Gauss on JBL box

[retro soulman]

Hello! I just finish my last project, JBL 4507 using Gauss 4580, with 2425 on smith horns and 2404 tweeters. That combo will be my studio monitors. For start i realise that smith horns dont work nice for that short distance ( 1meter) so i replace them with the JBL 2370 horns. The real problem is that the Gauss didnt work that good in the 4507. They sound a little boomy. I close the 2 vents and the bass became a little more tigh but less. Any suggestions? Maybe the box is big for the gauss? My 4580 is the late version witjout the aluminium dust cap!

[RMC]

Hi Retro Soulman,

I'd like to help you but I need to know a few things also.

RE: "They sound a little boomy"

I modeled the driver in Winspeakerz to try to see what may be the cause. Standard 4507 is said by JBL to have 5 cu.ft. (142 L.) tuned at 40 hz.

RE: "I close the 2 vents" As seen on a picture of original 4507 that box has FOUR vents originally, yours has two. You may have made two larger ones equivalent to the four, I don't know. But this raises a question in my mind: are your boxes an EXACT copy of original in terms of volume and tuning frequency or are there some variations made to the original box design ?

Since you indicated the boxes being your studio monitors, their placement is another question. Are these located on the floor away from wall(s) or on a wall or floor/wall junction or near a corner?

In the first picture of modelings done (5 cu.ft., Fb 40 hz), the 45 hz bump in response is at a level about 1.25 db below the 98 db darker black line (i.e. driver rated sensitivity). Then response rises progressively from about 100 hz up. So I'm wondering what are you hearing actually? The 45 hz peak, the rising mid- bass or the combination of the two? And/or some room effect depending on box placement (room gain)?

In the second picture (3 cu.ft./tuned to 50 hz, F3 48 hz) it can be seen that response is flatter, though not flat, which indicates to me the driver is more "at ease" in a smaller volume box, with less droppy low end.

In the third picture you see both modeled response curves kept on the same graph for comparison purposes. Personnaly, I much prefer the response curve of the smaller box since its flatter than larger box but doesn't go as deep...

Note the red (solid and dotted) lines on graphs are woofer excursion (limit is dotted, actual is solid) and the modelings done as usual with 1W, half-space and QL 7.

The 4580 driver isn't made for deep bass output, its more for high level sound without really low bass capability. Some driver parameters point in that direction: Fs 31 hz, Qts 0.23, Vas 198 L. (7 cu.ft.), Xmax 2.3 mm. Qts is small, Vas not large either and Xmax is quite limited. Qts and Vas both influence optimum box size and here they point in the direction of smaller. Xmax says here don't push me too much VLF wise.

BTW for the 4507 box JBL recommends the 2225 driver which has a higher Qts of 0.28 and Xmax of 5 mm.

I tend to agree with you that 4507 may be too large for the driver, though Gauss uses a 5 cu.ft. box as an example in the data sheet. The shape of their response curves is similar to what I get. I tried different combinations with reduced box size using other tuning frequencies.

I stopped reducing box size at 3 cu.ft. NET (85 L.) because smaller than that you may start getting problems fitting the 15" woofer in the box! So, this in my view is more a driver for 3 cu.ft./ 50 hz box than a 4507. Regards,


Richard

[retro soulman]

Hi Retro Soulman,

I'd like to help you but I need to know a few things also.

RE: "They sound a little boomy"

I modeled the driver in Winspeakerz to try to see what may be the cause. Standard 4507 is said by JBL to have 5 cu.ft. (142 L.) tuned at 40 hz.

RE: "I close the 2 vents" As seen on a picture of original 4507 that box has FOUR vents originally, yours has two. You may have made two larger ones equivalent to the four, I don't know. But this raises a question in my mind: are your boxes an EXACT copy of original in terms of volume and tuning frequency or are there some variations made to the original box design ?

Since you indicated the boxes being your studio monitors, their placement is another question. Are these located on the floor away from wall(s) or on a wall or floor/wall junction or near a corner?

In the first picture of modelings done (5 cu.ft., Fb 40 hz), the 45 hz bump in response is at a level about 1.25 db below the 98 db darker black line (i.e. driver rated sensitivity). Then response rises progressively from about 100 hz up. So I'm wondering what are you hearing actually? The 45 hz peak, the rising mid- bass or the combination of the two? And/or some room effect depending on box placement (room gain)?

In the second picture (3 cu.ft./tuned to 50 hz, F3 48 hz) it can be seen that response is flatter, though not flat, which indicates to me the driver is more "at ease" in a smaller volume box, with less droppy low end.

In the third picture you see both modeled response curves kept on the same graph for comparison purposes. Personnaly, I much prefer the response curve of the smaller box since its flatter than larger box but doesn't go as deep...

Note the red (solid and dotted) lines on graphs are woofer excursion (limit is dotted, actual is solid) and the modelings done as usual with 1W, half-space and QL 7.

The 4580 driver isn't made for deep bass output, its more for high level sound without really low bass capability. Some driver parameters point in that direction: Fs 31 hz, Qts 0.23, Vas 198 L. (7 cu.ft.), Xmax 2.3 mm. Qts is small, Vas not large either and Xmax is quite limited. Qts and Vas both influence optimum box size and here they point in the direction of smaller. Xmax says here don't push me too much VLF wise.

BTW for the 4507 box JBL recommends the 2225 driver which has a higher Qts of 0.28 and Xmax of 5 mm.

I tend to agree with you that 4507 may be too large for the driver, though Gauss uses a 5 cu.ft. box as an example in the data sheet. The shape of their response curves is similar to what I get. I tried different combinations with reduced box size using other tuning frequencies.

I stopped reducing box size at 3 cu.ft. NET (85 L.) because smaller than that you may start getting problems fitting the 15" woofer in the box! So, this in my view is more a driver for 3 cu.ft./ 50 hz box than a 4507. Regards,


Richard

Thank you for the answer!! The speakers are on stands close tou ears/ head level. Yeap i was waiting that the speakers are two large but i hate 2226 (i dont know why really ). Today i bring the 2 speakers closer each other (the photo is from yesterday) and i remove the vent blockers. Maybe a little more bass. What i was thinking is to add a pillow in each cabinet to "eat" some liters. What do u think? Best regards!

[RMC]

Hi Retro Soulman,

Very nice setup you have there as seen on your picture, including acoustic panels on the walls!

RE: "Today i bring the 2 speakers closer each other (the photo is from yesterday) and i remove the vent blockers"

That is TWO changes at the time, not good if you want to isolate a problem, how do you know which of the two is the issue? Better to go one modification at a time. You listen before making a change, then make a change, after listen again to know if there's an impact from that particular change. You repeat the same process for each modification. I know its a pain in the neck each separately but its the best way to go.

The speakers are on stands but before you put them closer together they were in the corner (2 walls) from what I see on the picture. A little away from wall corners may be better. You may lose a little on stereo separation but rooms are not elastic either...

You don't need to love or hate 2225/2226 for 4507. Lets try to make something acceptable with what you have instead of don't have here.

RE: "i was waiting that the speakers are two large" and "What i was thinking is to add a pillow in each cabinet to "eat" some liters."

Unfortunately in this case, pillows are soft material and may end up creating MORE virtual box volume by absorption (this you don't need) than reducing it which is what you need.

So instead of pillows you must use rigid stuff like books, pieces of wood such as 2X4" or 4X4" or bricks though these are heavy. Anything rigid on the outside and filled inside (not empty inside as it may resonate).

Best regards,

Richard

P.S. I'll be back with a question for you, no time now I have to go eat...

[RMC]

Hi Retro Soulman,

I noted from the picture you posted your turntables look like the one I use: Audio-Technica AT120 LP USB? I'm seeking some feedback from you and others about this model I purchased about a year ago (retail here at the time $500.+, paid $400. + tx, and from what seen today AT Canada seems to have reduced its prices).

This new one replaced my old Technics SLQ2, sent to recycling, purchased around 1979 and lasted a very long time. No frills basic model, good torque and tonearm, well made in Japan. A $275 or so turntable paid $229. + tx back then. Also had some belt drive models (AR, Dual, Thorens) but the Technics stayed with me. I like high torque direct drive turntable for mixing, and no belt to replace (many obsolete?).

I'm somewhat disapointed at the quality build of the AT, considering its price and my old Technics. Maybe I'm too fussy. I kept a few parts of the old SLQ2 before it went to recycling: thick rubber mat, headshell, cartridge protractor or alignment tool (didn't see any in AT box). Saw some on the Net now. I didn't unwrap the felt mat I don't really need/like, instead I put my still nice thicker rubber mat from the Technics!

I don't see the AT 120 LP having that good of a tonearm, in terms of precision compared to my SLQ2. I don't get the same precision feeling when trying to balance the tonearm for example, seems more "sloppy" and difficult to do accurately, takes longer.

I use a few different cartridges, 4-5 premounted in headshells, for easy replacement from one to another: AT 95E, 408EP, ATP-3 (DJ); Shure SC35C (DJ), M95ED (with some needle options) and V15 type IV. In the past I rarely needed to use the small Bang & Olufsen or Shure's more fancy scale to be sure of tracking force, but now feel less confident and this would seem to be the norm?

The AT definitely has more features than my old Technics but I don't really see it having as much quality built in, even for the higher price.

At this point I'm not sure what I'll do with it, give, sell or keep? I kept the original box plus everything in it, and haven't used it much up to now. Perhaps I should give it another chance, based on the more use the more love principle?

Could be also that the wife may get the AT 120 turntable for her audio system upstairs (haven't told her), then I get myself something else in the new year, e.g. the better AT LP 1240 USB XP? Now that retail price has gone down. Need to assess its tonearm though, is it really better? Let me know what you guys think. Regards,

Richard

[retro soulman]

Hi Retro Soulman,

I noted from the picture you posted your turntables look like the one I use: Audio-Technica AT120 LP USB? I'm seeking some feedback from you and others about this model I purchased about a year ago (retail here at the time $500.+, paid $400. + tx, and from what seen today AT Canada seems to have reduced its prices).

This new one replaced my old Technics SLQ2, sent to recycling, purchased around 1979 and lasted a very long time. No frills basic model, good torque and tonearm, well made in Japan. A $275 or so turntable paid $229. + tx back then. Also had some belt drive models (AR, Dual, Thorens) but the Technics stayed with me. I like high torque direct drive turntable for mixing, and no belt to replace (many obsolete?).

I'm somewhat disapointed at the quality build of the AT, considering its price and my old Technics. Maybe I'm too fussy. I kept a few parts of the old SLQ2 before it went to recycling: thick rubber mat, headshell, cartridge protractor or alignment tool (didn't see any in AT box). Saw some on the Net now. I didn't unwrap the felt mat I don't really need/like, instead I put my still nice thicker rubber mat from the Technics!

I don't see the AT 120 LP having that good of a tonearm, in terms of precision compared to my SLQ2. I don't get the same precision feeling when trying to balance the tonearm for example, seems more "sloppy" and difficult to do accurately, takes longer.

I use a few different cartridges, 4-5 premounted in headshells, for easy replacement from one to another: AT 95E, 408EP, ATP-3 (DJ); Shure SC35C (DJ), M95ED (with some needle options) and V15 type IV. In the past I rarely needed to use the small Bang & Olufsen or Shure's more fancy scale to be sure of tracking force, but now feel less confident and this would seem to be the norm?

The AT definitely has more features than my old Technics but I don't really see it having as much quality built in, even for the higher price.

At this point I'm not sure what I'll do with it, give, sell or keep? I kept the original box plus everything in it, and haven't used it much up to now. Perhaps I should give it another chance, based on the more use the more love principle?

Could be also that the wife may get the AT 120 turntable for her audio system upstairs (haven't told her), then I get myself something else in the new year, e.g. the better AT LP 1240 USB XP? Now that retail price has gone down. Need to assess its tonearm though, is it really better? Let me know what you guys think. Regards,

Richard

Thank you for your suggestions about the 4507! Ill try them soon! My turntables are the Technics sl1200 mk2. I suggest you to sell the AT and buy a sl1200, a real workhorse but the best part of it is that you can upgrade it easy with different tonearms , external psu and many more things that will improve the sound! Best regards!

[RMC]

Hi Retro Soulman,

RE: 4507:

To "stuff" the boxes you should make "packs" of one cubic foot of something rigid (e.g. books, wood). Measure their volume to be sure of quantity of what you put in the boxes. One pack per box may not be enough, since I remember doing a modeling with 4 cu.ft./40-5 hz and the response shown was not a whole lot better than 5 cu.ft.

I think you may need two or so such packs per box to get down closer to 3 cu.ft where the response gets flatter (as shown in picture posted). The other benefit of smaller box here, along with re-tuning it, is that it reduces the demand or pressure for deeper bass on that driver which has an Xmax of 2.3 mm only... If you do F3 48 hz - 20 Khz or so with your monitors its still a nice achievement in my view.

Most types of rigid stuffing material (books, wood pieces, etc.) should be held tight together between enclosure walls or with tape or rope so they don't move. Hardcover books tend to hold better together but softcover will work too. Make sure you don't get too close to vents as this may interfere with their proper operation.

Let me know exactly how much stuff you end up putting in the boxes, I can re-model it in software for you if you want and look at the same time at the box re-tuning issue. In a JBL paper I have the 4507 vents are said to be 3" (76.2mm) diameter and 6" (152.4 mm) long. Do you confirm its about the right size for yours?

The 4507 data sheet says box volume of 5 cu.ft. is NET, so should include space taken by recommended JBL 2225? I haven't seen a specific mention that driver volume is considered or not...

A 15" driver takes 0.2 cu.ft. (6 L.) of space inside a box according to JBL, yours are Gauss not JBL, but it should be reasonably close to that. Usually within 5% error margin of the target box volume isn't enough for drama (EV: "... will not materially affect performance"; JBL: "...the nonlinearity can be neglected", Eargle).

RE: Technics SL-1200

Thanks for your comments on this. I agree all the way, but...

The Technics SL 1200 is VERY nice, THE perfect one for me, and has been re-issued as Grand Class SL-1200G or GR. However, the price of it is Grand Class too! Seen it here from one of the few authorized dealers at $2,500. + TX, SNIFF! Since I never purchase used gear, gray market, nor Internet except small or low-cost stuff 95+% of the time , then it won't fly budget wise for the time being...

BTW my older Technics rubber mat looks pretty much the same as the one on SL-1200G! Other good but less expensive suggestions welcomed! Best Regards,

Richard