tapped Horn Vs. Bass Reflex Case Study - diyAudio

At any rate, with a good tapped horn such as the DSL TH-118 (or my Keystone design) using a single B&C 18SW115-4 there is no doubt that it has around 5 dB more output potential (and a similar LF extension) than an SRX 728 in a smaller size (and weight) package.
And if you don't care about low bass, the TH mini has a similar response, sensitivity and Xmax as the 4883 in an even smaller (but 12 pound heavier) package.

Art Welter

 

[TJ Cornish]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Thanks Art, Ivan, Phil, Silas, and everyone else for a great thread. I've learned a lot. I really like the "system" concept of having matching subs and mains, but there are limits to how far to take that. I'm still looking forward to hearing these (and the 4886), but will have more realistic expectations. I'm still interested in TH115/TH118s, but they're a little big for some of my smaller gigs. I'll look more closely at the TH-Mini too.

 

[Phil Graham]

Re: Subwoofer comparison SRX728 vs Vertec 4883

TJ,

Sorry for the delay. I'll try to fill in the blanks in this thread as time allows, but this week got really busy.

Thanks for your response Phil. The 4883 spec sheet claims it's a bandpass box, which I believe has some differences compared to a reflex box. There's a significant impedance maximum at 68Hz, and the impedance minimum is about 40Hz. Does this indicate a box tuning of about 40Hz?

Regardless of what the marketing department says, the impedance curve doesn't lie This is a vented box design tuned to about 40Hz.

A bandpass box has the same general limitations I discussed above as a ported box, as it is one or two Helmholtz resonators in series with the driver.

A sealed vented bandpass box will have the characteristic double-humped impedance curve of a standard vented box, but tuning frequency will be much higher. The sealed vented bandpass will have one excursion minima at this tuning frequency, and the sealed enclosure will reduce the excursion at lower frequencies, with the concomitant reduction in output.

A tapped horn, double vented reflex, or classic "Scoop" enclosure will show a double excursion minima and a triple humped impedance curve. A scoop and a tapped horn will also show additional humps in the impedance curve outside the sub passband at higher frequencies.

The fishiness in comparing the 4883 and the SRX728 is they have the same power handling. The 4883 driver has a 25mm xmax. The SRX728 driver has a 23mm xmax. Definitely not a 1.8X difference.

Power handling means very little. The AES standard power test rolls off at 50Hz, and therefore is testing primarily for thermal dissipation, as the driver is more than likely not excursion limited at this frequency. Both of the JBL drivers in question have Differential Drive configuration with a 3" voice coil, so that they have the same AES power rating is not surprising.

With real world music signals that extend below 50Hz and have higher crest factors, the excursion limit will be reached before the AES power handling limit. Also, to keep the driver T/S parameters reasonably stable, and therefore the box performance reasonably linear, its is a good idea to limit long term power input to the driver to 5-6dB below AES rating for the typical modern top-shelf driver.

 

[Phil Graham]

Re: Subwoofer comparison SRX728 vs Vertec 4883

NO.

Is the measurement ground plane or whole space? That can make for another 6dB difference at some freq.

JBL measures in half space on the large roof of their facility, as they have been since at least the late 80s when I've seen it mentioned in their AES papers of that vintage.

I still have the question of any processing boost.

Clearly it is better to get the output without a boost, but they're not as detrimental as one might think.

You have to look at ALL of the parameters involved

Agreed 100%

 

[Peter Morris]

Re: Subwoofer comparison SRX728 vs Vertec 4883

TJ,

Sorry for the delay. I'll try to fill in the blanks in this thread as time allows, but this week got really busy.



Regardless of what the marketing department says, the impedance curve doesn't lie This is a vented box design tuned to about 40Hz.

A bandpass box has the same general limitations I discussed above as a ported box, as it is one or two Helmholtz resonators in series with the driver.

A sealed vented bandpass box will have the characteristic double-humped impedance curve of a standard vented box, but tuning frequency will be much higher. The sealed vented bandpass will have one excursion minima at this tuning frequency, and the sealed enclosure will reduce the excursion at lower frequencies, with the concomitant reduction in output.

A tapped horn, double vented reflex, or classic "Scoop" enclosure will show a double excursion minima and a triple humped impedance curve. A scoop and a tapped horn will also show additional humps in the impedance curve outside the sub passband at higher frequencies.



Power handling means very little. The AES standard power test rolls off at 50Hz, and therefore is testing primarily for thermal dissipation, as the driver is more than likely not excursion limited at this frequency. Both of the JBL drivers in question have Differential Drive configuration with a 3" voice coil, so that they have the same AES power rating is not surprising.

With real world music signals that extend below 50Hz and have higher crest factors, the excursion limit will be reached before the AES power handling limit. Also, to keep the driver T/S parameters reasonably stable, and therefore the box performance reasonably linear, its is a good idea to limit long term power input to the driver to 5-6dB below AES rating for the typical modern top-shelf driver.

Hi Phil,

JBL actually describe it as a band-pass, however it is not your typical band pass design, it’s more of a reflex enclosure with cavity added to the front – i.e. the second enclosure is tuned very high. …so …. the impedance curve does not look like your typical band pass. It’s a bit like an EAW SB1000.

If you do a simulation, you will see what is happening – you get a bit more SPL at the higher frequencies for adding the cavity.

http://www.jblpro.com/BackOffice/ProductAttachments/JBL_VT4883_v3.pdf

http://www.eaw.com/info/EAW/Loudspeaker_Product_Info/Current_Loudspeakers/SB1000z/SB1000zP_SPECS_revA.pdf

 

[Phil Graham]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Hi Phil,

JBL actually describe it as a band-pass, however it is not your typical band pass design, it’s more of a reflex enclosure with cavity added to the front – i.e. the second enclosure is tuned very high. …so …. the impedance curve does not look like your typical band pass. It’s a bit like an EAW SB1000.

If you do a simulation, you will see what is happening – you get a bit more SPL at the higher frequencies for adding the cavity.

http://www.jblpro.com/BackOffice/ProductAttachments/JBL_VT4883_v3.pdf

http://www.eaw.com/info/EAW/Loudspeaker_Product_Info/Current_Loudspeakers/SB1000z/SB1000zP_SPECS_revA.pdf

Peter,

Let's agree to disagree here. The impedance curve does indeed show a tiny bump from the mass reactance at 300Hz, and this is characteristic of a bandpass. However, the effect is so subtle, and so high in frequency, that it defies the semantic notion of a bandpass as people tend to think of it. You can see a similar effect from the recessing of a driver baffle to allow for excursion.

-Phil

 

[Phil Graham]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Awesome post, Phil. A must read for everyone who is interested in vented boxes, and processing for them.

Did your article on ports get published yet?

Back in November of last year. You can find links to the articles I have written for FOH at PASSBAND, llc | Articles

 

[Jay Barracato]

Re: Subwoofer comparison SRX728 vs Vertec 4883

View attachment 4495
After further thought, I don't see any harm in posting the graph from JBL, so here it is. As far as I can tell it is unprocessed. It looks very different than the processed graph in the 4883 spec sheet.
Agreed on all counts. The measured graph from JBL says that 2.83v are applied to both 8ohm drivers in parallel, so this is a 2 watt measurement at 4 meters, meaning we need to add 6dB to the graph to get a 1w/1m equivalent.

I guess we could also keep that as an example of where to apply an out of band eq filter?

 

[Bennett Prescott]

Re: Subwoofer comparison SRX728 vs Vertec 4883

I guess we could also keep that as an example of where to apply an out of band eq filter?

Yes, clearly it needs a very narrow 20dB boost at 700Hz!

 

[Jason Phair]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Lots of good discussions about measuring methods and specs.

When we demo'd the 4883's along with the 86's and some sort of double 18" install box they brought along, the 83's sounded awful, no matter which mode they were in.

 

[Peter Morris]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Peter,

Let's agree to disagree here. The impedance curve does indeed show a tiny bump from the mass reactance at 300Hz, and this is characteristic of a bandpass. However, the effect is so subtle, and so high in frequency, that it defies the semantic notion of a bandpass as people tend to think of it. You can see a similar effect from the recessing of a driver baffle to allow for excursion.

-Phil

Hi Phil,
http://www.eighteensound.com/staticContent/applications/kits/18Sound_kit_dual21_%20Prel.pdf
Have a look at this design, although it’s a dual 21, the loading is similar to the 83 – the SPL and impedance curves match relatively speaking.
@ Jay … no you should not try to EQ that notch, but you should EQ the bump at 250. Have a look at what 18 sound do above.

 

[Phil Graham]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Hi Phil,
http://www.eighteensound.com/staticContent/applications/kits/18Sound_kit_dual21_%20Prel.pdf
Have a look at this design, although it’s a dual 21, the loading is similar to the 83 – the SPL and impedance curves match relatively speaking.

Peter,

Again I disagree with you in the comparison to the 4883. This manifold/bandpass(ish) box clearly shows some effects of the mass reactance of the air in front of the drivers in the 100-200Hz octave. There is no such equivalent reactance effects in this range for the 4883.

P.S. I'm glad we've had so many fun agreements and disagreements on topics like this over the years. Beers on me if the wife and I make it to outback.

 

[Peter Morris]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Peter,

Again I disagree with you in the comparison to the 4883. This manifold/bandpass(ish) box clearly shows some effects of the mass reactance of the air in front of the drivers in the 100-200Hz octave. There is no such equivalent reactance effects in this range for the 4883.

P.S. I'm glad we've had so many fun agreements and disagreements on topics like this over the years. Beers on me if the wife and I make it to outback.

...and when I make it back to the US ... Beers on me .. I figure when we agree on everything we will have had enough beer ~~:smile:

anyway a bit more - the top graph is the 4883 – the area where the front cavity has some (small) effect on the impedance curve is 180 – 360hz, the 18sound box 80 – 160 Hz (ish)
.. and it’s that cavity that enables it to make 105 dB/2w/m with a 12 inch bass driver at 250Hz (TJ’s post)

The trick is to get a couple of extra dB at 80Hz where you need it most for the kick drum.
Then you use the signal processing to EQ it flat and all’s well.

 

[Emil Gawaziuk]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Well. Tell y'all what. One of the rigs I drive and hang quite frequently just happens to contain 4 of the 4883 subs. This is going to be a subjective observation, nothing measured, just strictly a performance observation on the boxes in question, in real world use. They are powered off a single iT12000, 2 per channel, in a JBL Vrack. The other 2 amps are driving 6 of the 4886 per side in the hang.

For what they are, they do work quite well. In their intended use, which a pair directly under the array frame up in the air atop the 4886. Fills in the gap down to 65ish Hz rather nicely. At a decent level, say 95-98dB, they keep up pretty well to 6 of the 4886 for most of what one would expect these boxes to be doing. Light duty, smaller stuff. More often than not, we add 4 of the VRX single 18" underneath per side to fill in the low end and give it more wampum (or in the case of the past weekend, I stuck a single VDosc dual 18" per side in there. Worked nicely). Still, the 4883 is a solid little box. But personally, if you are doing higher level and more rawk type shows, you will be happier with the 728. And if you are rolling with a stack of 4886, then you will be very OK with a pair of the 83 and 6 86 per side for the most part, keeping in mind that the 83 are there to fill in a big chunk of the 60-250Hz spectrum that just isn't there on the 4886 boxes (hey....they are 6.5" drivers. remember) and you will have a bigger smile having something that can move some air reliably on the ground.

Just my .02

 

[TJ Cornish]

Re: Subwoofer comparison SRX728 vs Vertec 4883

Thanks Emil. I have a chance to listen to them this coming week. The local rep has 3 4886 boxes and 2 4883 boxes that I will be able to compare to my JFLs and his VRX. I will have my JFL subs and he will have SRX728s to compare as well.

I will report back!

 

[Jay Barracato]

Hey Peter,

My thought was never to try and fill in the notch. Instead I was thinking as you said to smooth out the 200 range and decrease the peak at 1000 so the response was falling off the same way it was before the notch.

I was assuming Bennett's response was humorous because that had never even crossed my mind as a possibility until he posted it.

Anyways, as I still try to wrap my head around what out of band filters can do, this still looks to me like an example where a couple of filters will help you get flatter response a couple of octaves above the typical crossover and then fall off smoothly.